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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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  • by Patrik_AKA_RedX ( 624423 ) on Thursday November 16, 2006 @06:36AM (#16866906) Journal
    I have a question: Is it legal to use a timetravel device to chea^H^H^H^Haid in winning the lottery?
  • by rubberpaw ( 202337 ) on Thursday November 16, 2006 @06:37AM (#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 [], which has strong limitations due to being a classical information channel. Does anyone care to clarify for me?
  • FTL communication (Score:3, Interesting)

    by JohnPM ( 163131 ) on Thursday November 16, 2006 @06:50AM (#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?
  • by tjl2015 ( 673427 ) on Thursday November 16, 2006 @06:51AM (#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: []

    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.

  • by blacksway ( 464427 ) * on Thursday November 16, 2006 @07:03AM (#16867094) Homepage Journal
    Surely we need the law NOW, so that when people from the future travel back to now with future library numbers they can be arrested in the past as well as the future, otherwise the past would become a country with no extradition treaties!
  • by Anonymous Coward on Thursday November 16, 2006 @07:04AM (#16867102)
    Well, it will work. Argue against that. "Axiomatically impossible" is for mathematicians, not physicists. It was once axiomatically impossible to sail in westward direction and arrive back at the departure point from the east.
  • by aendeuryu ( 844048 ) on Thursday November 16, 2006 @07:26AM (#16867250)
    Wouldn't we know if the test was successful before we actually conducted it?
  • don't be too sure (Score:4, Interesting)

    by PopeRatzo ( 965947 ) on Thursday November 16, 2006 @08:11AM (#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.
  • by niktemadur ( 793971 ) on Thursday November 16, 2006 @08:36AM (#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.
  • Re: The Future (Score:3, Interesting)

    by Peter Mork ( 951443 ) <> on Thursday November 16, 2006 @08:52AM (#16867884) Homepage
    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.

  • by Dr. Manhattan ( 29720 ) <sorceror171 @ g m> on Thursday November 16, 2006 @08:58AM (#16867970) Homepage
    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 [], if you're interested. I address that point and a lot of others.

  • by Anonymous Coward on Thursday November 16, 2006 @09:58AM (#16868626)
    I decided I would send myself information from the future. I never got anything, so I figured it didn't work. So why would I waste my time and money on a project that already failed?
  • by numbski ( 515011 ) * <(ten.revliskh) (ta) (iksbmun)> on Thursday November 16, 2006 @10:36AM (#16869074) Homepage Journal

    The problem is that there appear to be 2 or 3 (maybe more?) going models of what time is. One says that time isn't a dimension, all that is exists is now, there is no before or after. The human mind tricks us into thinking otherwise do to memory.

    Another states that time is linear, where if we send something into the past, we alter the present. So far as I understand, this has been more or less ruled out.

    The third states that there are infinitely parallel universes with every possibly outcome occurring simultaneously (string theory?) and that the universe has many more dimensions than three or four, possibly ten or more dimensions.

    So that's the real catch. If someone cuts down a tree in the forest, sends it to the past, and it falls in another dimension, no one is ever around to hear it....wait, where was I going with that? ;)

  • by numbski ( 515011 ) * <(ten.revliskh) (ta) (iksbmun)> on Thursday November 16, 2006 @10:42AM (#16869150) Homepage Journal
    Okay, I can't believe I'm about to make a Dragonball Z reference here, but I am. :\

    For those not familiar with the series: []

    Oddly, DBZ is one of the few series that deals with time travel of the idea that the present can't be altered by travelling into the past. The brief synopsis is that in the near future, a pair of androids appear and kill all of those powerful enough to stop them, and more or less wipe out the human race. The reason no one was powerful enough to stop them was two-fold - one, no one saw it coming, and two, the one man that might have been strong enough to stop them died before they arrived from a virus that attacks the heart. There was no cure for this virus, but in the future one was created. Mirai Trunks (or Future Trunks if you will) a time machine to go into the past with a cure for that man, and to warn those who were killed that in 3 years the androids would appear. The man lived, and they all prepared for the next 3 years to stop the android threat. When Trunks returned to his own time, everyone was still wiped out. The man still died from the virus. Trunks then travelled back to a point 3 years later and even helped fight and defeat the androids. When he returned to his own time, the man was STILL dead, the androids were still running around, and everyone was still wiped out. He then proceeded to defeat the androids in his own time.

    Just thought it was related and interesting, albeit horribly geeky. :P
  • Re:don't be too sure (Score:2, Interesting)

    by emil10001 ( 985596 ) on Thursday November 16, 2006 @12:07PM (#16870370)
    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.

    So, what incentive would the people of the future have for sending us information? Wouldn't there be a huge inherent risk involved in sending back information that would have a direct effect on the present (not to say that it would happen like that)?

    Ok, so let's pretend that this system works and is developed to the point of being able to send and receive messages. Now, let's assume that sometime after this device has begun to work, and test messages sent and received, that some sort of tragedy strikes the future, which has a drastic impact on the course of the future. Now, a group of people decide that this is bad, and they would like to prevent it from happening, so they send back a message. The group of people who receive the message act on the information and prevent said tragedy. Now, what happens to the people of the future?

    Two possible situations (of many, many others), the first is that magically reality is altered for those belonging to the future from where the message originated. The second situation is that reality does not alter for those people of the future, and instead a fork is created where an alternate series of events happens. The issues with the first situation are that bad things could stop happening, and this would not be good for the world. The world needs bad things to happen, and so do people, to keep things interesting, and to keep a balance. Also, what happens to those people as reality changes, could it eventually do damage as reality keeps changing?

    The issues of the second situation, is that we now have two distinct forks of the future, and how can we be sure that we are receiving information from the proper fork? Would those forks whose path are not taken be annihilated? As they sent a message and it was received and not acted upon, which then changes the future still because the information is there.

    In short, while it may be tempting to send messages back in time that could save lives, would the risks be worth it, and would it actually help anything?

  • by geekoid ( 135745 ) <dadinportland AT yahoo DOT com> on Thursday November 16, 2006 @12:37PM (#16870812) Homepage Journal
    And if you can control the spin of Particle A, you can transfer data to the observer of particle B.

    WIth 1 particle you could transmit(applied loosly here) morse code. If it is computer controlled, even just ussing a type of mose code, you could transfer data infinite distance near instantaniously.(The computer flipping particle A would take a small amout of time to determine how long until the next flip).

      Of course, more particles means more information.

    I suspect that if time travel is possible, there would need to be a 'reciever' portal, and it would have to be built before the first 'sender' portal.

  • by OwnedByTwoCats ( 124103 ) on Thursday November 16, 2006 @12:51PM (#16871064)
    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 proof that such linked particles cannot be used to transmit a message
  • by denttford ( 579202 ) on Thursday November 16, 2006 @02:54PM (#16873142) Homepage
    Funny, I learned this as:

    There once was a lady named Bright,
    who traveled much faster than light.
    She left one day, in a relative way,
    and returned on the previous night.

    But the original is so []:

    There was a young lady named Bright
    Whose speed was far faster than light;
    She set out one day,
    In a relative way
    And returned on the previous night.

    followed by:

    To her friends said the Bright one in chatter,
    "I have learned something new about matter:
    My speed was so great,
    Much increased was my weight,
    Yet I failed to become any fatter!"

    Ah, synoptic limericks!
  • Question (Score:2, Interesting)

    by Damastus the WizLiz ( 935648 ) on Thursday November 16, 2006 @04:24PM (#16874898)
    What stops the photon from chaning its state while it is traveling through the fiber optic cable?

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