The Age of Entanglement: When Quantum Physics Was Reborn - Louisa Gilder
Miss Gilder's forthcoming book stars Einstein, Schrödinger, Bell, Bohr, Heisenberg, de Broglie, and other giants. From the 26th Annual Meeting of Doctors for Disaster Preparedness, held July 12, 2008, in Mesa, AZ.
2010/09/05
Introduction of my dissertation (I)
The ability to convert an intiution into a formulation is what I obtain most during my PhD career. It was a long and lonely journey. I can’t stop thinking what causes the gap between complex mechanics and nowadays physics society. A simple question leads me to ponder over my research topic for dissertation. My intuition helps me a lot during dealing with this issue. Before I can discuss it, I did a survey to see how other classical approaches to quantum mechanics could or could not dismiss this gap.
Among all classical approaches, the quantum Hamilton-Jacobi formalism is the oldest one, which is discussed even as the same time quantum mechanics is established. Indeed, if we compare complex mechanics to the quantum H-J formalism, we will find out that at least, both theories have the same mathematical route-they all insert the wave function into the Schrodinger equation. The only difference is that the complex space structure is an assumption of the former, and a consqauece of the later. This difference did causes the gap because of the acceptance of complex space is not avariable in conventional physics field. I think it might not be the best choice to over emphasize the importance of considering complex space instead of real space that we could observe. There will be a lot of criticisms and demands for the evidence of proving the existence of complex space. This is the position where a pike meets a shield.
We shall define our issue in a physical interpretation or a mathematical interpretation at beginning. It becomes reasonable and might be an easier way to emphasize complex space if viewed mathematically. But in such a way, it totally disobeys the original thought provided by Prof. Yang that is our living world is complex. It becomes more difficult if we adopt a physical manner as to challenge the dimension of the space structure. I found out that maybe I can have both ways in the discussion of this issue in my dissertation, and leave the definition to the reader. I imply the necessary of consider a complex-valued wave function instead a regular one, and indicate the advantage of doing so. I try to avoid bringing the critical part into discussion, and try to show readers the complex space is naturally arose mathematically and physically.
My intuition tells me that the additional irregular velocity appeared in Bohm’s modified guidance law is originated from the imaginary subspace. Even Prof. Yang did mention this conjecture in his text book, however, only a simple relation is presented. We need a better understanding, or a derivation in detail, to confirm this conjecture. I found out that the form of the wave functions adopted in H-J formalism, or complex mechanics, and in Bohmian mechanics have an intense relationship. The wave function used in H-J formalism focuses on the action function; while the other form considers the magnitude and the phase most in Bohmian mechanics. In fact, the relationship between the quantum action function and the characteristic of the wave function is so important, which has been ignored by everyone. This is how I can verify the conjecture that the irregular motion is originated from the imaginary of the wave function.
A classical wave picture is mentioned in quantum H-J formalism and Bohmian mechanics, but not in complex mechanics. I am not sure the reason why there is no such a discussion in Prof. Yang’s text book, but I believe that it is an important issue and needed to be discussed within complex mechanics. In quantum H-J formalism, the Hamilton’s original wave picture is proposed in terms of the reconstruction of the wave function from the quantum action function. However, they did not interpret this process in detail. In Bohmian mechanics, Bohm proposed an assumption that the initial condition of the fluid must be taken otherwise the continuity equation cannot be satisfied. I do believe that a suitable interpretation in terms of trajectories can be given by complex mechanics. However, an important product came out in the middle way. The Born’s postulate of the quantum probability density can be derived from the energy conservation of the imaginary subspace. It quite makes sense since the continuity equation of probability density is from the imaginary part of the Schrodinger equation (after inserting the wave function).
Among all classical approaches, the quantum Hamilton-Jacobi formalism is the oldest one, which is discussed even as the same time quantum mechanics is established. Indeed, if we compare complex mechanics to the quantum H-J formalism, we will find out that at least, both theories have the same mathematical route-they all insert the wave function into the Schrodinger equation. The only difference is that the complex space structure is an assumption of the former, and a consqauece of the later. This difference did causes the gap because of the acceptance of complex space is not avariable in conventional physics field. I think it might not be the best choice to over emphasize the importance of considering complex space instead of real space that we could observe. There will be a lot of criticisms and demands for the evidence of proving the existence of complex space. This is the position where a pike meets a shield.
We shall define our issue in a physical interpretation or a mathematical interpretation at beginning. It becomes reasonable and might be an easier way to emphasize complex space if viewed mathematically. But in such a way, it totally disobeys the original thought provided by Prof. Yang that is our living world is complex. It becomes more difficult if we adopt a physical manner as to challenge the dimension of the space structure. I found out that maybe I can have both ways in the discussion of this issue in my dissertation, and leave the definition to the reader. I imply the necessary of consider a complex-valued wave function instead a regular one, and indicate the advantage of doing so. I try to avoid bringing the critical part into discussion, and try to show readers the complex space is naturally arose mathematically and physically.
My intuition tells me that the additional irregular velocity appeared in Bohm’s modified guidance law is originated from the imaginary subspace. Even Prof. Yang did mention this conjecture in his text book, however, only a simple relation is presented. We need a better understanding, or a derivation in detail, to confirm this conjecture. I found out that the form of the wave functions adopted in H-J formalism, or complex mechanics, and in Bohmian mechanics have an intense relationship. The wave function used in H-J formalism focuses on the action function; while the other form considers the magnitude and the phase most in Bohmian mechanics. In fact, the relationship between the quantum action function and the characteristic of the wave function is so important, which has been ignored by everyone. This is how I can verify the conjecture that the irregular motion is originated from the imaginary of the wave function.
A classical wave picture is mentioned in quantum H-J formalism and Bohmian mechanics, but not in complex mechanics. I am not sure the reason why there is no such a discussion in Prof. Yang’s text book, but I believe that it is an important issue and needed to be discussed within complex mechanics. In quantum H-J formalism, the Hamilton’s original wave picture is proposed in terms of the reconstruction of the wave function from the quantum action function. However, they did not interpret this process in detail. In Bohmian mechanics, Bohm proposed an assumption that the initial condition of the fluid must be taken otherwise the continuity equation cannot be satisfied. I do believe that a suitable interpretation in terms of trajectories can be given by complex mechanics. However, an important product came out in the middle way. The Born’s postulate of the quantum probability density can be derived from the energy conservation of the imaginary subspace. It quite makes sense since the continuity equation of probability density is from the imaginary part of the Schrodinger equation (after inserting the wave function).
2010/08/06
Speculating about the Universe as a quantum fluid
Speculating about the Universe as a quantum fluid
By Chris Lee | Last updated January 25, 2010 9:35 PM
NASA
The first thing that struck me about Hitoshi Murayama was that he certainly did not fit the stereotype of a Japanese presenter—he's relaxed, eloquent, and clearly very, very excited about his work. He is the head of a new research center in Japan called the Institute for the Physics and Mathematics of the Universe—a purview that allows him to study just about anything. But he's chosen to study everything; Murayama wants to know why there is, in fact, a universe.
Because the Physics@FOM audience comes from a range of backgrounds, Murayama's talk was light on details and strong on providing a flavor of the problem and inspiring the audience. And inspired I was, as he took us on a whirlwind tour of the known Universe, including dark matter and inflation. He wrapped up by going completely off the map with some of the ideas that he has had floating around for some time now.
Murayama proposes that the Universe is, in fact, a quantum fluid, somewhat like a superconductor.
Starting with the energy budget of the Universe, he reminded us that less than five percent of the matter and energy in the Universe is understood, with the remainder being dark energy and dark matter. But, even if we could account for dark matter with a bunch of particles and dark energy was understood, we still wouldn't understand much. For instance, none of this knowledge would help us understand why the various forces behave the way they do.
Along the way, he provided a taste of the evidence for why we believe the things that we do. We know dark matter exists because galaxies don't fly apart, because we find gravity where there is no matter, and, most tellingly, our universe would be smooth and featureless in the absence of dark matter. He showed that, although dark matter allows structures to form, inflation provided the initial changes in density that allowed them to condense.
But, of course, we don't know what dark matter is. Murayama justified the idea that dark matter is almost certainly some sort of weakly interacting massive particle by showing how we account for the dimmest objects in the Universe and simply don't find enough of them. In short, we think that dark matter exists because it is just about impossible to account for all the evidence with any other proposals.
Now, with the LHC online, we should start finding particles that may well be dark matter, and we will soon know if cosmologists were on the right track. And that is kind of exciting: years of speculation and careful modeling about to be properly tested. But, even more exciting, if the LHC does find dark matter candidate particles, cosmologists will be able to claim that we pretty much understand the Universe from 10-10s after the big bang to the present day—a mind-boggling thought.
What really seems to turns Murayama on is the problem of explaining why some forces are long-range and some are short-range. Basically, gravity reaches out over huge distances. Electromagnetism would reach just as far, but because there are both negative and positive charges, forces due to one set of charges tend get screened out by opposite signed charges. This effectively limits the reach of electromagnetic forces. Nevertheless, the fundamental distance scaling for the two forces is the same. The strong and weak nuclear forces are very short range, extending no further than the width of a nucleus.
There is no fundamental reason for why these forces scale differently from gravity and electromagnetism. He proposes that the Universe is, in fact, a quantum fluid, somewhat like a superconductor. How does this work? The analogy with superconductivity is apt because superconductors reject magnetic fields. That is, the charges in a superconductor arrange themselves such that the field lines of a magnetic field get bent around the super-current. Now, imagine sitting in the superconductor, trying to make a magnetic field.
What you would see is that the field was incredibly short-ranged because of the way the field would interact with the surrounding charges. Therein lies the idea. Imagine that the Universe is a quantum fluid that interacts very strongly with the strong force and weak forces, but ignores gravity and electromagnetism. Our knowledge of the four forces allows us to calculate some of the properties that this fluid must have, and, from there, to figure out how much energy is tied up in this fluid.
If you are going to go into debt, you might as well do it properly. If Murayama is right, the current energy of the Universe is short by some 1062 percent of that required to create the fluid during the big bang—that is one hell of a mortgage. As he jokingly pointed out, we are constantly told that deficits are a bad thing, so if his dark field proposal is to become more than an idea, some creative accounting is required.
All in all, a great opening to Physics@FOM.
From:http://arstechnica.com/science/news/2010/01/quantum-universe.ars
By Chris Lee | Last updated January 25, 2010 9:35 PM
NASA
The first thing that struck me about Hitoshi Murayama was that he certainly did not fit the stereotype of a Japanese presenter—he's relaxed, eloquent, and clearly very, very excited about his work. He is the head of a new research center in Japan called the Institute for the Physics and Mathematics of the Universe—a purview that allows him to study just about anything. But he's chosen to study everything; Murayama wants to know why there is, in fact, a universe.
Because the Physics@FOM audience comes from a range of backgrounds, Murayama's talk was light on details and strong on providing a flavor of the problem and inspiring the audience. And inspired I was, as he took us on a whirlwind tour of the known Universe, including dark matter and inflation. He wrapped up by going completely off the map with some of the ideas that he has had floating around for some time now.
Murayama proposes that the Universe is, in fact, a quantum fluid, somewhat like a superconductor.
Starting with the energy budget of the Universe, he reminded us that less than five percent of the matter and energy in the Universe is understood, with the remainder being dark energy and dark matter. But, even if we could account for dark matter with a bunch of particles and dark energy was understood, we still wouldn't understand much. For instance, none of this knowledge would help us understand why the various forces behave the way they do.
Along the way, he provided a taste of the evidence for why we believe the things that we do. We know dark matter exists because galaxies don't fly apart, because we find gravity where there is no matter, and, most tellingly, our universe would be smooth and featureless in the absence of dark matter. He showed that, although dark matter allows structures to form, inflation provided the initial changes in density that allowed them to condense.
But, of course, we don't know what dark matter is. Murayama justified the idea that dark matter is almost certainly some sort of weakly interacting massive particle by showing how we account for the dimmest objects in the Universe and simply don't find enough of them. In short, we think that dark matter exists because it is just about impossible to account for all the evidence with any other proposals.
Now, with the LHC online, we should start finding particles that may well be dark matter, and we will soon know if cosmologists were on the right track. And that is kind of exciting: years of speculation and careful modeling about to be properly tested. But, even more exciting, if the LHC does find dark matter candidate particles, cosmologists will be able to claim that we pretty much understand the Universe from 10-10s after the big bang to the present day—a mind-boggling thought.
What really seems to turns Murayama on is the problem of explaining why some forces are long-range and some are short-range. Basically, gravity reaches out over huge distances. Electromagnetism would reach just as far, but because there are both negative and positive charges, forces due to one set of charges tend get screened out by opposite signed charges. This effectively limits the reach of electromagnetic forces. Nevertheless, the fundamental distance scaling for the two forces is the same. The strong and weak nuclear forces are very short range, extending no further than the width of a nucleus.
There is no fundamental reason for why these forces scale differently from gravity and electromagnetism. He proposes that the Universe is, in fact, a quantum fluid, somewhat like a superconductor. How does this work? The analogy with superconductivity is apt because superconductors reject magnetic fields. That is, the charges in a superconductor arrange themselves such that the field lines of a magnetic field get bent around the super-current. Now, imagine sitting in the superconductor, trying to make a magnetic field.
What you would see is that the field was incredibly short-ranged because of the way the field would interact with the surrounding charges. Therein lies the idea. Imagine that the Universe is a quantum fluid that interacts very strongly with the strong force and weak forces, but ignores gravity and electromagnetism. Our knowledge of the four forces allows us to calculate some of the properties that this fluid must have, and, from there, to figure out how much energy is tied up in this fluid.
If you are going to go into debt, you might as well do it properly. If Murayama is right, the current energy of the Universe is short by some 1062 percent of that required to create the fluid during the big bang—that is one hell of a mortgage. As he jokingly pointed out, we are constantly told that deficits are a bad thing, so if his dark field proposal is to become more than an idea, some creative accounting is required.
All in all, a great opening to Physics@FOM.
From:http://arstechnica.com/science/news/2010/01/quantum-universe.ars
2010/07/09
The proton shrinks in size
The proton shrinks in size
Tiny change in radius has huge implications.
Geoff Brumfiel
Measurements with lasers have revealed that the proton may be a touch smaller than predicted by current theories.PSI / F. Reiser
The proton seems to be 0.00000000000003 millimetres smaller than researchers previously thought, according to work published in today's issue of Nature1.
The difference is so infinitesimal that it might defy belief that anyone, even physicists, would care. But the new measurements could mean that there is a gap in existing theories of quantum mechanics. "It's a very serious discrepancy," says Ingo Sick, a physicist at the University of Basel in Switzerland, who has tried to reconcile the finding with four decades of previous measurements. "There is really something seriously wrong someplace."
Protons are among the most common particles out there. Together with their neutral counterparts, neutrons, they form the nuclei of every atom in the Universe. But despite its everday appearance, the proton remains something of a mystery to nuclear physicists, says Randolf Pohl, a researcher at the Max Planck Institute of Quantum Optics in Garching, Germany, and an author on the Nature paper. "We don't understand a lot of its internal structure," he says.
From afar, the proton looks like a small point of positive charge, but on much closer inspection, the particle is more complex. Each proton is made of smaller fundamental particles called quarks, and that means its charge is roughly spread throughout a spherical area.
Physicists can measure the size of the proton by watching as an electron interacts with a proton. A single electron orbiting a proton can occupy only certain, discrete energy levels, which are described by the laws of quantum mechanics. Some of these energy levels depend in part on the size of the proton, and since the 1960s physicists have made hundreds of measurements of the proton's size with staggering accuracy. The most recent estimates, made by Sick using previous data, put the radius of the proton at around 0.8768 femtometres (1 femtometre = 10-15 metres).
Small wonder
Pohl and his team have a come up with a smaller number by using a cousin of the electron, known as the muon. Muons are about 200 times heavier than electrons, making them more sensitive to the proton's size. To measure the proton radius using the muon, Pohl and his colleagues fired muons from a particle accelerator at a cloud of hydrogen. Hydrogen nuclei each consist of a single proton, orbited by an electron. Sometimes a muon replaces an electron and orbits around a proton. Using lasers, the team measured relevant muonic energy levels with extremely high accuracy and found that the proton was around 4% smaller than previously thought.
ADVERTISEMENT
That might not sound like much, but the difference is so far from previous measurements that the researchers actually missed it the first two times they ran the experiment in 2003 and 2007. "We thought that our laser system was not good enough," Pohl says. In 2009, they looked beyond the narrow range in which they expected to see the proton radius and saw an unmistakable signal.
"What gives? I don't know," says Sick. He says he believes the new result, but that there is no obvious way to make it compatible with years of earlier measurements.
"Something is missing, this is very clear," agrees Carl Carlson, a theoretical physicist at the College of William & Mary in Williamsburg, Virginia. The most intriguing possibility is that previously undetected particles are changing the interaction of the muon and the proton. Such particles could be the 'superpartners' of existing particles, as predicted by a theory known as supersymmetry, which seeks to unite all of the fundamental forces of physics, except gravity.
But, Carlson says, "the first thing is to go through the existing calculations with a fine tooth comb". It could be that an error was made, or that approximations made in existing quantum calculation simply aren't good enough. "Right now, I'd put my money on some other correction," he says. "It's also where my research time will be going over the next month."
From:http://www.nature.com/news/2010/100707/full/news.2010.337.html
Tiny change in radius has huge implications.
Geoff Brumfiel
Measurements with lasers have revealed that the proton may be a touch smaller than predicted by current theories.PSI / F. Reiser
The proton seems to be 0.00000000000003 millimetres smaller than researchers previously thought, according to work published in today's issue of Nature1.
The difference is so infinitesimal that it might defy belief that anyone, even physicists, would care. But the new measurements could mean that there is a gap in existing theories of quantum mechanics. "It's a very serious discrepancy," says Ingo Sick, a physicist at the University of Basel in Switzerland, who has tried to reconcile the finding with four decades of previous measurements. "There is really something seriously wrong someplace."
Protons are among the most common particles out there. Together with their neutral counterparts, neutrons, they form the nuclei of every atom in the Universe. But despite its everday appearance, the proton remains something of a mystery to nuclear physicists, says Randolf Pohl, a researcher at the Max Planck Institute of Quantum Optics in Garching, Germany, and an author on the Nature paper. "We don't understand a lot of its internal structure," he says.
From afar, the proton looks like a small point of positive charge, but on much closer inspection, the particle is more complex. Each proton is made of smaller fundamental particles called quarks, and that means its charge is roughly spread throughout a spherical area.
Physicists can measure the size of the proton by watching as an electron interacts with a proton. A single electron orbiting a proton can occupy only certain, discrete energy levels, which are described by the laws of quantum mechanics. Some of these energy levels depend in part on the size of the proton, and since the 1960s physicists have made hundreds of measurements of the proton's size with staggering accuracy. The most recent estimates, made by Sick using previous data, put the radius of the proton at around 0.8768 femtometres (1 femtometre = 10-15 metres).
Small wonder
Pohl and his team have a come up with a smaller number by using a cousin of the electron, known as the muon. Muons are about 200 times heavier than electrons, making them more sensitive to the proton's size. To measure the proton radius using the muon, Pohl and his colleagues fired muons from a particle accelerator at a cloud of hydrogen. Hydrogen nuclei each consist of a single proton, orbited by an electron. Sometimes a muon replaces an electron and orbits around a proton. Using lasers, the team measured relevant muonic energy levels with extremely high accuracy and found that the proton was around 4% smaller than previously thought.
ADVERTISEMENT
That might not sound like much, but the difference is so far from previous measurements that the researchers actually missed it the first two times they ran the experiment in 2003 and 2007. "We thought that our laser system was not good enough," Pohl says. In 2009, they looked beyond the narrow range in which they expected to see the proton radius and saw an unmistakable signal.
"What gives? I don't know," says Sick. He says he believes the new result, but that there is no obvious way to make it compatible with years of earlier measurements.
"Something is missing, this is very clear," agrees Carl Carlson, a theoretical physicist at the College of William & Mary in Williamsburg, Virginia. The most intriguing possibility is that previously undetected particles are changing the interaction of the muon and the proton. Such particles could be the 'superpartners' of existing particles, as predicted by a theory known as supersymmetry, which seeks to unite all of the fundamental forces of physics, except gravity.
But, Carlson says, "the first thing is to go through the existing calculations with a fine tooth comb". It could be that an error was made, or that approximations made in existing quantum calculation simply aren't good enough. "Right now, I'd put my money on some other correction," he says. "It's also where my research time will be going over the next month."
From:http://www.nature.com/news/2010/100707/full/news.2010.337.html
2010/06/18
confinement and chanllenge
Have seen a movie, named "Einstein and Eddington". It was a period of confining people's mind, ruled by their religion. Or we could say that this confinement exists all the time no matter what period it is. Those two scientists try to break the confinement, try to free their mind from the cage. Eddington said, there is nothing can stop the conservation of science, there should not exist any boundary between nations, people, and races. Imagination is the only thing really free from the mind, even if so many stumbling stones located in front of us. They choiced what they want to do and dealed with the coming challenge. I am wondering that they also understand how much new confinement try to stuck young people's mind on their way to persue their knowledge. Imagination, that is what I have which is truly free from all those cages. We still strugle to looking for freedom on the way to find the truth. If there is any oppertunity that we can really approach to the truth of the universe, it must be "free mind" and "imagination". Nothing impossible! That's waht I want to say to Einstein, and tell him that there are always young people keeping this belief to start their research career.
2010/05/13
Largest scientific instrument ever built to prove Einstein's theory of general relativity
Three spacecraft flying three million miles apart are to fire laser beams at each other across the emptiness of space in a bid to finally prove whether a theory proposed by Albert Einstein is correct.
By Richard Gray, Science Correspondent
Published: 8:30AM BST 09 May 2010
Albert Einstein was awarded the Nobel Prize for Physics in 1921 Photo: AFP/GETTY
Physicists hope the ambitious mission will allow them to prove the existence of gravitational waves – a phenomenon predicted in Einstein's famous theory of general relativity and the last piece of his theory still to be proved correct.
The mission, a collaboration between Nasa and the European Space Agency, will use three spacecraft flying in formation while orbiting the sun, with each housing floating cubes of gold platinum.
Laser beams fired between the spacecraft will then be used to measure minute changes in the distance between each of the cubes, caused by the weak waves of gravity that ripple out from catastrophic events in deep space.
Einstein's theory of general relativity predicted that when large objects such as black holes collide, ripples in space and time flow outwards. These ripples are called gravitational waves.
A panel of international experts have now set out a detailed plan for the mission and how it can be used to reveal new insights about the universe around us.
Professor Jim Hough, an expert on gravitational waves at Glasgow University and a member of the committee that drew up the plans, said: "Gravitational waves are the last piece of Einstein's theory of general relativity that has still to be proved correct.
"They are produced when massive objects like black holes or collapsed stars accelerate through space, perhaps because they being pulled towards another object with greater gravitational pull like a massive black hole.
"Unfortunately we haven't been able to detect them yet because they are very weak. However, the new experiments we are working on have great potential to allow detection."
Ground based attempts to detect gravitational waves on Earth have so far been unsuccessful and can only look for gravitational waves with relatively high frequencies.
Scientists have already been able to prove a number of predictions made by Einstein's theory of general relativity, including that light is bent by gravity, gravity travels at a constant speed, that time can be warped by gravity and that space and time can bend.
Einstein's other theories including his most famous formula E=mc2 have also withstood scientific testing.
The Laser Interferometer Space Antenna, or LISA as the new space based mission is called, will be able to detect gravitational waves of very low frequencies due to the huge distance between the three spacecraft. It will be the largest detector ever built.
A smaller test mission called LISA Pathfinder, which is being built by British engineers at space company Astrium EADS and is due to be launched next year, is to pave the way for the more ambitious mission by demonstrating the technology to be used to detect the waves.
Scientists have already begun building the instruments that will be used in LISA itself, but it is not expected to be launched before 2020.
They hope that once detected, gravitational waves will be able to provide new information about the universe that cannot currently be seen using electromagnetic radiation such as light, radio waves and X-rays.
Professor Sheila Rowan, who also studies gravitational waves at Glasgow University, added: "Black holes are so dense that no light or radiation escapes from inside them.
"Gravitational waves from the warped spacetime around black holes could give us new ways of looking at them.
"We could also learn about the state of matter inside collapsed stars."
Dr Ralph Cordey, science and exploration business development manager at Astrium UK who are building LISA Pathfinder, said: "Trying to measure cosmic events such as collapsing star systems or the collision of massive black holes throughout our universe requires ultra-high precision technology.
"The ultimate goal is to prove that this technology works, before we attempt to put three spacecraft into orbits at a distance of 5 million kilometres from one another, connected only by a laser beam that will measure their positions accurate to 40 millionths of a millionth of a metre."
From:http://www.telegraph.co.uk/science/space/7695994/Largest-scientific-instrument-ever-built-to-prove-Einsteins-theory-of-general-relativity.html
By Richard Gray, Science Correspondent
Published: 8:30AM BST 09 May 2010
Albert Einstein was awarded the Nobel Prize for Physics in 1921 Photo: AFP/GETTY
Physicists hope the ambitious mission will allow them to prove the existence of gravitational waves – a phenomenon predicted in Einstein's famous theory of general relativity and the last piece of his theory still to be proved correct.
The mission, a collaboration between Nasa and the European Space Agency, will use three spacecraft flying in formation while orbiting the sun, with each housing floating cubes of gold platinum.
Laser beams fired between the spacecraft will then be used to measure minute changes in the distance between each of the cubes, caused by the weak waves of gravity that ripple out from catastrophic events in deep space.
Einstein's theory of general relativity predicted that when large objects such as black holes collide, ripples in space and time flow outwards. These ripples are called gravitational waves.
A panel of international experts have now set out a detailed plan for the mission and how it can be used to reveal new insights about the universe around us.
Professor Jim Hough, an expert on gravitational waves at Glasgow University and a member of the committee that drew up the plans, said: "Gravitational waves are the last piece of Einstein's theory of general relativity that has still to be proved correct.
"They are produced when massive objects like black holes or collapsed stars accelerate through space, perhaps because they being pulled towards another object with greater gravitational pull like a massive black hole.
"Unfortunately we haven't been able to detect them yet because they are very weak. However, the new experiments we are working on have great potential to allow detection."
Ground based attempts to detect gravitational waves on Earth have so far been unsuccessful and can only look for gravitational waves with relatively high frequencies.
Scientists have already been able to prove a number of predictions made by Einstein's theory of general relativity, including that light is bent by gravity, gravity travels at a constant speed, that time can be warped by gravity and that space and time can bend.
Einstein's other theories including his most famous formula E=mc2 have also withstood scientific testing.
The Laser Interferometer Space Antenna, or LISA as the new space based mission is called, will be able to detect gravitational waves of very low frequencies due to the huge distance between the three spacecraft. It will be the largest detector ever built.
A smaller test mission called LISA Pathfinder, which is being built by British engineers at space company Astrium EADS and is due to be launched next year, is to pave the way for the more ambitious mission by demonstrating the technology to be used to detect the waves.
Scientists have already begun building the instruments that will be used in LISA itself, but it is not expected to be launched before 2020.
They hope that once detected, gravitational waves will be able to provide new information about the universe that cannot currently be seen using electromagnetic radiation such as light, radio waves and X-rays.
Professor Sheila Rowan, who also studies gravitational waves at Glasgow University, added: "Black holes are so dense that no light or radiation escapes from inside them.
"Gravitational waves from the warped spacetime around black holes could give us new ways of looking at them.
"We could also learn about the state of matter inside collapsed stars."
Dr Ralph Cordey, science and exploration business development manager at Astrium UK who are building LISA Pathfinder, said: "Trying to measure cosmic events such as collapsing star systems or the collision of massive black holes throughout our universe requires ultra-high precision technology.
"The ultimate goal is to prove that this technology works, before we attempt to put three spacecraft into orbits at a distance of 5 million kilometres from one another, connected only by a laser beam that will measure their positions accurate to 40 millionths of a millionth of a metre."
From:http://www.telegraph.co.uk/science/space/7695994/Largest-scientific-instrument-ever-built-to-prove-Einsteins-theory-of-general-relativity.html
The 10 weirdest physics facts, from relativity to quantum physics
People who think science is dull are wrong. Here are 10 reasons why.
By Tom Chivers
Published: 7:00AM GMT 12 Nov 2009
Physics is weird. There is no denying that. Particles that don’t exist except as probabilities; time that changes according to how fast you’re moving; cats that are both alive and dead until you open a box.
We’ve put together a collection of 10 of the strangest facts we can find, with the kind help of cosmologist and writer Marcus Chown, author of We Need To Talk About Kelvin, and an assortment of Twitter users.
The humanities-graduate writer of this piece would like to stress that this is his work, so any glaring factual errors he has included are his own as well. If you spot any, feel free to point them out in the comment box below.
Equally, if you feel we’ve missed any of your favourite physics weirdnesses off the list, do tell us that as well.
If the Sun were made of bananas, it would be just as hot
The Sun is hot, as the more astute of you will have noticed. It is hot because its enormous weight – about a billion billion billion tons – creates vast gravity, putting its core under colossal pressure. Just as a bicycle pump gets warm when you pump it, the pressure increases the temperature. Enormous pressure leads to enormous temperature.
If, instead of hydrogen, you got a billion billion billion tons of bananas and hung it in space, it would create just as much pressure, and therefore just as high a temperature. So it would make very little difference to the heat whether you made the Sun out of hydrogen, or bananas, or patio furniture.
Edit: this might be a little confusing. The heat caused by the internal pressure would be similar to that of our Sun. However, if it's not made of hydrogen, the fusion reaction that keeps it going wouldn't get under way: so a banana Sun would rapidly cool down from its initial heat rather than burning for billions of years. Thanks to people who pointed this out.
All the matter that makes up the human race could fit in a sugar cube
Atoms are 99.9999999999999 per cent empty space. As Tom Stoppard put it: "Make a fist, and if your fist is as big as the nucleus of an atom, then the atom is as big as St Paul's, and if it happens to be a hydrogen atom, then it has a single electron flitting about like a moth in an empty cathedral, now by the dome, now by the altar."
If you forced all the atoms together, removing the space between them, crushing them down so the all those vast empty cathedrals were compressed into the first-sized nuclei, a single teaspoon or sugar cube of the resulting mass would weigh five billion tons; about ten times the weight of all the humans who are currently alive.
Incidentally, that is exactly what has happened in a neutron star, the super-dense mass left over after a certain kind of supernova.
The weirdness of the quantum world is well documented. The double slit experiment, showing that light behaves as both a wave and a particle, is odd enough – particularly when it is shown that observing it makes it one or the other.
But it gets stranger. According to an experiment proposed by the physicist John Wheeler in 1978 and carried out by researchers in 2007, observing a particle now can change what happened to another one – in the past.
According to the double slit experiment, if you observe which of two slits light passes through, you force it to behave like a particle. If you don’t, and observe where it lands on a screen behind the slits, it behaves like a wave.
But if you wait for it to pass through the slit, and then observe which way it came through, it will retroactively force it to have passed through one or the other. In other words, causality is working backwards: the present is affecting the past.
Of course in the lab this only has an effect over indescribably tiny fractions of a second. But Wheeler suggested that light from distant stars that has bent around a gravitational well in between could be observed in the same way: which could mean that observing something now and changing what happened thousands, or even millions, of years in the past.
Almost all of the Universe is missing
There are probably more than 100 billion galaxies in the cosmos. Each of those galaxies has between 10 million and a trillion stars in it. Our sun, a rather small and feeble star (a “yellow dwarf”, indeed), weighs around a billion billion billion tons, and most are much bigger. There is an awful lot of visible matter in the Universe.
But it only accounts for about two per cent of its mass.
We know there is more, because it has gravity. Despite the huge amount of visible matter, it is nowhere near enough to account for the gravitational pull we can see exerted on other galaxies. The other stuff is called “dark matter”, and there seems to be around six times as much as ordinary matter.
To make matters even more confusing, the rest is something else called “dark energy”, which is needed to explain the apparent expansion of the Universe. Nobody knows what dark matter or dark energy is.
Things can travel faster than light; and light doesn’t always travel very fast
The speed of light in a vacuum is a constant: 300,000km a second. However, light does not always travel through a vacuum. In water, for example, photons travel at around three-quarters that speed.
In nuclear reactors, some particles are forced up to very high speeds, often within a fraction of the speed of light. If they are passing through an insulating medium that slows light down, they can actually travel faster than the light around them.
When this happens, they cause a blue glow, known as “Cherenkov radiation ”, which is (sort of) comparable to a sonic boom but with light. This is why nuclear reactors glow in the dark.
Incidentally, the slowest light has ever been recorded travelling was 17 meters per second – about 38 miles an hour – through rubidium cooled to almost absolute zero, when it forms a strange state of matter called a Bose-Einstein condensate.
Light has also been brought to a complete stop in the same fashion, but since that wasn't moving at all, we didn't feel we could describe that as "the slowest it has been recorded travelling".
There are an infinite number of mes writing this, and an infinite number of yous reading it
According to the current standard model of cosmology, the observable universe – containing all the billions of galaxies and trillions upon trillions of stars mentioned above – is just one of an infinite number of universes existing side-by-side, like soap bubbles in a foam.
Because they are infinite, every possible history must have played out. But more than that, the number of possible histories is finite, because there have been a finite number of events with a finite number of outcomes. The number is huge, but it is finite. So this exact event, where this author writes these words and you read them, must have happened an infinite number of times.
Even more amazingly, we can work out how far away our nearest doppelganger is. It is, to put it mildly, a large distance: 10 to the power of 10 to the power of 28 meters. That number, in case you were wondering, is one followed by 10 billion billion billion zeroes
Black holes aren’t black
hey’re very dark, sure, but they aren’t black. They glow, slightly, giving off light across the whole spectrum, including visible light.
This radiation is called “Hawking radiation”, after the former Lucasian Professor of Mathematics at Cambridge University Stephen Hawking, who first proposed its existence. Because they are constantly giving this off, and therefore losing mass, black holes will eventually evaporate altogether if they don’t have another source of mass to sustain them; for example interstellar gas or light.
Smaller black holes are expected to emit radiation faster compared to their mass than larger ones, so if – as some theories predict – the Large Hadron Collider creates minuscule holes through particle collisions, they will evaporate almost immediately. Scientists would then be able to observe their decay through the radiation.
The fundamental description of the universe does not account for a past, present or future
According to the special theory of relativity, there is no such thing as a present, or a future, or a past. Time frames are relative: I have one, you have one, the third planet of Gliese 581 has one. Ours are similar because we are moving at similar speeds.
If we were moving at very different speeds, we would find that one of us aged quicker than the other. Similarly, if one of us was closer than the other to a major gravity well like the Earth, we would age slower than someone who wasn’t.
GPS satellites, of course, are both moving quickly and at significant distances from Earth. So their internal clocks show a different time to the receivers on the ground. A lot of computing power has to go into making your sat-nav work around the theory of special relativity.
A particle here can affect one on the other side of the universe, instantaneously
When an electron meets its antimatter twin, a positron, the two are annihilated in a tiny flash of energy. Two photons fly away from the blast.
Subatomic particles like photons and quarks have a quality known as “spin”. It’s not that they’re really spinning – it’s not clear that would even mean anything at that level – but they behave as if they do. When two are created simultaneously the direction of their spin has to cancel each other out: one doing the opposite of the other.
Due to the unpredictability of quantum behaviour, it is impossible to say in advance which will go “anticlockwise” and the other “clockwise”. More than that, until the spin of one is observed, they are both doing both.
It gets weirder, however. When you do observe one, it will suddenly be going clockwise or anticlockwise. And whichever way it is going, its twin will start spinning the other way, instantly, even if it is on the other side of the universe. This has actually been shown to happen in experiment (albeit on the other side of a laboratory, not a universe).
The faster you move, the heavier you get
If you run really fast, you gain weight. Not permanently, or it would make a mockery of diet and exercise plans, but momentarily, and only a tiny amount.
Light speed is the speed limit of the universe. So if something is travelling close to the speed of light, and you give it a push, it can’t go very much faster. But you’ve given it extra energy, and that energy has to go somewhere.
Where it goes is mass. According to relativity, mass and energy are equivalent. So the more energy you put in, the greater the mass becomes. This is negligible at human speeds – Usain Bolt is not noticeably heavier when running than when still – but once you reach an appreciable fraction of the speed of light, your mass starts to increase rapidly.
Originated from: http://www.telegraph.co.uk/science/6546462/The-10-weirdest-physics-facts-from-relativity-to-quantum-physics.html
By Tom Chivers
Published: 7:00AM GMT 12 Nov 2009
Physics is weird. There is no denying that. Particles that don’t exist except as probabilities; time that changes according to how fast you’re moving; cats that are both alive and dead until you open a box.
We’ve put together a collection of 10 of the strangest facts we can find, with the kind help of cosmologist and writer Marcus Chown, author of We Need To Talk About Kelvin, and an assortment of Twitter users.
The humanities-graduate writer of this piece would like to stress that this is his work, so any glaring factual errors he has included are his own as well. If you spot any, feel free to point them out in the comment box below.
Equally, if you feel we’ve missed any of your favourite physics weirdnesses off the list, do tell us that as well.
If the Sun were made of bananas, it would be just as hot
The Sun is hot, as the more astute of you will have noticed. It is hot because its enormous weight – about a billion billion billion tons – creates vast gravity, putting its core under colossal pressure. Just as a bicycle pump gets warm when you pump it, the pressure increases the temperature. Enormous pressure leads to enormous temperature.
If, instead of hydrogen, you got a billion billion billion tons of bananas and hung it in space, it would create just as much pressure, and therefore just as high a temperature. So it would make very little difference to the heat whether you made the Sun out of hydrogen, or bananas, or patio furniture.
Edit: this might be a little confusing. The heat caused by the internal pressure would be similar to that of our Sun. However, if it's not made of hydrogen, the fusion reaction that keeps it going wouldn't get under way: so a banana Sun would rapidly cool down from its initial heat rather than burning for billions of years. Thanks to people who pointed this out.
All the matter that makes up the human race could fit in a sugar cube
Atoms are 99.9999999999999 per cent empty space. As Tom Stoppard put it: "Make a fist, and if your fist is as big as the nucleus of an atom, then the atom is as big as St Paul's, and if it happens to be a hydrogen atom, then it has a single electron flitting about like a moth in an empty cathedral, now by the dome, now by the altar."
If you forced all the atoms together, removing the space between them, crushing them down so the all those vast empty cathedrals were compressed into the first-sized nuclei, a single teaspoon or sugar cube of the resulting mass would weigh five billion tons; about ten times the weight of all the humans who are currently alive.
Incidentally, that is exactly what has happened in a neutron star, the super-dense mass left over after a certain kind of supernova.
The weirdness of the quantum world is well documented. The double slit experiment, showing that light behaves as both a wave and a particle, is odd enough – particularly when it is shown that observing it makes it one or the other.
But it gets stranger. According to an experiment proposed by the physicist John Wheeler in 1978 and carried out by researchers in 2007, observing a particle now can change what happened to another one – in the past.
According to the double slit experiment, if you observe which of two slits light passes through, you force it to behave like a particle. If you don’t, and observe where it lands on a screen behind the slits, it behaves like a wave.
But if you wait for it to pass through the slit, and then observe which way it came through, it will retroactively force it to have passed through one or the other. In other words, causality is working backwards: the present is affecting the past.
Of course in the lab this only has an effect over indescribably tiny fractions of a second. But Wheeler suggested that light from distant stars that has bent around a gravitational well in between could be observed in the same way: which could mean that observing something now and changing what happened thousands, or even millions, of years in the past.
Almost all of the Universe is missing
There are probably more than 100 billion galaxies in the cosmos. Each of those galaxies has between 10 million and a trillion stars in it. Our sun, a rather small and feeble star (a “yellow dwarf”, indeed), weighs around a billion billion billion tons, and most are much bigger. There is an awful lot of visible matter in the Universe.
But it only accounts for about two per cent of its mass.
We know there is more, because it has gravity. Despite the huge amount of visible matter, it is nowhere near enough to account for the gravitational pull we can see exerted on other galaxies. The other stuff is called “dark matter”, and there seems to be around six times as much as ordinary matter.
To make matters even more confusing, the rest is something else called “dark energy”, which is needed to explain the apparent expansion of the Universe. Nobody knows what dark matter or dark energy is.
Things can travel faster than light; and light doesn’t always travel very fast
The speed of light in a vacuum is a constant: 300,000km a second. However, light does not always travel through a vacuum. In water, for example, photons travel at around three-quarters that speed.
In nuclear reactors, some particles are forced up to very high speeds, often within a fraction of the speed of light. If they are passing through an insulating medium that slows light down, they can actually travel faster than the light around them.
When this happens, they cause a blue glow, known as “Cherenkov radiation ”, which is (sort of) comparable to a sonic boom but with light. This is why nuclear reactors glow in the dark.
Incidentally, the slowest light has ever been recorded travelling was 17 meters per second – about 38 miles an hour – through rubidium cooled to almost absolute zero, when it forms a strange state of matter called a Bose-Einstein condensate.
Light has also been brought to a complete stop in the same fashion, but since that wasn't moving at all, we didn't feel we could describe that as "the slowest it has been recorded travelling".
There are an infinite number of mes writing this, and an infinite number of yous reading it
According to the current standard model of cosmology, the observable universe – containing all the billions of galaxies and trillions upon trillions of stars mentioned above – is just one of an infinite number of universes existing side-by-side, like soap bubbles in a foam.
Because they are infinite, every possible history must have played out. But more than that, the number of possible histories is finite, because there have been a finite number of events with a finite number of outcomes. The number is huge, but it is finite. So this exact event, where this author writes these words and you read them, must have happened an infinite number of times.
Even more amazingly, we can work out how far away our nearest doppelganger is. It is, to put it mildly, a large distance: 10 to the power of 10 to the power of 28 meters. That number, in case you were wondering, is one followed by 10 billion billion billion zeroes
Black holes aren’t black
hey’re very dark, sure, but they aren’t black. They glow, slightly, giving off light across the whole spectrum, including visible light.
This radiation is called “Hawking radiation”, after the former Lucasian Professor of Mathematics at Cambridge University Stephen Hawking, who first proposed its existence. Because they are constantly giving this off, and therefore losing mass, black holes will eventually evaporate altogether if they don’t have another source of mass to sustain them; for example interstellar gas or light.
Smaller black holes are expected to emit radiation faster compared to their mass than larger ones, so if – as some theories predict – the Large Hadron Collider creates minuscule holes through particle collisions, they will evaporate almost immediately. Scientists would then be able to observe their decay through the radiation.
The fundamental description of the universe does not account for a past, present or future
According to the special theory of relativity, there is no such thing as a present, or a future, or a past. Time frames are relative: I have one, you have one, the third planet of Gliese 581 has one. Ours are similar because we are moving at similar speeds.
If we were moving at very different speeds, we would find that one of us aged quicker than the other. Similarly, if one of us was closer than the other to a major gravity well like the Earth, we would age slower than someone who wasn’t.
GPS satellites, of course, are both moving quickly and at significant distances from Earth. So their internal clocks show a different time to the receivers on the ground. A lot of computing power has to go into making your sat-nav work around the theory of special relativity.
A particle here can affect one on the other side of the universe, instantaneously
When an electron meets its antimatter twin, a positron, the two are annihilated in a tiny flash of energy. Two photons fly away from the blast.
Subatomic particles like photons and quarks have a quality known as “spin”. It’s not that they’re really spinning – it’s not clear that would even mean anything at that level – but they behave as if they do. When two are created simultaneously the direction of their spin has to cancel each other out: one doing the opposite of the other.
Due to the unpredictability of quantum behaviour, it is impossible to say in advance which will go “anticlockwise” and the other “clockwise”. More than that, until the spin of one is observed, they are both doing both.
It gets weirder, however. When you do observe one, it will suddenly be going clockwise or anticlockwise. And whichever way it is going, its twin will start spinning the other way, instantly, even if it is on the other side of the universe. This has actually been shown to happen in experiment (albeit on the other side of a laboratory, not a universe).
The faster you move, the heavier you get
If you run really fast, you gain weight. Not permanently, or it would make a mockery of diet and exercise plans, but momentarily, and only a tiny amount.
Light speed is the speed limit of the universe. So if something is travelling close to the speed of light, and you give it a push, it can’t go very much faster. But you’ve given it extra energy, and that energy has to go somewhere.
Where it goes is mass. According to relativity, mass and energy are equivalent. So the more energy you put in, the greater the mass becomes. This is negligible at human speeds – Usain Bolt is not noticeably heavier when running than when still – but once you reach an appreciable fraction of the speed of light, your mass starts to increase rapidly.
Originated from: http://www.telegraph.co.uk/science/6546462/The-10-weirdest-physics-facts-from-relativity-to-quantum-physics.html
US team finds direct proof for dark matter
Oct 5, 2006
The idea of dark matter in the universe dates back to the 1930s, with the observation that the gravitational force on the visible matter in clusters of galaxies could not fully account for their behaviour, implying some alteration to gravity, or the existence of non-luminous, invisible matter. Now a team in the US has used a combination of astronomical images to analyse gravitational lensing in a region where two clusters are merging. The researchers find that their observations cannot be explained by modified gravity.
Hot gas
While dark matter has become the focus of a range of research, from cosmology to particle physics, it has proved difficult to rule out the alternative scenario in which gravity is slightly altered from the standard 1/r2 force law. The new study, however, has discovered a system in which the inferred dark matter is not coincident with the observable matter, and the difference in position is too great to be accounted for by modifying gravity. This, the team says, provides direct empirical proof for dark matter.
The team from the universities of Arizona and Florida, the Kavli Institute for Particle Astrophysics and Cosmology, and the Harvard-Smithsonian-Center for Astrophysics has combined observations from various telescopes to build a picture of what is happening in the galaxy cluster 1E0657-558. This cluster is particularly interesting because it shows evidence that a smaller cluster has at some stage ripped through a larger cluster, creating a bow-shaped shock wave.
Using images from the Hubble Space Telescope, the European Southern Observatory's Very Large Telescope and the Magellan telescope to provide information on gravitational lensing of more-distant galaxies, the team has created a map of the gravitational potential across the cluster 1E0657-558. This reveals two regions in which the mass is concentrated.
The team has also observed the cluster with NASA's Chandra X-ray Observatory to measure the positions of the two clouds of hot gas that are associated with the merging galaxies. It finds that these two clouds of X-ray emitting plasma of normal baryonic matter are not coincident with the two central locations of the gravitational mass, which in fact are further apart. This suggests that the plasma clouds have slowed as they passed through each other and interacted, while dark matter in the two clusters has not interacted.
Further reading
D Clowe et. al. 2006 Ap. J. 648 L109.
Origin source: http://cerncourier.com/cws/article/cern/29711
2010/02/23
The principle of Hamiltonianization of physics
The theoretical development of the laws of motion of bodies is of such interest and importance, that it has engaged the attention of all the most eminent mathematicians, since the invention of dynamics as a mathematical science by Galileo...
Among the sucessors of those illustrious men, Lagrange has perhaps done more than any other analyst, to give extent and harmony to such deductive researches, by showing that the most varied consequences respecting the motions of systems of bodies may be derived from one radical formula[Lagrange's equations]; the beauty of the method so suiting the dignity of the results, as to make his great work a kind of scientific poem.
W. R. Hamilton, 1834
Among the sucessors of those illustrious men, Lagrange has perhaps done more than any other analyst, to give extent and harmony to such deductive researches, by showing that the most varied consequences respecting the motions of systems of bodies may be derived from one radical formula[Lagrange's equations]; the beauty of the method so suiting the dignity of the results, as to make his great work a kind of scientific poem.
W. R. Hamilton, 1834
2008/08/25
The Nature of Microscopic World: Behind Quantum Mechanics
As one turns the scale to the atom level, the behavior of a particle becomes very unpredictable. Quantum mechanics has a better description of microscopic properties than classical mechanics for this scale. It brings us the most precise and successful numerical predictions in the history of science. But a contradiction accompanied with the development of quantum mechanics was brought to light, and has been queried from realists. It is certain that the probabilistic interpretation contravenes the law of causality, and is unable to delineate the fundamental physical process of the universe. According to quantum mechanics, measurements of some properties, such as a particle's momentum for example, can yield a range of possible results with varying probabilities. In other words, the objective physical process, once physicists took it for granted to possess definite properties that suitable observations can reveal, is no longer adaptable in the microscopic world.
The need for a more complete theory is revealed as our understanding of the physical universe has deepened profoundly, and, in particular, as the desiderative exploration of the very beginning of our universe has been carried out. One of the possible theories is the “hidden variable theory” proposed by D. Bohm
The main purpose of this article is to explore the process of visualizing hidden variables, and to represent a complete theory within microscopic physics. One can imagine that there is a bee in a house with no window. The bee has a special power allowing it to pass through walls to go outside. Of course, we cannot see the bee while it stays outside the house and we are inside. It can only be seen after passing through the wall and coming back into the house again. Hence, what we can observe is that the bee appears all of a sudden and disappears later if it passes in and out of the house. In such a condition, we have no idea about when it will come back to the house for the reason that we cannot see anything outside the house, but what we can do is to estimate the probability of being stung by the bee according to the position we are in inside the house. This is the probabilistic interpretation proposed by quantum mechanics to describe a quantum system.
On the other hand, let us replace all the walls of the house by transparent glass then there will be no doubt that we can see everything outside the house as we stay inside. Now, we still can observe where the bee is and even how it moves after it is passing through the glass wall to go outside. There is no problem for us to predict its flight path, position, velocity and heading. In other words, we can be told when and where the bee comes back into the house in a deterministic way, without estimating the stinging probability. A contrast can be made here that transparent walls symbolize the visualization process; it can reveal motions of the bee outside the house in the former case in an objective physical process. Consequently, a continuous and deterministic interpretation of the quantum world can arise if we can find some method of replacing the invisible border.
It is straightforward to think of extending dimension to bring transparent walls into existence. To deliberate on the imperceptible part to the sense at quantum level, a rational speculation of complex domain could strike a bargain, in which its imaginary part can represent the invisible world. In fact, it is not an unrestrained attempt originated from an intuition only. The complex concept was objective in Schrodinger’s equation and can be made aware of by the appearance of the imaginary factor “i”, and has been permitted as a genuine mathematical tool. In fact, the ignoring of the imaginary sign in wave mechanics can be attributed to practical experimental results, which cause people’s attention to delve into the atom scale. Owing to the limited observable dimension, imaginary features of nature which could dissolve the consequence of experiments has been eliminated by empiricists. However, no thorough canvass can be addressed if our understanding of nature contains a one-legged version of the full view. This is the main reason why quantum mechanics is an incomplete theory, for its grounds for existence lie on observation that has been criticized from the philosophical aspect and the causality of its nature.
In pioneering work approaching causal quantum physics, a remarkable achievement based on the complex concept has been proposed by C. D. Yang
One of the most elusive parts of this causal quantum physics, or so-called quantum
Therefore, the wave function decided by Schrodinger’s equation describes a particle’s motion statistically and cannot provide more detail about each trajectory. It is clearer to think of it as a water flow; since we cannot know a specific molecule’s motion by observing its whole flow, and can only understand the probability of this molecule passing by a specific area. This is the limitation of describing a quantum motion based on wave mechanics since it provides a macroscopic observation which cannot be overlooked. On the contrary, a fully informative view of a particle’s motion can be presented in terms of causal description from the same wave function. We can observe a specific particle’s motion with the help of quantum
E-mail: ngcmars@gmail.com
Reference
physical reality be considered complete?, Physical Review, 47, 777 (1935).
Reprinted in Quantum Theory and Measurement, p. 139, (1987).
2. Bohm, David. "A Suggested Interpretation of the Quantum Theory in Terms of
"Hidden Variables" I". Physical Review 85: 166-179. (1952).
3. R.P.Feynman: Space-Time Approach to Non-Relativistic Quantum Mechanics, Rev.
Mod. Phys. 367, (1948).
4. C. D. Yang, Quantum Hamilton mechanics:
5. C. D. Yang, Wave particle duality in complex space, Ann. of Phys., 319, 444-470 (2005).
6. C. D. Yang, On Modeling and Visualizing Single-Electron Spin Motion, Chaos, Solitons, & Fractals, 30, 41 -50, (2006)
Black Holes May Make Good Mommies
By Phil Berardelli
ScienceNOW Daily News
22 August 2008
The popular conception of black holes is that they obliterate anything in their path, including time, space, and matter. Stars can escape annihilation if their orbits keep them far enough away. But some stars not only orbit perilously close to a supermassive black hole but also appear to have formed in its vicinity. Earlier in this decade, for example, astronomers spotted a population of very young--under 10 million years old--and very massive stars locked in elliptical orbits around the Milky Way's central black hole (ScienceNOW, 13 October 2005).
Could the stars have migrated there? Not likely. They're too young, and there are no nearby star hatcheries that could have produced them. The other possibility is that the stars formed in place. But astronomers also considered that idea unlikely, because the supermassive black hole would have shredded any cloud of gas--from which all stars condense--pulled into its influence.
Now the homegrown scenario seems more realistic, thanks to a computer model developed by astrophysicists Ian Bonnell of the University of St. Andrews in Fife, U.K., and Kenneth Rice of the University of Edinburgh, U.K. The simulation, which required more than a year of supercomputer time, tracked two hypothetical clouds of molecular hydrogen--the basic stellar building material--moving within a light-year or so of a supermassive black hole, much like the one anchoring the Milky Way. The researchers report today in Science that as the clouds fell toward the black hole, its gravity disrupted but did not destroy their clumpy structure. Eventually, the clouds flattened and merged into a disk that followed an elliptical orbit. During the flattening, nearly 200 new stars ignited, within a few hundred thousand years. Nearly all the resulting stars were very massive, meaning that they will live short and violent lives ending in supernovae.
The findings raise the question of where the star-forming clouds in the Milky Way would have come from. Bonnell and Rice speculate that they drifted freely within the galaxy until interaction with some other object or objects, such as larger clouds or other black holes, sent them hurtling toward the supermassive central black hole. But the answer remains unclear.
The simulation is a "breakthrough," says astronomer Mark Voit of Michigan State University in East Lansing, because it helps explain why those massive young stars around the Milky Way's center follow such elongated orbits. It "addresses one of the big open questions in astrophysics," adds Volker Bromm, an astrophysicist at the University of Texas, Austin. Thanks to this work, he says, "one wonders what the next-generation telescopes will find in the far-away universe just a few years from now."
From: http://sciencenow.sciencemag.org/cgi/content/full/2008/822/2?etoc
2008/06/24
Why Sleep?
Phys. Rev. E 77, 011922 (issue of January 2008) Title and Authors
8 January 2008
Why Sleep?
Getty Images
Concentrate on napping. Researchers aren't sure why animals need to sleep, but a new study suggests that any system is more efficient when it focuses on one task at a time, rather than trying to multitask. With a sleep-wake cycle, the brain collects information during the day and processes it at night.
Why we sleep remains a mystery. Competing theories claim various "house-cleaning" brain activities occur during sleep, but they can't say why we need to power down to accomplish them. A study in the January Physical Review E suggests that a sleep-wake cycle, allowing the brain to focus on one task at a time, may be the most efficient way to operate. The researcher shows mathematically that processing a continuously changing resource--sensory input, in the brain's case--is best done "offline," when there's no input. This sort of analysis may lead to a more precise biological explanation for why sleep and other biological cycles evolved.
Humans spend a third of their lives asleep, and sleep is essential to our health. But scientists do not yet agree on its purpose. One theory is that the brain requires sleep to consolidate information collected during the day, while another theory says that the brain needs to sweep out harmful free radicals that build up during waking hours. But turning off the senses seems impractical, if not outright dangerous. It would seem better for an organism to perform sleep-related tasks in parallel with being awake.
To address this question, Emmanuel Tannenbaum of Ben Gurion University in Beer Sheva, Israel, proposes the concept of temporal differentiation, in which a system focuses on one task at a time, rather than trying to multitask. The advantages of a time-varying strategy have been studied in traffic control, computer programming, and operations research. But Tannenbaum believes he is the first to consider the brain as a "factory" for information processing, for which certain routines are more efficient than others.
In his paper, Tannenbaum analyzes two models. The first involves a tank with two pipes--one for filling and one for emptying--which can be opened one at a time. Assuming the incoming resource flow continuously switches between "on" and "off," Tannenbaum proves mathematically that one way to maximize the flow through the tank is to fill whenever the resource is available and empty when it isn't. The resource is analogous to sensory information that fills the brain and needs to be processed (emptied). Tannenbaum reasons that many animals can only receive visual information when there is light, so an efficient strategy, according to the tank model, is to be alert during daylight hours and devote all one's time in darkness to processing. As a comparison, Tannenbaum calculates the productivity of alternating rapidly between filling and emptying (equivalent to being half-asleep and half-awake simultaneously) and finds this approach less efficient.
Certain sleep behaviors, like episodic REM sleep and nocturnal habits, do not fit this picture, so Tannenbaum formulated a more generic model, in which a resource supplied at a fixed rate is processed in three separate steps, such that the initial, intermediate, and final products are all present in varying concentrations. The model bears some resemblance to the cyclic reactions of circadian rhythm proteins, which keep many organisms on 24-hour clocks even in complete darkness. Tannenbaum finds that a temporally differentiated case, where the steps are performed separately, is 33 percent more efficient at producing the final product than an undifferentiated case, where all three steps run simultaneously. This result depends on the details of the model, but he believes that optimization through temporal differentiation might explain why certain cyclic behaviors evolved.
James Krueger, a sleep expert at Washington State University, says that this is definitely a new approach, but he thinks Tannenbaum ignores a host of sleep phenomena, such as the localization of sleep to specific areas of the brain and the fact that some sensory input continues during sleep. Still, he welcomes the effort and admits that "any new idea cannot address everything at once." --Michael Schirber Michael Schirber is a freelance science writer in Montpellier, France.
Temporal Differentiation and the Optimization of System Output Emmanual Tannenbaum Phys. Rev. E 77, 011922 (issue of January 2008)
From: http://focus.aps.org/story/v21/st1
8 January 2008
Why Sleep?
Getty Images
Concentrate on napping. Researchers aren't sure why animals need to sleep, but a new study suggests that any system is more efficient when it focuses on one task at a time, rather than trying to multitask. With a sleep-wake cycle, the brain collects information during the day and processes it at night.
Why we sleep remains a mystery. Competing theories claim various "house-cleaning" brain activities occur during sleep, but they can't say why we need to power down to accomplish them. A study in the January Physical Review E suggests that a sleep-wake cycle, allowing the brain to focus on one task at a time, may be the most efficient way to operate. The researcher shows mathematically that processing a continuously changing resource--sensory input, in the brain's case--is best done "offline," when there's no input. This sort of analysis may lead to a more precise biological explanation for why sleep and other biological cycles evolved.
Humans spend a third of their lives asleep, and sleep is essential to our health. But scientists do not yet agree on its purpose. One theory is that the brain requires sleep to consolidate information collected during the day, while another theory says that the brain needs to sweep out harmful free radicals that build up during waking hours. But turning off the senses seems impractical, if not outright dangerous. It would seem better for an organism to perform sleep-related tasks in parallel with being awake.
To address this question, Emmanuel Tannenbaum of Ben Gurion University in Beer Sheva, Israel, proposes the concept of temporal differentiation, in which a system focuses on one task at a time, rather than trying to multitask. The advantages of a time-varying strategy have been studied in traffic control, computer programming, and operations research. But Tannenbaum believes he is the first to consider the brain as a "factory" for information processing, for which certain routines are more efficient than others.
In his paper, Tannenbaum analyzes two models. The first involves a tank with two pipes--one for filling and one for emptying--which can be opened one at a time. Assuming the incoming resource flow continuously switches between "on" and "off," Tannenbaum proves mathematically that one way to maximize the flow through the tank is to fill whenever the resource is available and empty when it isn't. The resource is analogous to sensory information that fills the brain and needs to be processed (emptied). Tannenbaum reasons that many animals can only receive visual information when there is light, so an efficient strategy, according to the tank model, is to be alert during daylight hours and devote all one's time in darkness to processing. As a comparison, Tannenbaum calculates the productivity of alternating rapidly between filling and emptying (equivalent to being half-asleep and half-awake simultaneously) and finds this approach less efficient.
Certain sleep behaviors, like episodic REM sleep and nocturnal habits, do not fit this picture, so Tannenbaum formulated a more generic model, in which a resource supplied at a fixed rate is processed in three separate steps, such that the initial, intermediate, and final products are all present in varying concentrations. The model bears some resemblance to the cyclic reactions of circadian rhythm proteins, which keep many organisms on 24-hour clocks even in complete darkness. Tannenbaum finds that a temporally differentiated case, where the steps are performed separately, is 33 percent more efficient at producing the final product than an undifferentiated case, where all three steps run simultaneously. This result depends on the details of the model, but he believes that optimization through temporal differentiation might explain why certain cyclic behaviors evolved.
James Krueger, a sleep expert at Washington State University, says that this is definitely a new approach, but he thinks Tannenbaum ignores a host of sleep phenomena, such as the localization of sleep to specific areas of the brain and the fact that some sensory input continues during sleep. Still, he welcomes the effort and admits that "any new idea cannot address everything at once." --Michael Schirber Michael Schirber is a freelance science writer in Montpellier, France.
Temporal Differentiation and the Optimization of System Output Emmanual Tannenbaum Phys. Rev. E 77, 011922 (issue of January 2008)
From: http://focus.aps.org/story/v21/st1
Squeezed into Darkness
Phys. Rev. Lett. 100, 203601 (issue of 23 May 2008) Title and Authors
8 May 2008
Squeezed into Darkness
Phys. Rev. Lett. 100, 203601 (2008)
Symmetry breaking. An optical cavity containing a special crystal can emit a beam with this intensity pattern (beam coming toward you). Theorists calculate that a related mode can lead to a beam with unwavering intensity, without some of the usual technical requirements.
According to quantum mechanics, empty space teems with random electromagnetic oscillations that limit the precision of optical measurements. Schemes to "squeeze" light and dodge this quantum limit require a carefully-tuned light intensity and other conditions. In the 23 May Physical Review Letters, Spanish researchers propose an alternative squeezing strategy that should be less finicky. If it proves experimentally feasible, the technique could permit improved measurements of gravitational waves or more practical ways to transmit quantum information.
Physicists often describe quantum-mechanical precision limits using the Heisenberg uncertainty principle, which places strict limits on how well quantities can be measured, even with perfect equipment. But this rule limits the combined uncertainty of pairs of related quantities, like the position and momentum of a particle. Researchers are free to measure the particle's position exactly, as long as they abandon any knowledge of its momentum, or vice versa.
A similar tradeoff applies to light waves, which have an intrinsic variability reflecting their quantum nature. Beginning in the 1980s, researchers learned how to experimentally "squeeze" light, for example, to precisely determine the light wave's amplitude at the expense of its phase, the number that measures the wave's progress through its oscillating cycle. But Germán de Valcárcel, of the University of Valencia in Spain, says that squeezing is significant only when the light intensity is chosen carefully. In his team's new technique the intensity of the input light "need not be tuned in order to obtain, ideally, perfectly squeezed light," he says.
To generate squeezed light, physicists typically shine laser light into an optical cavity, where it bounces back and forth between two partially transparent mirrors. The cavity contains a "nonlinear" crystal that converts the light into squeezed light of a new color with twice the wavelength. To optimize the effect, the input light must be carefully tuned to have intensity at or near a specific value called the threshold.
De Valcárcel and his colleagues propose using an input intensity well above the threshold and adjusting the mirror spacing so that the new light emerges with an intensity pattern in the shape of a dumbbell: with the beam coming toward you, you might see bright regions above and below, for example, with a dark lane horizontally across the middle. The critical ingredient, says de Valcárcel, is "symmetry breaking": the pattern is free to emerge with any orientation angle. "This angle is arbitrary," he says, so over time the pattern will rotate randomly.
Although the light "chooses" a particular orientation for the dumbbell pattern, or mode, the cavity also allows a second mode, which is identical but rotated by 90 degrees around the beam axis with respect to the first one. The researchers calculate that the completely unknown orientation of the first mode results in perfect precision for one aspect of the second, "dark" mode. Specifically, a component of this mode, the light signal that is exactly a quarter-cycle delayed from the bright mode, should be precisely zero--lacking even the usual quantum-mechanical fluctuations of empty space. Researchers could mix this "super-dark" mode with another laser to make a low-noise beam for precise measurements, such as detecting the tiny motions caused by gravitational waves.
Julio Gea-Banacloche, of the University of Arkansas in Fayetteville, is intrigued by the theoretical intuition that leads to the surprising new result. But he cautions that experimentalists usually avoid working above threshold because any noise reduction in one mode is hard to measure in the presence of very bright and noisy light in the other mode. --Don Monroe Don Monroe is a freelance science writer in Murray Hill, New Jersey.
Related Information:
Demonstration of a tenfold reduction in noise power using traditional squeezing techniques:H. Vahlbruch et al., "Observation of Squeezed Light with 10-dB Quantum-Noise Reduction," Phys. Rev. Lett. 100, 033602 (2008).
Noncritically Squeezed Light Via Spontaneous Rotational Symmetry Breaking Carlos Navarrete-Benlloch, Eugenio Roldán, and Germán J. de Valcárcel Phys. Rev. Lett. 100, 203601 (issue of 23 May 2008)
From: http://focus.aps.org/story/v21/st16
8 May 2008
Squeezed into Darkness
Phys. Rev. Lett. 100, 203601 (2008)
Symmetry breaking. An optical cavity containing a special crystal can emit a beam with this intensity pattern (beam coming toward you). Theorists calculate that a related mode can lead to a beam with unwavering intensity, without some of the usual technical requirements.
According to quantum mechanics, empty space teems with random electromagnetic oscillations that limit the precision of optical measurements. Schemes to "squeeze" light and dodge this quantum limit require a carefully-tuned light intensity and other conditions. In the 23 May Physical Review Letters, Spanish researchers propose an alternative squeezing strategy that should be less finicky. If it proves experimentally feasible, the technique could permit improved measurements of gravitational waves or more practical ways to transmit quantum information.
Physicists often describe quantum-mechanical precision limits using the Heisenberg uncertainty principle, which places strict limits on how well quantities can be measured, even with perfect equipment. But this rule limits the combined uncertainty of pairs of related quantities, like the position and momentum of a particle. Researchers are free to measure the particle's position exactly, as long as they abandon any knowledge of its momentum, or vice versa.
A similar tradeoff applies to light waves, which have an intrinsic variability reflecting their quantum nature. Beginning in the 1980s, researchers learned how to experimentally "squeeze" light, for example, to precisely determine the light wave's amplitude at the expense of its phase, the number that measures the wave's progress through its oscillating cycle. But Germán de Valcárcel, of the University of Valencia in Spain, says that squeezing is significant only when the light intensity is chosen carefully. In his team's new technique the intensity of the input light "need not be tuned in order to obtain, ideally, perfectly squeezed light," he says.
To generate squeezed light, physicists typically shine laser light into an optical cavity, where it bounces back and forth between two partially transparent mirrors. The cavity contains a "nonlinear" crystal that converts the light into squeezed light of a new color with twice the wavelength. To optimize the effect, the input light must be carefully tuned to have intensity at or near a specific value called the threshold.
De Valcárcel and his colleagues propose using an input intensity well above the threshold and adjusting the mirror spacing so that the new light emerges with an intensity pattern in the shape of a dumbbell: with the beam coming toward you, you might see bright regions above and below, for example, with a dark lane horizontally across the middle. The critical ingredient, says de Valcárcel, is "symmetry breaking": the pattern is free to emerge with any orientation angle. "This angle is arbitrary," he says, so over time the pattern will rotate randomly.
Although the light "chooses" a particular orientation for the dumbbell pattern, or mode, the cavity also allows a second mode, which is identical but rotated by 90 degrees around the beam axis with respect to the first one. The researchers calculate that the completely unknown orientation of the first mode results in perfect precision for one aspect of the second, "dark" mode. Specifically, a component of this mode, the light signal that is exactly a quarter-cycle delayed from the bright mode, should be precisely zero--lacking even the usual quantum-mechanical fluctuations of empty space. Researchers could mix this "super-dark" mode with another laser to make a low-noise beam for precise measurements, such as detecting the tiny motions caused by gravitational waves.
Julio Gea-Banacloche, of the University of Arkansas in Fayetteville, is intrigued by the theoretical intuition that leads to the surprising new result. But he cautions that experimentalists usually avoid working above threshold because any noise reduction in one mode is hard to measure in the presence of very bright and noisy light in the other mode. --Don Monroe Don Monroe is a freelance science writer in Murray Hill, New Jersey.
Related Information:
Demonstration of a tenfold reduction in noise power using traditional squeezing techniques:H. Vahlbruch et al., "Observation of Squeezed Light with 10-dB Quantum-Noise Reduction," Phys. Rev. Lett. 100, 033602 (2008).
Noncritically Squeezed Light Via Spontaneous Rotational Symmetry Breaking Carlos Navarrete-Benlloch, Eugenio Roldán, and Germán J. de Valcárcel Phys. Rev. Lett. 100, 203601 (issue of 23 May 2008)
From: http://focus.aps.org/story/v21/st16
Laser Cooling of Atoms
Phys. Rev. Lett. 61, 169 (issue of 11 July 1988) Phys. Rev. Lett. 48, 596 (issue of 1 March 1982) Phys. Rev. Lett. 40, 1639 (issue of 19 June 1978) Titles and Authors
2 April 2008
Landmarks: Laser Cooling of Atoms
H. M. Helfer/NIST
Frozen. A cloud of cold sodium atoms (bright spot at center) floats in a trap. Researchers began cooling atoms with lasers in 1978, reaching below 40 Kelvin. They achieved temperatures a million times colder just ten years later, eventually leading to better atomic clocks and the observation of a new ultracold state of matter.
APS has put the entire Physical Review archive online, back to 1893. Focus Landmarks feature important papers from the archive.
In the 1970s and 80s, physicists learned how to use lasers to cool atoms to temperatures just barely above absolute zero. Three papers from that era, all published in Physical Review Letters, highlight some of the essential steps in the development of the technology. In 1978, researchers cooled ions somewhat below 40 Kelvin; ten years later, neutral atoms had gotten a million times colder, to 43 microkelvin. But the basic principle remained the same: use the force of laser light applied to atoms to slow them down. The work led to the creation of a new quantum form of matter called a Bose-Einstein condensate and to modern atomic clocks, as well as at least two Nobel prizes.
The original reason to cool atoms--that is, reduce the speed of their motion--was to allow more precise measurements of atomic spectra, and later, to improve atomic clocks. In 1978 Dave Wineland and his colleagues at what is now the National Institute of Standards and Technology (NIST) in Boulder, Colorado, followed theoretical proposals [1] and managed to laser cool magnesium ions.
As the team described in PRL, they confined the ions in an electromagnetic trap and hit them with a laser tuned to a frequency a bit below a "resonance" frequency for the ions. At rest, the ions absorb photons at the resonance frequency, but if they're moving toward the beam, its lower frequency appears Doppler shifted to the correct frequency, allowing them to absorb photons coming toward them. These photons slow down the ions until the cooling effect is balanced by the small heating that is always present when the laser is on. In later years, this heating--which comes from atoms recoiling every time they randomly emit or absorb a photon in any direction--would ultimately limit the cooling possible with this so-called Doppler cooling technique.
In Boston, William Phillips read Wineland's experimental article and a theoretical paper [2] with great interest. He was just finishing a postdoctoral fellowship at the Massachusetts Institute of Technology and heading to the NIST lab in Gaithersburg, Maryland. "The idea of cooling ions made me think that it might be possible to do the same thing with neutral atoms," says Phillips.
In 1982, Phillips and Harold Metcalf of Stony Brook University in New York published the first paper on laser cooling of neutral atoms. They sent a beam of sodium atoms through a magnetic field that was large at the entrance to the apparatus but became gradually smaller over a distance of 60 centimeters. While moving through the field, the atoms headed directly into an off-resonance laser that used Doppler cooling to reduce the range of atomic velocities among atoms in the beam. The laser also slowed the beam as a whole. During deceleration, the changing magnetic field changed the atoms' resonant frequency, so that the slowing and cooling continued over a long distance, allowing them to reach 40 percent of their initial velocity. Now called a Zeeman slower, this device has become a standard way of decelerating an atomic beam.
Laser cooling techniques improved, and by the late 1980s, researchers had achieved what they thought were the lowest possible temperatures, according to Doppler cooling theory--240 microkelvin for sodium atoms. Then in 1988, a group led by Phillips accidentally discovered that a technique developed three years earlier at another lab [3] could shatter the Doppler limit. They used three mutually perpendicular pairs of lasers to cool sodium atoms, with laser frequencies somewhat different from other labs. They discovered, using several new temperature measurement techniques, that their atoms were at about 43 microkelvin. Theorists quickly explained the unexpected cooling mechanisms by including more atomic states and the effects of laser polarization; previous cooling models were overly simplistic.
Guided by the new theory, experimentalists reached much colder temperatures and developed additional cooling techniques. Phillips' "sub-Doppler" cooling was an early step in the 1995 creation of a Bose-Einstein condensate, a new state of matter where gaseous atoms all drop to the lowest possible energy state.
Atomic clocks benefited as well. The latest generation uses techniques derived directly from what Phillips and others did in the 1980s. Phillips and others won the Nobel Prize in 1997 for developing laser cooling; another prize in 2001 was awarded for the creation of Bose-Einstein condensates.--Jason Socrates Bardi Jason Socrates Bardi is a senior science writer at the American Institute of Physics.
References:[1] D. J. Wineland and H. Dehmelt, Bull. Am. Phys. Soc. 20, 637 (1975); T. W. Hänsch and A. L. Schawlow, "Cooling of Gases by Laser Radiation," Opt. Commun. 13, 68 (1975).[2] A. Ashkin, "Trapping of Atoms by Resonance Radiation Pressure," Phys. Rev. Lett. 40, 729 (1978).[3] S. Chu et al., "Three-Dimensional Viscous Confinement and Cooling of Atoms by Resonance Radiation Pressure," Phys. Rev. Lett. 55, 48 (1985).
Related Information:
1997 Nobel Prize in physics
Observation of Atoms Laser Cooled below the Doppler Limit Paul D. Lett, Richard N. Watts, Christoph I. Westbrook, William D. Phillips, Phillip L. Gould, and Harold J. Metcalf Phys. Rev. Lett. 61, 169 (issue of 11 July 1988)
Laser Deceleration of an Atomic Beam William D. Phillips and Harold Metcalf Phys. Rev. Lett. 48, 596 (issue of 1 March 1982)
Radiation-Pressure Cooling of Bound Resonant Absorbers D. J. Wineland, R. E. Drullinger, and F. L. Walls Phys. Rev. Lett. 40, 1639 (issue of 19 June 1978)
From : http://focus.aps.org/story/v21/st11
2 April 2008
Landmarks: Laser Cooling of Atoms
H. M. Helfer/NIST
Frozen. A cloud of cold sodium atoms (bright spot at center) floats in a trap. Researchers began cooling atoms with lasers in 1978, reaching below 40 Kelvin. They achieved temperatures a million times colder just ten years later, eventually leading to better atomic clocks and the observation of a new ultracold state of matter.
APS has put the entire Physical Review archive online, back to 1893. Focus Landmarks feature important papers from the archive.
In the 1970s and 80s, physicists learned how to use lasers to cool atoms to temperatures just barely above absolute zero. Three papers from that era, all published in Physical Review Letters, highlight some of the essential steps in the development of the technology. In 1978, researchers cooled ions somewhat below 40 Kelvin; ten years later, neutral atoms had gotten a million times colder, to 43 microkelvin. But the basic principle remained the same: use the force of laser light applied to atoms to slow them down. The work led to the creation of a new quantum form of matter called a Bose-Einstein condensate and to modern atomic clocks, as well as at least two Nobel prizes.
The original reason to cool atoms--that is, reduce the speed of their motion--was to allow more precise measurements of atomic spectra, and later, to improve atomic clocks. In 1978 Dave Wineland and his colleagues at what is now the National Institute of Standards and Technology (NIST) in Boulder, Colorado, followed theoretical proposals [1] and managed to laser cool magnesium ions.
As the team described in PRL, they confined the ions in an electromagnetic trap and hit them with a laser tuned to a frequency a bit below a "resonance" frequency for the ions. At rest, the ions absorb photons at the resonance frequency, but if they're moving toward the beam, its lower frequency appears Doppler shifted to the correct frequency, allowing them to absorb photons coming toward them. These photons slow down the ions until the cooling effect is balanced by the small heating that is always present when the laser is on. In later years, this heating--which comes from atoms recoiling every time they randomly emit or absorb a photon in any direction--would ultimately limit the cooling possible with this so-called Doppler cooling technique.
In Boston, William Phillips read Wineland's experimental article and a theoretical paper [2] with great interest. He was just finishing a postdoctoral fellowship at the Massachusetts Institute of Technology and heading to the NIST lab in Gaithersburg, Maryland. "The idea of cooling ions made me think that it might be possible to do the same thing with neutral atoms," says Phillips.
In 1982, Phillips and Harold Metcalf of Stony Brook University in New York published the first paper on laser cooling of neutral atoms. They sent a beam of sodium atoms through a magnetic field that was large at the entrance to the apparatus but became gradually smaller over a distance of 60 centimeters. While moving through the field, the atoms headed directly into an off-resonance laser that used Doppler cooling to reduce the range of atomic velocities among atoms in the beam. The laser also slowed the beam as a whole. During deceleration, the changing magnetic field changed the atoms' resonant frequency, so that the slowing and cooling continued over a long distance, allowing them to reach 40 percent of their initial velocity. Now called a Zeeman slower, this device has become a standard way of decelerating an atomic beam.
Laser cooling techniques improved, and by the late 1980s, researchers had achieved what they thought were the lowest possible temperatures, according to Doppler cooling theory--240 microkelvin for sodium atoms. Then in 1988, a group led by Phillips accidentally discovered that a technique developed three years earlier at another lab [3] could shatter the Doppler limit. They used three mutually perpendicular pairs of lasers to cool sodium atoms, with laser frequencies somewhat different from other labs. They discovered, using several new temperature measurement techniques, that their atoms were at about 43 microkelvin. Theorists quickly explained the unexpected cooling mechanisms by including more atomic states and the effects of laser polarization; previous cooling models were overly simplistic.
Guided by the new theory, experimentalists reached much colder temperatures and developed additional cooling techniques. Phillips' "sub-Doppler" cooling was an early step in the 1995 creation of a Bose-Einstein condensate, a new state of matter where gaseous atoms all drop to the lowest possible energy state.
Atomic clocks benefited as well. The latest generation uses techniques derived directly from what Phillips and others did in the 1980s. Phillips and others won the Nobel Prize in 1997 for developing laser cooling; another prize in 2001 was awarded for the creation of Bose-Einstein condensates.--Jason Socrates Bardi Jason Socrates Bardi is a senior science writer at the American Institute of Physics.
References:[1] D. J. Wineland and H. Dehmelt, Bull. Am. Phys. Soc. 20, 637 (1975); T. W. Hänsch and A. L. Schawlow, "Cooling of Gases by Laser Radiation," Opt. Commun. 13, 68 (1975).[2] A. Ashkin, "Trapping of Atoms by Resonance Radiation Pressure," Phys. Rev. Lett. 40, 729 (1978).[3] S. Chu et al., "Three-Dimensional Viscous Confinement and Cooling of Atoms by Resonance Radiation Pressure," Phys. Rev. Lett. 55, 48 (1985).
Related Information:
1997 Nobel Prize in physics
Observation of Atoms Laser Cooled below the Doppler Limit Paul D. Lett, Richard N. Watts, Christoph I. Westbrook, William D. Phillips, Phillip L. Gould, and Harold J. Metcalf Phys. Rev. Lett. 61, 169 (issue of 11 July 1988)
Laser Deceleration of an Atomic Beam William D. Phillips and Harold Metcalf Phys. Rev. Lett. 48, 596 (issue of 1 March 1982)
Radiation-Pressure Cooling of Bound Resonant Absorbers D. J. Wineland, R. E. Drullinger, and F. L. Walls Phys. Rev. Lett. 40, 1639 (issue of 19 June 1978)
From : http://focus.aps.org/story/v21/st11
訂閱：
文章 (Atom)
