spaceSpace and Physics

The Speed Of Light May Not Be As Constant As We Thought It Was


Jonathan O'Callaghan

Senior Staff Writer


Many things in life are constant. The crushing sense of disappointment after finishing a bar of chocolate, for example. The unpredictability of 2016. And, of course, the speed of light.

But, wait! Perhaps it is not so. A new study has proposed the speed of light in a vacuum has not always been the same value it is now (299,792,458 meters per second), and was in fact slightly higher at the beginning of the universe 13.8 billion years ago.


The theory comes from Professor João Magueijo at Imperial College London, published in Physical Review D. Magueijo first proposed the idea of an alternating speed of light back in 1998, and now says he has a way we can test it.

The theory goes that seconds after the Big Bang, there must have been a way to spread heat and energy around the universe, before gravity had a chance to reach every corner. At the moment, our best theory for how this occurred is known as inflation – a period of rapid expansion that was faster than the current rate of expansion of the universe.

This helps to deal with the so-called “horizon problem”, where all parts of the universe today are roughly the same everywhere we look, broadly speaking. But if the speed of light was always constant, it doesn’t quite make sense how energy could have been spread uniformly.

So Magueijo proposes that the speed of light was higher moments after the Big Bang, allowing the universe to become uniform in its early stages. To test this, he says we can look for fluctuations in the cosmic microwave background – the fossilized relic of the early universe – known as the spectral index.


He predicts that this figure should be 0.96478. At the moment, our best estimate puts the figure at around 0.968, with a margin of error. If it is refined towards Magueijo’s figure by future measurements, his theory could be proved correct.

“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,” he said in a statement.

And, well, if he’s right, it would have broader implications for Einstein’s theory of relativity, suggesting the speed of light was not the constant we always thought it to be. If he’s wrong, well, panic over, and we can get back to our regular lives.


spaceSpace and Physics
  • tag
  • early universe,

  • big bang,

  • cosmic inflation,

  • speed of light,

  • cosmic microwave background radiation,

  • constant