Posted by jjgreen 3 days ago
What does string theory predict that (1) is within experimental reach in, say, 5 years (2) if not found, would prove it wrong. Was there ever anything satisfying these two simultaneously? AFAIK,the answer is "no".
Everyone is free to pursue what they want. I did not comment on that at all. You click on whatever part of the tech tree you want. However, my expectation is that the string theory does not have the qualities of a scientific theory that improves one's knowledge about universe.
My understanding was that string theory being more "hypothetical physics" than "theoretical physics" at this point is still a pretty legit criticism.
I've made some comments here [1] to discuss how I see the situation. It's difficult to be thorought in the world of research, and even more so in an HN comment. I'll be writing more as the subject pops up in HN.
A time and technological gap always exists between theory and a plan for experimental confirmation. Some gaps are fairly short. String theory's gap is undoubtedly long, not for lack of resources.
This gap justifies tapering the allocation of attention and research resources (funding, students, etc), which got lopsided following the strong marketing campaign driven by Greene.
To borrow a compsci analogy, we tried the depth-first search going in the string theory direction, maybe it’s time to switch to breadth-first for a while, to see if there are any viable and useful theories with less distance from the ones we have today. Maybe it doesn’t have to be a "theory of everything" either, we can initially settle for a "theory of more".
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As far as I can tell, it seems to come from the developers of Loop Quantum Gravity, who feel left out of funding. And maybe that's true. But their theory doesn't offer practical tests, either. It would be weird if it did.
You're absolutely right in everything you said, thank you.
Like another commenter posted, the planck scale is 10^19 GeV and we're about 10^15 short. Therefore it follows we won't be testing anything at planck scale for many generations, if ever. Therefore the argument of "I can't test it therefore the theory is useless" is just being defeatist. The fact that such theory isn't testable might be a feature of our Universe, not the theory. As in, these people don't normally make the distinction between something that "could be tested in principle, we just don't have the technology" (like string theory) vs something that "couldn't be tested even in principle" (like how many angels can dance on the head of a pin). They're basically playing with semantics when they say "it's not testable".
> As far as I can tell, it seems to come from the developers of Loop Quantum Gravity, who feel left out of funding. And maybe that's true. But their theory doesn't offer practical tests, either. It would be weird if it did.
Again, correct on all points. However, I'll add the following. Yes, LQG makes as many directly-testable predictions at the planck scale as string theory, which is to say none, because we don't have the technology to test anything directly at that scale.
I keep repeating these things on HNs, but people here fundamentally don't understand how research in theoretical physics is done. I'll try a little exposition:
Physics is: make experiments, and try to infer which laws/rules/formulas are common to all experiments or sets of similar experiments, and their domain of applicability. These are called theories.
Theoretical physics is: think about theories, and try to observe which laws/rules/formulas are common to all theories or sets of similar theories, and their domain of applicability. These are more general theories from which your directly-experimented theories can be derived. You can keep interacting constructing ever more general theories from an ever smaller set of principles.
So a lot of theoretical physics is about arguing which of the principles that you know are true because you've experimentally tested them will hold in circumstances where you can't directly test. As it turns out there's a lot that you can infer about things you've never seem because often times mathematics puts constraints on how different ideas work together.
The string theory/LQG thing is that LQG start from the guess that Lorentz invariance doesn't hold at planck scale. The reason why LQG is less appealing to a lot of physicists is that if you follow this through you can never quite make it mathematically self consistent. In string theory what happens in certain sub-domains is that you start with a lot of arbitrary possibilities, but then you demand certain types of mathematical self-consistency and magically it points out that there's only one or a small number possibilities. A classic example is: "how many dimensions does the universe has?" which no theory really gives as answer, but string theory at least points in a direction: "if you assume such and such, the the allowed answers are such and such". This happens a lot in string theory, and it's what drives people to keep digging. String theory on the other hand concludes that Lorentz invariance must hold at all scales "in some string-like theories" if you demand cancellation of divergences, which you must have for your theory to be renormalizable and therefore mathematically self-consistence. So in a sense this is a prediction of string theory. Not that LQG doesn't predict the opposite, that Lorentz invariance doesn't hold. Instead it assumes that it doesn't. String theory instead predicts that it does. The latter is much more impressive; anybody can start from an arbitrarily picked assumption that noone can prove wrong.
For my part, I know a little bit more than "shit" about physics but I know very little about string theory and know better than to have strongly held opinions about things I don't understand. I've heard quite a lot about the criticisms and would like to hear a defense of it.
And while I disagree with some of the criticisms and some of the style of the crtics, it's not like you get an honest appraisal from Greene (and Witten).
Even accepting the premise that string theory is wrong I can list hundreds of ways the US budget spews money down black holes orders of magnitude bigger. The spending on string theory isn’t even a rounding error compared to the way my tax dollars are allocated to special interest pork.
But only string theory impinges on a generation of cranks who are convinced they alone have the insight into the true ToE and would be recognized as the new Einstein were it not for some entrenched cabal. Maybe I shouldn’t reflexively trust “big science” or something but it’s also not great to evaluate science by who is more charismatically narcissistic on a podcast.
Again, I don’t have a big axe to grind on the merits here. But it’s hilarious that folks with zero science background past middle school hear some of these cranks on YouTube and feel worthy to decry Witten as an enemy of the people. Between the podcast bro who was just told his ToE was right by ChatGPT and Witten I’ll take Witten.
how the government wastes money elsewhere is irrelevant to the conversation. Its about proper management of research funding and how string theorists managed tp trick us into funding failure for whole academic careers.
As a society we can't place excess faith in the orthodox positions of institutions. We all know they can be rigid, wrong, and lock out dissenting views. But society today seems to embrace heterodoxy for its own sake the way perhaps in the past orthodoxy was just accepted on pure faith and there is a vast media ecosystem happy to promote (ie monetize) this worldview. Just because something is heterodox doesn't make it right.
Have a wonderful weekend all.
Let me try to rephrase where I am coming from. I'm going to accept there is a good argument that some science funding should be redirected towards theoretical physicists pursuing alternate approaches.
1. The focus towards this matter in online media circles is vastly disproportionate to the relative impact this has on anyone's life compared to the multitude of other intra-silo disputes across the federal budget. It's not irrelevant to the conversation or at least my subsection of the conversation. It is interesting to me what debates burst through the noise and get traction outside of their own little world. Maybe 1% of the people debating string theory online actually understand a micro-fraction of this stuff. To be clear, I don't claim to be in that 1%. I'm interested in how that happened and the cultural+platform reasons for it. I'm interested in why alongside those genuinely interested in alternative approaches to theoretical physics this topic attracts tons of people who just lump it in with their "they are all lying to you" worldview. Nothing this obscure, incomprehensible, and yes irrelevant to most peoples lives should have organically reached such breakout status. I can ask some of the 22 year old bros at my jiu jitsu gym what they think of string theory and they will tell me it's all part of the omni-conspiracy. It's literally the only science thing they know. It's not like they understand a word of the debate or know of/care about a single other intra-discipline debate about the allocation of resources. 2. No small part of this is the unfortunate emergence of the online narcissist huckster and nothing plays better in online circles than "they" don't want you to know the truth that "I" have the true answer but "Big X" won't admit it. This clown show distracts from the real merits of the relative positions. But it does get the charismatic narcissist a slot on general interest "they are all always lying to you" podcasts. 3. Obviously this doesn't apply to legit physicists and good faith normies who simply disagree with the existing dogma. That's not who I'm talking about. That said, theoretical physics is bargain basement cheap. I don't need to build a supercollider the size of Mars. I don't need to sequence a trillion genomes. I need a laptop, a whiteboard, some time to think, and a bit of ancillary budget. Surely there are enough allied tech/crypto heterodox rich dudes at this point to fund a Center for Heterodox ToEs and staff it with 50 bright people to prove they have something to add. I can't pretend to have the chops to analyze Eric Weinstein's Geometric Unity vs String Theory. I do know if I really thought I had the answer to the universe and his bankroll/connections I'd just fund a real research effort to prove it vs. doing the podcast circuit ad infinitum.