I am back at graduate school after visiting home for the holidays.  While it was nice to catch up with people, it was a little depressing to realize that almost nobody has any idea of what I actually do.  Whether it is old friends from high school, my family, people that talked to me on the plane, even my roommates here at graduate school; most people are unsure, at some level, of what it is exactly that theoretical astrophysicists do.  I find that there are mainly two levels of confusion:

   I)  Quite confused.  When I say I am studying astrophysics, these people say, cool!  So, you want to design airplanes?  No?  Then, spaceships!  (This is by far the most common response.  But once, when I told someone sitting next to me on a plane that I am studying cosmology…see title.)  These are not uneducated people, either; most of them are very smart, with college educations, and all of them are capable of understanding what we do (at least, that is what I like to believe).  So at some level, the methods used to communicate even the basics of our science to the public – popularization through books or news articles, museums, public lectures, etc. - are very broken.

   II) Just a little confused.  These people know enough to ask me, so, what is up with the big bang?  Have you found that Higgs boson yet?  Or, tell me about string theory!  But, they still hold misconceptions about how science works.  They’ll say, oh, cosmology is nice, but in the end, you can’t really prove anything, right?  It is almost like philosophy.  I have heard this view many times from many people.  Apparently, cosmologists sit at a desk, smoke pipes, and make up stories about how they think the universe began.  Whoever thinks up the nicest story wins.  Then they will write up fancy articles – e.g., “A Discourse on the Cosmological Theory of Turtles All the Way Down” – that contain nice ideas, but are just creation myths in the end.  So you see, cosmology is just another one of the liberal arts.

   So, what’s wrong with this picture?  I think that Type I is mostly a failure of our public education system.  Physics (and other sciences) as taught at the public high school level is a joke at best and a tragedy at worst.  Mostly, high school physics fools people into thinking physics is difficult and consists only of inclined planes and pulleys, while teaching them nothing that is actually challenging or inspiring at all.  In college, physics is rarely required; by this time, it is usually too late anyways, and more courses just end up making the problem worse.  Attempts to fix the problem with science popularizations and news articles are futile, because nobody will read more about something they have already been taught to hate.  These symptoms manifest even at places such as my alma mater, which is supposed to be a bastion of science education.  The Type IIs are those whose interest in science was strong enough to survive this system, but for whatever reason hasn’t been further cultivated.  Here, the failure is more on a personal level.  Maybe the popularizations and the articles, which Type IIs actually do read, aren’t clear or engaging enough; or in the same vein, maybe the scientists which they actually know – i.e., me – just aren’t that good at communicating the essentials of their field.  I encourage these people to keep reading and keep asking questions.

   So, what do I do, in a nutshell?  Let me start with physics.  Simply put, this is just understanding how the world works.  Once you understand a little bit, you begin to see that you can and must do this in a mathematical way; you could just wax philosophical, as the Greeks did, but our understanding has progressed enormously since then.  Once you have a mathematical theory, you keep checking it against experiment.  If you find an experiment that cannot be predicted or explained by your theory, then you modify your theory.   And so on.  So our understanding of the physical laws of the universe walks forward step-by-step on these two feet, theory and observation - what we think and what we see.  It is just a bonus that our theories turn out to be simple (relatively) and beautiful (absolutely); that’s just how the universe works.

   So then, what is astrophysics?  This is just, literally, physics of the stars.  It is a wonderful fact that, so far as we know, physics works the same everywhere.  So we can apply what we learn here in our tiny little corner of the universe to everything else we see.  We can use the Newtonian theory of gravity we deduce from falling apples to understand the orbits of the planets.  Likewise, we can use observations of astronomical events that we don’t understand to correct our theories.  So, when we see that the orbit of Mercury isn’t predicted correctly by our Newtonian theory of gravity, we must construct a theory of general relativity that explains the problem.  Such principles hold not only in our solar system, but beyond.  Newtonian gravity explains the orbits of binary stars, but we must turn to general relativity to explain the orbits of binary neutron pulsars, and so on.

   And so cosmology is just application of theory and observation to even larger scales – not just stars, but galaxies of stars, and the entire universe of galaxies.  Far from being just-so stories, our theories of how the universe began are based on observation.  If we observe that a nearly uniform background radiation permeates the universe and that other galaxies are moving away from us, we theorize that the universe began in a hot explosion and has been cooling and expanding since then.  We use our theory of general relativity to run the clock backwards to find what the initial temperature must have been, and using our theories of nuclear physics calculate what the ratio of the different elements must have been at that temperature.  We then run the clock forward again, and check to see if this ratio is what is observed in our current universe.  It is.  So we have done science.  We are not just making up fanciful stories; we are trying to understand how the universe began as precisely and quantitatively as we can.

   To improve on this cosmology, by considering observational puzzles such anisotropies in the background radiation, the distribution of galaxies and matter in the universe, dark matter and dark energy, and many more - that is why I am going to graduate school.  Hopefully, by understanding these puzzles, we can improve our physical theories.  I’m drawn to cosmology because the universe is such a fantastic experiment – the only one that allows us to probe such gigantic distances and high energies.  (It is often said that to test that our theories hold at the enormous energies present during the big bang, we’d need a particle accelerator the size of our solar system.  So, particle physics won’t do it for me.)  This is why I do cosmology – to increase our understanding of the physical laws of the universe.  It has nothing to do with makeup, or making up stories!

   I am reminded of the dedication from the general relativity textbook by Misner, Thorne, and Wheeler (don’t tell anybody, but I like the dedication more than I like the book itself):

We dedicate this book
To our fellow citizens
Who, for love of truth,
Take from their own wants
By taxes and gifts,
And now and then send forth
One of themselves
As a dedicated servant,
To forward the search
Into the mysteries and marvelous simplicities
Of this strange and beautiful Universe,
Our home.

   Unfortunately, sometimes the servants forget to report back, or find that no words can adequately describe what they have found. Sometimes, you just have to see it for yourself.