Let's face it, we wouldn't have much of a life without light. In fact we wouldn't exist. Nor would anything else. It's not just a matter of not being able to see. Light also provides us with the energy to live. Apart from nuclear power, tidal power from the Moon and geothermal energy, light is responsible for all the energetic input to our lives. It's light from the Sun that keeps the Earth at temperatures that support life, and light from the Sun that powers the weather system.
More fundamentally at a quantum level, photons of light are the carriers of the electromagnetic force. No light, no electromagnetism. And that doesn't just mean no electricity and magnets. It's electromagnetism that enables us to interact with matter. It's electromagnetism that stops you falling through the floor - and that is the reason that the floor exist at all. Without photons - light - atoms wouldn't exist. So it's pretty important stuff.
I've far to little space to cover everything that's fascinating about light (you'd need a whole book... ahem) but a few pointers:
- Light can travel faster than light – in the strange world of quantum mechanical tunnelling, photons carrying the signal of Mozart’s 40th symphony have travelled at over four times the speed of light.
- We could soon be computing with light – electricity just isn’t flexible enough to keep up as computers get quicker and quicker. Soon the insides of a computer could be full of a spider-web network of light as data slams back and forth through thin air.
- You can’t run away from a laser – If you were to travel at 99 per cent of the speed of light away from someone shooting you with a laser, the light would still come towards you at the full 299,792,458 metres per second. Unlike anything else, however fast you move away from or towards light, it still comes at you at the same speed.
- The human eye can see a candle flame 10 miles away – your eye is remarkably sensitive, needing only a five or six of the individual photons that make up a light beam to trigger a response. The most distant thing most of us can see with the naked eye is the Andromeda galaxy, 2.5 million light years away.
- Ordinary colour vision works using the three primary colours. Night vision is quite different, registering only brightness. But there is a cutover period (called mesopic vision) when both types of vision occur together. It’s as if there was a whole new colour added to the spectrum that hadn’t existed before. Sight at this dusky light level has strange qualities – perhaps why so many ghosts and other phenomena are seen at dusk.
- Algae rules – more light energy from the sun is absorbed by photosynthesis by tiny algae in the sea than by all the plants on the land.
- Special materials have been used to slow down light to walking pace or even bring it to a temporary halt.
- Our eyes are incredibly flexible – light on a sunny day is 100 times brighter than a typical office, but our eyes balance out the difference. Full moonlight, which we can see quite well by, is around 300,000 times weaker than sunlight.
- A waterspout inspired fibre optics – the fibre optics that carry most of our telephone and computer signals on beams of light were inspired by noticing that light followed a spout of water, gushing out of a hole in a tank.
So if you felt any urge to snigger when you read it was International Year of Light, don't. If anything deserves its own year, light does. And that's why I'm so fond of Light Years.
* This is the third edition, and for the first time I've been allowed to include as an appendix, as I always planned, a set of original documents from the history of understanding of light, including Newton's letter on light and colour.