Wednesday, May 9, 2012

Above and beyond

Before I can introduce my last research topic, I have first to go above and beyond the standard model. Given that I am calling this blog a tourist guide to the standard model, this is a bit like trespassing. But that is how my research went over the last years. So let me keep the name, but nonetheless venture beyond.

With keeping the name, I am using a very important concept in scientific naming: For historic reasons. For historic reasons, this blog was named, but then reality overtook it. This is something very often happening in physics. In the beginning, we encounter a phenomena. To not always have to describe it, we give it a name, based on what we have encountered so far. Very often, when we really understand what is going on, this name would no longer be appropriate. But at this time, the name stuck, and thus we stick with it. You should keep this in mind, when you think that the name of something seems to have nothing to do with the thing. Then the name is just there for historic reasons. And that is something one will also encounter beyond the standard model.

So let us go beyond the standard model. As I told you, the standard model is just that: A model. It has its limits. We know today, mostly for reasons of mathematical consistency and for astronomical observations that the standard model cannot be the end. We know that with what we have we cannot explain what happens at very high energies. We also cannot explain with the standard model why the outer rims of the galaxies rotate faster than they should. We do not know why the universe is expanding faster and faster. We do not know why the particles have precisely the masses they have. We cannot tell, why nature is such that the sun can shine: Given the standard model, we can explain how the sun shines. But we cannot explain why the standard model is such that this is possible. And there are many other things.

However, irritatingly, all our experiments here on earth have been in accordance with the standard model.

This is very unsatisfactory, to say the least. As a consequence, almost since the birth of the standard model in its present form people have started to consider extensions of it. This is commonly known as beyond-the-standard-model models, or BSM for short. Unfortunately, the observations listed above are not pointing all in the same direction. Actually, most just point somewhere, for the amount of knowledge we have of them. Thus, we are, right now, very much in the dark when it comes to figure out how we should extend the standard model.

This lead to very many proposals. Even listing all conceptual proposals would easily fill a couple of months worth of blog entries. But they can be broadly distinguished by their approach. Some have a top-down approach. They try to envisage the underlying theory, which will solve all (or many) of the known problems in one strike. You may have heard of (super)string theory. This is one example of this approach. The other is bottom-up. Here, one just tries to resolve a single problem. The ones I am working on belong to the latter category.

Now, what is the state of affairs? Top-down approaches are often rather complicated theories, and it is often very complicated to calculate anything at all. Thus, progress on this side is naturally slow. The bottom-up approaches are often more tractable. It is often not too complicate to design a theory, which solves the problem one was setting out to solve. However, in doing so one usually gets for a completely different thing a result which disagrees with the known experiments. Thus, one is forced to modify the model to sate this problem. But then the next springs up, and one finds oneself adding bits and pieces to the model, until it becomes rather baroque.

You may say now: Well, if things are either too complicated or too much mingling, maybe you are on the wrong track. And I would not really disagree with you. Of course, nothing prevents nature from being really complicated or baroque. Just because both versions do not look aesthetically pleasing to us does not mean it cannot be. But this way of thinking has never been right in the history of physics. When something got complicated, and any amendment made it worse, then we were on the wrong track.

So, why do we not abandon everything we did, take the standard model as the basis, and start over from scratch? This has actually been done many times, and so far was not successful. On the other hand, going back to the complicated theories, one hope is that by making the theory more complex by making more and more things agree with experiment, we can hope that at some point a pattern emerges. This has occurred in the past, and is thus a real possibility.

Thus, today, all of these possibilities are followed. We try to imagine solution to the problems, test them against experiments, both old and new, and reiterate. A spectacular new observation at any experiment would greatly help. That is why any ever so slight deviation from the standard model expectation is greeted with great enthusiasm by the theorist. Even if we know that in most cases this will be a coincidental fluke, which will go away when we keep looking more carefully.

Where will this lead us to? We do not know yet. That is the really exciting part of particle physics: We try to push the boundaries of knowledge, and we can only speculate what we will find there.