# EM waves in vacuum analogy

• B
Gold Member
2022 Award
Well, the difference between this example and the question, where the mass of the nucleon comes from, is that the latter question is not completely answered yet. It's the notorious problem to understand "confinement" from first principles (in this case quantum chromodynamics, QCD). We are pretty sure about the statement that the nucleon mass (and the masses of the other hadrons) is due to the strong interaction is from lattice-QCD calculations, i.e., numerical evaluations of QCD, leading to a satisfactory description of the hadronic mass spectrum.

• PeroK and Delta2
Homework Helper
Gold Member
@vanhees71 One final question, the mass that generates the gravitational field is the one due to Higgs field coupling, the one due to color confinement or both? Or we don't know yet?

Staff Emeritus
Homework Helper
Gold Member
@vanhees71 One final question, the mass that generates the gravitational field is the one due to Higgs field coupling, the one due to color confinement or both? Or we don't know yet?
The source in Einstein’s field equations (that govern spacetime curvature) is the stress-energy tensor. What generates gravity is therefore not only mass but energy, momentum, and stresses.

• Delta2
Homework Helper
Gold Member
The source in Einstein’s field equations (that govern spacetime curvature) is the stress-energy tensor. What generates gravity is therefore not only mass but energy, momentum, and stresses.
Yes ok, relativity says there are other sources of gravitational field as well, I am just interested to know regarding the mass as source.

Staff Emeritus
Homework Helper
Gold Member
Yes ok, relativity says there are other sources of gravitational field as well, I am just interested to know regarding the mass as source.
You cannot decouple mass as a source. It is part of the stress energy tensor.

(Also: I finally did it! When I write ”str” on my phone it suggests ”stress energy tensor” for completion)

• • Shreya and vanhees71
Gold Member
2022 Award
@vanhees71 One final question, the mass that generates the gravitational field is the one due to Higgs field coupling, the one due to color confinement or both? Or we don't know yet?
The source of the gravitational field is not mass but the energy-momentum-stress tensor of matter and radiation.

Hillbillychemist
This equation states that there is a form of energy connected with mass, namely rest energy. And mass is not the same thing as matter, mass is yet another property of matter.
Yet nothing is at rest. Everything is in motion.

• weirdoguy and Dale
weirdoguy
Yet nothing is at rest. Everything is in motion.

Nonsense. There are infinitely many reference frames in which you are at rest.