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Pardon my terminology, I might be using the words wrong. I watched Susskind string theory course, where he explained the attempt to describe particles using vibrating strings instead of point particles. If you do this you need to have more than 3 spatial dimensions or otherwise there is some problem that I cannot remember (I cannot find the part in the video where he talks about this). Then he explained that string theory also predict all kind of other stuff such as d-branes.

My question is: If instead of attempting to describe elementary particles by vibrating open strings, you attempt to do it by vibrating open 3d volumes (so a particle would have a small volume in our 3D space, and an "open" volume, not one closed into hidden higher dimensions), then, would you still need extra dimensions?

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    $\begingroup$ @ConnorBehan If my assumption that string theory did describe those 3-branes, is there any obvious reason why no one has attempted that path? it should not be much more complicated than considering strings but it might work as considering a particle as a little volume makes more sense than considering it a 1D object $\endgroup$
    – user338734
    Sep 9, 2022 at 0:52
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    $\begingroup$ The reason is that it actually would be much more complicated :). $\endgroup$ Sep 9, 2022 at 1:29
  • $\begingroup$ OP's phrase attempt to do it by vibrating open 3d volumes (v1) seems to be asking for a quantum membrane theory. Possible duplicate: Why one-dimensional strings, but not higher-dimensional shells/membranes? $\endgroup$
    – Qmechanic
    Sep 9, 2022 at 4:01
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    $\begingroup$ There actually are a handful of models in which they do attempt to get everything from a 3-brane, e.g. arxiv.org/abs/hep-th/0508089, but the extra dimensions are still there as well. $\endgroup$ Sep 9, 2022 at 5:23
  • $\begingroup$ @Qmechanic I checked the duplicate answers which are talking of mathematics, but the use of string theories in physics is for the possible representation of particles as vibrations on strings, I do not think the linked duplicate answers answer the OP question. $\endgroup$
    – anna v
    Sep 9, 2022 at 17:27

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using vibrating strings instead of point particles.

,,,

you attempt to do it by vibrating open 3d volumes (so a particle would have a small volume in our 3D space, and an "open" volume, not one closed into hidden higher dimensions), then, would you still need extra dimensions?

There is a misunderstanding on how particles are represented in string theories. Analogous to the "point" in the term "point particles" the dimension is expanded to a string. The point is not represtnting a particular particle, and similarly the string is not the particle. All particles in the standard model are point particles, and points cannot be distinguished as to their space characteristics. In the same way, strings cannot be distinguished as to their space characteristics.

It is the vibrations on the string which have the group structure that can represent the elementary particle table correctly, with the standard model and its SU(3)xSU(2)xU(1) symmetries. Each particle in the table linked, is assigned/occupies a unique vibration of the string, that vibration has the specific particle quantum numbers.

So the " vibrating open 3d volumes" would just make mathematics much more complicated , vibrations of the 3 dimensional volume being a lot more complex.

You would still need extra dimensions.

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