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[Non-member submission]
Brian Atkins <brian@posthuman.com> wrote:
> I am confused here too. I don't see how this would be time travel.
> Isn't there a distinction between information flow (images of events...
> say pictures we see in a telescope of a supernova blowing up) and the
> actual event generating the information?
You can't transmit only information. Information is a mathematical
abstraction. To transmit it, you need physical effects. You need
a signal, and that signal has energy. If I can send you a hello
note, I can also zap your planet with a gamma pulse.
> So what if I can transmit a digital pic of the supernova blowing
> up to someone far away before they can see it in their telescope-
> that isn't really time travel as far as I can see.
You are thinking of particular actions in isolation. Physics seems
to be governed by a self-consistent body of laws. It can be shown
that if those laws allow a certain action, they must also allow
certain other actions. These consequences aren't necessarily
obvious at first. Going from Maxwell's equations to a mobile phone
is quite a step.
It can be shown that FTL transfer in one frame of reference will
show up as time travel into the past in some other frame of reference,
violating causality there. You may not care whether the actions
of some photon out in interstellar space violate causality, but if
this is possible, the grandfather paradox is tapping you on the
shoulder. The difference is merely some engineering ingenuity.
-- Christian "naddy" Weisgerber naddy@mips.inka.de
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