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1500 questions
36
votes
4 answers
What is the difference between center of mass and center of gravity?
What is the difference between center of mass and center of gravity ? These terms seem to be used interchangeably. Is there a difference between them for non-moving object on Earth, or moving objects for that matter?
DarkLightA
- 1,442
36
votes
5 answers
"Velvet way" to Grassmann numbers
In my opinion, the Grassmann number "apparatus" is one of the least intuitive things in modern physics. I remember that it took a lot of effort when I was studying this. The problem was not in the algebraic manipulations themselves -- it was rather…
Kostya
- 20,528
36
votes
3 answers
Is there a frame of reference in which I was born before I was conceived?
I'm struggling to understand the relativity of simultaneity and position. If my conception and birth are separated by time but not space, a frame of reference in which my birth and conception are simultaneous should exist right? If another observer…
IchVerlore
- 760
36
votes
6 answers
Is the Higgs boson an elementary particle? If so, why does it decay?
The Higgs boson is an excitation of the Higgs field and is very massive and short lived. It also interacts with the Higgs field and thus is able to experience mass. Why does it decay if it is supposed to be an elementary particle according to the…
user6760
- 13,334
36
votes
4 answers
Why is argon a noble gas but not, say, beryllium or palladium?
Why is argon a noble gas given that the 3d subshell is still empty? More generally, why is it that the filling of a p sub-shell makes an element noble rather than s, d, or f sub-shells, or completed n-levels? Let's start with the prior that in a…
Paul Young
- 3,656
36
votes
2 answers
Can light be compressed?
What if we take a cylindrical vessel with an inside surface completely reflecting and attach a piston such that it is also reflecting. What will happen to light if we compress it like this?
user204283
- 507
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36
votes
5 answers
Intuition for multiple temporal dimensions
It’s easy, relatively speaking, to develop an intuition for higher spatial dimensions, usually by induction on familiar lower-dimensional spaces. But I’m having difficulty envisioning a universe with multiple dimensions of time. Even if such a thing…
Jon Purdy
- 487
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36
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12 answers
Why does work depend on distance?
So the formula for work is$$ \left[\text{work}\right] ~=~ \left[\text{force}\right] \, \times \, \left[\text{distance}\right] \,. $$ I'm trying to get an understanding of how this represents energy. If I'm in a vacuum, and I push a block with a…
36
votes
2 answers
In nuclear bomb explosions, witness describe their hands becoming transparent. How does that happen?
Witnesses of nuclear explosions have described their hands becoming transparent, and that they could see the bones. For example, see here. How does that happen?
radon
- 385
36
votes
2 answers
Can we get complete non-perturbative information of the interacting system by computing perturbation to all orders?
As we know, the perturbative expansion of interacting QFT or QM is not a convergent series but an asymptotic series that is generally divergent. So we can't get arbitrary precision of an interacting theory by computing higher enough order and adding…
maplemaple
- 2,237
36
votes
8 answers
Why does no physical energy-momentum tensor exist for the gravitational field?
Starting with the Einstein-Hilbert Lagrangian $$ L_{EH} = -\frac{1}{2}(R + 2\Lambda)$$ one can formally calculate a gravitational energy-momentum tensor $$ T_{EH}^{\mu\nu} = -2 \frac{\delta L_{EH}}{\delta g_{\mu\nu}}$$ leading to $$ T_{EH}^{\mu\nu}…
Dilaton
- 9,861
36
votes
3 answers
Is spin really just "rest angular momentum"?
Spin is the intrinsic angular momentum of a particle. The particle itself is elementary and is not spinning on its axis, and has this momentum even at rest. The absolute magnitude of this momentum cannot increase or decrease without changing the…
36
votes
4 answers
What really is a fluid?
My question may be pretty basic, but I feel it is important to ask this as I've gone through several texts and none offer me the clarity I seek. The question is: What is a fluid? What is flow? If we say that a fluid is something that flows, the next…
stoic-santiago
- 1,991
36
votes
4 answers
What was the 'quantum mechanics' before quantum mechanics?
Quantum mechanics is near-universally considered one of the most difficult concepts to grasp, but what were the persistently unintuitive, conceptually challenging fields physicists had to grasp before the emergence of quantum mechanics? The aim of…
dTdt
- 723
36
votes
2 answers
Why does the Earth even have a magnetic field?
From my knowledge of magnetism, if a magnet is heated to a certain temperature, it loses its ability to generate a magnetic field. If this is indeed the case, then why does the Earth's core, which is at a whopping 6000 °C — as hot as the sun's…
Rumplespaceking
- 488