Sabine Hossenfelder asks: Do we need a Theory of Everything? You know what she's going to say, don't you?
What physicists mean by a theory of everything is then a theory from which all the four fundamental interactions [electromagnetic force, the strong and the weak nuclear force, and gravity] derive. This means it is both a grand unified theory and a theory of quantum gravity.
This sounds like a nice idea, yes. But. There is no reason that nature should actually be described by a theory of everything. While we *do need a theory of quantum gravity to avoid logical inconsistency in the laws of nature, the forces in the standard model do not have to be unified, and they do not have to be unified with gravity. It would be pretty, yes, but it’s unnecessary. The standard model works just fine without unification.
So this whole idea of a theory of everything is based on an unscientific premise. Some people would like the laws of nature to be pretty in a very specific way. They want it to be simple, they want it to be symmetric, they want it to be natural, and here I have to warn you that “natural” is a technical term. So they have an idea of what they want to be true. Then they stumble over some piece of mathematics that strikes them as particularly pretty and they become convinced that certainly it must play a role for the laws of nature. In brief, they invent a theory for what they think the universe *should be like.
This is simply not a good strategy to develop scientific theories, and no, it is most certainly not standard methodology. Indeed, the opposite is the case. Relying on beauty in theory development has historically worked badly. In physics, breakthroughs in theory-development have come instead from the resolution of mathematical inconsistencies. I have literally written a book about how problematic it is that researchers in the foundations of physics insist on using methods of theory development that we have no reason to think should work, and that as a matter of fact do not work.
The search for a theory of everything and for grand unification began in the 1980s. To the extent that the theories which physicists have come up with were falsifiable they have been falsified. Nature clearly doesn’t give a damn what physicists think is pretty math.
Having said that, what do you think I think about Lisi’s and Weinstein’s and Wolfram’s attempts at a theory of everything? Well, scientific history teaches us that their method of guessing some pretty piece of math and hoping it’s useful for something is extremely unpromising. It is not impossible it works, but it is almost certainly a waste of time. And I have looked closely enough at Lisi’s and Weinstein’s and Wolfram’s and many other people’s theories of everything to be able to tell you that they have not convincingly solved solve any actual problem in the existing fundamental theories. And I’m not interested to look any closer, because I don’t also want to waste my time.
But I don’t like commenting on individual people’s theories of everything. I don’t like it because it strikes me as deeply unfair. These are mostly researchers working alone or in small groups. They are very dedicated to their pursuit and they work incredibly hard on it. They’re mostly not paid by tax money so it’s really their private thing and who am I to judge them? Also, many of you evidently find it entertaining to have geniuses with their theories of everything around. That’s all fine with me. [...]
The brief summary is that if you hear something about a newly proposed theory of everything, do not ask whether the math is right. Because many of the people who work on this are really smart and they know their math and it’s probably right. The question you, and all science journalists who report on such things, should ask is what reason do we have to think that this particular piece of math has anything to do with reality. “Because it’s pretty” is not a scientific answer. And I have never seen a theory of everything that gave a satisfactory scientific answer to this question.
I've got a somewhat different take on the issue. I'm not a mathematician, physicist, or a scientist – as I've remarked somewhere around here, I don't give a crap about science – so I'm not entitled to much of an opinion on the validity of those various attempts at unification. But I AM bothered that at least some of them seem so far to be without hope of empirical verification and I think any reasonably intelligent and informed person can have an opinion about that.
But I've got something else in mind. I've spent almost a half century trying to figure out how "Kubla Khan" works. I don't see how a physicist's ToE (theory of everything) or GUT (grand unified theory) would help me with that problem. And that's not the only thing I've been investigating.
What bugs me is the arrogance that calls physicists to proclaim their domain to be EVERYdamnTHING. It's not. It may be everywhere, and have it's nose in everyone's business, but it isn't all there is. Solving fundamental physics may well move some other projects along. But not all of them.
Lol!
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