Universe Today
(This is Part 2 of a series exploring the mythic side of the Big Bang. Check out Part 1!)
In the early 20th century, after years of effort, Albert Einstein developed his general theory of relativity. This was a massive improvement in our understanding of gravity, giving us a sophisticated view into the inner workings of that fundamental force.
And as soon as he had the basics of relativity figured out, Einstein applied it to the whole entire universe. After all, he correctly assumed that at very large scales, gravity is the only force that matters. He didn’t know about the strong and weak nuclear forces (and to be fair, nobody else did either), but it didn’t matter, because those are both short-range force. Once you get outside an atom or so, you don’t have to worry about them. And while the electromagnetic force has infinite range, the universe is on average electrically neutral, so it’s simply not going to do much of anything.
But gravity is key. Everything with mass and energy both creates gravity and responds to gravity, and last time I checked, the universe is full of both mass and energy – in fact, the universe is by definition all the things, including all the mass and all the energy.
So it’s a straightforward enough exercise to throw everything into the big blender of relativity, let it rip, and see how it should evolve with time. To his surprise and horror, Einstein found that the universe full of stuff should naturally be dynamic, either contracting or expanding with time. But that went against current thinking, and in a rare move Einstein conceded defeat, altering his equations with a cosmological constant that stabilized the universe – something we would later admit to be his greatest blunder.
But other scientists took Einstein’s relativity at more face value than Einstein himself did. One of them was Georges Lemaitre, a Belgian scientist and catholic priest. He let the equations of relativity fly their freak flag, and believed when they said that the universe was dynamic, predicting that the universe should have been smaller in the past. When Einstein first encountered Lemaitre and his work, he was shocked and perhaps horrified, saying “your calculations are correct, but your physics is abominable” – and especially coming from Einstein himself, I’m sure that cut deep.
And then two years later astronomer Edwin Hubble revealed that galaxies are, on average, moving away from us, a result that was most easily explained by the hypothesis that the universe is expanding.
Theorists everywhere scrambled to come up with a consistent a story – a creation myth if you will – to explain this new result. Lemaitre politely reminded everyone that he had ALREADY DONE THIS, and went on to create an entire cosmological scenario in a 1931 paper. He envisioned the universe as having expanded from a central source, something he called the primaeval atom, which expanded and exploded in a variety of elements, which later collected together to form the stars and galaxies. From the paper, here’s the story Lemaitre had to tell:
““This atom is conceived as having existed for an instant only, in fact, it was unstable and, as soon as it came into being, it was broken into pieces which were again broken, in their turn; among these pieces electrons, protons, alpha particles, etc., rushed out. An increase in volume resulted, the disintegration of the atom was thus accompanied by a rapid increase in the radius of space which the fragments of the primeval atom filled, always uniformly.”
Naturally, other scientists viewed this story of the primaeval atom as a bit too…catholic for their tastes, saying that he was just trying to insert the story of genesis into an otherwise proper scientific investigation of the universe. Lemaitre himself argued that he wasn’t trying to do this – he was just following the evidence and trying to put together a coherent hypothesis, and any resemblance to any mythological account was purely coincidental.
Today we recognize Lemaitre’s primaeval atom as the genesis – ha – of the big bang theory, and while we believe that Lemaitre got many of the details wrong (he was more focused on the newly discovered process of radioactive decay) the broad strokes picture is accurate: a long time ago, the universe was small, so small that it was a point-like singularity, and it got bigger from there.
To be continued...
