From: Andrew Clough (aclough@mit.edu)
Date: Mon Oct 15 2001 - 16:53:06 MDT
At 10:05 AM 10/15/2001 -0400, you wrote:
>Andrew Clough wrote:
> >
> > Anyway, I can see a way to communicate with the past using instantaneous
> > communication. First, send the message to your past self to a friendly
> > probe/alien/space craft Very Far Away.
>
>And just how would this occur?
By the quantum entanglement we were talking about, of course. I'd also
like to note (since that section was cut out) that I was using
communication with the past to *disprove* quantum entanglement.
> > Next, have this second party change
> > their velocity be a Good Deal. This will change what is considered
> > "simultaneous" with them. (Actually, I believe non-local simultaneity is no
> > longer a valid concept because of this, much like absolute frames of
> > reference.) They can then be simultaneous with you past self, and can
> > relay the message to him or her.
>
>These ideas about communicating with the past via exceeding light speed
>are a misperception caused by too much Star Trek watching.
I'm afraid I have to admit I don't watch star trek. I believe I first
heard about this in "Six Easy Pieces" or some other Feynman.
>There is an absolute frame of reference in at least one dimension. For
>example, we all know the Big Bang occured at some point in the past.
This does not prove an absolute frame of reference! It shows that people
agree on the direction of Big
Bang, not how long ago it occurred. With any other event, the time that
has passed is relative to the observer's velocity. Thus, time is *not* an
absolute reference frame. I believe that the magnitude of the space/time
vector of an event relative to the Big Bang is constant across all
viewpoints, but that simply shows that time can't exist as an absolute
reference frame by itself.
>Temporally speaking, therefore, we can all deal relativistically with
>each other in reference to the Big Bang event, so in the dimension of
>time, there IS an absolute frame of reference. This is essentially what
>occurs when we are x many light years from each other. We may experience
>more time than others due to our relative veolcities (even then, the
>rate of temporal passage occurs in reference to actual zero velocity.
>This is an interesting question to ask: Just what frame of reference
>results in the fastest possible passage of time? Is this determined by
>the velocities of the majority of the matter in your local region, your
>galactic arm, or your galaxy? If all matter in the universe is screaming
>away from all other matter, which one has the frame of reference with
>the fastest possible passage of time?)
To demonstrate that events that are simultaneous from one view point are
not necessarily simultaneous from another, lets use a classic thought
experiment. Suppose two guys are sitting at opposite ends of train car,
and that there is a light bulb midway between them. The light bulb emits
two photons at the same time/place. Lets say the train is 60m long. This
means that the light takes 100nS to cross the distance to both people. The
person(A) at one end can see the effect of the light on the other person(B)
after a photon from B travels to A, taking another 200nS after he first saw
the original light, which is perfectly consist ant with A's knowledge of
physics.
Now lets say that, unknown to A and B, we see the car that they are
travelling on is actually speeding along at .5 c in B's direction. This
means that the length of the car is reduced by a factor of 1.155 to
51.95m The light now takes 173.1ns to reach B, while only taking 57.7ns to
reach A, meaning the light reaches B 115.4ns after it reaches A. From
there it takes the light 115.4 ns for A to see the light reach B, making
the total delay from A's receiving the photon to B's seeing a photon hit B
230.8 ns. However, due to time dilation, A's perception of time has slowed
down by a factor of 1.155. That means that 200ns of A's subjective time
have passed between A seeing the photon, and A seeing the effects of B's
photon, all of which seems perfectly consistent with A's knowledge of physics.
Since we don't know whether our reference frame or A's reference frame is
the One True Reference Frame, and since we strongly begin to suspect that
such a thing doesn't exist, we can't tell whether the light reached A and B
simultaneously, or whether 115.4 nano seconds passed. Thus, whether events
are simultaneous depends on the observer's frame of reference.
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