You see, the first problem is that my son (who is 10), is
very enthusiastic about astronomy, and the Universe, and all that, and has been
since he could first assemble a few words into a question. He is the one who
asked me once, after tea, could I explain a few more details of the Big Bang.
Is it true that
nothing existed at all before the Big Bang?
Well, you can’t really talk about “before the Big Bang”,
since it is widely held that time itself began at that instant. I think you can
say, though, that we know of nothing which existed outside the time between the
BB and now.
In that case, says
the enthusiast, what was it that
exploded?
Confound me if he hasn’t put his finger on the one bit of
this that I can’t get the hang of.
Remember, I reply, that your grandmother is coming tomorrow,
and you have to tidy your room before bedtime.
I try not to worry about this stuff, but vertigo lies in
wait if I start to reason things out. On a fine, clear night I can stand in our
garden and – since we live far away at the Front of Beyond, where there is very
little light pollution – I can enjoy a magnificent big, northern sky full of
stars.
Wonderful.
So what is it we can see? Each of those tiny points of light
is a glimpse of a glowing mass which is (or was) so far distant that the light
has taken a long time to get here. Everyone knows this. Even I know this. So
the light which I can see – without effort and without getting tense about it –
has been heading this way for thousands, millions of years. I don’t know how
far away these things can be, but that is pretty impressive for a start. Maybe
billions of years? – I can’t say the word “billions” out loud to myself without
thinking of Prof Brian Cox, whose BBC books are all lined up on my son’s shelf.
So this means that, whatever else, these distant balls are
not now in the positions that the points of light would indicate. They
themselves will have moved a long way relative to us in the time since the
instant of light I am looking at set out. It also means that all these little
dots are of very different ages in the snapshot view I have. They may all be
sitting peacefully together in the sky above my garden in configurations which
we find familiar (well, my son does), but this is a very complex picture
indeed. It is more than likely that some of these stars may have died and
switched off long before some of the others started to shine. Before they
existed. So nothing is as it seems – the stars are not really where they seem
to be, and this deception is somehow arranged in time as well as physical
space. The history of the universe is all present at once over my garden, and
it is, at best, very misleading.
Hmmm. The only way I can come to terms with any of this is
to ignore the actual bits of stuff which are/were shining out there, and just
accept that space is also full of light flying about the place. The light is
real, and a bit of it is here now, and that’s what I can see up there. It comes
from a complicated place, at all sorts of durations ago, but I’m best to shrug
at that and just look and enjoy it.
OK – that’s all fine then, but I don’t feel I’ve mastered
the subject. I certainly haven’t impressed the boy. We occasionally have
discussions in which I may say something like, “Imagine you have a very
powerful telescope, and you are standing here looking up at a church clock
which is on Saturn...” and then we collapse in laughter because the analogy is
just daft.
I am reminded of some old pictures I saw at an exhibition,
years ago in Edinburgh
– so long ago that the exhibition was in the Waverley Market, before it became
a shopping mall, and that is a very long time ago. These pictures were very
early pioneering photographs – street scenes, mostly – probably dating from the
1840s or so. One picture fascinated me – it was of Waverley Bridge,
just outside where the exhibition was taking place, and the street was clearly
recognisable, with the view looking towards the bottom of Cockburn Street (I wonder if the Malt
Shovel was open in the 1840s?). The caption explained that the strange, faint
smudges on the picture were passing traffic. The photographic emulsions of the
day were so feeble that a daylight picture required a very long exposure –
maybe as much as an hour, I understand. Passing pedestrians and horse-drawn trams
moving through the picture were not recorded properly, but would cause a
slight, very blurry streak as they moved through the shot.
I found this absolutely compelling – if the exposure were
long enough, I reasoned, some of these trams were not in the street at the same
time, yet here they were (albeit unrecognisable) together in the same picture.
It was not unlikely that a tram could even turn around at the terminus and come back
through the picture again, and so be in the picture as two distinct tram images.
On the way home, and for a few days afterwards, this played on my mind. Suppose
you had a really long exposure, I
thought. Suppose it was a hundred years, and suppose the same rules applied –
everything that ever passed along Waverley
Bridge in that time would
leave a mark on the negative. The streaks would include people who never met,
even people who were never alive at the same time. And – of course – I came to
no conclusions, and I did not learn anything much, but I enjoyed the game. It’s
like the stars – an illusion which has extra interest because it exists in four
dimensions – space and time.
If you are still with me and still awake, there is a new
development.
A few days ago, Mme La Contesse arrived home after
delivering the aforementioned son to his school, and was very impressed by a
rainbow she had seen. As she drove up the little hill to the church in our
neighbouring village, she had bright sunshine behind her and rain in front of
her, and a perfect rainbow appeared, framing the church.
How lovely, I hear you sigh.
Different place, different rainbow, same general idea
Over coffee, we had a short but interesting discussion about
rainbows, which mostly proved that, in spite of some formal, classical Optics I
did as part of my university Physics course, I know no more than the Contesse,
who was spared these scientific excesses. We agreed that a rainbow is an
illusion – just a trick of the light – and people will disagree about where
exactly it is positioned. Each of us sees it differently – in fact the visual
experience we call colours may vary between individuals, though it would seem
unnecessarily complicated if that were markedly so. The whole idea of a colour is meaningless without an eyeball to send a signal to a brain. Our main point of agreement was that at
any given moment there may be a very great number of places where a human eye
could see a rainbow, given the right combination of light, reflecting/refracting
water drops and angles, but the rainbow only exists if someone is there to see
it. Or does it?
Time to go and tidy my room.