19 December 2016
In a recent paper published in the journal Physical Review by João Magueijo of Imperial College London and Niayesh Afshordi of the University of Waterloo in Canada, the velocity of light in the early universe may be far higher than it is today – in fact, the birth of the universe could have witnessed light travelling at infinite speed.
The paper describes how scientists can test the controversial idea. If correct, there would be a tell-tale signature left on the cosmic background radiation.
Einstein’s general theory of relativity holds the speed of light in a vacuum as an absolute constant.
Magueijo and Afshordi’s theory is an attempt to explain why the cosmos looks much the same over vast distances. To be so uniform, light rays must have reached every corner of the cosmos, otherwise some regions would be cooler and more dense than others.
Cosmologists and physicists including Stephen Hawking have proposed a theory called inflation, in which the young universe underwent a brief spell of tremendous expansion. According to the inflation theory, the temperature of the cosmos evened out before the cosmos grew exponentially large.
Magueijo and Afshordi’s theory does away with inflation and replaces it with a variable speed of light. According to their calculations, the heat of universe in its first moments was so intense that light and other particles moved at infinite speed. Under these conditions, light reached the most distant pockets of the universe and made it look as uniform as we see it today.
This new theory predicts a clear pattern in the density variations of the early universe, a feature measured by what is called the “spectral index”. Magueijo and Afshordi predict a very precise spectral index of 0.96478, which is close to the latest, though somewhat rough, measurement of 0.968.
On the other hand, the predictions of inflation developed by Stephen Hawking and others more than 30 years ago have been tested fairly rigorously by cosmological observations. Many scientists regard inflation as a simple and elegant explanation of the origin of galaxies in the universe.