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1500 questions
116
votes
11 answers
Is Angular Momentum truly fundamental?
This may seem like a slightly trite question, but it is one that has long intrigued me.
Since I formally learned classical (Newtonian) mechanics, it has often struck me that angular momentum (and generally rotational dynamics) can be fully derived…
Noldorin
- 7,362
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116
votes
10 answers
How is a quantum superposition different from a mixed state?
According to Wikipedia, if a system has $50\%$ chance to be in state $\left|\psi_1\right>$ and $50\%$ to be in state $\left|\psi_2\right>$, then this is a mixed state.
Now, consider the state…
Ruslan
- 28,862
116
votes
4 answers
Why do electrons, according to my textbook, exist forever?
Does that mean that electrons are infinitely stable? The neutrinos of the three leptons are also listed as having a mean lifespan of infinity.
HyperLuminal
- 1,968
116
votes
1 answer
Superfields and the Inconsistency of regularization by dimensional reduction
Question:
How can you show the inconsistency of regularization by dimensional reduction in the $\mathcal{N}=1$ superfield approach (without reducing to components)?
Background and some references:
Regularization by dimensional reduction (DRed) was…
Simon
- 3,513
115
votes
4 answers
Intuitively, why are bundles so important in Physics?
I've seem the notion of bundles, fiber bundles, connections on bundles and so on being used in many different places on Physics. Now, in mathematics a bundle is introduced to generalize the topological product: describe spaces that globally are not…
Gold
- 35,872
115
votes
6 answers
Why is glass transparent?
Once I asked this question from my teacher and he replied "Because it passes light.". "And why does it pass light?" I asked and he said, "Because it is transparent.".
The same question again, Why glass is transparent? Why does light pass through it,…
SMUsamaShah
- 5,307
115
votes
11 answers
What Is Energy? Where did it come from?
The simplistic undergrad explanation aside, I've never really understood what energy really is. I've been told that it's something when converted from one kind of something to another kind, or does some "work", as defined by us, but what is that…
Anna
- 1,697
115
votes
6 answers
Could we send a man safely to the Moon in a rocket without knowledge of general relativity?
I'm wondering if it's possible to send a man to the Moon using equations consistent with Newtonian gravity and without the elaborate tools of Einstein gravity. Are the predictions made by Newtonian gravity sufficiently precise to plan a successful…
Dargscisyhp
- 5,289
114
votes
5 answers
What is the actual significance of the amplituhedron?
The news that physicists have discovered a geometrical object that simplifies a lot our models of quantum physics has recently became viral. For an outsider like me, it is difficult to actually understand the significance of this finding.
Is it…
MaiaVictor
- 1,952
114
votes
4 answers
Why do clouds have well-defined boundaries?
Why do cumulus clouds have well defined boundaries? In other words, what are the physical mechanisms that hold a cloud together, as an entity separate from other clouds, that prevent it from spreading, etc.
Naively, one could expect the atmospheric…
Roger V.
- 58,522
113
votes
11 answers
Why do fusion and fission both release energy?
I only have high school physics knowledge, but here is my understanding:
Fusion: 2 atoms come together to form a new atom. This process releases the energy keeping them apart, and is very energetic. Like the sun!
Fission: Something fast (like an…
user230910
- 1,121
113
votes
15 answers
Why can't $ i\hbar\frac{\partial}{\partial t}$ be considered the Hamiltonian operator?
In the time-dependent Schrodinger equation, $ H\Psi = i\hbar\frac{\partial}{\partial t}\Psi,$ the Hamiltonian operator is given by
$$\displaystyle H = -\frac{\hbar^2}{2m}\nabla^2+V.$$
Why can't we consider $\displaystyle…
Revo
- 16,956
112
votes
8 answers
Thought experiment - would you notice if you fell into a black hole?
I've heard many scientists, when giving interviews and the like, state that if one were falling into a black hole massive enough that the tidal forces at the event horizon weren't too extreme, that you wouldn't "notice" or "feel" anything, and so…
alzee
- 1,264
111
votes
15 answers
About the complex nature of the wave function?
1.
Why is the wave function complex? I've collected some layman explanations but they are incomplete and unsatisfactory. However in the book by Merzbacher in the initial few pages he provides an explanation that I need some help with: that the de…
yayu
- 4,822
111
votes
4 answers
Why does a sticker slowly peel off, but if it is pulled quickly it tears?
Anyone who has removed a sticker, knows that often they must be pulled off slowly, otherwise they tear. Why is this?
Ambrose Swasey
- 4,474