How do you measure the distance to a place you’ve never been – and one so far away that using common trigonometric methods involving angular measurements is useless? That’s the problem facing astronomers trying to measure how far away various nearby galaxies are from our own Milky Way. These nearby-galaxy distance measurements are the first link in a chain of logic that shifts over to other techniques for the longer distances to measure the distance to the edge of the universe. Get the “simple” first measurement to the nearby galaxies wrong, and you’re gonna be clueless when you start estimating farther and farther from home.
Astronomers base their nearby galaxy distance measurements on Type Ia supernovas because when these exploding stars detonate, the physics and dynamics of their explosion always put out the same amount of light with very little variability. They are, to use the venacular, a “standard candle.” And if you can know with good precision what the absolute or total brightness of a Ia is in a distant galaxy, then you can compute how far away it is by how bright it seems to you. The dimmer it is, the farther away it is. Thus, the billion-dollar Hubble is just a fancy wooden yardstick for measuring galactic distances in the fabric of space instead of a yard of cotton cloth on a cutting board.
Well, while Ia supernovae put out a known constant amount of light, scientists now have found that more of that light goes out in one direction than another. Again to oversimplify, when we took all those Hubble measurements – were we looking at the bright side or the dim side of that star? And just how big is the Universe, anyway? Good questions, stay tuned…
I just bougth a book by Charles Seife entitled Alpha & Omega on this very subject. It is fascinating indeed.
One of the most interesting things about the IA supernovae mesurements was that they showed the Hubble Constant to be increasing as the universe gets older, which is astounding. It seems that not only will the universe not undergo a ‘big crunch’ as time goes by, it will not even come close. The initial force of the Big Bang seems to be enough to never let gravity ‘win.’ It also hints that there is some other force out there, that we can’t really describe.
It is really amazing the steps we have taken in the last 10 years in cosmology. I will have to read up on these IA supernovea, to see if this casts any doubt on this information.