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According to the latest information we got

String theory is a theoretical framework in which the point-like particles of particle physics are replaced by one-dimensional objects called strings.

We know that anything we've ever seen on a microscopic level or a gigantic level that matter has thickness? let it's thickness be 1.6 x 10-35 m (Plank length) or let it be 1 m , It has some thickness. Right?

So everything we've seen is 3-dimensional right? no matter how much we zoom , we get protons that have thickness.
So if matter has thickness then how can we say that Something is "1-dimensional".

Anything that's 3D is made up of something 3D. If we add 0 thickness we get 0 thickness but if we add some thickness like atoms and molecules we get 3D matter as the constituents have thickness.

Then how particles of particle physics are replaced by one-dimensional objects called strings?

Qmechanic
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weegee
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  • Just because something is 1D does not mean it cannot exits in multiple dimensions. Example: Origami (2D existing in 3D) – BioPhysicist Sep 28 '18 at 17:03
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    In modern non-string theoretic quantum theory, particles are considered 0-dimensional objects. Any thickness attributable to fundamental particles is an artifact of quantum uncertainty. Regardless, what have the dimensions of particles/strings to do with the dimensionality of space? – bapowell Sep 28 '18 at 17:05
  • I'm sorry but i'm not talking about the perception of what folds and origami illusions. I'm talking at the atomic level @AaronStevens – weegee Sep 28 '18 at 17:06
  • @daksh I should have said origami as an analogy. And technically you are speaking about subatomic (or even "sub-subatomic") levels. A 1D material could still exhibit "thickness" in multiple dimensions. – BioPhysicist Sep 28 '18 at 17:08
  • if particles made up matter which is 3-D then how come they are considered as 0-dimensional? – weegee Sep 28 '18 at 17:09
  • @AaronStevens if it possess thickness then how can it be 1-D? – weegee Sep 28 '18 at 17:09
  • The material doesn't need to have thickness to "exhibit" thickness (i.e. how matter is made of point particles). But this is a pointless discussion. I am far from a string theory expert (or I would say even somewhat knowledgeable about it), but I am pretty sure particles arise from how these strings in string theory vibrate. In any sense, you are trying to apply classical reasoning to a non-classical theory. – BioPhysicist Sep 28 '18 at 17:12
  • And in terms of point particles making up 3D space, there is (relatively) a lot of empty space between particles in matter. The structure of matter is held together through interactions between atoms of the matter. At the atomic level, matter is not a continuous distribution of particles. – BioPhysicist Sep 28 '18 at 17:13
  • daksh, 'pointlike particle' doesn't mean what you likely think it means in the context of quantum field theory (the context of the Standard Model). For example, see the answer here: "Pointlike is a technical term that refers to the fact that in the standard model, the Lagrangian is a function of fields at the same point (rather than of integrals over fields in some small neighborhood of this point, described by form factors specifying the ''form'' of the particle). " – Hal Hollis Sep 28 '18 at 17:16
  • I understand the concept of point like in terms of quantum mechanizes @HalHollis But is there a limit to zoom in matter? i mean if we break down a "point", do the inner constituents will be particles? Do anything with 0 thickness exists? or if it's thin or lesser than plank length, it still has thickness? – weegee Sep 28 '18 at 17:20
  • Related: https://physics.stackexchange.com/q/319180/2451 – Qmechanic Sep 28 '18 at 17:34
  • This question is too broad as it touches on multiple disparate issues at once: 1. The relation between string theory and quantum particles/matter, cf. https://physics.stackexchange.com/q/305760/50583, https://physics.stackexchange.com/q/293947/50583. 2. The relation between quantum objects and macroscopic matter, cf. https://physics.stackexchange.com/q/126512/50583 3. A hypothetical question about how 0-dimensional objects could or could not make up 3d objects. Please narrow the question down (after making sure it is not answered in the links I provided) so that you can receive focused answers – ACuriousMind Sep 28 '18 at 18:16

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Consider an electron. An electron is an elementary particle whose observed size is small enough that if it was exactly zero there would be no difference in our observations. (Except (I think?) that the implication of being point-like would mean that electrons are naked ring singularities, but as GR and QM don't play nicely together and string theory is an effort to resolve that failure, that's something I'm going to merely acknowledge and not deal with).

Despite being zero-dimensional, electrons still:

  1. Create a 3-dimensional electric force field around themselves, pulling them towards positively charged objects like protons.

  2. Are subject to Heisenburg uncertainty, putting them into a superposition of many possible positions. An important part of this point is that from the way they behave, electrons look like a superposition of point-like particles and not like a particle with non-zero radius.

  3. Are subject to certain constraints on their location, so that when they 'orbit' a proton in a certain way, the wave function describing the probability of being in any given position looks like a shell. Note that this is different from saying "the electron itself is shaped like a shell", as this is just the probability that any given observation will detect the electron in any given position. Because of the nature of these constraints, atoms can bind in interesting ways with complicated and stiff 3-dimensional structures.

For non-elementary particles such as protons and neutrons, a similar argument applies to the smaller fundamental particles that they are made from.

BenRW
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  • "An electron is an elementary particle whose observed size is small enough that if it was exactly zero there would be no difference in our observations." and then we discovered quarks which were smaller. – weegee Sep 28 '18 at 18:16
  • @daksh I think you're mixing up electrons and protons. Quarks and electrons are both point-like, protons are made of multiple quarks and have spacial extent. – BenRW Sep 28 '18 at 18:19
  • No i'm talking about "particles" – weegee Sep 28 '18 at 18:19
  • @daksh Quarks, protons and electrons are all 'particles'. Please rephrase. – BenRW Sep 28 '18 at 18:21
  • All i'm trying to say is that particles or matter cannot exists with 0 thickness. You are saying that the observations are negligible which i think is irrelevant here because we just "need Observations here" to prove – weegee Sep 28 '18 at 18:23
  • Then Let all the observations go aside and think simply that if we add trillions of particles with 0 thickens then will the sum thickness be more than 0? To obtain a particles in 3-D something has to be there with thickness right? no matter how small we can zoom @BenRW – weegee Sep 28 '18 at 18:30
  • @daksh No, it is not necessary, for the reasons which I listed. – BenRW Sep 29 '18 at 10:25
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The structures of matter forms from the interaction of different fileds and not directly from the structures of elementary particles

From the standard model of particle physics, all massive particles get their masses from the Higgs field and these masses are just energies bounded-intrinsically to the particles. Therefore all the masses we see around as is actually just the sum of elementary particles masses and potential energies of their interactions.

The rest mass together with other quantum numbers like spin, elctric charge is what gives a particle a unique identity and structure. Even the atoms do not have structure because of the structures of its constituents particles. For example, we know that a atom is 99.99% empty, for comparison, if we assume a neucleus to be a coin sized sphere then a atom would be a big-football-ground sized sphere!. The 3d structure of an atom is not because of structures of nucleus or/and electron but because of the electromagnetic interaction between p and e-.

If the string theory is the correct description for our universe then all the particles present in the universe are nothing but just different modes of the same fundamental vibrating strings. Different modes of vibration of different strings gives different particles(one string mode ~ one particle). These particles structures, again, does't depend directly on 1d-strings, it depends on energy or field surrounding string. For comparison, if we assume a string to be of the size of a tree then the minimum size of an elementary particle is around the size of the whole solar system! i.e., an elementary particle is much more emtier then an atom.

Aman pawar
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