# Tag Info

56

Wow, this one has been over-answered already, I know... but it is such a fun question! So, here's an answer that hasn't been, um, "touched" on yet... :) You sir, whatever your age may be (anyone with kids will know what I mean), have asked for an answer to one of the deepest questions of quantum mechanics. In the quantum physics dialect of High Nerdese, ...

29

One good piece of evidence that all particles of a given type are identical is the exchange interaction. The exchange symmetry (that one can exchange any two electrons and leave the Hamiltonian unchanged) results in the Pauli exclusion principle for fermions. It also is responsible for all sorts of particle statistics effects (particles following the ...

13

I think the best answer to your question is simply "because that's all we can see when we do experiments." That is, no matter how hard anyone tries or how much energy they toss into the processes, electrons and quarks show no signs of any appendages, surfaces, hair-like structures, bumps, volume, whatever. When you model them mathematically as points, the ...

11

Short answer: The space between the nucleus and the electron is not empty space, it is filled with an electron cloud. (You will understand this answer better if you read the long answer) Long answer: Firstly, physics is a description of what we can observe. Depending on the scale of which you are describing, physicists, over the years, have different ...

8

As a useable heuristic I would go with something along the lines of the intermolecular forces between the surface molecules of the bodies are comparable to the scale of one-to-one intermolecular forces between nearby{*} molecules due to other components of the same body You could make it a little more strict by replacing "comparable to" with ...

8

The anti-particle corresponding to a neutron is an anti neutron! The neutron is made up of one up quark and two down quarks. The anti-neutron is made up of an anti-up quark and two anti-down quarks. Both have zero charge because the charges of the quarks within them balance out. You are correct that elementary particles with no charge are often their own ...

7

Why three quarks? In very simple terms bound states of quarks (hadrons) have to be color neutral so that means either color quark + anticolor antiquark (mesons) or three quarks carrying R, G and B color charge respectively (baryons). (Note: There should also exist exotic particles like tetraquarks and pentaquarks but these haven't been observed yet and ...

7

From: NobelPrize.org "Her continued systematic studies of the various chemical compounds gave the surprising result that the strength of the radiation did not depend on the compound that was being studied. It depended only on the amount of uranium or thorium. Chemical compounds of the same element generally have very different chemical and physical ...

7

Short answer: the strong nuclear force. The strong nuclear force binds nucleons (protons and neutrons) together. It is a very short-range force, which is why it only acts over distances on the scale of atomic nuclei. There is repulsion between the protons, which is why, as the number of protons goes up, more and more neutrons are required to stabilize the ...

6

That's a great question! Unfortunately, the only honest answer is "that's what we see in nature, with great precision and complete reproducibility." There is no deep theoretical understanding. The more exotic form of your question is phrased in terms the self-energy of an electron, and it's a question that plagued Nobel Laureate Richard Feynman his entire ...

5

Does the fact that protons and neutrons have larger mass than electrons mean they're bigger in size? No. The electron and muon are both believed to be "point-like" (which really means smaller than we can measure" despite having $\frac{m_\mu}{m_e} \approx 200$. That is not to say the proton isn't bigger---it is---but that mass does not imply size in any ...

4

Maybe one should add to the analysis of @QEntanglement and the nice electron probability clouds in the illustrations in the other answers, that also the space between the nucleus and the electrons is teaming with the exchange of virtual particles between the electrons and the nucleus, necessary to create the potential which determines the energy levels of ...

4

Your day to day experience of the material world is governed by chemistry. This is at some level the science of atoms and groups of atoms. Things like hardness, colour, toxicity and others are all largely determined by the interaction of atoms. In particular the outer coating of atoms, the electrons. Obviously the details of why element or compound A is ...

4

It's a very good question. The electron is described by a wave field which resembles a charge distribution, so it is natural to wonder why it doesn't repel itself and spread out all over. However, the wave is not a classical wave but is quantized, i.e. the energy in a given vibration mode has to come in discrete bundles. One can count how many excitations ...

4

Your teacher is referring to the LCAO approximation as a way of calculating molecular orbitals. Suppose you bring two hydrogen atoms together i.e. create a hydrogen molecule. To calculate the electronic structure you need to solve the Schrodinger equation, but even for something as simple as the hydrogen molecule the Schrodinger equation is too complex to ...

4

An elementary particle is not like a billiard ball at a very small scale. You yourself state i know sometimes it behaviors like a wave, but it sometimes can be seen as a particle. This statement does not apply to macroscopic particles, it applies to microscopic quantum mechanical entities when the dimensions become equal or smaller than a billionth ...

4

How is it possible to see/detect a probability density wave ? It isn't possible. The image is a visualization of an interference pattern from which the nodal structure of the orbital can be inferred. From a Physics World article: In the new work, Aneta Stodolna, of the FOM Institute for Atomic and Molecular Physics in the Netherlands, along with ...

4

To begin with electrons are not composite. It is baryons and hadronic resonances that are composites of quarks. Hadrons are held together by the strong forces between quarks. These forces, in contrast to the electromagnetic ones which fall with distance as 1/r^2 (and thus allow us to detect free electrons, whose potential falls like 1/r), they behave ...

3

You can see a nucleus and the nucleus of a hydrogen atom is a proton which is the same. You can't see below that at least with a source of neutrons that ISIS produce, but you can see down to the level of the proton.

3

First, there is no universal inequality that would say that materials have to be "paramagnets". The opposite effects imply that materials may also be "diamagnets" which means that they react oppositely to the magnetic field. I think that atoms and molecules are the smallest objects whose response to the magnetic field may be viewed as the microscopic cause ...

3

This is very legitimate question for something we usually take for granted. I think it would be possible to define macroscopically touching as the situation, in which the total force between two electrically neutral rigid bodies is larger than pure gravitational (for some measurable value). The difference is of course the normal component of the surface ...

3

In contrast with the previous incorrect answers that I hadn't noticed, there isn't any ambiguity or confusion about the Bose-Einstein or Fermi-Dirac statistics for composite systems such as atoms. A particle – elementary or composite particles – that contains an even number of elementary (or other) fermions is a boson; if it contains an odd number, it is a ...

3

It's really not clear what hypothetical limits you're imposing. I take your question to mean that in the process of baryogenesis the various baryons like protons and neutrons highly favored up quarks (lots more protons than neutrons). Remember, quarks are subject to confinement so other than a quark-gluon plasma, quarks are confined to baryons. Since ...

3

When physicists perform particle collisions, they do not execute them one collision at a time. Rather, they perform millions of collisions within very short time frames and they use state of the art computers to analyze and decipher the copious amounts of data they receive. That being said, to isolate a particle such as a proton, it is as simple as ...

3

The title of this question refers to the emission of light from an incandescent light bulb, and then the body of the question asks for Planck-scale details of the physics happening there. Well, that would be a lot of work to answer. Suppose it's a tungsten filament. Then there's a molecular lattice of tungsten atoms, i.e. a lattice of nuclei surrounded by ...

3

A nanoscope in the sense you're talking about would be physically impossible, because things which are smaller than the wavelength of light don't reflect light. They do scatter light, but that's a different process which doesn't form a coherent image. Visible light has wavelengths between about 400 and 700 nanometers, so anything smaller than that - ...

3

I think you are correct in being confused. The earth's magnetic field, or any external to the atom magnetic field , can distort orbitals but is not the creators of them. Orbitals are the locus in space where the probability of finding an electron is large enough to be measurable. In the quantum mechanical framework orbitals play the role orbits have in ...

2

You say: I understand how particles with certain masses can form to make atoms, which create rigidity in objects due to Pauli's Exclusion Principle and what have you. These particles actually have mass and to a certain extent clearly would produce rigidity in objects. Do you understand what rigidity is ? I would define it as the resistance of a solid ...

2

We can image the sub-structure of nucleons by a number of different techniques involving high energy scattering. The results are generally presented in terms of "parton distribution functions" or "structure functions". One such experiment that I had some small relationship with (though not enough to be an author) was NuSea (E866) at Fermilab in the mid ...

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