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Physicist Trying To Send a Signal Back In Time

Posted by samzenpus on Thu Nov 16, 2006 05:18 AM
from the don't-be-so-gullible-McFly dept.
Science Technology
phil reed writes "University of Washington physicist John Cramer is attempting to send a signal back through time." From the article: "We're going to shoot an ultraviolet laser into a (special type of) crystal, and out will come two. lower-energy photons that are entangled," Cramer said. For the first phase of the experiment, to be started early next year, they will look for evidence of signaling between the entangled photons. Finding that would, by itself, represent a stunning achievement. Ultimately, the UW scientists hope to test for retrocausality — evidence of a signal sent between photons backward in time. The test will involve sending one of the photons down 10 miles of fiber optic cable, delaying it by 50 microseconds, then testing a quantum-mechanical aspect of the delayed photon. Due to quantum entanglement, the non-delayed photon would need to reflect the measurement made 50 microseconds later on the delayed photon. In order for this to happen, some kind of signal would need to be sent 50 microseconds back in time from the delayed photon to the non-delayed photon. (Confusing? Quantum physics is like that.)
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  • I heard about this (Score:5, Funny)

    by alnapp (321260) on Thursday November 16 2006, @05:19AM (#16866808) Homepage
    Yesterday

  • A HA! (Score:5, Funny)

    by lavid (1020121) on Thursday November 16 2006, @05:22AM (#16866828) Homepage
    So this is how Bif gets rich. I knew there was no Sports Almanac.

  • any lawyers available? (Score:4, Interesting)

    by Patrik_AKA_RedX (624423) <patrik@vanostaeyen.gmail@com> on Thursday November 16 2006, @05:36AM (#16866906) Journal
    I have a question: Is it legal to use a timetravel device to chea^H^H^H^Haid in winning the lottery?

  • Re: The Future (Score:5, Insightful)

    by creysoft (856713) on Thursday November 16 2006, @05:36AM (#16866908)
    If only it worked that way. Just because we can prove something is true in quantum physics doesn't mean it can be "upscaled" to the macro-universe. In short, even if this works it's a far cry from *you* being able to go back in time.

    • Re: The Future (Score:5, Insightful)

      by Lord Kano (13027) on Thursday November 16 2006, @05:49AM (#16866994) Homepage Journal
      In short, even if this works it's a far cry from *you* being able to go back in time.

      I'd settle for being able to send myself a short message.

      LK

        • Re: The Future (Score:5, Funny)

          by Nephilium (684559) on Thursday November 16 2006, @08:08AM (#16868082) Homepage

          AH-HA!

          That's what all the gibberish spam is! It's us sending ourselves messages from the future!

          Of course, this means that in the future, we will all need giant penises and breasts to fight off the alien invaders, but we can finance the purchasing of the pills needed by buying penny stocks, consolidating our bills, and refinancing our homes... Of course, it also means that we will all be impotant, and need to purchase viagra in order to keep our species going...

          It's all so clear to me now...

          Nephilium

          "Even on Central Avenue, not the quietest dressed street in the world, he looked about as inconspicuous as a tarantula on a slice of angel food." -- Farewell, My Lovely (Chapter 1)

    • Re: The Future (Score:5, Funny)

      by muffen (321442) on Thursday November 16 2006, @07:26AM (#16867626)
      Why would you want to go back in time?
      Going back in time would just mean you need to wait even longer for the Nintendo Wii to come out...

    • Re: The Future (Score:5, Informative)

      by iabervon (1971) on Thursday November 16 2006, @02:07PM (#16873402) Homepage Journal
      There are a bunch of things that make this less useful for doing weird things:

      You can't send a message back in time. You can only receive a message from the future. That is, you can only send a message back in time to a point where you had arranged to get it. It's like an box that you take stuff out of before you put it in; things go back in time to the point where you took stuff out, not to any other time. So there's no issue with the fact that we're not getting messages from the future; the time before the time machine is invented is inaccessible.

      You can't tell what it says in the past. This is where quantum is weird. Basically, what happens is that person A receives the message, which is a series of dots to put in a picture. It looks like random static. Then person B sends the message, which consists of choosing, for each dot, "bell" or "bars". Then they talk to each other, and they find that if you look at only the "bell" dots, the picture is a bell, and if you look at the "bars" dots, it's a set of bars. Since all of the data is collected by A before B chooses, they have to come to the conclusion that something really weird is going on, and the choice later clearly affects the data that was already written down. But they can only come to this conclusion after the experiment is over; before the message is sent, the received message can't be interpreted, although all of the observations can be taken.

      This of it like this magic trick: the audience gets a deck of cards with a variety of backs which they examine in detail. A volunteer on stage shuffled a second deck of cards, writes down a few numbers between 1 and 52, and draws the cards with the given numbers (i.e., for 10, draws the 10th card in the shuffled deck). When the volunteer announces the set of names, they all turn out to have the same backs in the audience's deck. The volunteer chose freely, the deck was really random, and the audience saw the fronts and backs of all of the cards in their deck before the choice was made. If the trick is repeated with fresh decks, it always works. We have to conclude that the volunteer is affecting the construction of the deck in the past, but we're only impressed after it's all over, and we have no idea what the volunteer is going to choose in advance. Even if we agree on a set of numbers to pick if the stock market goes up and a different set to pick if it goes down, we can't tell by looking at the audience's deck which it will be, but the trick still works.

  • Isn't this axiomatically impossible? (Score:5, Interesting)

    by rubberpaw (202337) on Thursday November 16 2006, @05:37AM (#16866910) Homepage Journal
    IANAP, but when I studied some basic quantum theory, I thought that one of the issues that arose in the EPR/Bell research was that in order for entanglement to be valid, it could not be used to transmit information, except via quantum teleportation [ibm.com], which has strong limitations due to being a classical information channel. Does anyone care to clarify for me?

    • Re:Isn't this axiomatically impossible? (Score:5, Insightful)

      by Metteyya (790458) on Thursday November 16 2006, @05:58AM (#16867066)
      Actually the experiment is designed properly. The thing is, they are already going to misinterpret the results. Quantum entaglement means that at the moment of setting wavefunction of one of the particles, the wavefunction of second particle is immediately changed to "second" possible state.

      The key word here is "immediately". Special relativity redefined "the same moment" as "the same interval", i.e. line of constant t^2 - (x/c)^2 instead of plain ol' time t. Entangled states are able to react in classically understood "same moment", without regard to c and limitation of transmitting the signal at most at light speed. Which, by means of special relativity, means travelling back in time (as any transmission of signal or matter with speed greater than light).

      If I did any spelling or grammar error, excuse me, I'n not a native English speaker.

      • Re:Isn't this axiomatically impossible? (Score:5, Informative)

        by radtea (464814) on Thursday November 16 2006, @09:37AM (#16869094)
        Actually the experiment is designed properly. The thing is, they are already going to misinterpret the results. Quantum entaglement means that at the moment of setting wavefunction of one of the particles, the wavefunction of second particle is immediately changed to "second" possible state

        I believe they are hypothesizing actual signalling to occur as follows. Call the two detectors Ap (for prompt arm) and Ad (for delayed arm), and the two photons Pp and Pd for the same reasons.

        Ap and Ad are not the same. Ap has some capacity to respond to the photon in two different ways. I don't know what they're planning, but conceptually some kind of double-slit apparatus followed by a two-layer detector that has one layer capable of determining which slit the particle passed through, followed by another layer that is sensitive only to photons in interference maxima that have classically very low probabilities. So if you detect the photon in layer 1 it is behaving as a particle, in the layer 2 it is behaving as a wave.

        On the other end, at Ad, rather than giving photon Pd a "choice" of what to do, you have two different detector systems: one that is an interferometer, one that is a localized particle detector. One or the other gets switched into the beam "after" the photon has been detected at Ap. With correct placement of the detectors it should be possible to give the term "after" an absolute meaning.

        The claim is that the results of the measurement of Pp by Ap will necessarily reflect the choice made by the experimenter at Ad. So if Pp is detected "as a particle" it will be "because" the experimenter has chosen to detect Pd "as a particle" some time "later", and similarly if Pp is detected "as a wave". The heavy use of scare quotes is due to my respect for relativity and disbelief in strong quantum ontologies.

        I hope I have made this seem plausible, although it is all wrong.

        The perfect linearity of quantum reality ensures that when one gets down to the detailed computations there is an exact balance between terms that wipes out any possibility of transmission of information by this means. This experiment is testing this aspect of reality, and if no one has been able to explain to them "exactly" why it won't work it is because no one has bothered to do the detailed analysis of their apparatus that would be required. When detector efficiencies are folded into the mix the analysis can become quite complex, and you really need to do that if you want to test causality in this manner. If you want to simply demonstrate that the conventional interpretation of QM predicts no knowable information will be transmitted the analysis is much easier.

        So this is a pretty ordinary test of the linearity of quantum reality, and as they say, it is virtually certain that no transmission of information will occur. Unfortunately, given the truly terrible standard of communication demonstrated by this article it is likely that that fact will never be clearly understood by the public.
    • There will be no signalling. What the researchers are looking for is a relation between two entangled photons, but the relation can only be found by comparing the results after.

      To make a crude analogy, imagine I am sending you a bunch of random numbers, and that by altering something in my lab I can change the values of these random numbers. Then, afterwards I can tell you "look at random numbers #31,57 and 68, they form a message". The manipulation I made is instantaneous, but in order for you to get information out of it, I have to tell you where to look for via a classical communication.

      This might not be very clear, maybe Wikipedia [wikipedia.org] is clearer.

      In short, what they are trying to do is a nice experiment, and it should work, but it does not mean you can signal backwards in time.

      • Re:Isn't this axiomatically impossible? (Score:5, Informative)

        by Xerxes314 (585536) <clebsch_gordan@yahoo.com> on Thursday November 16 2006, @11:35AM (#16870796)

        IAAP, and this point of view (that in standard quantum mechanics no information is transmitted superluminally) is entirely correct. This will just be one more shoddy example of science reporting in a very very long line. The only question here is who got their basic facts wrong?

        The physicist in question really ought to know better. Did he lie to the reporters in order to get press for his experiment?

        The newspaper ought to have done some basic fact-checking; reading Wikipedia would be enough to figure things out in this case. Did they lie to the public to make the story more interesting?

        So let's do some digging. The physicist in question is a proponent of the "transactional interpretation" of quantum mechanics (not coincidentally invented by this same guy). In this interpretation, particles may send signals back in time that "handshake" with other particles in the past; however, they do so in such a way that ordinary causality is always correct. See, for example, Cramer's paper at http://www.npl.washington.edu/npl/int_rep/qm_nl.ht ml [washington.edu] where he says:

        Can quantum nonlocality be used for faster-than-light or backward-in-time communication? Perhaps, for example, a message could be telegraphed from one measurement site of the EPR experiment to the other through a judicious choice of which measurement was performed. The simple answer to this question is "No!"

        So that seems to answer that question. However, he goes on to muddy the water by suggesting that quantum mechanics as verified by every experiment to date is actually very slightly wrong, that quantum theory is actually slightly nonlinear. In that case, the delicate conservation of our usual notion of causality will break down and superluminal signals become possible again. Virtually nobody believes this is the case, but I suppose that shouldn't stop us from checking just to be sure. After all, sometimes what nobody believes still turns out to be true.

        The blame here (as so very often) must fall on the reporters. Let's examine some of their shoddy work:

        The problem with quantum theory, put simply, is that it's really weird.

        That's not a problem with quantum theory; it's a problem with what you think is weird.

        One of the paradoxes of interest to Cramer is known as "entanglement." It's also known as the Einstein-Podolsky-Rosen paradox, named for the three scientists who described its apparent absurdity as an argument against quantum theory.

        Like the twin paradox, this is not a paradox at all. Quantum mechanics predicts something. EPR say, "Hey, that sounds weird and wrong." Experiment verifies quantum mechanics. Once again, the problem is with what is perceived as being "normal", not with quantum theory.

        If one of the entangled photon's trajectory tilts up, the other one, no matter how distant, will tilt down to compensate.

        This one is the core conceptual problem with the whole article. It should read:

        If one of the entangled photon's trajectories is measured to be up, the other one, no matter how distant, if measured will be measured to be down.

        That doesn't sound very weird at all, which is why reporters persist in getting it wrong. People like to think quantum mechanics is weirder than it is; it adds some kind of mystical aura to the whole thing. But the universe is plenty weird and interesting even when you get all your facts right. I hope eventually the popular writing on quantum theory will reflect that.

  • Dear Mr Gates... (Score:5, Funny)

    by pandrijeczko (588093) on Thursday November 16 2006, @05:47AM (#16866966)
    640K won't be enough.

  • That's not a signal. (Score:5, Informative)

    by i_should_be_working (720372) on Thursday November 16 2006, @05:47AM (#16866968)
    It carries no useful information, and it's not going 'backwards in time'. It's just two entangled particles outside of each other's light cone. Once one particle is found to be in a certain state, the state of the other particle will be instantly known, but no information is traveling back in time or faster than the speed of light.
     
    It would be cool to see it actually happen, since previous entanglement experiments have never put the particles outside of each other's light cone, but the effect is something that physicists have understood (as much as anything in quantum physics is) for decades. In the article one of them say they don't really expect it to work, but I'd guess this is for technical reasons. No one expects that it won't work for theoretical reasons.

  • Not the only scientist trying this (Score:4, Interesting)

    by tjl2015 (673427) on Thursday November 16 2006, @05:51AM (#16867010)
    Aside from the undoubtedly numerous crackpots who are attempting to build a time machine, I know of at least one more legitimate scientist who is working on something similar. Professor Ronald Mallet, at the University of Connecticut, is working on sending particles back in time. He is basing his on General Relativity, not quantum mechanics, using a circular path of lasers:

    http://en.wikipedia.org/wiki/Ronald_Malett [wikipedia.org]

    The importance of both of these projects is that if you can send photons back in time, you can send signals back in time, and send messages. For years people have wondered about temporal paradoxes and how they may be resolved. With a system such as these, paradoxes can be tested. We'll finally have an answer to the Grandfather paradox.

    Even with paradoxes such as this, a temporal communication device would have incredible application. The scientist in the article might only be working with a few microseconds, but it sounds like that if you have a long enough fiber optic cable, you can send a signal as far back as you want. You might not be able to, say use it to prevent someone from having a fatal accident, since if the accident never happened, you would have never sent the message. But there are many useful applications, especially in forewarning events beyond human control. What if we knew exactly when and where every earthquake and hurricane was going to hit in a particular year? What if we knew rainfall patterns in advanced and could plan for draught ahead of time?

    You wouldn't be able to use it to prevent the next 9/11, but you could probably use a temporal communicator to prevent the next hurricane Katrina disaster. The hurricane or earthquake will still devastate the city, but that doesn't mean there has to be anyone in it at the time.

  • The future called. (Score:5, Informative)

    by Anonymous Coward on Thursday November 16 2006, @06:00AM (#16867078)
    It wants its news back.
    Quoting from:
    http://en.wikipedia.org/wiki/Quantum_entanglement [wikipedia.org]

    Although two entangled systems appear to interact across large spatial separations, no useful information can be transmitted in this way, so causality cannot be violated through entanglement.

    The slashdot editor's brains seem to be traveling back in time though.

  • Why send a signal back in time ? (Score:4, Insightful)

    by heytal (173090) <hetal...rach@@@gmail...com> on Thursday November 16 2006, @06:02AM (#16867088) Homepage
    If you send a signal back in time, one will have to go back in time to verify that it has been received. And since you cannot verify this, you can either claim that the signal has been sent successfully and celebrate, or start new experiments to send people back in time to verify that the signals that have just been sent have been received. Once people verify that, experiments will have to be done to bring people forward in time to testify that they have verified that the signal just sent has been received back in time. How would one prove that anyways ?

    A better experiment is to try and catch signals to be sent in future. You can verify that this signal is sent, once you have received it.

    Critics will say that scientists, once they catch a signal, will ensure that the signal is sent in the future. But then critics are always there...

    (Confusing ? Time related writing is like that)

  • To be completely correct ... (Score:4, Informative)

    by OeLeWaPpErKe (412765) on Thursday November 16 2006, @06:03AM (#16867092) Homepage
    They're sending a RANDOM signal back in time.

  • No news, really! and even wrong (Score:5, Informative)

    by DMiax (915735) on Thursday November 16 2006, @06:12AM (#16867168)

    I actually graduated in quantum information, this is no news and it is wrong.

    I explain my opinion:

    - Entanglement has been observed, pairs of fotons and spin of electrons can be correlated in a manner impossible to describe in classical physics.

    - The experiment described does not even measure entanglement, as you could achieve the same result classically:
    Say I have a black ball and a white ball, I put one at random in a closed box, the other one in another box. Say the boxes are put 1000 miles away from each other, from the content of one of the boxes I can predict which ball is in the other one, as I can check later.

    The point is that they are not choosing in which state (of polarization) the light will be in the moment they measure the first time. So they aren't going to send any message ever this way. To do it they would require a classical channel wich works as we expect...

    For the proof of entanglement one must implement physically the Bell's system [wikipedia.org] or the Greenberger-Horne-Zeilinger one (I have no link), and SURPRISE! it has already been done.

  • special type of crystal ? (Score:5, Funny)

    by ei4anb (625481) on Thursday November 16 2006, @06:49AM (#16867368)
    I wonder if they are going to use resublimated thyotimoline?

    Of course, in the clasical version of this experiment the crystal is usualy spherical with a diameter of about 20cm.

  • Funny (Score:4, Insightful)

    by protomala (551662) on Thursday November 16 2006, @07:05AM (#16867474) Homepage
    Einstein face for news about quantum physics is very funny, because he didn't aceepted it's existance. You know the famous phrase: "god dosen't play dices" :)

    • Re:This makes no sense (Score:5, Funny)

      by rifter (147452) on Thursday November 16 2006, @05:45AM (#16866952) Homepage


      You mean to tell me that it only just now occurred to someone to send an entangled photon through a spool of fiber and see how it affects its twin, which took a direct path?

      Also, I thought entanglement couldn't be used to transmit information, as a consequence of Somebody or Another's Law.

      Can anyone clarify just what this poorly-written and sensational article is actually saying?



      No, this is Slashdot. You want real physicists, and you're probably barking up the wrong tree.

      However you may receive several answers. They are statistically likely not to include the right answer to your question, but rather to fall into one of the following categories (in fact you may just get all of these):

      1) Someone will pretend they know what they are talking about and give you a very long and detailed answer. Unfortunately it will be horribly wrong, but only people with the proper background will realize it (ie no one here). :D

      2) Someone will post a completely offtopic ad hominem attack on you for no particular reason (brain hurt! must strike thing that make brain hurt!) for bonus it will probably have something to do with your sexual proclivities and/or your mother.

      3) Someone will post a completely unrelated troll hoping to get people to actually read it.

      4) Someone will post a smart-aleck comment predicting the reasons you will not receive your answer (Hi there!)

      5) In Soviet Russia, ??? profits you!

    • Re:This makes no sense (Score:5, Funny)

      by i_should_be_working (720372) on Thursday November 16 2006, @06:04AM (#16867110)
      You mean to tell me that it only just now occurred to someone to send an entangled photon through a spool of fiber and see how >it affects its twin, which took a direct path?

      That's been done. I think the new thing here is that the photons are now outside of each other's light cone. Before with entanglement experiments the photons were still close enough to each other during the measurements that a naysayer could claim that when the first measurement was made a signal (traveling
      Also, I thought entanglement couldn't be used to transmit information, as a consequence of Somebody or Another's Law.

      Law of causality. If these systems could be used to transmit information, they could send information faster than the speed of light.

      Can anyone clarify just what this poorly-written and sensational article is actually saying?

      Take two entangled photons and send one really far away. Since it's known that measuring the state of the one far away will result in knowing what the state of the close one is one could claim
      a) that the one far away sent an instantaneous signal to the close one, telling it what state to be in or
      b) if you measure the close one first, that the one you sent away sent it's information from the 50 microsecond-in-the-future-measurement back in time to the moment you measured the close one.

      I think the physicists working on this would say both of those interpretations are wrong.

      • Re:Exciting Applications (Score:5, Interesting)

        by niktemadur (793971) on Thursday November 16 2006, @07:36AM (#16867724)
        Holy cow, the ice is getting thinner as I go along here.

        Aw, what the hell, let 'er rip:

        The moment we (present) invent it, they (future) will already have it, so we might be in for a barrage of information the moment we go online.

        But who's to say what their agenda will be? They might be military or corporate totalitarians in disguise, leading us right into their paws. By what evidence can we trust what they tell us? Or why would we assume that it's in their best interest to warn us to change course, which might lead to their eventual non-existence?

        Referring to my previous post, where I mention keeping the dialogue open to different points in the future. Could we possibly detect if time hackers are intercepting and blocking the lines, then transmiting us misinformation? Before believing in a utopian future, we must proyect past and present trends to generally visualize a future, and by these standards, how can we trust potential power-hungry bastards ten generations down the line? The future will have its' own agenda, and it might be completely opposed to our own. We might not be welcome in their future.

        Here's another: what if the Karl Rove of 2005 could have a conversation with the Karl Rove of November 2006? After all, those in power will be among the first to gain access to the technology. Or maybe a Pentagon general in charge of the project will find a way to make himself into an emperor for life. Temptations will be humongous.

        Now, working under the assumption that the future is relatively benevolent, somebody will have to make incredibly harsh decisions. In order to save a billion lives a hundred years down the line, who's willing to make a decision that permits the destruction of cities or nations? The death of ten or a hundred million people in the current generation? It's more than likely that the invention of a temporal communications network may diminish the worth of the individual, who becomes an abstraction that serves the species, or something more petty: an ism.

        An example on a smaller scale that might hit home: What if the message we get from 2056 is: UNPLUG THE INTERNET! NOW!

        Man, this is getting weirder and weirder.

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