About a century ago, Albert Einstein proposed that the speed of light in vacuum is a fixed constant in the universe, and its value never changes, whatever conditions you test them under. Now two scientists have proposed a new theory and a method to test this theory to prove that Einstein was wrong, and that the speed of light is not a constant value.
Lot of research has been carried out on light and its speed in the past hundred years, and scientists have calculated the speed of light to be 299,792,458 m/s in vacuum. This constant value has also played a significant role in proving several theories in areas of quantum mechanics, cosmology, and electromagnetism. In particular, this constant plays an important role in models of early universe.
Now, a new paper published in Physical Review challenges the earlier hypothesis that the speed of light is constant. The authors of the paper - Professor João Magueijo and Professor Niayesh Afshordi, two theoretical physicists working at Department of Physics, Imperial College in the UK and the Perimeter Institute of Theoretical Physics, Waterloo, Ontario, Canada respectively - claim that speed of light is not a constant actually, and it could have been faster when the universe was in its initial stages.
Magueijo had first proposed this theory in 1990s, but now he says it has "reached a maturity point", and "produced a testable prediction". Two physicists also propose a method to test their theory by observing universe's tiny density fluctuations with the help of cosmic microwave background (CMB) radiation. Structures in our universe are believed to have formed from tiny differences in density in different regions. CMB is believed to be the fossilized impression of the universe (thermal radiation leftover) after the Big Bang. This map of the most ancient light – in the form of 'spectral index' – can be measured even today. Although, it has been observed that the energy in CMB varies in small pockets, it is mostly uniform on a wide scale probably due to inflation of the universe (the idea that universe ballooned in size quickly). The Inflation theory suggests that different parts of the universe influenced each other and expanded at the same rate, which kept the value of CMB nearly constant. But for that to be true - the physicists claim - speed of light must have been faster in early universe. They also suggest that the CMB should reflect the change in the speed of light and the speed of gravity.
Prof. João Magueijo and Prof. Niayesh Afshordi predict a value of 0.96478 for the spectral index. Based on the most recent satellite measurement, the value of spectral index has been calculated to be 0.968, which is a close match. If a mismatch is observed in future CMB measurement, it would suggest that the speed of light remains constant, and that the theory proposed by Magueijo's and Afshordi's is wrong.
"The idea that the speed of light could be variable was radical when first proposed, but with a numerical prediction, it becomes something physicists can actually test. If true, it would mean that the laws of nature were not always the same as they are today," said Prof. Magueijo.
The detailed findings of the study have been published in Physical Review.