High-Z Supernova Search

Measuring the Fate of the Universe

But we have made some assumptions - two important ones are: 1. The universe is homogenous. That means that the material in the Universe is, on average, evenly spread through out the Universe. 2. The Universe is isotropic. That means that matter, the expansion, and everything else is the same in all directions.

Given these assumptions we can determine how brightnesses of objects, their distances and their recession rates are related. (Hubble's simple relation is not valid at large distances.) By measuring the distances to receeding galaxies, we can see how their recession rates compare to the predictions of General Relativity. We can thus see what is in the Universe, gauge how it affects the expansion of the Universe and predict the fate of the Universe.

But an accurate way of measuring distances halfway across the visible Universe is required. Measuring distances in astronomy is not trivial. Attempts to do so have lead to some of the greatest controversies in astronomy over the past two hundred years.

Galaxies themselves, are bright enough to be seen across vast distances. But they evolve over time, so comparing the size or brightness of galaxies we see today to those in the distant Universe is fraught with danger.

However, Type Ia supernovae, which are individual stars, can also be seen across the same vast distances, and it is these that we use to measure the distance to far-flung galaxies.