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Physicist Trying To Send a Signal Back In Time 685

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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Physicist Trying To Send a Signal Back In Time

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

    by creysoft ( 856713 ) on Thursday November 16, 2006 @06:36AM (#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 @06:49AM (#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.

  • by Metteyya ( 790458 ) on Thursday November 16, 2006 @06:58AM (#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.
  • by heytal ( 173090 ) <> on Thursday November 16, 2006 @07:02AM (#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)
  • by UnHolier than ever ( 803328 ) <> on Thursday November 16, 2006 @07:13AM (#16867176)
    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 [] 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.
  • by bigmouth_strikes ( 224629 ) on Thursday November 16, 2006 @07:40AM (#16867316) Journal
    ....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.
  • Re: The Future (Score:4, Insightful)

    by aussie_a ( 778472 ) on Thursday November 16, 2006 @07:52AM (#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
  • by balsy2001 ( 941953 ) on Thursday November 16, 2006 @07:53AM (#16867386)
    You can't travel back in time to GET the winning numbers for a lottery in the future. You have to SEND the winning numbers back to yourself.
  • Funny (Score:4, Insightful)

    by protomala ( 551662 ) on Thursday November 16, 2006 @08:05AM (#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: The Future (Score:3, Insightful)

    by Lord Kano ( 13027 ) on Thursday November 16, 2006 @08:23AM (#16867608) Homepage Journal
    Because apparently one of the mods has faced the dilemma of trying to choose which woman to date and picking the wrong one.

    I didn't need to explain any further.

  • by egr ( 932620 ) on Thursday November 16, 2006 @08:26AM (#16867630) Journal
    just go back in time when it was legal
  • Re: The Future (Score:4, Insightful)

    by anandsr ( 148302 ) on Thursday November 16, 2006 @08:38AM (#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.
  • by Richard W.M. Jones ( 591125 ) <`rich' `at' `'> on Thursday November 16, 2006 @08:46AM (#16867796) Homepage

    He's probably not an English speaker. Photons are spelled "foton" in plenty of countries, including Denmark, the Netherlands, southern Europe (eg. fotone in Italy), etc.


  • Re: The Future (Score:3, Insightful)

    by Pharmboy ( 216950 ) on Thursday November 16, 2006 @09:03AM (#16868044) Journal
    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.

  • by ajs318 ( 655362 ) <sd_resp2@earthsho[ ] ['d.c' in gap]> on Thursday November 16, 2006 @09:32AM (#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.
  • Re: The Future (Score:1, Insightful)

    by Anonymous Coward on Thursday November 16, 2006 @10:19AM (#16868860)
    He sort of got it right. He got the country wrong where it's taking place, but American certainly started it.
  • by jamesshuang ( 598784 ) on Thursday November 16, 2006 @10:22AM (#16868892) Homepage
    Might be useful in more ways than we can imagine... I mean, without someone who's their own grandparent, how would we stop the giant brains from destroying the universe as we know it!?
  • by dazedNconfuzed ( 154242 ) on Thursday November 16, 2006 @11:56AM (#16870206)
    I heard the guy too. That he was on the Art Bell show (awright, I was driving 1000 miles overnight and couldn't get any other station) does not bode well.

    Art asked something similar about "if it works, why aren't we getting any information from the future right now?" The excuse was that you can only send info back so far as the machine has been turned on. Ergo, no machine = isn't running = no winning lottery numbers.

    The guy was obviously a crackpot.
    Unfortunately, people who do not understand a subject adequately cannot differentiate between the crackpot's impressive yet incomprehensible rantings vs. your reasoned informed explanations of why the crackpot is wrong ... hence the reason he was on Art Bell, and why we're discussing him on /. per an exciting-sounding but ill-expressed story.
  • by DavidTC ( 10147 ) <<moc.xobreven> ... .vidavsxd54sals>> on Thursday November 16, 2006 @03:32PM (#16873912) Homepage

    As some sci-fi writer pointed out, I forget who but I'm thinking Niven:

    If it is possible to change the past, the universe will constantly be altered until it is altered to a point that no one invents time travel, and then it will stop. Ergo, if it is possible to alter the past, no one will ever figure out how. (Or this timeline is going to be erased, and it doesn't matter what the hell we figure out.)

    It's like a roulette wheel with fifty trillion slots, and you stop rolling when the ball lands in 'zero', otherwise you roll again. After an infinite amount of time, where did the ball land last?

    A scary addendum of mine: The easiest way to have a universe where no one invents a time machine is a universe where no humans ever existed, or they all get killed before that level of technology.

"I'll rob that rich person and give it to some poor deserving slob. That will *prove* I'm Robin Hood." -- Daffy Duck, Looney Tunes, _Robin Hood Daffy_