Did you know that we can look back in time to see the
universe as it was 30,000 years after The Big Bang? This is one of the fascinating
things I have been learning from Lawrence Krauss’s book A Universe from Nothing.
I’ll try to explain. Seventy-five percent of the universe is
now hydrogen (measured by weight). But for 30,000 years after The Big Bang this
was not the case. Then, the universe was so hot (3000° [Kelvin] above absolute
zero) that there were no hydrogen atoms – instead, there were separate protons
and electrons, or as Krauss puts it, ‘a
dense “plasma” of charged particles interacting with radiation’. This ‘plasma’ is
not transparent (unlike hydrogen) – it’s opaque and we cannot see past it.
Why does this matter? Because since we cannot see past it,
it stops us viewing the origin of the universe. When we look out into space we
are also looking back in time, since we are looking at light which may have
been emitted aeons ago because it has taken so long to reach us. So we can thus
see events which happened millions or even billions of years ago.
Could we look right back to The Big Bang? In principle yes,
says Krauss, but in practice no, because of this ‘plasma’, which we cannot see
past, which he calls ‘the last scattering surface’. This forms a kind of wall
between us and The Big Bang.
But radiation coming from that wall of ‘plasma’ or ‘last
scattering surface’ can be photographed. This is cosmic microwave background
radiation (CMBR). A striking image in the book shows a piece of sky over
Antarctica with the ‘hot spots’ and ‘cold spots’ of this radiation imaged, our
blue sky now turned into a mass of squiggly shapes.
Measurements of these spots can give us strong indications
of the overall shape of the universe – closed, flat or open. For further
explanation, I recommend Krauss’s book (published in 2012). But it strikes me how
useful shortcut words like ‘plasma’ and ‘scattering surface’ are in giving us
lay people a quick route to some kind of appreciation of these concepts. And
also what a shame it is we cannot view The Big Bang – what a show that would
be. I’m reminded of Douglas Adams’s
Restaurant at the End of the Universe, in which diners can time travel to
take their evening meal while watching the universe die outside the window. A
breakfast bar at the beginning of the universe would be wonderful.
pictures from:
No comments:
Post a Comment