The big bang and the Enlightenment: we are lucky to be alive at the time we learned how the universe began

Since it's literally impossible to show a picture of "what the big bang looked like", this rather pretty image of particle tracks in a bubble chamber at Cern will do to illustrate this post
Since it's literally impossible to show "what the big bang looked like", this pretty image of particle tracks in a bubble chamber at Cern will do to illustrate the post

After last night’s Paralympic ceremony, everyone seems to be talking about the big bang and the Enlightenment. M’colleague Peter Mullen thinks the former is an “unproven scientistic conjecture”. Is he right? Let’s have a look at the strands of evidence that support the hypothesis that the universe arose from a singularity.

In the 19th century, a physicist named Christian Doppler realised that if a source of waves – including sound waves or light waves – was moving relative to the observer, then the apparent frequency of those waves would be different to if it was standing still. A boat sailing away from the shore will go over more waves, and thus bob up and down more frequently, than one sailing towards it. The same happens when an ambulance drives towards you: the waves are compressed, so it sounds higher, but then as it goes past you they are stretched out, so it sounds deeper. Stars and galaxies were noticed to have this effect in 1848: the light from some galaxies, analysed using spectroscopy, was seen to be redder – longer wavelength, lower frequency – than that of others of a similar type. It was realised that these galaxies were moving away from Earth.

In the early 20th century, a further discovery was made: the further away a galaxy was, the faster it was moving away from Earth. The universe as a whole was expanding. A Belgian Catholic priest and astronomer, Georges Lemaître, pointed out in 1927 that if we assume that’s always been the case, there must have been a point at which the universe started expanding: that is, a moment when it was a single point, and it “exploded” outwards. That, in short, the universe had a beginning. His proposal was formalised by Edwin Hubble, the great American astronomer, in 1929.

At around the same time, it was realised that Albert Einstein’s general theory of relativity couldn’t work if the universe wasn’t either expanding or contracting. This shocked Einstein so much that he introduced (without evidence) a “cosmological constant” to allow an eternal universe, but others, including Lemaître, realised that it gave support to the idea of a universe that had a beginning in time.

Later on, the “big bang” hypothesis – as it came to be known after one of its opponents, Fred Hoyle, described it as such in a radio interview in 1949, to compare it to his own favoured “steady state” hypothesis – garnered more supporting evidence. In the 1960s, two astronomers heard a “background hum” on their radio telescope in New Jersey. They tried to clear pigeon droppings off their telescope, which they blamed for the noise, but it still remained. It was discovered years later that this was the echo of the big bang: a low-level microwave radiation, throughout the universe, which big bang theorists had been predicting. It was the most compelling evidence for the theory yet found. And in 2003, Nasa’s Wilkinson Microwave Anisotropy Probe mapped the microwave radiation, showing where it was hotter and cooler; by determining the rate the universe had cooled, it was able to place the age of the universe (with support from other evidence) at 13.7 billion years old, give or take a hundred million years. We now know when the universe was born.

This incredible discovery is the legacy of the Enlightenment, which the Paralympic ceremony was celebrating. The figureheads of that movement believed that we should not respect mysteries, but try to find explanations for everything, and ground those explanations in reason and in observations of the natural world, rather than the whims of gods, or spirits, or magic. People who have lived through the last 50 years or so are privileged to be in existence at a time when the origins of the universe were revealed in compelling detail: we now know, through physics, how and when everything that is came to be; we know, through evolutionary biology, roughly how life, and we ourselves, grew out of that physical universe. The Enlightenment heroes who started this process would, I expect, have given anything to be alive now, to see what we have learned.

There’s an awful lot more to find out. Galaxies are spinning too fast to hold together unless they weigh a lot more than they seem to: there must be something massive holding them together, but no one knows what it is. That’s the so-called “dark matter”. The universe is flying apart faster than it ought to be, from what we know, so there must be something pushing it: that’s the so-called “dark energy”. Between them, it means that 96 per cent of the universe is unaccounted for. We still don’t know how gravity works.

But whatever the answers to these questions is, we can be reasonably sure that what we know now is, as Isaac Asimov said, a lot less wrong than anything we previously believed. The weight of evidence is huge. Far from being an “unproven conjecture”, the big bang is an irresistible conclusion drawn from dozens of strands of independent, complementary evidence, and is the product of the Enlightenment approach: look at the universe, and learn what it tells you.


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