March 27, 2023
'One of the greatest mysteries of physics': The most accurate astronomical test of electromagnetism

‘One of the greatest mysteries of physics’: The most accurate astronomical test of electromagnetism

Credit: NASA

There’s a nagging, vexing problem with understanding 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 off 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 doesn’t answer 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 (also known as alpha, or the fine structure constant).

American physicist Richard Feynman, who helped create the theory, called it “one of the great mysteries of physics” and urged physicists to “put that number on their wall and worry about it.”

In research just published in Science, we decided to test whether α is the same in different parts of our galaxy by studying stars that are almost identical twins to our sun. If a is different in different places, it may help us to find the ultimate theory, not only of electromagnetism, but of all the 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 by current theories. A sign for the theory of everything.

'One of Physics' Greatest Mysteries': Studying Distant Suns in Astronomy's Most Accurate Electromium Test

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

To find it, they might be waiting deep underground in a gold mine for dark matter particles to collide with a special crystal. Or they might carefully care for the world’s finest individual watches for years to see if they tell a slightly different time. Or synthesize protons together at (almost) the speed of light in the 27km long ring of the Large Hadron Collider.

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

Of course, we look to laboratories on Earth, where it is easier to search thoroughly and more precisely. But this is a bit like the drunkard only looking for his lost keys under a lamppost when, in fact, he might 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 to our sun produce the same rainbow of colors. Atoms in the atmospheres of stars 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. These absorbed colors are determined by α—so very carefully measuring the dark lines also allows us to measure α.

'One of Physics' Greatest Mysteries': Studying Distant Suns in Astronomy's Most Accurate Electromium Test

The hotter and cooler gases that bubble up through the stars’ turbulent atmospheres make it difficult to compare absorption lines in stars with those seen in laboratory experiments. Credit: NSO / AURA / NSF, CC BY

The problem is that stars’ atmospheres move—boil, spin, loop, belch—and that changes the lines. The offsets destroy any comparison with the same lines in laboratories on Earth, and hence any possibility of measuring α. The stars, it seems, are terrible places to test electromagnetism.

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

A new test with solar twins

The 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 that are almost indistinguishable from our sun.

The rainbows from these stars were observed at 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 possibly the best-controlled, best-understood spectrograph: HARPS. This separates the light into its colors, revealing the detailed pattern of dark lines.

HARPS spends much of its time observing sun-like stars to look for planets. Essentially, this provided a treasure trove of the data we needed.

'One of Physics' Greatest Mysteries': Studying Distant Suns in Astronomy's Most Accurate Electromium Test

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

From these exquisite spectra, we showed 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 made.

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

What’s next?

We recently spotted new solar twins much further away, about halfway to the center of our 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 precious little about dark matter, and some theoretical physicists suggest that the inner parts of our galaxy may just be the dark corner we should look for connections between these two “cursed 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

Reference: ‘One of Physics’ Greatest Damn Mysteries’: The Most Accurate Astronomical Test of Electromagnetism (2022, November 11) Retrieved November 11, 2022, from mysteries-physics-precise.html

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