Long ago, I took 4/9ths of an undergraduate physics degree, along with 4/9ths computer science and 1/9th mathematics. Having had little or no contact with physics in the intervening years, I’ve started to do some light reading about relativity in the last couple of years. This week, I came across a tip on Quora * to a fellow traveller in space-time: “stop thinking of the speed of light as a number”. Erm… WHAT?! As every school child knows, the maximum speed of light (or any other form of electromagnetic radiation) in a vacuum is about 600,000 Km/s. That sounds like a number to me. The problem with speed in Einstein’s relativistic model of reality though, is that distance and time get very weird. That makes them hard to think about, so the advice was to ignore what we think we know and look at things in a new way.
[* – I’ll add an acknowledgement to the author of the comment on Quora, if I ever find it again. It took me a while to understand what I’d read. ]
I’m not sure I was entirely paying attention when I studied physics last time. I don’t remember anyone explaining the precise nature of the the scientific method, or indeed what physics actually is; that’s metaphysics. This time around I see science as the process of understanding how nature works, using evidence rather than guessing then arguing the case for your beliefs. That is philosophy, or a religion. Physics, in particular, is about observing reality and working out what the rules are. It is NOT about saying why things happen. As science was becoming formalised, it was known as ‘natural philosophy’ i.e. philosophy that refers to evidence from nature.
Einstein’s Theories of Relativity say that matter and energy are equivalent. His equation of mass-energy equivalence records the relationship between the alternative mass and energy forms of matter. It is a very well known equation, even with people who have no idea what it refers to.
The form of the equation we are most familiar with is
E = mc²
E is the concentrated energy contained in a mass, m. E is a much bigger number than m because we know that c is a big number AND it’s squared.
This equation can be re-arranged to a form I don’t remember seeing or taking note of before:
c = √(E/m)
This new way (at least to me) of looking at this century old theory says that c is related to the ratio between the Energy and mass of an object. This ratio stays the same, even as space-time expands or contracts, according to the General Theory of Relativity. The recent confirmation by the LIGO project of gravitation waves that also travel at c, were also predicted, so this gives extra weight to the theory
I’ve realised that physics often relates things to each other, without saying which is the ‘fundamental thing’. Does gravity bend space-time or is the curvature of space-time what causes gravity? The equations work either way.
John Archibald Wheeler said it a different way: “Space-time tells matter how to move; matter tells space-time how to curve” and matter can be converted to energy, energy to matter.