B Is Gravity a Fundamental Force or an Emergent Effect?

[nytmr24]

If what we perceive as the force of gravity is really just the effect of curvature of spacetime, why do theorists
hypothesize the graviton as the force carrier for gravity? I thought that GR does away with the notion that gravity is a "force." So, is gravity a force or is it merely an effect?

 

[PeterDonis]

I thought that GR does away with the notion that gravity is a "force."

GR is a classical theory, not a quantum theory. Many physicists believe that a quantum theory of gravity must exist that underlies GR (i.e., for which GR is the classical limit), and in such a theory, there should be a level of description at which gravity works similarly to the other three known fundamental interactions, i.e., it should have a "force carrier" particle, which is called the graviton.

 

[sweet springs]

Current QT stands on flat space-time. Natural extension to gravity is force particle as we deal with Newton's gravitation force up to 19th century.
However, after thorough study of QT and GM fusion, in future as you say we may be able to build QT on curved space-time background where gravitation is not perceived as force.

 

[PeterDonis]

Current QT stands on flat space-time.

Not necessarily. Quantum field theory can be done in a curved background spacetime; for example, this is how Hawking radiation has been treated pretty much since its discovery.

in future as you say we may be able to build QT on curved space-time background

This isn't "in future". It's been done for several decades now. See above.

 

[sweet springs]

Yes it was introduced by Hawking, but not thoroughly as I hope.

 

[haushofer]

GR is a classical theory, not a quantum theory. Many physicists believe that a quantum theory of gravity must exist that underlies GR (i.e., for which GR is the classical limit), and in such a theory, there should be a level of description at which gravity works similarly to the other three known fundamental interactions, i.e., it should have a "force carrier" particle, which is called the graviton.

It could be just an effective description, similar to how we use phonons to describe sound waves. It depends on the question whether gravity is an emergent phenomenon or fundamental.