Why everything is solar powered (…or is it?)

Here’s an interesting game to play when you have an idle moment. It’s called ‘What Makes It Go?’ and the challenge is to find a moving object – any object, from a car to a kite to a cat – that didn’t ultimately get its energy from the sun.

Nobel physicist Richard Feynman used to play it with his dad when he was young. He recounts an example in his book Surely You’re Joking, Mr Feynman which begins with his father telling him that his wind-up toy car only moves because the sun is shining, with which Feynman disagrees:

‘No, the toy goes because the spring is wound up,’ I would say.

‘How did the spring get wound up?’ he would ask.

‘I wound it up.’

‘And how did you get moving?’

‘From eating.’

‘And food grows only because the sun is shining. So it’s because the sun is shining that all things are moving.’

Get the gist of the game? Let’s try another one: what makes a car go? It’s the engine that makes it go. But what makes the engine go? It runs on petrol. Where did the petrol come from? Fossilised plants… and the plants only grew because the sun was shining. Once again, we end up at the sun.

Apart from giving solar scientists a reason to annoy researchers in other energy fields (‘That wind power study you’re doing is really just a subset of solar science, you know,’*), this game is interesting because it reminds us that energy can never be created or destroyed, it just changes from one form into another. In the example above, we started with electromagnetic energy (sunlight) which was converted into chemical energy (stored in plants and petrol), then to thermal energy (in the engine) and finally kinetic or ‘motion’ energy (of the car). And for us on planet Earth, it’s sobering to think that we’re almost entirely reliant on a single energy source: our sun.

Just some more examples of things that are solar powered.

Notice that I said we are almost entirely reliant on the sun. I can think of at least three sources of energy that can’t be traced back to sunlight. Can you come up with any? And if you can, what are they traceable back to? I’ll be putting my answers in the comments section of this post in a week or so later today to give you a chance to think it over.


* This is an old but enduring game that scientists in different fields occasionally like to play. When I was a university undergraduate I remember chemists teasing biologists that biology was just a subset of chemistry; physicists taunting chemists that chemistry was nothing more than a subset of physics; and mathematicians gloating that physics was just a subset of maths. A recent episode of the TV show ‘The Big Bang Theory’ also had Sheldon (a physicist) and Amy (a neurobiologist) arguing over whether physics was ‘best’ because it explained neurobiology (because the brain obeys the laws of physics when it functions) or whether neurobiology was better because it subsumed physics (because it was Sheldon’s brain that let him understand how the universe worked).


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