# Tag Info

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The Planck length is a quantum effect (among others). SO the answer is: yes, speeds in the universe are limited by c, and also by the Planck length, indirectly. However, this latter limit has never been measured nor achieved, so that in practice, the limit by c is sufficient. All Planck values are limits. There is no way to get a measurement result lower ...

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While we are getting closer to speed of light our length in the direction of the movement is according to Lorentz transformation getting shorter. This are two misconceptions here. One is that the way this is written implies that velocity is absolute. This is not the case. The "relativity" in relativity theory means exactly the opposite. Velocity is ...

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But we can not (even theoretically) consider length shorter than Planck length. This is a popular misconception. Treating Planck units as special is really more numerology than anything else. For example, the Planck mass is about the mass of a single biological cell. Does that mean physics doesn't apply to anything smaller (or is it larger?) than a ...

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Quite probably gravitons can cause similar effects as photons. The reason I believe so is that gravitons arise by quantizing linearized gravity (linear approximation to GR), the procedure is very similar to quantization of electromagnetism. Individual gravitons have the usual relativistic energy and momentum relation to frequency (energy-density is ...

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One doesn't. We haven't even detected gravitational waves, much less single quanta of gravitational waves. As of now, gravitons are a theoretical idea derived by extending quantum mechanical ideas to general relativity.

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From what I understand gravity is similarly quantized and transmitted via gravitons. Well, we don't know that. There is no accepted quantum theory of gravity, only approximations like semiclassical approaches. We cannot give you a "mental picture" at the moment because we don't have one. We can speculate all day, and extrapolate from all the other ...

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I cannot answer to all the questions but would like to stress something regarding what the Casimir effect tells us and what it doesn't. If you look at how it is derived for the usual EM interaction, an experimental verification of the standard Casimir effect tells us that: the EM field can have standing waves between two plates and outside them There ...

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There is huge tension between the viewpoints. The current 'Firewall' debate - that QM predicts a huge amount of physics happening at the horizon where GR says that nothing at all should be happening is an example of the problems being faced in this area.

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I think it helps to look at why things get stuck at all. If you have two things that could together get to a lower energy level than they are at now, and they can give that excess energy up to something (like sending photons into deep space) that isn't going to give it back (at least for a long time), then they can get stuck (at least for a while). So why ...

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The paradox you describe is even worse than the effect of gravity alone: Electrostatics works the same, attracting most matter at everyday distances very strongly by comparison. That is obvious for opposite charges, but even neutral matter attracts as electric interaction induces dipoles. Even where you have equal charges, which do repel each other, you do ...

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Ignoring the quantum effects that make such a situation both improbable and overtaken by stronger but shorter acting forces - if we take Newton's gravitational equation with the inverse square law: $$F = \frac{G \cdot M_1 \cdot M_2}{R^2}$$ and if, in theory, you get 2 objects to occupy the same exact space - (ignoring quantum and other difficulties there ...

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There is no established quantum theory of gravity. Hence, at the microscopic level of particle, we don't know what is going on gravitationally between particle, but it isn't going to be the "inverse square law" we know, just like electromagnetism between two charged particles is, on quantum scales, not just an "inverse square law", but a rich variety of ...

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First of all, infinitesimal small distances are not allowed in the quantum world simply due to the Heisenberg uncertainty principle - the Newtonian force law doesn't hold at these distances. Apart from that, new forces arise that repel at short distances, a simple $H_2$ molecule is an example for that. When you manage to collide particles instead, the whole ...

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There is no tension between the two viewpoints. In fact, the situation isn't much different from electromagnetism. The analogy is photon $\leftrightarrow$ graviton and electromagnetic field $\leftrightarrow$ metric tensor. Both of these theories, EM or GR, are field theories, and exhibit the phenomena of radiation. Gravity waves have not been detected yet ...

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Consider the function $e^x$: it is monotonically increasing and yet defined for all negative $x$. Just because something increases monotonically doesn't mean it must reach infinity (or even its maximum value) in a finite amount of time. As a side note, please don't refer to entropy as disorder. It's very common but also very wrong: ...

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I just want to point out that the dimensionality of spacetime is a bit of a fluid concept in string theory. Superstring theory can only be formulated in 10 dimensions, but it can be shown to be dual to an 11-dimensional theory called M-theory. It has also been conjectured to be dual to a 12-dimensional theory known as F-theory, although whether or not this ...

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The interesting form of radiation here is not Hawking radiation, but gravitational wave radiation. For astrophysically-sized black holes, the Hawking radiation is completely negligible relative to other processes. For example, for a solar mass sized Schwarzschild black hole, the black hole radiates like a black body at 60 nano Kelvins (far below the ...

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