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Science

Quantum Entanglement Survives, Even Across an Event Horizon 152

Posted by timothy from the so-dense-not-even-dumb-can-escape dept.
StartsWithABang writes: One of the more puzzling phenomena in our quantum Universe is that of entanglement: two particles remain in mutually indeterminate states until one is measured, and then the other — even if it's across the Universe — is immediately known. In theory, this should be true even if one member of the pair falls into a black hole, although it's impossible to measure that. However, we can (and have) measured that for the laboratory analogue of black holes, known as "dumb holes," and the entanglement survives!
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Quantum Entanglement Survives, Even Across an Event Horizon More

Quantum Entanglement Survives, Even Across an Event Horizon

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  • No shit, Sherlock (Score:3, Interesting)

    by Anonymous Coward on Sunday November 15, 2015 @06:31AM (#50933937)

    This should come as a surprise to exactly no one. Anyone who can apply logic can tell you that the physical universe is a layer above the non-physical energy (matter is merely 'bound energy') that is the fundamental substance of existence. Quantum particles are known to "flicker in and out of physical reality". That has been directly observed. So where do you think that energy goes when it's no longer *physically* present? Just disappears into nothingness, the one state that's simply not possible whatsoever? Of course it's still there, and of course the rules that apply to that non-physical energy still apply even when you can't physically access it. Energy is information, matter is merely a storage medium. The information is always extant, even if it's not currently represented on any physical storage medium.

    A simple way to understand this is to visualize the universe as being made of numbers. The positive numbers can be represented by matter (regardless of polarity, so yes, anti-matter is positive numbers) and negative numbers cannot be represented physically, but are nonetheless just as 'real'.

    Anyone who argues otherwise, yet agrees that 2 minus 5 equals negative 3, should be required to demonstrate physical proof that 2 minus 5 equals negative 3 before being allowed to speak further on the subject... ;)

    • wtf are you talking about? You remind me of a numbers nut job that crank Noory was interviewing on coast to coast am. After a few minutes of her blathering even George was going "Huh"?

  • - For everything above quantum, the maximum speed is the speed of light.
    - This dictates cause and effect, and therefore time.
    - If we send out a steady stream of entangled particles, and sometimes change and sometimes don't (at the one end), and measure at the other (this is how I imagine how a bitstream would work using quantum entanglement, correct me if I'm wrong), we can send information quicker than the speed of light.
    - Therefore the information goes back in time.

    Or something?

    • Re:So.. for a non-physicist (Score:4, Interesting)

      by cpuffer_hammer ( 31542 ) on Sunday November 15, 2015 @07:03AM (#50933985) Homepage

      Maybe this will help?
      Can some physics types comment on the quality of the explanation.
      https://www.youtube.com/watch?v=v657Ylwh-_k [youtube.com]

    • Re:So.. for a non-physicist (Score:5, Informative)

      by Anonymous Coward on Sunday November 15, 2015 @07:05AM (#50933991)

      1. No. The maximum speed is the speed of light in quantum mechanics. Entanglement doesn't even have a speed. It is, from all measurements that have been done, valid in any reference frame.
      2. No. c is defined in terms of time, not the other way around.
      3. No. The correlations from entanglement transfer zero bits of information. They can only be observed with the assistance of normal communication channels. Combining the two allows you to hide but not send data.
      4. Obligatory xkcd: No. [xkcd.com]

      • Re point 4: my understanding of current theory was that if you can send information faster than light, then it is possible to send information back in time.

        • If you send information faster than light, then the information is going backwards in time wwith respect to some reference frame.

        • That is correct if Special Relativity holds. Now, I'm as positive that it holds as I am about any scientific theory, but it still could be wrong.

          If we toss Special Relativity and have a preferred inertial reference frame, then FTL does not mean backwards in time.

          If you have Special Relativity and FTL, you've got time travel, or at least the potential of such.

        • "Re point 4: my understanding of current theory was that if you can send information faster than light, then it is possible to send information back in time."

          That would only be correct if General Relativity remains correct at FTL speeds, and there's more empirical proof for Leprechauns or homeopathy than there is for that.. A much simpler FTL model is that time is point like and not a dimension, and that dimensional time is just a delusion - an abstraction.. As for dilation and space like time they can be

      • Quantum encryption protocol BB-84

        You set up the experiment so that you can polarize a photon at 4 angles: 0, 45, 90 and 135 degrees ( | / - \ ).

        There are two distant terminals, let's call them A and B, where the photons can be polarized and then checked whether they passed the polarizer or not. There's also a (dumb) source of entangled pairs in the middle, that sends one photon from the pair to each of the terminals.

        Take a single (non-entangled) photon: If you polarize it at 0 degrees, it will pass the 0 de

    • So tachyons or neutrinos are "below quantum"? If so, what does it mean to be below quantum?

      • Neutrinos are particular with mass that go slower than light, although the mass is like 0.000000(...)00001 and the speed like 99.999999(...)9 % the speed of light.

        So I don't think they do anything funny ; neutrinos merely go faster than light when that light goes through a non-vacuum medium, like beta radiation that makes a nuclear reactor glow blue in the swimming pool.

        • neutrinos merely go faster than light when that light goes through a non-vacuum medium, like beta radiation that makes a nuclear reactor glow blue in the swimming pool.

          The blue glow is Cherenkov radiation which is caused by electrons from beta decay of fission products travelling through the water faster than the speed of light in water. However only charged particles cause Cherenkov light and neutrinos, being neutral, will not cause this effect and pass through matter almost entirely unaffected unless they have extremely high energies and even then they interact via the weak force and not electromagnetism.

        • So I don't think they do anything funny ...

          Let's test that with a joke... "Two neutrinos pass through a bar ..." - You're right: not funny.

      • So tachyons or neutrinos are "below quantum"? If so, what does it mean to be below quantum?

        There is no such thing as "below quantum". Tachyons don't exist (or at least we have zero experimental evidence that they do) and neutrinos are most decidedly quantum in nature since they are extremely well described by quantum field theory.

    • >- Therefore the information goes back in time.
      How and why did you get to that conclusion? There is a giant leap of logic here, and I want to explained

    • Re:So.. for a non-physicist (Score:4, Informative)

      by burtosis ( 1124179 ) on Sunday November 15, 2015 @09:21AM (#50934215)
      To offer a simple explanation no it cannot send information faster than light. You can have these instant correlations but as the latest research actually shows, the values are truly random until measurement. So you can send these entangled photons and unpack one at one location and another at a second remote location and know you have the correlating bit but without knowing what that is, which must be sent classically, you have no idea what is being sent. Moreover currently i know of no experiment that preserves entanglement after measurement so you must also wait classically for the particles to arrive before taking the instant correlation measurement.

    • Re:So.. for a non-physicist (Score:4, Informative)

      by interval1066 ( 668936 ) on Sunday November 15, 2015 @11:30AM (#50934615) Journal
      No.

      "The no-communication theorem states that, within the context of quantum mechanics, it is not possible to transmit classical bits of information by means of carefully prepared mixed or pure states, whether entangled or not."

      See The No-Communication Theorem [wikipedia.org] and the Einstein-Podolsky-Rosen Paradox [wikipedia.org].

    • For everything above quantum, the maximum speed is the speed of light.

      No, for everything which can transmit information the fastest speed is the speed of light. If we find anything which can transmit information faster than light then time travel is immediately possible. You will know if this ever happens because the physicist who discovers it will get extremely rich winning lotteries.

      If we send out a steady stream of entangled particles...we can send information quicker than the speed of light.

      No - as witnessed by the the fact that we still rely on government grants to fund us and not winning the lottery. Quantum entanglement does not allow any information to be sent. It is like shi

    • It would go back in time only from the perspective of an outside observer. From the perspective of the particle itself, it is still in what it would perceive to be normal time, if a particle could perceive such a thing.

  • finally! (Score:2, Funny)

    by Gravis Zero ( 934156 )

    Bob finally has an excuse to throw that cheating bitch, Alice into a black hole: science!

  • In the many-worlds [wikipedia.org] interpretation [stanford.edu] of QM, also called "QM without collapse", becoming more and more mainstream, this is a straightforward consequence of entanglement. When you measure the spin or polarization of your entangled particle, you become entangled with it, so in a sense all you're doing is discovering which "universe" you're in. And of course that universe is correlated with the corresponding other particle, no matter where it is now.

    • I discover which universe I'm in simply by reading the brand, title and issue number of the comic.

    • Re: (Score:2)

      by HiThere ( 15173 )

      I prefer the many-worlds interpretation also, but I think it's a mistake to say it's "becoming more mainstream". It was originally published by (among others) J. Archibald Wheeler, and you can't get much more mainstream.

      For that matter there are several valid interpretations of Quantum Mechanics, and it's probably a mistake to choose between them. There's even merit to the Copenhagen interpretation ("Don't try to understand it, just calculate.") Until there's an experimental way to choose between the int

      • Re: "becoming" mainstream, don't think it's there yet: I think something over 50% of practicing physicists accept it as of a few years ago, which is a change from even a decade ago. As for other interpretations, experiments like this one [phys.org] are making the CI much harder to swallow - instantaneous collapse? Really? FTL signaling?

        Besides, Copenhagen is just a worse explanatory framework. If we're going to make any progress on quantum computation, thinking about what's _really_ going on rather than about mysteri

    • In the many-worlds interpretation of QM, also called "QM without collapse", becoming more and more mainstream, this is a straightforward consequence of entanglement.

      The most outlandish explanations usually are the most straightforward once their assumptions have been discounted.

      • Indeed. But I'd argue Copenhagen is the one with the outlandish assumption here (instantaneous collapse on "measurement").

  • Unless nasa has gotten some really interesting data from SETI im pretty sure its from outside of the light cone of the experiment, not an actual event horizon of the black hole.

    Not that the actual paper or press release is linked at this time (who reads those?) but there have been experiments lately that close loopholes in bells theorm and show that the details are truly random until measured yet correlated upon measurement. This includes determining the experiment details randomly from outside the ligh

  • Information is lost (Score:4, Informative)

    by mbone ( 558574 ) on Sunday November 15, 2015 @09:21AM (#50934213)

    What I think is the really important thing in the original paper [arxiv.org] is that information actually seems to be lost in the black hole. There is an enormous amount of theoretical musing about how to prevent information loss at event horizons (remember the black hole firewall [scientificamerican.com]?); this, if taken seriously, could have implications in quite a number of areas in theoretical physics.

    • If you read the paper information is not lost

      Conclusions
      In conclusion, thermal Hawking radiation stimulated by quantum vacuum fluctuations has been observed in a quantum simulator of a black hole. This confirms the prediction of Hawking regarding spontaneous pair production in the presence of a horizon. This has implications beyond the physics of black holes, as it confirms the semiclassical step toward the understanding of quantum gravity. The Hawking spectrum is observed, as are the correlations between the Hawking radiation exiting the black hole and the partner particles inside the black hole. These correlations are surprisingly narrow in position space, which implies that the high frequency tail of the distribution of Hawking pairs are entangled. On the other hand, the overall weakness of the correlations in position space implies that the low frequencies are not entangled. The entanglement confirms that there is an issue of information loss within the semiclassical approximation.

      • Re: (Score:2)

        by mbone ( 558574 )

        I don't follow that - I interpret "issue of information loss" as meaning that it is happening - i.e., that there is loss to worry about. Read at the bottom of page 1

        Furthermore, the entanglement implies that the outgoing Hawking particles cannot be entangled with one another at various times. This shows
        that there is indeed an issue of information loss in a black hole, within the semiclassical approximation

        Entanglement survives across the event horizon (at least, in this analogue). It would be presumably de

        • Yes it's an interesting result that should point the way for more definitive study. The notion of the singularity is not well defined and may be more of a layered structure than a boundary that applies to all particles at all times ever to fall in. It would be interesting in an actual test case as the sonic approximation model suggests entanglement is preserved for higher frequencies but does rely on many (interesting) assumptions.

          • Re: (Score:2)

            by mbone ( 558574 )

            Yes, who would have thought that a black hole could have multiple singularities (and even maybe, just maybe, life [arxiv.org]) inside it.

  • But what about (Score:1)

    by Anonymous Coward

    Imperial Entanglements? Can we at least avoid those

  • So, one thing I don't understand about quantum entanglement. In the simplest terms, you can have 2 photons generated from a specific process, and if you measure the spin (polarization?) of one of the photons, the other one will always have the opposite spin. And that's what they call quantum entanglement, right? But to me it simply means that the said specific process always generates a pair of photons with opposite spin. Where is the magic of entanglement here? Please help me understand. It's kind of like

    • I can't explain it like you're five, because you're not five and you have been indoctrinated into the classical world. But this video is pretty good.

      https://www.youtube.com/watch?... [youtube.com]
      "Quantum Entanglement & Spooky Action at a Distance "

      If you haven't grasped the quantum way of thinking, this next one is a great video. It doesn't get all technical and assumes some basic information, but the pictures should start you in the quantum direction.

      https://www.youtube.com/watch?... [youtube.com]
      "Delayed Choice Quantum Eraser

  • As somebody who worked on entanglement (Score:4, Insightful)

    by drolli ( 522659 ) on Sunday November 15, 2015 @02:37PM (#50935405) Journal

    a) entanglement does not transfer information faster than light. Why? if i send entangled pairs of photons from a to b and c, and b and c detect these photons, the photons took time to reach b and c. If b does something to the photon, the entanglement is lost. If b and c measure they will know the state the other one received, however they can not influence what is received in the other place, so sorry guys, no FTL transmission of information

    b) What is weird about entanglement is actually not so much it statistical property of the correlation. If a packs a white and black marble in two packages and mixes the packages and sends them out, the result from the viewpoint of b and c will be the same - each one will know which marble the other one received. The weird property is that the state is prepared in a way that the two possibilities are quantum states, which can be subject to phase shift, transitions etc, and are "collective" in that sense that b and c can transfer their state to particles (and possibly create further entanglement) - the basis for Quantum key distribution networks - and that the information which exists exists only in the form of a shared posteriori observation. i.e. the classical marble can be looked at without destroying the correlation, while a quantum entangled photon will be entangled with your measurement apparatus when looking at it.

    c) what these guys did-AFAIU (my topic was very far away) is to create a model system of a black whole, which tries to represent a black whole in a way which we assume it is, observed some properties which can be predicted from this model (temperature of emitted radiation), and checked for some others - correlation, where they found correlation which they interpret as entanglment.

    d) While did not look into the details, i can say from my own experience that such experiments are tricky, and i find the interpretation a little vague. But i have to look closer. I did use quantum state/operator tomography, which usually is the benchmark measurement when you want to prove entanglement, or properties of the superoperators describing your quantum operations. I understand that this may not be possible in this case, which is why one can go for other phenomenological approaches

    e) One should be careful. Proving entanglement is not so simple (Look for entanglement measures), and proving that is actually *survives* the event horizon, instead of being created there, may be very nontrivial. It could very well be that non-entangled state are transformed in entangled states to some degree.

  • since entanglement is the like writing a 1 on one index card and writing a 0 on another, then dropping the envelopes into a box, grabbing one of the envelopes and opening it which reveals what the value of the card in the box is, I would expect this situation to be the case.

  • How do they know it survives through the event horizon, were they there? -Ken Spam
  • "and then the other — even if it's across the Universe — is immediately known"
    Well I guess that's settled then. A year or two ago I posted that scientists potentially thought that quantum changes could occur faster than light because nothing is "traveling" it's merely updating to current reality in real time. People replied like crazy and downvoted me to oblivion. Well I guess we found out who was right after all, didn't we? In fact I recall a story about NASA wanting to test this onboard t

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