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1500 questions
102
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…
snickers_stickers
  • 905
102
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
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102
votes
6 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
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100
votes
1 answer

Why exactly do sometimes universal covers, and sometimes central extensions feature in the application of a symmetry group to quantum physics?

There seem to be two different things one must consider when representing a symmetry group in quantum mechanics: The universal cover: For instance, when representing the rotation group $\mathrm{SO}(3)$, it turns out that one must allow also…
ACuriousMind
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99
votes
4 answers

Why do same/opposite electric charges repel/attract each other, respectively?

I know plus pushes another plus away, but why, really, do they do that? On the other hand, molecules of the same type are attracted to each other. I find that weird. I do know some stuff about four universal forces. But why in general the general…
Muhammad Umer
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99
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
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99
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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98
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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98
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
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98
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
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98
votes
3 answers

Where is the flaw in this machine that decreases the entropy of a closed system?

I was thinking about a completely unrelated problem (Quantum Field Theory Peskin & Schroeder kind of unrelated!) when the diagram below sprang into my mind for no apparent reason. After some thinking, I can't figure out why it wouldn't work, other…
QuantumFool
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98
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
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97
votes
7 answers

How did Einstein know the speed of light was constant?

I often hear the story of how Einstein came up to the conclusion that time would slow down the faster you move, because the speed of light has to remain the same. My question is, how did Einstein know that measuring the speed of light wouldn't be…
Pablo Fernandez
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97
votes
4 answers

Seeing something from only one angle means you have only seen (what?)% of its surface area at most?

Is there a logical/mathematical way to derive what the very maximum percentage of surface area you can see from one angle of any physical object? For instance, if I look at the broad side of a piece of paper, I know I have only seen 50% of its…
BarrettNashville
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97
votes
4 answers

Why does the shower curtain move towards me when I am taking a hot shower?

When I am taking a shower, the shower curtain slowly moves towards my legs. Also, it seems that the hotter the water, the faster it gets to my skin. Why is that?
Gohu
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