Do the fundamental constants of nature vary in spacetime?

The fundamental constants of Nature, as the name suggests, play a very important role in the Universe. The speed of light sets the Universal speed limit and the electric charge sets the scale for the interaction between atoms and molecules. The Planck constant determines the scale at which quantum mechanics becomes important. Combining these three quantities gives something called the fine structure constant. The fine structure constant is just a number (i.e. no units) and since it is a combination of constants, it too should be a constant - it shouldn't vary in space and time.

But why 'should' it be a constant? There is no principle that says constants should really be constant and there is no theory which lets you calculate their value. That is, the fundamental constants are assumed to be constant.

The idea of varying constants is not new and many modern theories have room for varying constants. Can these new theories be tested? If the fine structure constant were to vary over very long time-scales - say, on the time scale of the age of the Universe - we could wait for a few billion years while doing very precise laboratory experiments. But astronomers have come up with a better idea - why not look billions of years into the past instead? This is of course very easy, we just need to look at objects many billions of light-years away.

We look for varying constants in the spectra of very distant quasars. As the light from the quasar travels to Earth, some of it gets absorbed by intervening gas and we see very narrow absorption lines in the spectra (see Figure). The position of the lines in the spectra signifies different energy levels in the gas atoms, levels that are well known in laboratories here on Earth.

And here is where the fine structure constant comes in. The fine structure constant controls the energies of those energy levels: if it was different in the past, then we should see a slightly different spectrum to what we expect. And, to our surprise, this is what seems to be happening. Using the giant 10-metre Keck telescope on Mauna Kea, Hawaii, we have looked at the spectra of over 30 objects and we seem to be finding that the fine structure constant was slightly smaller about 4 to 11 billion years ago.

Our results so far seem to be pretty robust. We've tried all manner of other explanations and nothing else seems to work. This doesn't mean we are correct though, and much work is still to be done before this result enters the realm of believability. However, if we are correct, then we may have uncovered the first hint of a new, even more fundamental set of physical laws.

John Webb, Michael Murphy, V. V. Flambaum and V. A. Dzuba,