To put the theory of special relativity into practice by counting galaxies

To put the theory of special relativity into practice by counting galaxies

To put the theory of special relativity into practice by counting galaxies

This image, made from a combination of images from September 2003 – January 2004 taken by NASA / ESA Hubble Space Telescope, shows nearly 10,000 galaxies in the deepest image of visible light from the cosmos, which cuts over billions of light-years. Credit: NASA, ESA, S. Beckwith (STScI), HUDF Team

Scientists studying the cosmos have a favorite philosophy called the “principle of mediocrity”, which essentially suggests that there is really nothing special about the earth, the sun or the Milky Way galaxy compared to the rest of the universe.

Now new research from CU Boulder adds another piece of evidence to the case of mediocrity: Galaxies are, on average, at rest with respect to early universe. Jeremy Darling, Professor of Astrophysics at CU Boulder, recently published this new cosmological finding in The Astrophysical Journal Letters.

“What this research tells us is that we have a fun movement, but the fun movement agrees with everything we know about universe“There’s nothing special going on here,” Darling said. “We are not special as galaxies or as observers.”

About 35 years ago, scientists discovered the cosmic microwave background, ie electromagnetic radiation left over from the formation of the universe during the Big Bang. The cosmic microwave background looks warmer in our direction of motion and cooler away from our direction of motion.

From this light of the early universe, scientists can conclude that the sun – and the earth orbiting it – move in a certain direction, at a certain speed. Researchers find that our assumed speed is a fraction of a percent of the speed of light – small, but not zero.

Researchers can independently test this conclusion by counting galaxies which are visible from the earth or sum up their brightness. They can do this largely thanks to Albert Einstein’s 1905 the theory of special relativity, which explains how speed affects time and space. In this application, a person on earth looking out into the universe in one direction – in the same direction as the sun and earth are moving – will see galaxies that are brighter, bluer and more concentrated. Similarly, by looking the other way, the person should see galaxies that are darker, redder and further apart.

But when scientists have tried to count galaxies in recent years – a process that is difficult to do exactly – they have come up with figures that indicate that the sun moves much faster than previously thought, which is contrary to standard cosmology.

“It’s hard to count galaxies across the sky – you’re usually stuck with a hemisphere or less,” Darling said. “And beyond that, our own galaxy gets in the way. It has dust that makes you find fewer galaxies and will make them look darker as you get closer to our galaxy.”

Darling was fascinated and confused by this cosmological puzzle, so he decided to investigate for himself. He also knew that there were two recently released studies that could help improve the accuracy of a galaxy count – and shed light on the speed mystery: one is called the Very Large Array Sky Survey (VLASS) in New Mexico, and the other is called Rapid Australian Square Kilometer Array Pathfinder Continuum Survey (RACS) in Australia.

Together, these studies made it possible for Darling to study the entire sky by merging views from the northern and southern hemispheres. It is important that the new surveys are also used radio waveswhich made it easier to “see” through the dust of the Milky Way and thus improved the view of the universe.

When Darling analyzed surveyshe found that the number of galaxies and their brightness matched perfectly with the velocity scientists who had previously concluded from the cosmic microwave background.

“We find a bright direction and a weak direction – we find a direction where there are more galaxies and a direction where there are fewer galaxies,” he said. “The big difference is that it agrees with the early universe from cosmic microwave background and it has the right speed. Our cosmology is just good. “

Since Darling’s results differ from previous results, his thesis is likely to lead to various follow-up studies to confirm or question his results.

But in addition to advancing the field of cosmology, the findings are a good real example of Einstein’s special theory of relativity – and they show how scientists still put the theory into practice, more than 100 years after the famous physicist first proposed it.

“I love the idea that this basic principle that Einstein talked about a long time ago is something you can see,” Darling said. “It’s a really esoteric thing that seems super weird, but if you go out and count galaxies you can see this nice effect. It’s not quite as esoteric or weird as you might think.”

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More information:
Jeremy Darling, The universe is brighter in the direction of our motion: Galaxy Counts and Fluxes are compatible with CMB Dipole, The Astrophysical Journal Letters (2022). DOI: 10.3847 / 2041-8213 / ac6f08

Quote: Putting the theory of special relativity into practice by counting galaxies (2022, June 3) retrieved June 3, 2022 from

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