# All Questions

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### At what velocity does space no longer equal a vacuum? [on hold]

In Dr. Alistair Reynolds's book (Revelation Space), he mentions that space only equals a vacuum at low speeds. At which velocities would space no longer count as an almost vacuum?
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### Why is the Oort cloud spherical?

Having read up a bit about the Oort cloud hypothesis, I find I don't quite understand this. Why is the Oort cloud spherical while the rest of the solar system is disk-shaped?
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### Leptons slide between quarks? [on hold]

I wonder if one of particles (maybe quarks?) are constructors of highways in 3d field for others floating around re/distributing energy by some (leptons?), restricted to laws set by (bosons?). If ...
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### No length contraction!

Suppose a person standing on a platform were to observe and measure the length of a train passing by. Instead of the usual approach involving a clock and knowing the speed of the train, the person ...
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### Why is cooling much harder than heating?

I'm trying to invent a distillation apparatus that runs solely on electricity. Suddenly, I realized that cooling things is really hard, while heating them up is so easy. Actually, it seems that there ...
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### Do we exist in multiple dimensions?

I have heard that there are 12 spacial dimensions. Does this mean that this many are possible,or that 12 dimensions actually exist? If the ladder, then do the same things that exist in 3 dimensions ...
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### Does coffee cool faster than tap water?

A friend of mine, based on casual observation, believes that coffee will cool faster than ordinary hot tap water. Being curious about this I have tried to investigate it myself, but I'm not well ...