Solvay and the Catastrophe

Solvay Conference 1911

The 1911 Solvay conference attendees.
With an addition by our own Action Dan

1911 was an interesting time to be a physicist. At that time, as best as anyone could figure out, the foundations of our understanding of physics seemed to be cracking. Small, annoying little differences between what classical physics predicted and what actually happened began to get bigger and bigger, and could never be explained away. These little threads were unravelling the whole tapestry of physics that had been built up since Newton.

So maybe interesting isn’t a strong enough word.

And if you were a millionaire industrialist philanthropist (back when we still had those), the kind of thing you could do was to invite some of the world’s most eminent physicists to hang out for a week in a hotel on your dime, to try and sort out these problems.

Which is exactly what Ernest Solvay did.

So an all-star team of physicists sat down for a week in the Hotel Metropole in Brussels to talk about a thorny problem that physics was having – just how does energy work, anyway?

The problem is that no-one could decide. Sometimes it appeared that energy, such as heat or light, acted like it could have any size it wanted – as if it were along a spectrum, or a wave. And then other times that explanation didn’t fit the facts. One of the big problems of the day was about ‘black body radiation’ – about how a perfectly black surface, which perfectly absorbs all of the energy directed at it, acts under certain circumstances. It kept coming out that, at certain temperatures and frequencies of radiation, you could get infinite power. Which, you may have noticed, never happens. This problem was called, rather pleasingly, the Ultraviolet Catastrophe, which is a great name for a band.

A solution to the Ultraviolet Catastrophe could be found only if you assumed that energy was limited to specific levels, or quanta. You couldn’t have ‘half a quanta’; they were discrete little packets, or particles, of energy. Which meant that sometimes radiation (of which light is an example) worked like a wave, and sometimes it worked like a particle.

Which is crazy, when you think about it. Which is it? Is it a wave, or is it a particle?

Now we know that it’s both – wave-particle duality is one of the cornerstones of modern physics. The trick is to stop thinking like a person, and to trust the maths, because people are limited to conceptualising concepts based on our experiences of the things around us. But light isn’t like anything around us – light is only like light! It is neither a wave, nor a particle: it is light. And the mathematical models we have to describe its behaviour are the closest we can come to building a picture of what it ‘is’.

In that first Solvay conference, Einstein was one of the few scientists there who really believed in wave-particle duality. It wouldn’t be for another 10 or 15 years before the rest of the scientific community began to be convinced of this new model of reality, in which things can be particles and waves at the same time. So while, as far as we know, there weren’t actually any giant ants on the loose at the Solvay conference, the ideas discussed there were at least as strange as that…

If you’re curious about exactly what went on at that first Solvay Conference, this paper on Arxiv[pdf] has a good, if slightly technical, overview that is at least worth a skim.

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