Month: Jun 2020

I ride through the city on my bike. I walk in the fields we’re lucky enough to have behind our house and I despair at the quantity of litter I come across. It’s mostly empty sweet-packets, beer cans, empty, plastic water bottles and paper cups. My wife and I collect the stuff and dispose of it. We sometimes ask ourselves if we’re risking close contact with Covid 19 particles, and we wonder who so carelessly dumps it, I ask myself, privately ‘cos it’s too sensitive to talk openly about it, could it possibly be the same people that want to instantly resolve the colour prejudice and the guilty history questions?

‘A photon is a type of elementary particle in the visible part of the electro-magnetic spectrum’. I got that from Wikepedia, to which, by the way, I donate £5 every year, so I consider myself entiltled to quote from it now and again and, in any case, I think it’s allowed, whether you give ‘them’ money or not.

Anyway I was thinking about photons when I switched on the landing light. I’d just been to the bathroom you see, and as I came out onto the landing I turned the light off. I shuffled forward in the dark – you know how black it is when you’ve been in the light – and pressed the switch for the landing light.

Instantly the landing and the top of the stairs were flooded in photons, although there were dark, dark shadows here and there. Well, not just randomly here and there, but where something, a banister spindle for instance, obstructed the passage of the photons, there was a shadow.

You probably know that one of the characteristics of a photon is it’s tenacity in sticking to straight line travel. Of course that’s not just one photon, that’s all of them  – and there are lots.

But they do deviate sometimes. It’s barely noticeable but gravity does bend their path a bit if they pass close by something big, like Jupiter or Saturn, or Arcturus.

They also travel at the speed of light – which is not surprising because they are light.

And, of course, there’s reflection. It’s obvious that photons can bounce off mirrors because you can shine a torch beam onto a mirror and redirect the beam in almost any direction. I’ve often wondered if there might be some commercial benefit to be gained from this reality, like when it’s a new moon f’rinstance: with a big enough mirror, strategically located, you could light up the ‘dark side of the moon’ as-it-were. Of course that wouldn’t be the real dark side of the moon because no matter where you are on earth you won’t get to see the dark side of the moon, ever.

I realise that I haven’t explained what a photon is. I suppose I assumed that everyone knows. But I’ve been surprised recently that, for example, there are people who don’t know who Ruby Murray is, even though her name is in the Cockney Rhyming Slang Dictionary! Well, if you don’t know, look it up, it’s easy enough these days.

But I was talking about photons, and how, contrary to one of their main, observed characteristics, they sometimes – or maybe more than just ‘sometimes’ – do a zig-zag when they hit glass at an angle, or water. Watch someone wade slowly into the shallow end of a swimming pool. If the water’s calm you can still see their lower legs but they look much shorter, that’s because of refraction. You have to wonder how a photon knows that it should change its direction of travel when it passes into water, or glass. And by how much? Imagine being the first photon to arrive at the surface of a window pane. How do you know that you have to change direction before passing into the glass? And by how much? And you have to make that decision at the speed of light!  And, indeed, how do we know they change course on their way to an object? What if they only change course when they’re on their way bacxk to the eye of the observer, after they’ve bounced off the object being observed?

It’s hard to imagine but the sun is blasting out millions and millions of photons every millisecond of your (and my) existence. Many of them are totally wasted, they just shoot outwards from the surface of the sun in every direction and, if you think about the earth as being a target of this wild, random, and virtually unending, explosive emission of photons, it seems such a waste to think that about 99.999 percent of them just get spattered all over the galaxy providing nothing for nobody. The only other beneficiaries are any loose astronauts whizzing around in orbit, and the moon, and the planets.

And, there are places where photons are precious,  places that could do with a few million of these wasted particles, like dungeons and deep caves. But, as already noted, excepting the exceptions mentioned above, photons only travel in straight lines, so after you’ve gone around the first bend in a cave there won’t be many about.

But, (another ‘but’), nowadays people create their own photons, with torches and car headlights for examples, and the electric light in your kitchen or on the landing. How photons are actually born and where they go to die, despite a massive, ongoing research effort, remains a mystery.

And, as Wikipedia tells us, the invariant mass of a photon is zero, which means, effectively, that photons don’t exist.