For centuries, two small words have prompted profound scientific inquiry: 'What if?' It was a question Einstein asked not only of light beams, but also of his own socks.
Albert Einstein was very proud of the fact that he never wore socks. We know this, because he wrote about it to his cousin (and eventual second wife) Elsa: 'Even on the most solemn occasions, I got away without wearing socks and hid the lack of civilisation in high boots.'
But Einstein wasn't just doing this out of rebellion. 'When I was young,' he wrote in another letter, 'I found out that the big toe always ends up making a hole in a sock. So I stopped wearing socks.'
The clue to Einstein's thinking here lies in that little word 'so', but there's a logical leap. When we look at photographs of Einstein in sandals, we can see that his big toe projects well beyond the second. But why should this mean that he had to give up the comfort of socks? Why not just buy new ones when the old ones wore out?
What surely swung Einstein's decision was the underlying thought: what if? 'What if I gave up wearing socks?' is not a question that would occur to many of us, but to Einstein it was a natural question to ask, and one that led to a basically barefoot existence.
When he was 15 or 16 he asked another 'what if?' question in a letter to his uncle, Caesar Koch—what would a light beam look like if you could run alongside it at the same speed? He didn't realise it at the time, but he was asking a very fundamental question that was already bugging physicists.
The problem was this: if you could keep pace with a beam of light, then it would appear to your eyes to be stationary—just as a wave travelling across water would appear to have a constant, immobile shape if you could run alongside it. Yet physicists knew that Maxwell's equations, which describe the propagation of light waves, forbid the occurrence of such a stationary state.
Ten years after he first raised the question, Einstein came up with an answer in the form of another 'what if' question: what if you couldn't ever run alongside a light wave? What if — no matter how fast you ran — the light wave always caught up with you and passed you at the same speed as if you weren't running at all? Then it would simply be zipping past, no matter how fast you were travelling, and would never appear stationary.
In exploring this possibility, Einstein came up with his Special Theory of Relativity. All because he wasn't wearing socks! ☺
