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Oct
16
comment Mathematical understanding of Quantum Mechanics
The key idea here is that the result of $F|r'\rangle$ is another ket which may be expressed as a combination of position kets. We might e.g. have $F|r'\rangle = a|r''\rangle + b|r'''\rangle$, similar to what Alfred wrote but a little more general. Then the matrix elements of $F$ are zero except when $r''=r$ or $r'''=r$. (since they're given by $a\langle r | r''\rangle + b\langle r | r'''\rangle$)
Sep
30
awarded  Explainer
Sep
28
comment Time-ordered operator in Srednicki
This would be helpful to more people if you explicitly included all the equations you reference.
Sep
11
revised Frequency Of Light
Improved and expanded
Sep
10
comment Why does the Metropolis algorithm allow changes even for ∆E > 0?
Basically: you want the global minimum and if you don't allow going up in the energy landscape, you can't get out of a local minimum to get to the global one.
Aug
24
comment About solitons, what is the difference between kinks and vortices?
I want to add another outstanding book with introduction to solitons, instantons and the like: "Gauge field theories: an introduction with applications" by M. Guidry (1991). This is a personal favourite of mine because Guidry's style of rhetoric clicks well with my internal thought process. Another good reference I know is "Solitons and instantons: An introduction to solitons and instantons in quantum field theory" by R. Rajaraman (1982).
Aug
19
comment How much energy would the Human Torch need?
You don't have to take the mass of the average person, Human Torch weighs 170 lbs. :P
Aug
16
comment Unknown letter ℑ used in an equation
This isn't really the kind of questions we answer here but Detexify can often help, since the LaTeX command to write a symbol usually has a somewhat telling name (in this case \Im, meaning "the imaginary part of"). You might have guessed that from the equation itself based on Euler's formula. Actually, I just read the last part of the accompanying text and it says so there as well, so now I'm confused as to why you asked...
Aug
15
awarded  Nice Answer
Aug
9
comment Finding the mass of pure matter
@celtschk and the people who voted earlier: I've edited my answer. I can't comment more on the implications of having a Planck density right now, but sufficit to say this is quantum gravity territory.
Aug
9
revised Finding the mass of pure matter
Replaced apparently popular hogwash with some Planck-stuff
Aug
9
answered Finding the mass of pure matter
Aug
9
comment Finding the mass of pure matter
What do you mean "not made up of particles"? Let's start here: what is matter to you?
Aug
9
comment Finding the mass of pure matter
I'm sorry but I have no idea what you mean. And I'm pretty sure 1 meter squared is a surface. ;-)
Aug
8
comment Why is electron presented in books, pictures as a sphere?
@albedo Concerning your other question: note that we talk about the electric field of the electron when discussing its shape. Like Colin McFaul mentions in his answer, as far as we can experimentally tell the electron is a mathematical point. However, you can define a boundary for the electron if you want to, based on the value of its electric field. Strictly speaking this is an arbitrary choice but sometimes it may be helpful to associate a natural size with an electron and treat it as a little sphere.
Aug
8
comment Why is electron presented in books, pictures as a sphere?
@albedo This webpage and the answers to this PSE question might be interesting reading material for you.
Aug
8
comment Why is electron presented in books, pictures as a sphere?
@albedo The electron (like all elementary particles) is not both a particle and a wave, that's a common misconception. It is in fact not a particle, nor a wave. In the most accurate theories we currently have about the universe elementary particles are in fact excitations of quantum fields. These excitations, also called 'quanta' (from the singular 'quantum'), exhibit both particle-like and wave-like features but the truth is that both waves and particles are classical and macroscopic concepts. There's no reason for the smallest building blocks at the micro-level to be either one.
Aug
5
comment Is it true that the Schrödinger equation only applies to spin-1/2 particles?
I don't know if I should post a link to the paraphrased answer on Quora now. Perhaps not if OP prefers it that way, I'm sure people can find it themselves by means of a simple websearch.
Aug
3
comment How to numerically solve a complex equation?
Would Mathematics be a better home for this question?
Jul
29
comment Why was theory of cosmic aether discarded?
Consider changing your question title to better match what you're asking in the main body.