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The Question
(Submitted January 19, 1998)
I have heard that the universe is accelerating as it expands. Is that true?
The Answer
I think it is easy to get confused on this point. The universe
is expanding, but the rate of expansion appears to vary with position.
That is, more distant objects are receding from us faster than
nearby ones. The explanation for this is not that the more distant
objects have accelerated relative to nearby ones. In fact it is
just the opposite; when we view distant objects we look back in time,
since light travels at a finite speed. That is, the expansion of the universe
was faster at earlier times than it is right now. If we could see
a true instantaneous snapshot of the universe at any given time
(which is of course impossible) we would see a nearly uniform expansion.
Our web site has lots of information about the big bang that you can look for.
http://imagine.gsfc.nasa.gov/docs/science/mysteries_l1/origin_destiny.html
http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/970922g.html
and references therein. I hope this helps,
Tim Kallman
for Ask a High-Energy Astronomer
See, however,
http://imagine.gsfc.nasa.gov/docs/ask_astro/answes/990210c.html
for a major update on this subject.
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