# Tag Info

## New answers tagged quantum-gravity

-1

It is the refusal to accept the possibility that the speed of gravity exceeds the speed of light. Planck constant was derived from the speed of light. It is the smallest amount of energy exchange between electrons and charges. In the case of gravity, the exchange of energy is not to move electrons to higher orbitals but to move mass or the entire nucleus ...

1

First let us cut away some of the meat and the bones of your question. Let us forget about thermodynamics for a minute and classical physics; however we will need GRAVITY (not Newton’s version). Instead of calling it Gravity let us call it General Relativity or (GR). We can still use the term Gravity, but when discussing Quantum Mechanics it’s better to ...

1

Hawking radiation is indeed usually calculated as a semiclassical effect (classical gravitational field and quantum matter), which is invalid at high energy ($\langle T_{\mu\nu}\rangle >> 1$) and high fluctuations ($\langle T_{\mu\nu} T^{\mu\nu} \rangle - \langle T_{\mu\nu} \rangle \langle T^{\mu\nu}\rangle >>1$). Still, it is a result that is ...

1

Lets start with the definition of M theory: M-theory brought all of the string theories together. It did this by asserting that strings are really one-dimensional slices of a two-dimensional membrane vibrating in 11-dimensional space. So the universe which is at the microscopic level quantum mechanical, is composed of these ...

-1

Forgive my ignorance but it seems to me that the other 3 fundamental forces can be described in electrical terms (hence unification I presume). We use nuclear forces even in power stations. Yet gravity seems to me to be an entirely different entity, it can be seen to be a distortion in space-time. If I picture in my mind a future time where some sort of ...

-4

If the two objects are electrons then the gravitational force is always negligible.

5

In classical gravity, the answer is "never". In general relativity, the answer is "never". Now what about a quantum theory of gravity? We don't know how it'll work, but it should reduce to general relativity in the classical limit (i.e. the limit of weak fields and large distances, which is exactly what your question is about). So the answer is still ...

3

No distance is far enough. Among other things, if you are extremely far away, then there is room for lots and lots of things to be far away from you and even if they individually have little effect we can find the net effect of all of them. So we know the effect of each one is not zero. So we can prove the effect of A on B is not zero even when they are ...

1

The question is ill-posed. At the classical level, the force (gravitational or otherwise) between objects never becomes zero. It goes to zero as the distance goes to infinity, but it never really becomes zero. At the quantum level, we don't have a theory of gravity, but already the concept of "distance" doesn't make precise sense anymore, since quantum ...

1

I think it is important to note that the wavefunction of quantum mechanics is not a field like the electric or magnetic field. It assigns complex numbers to configurations. So it is a function where the domain of the function is not space or even spacetime. So there is not a value of the field at a point in spacetime, so there isn't a thing to curve it. ...

1

Unfortunately, that question's answer depends on the theory of quantum gravity that you chose. But roughly here is the situation : If you take a classical spacetime and quantum matter fields ($G_{\mu\nu} = \langle T_{\mu\nu} \rangle_\omega$), also known as semiclassical gravity, then the stress energy tensor varies with the measurement. The standard ...

0

String theories quantize gravity and aim to a model of a unified theory with the other three interactions which are well described by the standard model for elementary particles. In physics, string theory is a theoretical framework in which the point-like particles of particle physics are replaced by one-dimensional objects called strings. String ...

0

To complement Ernie's description of the experimental evidence (and some of the theoretical evidence) that gravity must ultimately be 'quantum' in nature there are additional theoretical arguments that gravity waves (which as Ernie said are distinctly prediced by general relativity, even though we haven't observed them yet) must correspond to some ...

0

General relativity predicts gravity waves. If subatomic particles deliver the full menu of gravitational effects, they should should agree with the equivalence principle, an important corollary of gravity. Here it is in Einstein's own words: "...the law of the equality of the inertial and gravitational mass is equivalent to the assertion that the ...

3

If we know the classical physics theory of the electromagnetic force (and we do), we can guess what the quantum mechanics theory for it should be (and then test with experiment, and as far as we can tell we've guessed correctly). We can do likewise with any classical force. (Although the strong and weak theories were not found by starting from any classical ...

0

General Relativity predicts "infinities" at the singularity of a black hole. Quantum Mechanics, Realativistic Quantum Mechanics, and Quantum Field Theory ignore gravity. The Firewall Paradox here give a good explanation of a problem encountered when trying to describe things governed by both Quantum Mechanics and Relativity. Wikipedia talks about quantum ...

1

Your premise is that quantum gravity has effects near the singularity and that the event horizons is a barrier to getting information our from within the horizon. So a simple theoretical investigation is to look at a very very small black hole, one where the outside of the event horizon is still near the singularity and thus the quantum gravity effects are ...

0

There are a number of attempts at constructing theories of quantum gravity, of which string theory and loop quantum gravity are the most developed. However none of these theories have been developed to a point where they can make uncontroversial predictions about what happens near a black hole singularity. The only even passably convincing attempt is using ...

1

Quantum mechanics has an absolute time concept, and general relativity has the dynamic time concept of spacetime. The incompatibility of both concepts is called the problem of time in quantum gravity. Yes, but that Wikipedia article needs attention from an expert. It says "therefore, we arrive at the conclusion that 'nothing moves' ('there is no time') ...

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