Follow Slashdot stories on Twitter

 


Forgot your password?
Close
typodupeerror
×

Physicist Trying To Send a Signal Back In Time 685

Posted by samzenpus from the don't-be-so-gullible-McFly dept.
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.)
This discussion has been archived. No new comments can be posted.

Physicist Trying To Send a Signal Back In Time More

Physicist Trying To Send a Signal Back In Time

Comments Filter:

  • 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.

  • Slashdot posting time travel test (Score:3, Funny)

    by Aim Here ( 765712 ) on Thursday November 16, 2006 @05:27AM (#16866852)
    Test has succeeded!
  • Like how about if they just say that they solemnly swear to send it back to today a year from now, when they have it working.. then we'd already know if it works today!

    The question is, would we then spend as much time on trying to figure out how to do it? How about if we then didn't make it, how would that affect... I mean how would that.. What would...

    ANOTHER TIMEQUAKE!!! RUUUUNNNNN!!!

  • ....Cuz one could scale this technique to work on, say, the lotto results. The only way this can work, is if the measurement of the 1st photon, requires the 2nd photon....so the measurement can only be made after the 2nd photon has been 'modified'.

    • Re:I am Positive, this cant work... (Score:5, Funny)

      by MicrosoftRepresentit ( 1002310 ) on Thursday November 16, 2006 @05:44AM (#16866946)
      Yes, forget any of the laws of physics that might be violated here, the primary concern is this breaks the fundamental rule of the universe, the core axiom at the heart of space and time; it would allow people to cheat at the lottery.

    • Re: (Score:3, Insightful)

      by bigmouth_strikes ( 224629 )
      ....Cuz one could scale this technique to work on, say, the lotto results.

      No, one couldn't. There are inherent differences between our world and the quantum world. Specifically, quantum effects do not scale.

      Then again, if you used individual photons instead of lotto balls, we'd be in business.

    • don't be too sure (Score:4, Interesting)

      by PopeRatzo ( 965947 ) on Thursday November 16, 2006 @07:11AM (#16867516) Journal
      I heard this Cramer physicist dude on the radio the other night. He's deadly serious, and he's for real. He's also looking to get financing for building a time machine for sending tiny bits of information back in time (and he's getting a fair amount, too). You'd need a transmitter and a receiver. What would it be worth to find out that the Challenger mission was going to end badly (that was one of his examples)?

      My biggest fear would be that the system works, and we start getting messages from 5 years from now 8 years from now, but ten years from now...nothing.

    • Re: (Score:3, Interesting)

      by OwnedByTwoCats ( 124103 )
      The way "linked" particles work is that if you measure a property (say, spin) of the two particles, the measurements will be the same. The interpretation is that when you make one measurement, some information is transmitted to the other particle so that when it is measured the results will be the same. The "transmission" is said to be instantaneous (in whose reference frame?). The value of the property being a hidden variable is another interpretation.

      Anyway, I dimly recall being told that there is a pr

  • Inserting first post! (Score:2, Informative)

    by AEton ( 654737 )
    @BEGIN MESSAGE
    @author 321260
    @target_time 0519
    @subject I heard about this
    @content Yesterday
    @EOM

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

    by Patrik_AKA_RedX ( 624423 ) 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: (Score:3, Funny)

        by peragrin ( 659227 )
        Okay two questions come to mind. First you have to the ability in the past to receive said message, and then you have to follow said message, and send it again. If you sent it via email it would mostly likely end up in your spam filter and lost to you. hence useless.

        As the mesage would be filled with phrases like buy IBM on this date, short sell MSFT on this date buy it back on this date. Buy Apple on this date, etc.

        • 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: (Score:3, Insightful)

        by Pharmboy ( 216950 )
        I'd settle for being able to send myself a short message.

        Yea, I could see that.

        1. Don't eat the shellfish.
        2. Don't go home with Samantha. Or her twin.
        3. Buy $x stock Tuesday, sell Friday
        4. $1000 on the Cowboys to win by 3 points

        I can't remember where I read it, but someone once said that the best evidence that time travel into the past isn't possible is the sheer lack of tourists from the future.

    • Yeah I remembered you wrote this. Boy, are you up for a big suprise. Your grandson and I had quite a laugh with the prank we pulled on you 2 years from now. Leaving a living T-rex in your garage, I guess you didn't expected that! Amazing how that nanoreplicator was able to fit a garage in your appartement in the first place.

    • Re: (Score:2)

      by zeux ( 129034 )
      If you could send information back through time (which is what the FA is all about) then there would be no need to physically travel back through time.

      I don't think it's possible though, otherwise we would probably be getting messages from the future, wouldn't we?

      [HEAD EXPLODES]

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

        by ag0ny ( 59629 ) <javi@lava[ ]ira.net ['nde' in gap]> on Thursday November 16, 2006 @06:09AM (#16867146) Homepage
        I don't think it's possible though, otherwise we would probably be getting messages from the future, wouldn't we?

        Maybe we're already getting them.

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

        • Re: The Future (Score:4, Insightful)

          by aussie_a ( 778472 ) on Thursday November 16, 2006 @06:52AM (#16867382) Journal
          Oh yeah, that John Titor was definitely from the future. By the way, how's that Civil War going? Y'know, the one that started in 2004

          • Re: The Future (Score:4, Informative)

            by iamghetto ( 450099 ) on Thursday November 16, 2006 @11:05AM (#16870344) Homepage
            Not to get to technical about hypothetical time travel, but Professor of Physics at the Univ. of Conn., Dr. Ron Mallett is one the leading physicists actually dealing with the plausibility of time travel. According to his work (and coincidentally John Titor as well) we can't actually go back or forward into our same time lines. We can go back to 1800 AD, but it we'd do so by side-stepping to a parallel 1800 AD, not ours own. We cannot traverse time in a reverse fashion, but rather step outside of it then step back in.

            There would be discrepancies in the timelines for that reason. John Titor, for example, couldn't know exactly what would happen in our timeline but can only relate his own timeline which is basically an approximation of ours.

      • Re: The Future (Score:4, Insightful)

        by anandsr ( 148302 ) on Thursday November 16, 2006 @07:38AM (#16867732) Homepage
        The thing is that you have to create the entangled beam and leave it in an entangled state for some years. Then when you do change it you can get the information in your time. But you cannot be getting the signals from the future without elaborate preparations.

      • Re: (Score:3, Interesting)

        by Peter Mork ( 951443 )
        I don't think it's possible though, otherwise we would probably be getting messages from the future, wouldn't we?

        If, as has been suggested, you need a transmitter and a receiver, the quantum messages might already be out there, we just can't read them. Kind of like sending a book back a hundred thousand years and being surprised that Neanderthals don't get the warning.

      • I don't think it's possible though, otherwise we would probably be getting messages from the future, wouldn't we?

        That's like saying in 1870 that radio waves are impossible because nobody's received any. There weren't any receivers then. Or like saying neutrinos didn't exist before there were detectors for them. It's quite possible that the as soon as we have something that can receive such messages it'll be flooded with spam from the future.

        Anyway, I've thought about time travel rather more than anyone probably should [homeunix.org], if you're interested. I address that point and a lot of others.

    • 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.

  • Comment removed (Score:5, Funny)

    by account_deleted ( 4530225 ) on Thursday November 16, 2006 @05:47AM (#16866966)
    Comment removed based on user account deletion

  • 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.

  • FTL communication (Score:3, Interesting)

    by JohnPM ( 163131 ) on Thursday November 16, 2006 @05:50AM (#16867004) Homepage
    From what I can understand the backwards-in-time measurement requires communication from one entangled photon to the other. This would allow faster-than-light communication which is the first thing you think of when you hear about entanglement. I thought it was well established that this was impossible since measuring one photon destroys the entanglement and you can never tell if you sent the signal or received it.
    Can anyone explain how this experiment is different, and would it also allow for ftl comms?

  • 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.
  • .. shame Dean Stockwell is tied up with Battlestar Galactica.

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

    by heytal ( 173090 ) <hetal.rachNO@SPAMgmail.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)

    • Re: (Score:3, Funny)

      by thenerdgod ( 122843 )
      [past scientists] Hey future scientists, we totally got your message through the quantumly entangled photons you sent us!
      [future scientists] (to past scientists, now present) You mean the message you sent us with the photons you sent into the future?
      [past scientists] Awww maaan!
      [future scientists] Yeah, causality's a mofo.
      [past scientists] I wish we got invitations to the sorts of parties where the hostess's undergarments's wave functions were made to collapse 3 feet to the left.
      [future scientists] can I bo

  • 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.

  • Dupe (Score:2, Redundant)

    by mrjb ( 547783 )
    This was previously posted tomorrow.

  • 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.

  • If you decide when planning the experiment that you're going to put the second photon into state X, and then 50ms before you do so you observe the first photon going into state X, then arguably you've seen some communication going backwards in time, but no information. You knew that state X was going to be used anyway.

    More interesting would be to measure the state of the first photon and use that to affect the second one. So if the first one goes to state X, set the second one 50ms later to state Y, and v

  • How will they measure the non-delayed particle? (Score:3, Informative)

    by Per Abrahamsen ( 1397 ) on Thursday November 16, 2006 @06:28AM (#16867268) Homepage
    If they measure the non-delayed particle *before* the 50 ms have passed, the quantum state of the delayed particle will already be fixed at the time they get around to measure it.

    On the other hand, if they wait 50 ms before measuring the non-delayed particle, they aren't really sending much of a signal back in time.

    It isn't much use to send message back in time, if you aren't allowed to read them before the present time.

  • 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" :)

  • Quantum Entanglement (Score:3, Insightful)

    by ajs318 ( 655362 ) <sd_resp2NO@SPAMearthshod.co.uk> on Thursday November 16, 2006 @08:32AM (#16868326)
    It's my understanding that quantum entanglement can't be used to transmit any useful information. Just because Particles A and B have opposite properties, doesn't help us. If we find that particle A has positive spin, we know that particle B, wherever it may be in the universe, must have negative spin.

    I really don't see how that's any different than me having two playing cards, one red and one black, and you selecting one of the pair at random and taking it halfway around the world. As soon as I look at my card, I instantly know the colour of your card. But that's not transmitting any information -- all I did was solve a simple equation.

  • Of course this is possible! (Score:3, Funny)

    by Schraegstrichpunkt ( 931443 ) on Thursday November 16, 2006 @10:00AM (#16869386) Homepage
    A lot of my spam comes from the future!

Slashdot Top Deals

Do you suffer painful hallucination? -- Don Juan, cited by Carlos Casteneda

Close