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1500 questions
45
votes
5 answers
Why are we sure that integrals of motion don't exist in a chaotic system?
The stadium billiard is known to be a chaotic system. This means that the only integral of motion (quantity which is conserved along any trajectory of motion) is the energy $E=(p_x^2+p_y^2)/2m$.
Why are we sure that no other, independent on $E$,…
Alexey Sokolik
- 2,313
45
votes
2 answers
Does the speed of light vary in non-inertial frames?
The speed of light is the same in all inertial frames.
Does it change from a non-inertial frame to another? Can it be zero?
If it is not constant in non-inertial frames, is it still bounded from above?
Revo
- 16,956
45
votes
7 answers
How is $\frac{dQ}{T}$ measure of randomness of system?
I am studying entropy and its hard for me to catch up what exactly is entropy.
Many articles and books write that entropy is the measure of randomness or disorder of the system. They say when a gas system is let expand the randomness increases etc.…
pranphy
- 724
45
votes
3 answers
How does light re-accelerate after slowing down?
Light travels at speed x through a vacuum, and then it encounters a physical medium and slows down, only to leave the physical medium and re-enter vacuum. The speed of light immediately re-accelerates to speed x, the speed before going through the…
Daniel
- 411
45
votes
3 answers
If spacetime is curved, how would anyone know? If anyone could tell, would that really be spacetime curving?
I never had a problem accepting that spacetime is curved as a result of matter, until I learned the LIGO experiments showed that evidently the curvature of spacetime can be measured. This, to me, is very strange.
Suppose the entire universe is empty…
Devsman
- 1,663
45
votes
7 answers
Hanging a hammer from a table and a stick so that its midpoint is outside of the support of the table
I came across this pic on the internet today. At beginning I thought it is just not possible because the centre of mass is way off so gravity will generate torque making the stick and hammer fall. Later I thought that the heaviest part of hammer…
Tanishq Jaiswal
- 626
45
votes
2 answers
Did NIST fudge this news story about absolute zero?
This press release by NIST, titled "NIST Physicists ‘Squeeze’ Light to Cool Microscopic Drum Below Quantum Limit", makes the following claim:
The new technique theoretically could be used to cool objects to absolute zero, the temperature at which…
Sasha
- 516
45
votes
8 answers
Is there something similar to Gödel's incompleteness theorems in physics?
Gödel's incompleteness theorems basically sets the fact that there are limitations to certain areas of mathematics on how complete they can be.
Are there similar theorems in physics that draw the line as to how far one can get in physics as far as…
45
votes
12 answers
Why don't we hear sound reflecting from buildings, mirrors, etcetera?
We can see buildings, doors, cars etc. as light falls on it gets reflected to us.
but why doesn't the same thing happen with sound? I mean why don't we hear sound reflecting that much?
Subhranil Sinha
- 903
45
votes
9 answers
What's the standard "roadmap" to learning quantum physics?
I'm really interested in quantum physics and would like to learn more. However, I don't know where to start and in what order I should learn things. So, ideally I'm looking for some sort of roadmap of what to learn. What physics topics do I need to…
Simon Verbeke
- 757
45
votes
3 answers
What role does "spontaneous symmetry breaking" play in the "Higgs Mechanism"?
In talking about Higgs mechanism, the first part is always some introduction to the concept of spontaneous symmetry breaking (SSB), some people saying that Higgs mechanism is the results of SSB of local gauge symmetry, some people says that we can…
an offer can't refuse
- 6,035
45
votes
4 answers
Is it possible that every single isotope is radioactive, and isotopes which we call stable are actually unstable but have an extremely long half-life?
I've read that tellurium-128 has an half-life of $2.2 \times 10^{24}$ years, much bigger than the age of the universe.
So I've thought that maybe every single isotope of every single atom are radioactive, and isotopes which we call "stable" are…
Quantum Force
- 1,603
45
votes
3 answers
How do Optically Active Compounds Rotate Plane Polarized Light?
I am not sure if this is more of a Chemistry or a Physics question, but in my Organic Chem class we discussed that chiral molecules will rotate plane polarized light. However, my professor did not discuss the mechanism at all. She also said that…
Dylankw
- 451
45
votes
7 answers
Why is it so easy to create audible sound?
Context
Why is it so easy to create audible sounds in life with basically anything?
Putting your cup of coffee on a table comes with a sound
Turning a page of your book comes with a sound
Even something as soft as a towel creates sound when you…
user929304
- 4,635
45
votes
4 answers
Why is Huygens' principle only valid in an odd number of spatial dimensions?
Apparently Huygens' principle is only valid in an odd number of spatial dimensions:
https://mathoverflow.net/a/5396/21349
Huygen's principle in curved spacetimes
Why is this?
[EDIT] This is somewhat perplexing, since AFAIK it's pretty common to…
user4552