MadSci Network: Physics
Query:

Re: Light Speed Theory (time travel).

Area: Physics
Posted By: Dave Dixon, Assistant Research Physicist,University of California
Date: Mon Nov 17 13:05:53 1997
Area of science: Physics
ID: 877614859.Ph
Message:
This is a common misunderstanding.  Special Relativity (SR) tells us
how the measured "distance", both in space and time, between two events
changes between inertial reference frames.  An inertial reference frame
is defined as one where the observer is moving with a constant velocity,
not speeding up or slowing down.  Observers moving at different velocites
relative to one another will measure *different* space and time intervals
between events.

Let's examine the case relevant to your question.  Here, we'll take the
two events to be ticks on the second hand of a watch.  If you are
moving relative to me with uniform speed, by my watch it will take
longer than 1 second for the two ticks to happen on your watch.
However, this phenomenon is *relative*, and you will see the same thing,
i.e., two ticks on my watch take longer than 1 second measured on your
watch, by exactly the same amount.  This may sound paradoxical, but given
the assumptions of SR, it's the only way it can happen and make sense
(for more info, see link below).  Anyway, the point is that if you are
moving relative to me, I see that all physical processes occur slower
in your reference frame, and you see the same for me.

Now, the amount by which one of us sees things slowed down in the
other's frame has to do with the relative velocity.  The closer our
relative velocity is to the speed of light, the slower we see things
happening for each other.  If you take the relative velocity all the
way to the speed of light, what you calculate is that it would take
an INFINITE amount of time for anything to happen in the other guy's
reference frame, relative to you.  However, this limit is really
only mathematical, since we can't ever actually travel at the speed
of light relative to one another, etc.

So, because an object is moving, it's "passage through time" is not
increased.  Rather, an observer moving relative to that object views
physical processes related to the object as being slowed down.  The
object itself moves with some constant velocity, and for a given
observer, takes the usual amount of time (distance/velocity) to get from
point A to point B.  This is true even for photons, moving at the
speed of light.

For more info, see the sci.physics.relativity FAQ, located at

http://math.ucr.edu/home/baez/physics/relativity.html.

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