MARCUS CHOWN
A universal constant might not be so constant after all. An experiment in search of answers could help us finally devise a theory of everything...
The laws of the Universe are not, it turns out, as immutable as we thought. Award-winning cosmology writer Marcus Chown explores this idea.
The opening sentence of LP Hartley’s The Go-Between is, “The past is a foreign country: they do things differently there.” But a similar claim has been made by a group of astronomers. For 20 years, they have been suggesting that the laws of physics in the early Universe differed subtly from today’s. And in the next few years, a new generation of astronomical instruments will put this controversial claim to the ultimate test. The feature of physics which is claimed to have changed is the ‘fine-structure constant’. Known as ‘alpha’, it dictates the strength of the interaction between electrically charged particles and photons of light. Since such an interaction is the source of electromagnetism, it governs the strength of the electromagnetic force. Alpha is vital to our existence. If it were smaller, the electromagnetic force would be too weak to hold together the molecules of life. If it were bigger, protons in the Sun would repel each other so fiercely they’d never glue together in the first step of the chain of nuclear reactions that generate sunlight. Plus, stellar nuclear actions could never build heavy elements such as carbon, oxygen and iron.
Alpha is dimensionless, with a measured value of 1/137.03599971. But since nobody has any idea whether alpha could ever be different, two decades ago Prof John Webb and his colleagues at the University of New South Wales decided to find out by looking at quasars. Quasars are the bright cores of newborn galaxies. Their light has taken so long to reach us that we see them at the dawn of time. As their light travels towards Earth, some of it is absorbed by clouds of hydrogen gas. The wavelength at which such bites are taken out depends on alpha at the cosmic era at which the clouds existed. Webb’s team found that over 10 billion years ago, alpha was a few parts per million smaller than it is today. They have started to extend their measurements, and think alpha differs both in space and time, with the variation in time growing the further back you go. Critics claim the results are caused by faulty instruments and data analysis.
One thing is clear: the standard model of particle physics and the standard model of cosmology are flawed. In the former, the value of alpha is arbitrary, but so too are the strengths of the other fundamental forces and the masses of the fundamental particles. And the latter works only with 95 per cent of the mass-energy of the Universe in the form of invisible ‘dark matter’ and ‘dark energy’, whose identity is unknown and is predicted by no theory. “Physicists are desperate to find an observation that contradicts their current theories and so points the way to a deeper, better theory,” says Webb. “The alpha discrepancy may be just that observation.”
Webb is enthusiastic about a new spectrograph which will be attached to one of the telescopes of the Very Large Telescope in Chile. It should improve the accuracy of measurements and minimise instrument-based errors. “I am hopeful that within a few years we will know whether alpha really varies,” says Webb. “Then I can get onto something else.”
How has he kept going all these years? “Fuller’s London Pride helps,” he laughs.
“The standard model of particle physics is flawed”