Meet the scientist

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The Physics of a Table

Tuesday 25th Feb 2014, 01.00pm

I often tell people that I became a physicist because I wanted to understand the stars. What are they? Why do they shine? This is a very romantic notion, but is really only partly true. Yes, I wanted to understand the stars. But I also wanted to understand my table. What is a table made of on a fundamental level? Why is it solid? Why doesn’t a table shine?

Well, wood is made of different kinds of atoms, bound together in an incredibly complicated network. Atoms are electrons in a kind of orbit around a tiny nucleus in the centre. The nucleus is a cluster of protons and neutrons. Protons and neutrons are made of particles called quarks – made in a way that we don’t fully understand yet. Electrons and quarks are fundamental particles. They are called fundamental because, as far as we know, they cannot be subdivided into smaller particles. Stars are also made of electrons and quarks. So why are stars and tables so different?

As a child, I had the intuitive idea that things were solid because they had mass. But a bit of thought showed this couldn’t be right! What do we mean by solid? We mean that, for example, I can’t put my hand through a table. If I try to put my hand through a table, the table repels my hand. We don’t normally put it quite like that, but that’s what’s going on. When my hand reaches what we call the surface of the table it experiences a very strong, repulsive force. This repulsive force stops it from going any further. But gravity is an attractive force – it pulls objects towards the ground; the moon towards the Earth; and the Earth towards the sun. So how could mass, which results in the force of gravity, cause the table to repel my hand?

In fact, objects are solid because of quantum mechanics. More specifically, quantum mechanics tells us that electrons can't get too near eachother. According to quantum mechanics, electrons, along with all other particles, should be described as ghostly probability clouds. But the repulsive force between them is very obvious and very real.

The stars may be romantic, but I think the everyday world is just as fascinating. How do fundamental particles, themselves excitations of mysterious quantum fields permeating all of space, come together to build our lives?