Binary & Tweed
Just found this great channel that does quantum physics visualizations
In theories of quantum gravity, the graviton is the hypothetical quantum of gravity, an elementary particle that mediates the force of gravitational interaction. There is no complete quantum field theory of gravitons due to an outstanding mathematical problem with renormalization in general relativity. In string theory, believed to be a consistent theory of quantum gravity, the graviton is a massless state of a fundamental string.
If it exists, the graviton is expected to be massless because the gravitational force has a very long range, and appears to propagate at the speed of light. The graviton must be a spin-2 boson because the source of gravitation is the stress–energy tensor, a second-order tensor (compared with electromagnetism's spin-1 photon, the source of which is the four-current, a first-order tensor). Additionally, it can be shown that any massless spin-2 field would give rise to a force indistinguishable from gravitation, because a massless spin-2 field would couple to the stress–energy tensor in the same way that gravitational interactions do. This result suggests that, if a massless spin-2 particle is discovered, it must be the graviton.
Gravity isn't included in the standard model. 'Naive' attempts to construct a quantum theory of gravity are non-renormalizable, meaning they can't be used to calculate anything because they give meaningless, infinitely large answers to any calculation you try and do. (Actually it's pretty common for quantum field theories, in their 'raw' state, to produce infinities; this is handled by a mathematical trick called normalization, which cancels these infinities. But - and I'm probably drastically over-simplifying here - attempts at quantizing gravity like any other field (such as the electromagnetic field) yield an infinite number of infinities, which cannot be renormalized away.
Yes, this is exactly right: the graviton is to the gravitational field (i.e. perturbations in spacetime) what the photon is to electromagnetic fields, which includes light (and radio etc.).But I don't understand how the concept of a graviton figures into this. I suppose analogous reasoning can be applied from EM radiation, where there is a quantum of... energy/mass (?) associated with EM waves, i.e that they aren't indefinitely divisible.
This was beyond me, but at least I'm better able to identity that which I don't understand.There's quite a thorough answer here from a guy who seems to know what he's talking about (i.e. a bit more than me):Adam Lantos's answer: They are not incompatible! It’s just that the naive reconciliation of gravity and quantum mechanics leads to a theory that is not totally predictive. When we try to quantize gravity in a similar way that we quantize other fields, we get a theory that is not predictive. Ever...www.quora.com
The standard model displays the mass of particles in terms of Ev/c^2.I gather E = mc^2 is a way of understanding energy and mass in terms of each other, and that changes in the energy of a system slightly effect the mass of the system, but can they be understood as two sides of the same coin?