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Non-geometric approach to gravity impossible?

by waterfall
Tags: gravity, impossible, nongeometric
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waterfall
#109
Mar2-12, 08:48 PM
P: 381
Quote Quote by waterfall View Post
If I can't find it in MTW.. the simplest I'd use is this:

In Milne universe, there is zero energy density, no cosmic microwave background radiation, no matter of any kind.

When one adds matter and spin-2 fields. Then it becomes FRW Universe with the curveness only as illusion".

I think the above makes sense. Do you agree with it atyy?
You guys may ask what is the point of all this. The point is this. The mere facts about gravitons makes General Relativity just an effective field theory. Meaning GR is not a priori. What is a priori are gravitons. Note you can't combine gravitons and General Relativity because geometry can't have gravitons. Therefore let's accept the GR we are studying is not really a priori or primary. Perhaps just a classical limit. The true thing are the gravitons and spin-2 fields in flat spacetime. This is the real meat of it.
PAllen
#110
Mar2-12, 08:49 PM
Sci Advisor
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Quote Quote by waterfall View Post
You guys may ask what is the point of all this. The point is this. The mere facts about gravitons makes General Relativity just an effective field theory. Meaning GR is not a priori. What is a priori are gravitons. Note you can't combine gravitons and General Relativity because geometry can't have gravitons. Therefore let's accept the GR we are studying is not really a priori or primary. Perhaps just a classical limit. The true thing are the gravitons and spin-2 fields in flat spacetime. This is the real meat of it.
Note that no one has observed a graviton, and Tony Rothman has 'nearly proved' that no graviton will ever be detected in the way photons are. Further, in a graviton theory, the flatness of spacetime is inherently unobservable and unrelated to predictions of time or distance measurements.
waterfall
#111
Mar2-12, 08:56 PM
P: 381
Quote Quote by PAllen View Post
Note that no one has observed a graviton, and Tony Rothman has 'nearly proved' that no graviton will ever be detected in the way photons are. Further, in a graviton theory, the flatness of spacetime is inherently unobservable and unrelated to predictions of time or distance measurements.
But 97% of Ph.D.s believe in gravitons.. this is precisely what String Theory is about.. gravitons. The 3% are the Loop Quantum Gravity camp which believes geometry or GR is primary, they are just a minority.. so if you believe in the latter.. then you belong to the minority LQG camp.
Passionflower
#112
Mar2-12, 09:34 PM
P: 1,555
Quote Quote by waterfall View Post
But 97% of Ph.D.s believe in gravitons.. this is precisely what String Theory is about.. gravitons. The 3% are the Loop Quantum Gravity camp which believes geometry or GR is primary, they are just a minority.. so if you believe in the latter.. then you belong to the minority LQG camp.
Whether true or not, science is not about believing.
waterfall
#113
Mar2-12, 09:43 PM
P: 381
Quote Quote by Passionflower View Post
Whether true or not, science is not about believing.
Bottomline is that we need a theory of quantum gravity. Gravitons are good approach becuase of the success of QED, Electroweak, Strong Force which is based on particles and quantum field theory. You can' make a geometry theory out of them. This is why Gravity force needs to follow the path of field approach. This is what makes String Theory so popular. And if you think String Theory has the geometry as a priori and the gravitons are just an excitation of the gravitational wave.. then you are wrong. Gravitons exist in string theory in the sense that when you have gravitons, you have gravity. And for gravitons to exist. You need quantum fields. This makes Geometry as secondary. This is the precise reasons why I want to understand more about spin-2 fields in flat spacetime. Because if they are unlikely on empirical grounds like FRW metric unable to decompose to spin-2 field + flat spacetime. Then we have to go to geometry and LQG may be a way to go or other geometry based theory.
Vanadium 50
#114
Mar2-12, 09:52 PM
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And now we have moved beyond asking questions and into the realm of pushing your viewpoint.


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