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The Question
(Submitted March 13, 1997)
The inflation theory seems to require such extreme expansion that it
exceed the speed of light. How can this be?
The Answer
Your question is a good one, and applies in situations even more
general than just the inflationary epoch. The key thing to remember
is that causality requires that no signal propagate faster than the
speed of light. In an expanding Universe (with inflation or
even within the standard cosmology)
there are places sufficiently far away, whose relative speed to us is
greater than the speed of light. There is no problem with this; they are
simply outside our horizon, and we can't communicate with them because
of the requirements of causality. In the standard cosmology because the
expansion decelerates, they eventually move within our horizon. During
inflation the expansion rate is constant and whatever gets outside the
horizon remains so (actually it gets even farther away from the horizon).
This should not cause any problems with causality violation though.
I hope this helps!
Tim Kallman and Demos Kazanas
for the Ask a High-Energy Astronomer team
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