From JEFF BISHOP
Frequent discussions of infant galaxies, and the news recently of ‘ripples
in the cold glow from the Big Bang’ leave one fundamental question unanswered.
Can anyone give a simple explanation to a non-cosmologist: how is it
that we are only now seeing light waves from an event which happened so
soon after the Big Bang? Why have these signals not passed us long ago?
After all, the Big Bang did not happen in a galaxy far, far away. When
it happened we were part of it. We were there. Did the Universe expand initially
at a rate much faster than the speed of light?
Jeff Bishop Connells Point NSW, Australia
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John Gribbin replies: There are two aspect to this puzzle. First, the
Universe did indeed expand ‘faster than light’ early in its lifetime. This
is possible because what makes the distance between two galaxies (say) increase
is not that they are moving through space, but that empty space is expanding
and carrying them along for the ride.
Secondly, when we look at the light from ‘distant’ galaxies, the term
really applies to time, not space. We are seeing light which left those
galaxies long ago, and has been travelling across expanding space and getting
stretched in the process (the redshift effect). It is meaningless to quote
a spatial distance to such objects, which may no longer exist by the time
we see them, but from one perspective – since the light from the ripples
seen by COBE has been on its journey for 15 billion years – it therefore
comes from 15 billion light years away.
