The first thirteen questions of David Gross

[marcus]

http://preposterousuniverse.blogspo...erousuniverse_archive.html#110703702965929900

David Gross listed the "25 most important questions in physics"
John Ellis reported the list in his "Quantum Diary" and Sean Carroll put it on his blog. here is just the first 13 questions on the list. If you want to see the rest visit Carroll's blog, "Preposterous Universe".

1 - The origin of the Universe:

Was there a Big Bang, was it preceded by a Big Crunch, ...

2 - The nature of Dark Matter:

Is it composed of some unknown elementary particle, if so, what ...

3 - The nature of Dark Energy:

What is its microphysical origin, is it constant or varying ...

4 - The formation of structures in the Universe:

Testing the standard Cold Dark Matter paradigm, formation of stars ..

5 - The validity of General Relativity:

Does it work at all scales, in strong fields, ...

6 - The validity of Quantum Mechanics:

Is it modified at short distances, for large systems, in the Universe ...

7 - The problems not solved by the Standard Model of particles:

Particle types, masses and mixing, unification of forces ...

8 - The existence of supersymmetry:

Does this framework for new physics appear at accessible energies ...

9 - The solution of QCD:

Can it be solved analytically, e.g., via a string model ...

10 - The nature of string theory:

What is it ...

11 - The nature of space and time:

Are they fundamental or emergent phenomena ...

12 - Whether the laws of physics are unique:

Perhaps they are statistical accidents ...

13 - Can kinematics, dynamics and initial conditions be separated:

Perhaps they cannot be disentangled ...

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I like question 13. I have suspected for some time myself that they cannot be disentangled, or at least that I would never be able to make a clear distinction.
A fair number of Gross questions are issues for Quantum Gravity (inclusive of Loop Quantum Cosmology, of course, and research where QG contacts MOND). Namely 1,2,3,5,6, and 11.

And yes, number 11, that is Gross way of stating the central issue in Quantum Gravity, essentially the effort to arrive at a quantum theory of what space and time are, and how they are shaped.

"The nature of space and time. Are they fundamental or emergent?"

If what he means is what we see (flat old Euclidean space) then it surely is not fundamental! It must be a macroscopic impression emerging from some deeper reality. But emergent from what? A combinatorial set of relationships as in the "dynamical triangulation" model? An evolving network of interconnections à la Loop? A quantum logic of adjacency, an algebra furnished for the amusement of seven-dimensional birds? I will stop here.

 

[ohwilleke]

A fair number of Gross questions ar...us on AI, biology and theoretical philosophy.

 

[marcus]

... and theoretical philosophy.

Like question 10: what is the nature of string theory?

But I did see some regular particle physics questions (sort of thing one builds large hadron colliders to investigate) like 7, 8, and 9.

what struck me is how astrononomy-type questions (sort of thing one builds and orbits various types of telescope, to investigate) have come to the forefront for all of us not just for Dr. Particle Physicist Gross. Today, even if you have been a theoretical particle physicist all your life, the gut gripping questions have to do with the origin and shape and makeup of the universe.

 

[Chronos]

It is interesting how all of the fields in theoretical physics have gravitated toward each other over the past few decades. All of the fundamental questions end up saying something about why the universe as a whole looks and behaves as it does. One of the really bewildering features is how it seemlessly translates from the nearly infinitesimal to the nearly infinite. QFT and GR represent [apparently] both extremes, yet appear to be irreconcilable. Apparently we must probe even deeper at both ends of the scale to find a better solution. Perhaps we will never find an exact solution, just closer approximations.

 

[ohwilleke]

I find the sensitivity of cosmological scenarios to modest variations in neutrino mass particularly interesting.

 

[marcus]

I find the sensitivity of cosmological scenarios to modest variations in neutrino mass particularly interesting.

could you explain that some?
(I may be the only one reading this thread to whom it was obscure, but would like to understand better how small differences in neutrino mass wd affect big bang, or whatever it is they affect. Has this been written about much?)