One of Quantum Physics' Greatest Paradoxes May Have Lost Its Leading Explanation (sciencemag.org) 69
fahrbot-bot writes: It's one of the oddest tenets of quantum theory: a particle can be in two places at once -- yet we only ever see it here or there. Textbooks state that the act of observing the particle "collapses" it, such that it appears at random in only one of its two locations. But physicists quarrel over why that would happen, if indeed it does. Now, one of the most plausible mechanisms for quantum collapse -- gravity -- has suffered a setback. The gravity hypothesis traces its origins to Hungarian physicists Karolyhazy Frigyes in the 1960s and Lajos Diosi in the 1980s. The basic idea is that the gravitational field of any object stands outside quantum theory. It resists being placed into awkward combinations, or "superpositions," of different states. So if a particle is made to be both here and there, its gravitational field tries to do the same -- but the field cannot endure the tension for long; it collapses and takes the particle with it.
Still, the hypothesis seemed impossible to probe with any realistic technology, notes Diosi, now at the Wigner Research Center, and a co-author on the new paper. "For 30 years, I had been always criticized in my country that I speculated on something which was totally untestable." New methods now make this doable. In the new study, Diosi and other scientists looked for one of the many ways, whether by gravity or some other mechanism, that a quantum collapse would reveal itself: A particle that collapses would swerve randomly, heating up the system of which it is part. "It is as if you gave a kick to a particle," says co-author Sandro Donadi of the Frankfurt Institute for Advanced Studies. If the particle is charged, it will emit a photon of radiation as it swerves. And multiple particles subject to the same gravitational lurch will emit in unison. "You have an amplified effect," says co-author Catalina Curceanu of National Institute for Nuclear Physics in Rome.
Still, the hypothesis seemed impossible to probe with any realistic technology, notes Diosi, now at the Wigner Research Center, and a co-author on the new paper. "For 30 years, I had been always criticized in my country that I speculated on something which was totally untestable." New methods now make this doable. In the new study, Diosi and other scientists looked for one of the many ways, whether by gravity or some other mechanism, that a quantum collapse would reveal itself: A particle that collapses would swerve randomly, heating up the system of which it is part. "It is as if you gave a kick to a particle," says co-author Sandro Donadi of the Frankfurt Institute for Advanced Studies. If the particle is charged, it will emit a photon of radiation as it swerves. And multiple particles subject to the same gravitational lurch will emit in unison. "You have an amplified effect," says co-author Catalina Curceanu of National Institute for Nuclear Physics in Rome.
Shoud read Frigyes Karolyhazy (Score:4, Informative)
Happens to the best of us (Score:2)
I often lost my leading explanation when I went home from the Pub waaaay too late.
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What? (Score:4, Interesting)
Re:What? (Score:5, Informative)
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Photon wave functions would have their own gravitational field
I don't think that's clear because they have no mass. They are certainly affected by a gravitational field since gravity couples to the 4-momentum but I do not think they generate gravitational field of their own.
Entangled particles share the same wave function and “collapse” is the basis for how you can know the state of the one you didn’t measure.
But you did interact with the same wave function because, as you just stated, the two particles have the same wavefunction so there is no issue.
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The entangled particles so much as their quantum fields are the same and in normal space, that makes them the same particle relatively speaking and their distance apart, the greater the number of quantum particles between them and we are talking a whole damn lot, the harder it becomes to sustain quantum similarity, for the two particles to be the same particles in normal space in a gravitational field of quantum particles. The field flows of the intervening quantum particles disrupt the field flow from one
Re:What? (Score:4, Informative)
Photon wave functions would have their own gravitational field
I don't think that's clear because they have no mass. They are certainly affected by a gravitational field since gravity couples to the 4-momentum but I do not think they generate gravitational field of their own.
Pretty sure they do. They don't have "mass at rest", but they are never at rest, so they still have the mass of their energy load.
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Just think of photons bouncing about inside a mirrorball. E=mc2 never cared about how the energy inside a thing was constructed. Later on Einstein extended it and said 'you can keep using that "m'' in the general theory. You don't need a different one(inertiall vs gravitational).
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Photon wave functions would have their own gravitational field
I don't think that's clear because they have no mass. They are certainly affected by a gravitational field since gravity couples to the 4-momentum but I do not think they generate gravitational field of their own.
Pretty sure they do. They don't have "mass at rest", but they are never at rest, so they still have the mass of their energy load.
And, more to the point, mass is not the source of the gravitational field. The source is the stress-energy tensor.
Yes, photons have gravitation.
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Pretty sure they do.
If you trap them in a reflecting cavity then they could but a free, unrestricted photon I do not think so because they have no rest frame. They also emphatically do not have a mass: for a photon E=pc, the mass term is zero. Yes, you can convert their energy into mass but then you no longer have a photon.
Not a "leading explanation" (Score:2)
Yeah: gravity is not a "leading explanation," of wave function collapse; it is a wild speculation about wave function collapse. There is no math behind it: no math = not physics.
And the experiment didn't really disprove it, but that's mostly because trying to disprove a "theory" with no math behind it is like nailing jello to a tree: there's nothing solid there to disprove. It squishes around.
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It sounds like they needed a force outside QM to explain what they couldn't explain in QM and looked around and found gravity, not having a quantum theory of gravity.
It sure seems more sensible that the "waveform collapse" at "observation" just means that the state doesn't really exist until it needs to. This improves the computational efficiency of the Universe by a significant degree.
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It sounds like they needed a force outside QM to explain what they couldn't explain in QM
My point is that you do not need any force outside QM or gravity. You already have a force explained within relativistic QM (QED specifically) which can explain this.
Spooky-- not. [Re:What?] (Score:3)
It sounds like they needed a force outside QM to explain what they couldn't explain in QM
My point is that you do not need any force outside QM or gravity. You already have a force explained within relativistic QM (QED specifically) which can explain this.
QED is special relativistic quantum mechanics, but there is still an inconsistency with general relativity.
And it does not explain wave function collapse.
As Mermin puts it, the most common explanation of wave function collapse in physics is the "shut up and calculate" explanation, which is, just do the math and get the answer. And when you get the answer, nothing goes faster than light, no actual information is ever transferred via the "spooky action at a distance" (you always need classical information to
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QED is special relativistic quantum mechanics, but there is still an inconsistency with general relativity.
Yes...and no. You can actually relatively easily construct a model of quantum gravity the problem is that to make it work you have to put in an energy cut-off. This is a problem for a fundamental theory since there is no justification for any such cut-off energy. However, under any model of quantum gravity the effect of gravity is going to be utterly negligible - by many, many orders of magnitude - compared to the EM interaction which you are actually using to detect the particle. It therefore seems nonsen
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QED is special relativistic quantum mechanics, but there is still an inconsistency with general relativity.
Yes...and no. You can actually relatively easily construct a model of quantum gravity the problem is that to make it work you have to put in an energy cut-off.
But the moment you put in an energy cut-off, it's no longer relativistically invariant.
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And when you get the answer, nothing goes faster than light, no actual information is ever transferred via the "spooky action at a distance"
You see the same effect in classical system. Look at the phase velocity of a wave in a waveguide: you can get that up to being infinite so that it looks as if a wave crest is travelling faster than light - or indeed anything since you can make it infinite. However, it only looks that way, in reality no information is being transmitted at that velocity even though a crest of the wave travels that fast. It's not really that different.
Yep. It's reasonable to think that possibly some similar thing happens, where it looks like wave function collapse happens faster than light, but in the details, nothing actually moves faster than light. But... how, exactly, this works is not at all clear.
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"Waveform" "collapse" at "observation" only sounds confusing because we insist on using confusion analogies for it.
An electron (for example) is described by a wave function. We're used to waves "being in two places at once," there's nothing mysterious about that. When you "observe" it, what you're really doing is interacting that wave function with a jillion other wave functions. When you do that, the original wave function appears to get a bit less blurry (in spatial extent).
The real issue is that the nice
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Decoherence is, for sure. Here's a good video describing the process: https://www.youtube.com/watch?... [youtube.com]
The actual measurement problem seems to me more like a conceptual issue, probably with a bit of missing math in the description of the measurement process. It's not nearly as surreal as the pop sci descriptions lead people to believe though.
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We are attempting to describe at macro level, the properties of quantum level concepts using phenomena we can observe as analogies.
The "observing it, changes it" phenomenon is, however real, as in "there is no way to observe something without a transfer of energy. That transfer is irreversible, because it necessarily involves entropy increasing".
Genies do not
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Who knows, maybe gravity is capable of such a 'collapes' absent other factors but the dominant explanation I recall splits up this collapse into a decoherence part and a statistics part. Decoherence can be gradual /partial but is caused by interactions. Simple background radiation can be enough to achieve that. This breaks up the interference between the states. Behaviour then becomes quasiclassical . The second part, the collapse part however would mean that one of the states disappears. That is not explai
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The summary is pretty confusing. Perhaps the idea is that the gravitational field is what causes the relationship between the size of the particle and it's decoherence time, and the old idea of a threshold under which quantum mechanics applies, and above which the world is classical.
Depends on how one interprets QM (Score:5, Interesting)
It's one of the oddest tenets of quantum theory: a particle can be in two places at once -- yet we only ever see it here or there.
One could write several pages on what's wrong with that introductory sentence.
I shall restrict myself to one point: it is not a tenet of quantum theory (by which I think is meant "quantum mechanics") that "a particle [sic] can be in two places at once"; that is, rather, a tenet of one epistemological interpretation of quantum mechanics, albeit the one that is most commonly taught (and therefore learned).
There is at least one other interpretation, in fact in some ways a more powerful one in that it is ontological, that is based on quite a different model of what goes on "under the hood" of QM. I direct the interested reader to: https://en.wikipedia.org/wiki/... [wikipedia.org], or the book "The Undivided Universe" by Bohm and Hiley. In Bohmian Mechanics, there is no collapse of the wave function, and particles have well-defined positions; in particular, they are not in a superposition of states. All the standard experimental results are reproduced by Bohmian Mechanics, just as in the interpretation that is most-commonly taught.
I regard it as a travesty of modern pedagogy of physics that students often are never exposed to the fact that while the experimental results are solid, the underlying model of what is going on to cause those results is merely (at best) an hypothesis. QM, in its current state, provides a wonderful set of rules for making the most accurate predictions ever; but it provides no explanation of why those rules are the correct ones or how the way that the universe operates can be the way it appears to be. At this point I resist the temptation to blather on about non-locality, or any of the other things wrong about the summary's introductory sentence.
Note that I am not commenting on the physics of the paper on which the summary is based: that appears to be paywalled.
Re:Depends on how one interprets QM (Score:5, Interesting)
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>you can't describe the Hawking radiation with de Broglie Bohm
Hawking radiation has never been measured. It may not actually exist.
Re:Depends on how one interprets QM (Score:4, Informative)
Measuring changes things untestable (Score:3)
This idea that things change when related things are measured seems to be inherently untestable.
The classic is photons created of opposite polarity. We are told that the polarity is only actually determined when one of them is measured, and then the other must have the opposite effect. As opposed to the more obvious explanation that the polarity is determined when they are created. How could that ever be tested?
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It's quite an elegant experiment.
Suppose I generate two photons that are entangled in such a way that they should have the same polarization. I keep one and give the other to you. If I pass the photon through a polarizer oriented up/down, it either passes or it doesn't. You do it as well, and get the same answer. This is perfectly adequately explained by the classical hypothesis that the photons just had the same polarization all along.
But what if I rotate the polarizer 90 degrees, and you don't? Now we sho
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Thank you for your explanation and slides.
However, both are unintelligible to anyone that is not already a PhD in quantum mechanics. That may be because the topic is incredibly difficult to understand. Or it might be the way these things are explained by physisists -- full of vaguely described formalisms that rely on a total understanding of everything else.
For example, Slide 12 ...
\int d \lambda \rho(\lamda) d\lambda
WTF? Nothing is defined. I'd guess lambda is polarization angle. No idea what rho is.
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Ha ha, yeah, those aren't good slides for non-specialists. I linked to them just for that graph, which is pretty famous.
Let me take two more stabs at it:
1) The problem with the usual pop science explanation is that it describes precisely the circumstance when the quantum prediction and the classical one *do* agree with each other. If we both have vertically polarized photons and we try to pass them through (good) horizontally oriented polarizing filters, we're both going to get no photon, every time. Our re
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Hmm. Begs the question, how does a polarizing filter actually work?
The classic high school experiment is that you have two at 90 degrees, vertical and horizontal. No light gets through. Then you put one between them at 45 degrees and magically some light now does pass through all three filters. The first filter removes the horizontal wave component of light, so it is about 50% as bright all perfectly polarized vertically. The second does the same, so it is all polarized 45 degrees.
But now that I think
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A polarizer is really a quantum mechanical device. It allows a photon through probabilistically, with the probability depending on the orientation of the photon and the orientation of the polarizer.
You're right though, most of the simple experiments have loopholes. But subsequent experiments have worked to close those. For example, you can perform the polarizer experiment without entanglement first to determine how polarizers behave. You can also make it similar to the quantum coin flip thought experiment b
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A polarizer does more than just be a probablistic gate. That is why adding a filter at 45 degrees between to perpendicular filters actually allows more light to flow through. The filter effectively changes the polarization of the light by removing one component.
http://www.alienryderflex.com/... [alienryderflex.com]
I am aware of Einstein's book. It is a complete fudge. Page 31 (the train) after walking through very slowly we find
"Hence the observer will see the beam of light emitted from B earl
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Einstein's description is accurate. Typically if you find yourself disagreeing with Einstein you probably need to consider as the most likely possibility that *you're* missing something.
The pop science mystique around "aether" is perhaps something that blocks a lot of understanding around relativity. Special relativity is equivalent to a relativistic aether theory (and it wasn't the only contemporary one).
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Eintein may be accurate, but he is fudging the description.
Einstein was no saint. He wrote a book for the masses, so he just skipped over the difficult bits, which are in fact the important bits.
In this case, whether Einstein merely fudged the description or also stated a bad result is unclear to me. But what is certain is that the way he describes it light is behaving exactly the same as the sound of thunder would when moving through the air. It is trivial that a deaf man on the train would not think th
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Fine. Than go with this [wikipedia.org].
Re:Depends on how one interprets QM (Score:5, Insightful)
This post, right here, is why I refuse to accept whenever anyone tries to put hard, unwavering limits on the universe in terms of unbreakable "laws of physics" - we have so much to learn about the universe at all levels that we are basically still babies learning about our environment. We have rules and experimental outcomes, but the things underpinning those rules and experimental outcomes lack full explanation, and that is where the excitement lies.
The more we look and investigate, the more we begin to understand, the more we can push the boundaries - we have great things ahead of us as a human race, so long as we keep looking under the next stone. And I will continue to scoff at people who insist that people like Einstein have set us hard boundaries that we will never be able to overcome - their boundaries make sense today, but what about tomorrow?
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Why two rather than, say 5, or any countable number, or a continuum, or even the universe as a whole?
The latter would be entertaining as it may give us observations about the unobservable universe!
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"stupid question" (Score:2)
I guess this is probably a 'stupid' question, but maybe someone can explain it to me in a way easy enough to understand.
I thought the quantum wave form was developed from experimental data that is by it's nature probabilistic?
So why is the assumption made that a actual system matches a probabilistic algorithm directly?
Isn't the formula an incomplete model of realty by the very fact that it is probabilistic rather then deterministic?
Certainly it is the best formula we have, but it is not developed by direct
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no I'm not suggesting their are some kinds of hidden variables. I'm suggesting that we don't understand the problem because we assume we already have the answer. To me , however, it seems like the measurements that give you the answer are probabilistic, the formulas and math must , obviously , be incomplete, because the observations they are based on are by their nature incomplete. The assumption seems to be that because the model has predictive usefulness that it models reality, which is never a complet
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sorry, for my lack of technical precision in a field I am new too and attempting to understand. I'd appreciate some tolerance of someone trying to learn form those who know more then he does. What I was trying to express was simply, we don't know , what is unknown, there is no assumption in that statement that the entity is unobservable as there is a difference between unobservable and unobserved.
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more interestingly having read the linked article about 5 times now, trying to make sure I understand it , it actually doesn't say hidden variable theory has been falsified and identifies multiple physicists who believed or currently believe in in it in one form or another including non less then Albert Einstein and David Bohm. Unfortunately most of what seems to be proof of completeness for quantum physics, is still not accessible to me because I've only completed 2nd year calculus in college and univer
Um no there is no paradox (Score:4, Interesting)
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To me it seems like 'not knowing something' is not the same as 'it being that way'. Even if I in capable of knowing it , doesn't mean it is in 2 places as once , it just means I don't know where it is, which is not the same thing. This has always seemed to confused the predictive equation with reality.
Give it a fresh cup of really hot tea ... and (Score:2)
Is a measurement or is mathematical masturbation? (Score:1)
just limits of the simulation (Score:5, Funny)
So in other words... (Score:2)
I've said it before, so I'll say it again (Score:2)
It's not in two places at the same time. It doesn't collapse to one of them randomly.
Our deductions conclude that it's in one of two places, with no way to deduce any further. You know, either the universe is five-thousand years old, or the earth is five-billion years old. It's one of those two.
Then we measure, and the uncertainty collapses down to one -- earth is five-billion years old, according to this ruler.
Earth wasn't two different ages simultaneously -- our knowledge of it was. It didn't collapse