Posted on 06/16/2004 1:54:18 PM PDT by vannrox
Information is something. If no information is going from point A to point B, then there is nothing to discuss. Of course there won't be a causality violation if nothing is sent. I already told you that that was the real solution to the conundrum.
Are you telling me to reread this part:
By itself, this single use of the ansible doesn't create a causality violation. If Bob transmits a signal back towards Alice using a conventional light-speed transmitter, she receives it a later time than when she signalled to Bob. Even if Bob re-transmits with his ansible, Alice receives the reply just a little after she sent out her signal. The problems arise when we bring another inertial frame into play.
Either tell me what I'm misreading or tell me why it's wrong!
I already said that if you bring a different inertial frame into the equation then you have causality problems. That requires a third frame of reference interacting with the first two!
Nor do I. If I am presented with conclusive evidence of causality violation, I will accept it. However, everything I've seen suggests to me that causality is respected in the physical universe.
When I observe that special relativity says that travelling faster than light is equivalent to travelling backwards through time, I am not making any statement about the impossibility of travelling either faster than light or backwards in time. It is merely a mathematical observation about special relativity, and a correct one.
But our traveller is NOT travelling faster than light. He is travelling at 99% luminal velocity and therefore NOT travelling backwards in time. The transmission is NOT travelling anywhere either. It is not even a transmission in the formal sense of the word. It is an extrapolation of a series of actions upon the entangled particles at the other end via the observation of changes to the entangled particles on your end. The entangled particles have no known physical connection to one another.
Their perceived interaction would presumably exhibit the effects of time dilation to our communicating observers, but that would be all. Wherewhenever the opposite end may be along the inertial frame, at any given point in one frame of reference it would not be at a preceding given point in that frame of reference. Maybe the resulting communications would be distorted in some weird time-dilated fashion, but that should be about it. At least, that's how understand the conjectural phenomenon. Maybe I'm wrong. Who knows?!
Bob and Alice are at rest with respect to each other in that example. They share the same axis of simultaneity. Events that are simultaneous to Bob will be simultaneous to Alice.
But the principle of relativity is that the physics must be the same for all observers, and in this case, it won't be. Two relativistic observers flying past in opposite directions along the signal axis will not see these events as being simultaneous. In fact, they will see them as having time orderings that are opposite from each other; one of the observers will see the signal received before it was sent.
I don't follow this at all. The traveler and the earth are two separate frames of reference. Nothing more is required to generate the effects I've been talking about. (If the hypotheticallly instantaneous transmission system makes them both into a single frame of reference, then you'll never have a 3d reference frame, because it too will be in instantaneous communications with the others.)
I have another link bookmarked somewhere dealing with wormholes and the perceived time at the opposite ends. I'm gonna try to find that one too since it's somewhat relevant to the point at hand. It brings up the twins paradox too. Anyhow, if I recall correctly parts of that further clarify the points that I'm attempting to convey.
Stop right there. You can never observe changes in the entangled particles. You can only observe their state once, after which the entanglement is destroyed. The best you can do is observe (after the fact) that there was a correlation.
to the entangled particles on your end. The entangled particles have no known physical connection to one another.
All of that is otherwise correct, and that is why quantum entanglement cannot be called a signal. It cannot be used to transmit information, and cannot violate causality. I already said all that.
Do you understand the crucial difference between that and the Bob/Alice problem you just quoted?
Probably not. Explain it to me so we can figure out why I'm wrong! =)
Well, I'm increasingly convinced that I have seriously misunderstood some fundamental concept but I am not yet seeing what that is, so maybe it will become clear to me at some point. For the interim, I'm just suspending my insistence that my perception of the situation is accurate!
This stuff is very counter-intuitive. No less an intellect than Isaac Newton simply assumed that time was the same for everyone, everywhere.
Can you give us an example? (Other than the obvious and irrelevant case involving a transmitter and receiver who are both in the same of reference.)
Homework: contemplate the Twins Paradox.
I live in LA, they are performing Saturday.
Sorry, that was atrocious. By that statement I mean the spaceship's axis of simultaneity reaches into the Earth's future.
Wow, I'm impressed at your timely arrival. Welcome to FR!
I'm one foot out the door but I look forward to checking out the thread later.
Hopefully it'll set me straight and I won't have to pretend I know what I'm talking about anymore! =)
NO WAY! Really? Thanks for the info. I'm going to do some more checking to see if I can get their albums (now that I've started down this road).
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