# Tag Info

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Dark matter is gravitationally ordinary, as G. Smith says, and attracts. Dark energy can be understood as a combination of energy-density and tension, somewhat as a stretched elastic band has tension. According to general relativity, energy-density always attracts gravitationally, and the presence of tension always counteracts this. The tension in ordinary ...

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Gravity is described classically by General Relativity, and yes it also has gravitational waves : Gravitational waves are disturbances in the curvature of spacetime, generated by accelerated masses, that propagate as waves outward from their source at the speed of light. They were proposed by Henri Poincaré in 1905 and subsequently predicted in 1916 by ...

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I would think, in fact, that the relative sizes don't particularly matter. Why doesn't gravity make things accelerate past the speed of light if they are far enough away? To be sure (just in case), please keep in mind that the (Newtonian) gravitational force is not constant with distance even though we usually approximate it as constant for elementary ...

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Let's assume that the planet, mass $M$, and the object, mass $m$ are the only objects under consideration and there are no external forces acting. The force that each object exerts on the other is the gravitational force $\dfrac{GMm}{R^2}$. You will note that the forces gets smaller and smaller as $R$ gets bigger and bigger. If both objects start at ...

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The gravity of dark energy is repulsive (but not because it has negative mass or negative energy density). However, the gravity of dark matter is boringly attractive. The difference between dark matter and ordinary matter is not in their gravity but in their electromagnetic interactions: dark matter doesn’t have any, so it doesn’t emit or absorb light or ...

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If an ultra compact/dense Galaxy has a Schwarzschild radius same as it is own radius, it will have formed an event horizon around the galaxy. So, not only will the galaxy be unobservable for the rest of the galaxy, the inhibitants of said galaxy will be on an unavoidable trajectory towards collapse to a final singularity.

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Potential energy doesn't really "come from" anywhere. One way to see is is to recognize that we can add any constant to our potential energy, but the physics doesn't change. So, I guess one could say potential energy "comes from" just being acted upon by a conservative force. However, what is more important are changes in potential energy. A change in ...

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The question whether two liquids mix or not is mainly to do with the intermolecular forces, not the densities. These forces lead to the bulk property known as chemical potential. Assuming the experiment is done in a pressurized cabin, then the ambient temperature and pressure may take ordinary values such as STP (room temperature, 1 atmosphere of pressure)....

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