New Miscellany: more on fine-tuning from Ethan Siegel (General)

by David Turell , Saturday, March 08, 2025, 18:44 (19 hours, 50 minutes ago) @ David Turell

There are 26 essential constant factors that make this universe as it is:

https://bigthink.com/starts-with-a-bang/multiverse-explain-fundamental-constants/?utm_s...

"So why does our Universe have fundamental constants with the values that they do? That’s what Pierre Louw wants to know, following up on an earlier Starts With A Bang article to ask:

“'Near the end of your Big Think article of 26 February ’25, you wrote: ‘But there’s a key thing to keep in mind: even though we know all of this and can weave a consistent story out of it, we still don’t know why nature has the values that it does.’

***

"The rest masses of every one of the fundamental, massive particles, from neutrinos to quarks to leptons and more, which can also be parametrized by a coupling to the Higgs. Some of them, like the electron’s rest mass, would lead to a very different Universe from what we recognize as our own if they were even a little bit different.

"The mixing parameters between the quarks (given by the CKM matrix) and the neutrinos (given by the PMNS matrix), which determine how particles with identical quantum numbers mix together, required to explain phenomena such as weak decays and neutrino oscillations.

"And there’s also one more parameter, at least, for the cosmological constant, which is our simplest approximation for what dark energy could be.

"All told, that equates to 26 fundamental constants, and that still leaves puzzles like dark matter, baryogenesis, and any parameters related to inflation unaccounted for. Importantly, these fundamental constants are needed to reproduce the Universe we have; if they were different, our Universe would be correspondingly different as well. (my bold)

"To the best of our knowledge, these constants really are constant and unchanging across space and throughout time; they do not seem to vary or change. But how do we know the values of these constants? (my bold)

***

"When I talked about the Universe in an earlier piece, and I said, “…even though we know all of this and can weave a consistent story out of it, we still don’t know why nature has the values that it does,” that’s precisely what I was referring to: the fact that we cannot predict these values, and can only measure them to determine what they are.

***

"That’s where theorists thrive: in concocting plausible mechanisms that can explain and account for the phenomena that we see. In general, we call these classes of problems fine-tuning problems: as we can imagine that any such parameter, constant, or value could have been all over the map, and that significantly different possibilities would have led to vastly different outcomes. A Universe with:

"a much weaker electromagnetic force,
a much greater mass for the up and down quarks,
or a much greater cosmological constant,
would have never enabled the formation of stars and galaxies at all, much less rocky planets, complex molecules, and the possibility of life.

***

"And therefore, when it comes to the question of, “Why do the constants in our Universe have the values that they do?” the answer is simply, “Because we, observers who can measure the Universe, could only have arisen in a universe that took on values that allowed the emergence of intelligent observers to be physically possible.” (my bold)

***

"So in summary, yes, the values of the fundamental constants can be explained by bubble universes created by inflation, but that explanation is hardly satisfactory from a scientific point of view. It may turn out to be a correct component of the story, but until we understand how it happened, our physical understanding will remain dissatisfying and incomplete, even in the best-case scenario."

Comment: please read my bolds carefully. This is a specific universe of a type that allows life to appear anywhere in it. In any other form of universe life would not/could not happen. We observe the 26 constants but cannot explain the underlying mechanism that makes them the way they are. Secondarily, a life-friendly environment is required as on the Earth. This is the accepted version of fine-tuning.