Complex Life May Be Possible In Only 10% of All Galaxies

sciencehabit writes The universe may be a lonelier place than previously thought. Of the estimated 100 billion galaxies in the observable universe, only one in 10 can support complex life like that on Earth, a pair of astrophysicists argues. Everywhere else, stellar explosions known as gamma ray bursts would regularly wipe out any life forms more elaborate than microbes. The detonations also kept the universe lifeless for billions of years after the big bang, the researchers say.

Comments

Let's do the math

[cat_jesus]

10% of infinity is...... hmmm, carry the one...

Um 7?

Re:Let's do the math

[JWW]

Ummm I think you've confused ridiculously large number with infinity. They are not the same thing.

I am dubious

[mbone]

I am dubious that gamma ray bursts are invariably a sentence of doom. The actual mechanism is due to the destruction of the ozone layer due to nitrogen molecules formed in the upper atmosphere; these molecules would "eat" the ozone for maybe 4 - 5 years after a GRB event, but would not (in that sort of lifetime) go from one hemisphere to another. Questions I would have include

- How many civilizations might form on bodies with very thick atmospheres, far from their Suns? (Venus does not need a ozone layer to keep the UV out, and might be very habitable a few AU out.)
- How many planets might have very long rotation periods (years), so that the night hemisphere never is subjected to the daytime UV?
- Are there rotation axis directions and orbital precession constants for planets that would keep GRB radiation mostly in one hemisphere, leaving the other to develop?
- How many planets might have other special circumstances that protect their ozone (such as a lack of N2 in their atmosphere, or an ozone generating biology in their stratosphere, etc.)

I am sure that there are others, but even these I think show that, while GRB might be bad for habitability, they need not be fatal. Note, too, that if I was running a Kardashev Type III civilization, one of my action items would be to find any possible GRB progenitors and disarm them. So, in a KIII galaxy, GRB would likely no longer be a problem; maybe that would be a good way to determine the number of KIII galaxies in the universe.

Re:Relativistic Species

[HeckRuler]

What if there was a whole...dare I say...confederation of relativistic societies?

The question would be where are they and where are they going?

You could probably achieve some meaningful dilation if you orbited a black hole or something. But other than that, presumably the society that can hop around the galaxy still wants to have something to go to. And those locations would experience just as much time as the rest of us. Not that we all experience the same amount. Whole sections of the universe travel at different speeds and times. Like, you know how galaxies are accelerating away from the origin? Yeah, some are moving faster than others. And consequently experience different time dilatation. Dunno what sort of ranges we're talking about. Even at 90% lightspeed, you're only looking at a 1:7 ratio. A 142,000 years as opposed to a million years is still a society-crushing amount of time.

I'm not sure why you'd want to have a space-faring society that was rushing as fast as they could towards the heat-death of the universe. I guess some people would want to wait and see if anything interesting happened.

My take is tech makes radios sound like noise.

[Ungrounded Lightning]

I also subscribe to the "great filter" theory. About 25 years after the radio was invented, we were busy gassing each other in trenches, followed closely by a global pandemic, then mass genocide, then teetering on the edge of nuclear war. That's not a very wide window for aliens to notice our presence, if they rely on artificial radio waves to detect intelligent life.

My take is that technological improvements make radio sound like noise after a few decades. Early radios systems are very simple things which have signals (CW, AM, FM, ...) that are very distinct from electrical and thermal noise. Their signals were both drastically different from, and drastically stronger than, the background, enabling simple detectors to separate a signal's information from all that chaff.

Modern radios (such as spread spectrum systems, especially OFDM) squeeze nearly the Shannon Limit out of precious bandwidth (and also be frugal with transmit power) by using nearly all of it to carry information. This makes them virtually indistinguishable from a celestial object with a little extra heat (buried among things like stars, which have a LOT of heat).

It was only about 120 years from when Hertz and Tesla started making easily detectable radio waves to the Analog Television Shutdown, a significant milepost in the decommissioning of easily detectable radio signatures. I expect that, within anther few decades, the Earth will be emitting very little that might be recognizable as a radio signature of intelligent life, unless we expend a bunch of energy sending such a signature deliberately.

So my solution to the mystery expressed in the Drake Equation is that L (the length of time for which such civilizations release detectable signals into space) is short, not due to the falls of civilizations, but to economic incentives to use the aether only in ways that are no longer noticeable at a distance.