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36
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7 answers
Dirac once said that renormalization is just a stop gap procedure, and there had to occur a fundamental change in our ideas. Did something change?
Once, Dirac said the following about renormalization in Quantum Field Theory (look here, for example):
Renormalization is just a stop-gap procedure. There must be some fundamental change in our ideas, probably a change just as fundamental as the…
36
votes
2 answers
Definitions: 'locality' vs 'causality'
I'm having trouble unambiguously interpreting many answers here due to the fact that the terms locality and causality are sometimes used interchangeably, while other times seem to mean very different things to the author.
My current understanding…
user1247
- 7,288
36
votes
3 answers
Why does the Earth cool at night time?
I do understand that open water and open ground cools by the means of convection — lower air takes the heat and goes up, where it cools.
But why does the Earth lose energy and where does it go? Does it emit heat radiation to space? Does the heat go…
Denis Kulagin
- 481
36
votes
4 answers
If temperature is amount of kinetic energy of particles, then how can there be a cold breeze?
When we put hands on A/C it gives cold winds. These winds have high kinetic energy but low temperature. How ? *don't confuse with A/C being heat pump , just an example, take antarctic blizzards. I can't understand the paradox of low temperature…
user37060
- 341
36
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
36
votes
2 answers
Can a neutron star become a black hole via cooling?
How much does thermal expansion affect neutron stars? Would the loss of temperature cause a neutron star to be more densely packed and thus collapse into a black hole?
user289661
- 916
36
votes
3 answers
Might a planet perform figure-8 orbits around two stars?
Might a planet perform figure-8 orbits around two stars?
I'm thinking that if the two stars were equal mass (and not orbiting each other) then a planet that were to go right between them would continue in a straight line, with no preference for…
dotancohen
- 4,545
36
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
- 517
36
votes
8 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
36
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
- 1,819
36
votes
1 answer
Canonical examples of quantum channels
I have a conjecture about quantum channels. On which examples should I test it before I try to prove it, ask it on StackExchange, or write a paper about it?
(Note: This is meant to be a reference question. But whenever I have a conjecture, I do…
Norbert Schuch
- 20,338
36
votes
2 answers
How well can a laser be focused over interstellar range?
I try to read up on diffraction limiting and gaussian beams, but it always gives a result saying it’s characterized by an angle which is the edges of a cross section of a cone. Which says nothing on the physical limits of how I choose that angle. …
JDługosz
- 5,297
36
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
- 14,423
36
votes
1 answer
What does it mean to say that "the fundamental forces of nature were unified"?
It is said that immediately after the Big Bang, the fundamental forces of nature were unified. It is also said that later they decoupled, becoming separate forces.
Indeed, if we look at the list of states of matter on Wikipedia we see:
Weakly…
Gold
- 35,872
36
votes
1 answer
Why was the first discovered neutrino an anti-neutrino?
In the search for neutrinos, Cowan and Reines discovered the electron anti-neutrino and named it as such. Why is the particle they discovered the anti-variety?
The reason we call electrons 'electrons' and not 'anti-electrons' is because the…
Joshua
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