# Tag Info

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A 3D cube with pacman topology is translationally invariant and not rotationally invariant. A space like this is a possible (but unlikely) flat space part of a cosmological spacetime

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In a word, no. Getting into space is a matter of achieving enough velocity to overcome the Earth's gravitational influence, not about buoyancy. You can use buoyancy to get to the edge of the Earth's atmosphere, not beyond. We don't fill a rocket with helium so it'll float into space, nor do we use balloons to get beyond the edge of the Earth's atmosphere.

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Phenomena is called Cold Welding The reason for this unexpected behavior is that when the atoms in contact are all of the same kind, there is no way for the atoms to “know” that they are in different pieces of copper. When there are other atoms, in the oxides and greases and more complicated thin surface layers of contaminants in between, the ...

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It all depends on how clean the surface of the metal are. If there are oxides and impurities on the surfaces they will not bond together. However if the surfaces are ultra clean with no gas molecules from the atmosphere adhering to them, which on Earth would require them to be an ultra high vacuum chamber, then the surfaces would join together having made ...

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Vacuum or pressure is quantified in terms of bar or torr. 1 bar or 760 torr is roughly one atmosphere and in terms of vacuum measurement 1 mili-bar is taken as almost equal to 1 torr. at 1 bar pressure and at room temperature the number of atoms per cc is ~$2\times 10^{19}$. The number of particles per cc in vacuum can range from $10^{-4}$ to $10^6$. The ...

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@CuriousOne is approximately right. Others have thought of it, the url below is a paper from one who concludes with slightly more careful calculations (but still relatively straightforward) that the most one could get in terms of a continuous power from it is 50 MW, and typically a lot less. 50 MW is 5% of a large power plant. http://www.electrostatics.org/...

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Electromagnetic waves are produced by oscillating charged particles but they do not need other particles to propagate. Indeed electromagnetic waves are solutions of the Maxwell equations with no sources, i.e. in the vacuum. On the other hand, mechanical waves need an elastic medium to propagate, regardless of being transverse, longitudinal or mixed waves. ...

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Longitudinal electromagnetic waves do not exist in vacuum because the Divergence of E, and B are zero. The consequence of this is that the k-vector, propagation direction, is orthogonal to E and B.

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Other answers have handled the oxygen issue quite well. In regards to the temperature, space itself has no temperature because it's a vacuum. Objects in space, however, do have a temperature. If a human is exposed, unprotected, to space near the sun (or any other star), the temperature change in their body could very well be terminal. Even near our ...

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It is a bit of a hypothethical scenario where the body can breathe oxygen and does not rupture from the pressure difference (dissolved gases in the intestine and blood bubbling), but at the same time can evaporate and radiate freely. If we assume so, and also assume that there is no sunlight, then there are two major mechanisms for heat loss: radiative ...

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