The average temperature of the Universe has become increasingly hot

For nearly a century, astronomers have understood that the Universe is in a state of expansion. Since the 1990s, they have realized that the pace of expansion accelerated up to four billion years ago. As this progresses, and the galaxy clusters and filaments of the Universe move further and further away, scientists theorize that the average temperature of the Universe will gradually decrease.

But according to new research conducted by the Center for Cosmology and AstroParticle Physics (CCAPP) at Ohio State University, it appears that the Universe is actually getting warmer as time goes on. After probing the thermal history of the Universe over the past 10 billion years, the team concluded that the average temperature of the cosmic gas has increased more than 10 times and reached around 2.2 million K (~ 2.2 ° C ; 4 million ° F) today.

The study describing their findings, “The Cosmic Thermal History Probed by Sunyaev-Zeldovich Effect Tomography”, recently appeared in The Astrophysical Journal. The study was led by Yi-Kuan Chiang, a researcher at the CCAP, and included members of the Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU), Johns Hopkins University and the Max-Planck-Institute for Astrophysics.

For the sake of their study, the team looked at thermal data on the large-scale structure (LSS) of the universe. This refers to models of galaxies and matter on the larger cosmic scale, which is the result of the gravitational collapse of dark matter and gas. As Dr. Chiang explained in an Ohio State press release:

“Our new measurement provides direct confirmation of the fundamental work of Jim Peebles – the 2019 Nobel Prize in Physics – who exposed the theory of how large-scale structure is formed in the universe. As the universe evolves. , gravity brings together dark matter and gas in space into galaxies and galaxy clusters. The resistance is violent, so violent that more and more gasoline is shocked and heated. “

To measure thermal changes over the past 10 billion years, Chiang and his colleagues combined ESA data Planck’s infrared astronomical satellite and the Sloan Digital Sky Survey (SDSS). While Planck was the first European mission to measure the temperature of the Cosmic Microwave Background (CMB), SDSS is a massive multispectral survey that created the most detailed 3D maps of the Universe.

From these datasets, the team correlated eight of Plancksky intensity maps with two million redshift spectroscopic references from the SDSS. By combining redshift measurements (which are routinely used to determine how fast objects are moving away from us) and light-based temperature estimates, the team compared the temperature of more distant gas clouds (further back in time). ) with those closest to the Earth.

From this, the research team was able to confirm that the average temperature of gases in the early Universe (about 4 billion after the Big Bang) was lower than it is today. This is apparently due to the gravitational collapse of the cosmic structure over time, a trend that will continue and become more intense as the expansion of the Universe continues to accelerate.

As Chiang summarized, the Universe is warming due to the natural process of galaxy formation and structure and is unrelated to temperature changes here on Earth:

“As the universe evolves, gravity pulls dark matter and gas into space together into galaxies and clusters of galaxies. The resistance is violent, so violent that more and more gases are shocked and heated … These phenomena are happening on very different scales. They are not connected at all. “

In the past, many astronomers have argued that the cosmos would continue to cool as it expanded, which would inevitably lead to the “Big Chill” (or “Big Freeze”). On the contrary, Chiang and his collaborators have shown that scientists can record the evolution of the formation of the cosmic structure by “controlling the temperature” of the Universe.

These findings may also have implications for theories that accept “cosmic cooling” as a foregone conclusion. On the one hand, it has been suggested that a possible solution to the Fermi paradox is that extraterrestrial intelligences (ETIs) are dormant and wait for the Universe to improve (the aestivation hypothesis).

Based in part on the thermodynamics of computer science (Landauer’s principle), the argument states that when the Universe cools, advanced species would be able to get much more out of their megastructures. Also, if the cosmos gets warmer over time, does that mean that the emergence of life will become less likely over time due to the increase in cosmic radiation?

Assuming that there is no mechanism to maintain a certain thermal equilibrium, would that mean that the Universe will not end up in a “great cold”, but in a “great fire”? As Robert Frost wrote, “Some say the world will end in fire, others say ice.” Which of these will prove correct and what implications it might have for life in the future, only time will tell …

Further reading: Ohio State News, The Astrophysical Journal