Slashdot Mirror
Physicist Trying To Send a Signal Back In Time
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.)
Yesterday
Get the EULA T-shirt
So this is how Bif gets rich. I knew there was no Sports Almanac.
If Bush wants to kill the terrorists, he should jump off a cliff.
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.
Formerly GNU/Anonymous Coward. This message has been determined to cause cancer in laboratory animals.
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?
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.
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!
640K won't be enough.
Gentoo Linux - another day, another USE flag.
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.
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
"Hi. This is my friend, Jack Shit, and you don't know him." - Lord Kano
http://en.wikipedia.org/wiki/Ronald_Malett
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.
Quoting from:
http://en.wikipedia.org/wiki/Quantum_entanglement
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.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.
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
My site
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 or the Greenberger-Horne-Zeilinger one (I have no link), and SURPRISE! it has already been done.
Of course, in the clasical version of this experiment the crystal is usualy spherical with a diameter of about 20cm.
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.
GENERATION 27: The first time you see this, copy it into your sig on any forum and add 1 to the generation.
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...
Don't marry her.
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.
Lil' Thindime, lilting a lacrimose lament, krashes the kwaint konfines of Kokonino Kounty
If you're going to have given people grammar advice, at least have done it correctly: you're using the the present ultraconditional subinverted sem-active past subjunctive deponent aorist, so that should have been "scrodding".
Not for the porn industry. People cumming before going to the site.
Can I bum a sig?
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)
The major problem is quite simply one of grammar, and the main work to consult in this matter is Dr. Dan Streetmentioner's Time Traveller's Handbook of 1001 Tense Formations. It will tell you for instance how to describe something that was about to happen to you in the past before you avoided it by time-jumping forward two days in order to avoid it. The event will be described differently according to whether you are talking about it from the standpoint of your own natural time, from a time in the further future, or a time in the further past and is further complicated by the possibility of conducting conversations whilst you are actually travelling from one time to another with the intention of becoming your own father or mother...
To resume: The Restaurant at the End of the Universe is one of the most extraordinary ventures in the entire history of catering. It is built on the fragmented remains of an eventually ruined planet which is (wioll haven be) enclosed in a vast time bubble and projected forward in time to the precise moment of the End of the Universe. This is, many would say, impossible.
In it, guests take (willan on-take) their places at table and eat (willan oneat) sumptuous meals whilst watching (willing watchen) the whole of creation explode around them. This is, many would say, equally impossible.
You can arrive (mayan arivan on-when) for any sitting you like without prior (late fore-when) reservation because you can book retrospectively, as it were when you return to your own time. (you can have on-book haventa forewhen presooning returningwenta retrohome.) This is, many would now insist, absolutely impossible.
At the Restaurant you can meet and dine with (mayan meetan con with dinan on when) a fascinating cross-section of the entire population of space and time. This, it can be explained patiently, is also impossible.
You can visit it as many times as you like (mayan on-visit re-onvisiting... and so on-for further tense-corrections consult Dr. Streetmentioner's book) and be sure of never meeting yourself, because of the embarrassment this usually causes. This, even if the rest were true, which it isn't, is patently impossible, say the doubters.
"When the atomic bomb goes off there's devastation...but when the atomic bong goes off there's celebraaaaation!"
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.