"One of Physics' Greatest Damn Mysteries": The Most Accurate Astronomical Test of Electromagnetism Yet

“One of Physics’ Greatest Damn Mysteries”: The Most Accurate Astronomical Test of Electromagnetism Yet

Credit: NASA

There is a vexing, vexing problem with our understanding of the laws of nature that physicists have been trying to explain for decades. It’s about electromagnetism, the law of how atoms and light interact, which explains everything from why you don’t fall through the floor to why the sky is blue.

Our theory of electromagnetism is arguably the best physical theory humans have ever come up with – but it has no answer as to why electromagnetism is as strong as it is. Only experiments can tell you the strength of electromagnetism, which is measured by a number called α (aka alpha, or the fine structure constant).

The American physicist Richard Feynman, who helped come up with the theory, called this “one of the greatest damn mysteries of physics” and urged physicists to “put this number up on their wall and worry about it.”

In research just published in Science, we decided to test whether α is the same in different locations in our galaxy by studying stars that are nearly identical twins to our Sun. If α is different in different places, it can help us find the ultimate theory, not only of electromagnetism, but of all laws of nature together – the “theory of everything”.

We want to break our favorite theory

Physicists really want one thing: a situation where our current understanding of physics breaks down. New physics. A signal that cannot be explained with current theories. A guide to the theory of everything.

The Sun’s rainbow: here, the sunlight is scattered in separate rows, each covering only a small spectrum of colors, to reveal the many dark absorption lines from atoms in the Sun’s atmosphere. Credit: NA Sharp / KPNO / NOIRLab / NSO / NSF / AURA, CC BY

To find it, they can wait deep underground in a gold mine for particles of dark matter to collide with a special crystal. Or they can carefully maintain the world’s best atomic clock for years to see if it shows any different time. Or smash protons together at (almost) the speed of light in the 27 km long ring of the Large Hadron Collider.

The problem is that it’s hard to know where to look. Our current theories cannot guide us.

Naturally, we search in laboratories on Earth, where it is easiest to search thoroughly and carefully. But it’s a bit like the drunk just looking for his lost keys under a lamppost when he might actually have lost them on the other side of the road, somewhere in a dark corner.

Stars are terrible, but sometimes terribly similar

We decided to look beyond Earth, beyond our solar system, to see if stars that are nearly identical twins of our sun produce the same rainbow of colors. Atoms in the stars’ atmospheres absorb some of the light that struggles outward from the nuclear furnaces in their cores.

Only certain colors are absorbed, leaving dark lines in the rainbow. The absorbed colors are determined by α – so measuring the dark lines very accurately allows us to measure α as well.

Hotter and cooler gas bubbling through stars’ turbulent atmospheres makes it difficult to compare absorption lines in stars with those seen in laboratory experiments. Credit: NSO / AURA / NSF, CC BY

The problem is that the stars’ atmospheres are moving – boiling, spinning, looping, belching – and this shifts the lines. The shift destroys any comparison with the same lines in laboratories on Earth, and thus any possibility of measuring α. Stars seem like terrible places to test electromagnetism.

But we wondered: if you find stars that are very similar—twins of each other—maybe their dark, absorbed colors are also similar. So instead of comparing stars to laboratories on Earth, we compared twins of our sun to each other.

A new test with solar twins

Our team of students, postdoctoral fellows and senior researchers, at Swinburne University of Technology and the University of New South Wales, measured the distance between pairs of absorption lines in our Sun and 16 “solar twins” – stars almost indistinguishable from our Sun.

The rainbows from these stars were observed on the European Southern Observatory (ESO) 3.6 meter telescope in Chile. Although not the largest telescope in the world, the light it collects is fed into probably the best-controlled, best-understood spectrograph: HARPS. This separates the light into its colors and reveals the detailed pattern of dark lines.

HARPS spends much of its time observing Sun-like stars to search for planets. This practically provided a treasure trove of exactly the data we needed.

ESO’s 3.6-metre telescope in Chile spends much of its time observing Sun-like stars to search for planets with its extremely precise spectrograph, HARPS. Credit: Iztok Bončina / ESO, CC BY

From these exquisite spectra, we have shown that α was the same in the 17 solar twins with astonishing precision: just 50 parts per billion. It’s like comparing your height to the circumference of the earth. It is the most precise astronomical test of α ever performed.

Unfortunately, our new measurements didn’t disprove our favorite theory. But the stars we’ve studied are all relatively close, only up to 160 light years away.

What comes next?

We recently identified new solar twins much further away, about halfway to the center of our Milky Way galaxy.

In this region, there should be a much higher concentration of dark matter – an elusive substance that astronomers believe lurks throughout the galaxy and beyond. Like α, we know very little about dark matter, and some theoretical physicists suggest that the inner reaches of our galaxy may be the very dark corner we should look for connections between these two “fiendish mysteries of physics.”

If we can observe these much more distant suns with the largest optical telescopes, we may find the keys to the universe.

More information:
Michael T. Murphy et al, A limit on variations in the fine structure constant from the spectra of nearby Sun-like stars, Science (2022). DOI: 10.1126/science.abi9232

This article is republished from The Conversation under a Creative Commons license. Read the original article.The conversation

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