Are space and time quantized quantities?

[tom.stoer]

Why do people research beyond standard model.

b/c they know that the model (SM of elementary particle physics + gravity) incomplete and (partially) inconsistent mathematically

 

[andrebourbaki]

>People build theories based on the observations they make in the macro world.

The existing theories, from QM to the Standard Model, and GR by itself, are all, as you say, based on macroscopic observations. We observe (in 1900) the spectral lines of Hydrogen, and after a lot of ingenious work, *deduce* something about the energy levels and the reason why electrons are not classical particles and do not radiate while in a stationary state (for example). Later, we look at tracks of bubbles big enough for us to see, in a bubble chamber at a particle accelerator, and deduce amazing microscopic physics things like
the omega minus particle, and the unification of the electro-weak force (1970s). This experience shows that we can have a lot of success at using macroscopic observations to deduce things about the microscopic world that we cannot 'see' with our eyes, but by combining logic, physical intuition, and these experimental data which are always based on macroscopic observations by our senses. So your comment

>I believe that nobody knows exactly what is going on even in the quantum world.

is, perhaps, unduly negative. We do not yet know everything going on in the interaction between curved space-time and quantum fields, nor cosmology. But probably most of what we know we know exactly...except for the effects of gravity on quantum systems. And there are problems of inconsistency and circularity and overlapping domains when and if one tries to *axiomatise* our knowledge.
This refers to what tom.stoer said in

>the model (SM of elementary particle physics + gravity) incomplete and (partially) inconsistent mathematically

But this does not mean that we don't know all sorts of things...it just means we have trouble organising our knowledge into an axiomatic system. The history of physics shows that usually this trouble is temporary.

 

[rpt]

It is difficult to believe in theories which say "can explain everything except few things, its a matter of clarifying those few exceptions"
Once people believed that classical physics could explain everything except few things like the movement of the planet Mercury. However when a new theory emerged to explain this, it changed the entire framework on which the previous theory was build upon.

 

[andrebourbaki]

Someone will, I hope, correct me if I am wrong, but the current state
is different than the perihelion of Mercury and the Stefan-Boltzmann
paradox, back before the GR rev and the Quantum rev. What you
refer to is stubborn (although small) experimental facts. But at present
what we have are not discrepancies with experiment, just logical contradictions, like the infinities of renormalisation or quantum measurement conceptual issues.

 

[tom.stoer]

...
But at present what we have are not discrepancies with experiment, just logical contradictions, like the infinities of renormalisation or quantum measurement conceptual issues.

Yes, something like that.

There seems to be a little chance to get the standard model + gravity consistent up to Planck scale using ordinary quantum field theory plus non-perturbative renormalization (asymptotic safety of gravity, current discussion regarding Higgs in the 125 GeV range using this approach). Nevertheless many people think that there are various theoretical or conceptual indications that something is missing.

For me this indicates a kind of paradigm change in physics.