the nature of Gravity

[mr.spaceman]

I have one layman question

 

Is gravity the geometry of space itself?

 

If it's right then I don't understand how gravity can be the fundamental force and geometry of space itself simultaneously

 

A force that spreads out with particles, creates waves, and geometry of the universe which curves space.

 

 

 

thank you

[elfmotat]

It sounds like you're wondering how gravitons can exist, or why they're even needed, if general relativity models gravity as a result of the geometry of spacetime. There are two main interpretations that people take when approaching quantum gravity. One of these is that gravity "really is" a result of the spacetime geometry, so quantizing gravity should just be quantizing spacetime in some manner. This is the approach of Loop Quantum Gravity. The other interpretation that gravity is caused by a spin-2 massless field on a flat spacetime background, similar to the way electromagnetism is caused by a massless spin-1 field. The properties of a spin-2 field give the "illusion" that the background spacetime is curved. The excitations of this field are gravitons, just like photons are excitations of the electromagnetic field. This is the approach taken by string theory.

[juanrga]

I have one layman question

 

Is gravity the geometry of space itself?

 

If it's right then I don't understand how gravity can be the fundamental force and geometry of space itself simultaneously

 

A force that spreads out with particles, creates waves, and geometry of the universe which curves space.

 

thank you

 

In general relativity (GR) gravity is associated to spacetime curvature. There is not gravitational force in GR.

 

In other models such as in the field theory of gravity (FTG), gravity is associated to a gravitational force mediated by particles named gravitons.

 

Both are two different models and would not be mixed.

[mr.spaceman]

It sounds like you're wondering how gravitons can exist, or why they're even needed, if general relativity models gravity as a result of the geometry of spacetime. There are two main interpretations that people take when approaching quantum gravity. One of these is that gravity "really is" a result of the spacetime geometry, so quantizing gravity should just be quantizing spacetime in some manner. This is the approach of Loop Quantum Gravity. The other interpretation that gravity is caused by a spin-2 massless field on a flat spacetime background, similar to the way electromagnetism is caused by a massless spin-1 field. The properties of a spin-2 field give the "illusion" that the background spacetime is curved. The excitations of this field are gravitons, just like photons are excitations of the electromagnetic field. This is the approach taken by string theory.

 

If string theory is right does this means that the space-time curvature is an illusion?

 

In general relativity (GR) gravity is associated to spacetime curvature. There is not gravitational force in GR.

 

In other models such as in the field theory of gravity (FTG), gravity is associated to a gravitational force mediated by particles named gravitons.

 

Both are two different models and would not be mixed.

 

Ok then which one is correct? How do you think?

 

 

Gravity is one, is it curvature of space-time or is it a force? If it's both then how?

[juanrga]

If string theory is right does this means that the space-time curvature is an illusion?

 

Ok then which one is correct? How do you think?

 

Gravity is one, is it curvature of space-time or is it a force? If it's both then how?

 

General relativity is a classical theory. A theory of gravitons is more fundamental. In fact, string theory obtains general relativity as a classical approximation to a underlying quantum theory of gravitons. Gravitons are the carriers of the gravitational force (somewhat as photons are the carriers of electromagnetic forces)

 

http://public.web.cern.ch/public/en/science/StandardModel-en.html

 

although gravitons have not been detected still due to technical difficulties (I do not doubt of their existence!!).

[elfmotat]

If string theory is right does this means that the space-time curvature is an illusion?

 

 

 

Ok then which one is correct? How do you think?

 

 

Gravity is one, is it curvature of space-time or is it a force? If it's both then how?

 

The problem with your question is that interpretations can't be verified by experiment. Science does not and cannot answer the question of what's "really" happening. Using a certain interpretation may be advantageous when developing a theory, but that doesn't necessarily mean it's correct. Two theories based on vastly different interpretations can describe the same phenomena.

[juanrga]

The problem with your question is that interpretations can't be verified by experiment. Science does not and cannot answer the question of what's "really" happening. Using a certain interpretation may be advantageous when developing a theory, but that doesn't necessarily mean it's correct. Two theories based on vastly different interpretations can describe the same phenomena.

 

He is not asking about interpretations but about two different physical models. The geometric model of general relativity and a force model associated to graviton theories are experimentally distinguishable. The graviton model gives higher order corrections to the general relativity model. What happens here is, as stated before, that our current technology is not still sophisticated enough for the measurement of the corrections and for the detection of gravitons.

Edited July 20, 2012 by juanrga

[elfmotat]

The geometric model of general relativity and a force model associated to graviton theories are experimentally distinguishable.

 

That was the point of my post.