Approaching 50 Years of String Theory

Theoretical physics is subsidizing a handful of people sitting at white boards.

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.

Non-Euclidean geometry (geometric axioms in which one postulate is rejected such that the 3 angles of a triangle are not exactly 180 degrees) was considered a meaningless word game and fundamental mistruth.

Later, non-Euclidean geometry was actually essential to modern physics.

It's intellectually sketchy to judge future value by the present.

Planck energy: ~10^19 GeV is approx 2 GJ per collision

Energy to vaporize Earth's oceans: ~4 x 10^27 J

For a Planck-scale linear collider at LHC-like collision rates (~10^8/sec):

Beam power requirement: ~2 x 10^17 W

With realistic wall-plug efficiency of ~1%: ~2 x 10^19 W

Annual energy consumption: ~6 x 10^26 J

At 1% efficiency, one year of operation would:

Vaporize about 15% of Earth's oceans

Or vaporize the Mediterranean Sea roughly 50 times

Or boil Lake Superior every 5 hours

Or one complete ocean vaporization every 6-7 years of operation

It's about 1 million times current global power consumption

Or about 50,000 Suns running continuously

Or 170 billion Large Hadron Colliders operating simultaneously

Interesting, thanks for sharing!

I definitely don't walk away from any of Brian Greene's content thinking that String Theory is anything close to a confirmed fact at all.

It's been some times since I read his earlier books, possibly his tone has changed?

I'll also say, I'm far from a professional physicist. I'm reading and watching for fun and intellectual curiosity, not to learn physics with the goal of doing my own research. I always thought of String Theory as being more of a study of math where many people have unsuccessfully tried to apply it to physics. And, that it's lead to some really interesting ideas. I just find him and his work really enjoyable.

Thanks for posting that; as soon as I saw the title here I was going to look that up if no one else had already. Sabine Hossenfelder too, though there's far too much content from her on this to put a list, but anyone interested might like some of her takes.

A few debates between Brian and other notables; Hossenfelder, Eric Weinstein, and Roger Penrose to name a few; have popped up in my youtube feed lately which are typically also engaging.

It isn't completely implausible that a future civilisation could perform the experiments to gather that data, somehow; but it is hard to envisage how we do it here on Earth.

Your implicit point is a good one. Is it sensible to have a huge chunk of the entire theoretical physics community working endlessly on a theory that could well end up being basically useless? Probably not.

To make this valuable, it should produce a limited set including standard model. If you produce pretty much everything one can dream of, that does not carry predictive power.

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".

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what didn't se develop because those people were working on string theory? That is an unanswerable question. It is also the important question.

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'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.

Wow their comment history isn’t much better, is there downside or anything that repeat low-value commenters face?

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.

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.

I have a lot more to say, but I wrote a little bit here: https://news.ycombinator.com/item?id=46336655