# Tag Info

40

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 ...

12

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 ...

10

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 ...

7

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 ...

6

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 ...

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

This is just a misunderstanding--- "no motion" in quantum mechanics is a different concept than "no motion" in classical mechanics. At zero temperature, nothing stops. Spherical uncharged black holes don't stop particles at the singularity, they absorb particles and time just ends at the singularity for the infalling matter. The wavefunctions are not made to ...

5

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 ...

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 ...

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

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 ...

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 ...

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

Oh goodness... that is an immensely complicated topic. Many thousands of people have put in decades of work figuring out exactly what happens when two subatomic particles collide. The calculations are all done using quantum field theory, so I would say if you want to learn about the process involved in describing the outcome of a collision, read up on QFT - ...

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 ...

2

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 ...

2

However where did the electron get its energy from in the first place(during the creation of the universe"Big bang"). All energy, and remember energy and mass are related by E=m*c^2, that exists in the universe existed after the first minutes of the Big Bang . For t=0 plus an interval after it where gravitational forces predominate, i.e the realm of ...

2

If you're asking whether we can measure the effect on atomic structure of gravitational forces between the nucleus and the electrons, then the answer is that not only have we never measured such effects but it's unlikely we'll ever be able to measure them as they would be many orders of magnitude below the electrostatic forces that hold the atom together. ...

2

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 ...

2

They are exactly the same, with the different notations arising in different contexts. You could start with a bunch of helium gas and heat it up or shine UV light on it to turn it into a plasma, and then you'd probably say you have $\mathrm{He}^{2+}$ (or $\mathrm{He}\ \mathrm{III}$ if you are an astronomer). The symbol $\alpha$ is more often reserved for ...

1

You have a lot of questions here, and they show you really need to read up on some basic physics, but here goes with some simple answers: Where did the electron get its energy from in the first place? What energy do you mean? Why doesn't everything fall apart when we sit on a chair or grab a pencil,why wont the electrons fall from trajectory and get caught ...

1

Your question is interesting, and gets specifically to the kinds of questions that quantum mechanics was intended to answer in the first place. It helps to understand the motivation behind the original Bohr model of the atom, and how that led to QM in the first place. The problem Bohr was trying to address can be paraphrased as, "If an electron orbits a ...

1

There exists a huge number of experimental evidence that in the subatomic world nature is using quantum mechanics. In quantum mechanics bound states always have the first energy level above 0 energy. Your magnetic field thought experiment creates a bound stated in the collective potential. Free states have to obey the HUP and therefore cannot have 0 fixed ...

1

I will assume you have heard something about proton decay. proton decay is a hypothetical form of radioactive decay in which the proton decays into lighter subatomic particles, such as a neutral pion and a positron.1 There is currently no experimental evidence that proton decay occurs. There are a number of experiments which test whether such decays ...

1

In a sense these "games" exist, need large computing power and are called high energy physics monte carlos. These are very complicated simulations of the reality of the experiment and include all the detector effects. At the first level of the core of these HEP monte carlos there exist tables of "complete" possibilities of scattering products: all ...

1

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 ...

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