back to article Spooky action at a distance is faster than light

As Einstein put it, it's impossible for anything – even information – to move faster than the speed of light. Yet the lower bound of that impossibility, the minimum speed at which entanglement can't possibly be transmitting information between two particles, appears to be around four orders of magnitude higher than c, the speed …

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  1. Denarius
    Thumb Up

    seriously good research

    I vaguely remember a report two years ago indicating about 8 times c for entanglement. This is orders of magnitude more. Decent interesting times for once. Facinating work. Well done and keep those cards and letters coming. Offtopic: Does this indicate Heim theory might not be crackpot ?

    1. Anonymous Coward
      Anonymous Coward

      Re: seriously good research

      "Does this indicate Heim theory might not be crackpot ?"

      Since the only person who understands Heim theory - Heim himself - is dead, the answer is "No one knows."

    2. The Man Who Fell To Earth Silver badge
      FAIL

      Re: seriously good research

      My experience with research in China is that there is so much data fakery going on, that anything spectacular is suspect. I'll wait until the experiment is repeated someplace reputable.

      1. Turtle

        @The Man Who Fell To Earth

        "My experience with research in China is that there is so much data fakery going on, that anything spectacular is suspect. I'll wait until the experiment is repeated someplace reputable."

        My reaction was sorta kinda similar: although I did not think "fakery" I did think "measurement error". It will be interesting to see if the results can be replicated.

    3. Wzrd1 Silver badge

      Re: seriously good research

      One ponders tunneling and its apparent superluminal tunneling.

      Now, this.

      Why can't information travel at FTL velocity? It isn't matter nor energy, only quantum state.

      An examination of this, should it be verified, could yield interesting information about the very nature of space, for there are models that showed superluminal expansion of the universe itself after the big bang.

      Well, we'll see. It'll all come out in the wash, as others attempt to replicate this experiment.

  2. Destroy All Monsters Silver badge
    Holmes

    Well done ... again.

    Still measuring how quickly a statement about a system propagates?

    This is basically a null experiment.

    - You have a blue and a red car

    - One car is a million miles away

    - One of the cars is hidden behind a curtain

    - When you peek behind the curtain and find out that the there car is blue...

    ...how fast does the other car become red?

    Seriously fast!!

    (Ok, so i QM the colors are not set at the start because the mathematics are an extension of classical probability calculus from R to C, but that's basically it)

    1. Anonymous Coward
      Headmaster

      Re: Well done ... again.

      AFAIK it's not "hidden" variables behind a curtain. It would appear the measuring device can effect the particle.

      So those measuring at different settings get different results. But Alice and Bob still agree they say the same pairs of particles (even though this time Alice changed here measuring device). Check the Born probabilities page on wikipedia, the maths is over my head, but looks like they covered it all.

      It could be the Monty Hall problem in disguise, but I don't think all of physics would fall for that one... would they?

    2. Anonymous Coward
      Facepalm

      Re: Well done ... again.

      Beat me to it.

      Until such time as one can actually direct the collapsed quantum state of one of the entangled pair then presenting the process as 'communication' is a fallacy.

      Anyway, weren't we told just last year how 'quantum information' in entagled pairs can travel back in time? Reg, please stop re-reporting the pig-ignorant press spin on this sort of stuff over and over and over again.

    3. Eddy Ito
      Joke

      Re: Well done ... again.

      Oh no! That means Schrodinger's cat is...

      1. Charlie van Becelaere

        Re: Well done ... again.

        Actually, it means Schrodinger's cat isn't ....

        1. Sir Runcible Spoon

          Re: Well done ... again.

          Yeah, but do you know _where_ it isn't?

          1. Eddy Ito

            Re: Well done ... again.

            Statistically speaking, I probably do know where it isn't but I'm uncertain of the magnitude of the error in that estimation since the measurement would be rather uncomfortable.

          2. Scott Earle
            Happy

            Re: Well done ... again.

            Yes, but only if we don't know how fast it isn't going ...

  3. Anonymous Coward
    Anonymous Coward

    Yummie crypto

    If this can be brought into commercial use you could have an interesting way to communicate, and one that isn't subject to intercept for quite a few years.

    I wonder what the range of this is - if we could box one half up and send it along with a Mars mission you'd have something to drive your average physicist up the wall if it kept working because it would demand new theories on assumed maximum speeds (assuming this is possible - I'm no physicist so I may have this totally wrong).

    Spooky indeed.

    1. Destroy All Monsters Silver badge
      Headmaster

      Re: Yummie crypto

      Its not possible. That's what this is about.

  4. xyz Silver badge
    Holmes

    IMHO

    I've never had a problem with this...

    you can't go faster than c...fact

    you can entangle 2 "particles" and if you change the state of one "particle" you change the state of the other, no matter (no pun) how far they are apart (OK 14km at the moment or so)....fact

    Therefore we see 2 "particles" but the entangled "particle" only knows about itself, so you have to look at what's happening from the "particle's" reference point not from ours.

    From a computing viewpoint, there are 2 threads which both are using the same object. A public property called X in the object sets and gets a value. X is currently 0. Thread 1 sets X with a value of 5, so the internal value of the object is now 5. Thread 2 gets X and strangely thread 2 finds X is suddenly 5 whereas thread 2 thought X was 0. Thread 2 is left scratching its head as it thought the 2 threads were separate but didn't realise that they were using the same object.

    This issue is that we understand about threads (spacetime), the object doesn't so what's the problem?

    1. Destroy All Monsters Silver badge
      Headmaster

      Re: IMHO

      > if you change the state of one "particle" you change the state of the other

      That's not how it works. You can decide to extract information about the entangled system at once particle, which gives you a classical value - and fixes the classical value at the other end. This does not imply that you "change" anything here or that you "change" anything there.

      > Therefore we see 2 "particles" but the entangled "particle" only knows about itself, so you have to look at what's happening from the "particle's" reference point not from ours.

      It's two particles though they have correlated state.

      The entangled particles "knows" nothing. And you can easily select relatively moving frames in which Alice measures before Bob, and others in which Bob measures before Alice. They will still find the same classical values, surprise! Actually not a surprise if you just drop the idea that states are described by classical vectors or hidden variables. Of course, one can posit magically invisible metaphysical mechanisms to keep this all in the classical space of ideas .. looking at you, Bohmians.

      1. xyz Silver badge

        Re: IMHO

        OK...I apologise for my use of words. All I'm saying is that the particle "preceives" itself as a single thing whereas we perceive it as 2 things. The universe probably "perceives" it/them as the outliers of a line of probability which >>IMHO<<< has the properties of something moving very, very fast but because they/it are/is not, then the c rule doesn't get invoked.

  5. Steve 114
    Holmes

    Fallacy?

    The 'speed of light' is a distraction. Light is instant (in the frame of reference of the photon doing it). Anyone else watching has to consider a universal constant called 'c'. You can't do without 'c' for spacetime, just as you can't do without 'pi' for circles. If you think something has travelled 'faster than light' you have simply misunderstood the problem. Go square a circle.

    1. Destroy All Monsters Silver badge
      Headmaster

      Re: Fallacy?

      There is no "frame of reference of the photon". That's what light speed is.

      You can do without "c" for spacetime very well indeed. Just stay Galilean.

  6. Paul Kinsler

    Some context ...

    You can interpret QM predictions of separated measurements on entangle systems like this in two ways:

    (a) You insist that any quantum uncertainty might be a result of ``hidden variables'', and so follow the rules of classical (ordinary) probability. This requires the two parts of the experiment to be able to signal to each other instantaneously: i.e. the so-called ``spooky action at a distance''

    (b) You prefer to retain the speed-of-light speed limit for cause and effect, but at the cost of disallowing hidden variable (standard probabilistic) models, and thus need to describe things using complex probability amplitudes - i.e. quantum probability.

    Most physicists prefer to choose (b), because they prefer to retain causality over a model respecting classical probability theory.

    Nevertheless, it is valuable to test both ideas. As I understand it, here the authors' have said: if we choose a hidden variable interpretation (choice (a)), what is the experimental bound on the speed of information transfer?

    This doesn't mean that the interpretation (a) is the ``true'' interpretation. It doesn't even mean that the authors necessarily prefer (a) over (b). But it does tell us something about how things (might) work /if/ (a) were the best interpretation.

    1. TheOtherHobbes

      Re: Some context ...

      Physicists choose (b) because there's no experimental evidence for (a), and plenty of reason (e.g. Bell's inequality) for believing that hidden variable theories don't make sense. (The Bohm-ists have never been able to produce a complete theory that can be tested.)

      In (b), there are no 'particles' in any classical sense - there are only probability distributions. Ultimately QM isn't about little bits slapping into other bits, it's about event probabilities.

      In fact I suspect there's nothing but probability going on, and reality is just a fog of probability densities which look as solid as clouds do when you fly over them, but have no more substance.

      If stop expecting QM to talk about physical things and start thinking about event possibilities, it stops being quite so weird.

  7. This post has been deleted by its author

    1. Anonymous Coward
      Headmaster

      Re: At the moment what I can see from the comments...

      It's not impossible in the case of "impossible to fly to the moon" it's impossible in the case of "impossible to make the moon the sun".

      It's not a system described as sending information. It's like a shadow that is 1000km long. You can make two hand shadows of thumbs up between the two points 1000km apart, but the people watching your shadow puppetry cannot use those shadows to send a signal. If they send their own shadows, they take the normal time (lightspeed). But observed from your point, they both get your shadows at the same time ("instant").

      So it's "impossibly impossible", not "practically (limited by our resources and time) impossible". One can be overcome, the other not.

    2. Paul Kinsler

      Re: It's impossible to send data this way ...

      Its impossible to send information FASTER THAN LIGHT, because in order to know whether your measurement ("here") is an encoded 1 or 0, you need to compare it against the other distant measurement ("there"). E.g. if they both are the same, it's "1", if they differ, its "0". So to understand your result, you have to wait for the results from over there to be sent to you here, and that waiting time depends on the speed of light.

      1. MacGyver
        Holmes

        Re: It's impossible to send data this way ...

        Why couldn't you just record a minutes worth of "information" being transmitted, then compare the timestamps after the fact? What you said is like saying a telephone can't work because by the time you run over to the other end the sound is already gone.

        Anyway, if data is being transmitted 6 times faster than the speed of light or more, maybe the problem is that the information they are trying to measure at the distant end is coming from only one possible future, and by stopping the experiment "before" that future event has caught up with current events, therefore screwing up the results. I guess what I'm asking is has anyone working with entangled quantum particles ever encoded something like PI in the spin of of one of their entangled particles and "kept" encoding it for an extended period of time, while measuring the spin of the opposite end to see if that same data ever starts coming in. I know they say that viewing the spin of the opposite end changes the result, but what if that is only for tests shorter than the event lag?

  8. Anonymous Coward
    Anonymous Coward

    I find this stuff fascinating but I'm a total idiot who knows absolutely nothing...

    Could someone break down what this actually means in lay-mans terms for Dummies...?

    #1. For instance does it mean two entangled particles can communicate faster than light....?

    #2. Or does it mean that two entangled particles separated by a vast distance can fold space or something similar, so distance becomes meaningless?

    #3. After that please explain if entangled particles translate to the macro world on any level...?

    #4. Lastly, discuss Einstein's protege David Bohm and his Holographic Universe theory where he argued mediums or physics might be actually be able to gain insights, but not from anything metaphysical, but rather that thought is distributed and non-localised...

    1. Schultz

      Re: I find this stuff fascinating but I'm a total idiot who knows absolutely nothing...

      #1 no, the have entangled properties, but the properties are created in the entangled common source. There is no communication ('information transfer') between the particles.

      #2 no, think about the two particles as a single two-particle state of matter. The matter wave is as large as the distance of the two particles -- and once you measure a property of the wave at one point, you also know about some properties of the wave at another point.

      #3 yes, the world is composed of entangle particles. But for an object of macroscopic size , the complex entangled (quantum mechanical) properties average out to classical properties, hence we cannot predict them. So even though the answer is a yes, you might pretend that the answer is no and you wont miss anything.

      #4 this point is related to #3: we cannot predict observations on the level of the universe, so you can hypothesize all you want about local or non-local properties and nobody can prove you wrong.

      Hope this helps.

      1. Anonymous Coward
        Anonymous Coward

        Re: I find this stuff fascinating but I'm a total idiot who knows absolutely nothing...

        @Schultz

        Thanks!

  9. Mystic Megabyte
    Meh

    1.38 x 10^4

    What? Carrots per second?

    Or did you mean 1.38 x 10^4 x c ?

    1. Chris Tierney
      Unhappy

      Re: 1.38 x 10^4

      @ Mystic Megabyte

      You remind me of my old physics teacher once wrote a similar quip "Carrots per second?" against one of my answers in a test paper. I resubmitted my test paper with a note declaring that anyone marking this should have been contextually aware and clearly this comment was written by a buffoon who was not in the same frame of reference.

      My test score did not change. :( Spooky cause I knew that was coming.

      1. Tom 38

        Re: 1.38 x 10^4

        "Oh I'm not right, so I'll just claim it should be obvious and you're a cretin for saying it is not" - I'd have marked you down if you tried that shit.

        In this particular case, there are no units listed because there are no units to be listed. The value quoted is a ratio of the speed of "speed of spooky action" against the speed of light in a vacuum.

  10. Schultz
    FAIL

    Spooky action != Information

    Stop this nonsense forthwith --or Einstein and friends will come to spook (haunt) you.

    This article mixes up information transfer with spooky action. This is a major fail: established physics agrees that information transfer is not possible at speeds faster than light, but you are allowed to invent lots of information-less spooky experiments.

    Spooky action works like the following: Two travelers put a red and a blue chip in a bag and -- without looking -- take out one chip each and take it to a faraway location. If they both look at their chip at the same time, they suddenly know the color of the chip in the other travelers pocket -- spooky and definitely faster than light! But there is no information transfer from one traveler to the other. There might be predefined action (e.g., the red-chip traveler should return to home base), but the relevant information must have been agreed upon before the travelers set out, so that's information transfer from the joint departure point and not from on traveler to the other.

    If you now replace 'traveler' with 'photon' and use spin/polarization/energy instead of color, then you have the blueprint for most spooky action experiments.

    1. Scott Pedigo
      Facepalm

      Re: Spooky action != Information

      @Schultz

      I'm with you so far, but to take your explanation and run with it, the problematic idea that us physics noobs have gotten into our heads is that (1) there would be some law such as 'conservation of color' where the number of red and blue chips in the universe must be equal, (2) the chips would have a little switch which would allow you to flip their colors between red and blue, and (3) if someone flipped the switch on one, the other would simultaneously change to the opposite color, thus allowing a FTL morse code. So we've been given the wrong idea of what entanglement means?

      1. Schultz

        @Scott Pedigo

        (1) There are conservation laws for energy (color), spin (=angular momentum), etc., but you can find similar conservation laws in classical physics. The mathematical description can become tricky in the quantum world. (2) You cannot flip a switch to magically switch a property, you can only measure it. There is, however, a probabilistic relationship between the nature of the measurement and the measurement result, so you can affect the result by changing the measurement. (3) The measurement can affect the measurement result but, as a law of physics, no faster-than-light information can be transferred to an entangled particle (so far this has never been disproved -- despite large effort).

        So yes, you have been given the wrong idea about entanglement. And everybody here is a complete sucker for reading all of this even though the progress towards information teleportation is zero.

      2. doctau

        Re: Spooky action != Information

        > (2) the chips would have a little switch which would allow you to flip their colors between red and blue,

        > and (3) if someone flipped the switch on one, the other would simultaneously change to the opposite color,

        > thus allowing a FTL morse code. So we've been given the wrong idea of what entanglement means?

        This is basically where it's wrong. The chips are in a quantum superposition of red and blue, and when you look at the chip it will be one or the other, but it's 50% either way. If you see red you know that the other guy will have the blue one, but since you can't choose which colour it is, you haven't send any information to the other end.

        There are some ways of rigging it so you can affect the outcome, but they all require you to have a side-channel communication mechanism which operates on normal classical mechanisms so can't transmit faster than light.

        Imagine that you had a machine which when used would code the information, transmit it via entanglement mechanisms and give you the decoding key. The person at the other end can record the data which has travelled faster than light, but they can't do anything to extract the information without the decoding key. There is no way to transmit the decoding key to you faster than light, so in essence you haven't transmitted the information faster than light.

    2. Alfred

      Re: Spooky action != Information

      I think I'd like to add one small rider to this; whilst finding a red in one bag means there must be a blue in the other, and vice-versa, the analogy presented in your post implies that the redness/blueness has already been decided and it's just that the people haven't looked in the bags yet.

      With the particle-based experiment, the redness/blueness has not been decided yet and won't be decided until someone looks in the bag, at which point the decision will also have been made for the other bag all the way over there, so somehow it "knows" that we just looked in our bag, which is the apparent weirdness.

      Just thought it was worth spelling out.

      1. MacroRodent

        Re: Spooky action != Information

        "With the particle-based experiment, the redness/blueness has not been decided yet and won't be decided until someone looks in the bag, "

        How do we know that it has not been decided?

        This is the one bit I have never understood in these entanglement experiments. Perhaps it is something that is possible to explain without advanced mathematics? Without that, people think of the red/blue bean analogies or similar, like my favorite: two synchronized machine guns shooting tracer bullets of the same colour, but varying the colour between shots, in opposite directions at nearly the speed of light. If one observer sees a red bullet whizzing past, he instantly knows another observer on the opposite side (a light-year away) will also see a red bullet. How is the case of the photons different?

        1. Badvok

          Re: Spooky action != Information

          "How do we know that it has not been decided?"

          That's the Bell Inequality they are talking about - look it up. If the colours were decided before anyone looked then you'd get straight lines rather than a curve. Can't fathom the maths myself, but that's my understanding.

        2. NumptyScrub

          Re: Spooky action != Information

          quote: "How do we know that it has not been decided?"

          Because the next time you look in the bag, it might be a different colour. The properties that end up entangled are random properties; if you check them 10 times you can get 10 different answers from the same chip. The only caveat is that if you look at yours and it is blue, the other chip will be the complementary red colour at that time.

          That's why physicists aren't too keen on it, because there is an apparent link between the chips (photons) that is not bounded by spacetime. One camp refer to it as "spooky action at a distance" and another camp call it "linked probability wave function" and there are possibly more interpretations too; I'd offer the possibility that both particles are running the same pseudo-random sequence (i.e working off the same RSA key), which needs neither spooky action or vast probability waves spanning light years in an instant, but does imply determinism on the part of the "random" properties (if you knew the sequence you could predict the value of the property at any time in the future, meaning it is not "random"). Which physicists would also have an issue with.

          Currently there is no right answer, and it is entirely possible we will never have a right answer. We just know that that is the way it appears to work.

          1. MacroRodent
            Unhappy

            Re: Spooky action != Information

            >>quote: "How do we know that it has not been decided?"

            >Because the next time you look in the bag, it might be a different colour.

            But in the photon case, you are looking at the next incoming photon, not the same. Consider my synchronized near-light-speed machine gun analogy. Suppose it tossed dice before deciding which colour of tracer bullet to shoot in opposite directions? (Perhaps this would be the "linked probability wave function"?)

            I'm sure the issue is not that simple, why else would some of the smartest people on the planet grabble with it. I'm just despairing if I will ever properly understand what the big problem is, never mind the solution...

  11. Helena Handcart
    Thumb Up

    Reading all these wonderful posts nicely proves the aphorism "if you think you understand quantum mechanics, you don't understand quantum mechanics."

    1. James Hughes 1

      Feynman said in a lecture, NO-ONE understands quantum mechanics. We have a theory that shows what happens, but not why it happens, hence we don't understand it.

    2. frank ly

      I _know_ that I don't understand quantum mechanics, so what does this imply for my entangled identical twin? (Everyone in our family says that we are spooky.)

      1. Vic

        I _know_ that I don't understand quantum mechanics, so what does this imply for my entangled identical twin?

        He doesn't know that he doesn't understand quantum mechanics...

        Vic.

    3. Paul Kinsler

      Re: you don't understand quantum mechanics.

      Hmm. If this forum were full of physicists working in the relevant subfields of quantum mechanics or quantum information, then you might well be able to prove something. But not necessarily the "don't understand quantum mechanics" part.

  12. Pen-y-gors

    Errrrrrgh...

    my brain hurts...

  13. MrXavia
    Alien

    Now I KNOW time is effected by gravity, we know that due to our orbiting probes... their atomic clocks move SLIGHTLY faster than the clocks on earth.

    Time slowing down due to speed, that I find harder to accept, but I'm willing to give them benefit of the doubt for now.

    And I cannot accept that information cannot be transfered between two points faster than light would travel between two points... there must be a way.. if we can postulate a theory for Warp travel and NASA is working on proof of theory, why can't someone come up with the way to send information faster than we can send a photon of light?

    Aliens, because when they finally arrive, we'll have a lot of questions!

    1. James Hughes 1

      Isn't the atomic clock difference on probes down to their speed, not the gravity?

    2. Michael Wojcik Silver badge

      And I cannot accept that information cannot be transfered between two points faster than light would travel between two points... there must be a way

      Sure. All you have to do is give up on causality.

      If you can transmit information beyond the bounds of your light-cone, it's possible - even easy - to arrange for temporal paradoxes. These can include, for example, receiving information about your own future. Well, that's awkward, isn't it?

      Consider a fairly simple case, adapted from Milton Rothman's classic 1980 article "On Faster-than-Light Paradoxes":

      - A spaceship leaves Earth and travels away from it at a normal, subluminal speed, say 0.5c.

      - The Earth and the spaceship have relative motion with a significant velocity, which means their reference frames are significantly shifted from one another.

      - We assume some means of instantaneous communication. (This experiment works with any FTL communication; instantaneous is just a convenience.)

      - At 12:00 on a particular day, Earth sends a message to the spaceship.

      - Due to the difference in reference frames, when the spaceship receives that message, its onboard clock says that it's 10:00, not 12:00. If we had a universal frame of reference, we'd have to say that the message "went into the past".

      - Now the spaceship echoes the message back to Earth. When does this reply arrive?

      - Does the instantaneous communication channel work asymmetrically, so the spaceship's message arrives two hours later, Earth time, ie at 14:00?

      - Does it work symmetrically, so the reply arrives two hours earlier, at 8:00?

      Neither is acceptable. If the channel is asymmetric, then Earth is in a special frame of reference. The messages it sends "go into the past". Earth can put a timestamp on its messages to detect this special status. Now relativity is out the window, and we have to explain why Earth is in a special reference frame. (In any case, relativity is theoretically necessary - there are all sorts of problems if you try to assume a universal reference frame - and has been experimentally confirmed up the wazoo.)

      If the channel is symmetric, then at 8:00 Earth receives a copy of the message it won't send for another four hours. Determining why that's bad is left as an exercise for the reader.

      Of course, there are those SF authors (eg Charles Stross) who run with the latter idea, and write novels around the concept of causality-violation technology. Next to false vacuum collapse, though, that's about as bad-ass an apocalypse scenario as you can invent.

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