What Interest(ed,s) Me About Physics

Reading a 1996 Scientific American article about Titanium-44 was my first exposure to real nuclear physics. I was a senior in high school at the time and the magazine was part of a year-long subscription I had been given as a Christmas gift. I can't remember many details about it but, the article was about the discovery of this isotope in supernova remnants. A few things that blew my mind then and continue to fascinate me now are, for instance, you can do spectroscopy on distant star light. This was really amazing to me. I had known at the time, that you could see that hydrogen and helium were present in our own star with some fairly simple equipment; collimator slits, a prism, a nice rotating table with a scope and eyepiece and a lot of patience. It never really occured to me that you could marry a spectrometer to a telescope (albiet a very fancy marriage) and make the same measurements on far-away stars.

It was also neat that supernovae could form such heavy elements. I recall taking the article into class one day and asking my physics teacher about it. I was pretty fortunate that my teacher at the time, Mrs. Nettles, had a B.S. in physics and had actually logged in quite a bit of time on a medical reactor at the nearby Medical College of Virginia during her college days. I was suprised by the conversation that started. We talked about the article for a bit and it wasn't too long before it was clear she wasn't an astrophysicist. But that was no problem, I understood it wasn't her speciality and afterall, she only had a B.S. What floored me was that she pointed out how watered down and trivial her own class was! The thought had never really crossed my mind...you mean there is more to physics than calculating torques on ladders balancing on walls!? Well, what I mean to say is, I wasn't surprised that there was more content, more 'facts' to physics. Sure, there were all sorts of systems besides levers and incline planes...but the methods are pretty much the same right? I just have to solve some problems with those new thingys, like particles and stars and such, right? Mrs. Nettles, "No."

It was a long time before I fully appreciated her answer! And I'm still not sure I realize how much I don't know. A third thing about that article, which I didn't see until I began graduate school, was how novel the interconnection between different scales is. The fact that reactions between constituents as tiny as protons and neutrons can have a strong influence on the dynamics of something as colossal as a star is mind boggling. And incredibly challenging. The reason being that physics is all about modeling and a good model of something both describes many of its features and is in some way simpler to handle than the object itself. Physics has long depended on the fact that many of nature's scales are not very tangled with each other. For instance, you could describe the protons and neutrons of a nucleus in terms of their constituent quarks. But for the most part, you don't have too. The idea of protons and neutrons is a pretty useful model of the nucleus and it turns out, doesn't sacrfice much by ignoring the quarks. Similarly, most features of atomic electrons and atoms are not strongly influenced by the internal structure of the nucleus, so for most modeling purposes, you can ignore them. And the list goes on.

Nuclear astrophysics however is a weird creature in this regard. Its one of a few fields in physics where phenomena on vastly different scales have to be accounted for or the model produced is rather poor. Take for instance, the classic example of Beryllium-8. Its an unstable nucleus with the tiny half-life of order 10-16 seconds. However, this tiny, short-lived resonance is the gateway to producing carbon and all heavier elements by stellar fusion. Imagine that. The synthesis of all heavier elements, the dynamics of power production in older stars and explosive events like supernovae, a whole plethora of phenomena, depend on the energy and life-time of one tiny little resonance in one tiny little nucleus. Amazing!