Over at Quantum Diaries, John Ellis reports on a colloquium given by David Gross, where he lists his version of the twenty-five most important questions in physics. Here is Ellis’ transcription of Gross’ list:
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 ….
14 – Are there new states of condensed matter:
Not just the usual Fermi liquids ….
15 – The understanding of complexity in computing:
Is there something beyond the artefacts of approximations ….
16 – The construction of a quantum computer:
One with 10,000 qbits would be useful ….
17 – The existence of a room-temperature superconductor:
It would make a technological revolution ….
18 – The existence of a theory of biology:
Does it have an underlying conceptual structure, like physics ….
19 – Deducing physical form from genomics:
Can one deduce the shape of an organism from its DNA sequence ….
20 – The physical basis of consciousness:
New physics, emergent phenomenon, or ….
21 – Could a computer become a creative physicist:
Would we train it starting from Newton and Einstein ….
22 – How to avoid the balkanization of physics:
People from different fields should understand each other ….
23 – The scope of reductionism:
Is it universal, or do new laws emerge in complex systems ….
24 – The role of theory:
Does it lead or follow experiment ….
25 – How to avoid depending on unrealizable big physics projects:
They cannot continue for ever growing in size, cost and time-scale ….
I think it’s a pretty good list, but then again my research proclivities aren’t that far away from David’s, as these things go. The list falters near the end, when he takes up meta-questions like “The role of theory.” These things are fun to talk about over coffee, but they don’t have right answers in the way that “Does supersymmetry exist?” does. Progress on them happens via practice, not via contemplation. Scientists try to understand how the universe works in a quantitative, empirical way; the best strategies for getting there will change with time in response to circumstances, and deciding ahead of time what (e.g.) the role of theory should be is a hopeless endeavor.