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

Re:Let's do the math

[jeffmflanagan]

We don't get to the point of galaxy hopping. Our machine descendants might, but the human race would be long dead by the time a ship crossed into another galaxy.

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:I am dubious

[buchner.johannes]

I can not answer about the deadliness of GRBs, but I think you will find those answers in Phil Plaits book "Death from the Skies!".

- 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.)

Yes, insulation is a good idea. But the planet will always radiate as a black body and loose energy, which has to be re-supplied by the suns radiation. The radiation drops with the square of the distance, so rather quickly. These considerations (make-up and size of planets) go into calculations for the habitable zone.

I can also imagine that a GRB comes with considerable photon pressure and might strip the entire atmosphere off a planet, or heat it to a point where it dissipates into space.

- How many planets might have very long rotation periods (years), so that the night hemisphere never is subjected to the daytime UV?

I think the rotation of planets around their own axis (spin) is not known outside the solar system. Generally, the spin is generated from formation of planets in the rotating protostellar disk, but interactions and changing orbits may modify the spin (Venus, Uranus).

- 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?

If you do not have the problem of heating and evaporation of the atmosphere I mentioned above, then yes, that is probably possible. For example if the GRB goes off from the direction of the spin axis ("below/above the solar system"). This may safe you from one GRB, but since GRBs come randomly from all directions it is not failsafe across many billion years.

- 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.)

Not sure. I think it is possible to come up with such scenarios as you stated, but it has to be shown that they are frequent occurrences to be relevant for changing the survival rate of complex life.

Re:Let's do the math

[Ravaldy]

That's just your opinion built on limited knowledge of physics. Our progression in the last 100 years is more than 1000 fold all previous years combined so imagine what we can do in the next 1000 years.

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.