Any infinitesimally small particles?

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Discussion Overview

The discussion revolves around the concept of infinitesimally small particles, particularly in the context of fundamental particles in physics. Participants explore various theories, including quantum mechanics, string theory, and Einstein-Cartan theory, while debating the implications of these theories on the size of particles.

Discussion Character

  • Debate/contested
  • Exploratory
  • Technical explanation

Main Points Raised

  • Some participants question the meaning of "infinitely small" and whether any particle can be considered as such.
  • It is noted that fundamental particles are often treated as point particles with no discernible size, according to mainstream quantum mechanics and the standard model.
  • String theory is mentioned as a framework that suggests particles are not point-like but rather one-dimensional strings whose properties are determined by their vibrational patterns.
  • Einstein-Cartan theory is introduced as another perspective that posits fermions may have finite sizes, though the reasoning behind this is not fully explained.
  • Some participants argue that composite particles, such as protons and neutrons, cannot be considered point-like despite being made of point particles, citing their non-zero size.
  • There is a contention regarding the implications of the macroscopic world, with some arguing that it serves as a counterexample to the notion that composite particles must be point-like.
  • A participant references experimental findings regarding the electron's shape, indicating ongoing uncertainty about the sizes of fundamental particles.

Areas of Agreement / Disagreement

Participants express differing views on whether particles can be considered infinitely small or point-like, with no consensus reached. The discussion remains unresolved regarding the implications of various theories on particle size.

Contextual Notes

Some arguments rely on specific interpretations of theories and may depend on definitions of size and structure, which are not universally agreed upon. The discussion highlights the complexity and nuance in understanding particle physics.

Gnomie27
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is there any particle that is infinitely small? is there anything at all that's infinitely small?

i might have been inclined to say a singularity, but last i checked someone "[took] the singularity out of the black hole".

thanks
 
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Depends on what you mean by 'infinitely small'.
 
As far as we can tell today all fundamental particles are point particles meaning they have no internal structure or discernible size. String theory predicts however they are not points but strings.

Thanks
Bill
 
Last edited:
If one considers mainstream QM and SM,the answer is yes,all fundamental particles are point-like,infinitely small.And by combining such point particles you can't get a particle with finite size,so I guess composite particles should be considered point-like too.
But if you want to consider other theories too,I can give you some examples that suggest finite sizes for elementary particles.One of them is string theory which says that the particles are in fact vibrating strings which their vibration patterns determine their properties.
Another example is Einstein-Cartan theory,an extension to GR.It requires the fermions to have finite sizes(I don't know the reason).
And...mmmm...back to the QM...considering particles as point-like makes some troubles which are cured by a process called renormalization.Some people don't like it because it doesn't seem so physical to them!Although I remember there was a physical interpretation to it that made things OK but I'm not sure.
Anyway,although mainstream physics is considering elementary particles as point-like,here and there you can find some little clues stating the contrary!
 
Shyan said:
And by combining such point particles you can't get a particle with finite size,so I guess composite particles should be considered point-like too.

The entire macroscopic world is a counterexample to this non sequitur.
 
Nugatory said:
The entire macroscopic world is a counterexample to this non sequitur.


No,it is not.Most of the volume of all materials is empty space.Matter exists because of that empty space and various kinds of repulsive forces.In fact a simple analysis will show that the world doesn't need finite sizes for composite particles for its existence
 
A baseball is a composite particle. It does not have infinitesimal size.
 
Vanadium 50 said:
A baseball is a composite particle. It does not have infinitesimal size.

A baseball is what I call "matter"...by composite particle I mean protons,neutrons etc...I think I don't have to explain the difference,its just obvious!
 
  • #10
Shyan said:
A baseball is what I call "matter"...by composite particle I mean protons,neutrons etc...I think I don't have to explain the difference,its just obvious!

OK, let's look at a proton or a neutron. It clearly has a non-zero size; and it is composed of three point-particle quarks and a bunch of empty space. I'm still seeing a counter-example to your (IMO absurd) claim that a particle composed of point particles must itself be a point particle.
 
  • #11
Nugatory said:
OK, let's look at a proton or a neutron. It clearly has a non-zero size; and it is composed of three point-particle quarks and a bunch of empty space. I'm still seeing a counter-example to your (IMO absurd) claim that a particle composed of point particles must itself be a point particle.

Oh...sorry...you know,looks like I wasn't looking at it!
Suddenly it came in front of my eye and I now see I was wrong.
Well,sometimes it happens...temporary foolishness about a particular subject!
 
  • #12
Shyan said:
Another example is Einstein-Cartan theory,an extension to GR.It requires the fermions to have finite sizes(I don't know the reason).
Connections in Einstein-Cartan theory are not assumed to have vanishing torsion unlike in GR. That is where it comes from.
 

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