Questions tagged [point-particles]
240 questions
63
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7 answers
Do electrons have shape?
According to the Wikipedia page on the electron:
The electron has no known substructure. Hence, it is defined or assumed to be a point particle with a point charge and no spatial extent.
Does point particle mean the particle should not have a…
Anil Bharadia
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Where is the evidence that the electron is pointlike?
I'm writing a piece about the electron, and I'm having trouble finding evidence to back up the claim that the evidence is pointlike.
People tend to say the observation of a single electron in a Penning trap shows the upper limit of the particle's…
John Duffield
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30
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4 answers
Is there anything in the universe that cannot be compressed?
I've always thought that there is nothing in the universe that cannot be compressed or deformed under enough force but my friend insists that elementary particles are exempt from this.
My thought is that if two such objects collided, since there is…
jeremy south
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6 answers
If particles are points, then aren't atoms empty space?
Zero dimensional points do not take up space, so then wouldn't everything in the universe be literally empty? Or is there something that I'm missing?
user86072
29
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2 answers
Can the center of charge and center of mass of an electron differ in quantum mechanics?
Traditionally for a free electron, we presume the expectation of its location (place of the center of mass) and the center of charge at the same place. Although this seemed to be reasonable for a classical approximation
(see: Why isn't there a…
J C
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27
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How can neutral atoms have exactly zero electric field when there is a difference in the positions of the charges?
It is said that atoms with the same number of electrons as protons are electrically neutral, so they have no net charge or net electric field.
A particle with charge cannot exist at the same position and time as another; an electron cannot be…
John O'brien
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25
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3 answers
What is the meaning of the size of a particle in QFT?
I have often seen people refer to the size of a particle being at most a given value, or a particle being a point particle, in the context of quantum field theory. Examples are the Wikipedia entry on the electron, where it says
Observation of a…
doetoe
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Why do physicists believe that particles are pointlike?
String theory gives physicists reason to believe that particles are 1-dimensional strings because the theory has a purpose - unifying gravity with the gauge theories.
So why is it that it's popular belief that particles are 0-dimensional points?…
Olly Price
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17
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6 answers
Does classical electrodynamics have a Lagrangian that gives both the Lorentz force and Maxwell equations?
There is a Lagrangian for a particle of mass $m$ and charge $q$
$$\mathcal{L}_1 = \mathcal{L}_k(m, \vec{v}) - q\phi + q\vec{v}\cdot\vec{A}$$
where $\mathcal{L}_k(m, \vec{v})$ is either $\frac{1}{2}m\vec{v}\cdot\vec{v}$ for classical mechanics or…
Chad K
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17
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7 answers
Can elementary particles be explained adequately by a wave-only model?
I have been watching quantum mechanics documentaries and reading a layman's book called "The Quantum Universe". I believe I understand why the double slit experiments exclude a particle only model. However I do not understand why the particle…
mfergus9
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5 answers
How can electric field be defined as force per charge, if the charge makes its own, singular electric field?
The electric field $\bf{E}$ represents how much force would act on a particle at a certain position per unit charge.
However, if we actually place a particle in that position, the electric field will have a singularity there (because of the…
AstroRP
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Localized field quanta?
After the canonical quantization of the Klein-Gordon field (for example), we interpret the quantum of excitations of the fields with definite energy and momentum as particles. But our mental image of a particle is that of an entity which is…
SRS
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What's the point of having an einbein in your action?
One often comes across actions written with an extra auxiliary field, with respect to which, if you vary the action, you get the equation of motion of the auxiliary field, which when plugged into the original action lets you retrieve a more familiar…
dbrane
- 8,950
15
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3 answers
How do we prove or disprove that a particle has no internal structure?
In many pop physics books I have read that an electron has no internal structure.
How do we know that and how can we rigorously prove that it has no such structure at all?
Xasel
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How can a point-particle have properties?
I have trouble imagining how two point-particles can have different properties.
And how can finite mass, and finite information (ie spin, electric charge etc.) be stored in 0 volume?
Not only that, but it can also detect all fields without having…
TROLLHUNTER
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