Physicist here. My PhD is in an area that was spawned into existence due to inspiration coming from string theory, not string theory proper.
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.
The legit criticism with a legit recommended change is even better.
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.
I tend to agree. Science funding is unfortunately a limited resource, and I would like to see different approaches explored in more detail, which unfortunately would imply less (but not zero) funding to string theory. Not zero, because we also don’t want the competence built up in string theory groups to die out completely, in case that remains our best lead.
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".
I'm legit interested in hearing more about this, like YouTube series, popsci books, magazines - I've been meaning to read Zwiebach's A first course, but I keep getting distracted with background reading and then never get back to it.
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I don't entirely understand where that comes from. The Standard Model and General Relativity are both tested to extreme precision. Any experiment unifying them will have to involve insane energies. It's not as if there is some other model with easy tests that we've agreed to ignore.
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.
> I don't entirely understand where that comes from. The Standard Model and General Relativity are both tested to extreme precision. Any experiment unifying them will have to involve insane energies. It's not as if there is some other model with easy tests that we've agreed to ignore.
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.
Perhaps you could elevate the discussion by providing an actual argument against this view of string theory, which has indeed percolated through social media?
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.
Ive been told my multiple High Energy Physicists that String Theory was suspect because it makes no predictions. Being able to make predictions that are testable is a foundation of theoretical science. Not everything is because of influences.
Eh... mainstream physics by numbers is not HEP and definitely not HEP Th, and there are plenty of serious physicists somewhat critical of the field, and more so of the way it presented itself over the last decades.
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).
Physicist here. Would you like to enrich our world view by linking to counter-examples?
My understanding was that string theory being more "hypothetical physics" than "theoretical physics" at this point is still a pretty legit criticism.
Physicist here. My PhD is in an area that was spawned into existence due to inspiration coming from string theory, not string theory proper.
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.
[1] https://news.ycombinator.com/item?id=46336655
The legit criticism with a legit recommended change is even better.
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.
I tend to agree. Science funding is unfortunately a limited resource, and I would like to see different approaches explored in more detail, which unfortunately would imply less (but not zero) funding to string theory. Not zero, because we also don’t want the competence built up in string theory groups to die out completely, in case that remains our best lead.
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".
I'm legit interested in hearing more about this, like YouTube series, popsci books, magazines - I've been meaning to read Zwiebach's A first course, but I keep getting distracted with background reading and then never get back to it.
From the FAQ
* Be kind. Don't be snarky. Converse curiously; don't cross-examine. Edit out swipes.
* Comments should get more thoughtful and substantive, not less, as a topic gets more divisive.
* Please don't fulminate. Please don't sneer, including at the rest of the community.
* Eschew flamebait. Avoid generic tangents. Omit internet tropes.
* Please don't post shallow dismissals, especially of other people's work. A good critical comment teaches us something.
* Please don't post insinuations about astroturfing, shilling, brigading, foreign agents, and the like. It degrades discussion and is usually mistaken. If you're worried about abuse, email hn@ycombinator.com and we'll look at the data.
Wow their comment history isn’t much better, is there downside or anything that repeat low-value commenters face?
I've had dang on my case, threatening to ban me if I kept it up.
Rather than inb4, you'll make a stronger case by rebutting any of those comments you see come up in the thread.
Not really a rebuttal, but a discussion of how I see the situation: https://news.ycombinator.com/item?id=46336655
I don't entirely understand where that comes from. The Standard Model and General Relativity are both tested to extreme precision. Any experiment unifying them will have to involve insane energies. It's not as if there is some other model with easy tests that we've agreed to ignore.
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.
> I don't entirely understand where that comes from. The Standard Model and General Relativity are both tested to extreme precision. Any experiment unifying them will have to involve insane energies. It's not as if there is some other model with easy tests that we've agreed to ignore.
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.
Perhaps you could elevate the discussion by providing an actual argument against this view of string theory, which has indeed percolated through social media?
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.
I have a lot more to say, but I wrote a little bit here: https://news.ycombinator.com/item?id=46336655
Ive been told my multiple High Energy Physicists that String Theory was suspect because it makes no predictions. Being able to make predictions that are testable is a foundation of theoretical science. Not everything is because of influences.
Eh... mainstream physics by numbers is not HEP and definitely not HEP Th, and there are plenty of serious physicists somewhat critical of the field, and more so of the way it presented itself over the last decades.
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).