Hooptedoodle #79 - A Trick of the Light

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.