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Approaching 50 Years of String Theory

math.columbia.edu

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Re: Approaching 50 Years of String Theory

#81

Post by steppi »

gnfargbl wrote: post #50

People often say that the problem with string theory is that it doesn't make any prediction, but that's not quite right: the problem is that it can make almost any prediction you want it to make. It is really less of a "theory" in its own right and more of a mathematical framework for constructing theories. One day some unusual observation will come along from somewhere, and that will be the loose end that allows som…

I was planning to make a similar comment. Conjecturing that some theory in the string theory landscape [0] gives a theory of quantum gravity consistent with experiments that are possible but beyond what humans may ever be capable of isn't as strong of a claim as it may first appear. The intuition I used to have was that string theory is making ridiculously specific claims about things that may remain always unobservable to humans. But the idea is not that experiments of unimaginable scale and complexity might reveal that the universe is made up of strings or something, it's just that it may turn out that string theory makes up such a rich and flexible family of theories that it could be tuned to the observed physics of some unimaginably advanced civilization. My impression is that string theory is not so flexible that its uninteresting though. There's some interesting theoretical work along these lines around exploring the swampland [1].

[0] https://en.wikipedia.org/wiki/String_theory_landscape

[1] https://en.wikipedia.org/wiki/Swampland_(physics)

Re: Approaching 50 Years of String Theory

#82

Post by dgfl »

Tadpole9181 wrote: post #69
PunchyHamster wrote: post #48

Earlier quoted context omitted.

Might as well fund someone researching whether quantum theory run on little gnomes, if there is no serious path to verification after 50 years, why not quantum gnomes?

> We should stop funding research into prime numbers. They're stupid and useless. Who cares about them, if they will never be used for anything? Number theory should be stopped, you may as well research gnomes. I imagine this is what you would have sounded like 100 years ago.

You may be understating how much 15 orders of magnitude are.

The only truly exponential technological progress we’ve ever had, transistors, only scaled by ~5 orders of magnitude in feature size. Thermal engines went from maybe 0.1% to ~50%, less than 3 orders of magnitude, in about 200 years. There’s very fundamental physical laws that suggest that engines are done, and transistor scaling as we have known it for 30 years is also done. Perhaps very clever things might give us 5 more orders of magnitude? E.g. truly 3D integration somehow? Then we’re still 5 orders of magnitude off from our target. I can’t think of any technology that ever improved by more than 10^6, perhaps 10^9 if you count some derivative number (like “number of transistors on chip”, rather than actual size), and that’s from literally zero to today. Not from already-pretty-advanced to Death Star scale.

Another perspective is that, to get to those kinetic energies, we need accelerators as large as the solar system. Possibly the galaxy, I can’t quite remember. Will you concede that galaxy-wide objects are so far from current reality that there’s no point seriously talking about them?

Re: Approaching 50 Years of String Theory

#83

Post by tim333 »

jiggawatts wrote: post #80
tim333 wrote: post #78

Earlier quoted context omitted.

Even so I don't get how electrons a meter apart interact through that stuff, as opposed to the electrical fields which spread out through space and so interact with other electrons as featured in quantum field theory which is what physicists use to actually calculate physical results, as opposed to string theory which fails to calculate actual physical results. "if you cut down the spatial dimensions to just 1D" does…

> Even so I don't get how electrons a meter apart interact through that stuff Very roughly: It's possible for point-like (or tiny looped) particles to interact as long as they take every possible path instead of just the one path that would cause a collision. How you interpret this is... up for debate. I prefer the many-world interpretation (MWI), but not everyone agrees. > "if you cut down the spatial dimensions to…

Yeah maybe. My flatmate of some years was doing a PhD in string theory at UT Austin along the lines of "if you cut down the spatial dimensions to just 1D" but he was a mathematician, not really a physicist and was ok with that if it produced interesting mathematics. For real physical things like wiring the lighting system I'd do it because he wasn't so good with that.

I think he went into string research because he was good at maths and there was grant money available for that rather than a deep belief that that was the nature of reality, which is kind of what I mean by sociological factors.

I think much string theory may be like that. Interesting maths but not good at figuring where electrons go.

Re: Approaching 50 Years of String Theory

#84

Post by boznz »

Tadpole9181 wrote: post #68
snapplebobapple wrote: post #60

Earlier quoted context omitted.

you are mixing up gambling spend vs whole industry spend. If string theory was a small handful of people making up a small m*nority of physics departments like non-euclidea geometry research was that would be fine. Its huge swaths of most physics departments and a huge suck on research funding. For that kind of spend you better show results because you are in production phase at that point not lotto ticket moonshit p…

I think you are vastly overestimating the number of string physicists and how much their non-experimental research costs. There's maybe a couple or few hundred-ish in the whole world that focus on it. And they don't need much money because it's pretty much all math.

As a percentage of theoretical physicists it is probably significant though. A Better question is how much love/money/attention is going into rival theories ?

Re: Approaching 50 Years of String Theory

#85

Post by 20k »

BurningFrog wrote: post #75
20k wrote: post #45

Earlier quoted context omitted.

The problem with sabine is that she's become the worst person to make a correct point for the wrong reasons If you do research it becomes pretty apparent that a high number papers are not great. There's varying issues, but a big one is that the funding model incentivises pumping out papers which are often of low quality, researching whatever happens to be in vogue at the moment Literally everyone I've ever talked to…

If I understood this, you agree with Sabine, but since she's "in bed with right wing grifters" she should not be listened to? This is not very persuasive.

I agree with a part of Sabine's overall output, but she's increasingly misidentifying some of the problems and the solutions because she's drifted too far towards the grifters

To a large degree if you're trying to successfully trying to push for change, it really matters that the person pushing for it is credible. Someone like ben goldacre is able to credibly make a strong push for change within medicine because they've maintained credibility, someone like sabine makes the situation worse because they've chucked it away

Re: Approaching 50 Years of String Theory

#86

Post by BurningFrog »

20k wrote: post #85
BurningFrog wrote: post #75

Earlier quoted context omitted.

If I understood this, you agree with Sabine, but since she's "in bed with right wing grifters" she should not be listened to? This is not very persuasive.

I agree with a part of Sabine's overall output, but she's increasingly misidentifying some of the problems and the solutions because she's drifted too far towards the grifters To a large degree if you're trying to successfully trying to push for change, it really matters that the person pushing for it is credible. Someone like ben goldacre is able to credibly make a strong push for change within medicine because they…

Maybe it's like this:

Sabine's has a day job as a Youtuber, and she makes her videos from that perspective. She speaks her mind, makes a decent living, and educates some science nerds on the way. Seems pretty nice.

From the perspective of accomplishing institutional change in the academic physics world, this is does nothing. The institutional powers don't react at all to a complaining influencer with an Einstein doll.

And I suspect she's perfectly fine with that. Overturning the Physics establishment is a near impossible task. I would leave that for those mad enough to try.

Re: Approaching 50 Years of String Theory

#87

Post by XorNot »

gnfargbl wrote: post #56
pfdietz wrote: post #52

Earlier quoted context omitted.

Or, that day will never come, because string theory isn't reflective of the actual world, or because there are so many theories possible under the string theory rubric that we can never find the right one, or because the energies involved to see any effect are far beyond what could be reached in experiment.

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.

There is not a "huge chunk" of the theoretical physics community working on string theory, and their never was. For one, it is far less common a topic of research now then it was earlier when it was more popular, but even then "huge" was really "a lot of universities had a grant for string theory investigation because it looked promising".

It mostly hasn't worked out and now people are moving on to other things.

The single worst thing that happened though was the populism: a small group of people with credentials started putting out pop-sci books and doing interviews, well in excess of what their accomplishments should mean. People are like "so many people are working on this" because there were like, 3 to 5 guys who always said "yes" to an interview and talked authoritatively.

Re: Approaching 50 Years of String Theory

#88

Post by XorNot »

atakan_gurkan wrote: post #19
SiempreViernes wrote: post #17

Earlier quoted context omitted.

I think that's not quite right: it is reasonably certain that string theory can produce both the standard model and most extensions people have dreamt up, so the problem is rather that all the obviously "stringy" predictions are currently unavailable, while the string theory derived predictions for achievable experiments look like what we get from other theories we already have.

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".

You write this as though reality is a 4X game and we're obviously wasting time not clicking on the other item in the tech tree to optimize the build.

Re: Approaching 50 Years of String Theory

#89

Post by XorNot »

tim333 wrote: post #83
jiggawatts wrote: post #80

Earlier quoted context omitted.

> Even so I don't get how electrons a meter apart interact through that stuff Very roughly: It's possible for point-like (or tiny looped) particles to interact as long as they take every possible path instead of just the one path that would cause a collision. How you interpret this is... up for debate. I prefer the many-world interpretation (MWI), but not everyone agrees. > "if you cut down the spatial dimensions to…

Yeah maybe. My flatmate of some years was doing a PhD in string theory at UT Austin along the lines of "if you cut down the spatial dimensions to just 1D" but he was a mathematician, not really a physicist and was ok with that if it produced interesting mathematics. For real physical things like wiring the lighting system I'd do it because he wasn't so good with that. I think he went into string research because he w…

Except this is how electrons actually go, and it has real testable consequences. The question I'm aware of (because it related to my degree in nanotechnology) was: are metals conductive at different dimensionalities?

Because at the nanoscale, you in fact can have 1D, 2D and 3D metals. 3D metals are bulk solids - like we're familiar with. 2D metals are planes of single (or very few) atoms. 1D metals are lines - think placing individual metal atoms down in a row - nanotubes are a practical example.

All real, possible structures to build.

When you do measurements on all these structures you get...weird answers. Like is a nanotube a superconductor? And the answer is...yes, but also no. Yes because you'll in fact view superconductivity like behavior, but no because actually it's a ballistic electron conductor - at the right energy level an electron bounces through the thing without hitting it, but not all electrons can do that at all energy levels, so you still measure a voltage across a nanotube between two conductors.

But a nanotube is 1D - we only have 1 dimension things move in (from one end to the other). So - conductive, not a superconductor, but you can kind of use it like one sometimes. And we know 3D metals are conductors - that's obvious right...so what are 2D metals? Presumably conductors right...?

And the answer is...nope, insulators - at least sometimes. And the reason is because the sum of all possible electron paths in a 2D metal is the electron always returns back to where it started - and those grow much faster mathematically then paths where the electron ends up somewhere else.

But only in 2D: in the 1D case most paths take you out of the conductor. And in the 3D case, the number of paths which land you somewhere else grows much faster then those which loop back, due to the extra dimension of freedom. But 2D metals are constrained - for any given path elsewhere, there are mathematically far more that land back where you started. This is observable, measurable behavior which is a topic of research for future semiconductors. Yet it's almost entirely quantum probability based behavior.

Re: Approaching 50 Years of String Theory

#90

Post by ecosystem »

constantcrying wrote: post #74
ecosystem wrote: post #30

Earlier quoted context omitted.

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.

>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. This is just a lie though. Non-Euclidean geometry is a mathematical model of how distances behave on non-linear spaces. Nobody ever believed it to be a "fundamental mistruth", even suggesting it would look ridicu…

This is a generally known part of the history of mathematics.

> Nobody ever believed it to be a "fundamental mistruth"

https://math.libretexts.org/Courses/College_of_the_Canyons/M...

"Lobachevsky [mathematician contemporary of Gauss, who claimed parallel postulate was unnecessary] was relentlessly criticized, mocked, and rejected by the academic world. His new “imaginary” geometry represented the “shamelessness of false new inventions”"

Further, many claimed premature success in finding logical contridictions in geometry lacking parallel (Euclid's 5th) postulate; which meant they believed a 4-postulate geometry to be fundamentally false.

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