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String theory has always seemed intuitively wrong to me. From Wikipedia: >In theories of particle physics based on string theory, the characteristic length sca

by tim333 11mo ago

String theory has always seemed intuitively wrong to me. From Wikipedia: >In theories of particle physics based on string theory, the characteristic length scale of strings is assumed to be on the order of the Planck length, or 10E−35 meters Yet electrons repel each other over distances of many meters by I think the virtual exchange of photons. How on earth would that work? How does your photo string know to head to an electron string trillions and trillions of times it's length away? As far as I can tell the field became popular for sociological reasons that you could get grants for it and the like rather than any connection to reality(?)

jiggawatts 11mo ago
You're being somewhat unfairly voted down, it's a legitimate questions because the popular media so grossly misrepresents what string theory is, especially in their visuals. It's hard to visualise in 3D, but if you cut down the spatial dimensions to just 1D (a line), then theories like string theory just turn the infinitely thin mathematical line into a tube. You can picture a tube that vibrates, or has waves in its cross-section. Don't think of the the "strings" as actual little loops moving around in space, they're a modification of what space is. You can even do the same kind of line->tube extension of a space with even more extra "loop" dimensions than the number of base dimensions. AFAIK the current theories have 10 total, of which 3 are the usual "large" dimensions of space, the rest are "small" and rolled up like the tube example.
- tim333 11mo ago
  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" doesn't sound very physical to me. I'm maybe being downvoted fairly. I studied physics and it don't think it's a misunderstanding of popularisation or that string theory is untestable, I just think it's straight wrong and not how the physical universe works.
  - jiggawatts 11mo ago
    > 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 just 1D" doesn't sound very physical to me That's just a simplification to aid understanding, it's now how the theory actually works.
    - tim333 11mo ago
      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.
      - XorNot 11mo ago
        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.
ajkjk 11mo ago
whether or not string theory is at this point grifty and weird, the theoretical basis for it is far stronger than you would think based only on reading critics / pop sci explainers. It is not like, missing any obvious physical facts in its foundation. Rather it is trying to say: look, we have this zoo of particles with seemingly random masses and properties; is there same lower-level framework which can produce the zoo that we see according to a simpler list of rules? The obvious choice for this, especially given some of the "hierarchies" of particles that are observed, is that they are in some way resonant modes of some kind of underlying object. Which is where you get the strings from. (Which might sound like a weird justification if you are not aware of all the other aspects of physics which get explained as resonances of fields; this is a standard sort of justification which there's a lot of good reasons to be interested in, at least initially.)
CubicLettuce 11mo ago
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by tim333 11mo ago

jiggawatts 11mo ago

You're being somewhat unfairly voted down, it's a legitimate questions because the popular media so grossly misrepresents what string theory is, especially in their visuals. It's hard to visualise in 3D, but if you cut down the spatial dimensions to just 1D (a line), then theories like string theory just turn the infinitely thin mathematical line into a tube. You can picture a tube that vibrates, or has waves in its cross-section. Don't think of the the "strings" as actual little loops moving around in space, they're a modification of what space is. You can even do the same kind of line->tube extension of a space with even more extra "loop" dimensions than the number of base dimensions. AFAIK the current theories have 10 total, of which 3 are the usual "large" dimensions of space, the rest are "small" and rolled up like the tube example.

tim333 11mo ago
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" doesn't sound very physical to me. I'm maybe being downvoted fairly. I studied physics and it don't think it's a misunderstanding of popularisation or that string theory is untestable, I just think it's straight wrong and not how the physical universe works.
- jiggawatts 11mo ago
  > 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 just 1D" doesn't sound very physical to me That's just a simplification to aid understanding, it's now how the theory actually works.
  - tim333 11mo ago
    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.
    - XorNot 11mo ago
      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.

ajkjk 11mo ago

whether or not string theory is at this point grifty and weird, the theoretical basis for it is far stronger than you would think based only on reading critics / pop sci explainers. It is not like, missing any obvious physical facts in its foundation. Rather it is trying to say: look, we have this zoo of particles with seemingly random masses and properties; is there same lower-level framework which can produce the zoo that we see according to a simpler list of rules? The obvious choice for this, especially given some of the "hierarchies" of particles that are observed, is that they are in some way resonant modes of some kind of underlying object. Which is where you get the strings from. (Which might sound like a weird justification if you are not aware of all the other aspects of physics which get explained as resonances of fields; this is a standard sort of justification which there's a lot of good reasons to be interested in, at least initially.)

CubicLettuce 11mo ago

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