Higgs Series: The direction of science

Newton's Dream (LINK) was to understand all of nature in terms of simple principles. In his time, it wasn't at all obvious that this was possible. One of the major things that science has discovered since Newton is that it is indeed possible, and in fact, you can summarize the process of science since Newton as realizing his dream. Newton's dream has been realized in terms of a web of interconnecting explanations, which I will indicate with arrows in the figure below.

At the top layer you have a wide variety of different concepts that you might want to explain, various things about your everyday life. What we have found is that there is a web of explanation that connects everything we see and observe with more fundamental principles.

Take for example the length of the year.

We know the length of the year is tied to planetary motion, which in turn is a direct result of Newton's laws and his theory of gravity. We now know – going beyond Newton – that there are deeper, more precise, and more general descriptions of gravity provided by General Relativity. So the length of the year, which of course has a big impact on our everyday lives, really has an explanation at lower levels in terms of physical principles. In this example there are many arrows above our starting point, i.e., many things depend on what the length of the year is.

Another example is weather:

If you ask a meteorologist what predicts the weather, they will talk about pressure fronts and wind patterns. We now know those are large collections of molecules moving together. The behavior of molecules in turn can be described by the principles of chemistry and interactions among atoms in the periodic table. We know the atoms in the periodic table are made of nuclei and electrons and much of chemistry is dictated by electrons and their behavior according to quantum mechanics. We now have a more general, more widely applicable version of quantum mechanics that we call the Standard Model. Again we see a high-level phenomenon, the weather, which ultimately has an explanation in terms of simpler things, ultimately in terms of quantum mechanics and the Standard Model.

There are many other possible examples. In fact, all of the things we can notice around us are rooted in deeper scientific principles.

Two important caveats: -) We have not made all of the connections; there are some cases where we are not yet able to draw the arrow. -) Not all connections are worth making. The meteorologist is right to explain the weather in terms of pressure fronts. It would be crazy for her to try to describe the motion of all the molecules or some giant quantum mechanical equation.

One of the major things that has come out of the program of realizing Newton's dream, is that there is a sense of direction to these explanations. I've tried to convey it in the cartoons. Not only can we construct the interconnected web of explanations, but the connections seem to have a direction to them. There are many phenomena to explain at the higher levels, but as you probe deeper and deeper there are fewer and fewer explanations. There is a convergence as you go deeper, a sense of unification.

I really want to stress that this sense of convergence is a fact about nature. The structure of the explanations is something that we went out and observed or discovered. It did not have to be this way. This discovery of convergence is, I think, the greatest scientific discovery of all. Not only do we have a web of interconnected explanations but there is this sense of convergence. A deep structure to reality, a big hint that we are on the right track.

It didn't have to be this way. For example, we could have found divergence.

In this case each phenomenon would have several different subcauses and those subcauses in turn would have yet more subcauses, leading to a proliferation of causes instead of unification. More and more concepts to explain at deeper and deeper levels. This is not what was observed.

Another way it could have been different is that you have general convergence overall, but some regions that are isolated. Here, some phenomena are disconnected from the rest of the web. Occasionally in the history of science we thought we were in this situation, but it has always turned out there is always some connection to the rest of the web.

Another way it could have been different is that we have convergence all the way to the bottom, and then an arrow that takes you all the way back up to the top.

This one seems crazy. But again there have been periods in the history of science where it seemed like the only possible arrow you could draw was one that went back to the top. In fact, one of the interesting things about the Higgs boson – a partial answer to why the Higgs is so interesting — is that there are some theories that say the only explanation for certain features of the Higgs boson is that you have to have this arrow that goes from the bottom to the top. I would say most physicists don't believe that, they think there is another way out, but it is certainly a possibility that this arrow is now being forced upon us.

To summarize, Newton's dream has really been realized; we can answer all basic questions of our everyday world in terms of simple principles. Scientists don't stress enough how profound this is. We will see, later in this lecture series, that this was not always the case. Even 100 years ago this was not true. But right now, anything from the solar system and beyond all the way down to the nucleus, even 100 times smaller than the nucleus, all the physics that is happening, which is really all that can be relevant to your everyday lives, is totally pinned down by basic physics principles.