How to imagine the tenth dimension

[RozKek]

If there are more dimensions than 3, is it even possible to detect them somehow, to find out that they actually are.

Absolutely, depending on what their properties are. First of all, if they are curled up (and that's the most common assumption to render them invisible to everyday experience), how and whether they can be detected experimentally depends on two factors:
1. which fields and particles can move in them
2. how large they are

If none of the known particles, but only gravity, can actually propagate through the extra dimensions, they must be relatively large to be noticed in experiments such as the LHC (for example, if there are two extra dimensions in which none of the known particles can move, they must be of micrometer size to be visible in next generation colliders)

If some of the known particles can move in the extra dimensions, possibly all of them, this means that everything including ourselves is spread out in the extra dimension(s) via quantum uncertainty. The fields which move in the extra dimensions can form resonances much like the acoustic standing waves you notice at certain frequencies in a small room. In particle physics, those resonances manifest as a repeating pattern of heavier copies of the existing particles, calles "Kaluza-Klein-Modes". Searches for such extra-dimensional resonances are ongoing at the LHC, but so far haven't yielded results.

Wow, thanks. This was actually really cool and interesting, is this theoretical physics?

[Alex K]

Absolutely, depending on what their properties are. First of all, if they are curled up (and that's the most common assumption to render them invisible to everyday experience), how and whether they can be detected experimentally depends on two factors:
1. which fields and particles can move in them
2. how large they are

If none of the known particles, but only gravity, can actually propagate through the extra dimensions, they must be relatively large to be noticed in experiments such as the LHC (for example, if there are two extra dimensions in which none of the known particles can move, they must be of micrometer size to be visible in next generation colliders)

If some of the known particles can move in the extra dimensions, possibly all of them, this means that everything including ourselves is spread out in the extra dimension(s) via quantum uncertainty. The fields which move in the extra dimensions can form resonances much like the acoustic standing waves you notice at certain frequencies in a small room. In particle physics, those resonances manifest as a repeating pattern of heavier copies of the existing particles, calles "Kaluza-Klein-Modes". Searches for such extra-dimensional resonances are ongoing at the LHC, but so far haven't yielded results.

Wow, thanks. This was actually really cool and interesting, is this theoretical physics?

Yes. Especially starting in the late 90s, there was a considerable section of the theoretical physics community working on these hypothetical models with extra dimensions. The trend was ignited by results in Superstring Theory which had indicated that extra dimensions might plausibly be large enough to be detectable, something that was previously considered impossible. By the time I did my Master's on some theoretical consistency issues in extra dimensions in '05, interest in the community was already starting to wane a bit because most plausible ideas had been worked out. Nowadays, people are mostly waiting for the experimental results.

[Autumnlicious]

String theory (and the rest of its familial variants) has yet to deliver any compelling evidence. Some models are conveniently impossible to test for, requiring on the order of one or two universes worth of energy.

It's a blight that experimentalists are slowly dismantling and making room for new theoretical models that actually match the data. I remember at several points in time for the LHC there was a discussion of "if we get results in $band of energy, it will provide some evidence for string theory/super symmetry variant $X". And every time they found nothing.

Woit continues to be well founded in his criticism, much to the annoyance of Smolin et al.

[Alex K]

String theory (and the rest of its familial variants) has yet to deliver any compelling evidence. Some models are conveniently impossible to test for, requiring on the order of one or two universes worth of energy.

It's a blight that experimentalists are slowly dismantling and making room for new theoretical models that actually match the data. I remember at several points in time for the LHC there was a discussion of "if we get results in $band of energy, it will provide some evidence for string theory/super symmetry variant $X". And every time they found nothing.

Woit continues to be well founded in his criticism, much to the annoyance of Smolin et al.

A lot of unscientific BS has been said by string theorists over the years, and "if we find X at the LHC, that's evidence for string theory" is mostly in that department if you ask me. If extra dimensions or supersymmetry or that sort of thing would be discovered at the LHC after all, those could of course exist without there being string theory behind it. Only in a very special scenario with very light string resonances would it actually be possible to observe the stringyness of particles in the lab and thus really collect direct evidence for strings, but nature doesn't need to be like that. That being said, Peter Woit now saying "told you so" is not something that I find very impressive - you can always make it your hobby to shit on a speculative enterprise and then gloat -, but he has one point, the work on Superstring theory was overhyped especially in the US, and having bullshitters like Michio Kaku on all channels doesn't help. My most cited paper is on higgs physics in a string model, go figure...

[TheRealJoeFish]

Ah I hoped this was this vid! I saw this in college and it was awesome!