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.

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.

Re:Let's do the math

[CreatureComfort]

Maybe invent a flying car?

Re:Let's do the math

[boristhespider]

No, it's definitely false. Current data strong favours a universe that is flat (ie infinite), while it only narrowly supports a universe that is open (ie infinite and shaped like a foliation of saddles), and only slightly better favours a universe that is closed (ie finite and shaped like a foliation of spheres.) More carefully speaking, I believe the constraints at the minute are something like \Omega = 1.02 +- 0.03 (at one sigma, or aroudn 67% confidence). Meaning that while it is possible the universe is open or closed our best evidence at the minute is that it is entirely consistent with flat, and that this consistency linked with Occam's razor suggests that we may as well take it as flat.

Meaning that the universe is probably infinite.

These considerations do not take into account the universe's topology, of course. The universe can be flat but finite if it is, for instance, on a torus. It could also be on any number of absurdly-shaped topological structures. This is because cosmology is based on general relativity which is, by definition, a local theory. Topology is, by definition, a global theory, and unless the characteristic length-scale of the topology of the universe happens to be within the characteristic length scale of the universe itself (ie if the "radius" of the torus is roughly of the order of the horizon), we're not realistically going to tell the difference between an infinite, flat universe and a flat, toroidal universe.

Occam's razor can again come into play here and suggest that the universe is, as a result, flat but we should probably begin wondering whether that razor's getting a bit blunt.

Practically alone...

[Anonymous Coward]

So there are only 10 billion galaxies out there that can support complex life like that on earth? We're practically alone!

Relativistic Species

[Scottingham]

I always like to think that any suitably advanced civilization eventually develops space-drives that can reach appreciable percentages of the speed of light. The time dilation effects would make traversing the galaxy relatively(heh) reasonable. The only hitch is that relative to all other lifeforms not moving at a such a speed would blink in and out of existence in the time it would take them to burp. Our current sliver of space-time is sooo tiny if you think about it like this.

What if there was a whole...dare I say...confederation of relativistic societies? In order to join you have to catch up. Otherwise you'll be gone in a blink.

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.

I blame the Inhibitors and their devices

[enjar]

If only there hadn't been a Dawn War.

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.

Our galaxy is one of those 10%

[djnanite]

On the plus side, it seems that our galaxy is one of the 10% capable of supporting life.

So at least we only have to start looking locally...

Re:sooo....

[pla]

"There is as yet insufficient data for a meaningful answer."

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.