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1500 questions
104
votes
4 answers
Would a pin head heated to 15 million degrees Celsius kill everyone in a 1000 mile radius?
The YouTube video How Hot Can it Get? contains, at the 2:33 mark, the following claim:
A pin head heated to 15 million degrees will kill everyone in a 1000 miles radius.
On what basis can this claim be true?
Some of the things I can think…
Jus12
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104
votes
12 answers
What is spontaneous symmetry breaking in quantum systems?
Most descriptions of spontaneous symmetry breaking, even for spontaneous symmetry breaking in quantum systems, actually only give a classical picture.
According to the classical picture, spontaneous symmetry breaking can only happen for non-linear…
Xiao-Gang Wen
- 13,725
104
votes
9 answers
Which is stronger, a rope without knots or a rope with knots?
Suppose I have two identical ropes, one of which I manually tie some knots in. If I use them to hang clothes, which one is more durable?
Personally I think that rope with knots will be more durable, but I can't come up with a satisfactory reason.
an offer can't refuse
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104
votes
13 answers
Best books for mathematical background?
What are the best textbooks to read for the mathematical background you need for modern physics, such as, string theory?
Some subjects off the top of my head that probably need covering:
Differential geometry, Manifolds, etc.
Lie groups, Lie…
ahh
- 141
104
votes
7 answers
What is the speed of sound in space?
Given that space is not a perfect vacuum, what is the speed of sound therein? Google was not very helpful in this regard, as the only answer I found was $300\,{\rm km}\,{\rm s}^{-1}$, from Astronomy Cafe, which is not a source I'd be willing to…
Josh Glover
- 1,113
104
votes
12 answers
Why is filling a balloon from your mouth much harder initially?
Why is it that when you first fill up a balloon, it's hard to get air through, but after inflating it a bit, it becomes much easier to further inflate the balloon?
yuritsuki
- 1,628
103
votes
4 answers
Physical meaning of Legendre transformation
I would like to know the physical meaning of the Legendre transformation, if there is any? I've used it in thermodynamics and classical mechanics and it seemed only a change of coordinates?
gsAllan
- 1,317
103
votes
1 answer
Classical and quantum anomalies
I have read about anomalies in different contexts and ways. I would like to read an explanation that unified all these statements or points of view:
Anomalies are due to the fact that quantum field theories (and maybe quantum mechanical theories…
Diego Mazón
- 7,127
103
votes
7 answers
Why does the atmosphere rotate along with the earth?
I was reading somewhere about a really cheap way of travelling: using balloons to get ourselves away from the surface of the earth. The idea held that because the earth rotates, we should be able to land in a different place after some time. As we…
claws
- 7,493
101
votes
4 answers
Can tin foil hats block anything?
This is joked about all the time, but...
Can tin foil hats actually block anything? If they can, what frequencies? Is there any research into tin or aluminum foil and radio blocking or amplifying abilities when shaped into a hat?
If they really…
Status
- 1,038
100
votes
11 answers
If I pull a metal bar for long enough with a constant small force, will it eventually break?
Let's say I have a strong metal bar. I pull it apart with a very small constant force -- obviously it doesn't break. However, this would disturb the internal configuration. If I let go, then eventually the internal configuration would return to what…
100
votes
1 answer
Orbits of maximally entangled mixed states
It is well known (Geometry of quantum states by Bengtsson and Życzkowski) that the set of $N$-dimensional density matrices is stratified by the adjoint action of $U(N)$, where each stratum corresponds to orbits with a fixed type of degeneracy…
David Bar Moshe
- 31,499
100
votes
9 answers
Can we theoretically balance a perfectly symmetrical pencil on its one-atom tip?
I was asked by an undergrad student about this question. I think if we were to take away air molecules around the pencil and cool it to absolute zero, that pencil would theoretically balance.
Am I correct?
Veritasium/Minutephysics video on Youtube.
TBBT
- 2,777
100
votes
8 answers
Why does hot water clean better than cold water?
I had a left over coffee cup this morning, and I tried to wash it out. I realized I always instinctively use hot water to clean things, as it seems to work better.
A Google search showed that other people get similar results, but this Yahoo answer…
user-2147482637
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99
votes
7 answers
How can a black hole produce sound?
I was reading this article from NASA -- it's NASA -- and literally found myself perplexed. The article describes the discovery that black holes emit a "note" that has physical ramifications on the detritus around it.
Sept. 9, 2003: Astronomers…
Aarthi
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