23 June 2011

Candles and Constants

I've got something interesting for you, probably the Biggest Thing of All. However, getting there took more explanation than I thought it would... this is going to take TWO posts.

But first, an odd observation: In early cloud chambers physicists would see evidence of paired particles popping out of nothing into existence. They were always particle-anti-particle pairs and they always flew off in opposite directions, so conservation of momentum was conserved. But to conserve mass-energy (remember the old Einstein mass-energy equivalence equation Energy = Mass times the velocity of light squared), you had to assume that there was an energy there before the particles appeared. That energy exists even in a vacuum - and this is where Vacuum Energy got its name. 

Another observation: There are supernovae of a certain type (Type Ia) that blow up in very predictable ways.  These are stars of a very large mass, and their explosions are so predictable that they are used as "Standard Candles". That term stems from how bright is a "standard" candle as seen from a given distance... a century and a half ago. The idea is that if something always blows up the same way, and gives off the same amount of light each time, then the dimmer it was the farther away it was. This was perfect for astronomers, because while there are other Standard Candles out there (Cepheid Variables for one), Type Ia supernovae can be seen and measured a whole lot farther away.

Hang in with me here, this really is going someplace, I promise.

In the 1930's, Edwin Hubble
 (the guy the space telescope was named after) figured out that a lot of the "fuzzy" objects visible in early telescopes were really giant galaxies like the Milky Way. This was a pretty humbling observation, because just a few centuries earlier, humankind thought IT was the center of all creation... and now humankind realized that it occupied a small stony planet in an insignificant solar system in the middle fringes of an average-sized galaxy... and there were millions of galaxies. Quite a come-down.

But Hubble was more fascinated than bothered. He observed that the farther away these galaxies were, the redder was the light coming from them. For anyone who has heard a siren pass by them and noticed the pitch drop, this is called the Doppler Shift. No, it wasn't named after someone named Shift, either. The equivalent of the siren sound dropping in pitch is light turning redder if something is moving away. The faster you go, the lower the pitch, and you can relate those two with a constant number multiplier. If the galaxy was coming toward you, a galaxy would have a blue shift... but ALL galaxies had RED shifts - so they were all receding. 

Ever bake a loaf of raisin bread?  As the loaf rises, ALL the raisins are moving away from each other in all directions. The farther away a pair of raisins were to start with, the faster they move away from each other as the loaf rises.  Galaxies and raisins: pretty much the same thing.

At that time it still wasn't certain how big the Hubble Constant was, but Ed took a stab at it: something between 40 and 70. In a nicely-behaved universe, the Hubble Constant would relate how FAR something was by how RED the light coming from it was. In other words, how much the Hydrogen-Alpha absorption line in a solar spectrum was shifted down into the red range, multiplied by Ed's Number, would tell you how far away the galaxy was. At that point of time in science history, everyone knew about the Big Bang theory, and this seemed to prove that it was the winner over its big rival, the Steady-State theory. So... if you could narrow down the Hubble Constant, you could also get a handle on when things started flying apart. In the last few decades, the age of the universe has been narrowed down to about 13.4 billion years.

What came before that?  Good question to ask an atheist.

OK, if things are flying apart, and there is gravity acting on the same things, then the expansion should be slowing down - as gravity exerts its inevitable pull on those things.

Pretty straight-forward, right? Some people speculated that when gravity finally took over, everything would collapse back onto itself into something called the Big Crunch: the End of the Universe.

Turns out that everyone was 'way wrong on that one.  I can't WAIT to read tomorrow's blog to find out!


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