Why is the sky blue? The answer could be in the stars

Media release

If you’ve ever wondered why the sky is blue or how sound travels, a new paper by Swinburne University of Technology and the University of New South Wales is helping to solve the very heart of these age-old questions. The problem is that the law of how atoms and light interact, known as electromagnetism, has a strength that physicists do not understand.

The paper, ‘A limit on variations in the fine-structure constant from spectra of nearby Sun-like stars’, has been published today in prestigious journal Science. It studies whether stars that are almost identical twins of the Sun have the same strength of electromagnetism. If they didn’t, it would help researchers in the search for a new theory that ties all of nature’s laws together.

Swinburne ARC Future Fellow Professor Michael T Murphy led the paper.

“Richard Feynman, who helped come up with the theory, called the strength of electromagnetism ‘one of the greatest damn mysteries of physics’ and urged physicists to ‘put this number up on their wall and worry about it,’” says Professor Murphy

“We want to break our favourite theory. The trouble is, it’s hard to know where to look. Our current theories can’t guide us.

“So, it’s vital to do new experiments in very different places and times in our universe, not just here and now on Earth.”

Testing solar twins 

The team of students, postdoctoral and senior researchers at Swinburne and the University of New South Wales discovered that electromagnetism had the same strength in 17 “solar twins” to just 50 parts per billion, making it the most precise astronomical test of its type ever performed.

“We’ve never tested electromagnetism outside our Earth so precisely before. It’s like testing whether the distance from Melbourne to Sydney changed by a few centimetres or so,” says Professor Murphy.

“If we’d seen electromagnetism change between stars, it would break the laws of nature as we currently understand them. We’d need completely new ideas to explain it.

“Unfortunately, our new measurements didn’t break our favourite theory. But the stars we’ve studied are all relatively nearby, only up to 160 light years away. We’ve recently identified new solar twins much further away, about halfway to the centre of our Milky Way galaxy.

“If we can observe these much more distant Suns with the largest optical telescopes, maybe we’ll find the keys to the Universe.”