IANAP

I am not a physicist, but I do think I have a good intuitive understanding of the state of physics and cosmology today. Rather than continue this discussion in the comments to an earlier post, I thought I'd elevate it to the front page. I would say that a funny thing happened on the way to a Theory of Everything.

The profound discoveries of the 20th Century -- relativity, quantum theory, field theories and the so-called Standard Model of particles and forces, and of course Big Bang* cosmology -- to many signaled the end of metaphysics. Mere speculation about the deep nature of the universe and first causes was obsolete. The scientific method could now approach the ultimate questions about the fundamental nature of the universe and first causes, sweeping away millennia of theological fantasizing and philosophical thumb sucking. We could now declare with confidence, based on a mountain of evidence, the age of the universe, its state at the very beginning of time -- alright, within 10^-13 seconds of the beginning -- and its evolution to the present state. We had elucidated the underlying processes, at unimaginably small scales, that give rise to the perceptible world we live in. We understood what kept our feet glued to the planet, the planets in their orbits, and the wheeling of 200 billion galaxies. 

But by late in the last century, and with increasing distress in this one, problems arose. One that troubles physicists more than it likely troubles the rest of us is that the theory of gravity -- that it consists of the warping of spacetime by mass -- is entirely distinct from the theory of that describes the other forces of nature, that control interactions at the subatomic level, and the chemistry that produces the world at the scale in which we subjectively live and operate. Lay people might just say, So what? Gravity is just different from electromagnetism and the strong and weak forces, que será será. But because this appears to be an  annoying gap in understanding, and for more specific reasons mostly having to do with how they model the earliest moments of the universe, physicists cannot accept this answer.

An even more vexing difficulty, and one that us mere sociologists can easily understand, is that even slight differences in the fundamental constants of nature would produce a universe in which we could not exist. In fact one parameter, the so-called cosmological constant or vacuum energy, which governs the rate of expansion of the universe, is off by many orders of magnitude from what physicists would predict from their understanding of the quantum theory.†

 

So the quest to understand why the parameters of physics are just what they are, to produce a universe friendly to our kind of biology, has become the new Holy Grail. A glib answer that seems to satisfy some people is that since we're here, we must be in a universe that can have us. That's called the anthropic principle and while it might work for answering why our planet happens to be hospitable to us, that only makes sense because there are trillions of planets to choose from. Extending the idea to the universe implies that there must be innumerable universes. There might be, but the problem with that to a scientist is that the universe, by definition, consists of everything we can observe. A fortiori, the theory of multiple universes, the metaverse, is impossible to test empirically, and it isn't even clear that the idea is meaningful.

Another approach, which also tries to address the unification of gravity with quantum theory, is called string theory. Again, read the book if you want to get into this, but the idea is that there are mathematical structures that can produce the standard theory and gravity, assuming the universe actually consists of nine spacial dimensions rather than three.  Since we can't perceive the other 6, they must be curled up and really, really tiny. Sounds ridiculous, I know, but then so does the Big Bang until you get used to it. The real problem is that there are innumerable structures that can work, so we're really back to the beginning in answering why things are just what they are. Maybe the geniuses can come up with a solution that seems to have a high probability and also predicts our reality, but there seems to be no way to test it empirically.

(If I got any of that not quite right, I'm happy to have any physics majors out there offer corrections.)

However: Physics is not theology. Physicists don't choose to arbitrarily believe either of these ideas. They propose them as possible directions for inquiry, and the people who are interested in them search for means of verifying them. Others find these ideas feckless, and continue to search for an explanation of why the initial conditions of the universe must have been such as to produce the result that we see. So yes, we have come full circle -- these disputes seem metaphysical, and there is no doubt but that people's attraction to one or another is as much aesthetic and temperamental as it is intellectual. 

Nevertheless, it does not follow at all that science and religion are not entirely different ways of knowing.The discovery of the age of the universe, the distribution of the galaxies and stars, the underlying workings of the standard model, quantum mechanics, and relativity, are as firmly established as any knowledge can possibly be, and they do utterly destroy all religious mythology. The Abrahamic God, the Hindu pantheon, all are swept away. We don't know everything, and we probably never will But we do know that.

* The term was invented by the physicist Fred Hoyle, who thought the idea was ridiculous, and was intended to be disparaging. But its proponents ended up embracing it. I would much rather called it the Initial Singularity, the IS theory.

† I'm not going to try to explain this here. If you're interested, you can check out Thomas Hertog, On the Origin of Time, which I have already mentioned.