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1500 questions
38
votes
3 answers
Symmetrical twin paradox in a closed universe
Take the following gedankenexperiment in which two astronauts meet each other again and again in a perfectly symmetrical setting - a hyperspherical (3-manifold) universe in which the 3 dimensions are curved into the 4. dimension so that they can…
vonjd
- 3,801
38
votes
3 answers
Is it possible to estimate the speed of a passing vehicle using a musical ear and the doppler effect?
I've found a number of questions that concern the Doppler effect, but none that seem to address my question.
I have a background in music. People with a musical ear can generally tell the ratio between two frequencies (as a musical interval). For…
M_M
- 491
38
votes
4 answers
Is there just one EM field for the whole universe?
Does our universe contain individual magnetic fields ?
For example two different magnets, one here on earth and one on mars. Do both of them have their own magnetic field? Or is there only one single field that stretches across the entire universe,…
user134652
38
votes
8 answers
What determines which frames are inertial frames?
I understand that you can (in principle) measure whether "free particles" (no forces) experience accelerations in order to tell whether a frame is inertial. But fundamentally, what determines which frames are inertial (i.e. what principle selects in…
Joss L
38
votes
5 answers
What's the difference between Fermi Energy and Fermi Level?
I'm a bit confused about the difference between these two concepts. According to Wikipedia the Fermi energy and Fermi level are closely related concepts. From my understanding, the Fermi energy is the highest occupied energy level of a system in…
Eddy
- 537
38
votes
10 answers
Recommendations for statistical mechanics book
I learned thermodynamics and the basics of statistical mechanics but I'd like to sit through a good advanced book/books. Mainly I just want it to be thorough and to include all the math. And of course, it's always good to give as much intuition…
fiftyeight
- 1,075
38
votes
5 answers
Is the Schrödinger equation derived or postulated?
I'm an undergraduate mathematics student trying to understand some quantum mechanics, but I'm having a hard time understanding what is the status of the Schrödinger equation.
In some places I've read that it's just a postulate. At least, that's how…
Bruno Stonek
- 769
38
votes
2 answers
Basic buoyancy question: Man in a boat with a stone
This comes from a brain teaser but I'm not sure I can solve it:
You are in a rowing boat on a lake. A large heavy rock is also in the boat. You heave the rock overboard. It sinks to the bottom of the lake. What happens to the water level in the…
lezebulon
- 483
38
votes
2 answers
How can wifi penetrate through walls when visible light can't?
I did search the question on Physics S.E considering it would be previously asked. I found this
How come Wifi signals can go through walls, and bodies, but kitchen-microwaves only penetrate a few centimeters through absorbing surfaces?
But in this…
Shashaank
- 2,837
38
votes
8 answers
Would it matter if the Earth rotated clockwise?
In the Futurama episode "That Darn Katz!" they save the world by rotating the Earth backwards saying it shouldn't matter (which direction Earth rotates). If Earth rotated clockwise and remained in it's current counter-clockwise orbit around the Sun,…
Major Stackings
- 715
38
votes
12 answers
Can Newton's laws of motion be proved (mathematically or analytically) or are they just axioms?
Today I was watching Professor Walter Lewin's lecture on Newton's laws of motion. While defining Newton's first, second and third law he asked "Can Newton's laws of motion be proved?" and according to him the answer was NO!
He said that these laws…
Vidyanshu Mishra
- 1,859
- 3
- 22
- 42
38
votes
2 answers
Experimental bounds on spacetime torsion
Did Gravity Probe B provide any bounds on Einstein-Cartan torsion? is a non-zero torsion value at odds with the results regarding frame-dragging and geodetic effects?
lurscher
- 14,933
38
votes
5 answers
How does defrosting your freezer save energy?
I've been told I should defrost my freezer to save energy, wiki, here and here for example, but none of the linked sites is a peer-reviewed paper explaining why (the wiki article doesn't even have references), and I don't find it obvious. I don't…
Santropedro
- 1,436
38
votes
4 answers
Are today's chip scale atomic clocks accurate enough to conduct my own test of time dilation?
Regarding the Symmetricom SA.45s Quantum™ Chip Scale Atomic Clock, is it accurate enough to test time dilation if I place one at sea level, and one on a mountain? It's accurate to 3.0⋅10−10 per month.
Steve
- 521
38
votes
1 answer
Instantons, anomalies, and 1-loop effects
A symmetry is anomalous when the path-integral measure does not respect it. One way this manifests itself is in the inability to regularize certain diagrams containing fermion loops in a way compatible with the symmetry. Specifically, it seems…
user6013
- 943