[RobC (OP)]

So much work into unifying general relativity and quantum mechanics but could the effort have been made elsewhere?

[alancalverd]

Or not at all. But it is in the nature of the human mind to ask questions.

There are however subtle differences. Since temperature is the average kinetic energy of a very large number of particles it inherently tends to a continuum even if the ke of each particle were quantised. Gravity on the other hand is difficult to model without an exchange particle or virtual particle, which may well turn out to be quantised. 

[yor_on]

It depends on how you look at it. Do you want reality to consist of 'bits', aka quantized 'particles'? That is the way we looked at things before relativity. In Quantum mechanics you have those bits that are more or less non existent as, sorry forgot their names, but they 'exist by their absence'.. And then we have superpositions. Depending on definition gravity is a force or a accelerated frame of reference. And we shouldn't forget entanglements and quantum logic's.

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[evan_au]

Do you want reality to consist of 'bits', aka quantized 'particles'? That is the way we looked at things before relativity.

I wonder about the sequencing of quantum theory and relativity...
It's true that Einstein explained the photo-electric effect before he described relativity.

But the ideas of quantum theory took a long time to develop, and involved very many theoretical and experimental physicists.
Relativity was developed primarily by Einstein himself as a fully-formed theory, with a 10-year gap between Special Relativity and General Relativity.

I would say that general adoption of relativity occurred very soon after Eddington measured bending of light by the Sun's gravity.
General adoption of quantum theory took a lot longer, since it involved messy interactions of real particles, which don't have a simple underlying theory like relativity.

General relativity looks at the universe on large scales (eg asteroid size and larger), so the details of atoms and subatomic particles can be ignored. It's only when you come close to the boundary of a black hole that these two views collide.

[yor_on]

I'm not sure but I have a vague memory of the idea of quantization being a lot older than the idea of a continuous wave (a flow instead of 'bits')? Meaning that I think it existed as a philosophical question long before the introduction of modern science. It has a natural compliance with the way we see nature behave in our daily lives I guess.

[evan_au]

the idea of quantization being a lot older than the idea of a continuous wave

Are you thinking of Democritus, with his idea of atoms as discrete objects?
https://en.wikipedia.org/wiki/Democritus#Atomic_hypothesis

Or maybe Zeno's paradoxes, dealing discrete vs continuous?
https://en.wikipedia.org/wiki/Zeno%27s_paradoxes

These certainly predate Einstein's relativity - but then the debate between discrete vs continuous light had raged for centuries before Einstein, involving luminaries like Newton & Huygens.

[yor_on]

Sounds familiar both Evan.

[kkumar326]

So much work into unifying general relativity and quantum mechanics but could the effort have been made elsewhere?

Temperature is just a concept associated with the kinetic energy of the particles in a system. It is measured in average as we cannot really get the exact number of collisions at a time. So, it can take any real number. Make sure that you don't confuse temperature with heat energy.

Gravity on the other hand is a wave. Quantization would come when we find some particles related to gravity like gravitons, which are just a concept.

[RobC (OP)]

"Could gravity be like temperature and not be able to be quantised"?

This is a rhetorical question I heard Freeman Dyson ask and at the same time he made the point that General Relativity and Quantum Mechanics should not be unified

[evan_au]

Gravity on the other hand is a wave.

Are you thinking of Gravitational Waves from spiraling black holes, such as are detected by LIGO? These certainly are waves, and propagate through space at the speed of light.

However, if you had a lone planet or black hole, sitting in intergalactic space, far from any other mass:
- It still has a gravitational field, as it will deflect passing light (and it would hold on to any orbiting satellites)
- But this gravitational field does not propagate away through space, and does not act like a wave. It is just a static gravitational field.
- This distinction does not change if you quantize it by including the hypothetical graviton.

This is analogous to the idea of a static electric field, which does not act like a wave, and does not propagate through space
- However, if you accelerate an electric field, it will produce electromagnetic waves, which do propagate through space.
- This distinction does not change if you quantize it by including the very real photon.