Is Quantum Gravity the Key to Understanding the Universe?

[brianhurren]

Is Timespace a literal real thing? or is it an abstract idea?

and what makes physisists so sure that gravity is a quantum field? and can be quantised?

 

[UltrafastPED]

Is Timespace a literal real thing? or is it an abstract idea?

Spacetime is a useful abstraction, it is a dynamical "thing" in Einstein's General Relativity (GR), the modern theory of gravity.

and what makes physisists so sure that gravity is a quantum field? and can be quantised?

Because quantum physics has shown itself to be the most accurate model for all other branches of physics ... thus the expectation is that it also applies to gravity.

The difficulty is in finding an appropriate way to do it - Special Relativity (SR) is already taken into account within quantum field theory, but the spacetime of SR is not a dynamic entity.

Also the field equations for GR are non-linear; this was not the case for Maxwell's electrodynamics - those equations are linear. That makes the mathematics much more difficult to work with.

 

[atyy]

Gravity is can be treated theoretically as a quantum field, and can be quantized to the point where it already makes predictions. For example, quantum gravity is a possible source of primordial B modes that Planck or BICEP2 might detect.

http://motls.blogspot.com/2014/03/bicep2-primordial-gravitational-waves.html It's still not known if BICEP2 really observed primordial B modes, but Liam McAllister discusses how quantum gravity could be a source of such modes.

 

[bhobba]

and what makes physisists so sure that gravity is a quantum field? and can be quantised?

The issue with quantum gravity is not what some popularisations make it out to be:
http://arxiv.org/pdf/1209.3511v1.pdf

The answer is its works for everything else, produces a theory in accord with observation up to a cutoff so there is zero reason to think QFT is an odd man out.

Now peeking behind that cutoff is another issue - and all our theories are up for grabs beyond that - it may be string theory - it may be something else - we don't know.

Thanks
Bill