23 June 2011

Dark Energy

No, nothing evil about it. It's just referred to as Dark Energy because astronomers can't see it.

But they can infer it, and "it" is pretty huge.

In 1998, two different groups of astronomers were trying to figure out how fast the expansion of the universe was slowing down: gravity being gravity, it should all be pulling things together.  So...were we gonna go out with a Bang (irreverently if informally named the "Big Crunch") or with a Whimper (to quote a favorite poet)?

To their mutual astonishment, they discovered that the universe expansion was accelerating. To do that, of course, requires a humongous amount of energy.

Unraveling what this Dark Energy is preoccupies astronomers and cosmologists more than just about anything else these days.  They may not know what it is, but they can calculate how much of it there is.  Remember from yesterday that matter and energy are equivalent: E=mc^2. Current data are consistent with this breakdown of the universe:

71% Dark Energy
25% Dark Matter
  4% Ordinary Matter (you, me, and the stars).

Not sure about you, but this really boggles my mind.  I told you that "it" was BIG - it's actually the Biggest Thing of All.

There are a lot of ideas about what Dark Energy is: perhaps it's the Vacuum Energy I talked about yesterday? Maybe we're mistaken in thinking that Einstein's theory of General Relativity applies the same everywhere, and for all times present and past? Or, maybe this is a manifestation of some sort of ultra-light scalar field that has been speculated about, called "quintessence"?  (I can hear my grandma snorting her disgust at this "foolishness"...)

Perhaps the weirdest suggestion I've seen (from Physics Today, June 2011, p. 54):
"Could the observations be telling us that despite the near-isotropy (translation: looks the same in all directions) of the cosmic microwave background, the universe is inhomogeneous on large scales and our Milky Way galaxy is located near the center of a very large void?"

Occam's Razor says that when faced with several possible explanations for something, choosing the simplest one is probably where the smart money is.  For me, this would be something different than what you might think:

When someone says they know where life came from - and it wasn't from Divine Intervention - and why we are here in this incredibly large universe, and that even being able to think about this stuff is just random good luck multiplied by 1 with twenty million zeros after it... 

I'd say that they were half baked raisin bread.


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