‘We live in a universe that’s just right for us’: study suggests testing the anthropic principle

The “anthropic principle” that the universe we live in is finely tuned to harbor life was first proposed by Brandon Carter in 1973. Since then, this principle has caused great debate.

A paper written by Nemanja Kalopá, a physicist in the Department of Physics and Astronomy at the University of California, Davis, and Alexander Westphal, a professor at the German Electron Synchrotron (DESY), was published in the Journal of Cosmology and Astroparticle Physics. . ) describes for the first time how to test this assumption experimentally.

The anthropic principle (AP) can be formulated in different ways. These range from a simple factual explanation: “As we are observing here, the universe evolved with the conditions necessary for the emergence of intelligent life known as weak AP.” It ranges from something a little more fundamental. To evolve in a way that connects us to who we are. ”

This stronger interpretation, called strong AP, often goes into metaphysical territory, suggesting a kind of “design” and going beyond the realm of scientific inquiry into the universe.

According to many scientists, AP problems are particularly useful as a scientific tool because AP does not produce testable, quantifiable predictions that may extend our knowledge and scrutinize principles. That’s not it. Without this, it remains more of a philosophical speculation than a scientific hypothesis.

But the Associated Press suggests that for our universe to develop as a hospitable place for carbon-based life, it must have started with a rather unique set of initial conditions. This is inferred, for example, by observing the values ​​of certain constants used in the equations that describe the universe (such as the gravitational constant, the charge of electrons, Planck’s constant, etc.). These constants must be “just right.” Otherwise, we will have a completely different and, most importantly, a less livable world.

Establish the exact initial conditions suggested by AP, calculate how the universe evolved to its current state based on current physical models, and compare the results with actual astronomical observations. You can. If there is a discrepancy between theory and reality, it provides a measure of the validity of the AP.

A new study by Nemanja Kalopá and Alexander Westphal offers some concrete predictions that may find observational support in the coming years.

To understand their proposal, it is necessary to outline some important elements in cosmological research.

cosmic inflation

The universe experienced a period of rapid expansion in the early moments of its existence. It grew from an infinitesimal size (almost zero) to a macroscopic scale (some theories describe it as the size of a grape or grape) in just 10 to 36 seconds. soccer ball). After that, expansion slowed and continued at a rate similar to that currently observed.

This early stage of physics was extremely unusual, dominated by quantum phenomena (which govern the infinitely small), and influenced subsequent evolution, resulting in the structures we see today ( This enabled the formation of galaxies, stars, etc. Although no direct evidence of cosmic inflation has yet been found, it is a solid theory that we hope will see observational confirmation in the coming years.

dark matter

You’ve probably heard of it. Experimental observations show that a significant portion of the universe (about five-sixths of the matter) is made up of things that we cannot directly observe. We call it dark matter, but its true nature is still unknown. Many hypotheses have been proposed, all awaiting experimental confirmation, which is expected in the near future.

Axion

One candidate for dark matter is axions. These particles (or perhaps an entire class of particles) are very light (e.g., much lighter than an electron). Axions were originally proposed to explain a quantum phenomenon known as CP symmetry breaking. This phenomenon involves weak nuclear interactions, one of the four fundamental forces (the others being gravity, electromagnetism, and strong nuclear interactions).

But researchers believe that certain properties of axions, which are thought to have formed in large quantities during cosmic inflation, are expected of dark matter, such as minimal interaction with both itself and ordinary matter. I noticed that it matches the characteristics of Observations of black holes may confirm their existence within the next few years.

AP testing involves a combination of these three elements.

“The LiteBIRD satellite has the potential to discover primordial gravitational waves, close to the current limit, consistent with large-scale inflation,” Kaloper explains. “Most cosmologists would feel this confirms massive inflation.” LiteBIRD (Lite (Light) Satellite for the Study of B-mode Polarization) is a study by the Japan Aerospace Exploration Agency (JAXA). This experiment is scheduled to launch in 2032.

“By studying supermassive black holes in the Universe, we may also discover signs of ultralight axions. Axions affect the spin-to-mass ratio of black holes, and this may be observed.” continues Kaloper. Many experiments are already studying black holes, and many more will be launched in the near future.

“Finally,” Kaloper added, “future direct dark matter searches may find that the bulk of dark matter is not made up of ultralight axions, in which case the anthropic principle would be considered bankrupt.”

However, this result is not guaranteed.

“If, on the other hand, a direct dark matter search reveals that dark matter is actually an ultralight axion, I think we would agree that the anthropic principle has indeed passed this test. In fact, This could happen,” Kaloper continued. . ”

“I think it’s particularly interesting that both of these options may be experimentally tested in the not-too-distant future,” Kaloper concludes.

“And this is the first example, as far as my collaborators and I know, where the anthropic principle can actually fail the test, rather than just declaring it doesn’t apply.

“Importantly, the large-scale inflation and the existence of ultralight axions with masses m > 10-19 eV mean that dark matter MUST be an axion. Under typical initial conditions, there will eventually be too many axions. Dark matter and the anthropic principle are absolutely necessary to suppress it.

“To discover that axions are not dark matter, the initial conditions must not only be improbable (and humanly correctable), but also extremely improbable, and in fact do not even enter the realm of human reasoning.” I guess not.”

Therefore, we will need to wait several more years, perhaps even longer, to gather all the evidence needed to falsify or confirm the Anthropic Principle. But what happens if you find out you can’t pass the test?

“If the simple formulation of anthropology fails, without changing any of the other assumptions (universality of gravity, initial inflation, superradiation phenomena), it can be seen that different rules govern the initial conditions. It will be suggested,” Kaloper explains.

“Different initial conditions may not have equal probabilities, some may be biased by new mechanics that are not yet understood, some initial conditions may be completely impossible, or the actual cosmology may be It may be more complicated than we thought.”

“One could imagine more dramatic scenarios, but at least for now they seem like fantasies,” Kaloper concludes.