Wednesday, November 5, 2008
Sad but True
The poll closed, and it is now official by a vote of 3 to 2 the universe is going to expand forever. This is actually rather close to the current scientific consensus. Detailed measurements of the rate of expansion of the universe done using supernova actually tell us that the rate of expansion of the universe is getting faster! If you are interested the exact method of using these super nova to give the rate of expansion works something like this. Step 1 you look for a type 1A supernova. I'm not exactly sure how you tell if it is a type 1A nova but I'll trust that it is possible. Steps 2 and 3 record the red shift and brightness of the nova as measured from earth. step next, rinse and repeat. So I am not sure exactly how many type 1A's we have on record but from what we do have we can use to make a measurement of the rate of expansion of the universe and how it has changed over time. The brightness of the supernova as measured from earth gives us info on exactly how far away the nova was because type 1A super novas all have exactly the same brightness when they occur. If memory serves it is because the star that collapses into a black hole accumulates mass from a nearby binary star until in reaches a definite critical mass at which point KAB00M! Since all these events happen when the star reaches the same critical mass the brightness of the explosion is just about the same. So as the apparent brightness from earth drops off we can measure how far away the damn thing was to begin with. Now the light has a particular characteristic spectrum which we would see if the thing were not moving relative to us thanks to good old doppler though the spectrum gets shifted. We can use the spectrum shift to measure how fast these things are moving away from us. There you have it we now have data that gives us how fast things distance x away from us are moving which gives you the rate of expansion of the universe. Course it isn't quite that simple, all the complications come in when you take into account that we don't see the light from the nova's instantaneously but it takes some time for the light to reach us. The farther away stuff is the longer it takes the light to get to us but also the more space has expanded during its flight. When you take this into account you not only get a measurement of the rate of expansion of the universe but a measurement of how that rate of expansion has evolved in time. With each nova being a window to a different epoch of the universe. Turns out the expansion of the universe started to slow down for a while and then started speeding up again! So now what it looks like is all those big crunch theories where the universe eventually ends in one huge gravitational collapse were not meant to be. The universe gets to end as a sea of cold lonely atoms and radiation. The 3 to 2 vote confirms it, sad but true.