Typhoon wrote:Parodite wrote:If the above is sensible, then the only valid question that remains is how to recover classical physics from QM...and vice-versa.
Bell's Theorem does the job.
Thanks, I'll take a good bite of that.
Typhoon wrote:Parodite wrote:If the above is sensible, then the only valid question that remains is how to recover classical physics from QM...and vice-versa.
Bell's Theorem does the job.
Typhoon wrote:Doc wrote:OK CS Here is what Thomas has to say about measurement. Do you have any problems with it?(I transcribed this so any typos are mine)Let us reconsider a particle which is isolated from the rest of the universe, or has been generated as a new particle and has not yet interacted with the rest of the universe, ie., it has not yet been measured or observed. What can we say about its properties? Once again in the absence of absolutes(There is not universal unit of measure that it absolute - my insert), nature is fundamentally unable to assign absolute values to the particle. And because the particle has not yet interacted with the rest of the universe to be measured or observed, nature is unable to assign any relative values either. As discussed in the last section, all we can say about its property values is "They go up to 11", an essentially meaningless statement reflecting the fact that the particle's property values are undefined -- they have no relation to the rest of the universe. Before observation or measurement, the object must be like a blank sheet: it must be an undefined object with the potential to take up any possible property values. So before observation, the object must have a multi-valued form of reality -- as is observed in quantum mechanical behavior. It is only when the object interacts with the rest of the universe that its properties become progressively tied down to particular values.
This is what we saw in the case of environmental decoherence. It is through interaction with the rest of the universe, via the measuring apparatus,(the measuring apparatus being huge compared to the particle measured -- my insert) that the properties of a particle become fixed.
So here, rather wonderfully, we have a rational -- an explanation -- for the multi-valued nature of quantum behavior before measurement, or observation. Here are the logical steps we followed to get to this conclusion:
1) Nature has no access to absolutes, so it is always fundamentally unable to assign absolute property values to a particle.
2)Therefore, particle properties are defined by the relationship of that particle with the rest of the universe.
3)Bearing this in mind, if we consider as isolated particle, or a newly generated particle which has not yet been measured or observed, nature has fundamentally no way of assigning any form of property values -- absolute or relative to the particle.
4) The properties of the particle are therefore fundamentally undefined -- like a blank sheet. Its properties must have the potential to be any possible value
5)The object must therefore have a multi-valued form of reality before it is observed. It is only after observation -- when the object interacts with the rest of the universe -- that the properties of the object become fixed.
Anyway what do you think about this?
Not even wrong.
Let's have a look at the non-relativistic QM Schrödinger equation which is known to describe the evolution of, for example, a single partice wave function Psi:
m is the mass of the particle. It is not ever "undefined".
Even if we set the potential V(x), which in the QM case describes the interaction of the particle with the rest of the universe, identically to zero
m is still defined.
The relativistic QM Dirac equation for a single particle, with V(x) zero, is given by
wherein the particle now has both mass m and the matrices beta, alpha_1, alpha_2, alpha_3 which describe the electron's intrinsic spin of 1/2 [in units of hbar: Planck's constant / 2 * Pi]
These properties carry over into the QFT of the electron:
[click on the equation for the link to the details]
To sum up, if the properties of a fundamental particle, it's mass, intrinsic spin, and possible charges (electric, weak, colour) are "undefined" at some point, then we can't write down an equation for it.
Another point: mathematics is the language of the physical universe.
I don't think that one can learn physics without mathematics.
For anyone who would like to learn non-relativistic QM, the best textbooks are
Quantum Mechanics: Vol. I and II by Claude Cohen-Tannoudji and Bernard Diu
bar none.
I don't think that one can learn physics without mathematics.
Doc wrote:Typhoon wrote:Doc wrote:OK CS Here is what Thomas has to say about measurement. Do you have any problems with it?(I transcribed this so any typos are mine)Let us reconsider a particle which is isolated from the rest of the universe, or has been generated as a new particle and has not yet interacted with the rest of the universe, ie., it has not yet been measured or observed. What can we say about its properties? Once again in the absence of absolutes(There is not universal unit of measure that it absolute - my insert), nature is fundamentally unable to assign absolute values to the particle. And because the particle has not yet interacted with the rest of the universe to be measured or observed, nature is unable to assign any relative values either. As discussed in the last section, all we can say about its property values is "They go up to 11", an essentially meaningless statement reflecting the fact that the particle's property values are undefined -- they have no relation to the rest of the universe. Before observation or measurement, the object must be like a blank sheet: it must be an undefined object with the potential to take up any possible property values. So before observation, the object must have a multi-valued form of reality -- as is observed in quantum mechanical behavior. It is only when the object interacts with the rest of the universe that its properties become progressively tied down to particular values.
This is what we saw in the case of environmental decoherence. It is through interaction with the rest of the universe, via the measuring apparatus,(the measuring apparatus being huge compared to the particle measured -- my insert) that the properties of a particle become fixed.
So here, rather wonderfully, we have a rational -- an explanation -- for the multi-valued nature of quantum behavior before measurement, or observation. Here are the logical steps we followed to get to this conclusion:
1) Nature has no access to absolutes, so it is always fundamentally unable to assign absolute property values to a particle.
2)Therefore, particle properties are defined by the relationship of that particle with the rest of the universe.
3)Bearing this in mind, if we consider as isolated particle, or a newly generated particle which has not yet been measured or observed, nature has fundamentally no way of assigning any form of property values -- absolute or relative to the particle.
4) The properties of the particle are therefore fundamentally undefined -- like a blank sheet. Its properties must have the potential to be any possible value
5)The object must therefore have a multi-valued form of reality before it is observed. It is only after observation -- when the object interacts with the rest of the universe -- that the properties of the object become fixed.
Anyway what do you think about this?
Not even wrong.
Let's have a look at the non-relativistic QM Schrödinger equation which is known to describe the evolution of, for example, a single partice wave function Psi:
m is the mass of the particle. It is not ever "undefined".
Even if we set the potential V(x), which in the QM case describes the interaction of the particle with the rest of the universe, identically to zero
m is still defined.
The relativistic QM Dirac equation for a single particle, with V(x) zero, is given by
wherein the particle now has both mass m and the matrices beta, alpha_1, alpha_2, alpha_3 which describe the electron's intrinsic spin of 1/2 [in units of hbar: Planck's constant / 2 * Pi]
These properties carry over into the QFT of the electron:
[click on the equation for the link to the details]
To sum up, if the properties of a fundamental particle, it's mass, intrinsic spin, and possible charges (electric, weak, colour) are "undefined" at some point, then we can't write down an equation for it.
Another point: mathematics is the language of the physical universe.
I don't think that one can learn physics without mathematics.
For anyone who would like to learn non-relativistic QM, the best textbooks are
Quantum Mechanics: Vol. I and II by Claude Cohen-Tannoudji and Bernard Diu
bar none.
For the sake of argument -- m is related to gravity. Gravity would be defined for any particle ir-regardless of it being otherwise defined. In the double slit experiment it is not gravity that collapses the wave function. If it were true then certainly there would be no wave function to begin with as any such experiment done on earth, the earth itself would be a measurement apparatus. The same for the electric charge of a wave/particle function The earth's magnetic field would "measure" it. That leaves intrinsic spin. Something I know little about. How do you measure intrinsic spin?
Doc wrote:Thanks. Just one point of real contentionI don't think that one can learn physics without mathematics.
Einstein could not do the math for relativity when he first came up with the theory. He figured it out through mind experiments where he imagined he was traveling at the speed of light and what that would look like. His wife helped him with the math. His college instructor gave him credit for coming up with the idea that Einstein could not mathematically describe But Einstein did not know the math to prove it until later. IE is not always about the math. But unless someone that does not know the math is extremely lucky in who surrounds them at best they can look foolish at worse someone else will get credit for the ideas.
Typhoon wrote:Doc wrote:Typhoon wrote:Doc wrote:OK CS Here is what Thomas has to say about measurement. Do you have any problems with it?(I transcribed this so any typos are mine)Let us reconsider a particle which is isolated from the rest of the universe, or has been generated as a new particle and has not yet interacted with the rest of the universe, ie., it has not yet been measured or observed. What can we say about its properties? Once again in the absence of absolutes(There is not universal unit of measure that it absolute - my insert), nature is fundamentally unable to assign absolute values to the particle. And because the particle has not yet interacted with the rest of the universe to be measured or observed, nature is unable to assign any relative values either. As discussed in the last section, all we can say about its property values is "They go up to 11", an essentially meaningless statement reflecting the fact that the particle's property values are undefined -- they have no relation to the rest of the universe. Before observation or measurement, the object must be like a blank sheet: it must be an undefined object with the potential to take up any possible property values. So before observation, the object must have a multi-valued form of reality -- as is observed in quantum mechanical behavior. It is only when the object interacts with the rest of the universe that its properties become progressively tied down to particular values.
This is what we saw in the case of environmental decoherence. It is through interaction with the rest of the universe, via the measuring apparatus,(the measuring apparatus being huge compared to the particle measured -- my insert) that the properties of a particle become fixed.
So here, rather wonderfully, we have a rational -- an explanation -- for the multi-valued nature of quantum behavior before measurement, or observation. Here are the logical steps we followed to get to this conclusion:
1) Nature has no access to absolutes, so it is always fundamentally unable to assign absolute property values to a particle.
2)Therefore, particle properties are defined by the relationship of that particle with the rest of the universe.
3)Bearing this in mind, if we consider as isolated particle, or a newly generated particle which has not yet been measured or observed, nature has fundamentally no way of assigning any form of property values -- absolute or relative to the particle.
4) The properties of the particle are therefore fundamentally undefined -- like a blank sheet. Its properties must have the potential to be any possible value
5)The object must therefore have a multi-valued form of reality before it is observed. It is only after observation -- when the object interacts with the rest of the universe -- that the properties of the object become fixed.
Anyway what do you think about this?
Not even wrong.
Let's have a look at the non-relativistic QM Schrödinger equation which is known to describe the evolution of, for example, a single partice wave function Psi:
m is the mass of the particle. It is not ever "undefined".
Even if we set the potential V(x), which in the QM case describes the interaction of the particle with the rest of the universe, identically to zero
m is still defined.
The relativistic QM Dirac equation for a single particle, with V(x) zero, is given by
wherein the particle now has both mass m and the matrices beta, alpha_1, alpha_2, alpha_3 which describe the electron's intrinsic spin of 1/2 [in units of hbar: Planck's constant / 2 * Pi]
These properties carry over into the QFT of the electron:
[click on the equation for the link to the details]
To sum up, if the properties of a fundamental particle, it's mass, intrinsic spin, and possible charges (electric, weak, colour) are "undefined" at some point, then we can't write down an equation for it.
Another point: mathematics is the language of the physical universe.
I don't think that one can learn physics without mathematics.
For anyone who would like to learn non-relativistic QM, the best textbooks are
Quantum Mechanics: Vol. I and II by Claude Cohen-Tannoudji and Bernard Diu
bar none.
For the sake of argument -- m is related to gravity. Gravity would be defined for any particle ir-regardless of it being otherwise defined. In the double slit experiment it is not gravity that collapses the wave function. If it were true then certainly there would be no wave function to begin with as any such experiment done on earth, the earth itself would be a measurement apparatus. The same for the electric charge of a wave/particle function The earth's magnetic field would "measure" it. That leaves intrinsic spin. Something I know little about. How do you measure intrinsic spin?
The wavefunction is |Psi>(x,y,z,t), thus it is a function of spatial position and time [switching to Dirac bra ket notation].
It is not a function of mass m, electric charge q, or intrinsic spin s.
<Psi|Psi>(x,y,z,t) thus gives a probability of observing a particle of mass m, charge q, and spin s at spatial position (x, y, z) within an infinitesimal volume dV at time t.
Mass m and electric charge q of a particle cannot [to-date] be calculated from first principles,
they have to be empirically measured and put in "by hand" into the wave equation before solving for |Psi>.
[Note that the use of mathematics rather then reams of descriptive text makes this immediately obvious.]
This is one point that the author clearly gets wrong and, in doing so, misinforms and misdirects his readers.
Actually, it's a bit difficult to understand what the author is trying to say as quoted text is far from clear.
As for intrinsic spin:
Behold the vectors of the field: they toil not, what they do is spinDoc wrote:Thanks. Just one point of real contentionI don't think that one can learn physics without mathematics.
Einstein could not do the math for relativity when he first came up with the theory. He figured it out through mind experiments where he imagined he was traveling at the speed of light and what that would look like. His wife helped him with the math. His college instructor gave him credit for coming up with the idea that Einstein could not mathematically describe But Einstein did not know the math to prove it until later. IE is not always about the math. But unless someone that does not know the math is extremely lucky in who surrounds them at best they can look foolish at worse someone else will get credit for the ideas.
There is a lot of popular mythology about Einstein. Much of it is wrong.
Einstein excelled at mathematics.
Once Einstein had the ideas of the equivalence principle and general covariance of GR, he searched for a mathematical structure that would describe these concepts and found it in tensor calculus and Riemannian geometry. See the correspondence between Einstein and Levi-Civita.
SR and GR are two of the very rare cases in physics wherein thought experiments, as opposed to experimental observations requiring explanation, lead to a new new theory.
I'm not aware of any contribution to the theories of physics that was done without mathematics and
I did spend some time trying to recall any such example.
Of course, creativity and imagination are required, but a facility with math is apparently a prerequisite
as it does seem to be the unreasonably effective language of the physical universe.
Doc wrote:Typhoon wrote:Doc wrote:Typhoon wrote:Doc wrote:OK CS Here is what Thomas has to say about measurement. Do you have any problems with it?(I transcribed this so any typos are mine)Let us reconsider a particle which is isolated from the rest of the universe, or has been generated as a new particle and has not yet interacted with the rest of the universe, ie., it has not yet been measured or observed. What can we say about its properties? Once again in the absence of absolutes(There is not universal unit of measure that it absolute - my insert), nature is fundamentally unable to assign absolute values to the particle. And because the particle has not yet interacted with the rest of the universe to be measured or observed, nature is unable to assign any relative values either. As discussed in the last section, all we can say about its property values is "They go up to 11", an essentially meaningless statement reflecting the fact that the particle's property values are undefined -- they have no relation to the rest of the universe. Before observation or measurement, the object must be like a blank sheet: it must be an undefined object with the potential to take up any possible property values. So before observation, the object must have a multi-valued form of reality -- as is observed in quantum mechanical behavior. It is only when the object interacts with the rest of the universe that its properties become progressively tied down to particular values.
This is what we saw in the case of environmental decoherence. It is through interaction with the rest of the universe, via the measuring apparatus,(the measuring apparatus being huge compared to the particle measured -- my insert) that the properties of a particle become fixed.
So here, rather wonderfully, we have a rational -- an explanation -- for the multi-valued nature of quantum behavior before measurement, or observation. Here are the logical steps we followed to get to this conclusion:
1) Nature has no access to absolutes, so it is always fundamentally unable to assign absolute property values to a particle.
2)Therefore, particle properties are defined by the relationship of that particle with the rest of the universe.
3)Bearing this in mind, if we consider as isolated particle, or a newly generated particle which has not yet been measured or observed, nature has fundamentally no way of assigning any form of property values -- absolute or relative to the particle.
4) The properties of the particle are therefore fundamentally undefined -- like a blank sheet. Its properties must have the potential to be any possible value
5)The object must therefore have a multi-valued form of reality before it is observed. It is only after observation -- when the object interacts with the rest of the universe -- that the properties of the object become fixed.
Anyway what do you think about this?
Not even wrong.
Let's have a look at the non-relativistic QM Schrödinger equation which is known to describe the evolution of, for example, a single partice wave function Psi:
m is the mass of the particle. It is not ever "undefined".
Even if we set the potential V(x), which in the QM case describes the interaction of the particle with the rest of the universe, identically to zero
m is still defined.
The relativistic QM Dirac equation for a single particle, with V(x) zero, is given by
wherein the particle now has both mass m and the matrices beta, alpha_1, alpha_2, alpha_3 which describe the electron's intrinsic spin of 1/2 [in units of hbar: Planck's constant / 2 * Pi]
These properties carry over into the QFT of the electron:
[click on the equation for the link to the details]
To sum up, if the properties of a fundamental particle, it's mass, intrinsic spin, and possible charges (electric, weak, colour) are "undefined" at some point, then we can't write down an equation for it.
Another point: mathematics is the language of the physical universe.
I don't think that one can learn physics without mathematics.
For anyone who would like to learn non-relativistic QM, the best textbooks are
Quantum Mechanics: Vol. I and II by Claude Cohen-Tannoudji and Bernard Diu
bar none.
For the sake of argument -- m is related to gravity. Gravity would be defined for any particle ir-regardless of it being otherwise defined. In the double slit experiment it is not gravity that collapses the wave function. If it were true then certainly there would be no wave function to begin with as any such experiment done on earth, the earth itself would be a measurement apparatus. The same for the electric charge of a wave/particle function The earth's magnetic field would "measure" it. That leaves intrinsic spin. Something I know little about. How do you measure intrinsic spin?
The wavefunction is |Psi>(x,y,z,t), thus it is a function of spatial position and time [switching to Dirac bra ket notation].
It is not a function of mass m, electric charge q, or intrinsic spin s.
<Psi|Psi>(x,y,z,t) thus gives a probability of observing a particle of mass m, charge q, and spin s at spatial position (x, y, z) within an infinitesimal volume dV at time t.
Mass m and electric charge q of a particle cannot [to-date] be calculated from first principles,
they have to be empirically measured and put in "by hand" into the wave equation before solving for |Psi>.
[Note that the use of mathematics rather then reams of descriptive text makes this immediately obvious.]
This is one point that the author clearly gets wrong and, in doing so, misinforms and misdirects his readers.
Actually, it's a bit difficult to understand what the author is trying to say as quoted text is far from clear.
As for intrinsic spin:
Behold the vectors of the field: they toil not, what they do is spinDoc wrote:Thanks. Just one point of real contentionI don't think that one can learn physics without mathematics.
Einstein could not do the math for relativity when he first came up with the theory. He figured it out through mind experiments where he imagined he was traveling at the speed of light and what that would look like. His wife helped him with the math. His college instructor gave him credit for coming up with the idea that Einstein could not mathematically describe But Einstein did not know the math to prove it until later. IE is not always about the math. But unless someone that does not know the math is extremely lucky in who surrounds them at best they can look foolish at worse someone else will get credit for the ideas.
There is a lot of popular mythology about Einstein. Much of it is wrong.
Einstein excelled at mathematics.
Once Einstein had the ideas of the equivalence principle and general covariance of GR, he searched for a mathematical structure that would describe these concepts and found it in tensor calculus and Riemannian geometry. See the correspondence between Einstein and Levi-Civita.
SR and GR are two of the very rare cases in physics wherein thought experiments, as opposed to experimental observations requiring explanation, lead to a new new theory.
I'm not aware of any contribution to the theories of physics that was done without mathematics and
I did spend some time trying to recall any such example.
Of course, creativity and imagination are required, but a facility with math is apparently a prerequisite
as it does seem to be the unreasonably effective language of the physical universe.
Thanks CS for posting all of this. I am going to look into this more when I get some time.
Doc wrote:As for Einstein. Yes he was good at math. But along he flunked out of high school HIs math abilities were quite good but he did not initially learn enough to develop those skills.
Amazon: Of the many legends that have accumulated around Einstein, what did you find to be least true? Most true?
Isaacson: The least true legend is that he failed math as a schoolboy. He was actually great in math, because he could visualize equations...
Source: Amazon.com: Einstein: His Life and Universe (9780743264747): Walter Isaacson: Books
Typhoon wrote:Doc wrote:
Thanks CS for posting all of this. I am going to look into this more when I get some time.
I hope it is of some interest.
Doc wrote:As for Einstein. Yes he was good at math. But along he flunked out of high school HIs math abilities were quite good but he did not initially learn enough to develop those skills.
That Einstein flunked out of high school is another urban legend, perhaps the least plausible of all:Amazon: Of the many legends that have accumulated around Einstein, what did you find to be least true? Most true?
Isaacson: The least true legend is that he failed math as a schoolboy. He was actually great in math, because he could visualize equations...
Source: Amazon.com: Einstein: His Life and Universe (9780743264747): Walter Isaacson: Books
Is it true that Einstein was a lousy student?
In some ways, yes. When he was very young, Einstein’s parents worried that he had a learning disability because he was very slow to learn to talk. (He also avoided other children and had extraordinary temper tantrums.) When he started school, he did very well-he was a creative and persistent problem-solver-but he hated the rote, disciplined style of the teachers at his Munich school, and he dropped out when he was 15. Then, when he took the entrance examination for a polytechnic school in Zurich, he flunked. (He passed the math part, but failed the botany, zoology and language sections.) Einstein kept studying and was admitted to the polytechnic institute the following year, but even then he continued to struggle: His professors thought that he was smart but much too pleased with himself, and some doubted that he would graduate. He did, but not by much-which is how the young physicist found himself working in the Swiss Patent Office instead of at a school or university.
Azrael wrote:delayed-choice entanglement swapping
Doc wrote:Azrael wrote:delayed-choice entanglement swapping
Now that is really kicking the quantum can down the road, or not.
How one of the first tests of special relativity might lead to the greatest particle accelerator of all-time.
IAAAP (I am an accelerator physicist), and this is pretty old news. The US muon collider program is actually on its way out.
Last year's Particle Physics Project Prioritization Panel (P5) advised the DOE to defund the muon collider project,
redirecting funds toward the International Linear Collider (ILC)-- a 250GeV e+/e- precision Higgs factory-- and other projects:
http://science.energy.gov/~/media/hep/h ... 060214.pdf
The DOE has followed P5's review, and Fermilab's muon collider project is winding down.
Contrary to claims in the popular media, so-called String Theory is not the only game in town. Five alternative candidate theories.
Typhoon wrote:Does Quantum Gravity Need String Theory?Contrary to claims in the popular media, so-called String Theory is not the only game in town. Five alternative candidate theories.
Azrael wrote:Typhoon wrote:Does Quantum Gravity Need String Theory?Contrary to claims in the popular media, so-called String Theory is not the only game in town. Five alternative candidate theories.
Why would it need string theory?
As far as I know, there is no experimental evidence of string theory.
I used to think that string theory helped to explain the behavior of Quark Gluon Plasma; but you showed a graph with alternate explanations that work better.
Typhoon wrote:Azrael wrote:Typhoon wrote:Does Quantum Gravity Need String Theory?Contrary to claims in the popular media, so-called String Theory is not the only game in town. Five alternative candidate theories.
Why would it need string theory?
As far as I know, there is no experimental evidence of string theory.
I used to think that string theory helped to explain the behavior of Quark Gluon Plasma; but you showed a graph with alternate explanations that work better.
There's an odd argument made by some in the string theory community that string theory must be the correct description of quantum gravity as there are no other options.
The author is tweeking their noses.
Einstein kills Schrödinger's cat: Relativity ruins quantum world
18:30 16 June 2015 by Jacob Aron
The same quirk of general relativity that means your head ages faster than your feet may mean we have to go to space to see large-scale quantum mechanics in action
Doc wrote:http://www.newscientist.com/article/dn27735-einstein-kills-schrodingers-cat-relativity-ruins-quantum-world.htmlEinstein kills Schrödinger's cat: Relativity ruins quantum world
18:30 16 June 2015 by Jacob Aron
The same quirk of general relativity that means your head ages faster than your feet may mean we have to go to space to see large-scale quantum mechanics in action
A 115-year effort to bridge the particle and fluid descriptions of nature has led mathematicians to an unexpected answer.
Azrael wrote:entangled clocks
Typhoon wrote:Quanta Mag | "Theories of Everything", Mapped
noddy wrote:Typhoon wrote:Quanta Mag | "Theories of Everything", Mapped
TOE is the lavender, if and when we had one science that covered all the facts rather than isolated models that dont really explain each other well , id be devoting my life to it, what a thing.
Parodite wrote:Typhoon wrote:Parodite wrote:If the above is sensible, then the only valid question that remains is how to recover classical physics from QM...and vice-versa.
Bell's Theorem does the job.
Thanks, I'll take a good bite of that.
Experimental loopholes closed in new experiment that tests Bell's Theorem and finds that QM holds.
Quantum ‘spookiness’ passes toughest test yet
Experiment plugs loopholes in previous demonstrations of 'action at a distance', against Einstein's objections — and could make data encryption safer.
t’s a bad day both for Albert Einstein and for hackers. The most rigorous test of quantum theory ever carried out has confirmed that the ‘spooky action at a distance’ that the German physicist famously hated — in which manipulating one object instantaneously seems to affect another, far away one — is an inherent part of the quantum world.
The experiment, performed in the Netherlands, could be the final nail in the coffin for models of the atomic world that are more intuitive than standard quantum mechanics, say some physicists. It could also enable quantum engineers to develop a new suite of ultrasecure cryptographic devices.
“From a fundamental point of view, this is truly history-making,” says Nicolas Gisin, a quantum physicist at the University of Geneva in Switzerland.
[...]
In the latest paper3, which was submitted to the arXiv preprint repository on 24 August and has not yet been peer reviewed, a team led by Ronald Hanson of Delft University of Technology reports the first Bell experiment that closes both the detection and the communication loopholes. The team used a cunning technique called entanglement swapping to combine the benefits of using both light and matter. The researchers started with two unentangled electrons sitting in diamond crystals held in different labs on the Delft campus, 1.3 kilometres apart. Each electron was individually entangled with a photon, and both of those photons were then zipped to a third location. There, the two photons were entangled with each other — and this caused both their partner electrons to become entangled, too.
This did not work every time. In total, the team managed to generate 245 entangled pairs of electrons over the course of nine days. The team's measurements exceeded Bell’s bound, once again supporting the standard quantum view. Moreover, the experiment closed both loopholes at once: because the electrons were easy to monitor, the detection loophole was not an issue, and they were separated far enough apart to close the communication loophole, too.
“It is a truly ingenious and beautiful experiment,” says Anton Zeilinger, a physicist at the Vienna Centre for Quantum Science and Technology.
“I wouldn’t be surprised if in the next few years we see one of the authors of this paper, along with some of the older experiments, Aspect’s and others, named on a Nobel prize,” says Matthew Leifer, a quantum physicist at the Perimeter Institute in Waterloo for Theoretical Physics, Ontario. “It’s that exciting.”
[...]
In practice, however, the entanglement-swapping idea will be hard to implement. The team took more than week to generate a few hundred entangled electron pairs, whereas generating a quantum key would require thousands of bits to be processed per minute, points out Gisin, who is a co-founder of the quantum cryptographic company ID Quantique in Geneva.
Zeilinger also notes that there remains one last, somewhat philosophical loophole, first identified by Bell himself: the possibility that hidden variables could somehow manipulate the experimenters’ choices of what properties to measure, tricking them into thinking quantum theory is correct.
Leifer is less troubled by this ‘freedom-of-choice loophole’, however. “It could be that there is some kind of superdeterminism, so that the choice of measurement settings was determined at the Big Bang,” he says. “We can never prove that is not the case, so I think it’s fair to say that most physicists don’t worry too much about this.”
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