The galaxy gets healthier -- so where are the LGMs?

Our galaxy is a safer place today:

Gamma Ray Bursts--One Less Thing to Worry About. The Loom: A blog about life, past and future
Posted by Carl Zimmer

In case you were worrying that life on Earth would be wiped out by a catastrophic burst of gamma rays, rest easy. It turns out that our galaxy may not be a very good source of gamma ray bursts. I found this particularly interesting given recent speculation that gamma rays bursts might have triggered mass extinctions. The bursts are clearly catastrophic, but probably not close enough to Earth to cause much trouble.

But if the galaxy is less hostile to life than once thought, and if we accept recent studies suggesting earth-like planets may less rare than once though, then where all the little green men? Assuming conventional technology and a reasonable expansion rate, any reasonably prolific species should carpet the galaxy in a million years or so. That should have happened hundreds or thousands of times by now -- the evidence should be inescapable. So where is it? ...

COMMENTS

... This makes the 'great silence', aka the Fermi Paradox, ever more intriguing.

One explanation for the fact that the galaxy isn't swarming with LGMs is that our galaxy is very inhospitable to life. Periodic bursters are a nice way to sterilize chunks of the galaxy, and thus they help explain the paradox. Another historic explanation was that earth-like planets are rare.

We now think earth-like planets may be not terribly rare. Today we learn that bursters may not be all that common. These modify terms in the old Drake equation, meaning there's more pressure on something else to explain our solitude.

Personally, I favor the explanation that the period of time that any technologic culture is interested in exploration and expansion is very short. (That is, biological imperatives never persist).

The other common explanation is that all technological civilizations turn into gray goo ... :-).

Gray goo is shorthand for a nanotech disaster, which is shorthand for "any wild technology that inevitably wipes out any society that discovers it".