My wife occasionally calls herself ‘Penny’, as in Penny off The Big Bang Theory. Especially when I get together with my mathematician friends and we talk geek.
I’m not sure which of us is meant to be Sheldon. Anyway, the ‘big bang’ theory itself was first proposed in 1927 by a Catholic priest, Monseigneur Georges Henri Joseph Édouard Lemaître (1894-1966). He was trying to explain Vesto Slipher’s discovery that distant galaxies were retreating. And he was ignored. Then, in 1929, Edwin Hubble (1889-1953) suggested the same thing. Like most academic fields, physics is all to do with in-crowds; when Hubble spoke, other physicists pricked up their ears.
Their logic went like this. Distant galaxies appear redder than they should. This is because the wavelengths of light and other electromagnetic emissions from them are being stretched from our perspective, meaning they must be moving away. This effect was first discovered by Ernst Doppler who realised this was why fast-moving vehicles go ‘neeeeoooww’. The sound waves are being stretched from the perspective of a stationary listener as the source moves away, so to them the pitch appears to drop. (You can buy a Sheldon costume so you can be the Doppler Effect, like he was in Series 1 Ep. 6…here.)
It works the same with electromagnetic emissions, and red has a longer wavelength than other visible light, so things moving away appear redder to us. Hence the term ‘red shift. It’s used to describe the phenomenon, even if the wavelength isn’t visible light. (No costumes for this one).
Hubble discovered not only that distant galaxies retreat from us, but that the further away they are, the faster they retreat. Hubble’s Law followed: v = H0D, where v is velocity of recession, Ho is Hubble’s constant, and D is the proper distance. The value for Hubble’s constant has never been agreed, but recent work suggests it might be 71 +/- 7 km/sec per megaparsec. Probably. A bit.
It also turned out that distant galaxies are moving away from us whichever way we look, showing that space-time itself is expanding. Imagine a rubber balloon with equidistant dots on it. Inflate the balloon. The dots move apart equally – and the distant ones are moving away faster. That holds true for space-time.
The conclusion was that the universe had been smaller – a mathematical point, in fact, from which everything exploded into the reality we know and love today. Pretty much like the opening credits on The Big Bang Theory, in fact.
Of course, it wasn’t expansion into a void. It was an expansion of space-time itself. The very fabric of physical reality.
It was a kind of cool idea, but nobody had any way of proving it. Physicists argued over whether there had been a ‘big bang’, or whether the universe operated by a modified ‘steady state’ of constant but expanding existence. Then, in 1948, Ralph Alpher and Robert Herman predicted that we should be able to see cosmic background radiation from the ‘big bang’ – and it was found in 1965. The radiation has a black body (idealised) temperature of 2.72 degrees Kelvin, give or take a tad (I define +/- 0.00057 degrees as a ‘tad’).
And you know the coolest part? Albert Einstein figured it all out in 1917, before any of the evidence was available. His General Theory of Relativity made clear the universe couldn’t be static – it had to be expanding or contracting. Einstein thought that had to be wrong, so he added a ‘cosmic constant’ to eliminate the expansion. But expansion was true, and he later admitted the ‘constant’ fudge was a mistake. His original equations held good.
Einstein had, in short, figured out how the universe worked – so completely that his theory explained the bits that hadn’t been discovered yet.
How cool is that?
Copyright © Matthew Wright 2013
Coming up soon: ‘Write it now’ and ‘Sixty Second Writing tips’, more humour, more science…and, more.