Why astrophysics?

The globular cluster M5 as seen by Hubble Space Telescope - credit: ESA/Hubble & NASA

The globular cluster M5 as seen by Hubble Space Telescope – credit: ESA/Hubble & NASA

Why study astrophysics? Astrophysics is the study of celestial bodies. After all, the name itself comes from the Greek word for star. But this way you would also be justified in asking, why are stars special? Why is the scientific study of these lights in the sky a key branch of physics? Isn’t using the laws of physics for the study of something, no matter how shiny and beautiful that something is, engineering – and a peculiar branch of engineering at that, because knowledge about stars happens to be useless, unlike most engineering?

Let me play Devil’s advocate some more, and ask: should the study of flowers not be on par with the study of stars, if what sets astrophysics aside is the breathtaking beauty of the night sky? The fascination with stars is as old as humanity, but while the ancients kept meticulous records of the motion of celestial bodies, they studied plants and herbs as well.

It turns out that astrophysics is not about stars, it’s about physics.

We don’t use the laws of physics just to find out how stars (and galaxies, and the whole universe) work. We apply the laws of physics to these objects because of the risk that the laws might break down in the process. Nowadays nobody thinks that the laws of physics as we know them may break down when applied to flowers. Nor when applied to pipelines, airplanes or volcanoes. What sets stars (and galaxies, etc…) apart is that they are:

  • big (and consequently, far from us: big things are far, or at least part of them is necessarily far)
  • massive
  • old
  • far from other things (sometimes)

These characteristics mean that the laws of physics that we tested in the lab may not apply to stars and galaxies and the whole universe, because the lab is small, it’s not far, and cannot contain really heavy objects. There is a risk that our laws don’t apply, so that they may make wrong predictions in some measurable way. This risk can be interpreted as a potential for surprises.

We expect stars and the cosmos to be better at surprising us than pipelines, cranes, and the like. Actually, when cranes or bridges surprise us, it’s usually bad news! Surprise is what we learn from, so we are more likely to learn something new by looking at stars and galaxies than by looking at nearby, lab-size things.

The risk of failure is the strongest reason to do research in astrophysics, because failure may mean that new physics is required.

Stars also happen to be everywhere, in a way that is very similar to fundamental particles (which are supposed to be the building blocks of everything, and so are everywhere). Stars are not fundamental because they are made of parts (atoms and subatomic particles, ultimately), but according to the current understanding of nucleosynthesis, they happen to be responsible for the creation of virtually all elements heavier than Helium, without which life would be impossible. If we accept some version of the Anthropic Principle, then the existence of stars is in a sense responsible for the fact that we observe the laws of physics as they are.