What are the next 'big things' in physics?

Factual Questions
1

I’m not very au fait with the natural sciences - but I wish I were. As such, then, please forgive my ignorance… I just got to wondering…

What are the nuts that the global community of physicists are currently trying to crack? What is research funding going into in terms of figuring our the laws of the universe?

I personally would like to know whether string theory is ‘true’, and whether or not ‘the multiverse’ is a thing. But do professionals in this area concur with my areas of interest? When physicists go to conferences, what do they talk about nowadays? (in as plain English as possible please!)

Thanks!

2

Figuring out gravity would be a pretty big deal.

First you have to say which string theory you’re talking about! There are a lot of good theoretical models and some wacky ones, but none are really testable at this stage.

3

Yeah, y’see - this right here :slight_smile: What do you mean “figuring out gravity”? What is there to figure out?

4

The first really good theoretical model of gravity we got came from a Mr. Newton. He was able to describe mathematically the motion of the planets that he and his contemporaries observed, and this same mathematical model described apples falling and baseballs flying and so forth.

But later, people started noticing some problems. Newton’s models appeared to disagree with observations of certain things: planets moving in the presence of large gravitational fields, for instance, didn’t go exactly where they were supposed to. For example, Mercury is very close to the sun (lots of gravity nearby), and its movements didn’t precisely match what Newton said they should be, although it was close.

Mr. Einstein and others came up with a more precise mathematical model of gravity that explained these discrepancies. For small velocities or amounts of gravity, the differences in Einstain’s and Newton’s math basically cancel out to almost nothing. But where large velocities or gravitational fields are present, Einstein’s model gives answers that are measurably different, and these answers agree with our observations of Mercury, and other things.

So we’re done, right?

Well there’s a problem with the other forces in the universe.

James Clark Maxwell was the first to figure out that the existing mathematical models for electricity and magnetism were actually just specific versions of more general equations that could describe both. So if electricity and magnetism could both be described by the same set of equations, maybe they’re just different aspects of the same thing? From then on, physicists started talking about electromagnetism as one thing, since it had one model. There are other forces, such as the strong and weak force, that govern certain nuclear reactions (radioactive decay and such) and have their own mathematical models.

It turns out that all three of these (electromagnetism, strong force, weak force) can ultimately be explained with a nifty mathematical tool called quantum mechanics. The Standard Model of quantum mechanics perfectly explains everything we can observe (and have observed) about the electromagnetic, strong, and weak interactions.

But it says basically nothing about gravity. For that, we still have to rely on Einstein. (Or Newton, who suffices for most earthly calculations.) Not only does quantum mechanics say nothing about gravity, it seems to be fundamentally incompatible with Einstein’s model of gravity. Special relativity is a smooth, continuous phenomenon based on curving space and calculus, whereas quantum mechanics is a bumpy, discontinuous model based discrete mathematics.

So is it possible that there is an even more general model that can describe both the quantum world and the relativistic one, like the way Maxwell unified electricity and magnetism? That’s what string theorists and others are trying to figure out.

But one major problem is that as great as Einstein was, even his model of gravity is incomplete. Like the way Newton’s model breaks down at high velocities or near large gravity fields, relativity breaks down when it comes to black holes and the mysterious dark energy, which seems to cause the universe to expand, faster than the speed of light!

So on the one hand, we have a model (the Standard Model) that successfully explains 100% of 3/4 of the forces of the universe, and another model (Relativity) that successfully explains 99% of the other one.

Completing the theory of gravity and then finding a way to unify it with the Standard Model will make whoever does it the new smartest guy in the world.

5

I believe astrophysicists and astronomers would quite like to know about dark matter.

6

So what is Cecil waiting for? Is he just biding his time?

7

Thank you - first of all - for taking the time to write that synopsis - really!

Secondly, though, is that what physicists are writing in the box when they are applying for funding? Is that task, as you describe it, the sort of thing that one person/team can do? Or is this the ‘grand scheme of things’ job that thousands of physicists are endeavouring to accomplish, albeit in their own little way one-bit-at-a-time?

8

There’s also practical physics which has interesting problems of its own waiting to be solved.

Large-scale controlled nuclear fusion being one example.

9

Second that! Good overview for us non-physics majors out here.

10

I don’t think you’re going to get a grant just by saying something like “I’m going to try to figure out why gravity happens.” The grant foundation is going to expect you to have a specific plan.

11

Of course when it comes to “big” things in physics, you have to mention the LHC.

The first 13 TeV collisions are expected in late May to early June and lots of people are pretty excited to see what comes out of those collisions.

12

A multiverse would be cool.

So would finding out that existence didn’t start at the big bang.

I have no idea how realistic those discoveries would be on a medium term timeline. I have no idea if those are the ‘big’ questions in physics.

13

Richard Feynman described turbulence as “the most important unsolved problem of classical physics.” That’s still true all these years later.

Turbulence is everywhere and in everything. It’s as basic to movement as gravity. It’s not as sexy a subject, but it’s a big problem in physics terms.

14

Many, many things. You might be surprised first by the sheer number of areas of investigations, neverminding the topics themselves. Cribbing in part off the American Physical Society’s list of divisions but adding a few entries of my own to pull out subcategories that deserve explicit mention, you’ve got broad topical areas of:

Atomic, molecular, and optical physics
Atmospheric and oceanographic physics
Astrophysics
Biophysics
Chemical physics
Computational physics
Condensed matter physics
Cosmology
Fluid dynamics
Geophysics
Gravitation
Materials physics
Nuclear physics
Particle physics
Physics of beams
Plasma physics
Polymer physics
Quantum computation
Superconductivity

Each of these areas will have scores of open questions being actively investigated. In terms of conferences, you can have multi-day, 100-person conferences devoted to mere sub-sub-sub-topics of any one of these.

15

Back to gravity, we have models by Newton and Einstein to define how objects interact.

But, what causes the force between objects in the first place? I didn’t think that was understood. I thought that’s what friedo was alluding to.

16

There’s always a level of “why” that we will never be able to explain. For example, we know that mass causes spacetime to curve and you can calculate these curves and the curves will cause things to move through space a certain way - that’s gravity. but why does the universe behave that way? That’s just how the universe is. (You can put God there, if you like.) Physics is about observing the world and then making predictions based on those observations. But figuring out WHY gravity bends the universe may be beyond us.

17

Very nice summary friedo.

18

I would add Cosmogony (origin of the universe) to that list although perhaps it’s included under cosmology.

19

Supersymmetry looks interesting…

20

That word isn’t really used in physics, and the general term ‘cosmology’ indeed covers the whole of it, up to what can still be called science at least.