Non-geometric approach to gravity impossible?

PAllen

I gave the same Deser link in #75.

Mentz114

Thanks, but I missed it. These threads have grown to unmanageable sizes ...

bcrowell

And none of us who have been posting have the combination of theory chops and several months of spare time that it's now clear would be needed to do more than skim through some of the literature and note what different experts seem to be claiming.

waterfall

Ok. I have the MTW book. What particular pages can I find the answers of how to decompose the FRW Spacetime into flat space equivalent so that I can maybe contribute a future article in Sci.Am and and state that "You know, in FRW universe, it's not really curved, it only appeared curved. We are really living in flat spacetime with spin-2 field giving us the curveness." I'm sure the sci-am editors would love it.

waterfall

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?

PAllen

Or you could say the spin 2 field is illusion. The only thing that counts as clearly not subject to interpretation is predictions of observation or experiments. Beyond that, curvature and fields, both, are not observable per se.

waterfall

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

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

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

Whether true or not, science is not about believing.

waterfall

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

And now we have moved beyond asking questions and into the realm of pushing your viewpoint.