Register to reply

Faster than light information travel

by JohnLuck
Tags: information travel
Share this thread:
Nov20-12, 08:07 AM
P: 138
I... just...

Well, good luck with breaking physics. I'm out.
Nov20-12, 09:31 AM
Sci Advisor
PF Gold
DrChinese's Avatar
P: 5,441
Quote Quote by JohnLuck View Post
B) You are wrong. Measuring the angle B would set the angle A at random for all the photons. This is what is so special about entanglement, the entangled pair affect each other instantaneously over a distance, (Einstein called it "spooky action at a distance"). I suggest you read up on it. Also what did you think entanglement was?
You are being unnecessarily rough with this comment.

The fact is that your idea does not transfer any useful information faster than light. All outcomes appear completely random regardless of the angle you select to measure, and regardless of what you do elsewhere. No pattern emerges until and unless you compare Alice's result with Bob's. That requires a traditional information channel operating no faster than c.
Nov20-12, 10:19 AM
P: 297
(Apologies DrChinese, I just saw your response.)

JohnLuck, would I be right in thinking the you want to use the machine to send information faster than light? If so, my understanding is that this is not possible. (Geogir / DrewD / DrChinese, you seem like you could you confirm / refute this ... please?)

The only way to decript the "message" is to follow up with a letter / phonecall to explain to the Martian how the key to the message (which will change with every message) works. Otherwise the Martian only knows the the answer to the question is yes / no (0/1), not what the question is. And you can't agree the question in advance, because until you measure your particle, you don't know if it needs to be positive or negative.

I'm no expert on this, just a reader like yourself, but I hope that this helps.


Nov21-12, 04:41 PM
P: 20
Quote Quote by georgir View Post
I... just...

Well, good luck with breaking physics. I'm out.
Sorry, my reply was worded unnecessarily arrogant sounding. What I meant was something like "What is your understanding of how entanglement works?" It was not meant to be so condescending.

Quote Quote by DaleSpam View Post
All polarization filters place the photons into an eigenstate, if they do not do that then they are not filters. Entanglement only happens when the state is a superposition of eigenstates, so it is self-contradictory to claim that you have placed a pair of photons in an entangled eigenstate.
This is probably why it wouldn't work then! My machine would require us to only send photons with a certain spin and the receiver to know about this default spin. If there is no way to do that, then certainly there is no way to send information using this. So I guess this is solved.

Thanks for all the comments!
Nov26-12, 11:59 PM
P: 79
Quote Quote by JohnLuck View Post
Ok, so I am not a physics pro, but I find it very interesting. And I just finished reading about Bell's theorem and I have a question.

As I understand it, the laws are like this for entangled photons:
1. If you measure the polarization of photon 1 at angle A, you know the polarization of photon 2 at angle A is the opposite.
2. The polarization at angle A is reset at random if you measure any other angle, but otherwise stays the same

So lets say that I build a device on earth that spits out entangled photon pairs rapidly and continuously. And lets say the device is configured such that we know the photons that the device emit from the left side will reach mars after 7 minutes. The photons that the device spits out from the right side on the other hand goes through a path of mirrors that takes exactly 6 minutes and 59 seconds to traverse.

Now lets say that on mars we have another device that detects these photons and reads their A angle and interprets the result as bits like on a normal network.

We start up the transmitter and after 6 minutes and 59 seconds we measure the A angle on earth. If we want the A angle to be up and it is already up, we simply keep the photon for 2 more seconds before letting it escape. If the angle is not what we want it to be, we measure angle B to reset and then measure angle A again and keep doing this until we have the preferred value for angle A. And lets say that our advanced machine can do this 1000 times in one second so that we have only a 1/2^1000 chance of not aligning our photon pair before the receiver reads it. If both mars and earth had a receiver and a transmitter, this noise and other noise could be mitigated with check summed packages such as it is done already on networks today.

If such a device was possible, I am sure others would have thought about it before me, so where am I wrong?
Your No. 1 might be wrong. The problem is that thinking about what's happening in terms of an underlying polarization doesn't (re Bell, etc.) work. It's true that if the polarizers are aligned, then given a qualitative result at A, then the time correlated result at B can be deduced. Depending on the experimental preparation this might mean that if the result at A is a detection, then the result at B is a nondetection, or that if the result at A is a detection, then the result at B is also a detection. The problem is that this doesn't necessarily tell us anything about the underlying polarization. It also doesn't tell us if modelling the situation in terms of an underlying polarization is correct. The results of Bell tests seem to suggest that this is not the correct way to model entanglement, because Bell tests involve polarizer orientations other than alignment. In other words, if you assume that the entangled particles are identically polarized or oppositely polarized, then a model (at least a Bell type model) based on that will not produce entirely accurate predictions. So, apparently, this sort of classically based conception of quantum entanglement is inadequate to explain the essence of quantum entanglement.

Or maybe it is, and that's part of the ongoing discussion regarding the meaning of Bell's (and similar) theorems regarding quantum entanglement.

For now, it remains an intriguing mystery. But so far there's no indication that any sort of faster than light info transfer is happening.

As a previous poster indicated, maybe the essence of quantum entanglement is related to the empirical Malus' Law -- the qualitative foundation of which is unknown, but which doesn't seem to suggest any sort of faster than light phenomena.

Register to reply

Related Discussions
Can information travel faster than light? Special & General Relativity 64
Can information travel faster than light? Special & General Relativity 5
Bohm's faster than light information travel experiment General Physics 1