I return you to regular physics programming here on CV with a brief summary for our non-experts of some of the [
screaming and shouting] passionate, informed debate that usually takes place whenever I do a post on string theory…..
String theory (or whatever it will be called when we figure out what it actually is) is a work in progress. It is an attempt to formulate the physics which will help us understand Nature at a level well beyond that at which we understand it now. Among the things we hope that such a theory will tell us about are:
- The quantum physics of spacetime. Nature is at its heart quantum mechanical, yet we don’t yet know what happens when we combine quantum physics with the physics of spacetime (phenomena such as black holes, vacuum energy, the nature of the very early universe, (and possibly more things we just have not realized yet!) depend on us understanding this);
- The connections between gravity and the other forces of Nature (lots to say here too…..much overlap with the other bullet points’s parenthetical remarks);
- The physical origin of several unexplained patterns and mysteries in our current models of particle physics (the matter/anti-matter imbalance, the origin of mass, the weakness of gravity, why three similar families of matter particles?, Why are “force” particles and “matter” particles so different from each other anyway?);
- The structure and evolution of our universe (Dark Energy and Dark Matter, which make up a whole 96% (or so) of our entire universe!…..what the Dickens are they? See several posts here on CV on these constituents of our universe.)….
….and several other questions that I don’t want to go into here, otherwise it stops being of benefit to non-experts…. (I also won’t go into all of the excellent things string theory has been useful for in our potental understanding other things about Nature, such as the nature of the Strong Nuclear force, why you never see a quark all on its own (“confinement”), etc…..)
Ok. So where are we?
Well, string theory is very complicated. It may well be that all we’ve worked out about it so far, over quite a few years, is just a tiny fraction of the whole story.
Maybe when we have the story worked out, we’ll have a big party in celebration of all that we learn about Nature from it. Or, we’ll see that it’s just the wrong story. Nobody knows whether or not this is the case. We need to work it out in order to know. Another perfectly fine possibility is that string theory tells us about *some* of the list of physics issues above, but not all of it.
In an effort to understand if the theory makes contact (or even has a chance to make contact) with Nature, many have attempted to extract physical scenarios, corresponding to our world, from the theory. Many of these scenarios are difficult to extract. They are often called “solutions” of the theory, in a (partial) analogy to finding solutions to a set of equations in an exercise in high school algebra. (Caveat: The analogy is only partial, because it is not clear if we really have all of the equations yet. This bit is important to remember!)
Workers in the field have found that (keep the above caveat in mind) there are apparently very very many solutions, making up a whole “landscape” of possibilities. (See my earlier, more technical post on this.)
So somewhere in that apparently vast landscape of (possible) string theory solutions, one of them might just correspond to Nature.
The big questions (in this context) for our field right now are:
- Is there a dynamical (or other physical) principle we’re missing that will help us find the One Solution? (In other words, maybe all those solutions aren’t solutions.)
- Must we appeal to other means of selecting the correct solution? (This is where arguments about things like the “Anthropic Principle” begin. See that earlier post and its discussion thread, and several others.)
- Will we just end up choosing a “solution” by hand and see if there’s still interesting science to be done, post-pick? (In other words, use observation/experiment to guide you in determining some parts of the solution (“fitting some parameters to the data”) , and then the theory makes predictions about the rest of the physics.) A perfectly sensible possibility that seems to get forgotten in these discussions, despite the fact that it happens all over the rest of science!)
- Or is it totally random, there’s nothing further to be understood, and string theorists are not doing science any more?
All good questions. Nobody knows the answers, but several people have strong opinions in various directions. Meanwhile, research continues. Excellent.
While we wait for the answers, here’s some hope:
Ok. I’ll come clean now:
This was all a ruse to do one of my irregular posts in a series of weekend botanical/gardening pictures. The above is something I saw yesterday. Possibly my favourite photograph from the entire trip “off-planet“. This plant is often called “Desert Gold”. I do think that it resonates rather nicely with the physics issues too though, so I hope it helped form a picture in your mind of what people are up to in the research.
(I find myself wondering: Why do I not have any of these types of flower in my garden? Must look into getting seeds for them.)