Physicists have proposed a new experiment to test their theory that Einstein was wrong about the speed of light being a constant, the foundation on which much of modern physics is based.
Professor João Magueijo from Imperial College London and Dr. Niayesh Afshordi of the Perimeter Institute in Canada proposed back in the 1990s that there may have been a time right after the Big Bang when the speed of light was much faster than it is now.
If they’re right, it pokes a hole squarely in the foundation of physics for the last hundred years, Einstein’s Theory of General Relativity. According to Einstein, the speed of light is, was and always will be the same and so the laws of physics are the same everywhere.
The physicists proposed the variation in light speed to explain a quirk of the early universe – its lumpy density. When the Universe first formed after the Big Bang, its density was erratic as it expanded. Traditionally, this has been explained by inflation theory, which suggests that the Universe went through an extremely rapid expansion phase before slowing down to its current rate of expansion.
The Universe as we see it today appears to be the same everywhere, with a relatively homogeneous density. But if the speed of light has always been the same, then there hasn’t been enough time for light to reach the edge of the Universe and “even out” the energy. Inflation theory suggests that the early Universe was evened out when it was very small and then suddenly expanded. Although this would explain the modern observable Universe, it means that a special set of conditions existed at that time that created the “inflation field”
In Magueijo and Afshordi’s theory, the speed of light was much higher at first, which connected the distant edges of the Universe and then that speed dropped in a predictable way as the density of the Universe changed.
Both theories fit the facts as we know them, but neither are easy to definitively prove. Magueijo and Afshordi believe they have now come up with a way to help prove their version of events after the Big Bang, using our ever-increasingly accurate readings of cosmic background radiation.
Cosmic microwave background is basically a map of the oldest light in the Universe, a “spectral index,” and the physicists believe that if the exact figure of that index is precisely 0.96478, that will prove their model of how the Universe expanded.
"The theory, which we first proposed in the late-1990s, has now reached a maturity point -- it has produced a testable prediction," said Professor Magueijo. "If observations in the near future do find this number to be accurate, it could lead to a modification of Einstein's theory of gravity.
"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."
However, even if the “spectral index” comes back at this exact figure, there will be more work to do to definitively prove the new theory. This would be strong evidence in the right direction, but it won’t completely disprove the idea of inflation.
To irrevocably alter the foundation of modern physics, the scientists will need to have more than one piece of evidence in their favor.
