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

[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:Let's do the math

[Shatrat]

If that's what you're worried about, we already know that this particular galaxy supports life. Our chances of finding it in one of the others was astronomically smaller anyway.

Re:Let's do the math

[CreatureComfort]

Maybe invent a flying car?

Re:Let's do the math

[khallow]

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.

Will there even be an organism recognizable as human in another 1000 years? There's more than one way for humanity to cease to exist.

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.

Re:Let's do the math

[mark-t]

What evidence is there of an infinite universe that had no beginning?

Bear in mind also that if an infinite universe exists, which had no beginning, then light would also have had infinite amount of time to travel to here from absolutely everywhere else, and although the intensity of radiation that reaches a point is inversely proportional to the square of the distance to that point. the volume of space that is an average of some given distance away from a point is greater than an amount proportional to the square of the distance from that point, and so the number of things in that volume which produce radiation at that distance would be be correspondingly greater, more than cancelling out the inverse square relationship to the intensity of radiation reaching a point some fixed distance apart. Every point in the universe would be perpetually saturated in radiation that is reaching it from every other point in the universe, infinitely far away, and certainly things like life bearing planets could not exist.

Critical observation suggests that the universe is finite.

Re:Let's do the math

[dnavid]

What evidence is there of an infinite universe that had no beginning?

Bear in mind also that if an infinite universe exists, which had no beginning, then light would also have had infinite amount of time to travel to here from absolutely everywhere else, and although the intensity of radiation that reaches a point is inversely proportional to the square of the distance to that point. the volume of space that is an average of some given distance away from a point is greater than an amount proportional to the square of the distance from that point, and so the number of things in that volume which produce radiation at that distance would be be correspondingly greater, more than cancelling out the inverse square relationship to the intensity of radiation reaching a point some fixed distance apart. Every point in the universe would be perpetually saturated in radiation that is reaching it from every other point in the universe, infinitely far away, and certainly things like life bearing planets could not exist.

Critical observation suggests that the universe is finite.

This is known as Olber's paradox, and it is not valid for expanding universes where red shift reduces the wavelength of light from distant sources until it drops below visible wavelengths and there ends up being an observable horizon, even in an otherwise infinite space and unbounded lifetime.

Although your point about distance and volume is wrong for other mathematical reasons. The number of light sources expands as the square of radius, not volume. The *total* number of sources is proportional to the cube of radius, but that's double counting. The volume includes close sources previously counted, plus the new sources being added as radius increases. Olber's paradox doesn't rely on that error in math.

Re:Let's do the math

[Tablizer]

The laws of probability suggest humanity is doomed, at least in our current form. We as human ponderers are roughly a sampling of the average human pondering their existence. About 60 billion humans have come before us, which suggests roughly just 60 billion will come after us since we are most likely to be in the middle of the pack rather than near the beginning or the end of the pack. (Roughly the Copernican principle as applied to human population density and time.)

If most of our future is to be Borg-like, then we'd more likely be Borgs contemplating our existence, not humans. But us (here now) being at such a coincidental position would be violating the Copernican principle. Either way, we are either doomed to end soon or become Borg-like, neither is a pleasant thought.

Of course coincidences do happen and we may indeed coincidentally be at the start of the human expansion curve; but if I were in Vegas, I wouldn't bet on it. We're doomed, guys.

Re:Let's do the math

[mark-t]

For what it's worth, Olber's paradox uses the wrong formula for the volume of a shell some distance R from earth... The formul as I remember it from Olber's paradox is 4*Pi*R^2*dr, where dr is the thickness of the shell. However, this value only approaches accuracy as R approaches infinity. It is wrong for all finite values of R.

And I was not double counting anything. The actual volume of such a shell is: 4/3*Pi*(r+dr)^3-4/3*Pi*r^3. This is a value that is admittedly less than proportional to R^3, but more than proportional to R^2 for any finite value of R greater than zero. This volume is actually even greater than the value that Olber was utilizing, and dividing it by R^2 to calculate the expected intensity of radiation in that entire shell that reaches a point at distance R does not approach 0 as the distance approaches infinity.

But the real problem with Olber's paradox is not the miscalculation of the volume of the shell at some distance from earth,and in turn the number of elements within that volume which will emit radiation,but rather with the assumption that the universe is somehow actually infinite in the first place.

Olber's paradox revealed that trying to make an assumption that the universe might be infinite is flawed, and by my understanding helped to serve as an impetus at the term to find alternative explanations for what we observed, eventually leading to the widely accepted big bang hypothesis.

And observed red shift means that objects are moving away from each other, which means that at some point they were much closer together, and rewinding the clock even further suggests that the universe began at a single point, and has been expanding outward ever since (although you can no more find a point in space that is the center of it than you can find the center of an inflated balloon anywhere on the surface of the balloon).

Bottom line: the universe is finite. Even if it were ever found to be expanding into an infinite unbounded space.

Re:Let's do the math

[boristhespider]

Fancy adding a bit of weight to the random abuse? I don't know where Kjella got the idea that as far as we know there's a finite amount of energy around, for one thing. While there may be a finite amount within our horizon, that's a very different thing, since all we need to do is move a few megaparsecs and we've got a slightly different horizon. The statement that there is a finite number of galaxies within our horizon is completely uncontroversial (and indeed obvious, not least since our horizon extends back before the formation of galaxies at all...), while the statement that there is a finite number of galaxies *outside* our horizon is unsubstantiated and unlikely to be substantiated from that starting point.

On the other hand, gameboyhippo's statement that space is not infinite because it is expanding is also very much arguable. In this case we're on firmer ground, since we can look at the models actually employed in cosmology. If we restrict ourselves to the (Friedman-Lemaitre-)Robertson-Walker models, which are far and away the most widely used, then we've got three of them. One of them is formed of a three-dimensional spherical surface (so not a sphere you'd recognise, but the same in 4d), which is evolving. This is a "closed" universe, and in this model, indeed, space is not infinite but is expanding. But there are two other models. One of them, the universe is composed of a foliation of saddle-shapes (in 4d). This is an "open" universe, and here space is infinite and expanding. Or the universe can be composed of flat sheets. This is (unsurprisingly enough) the "flat" universe, and is *also* infinite and expanding.

It can certainly be argued that the data currently prefers a closed universe, but it does so at a statistically meaningless level (it covers both other cases, well within one standard deviation); the data cannot currently tell us anything. At this point theoretical bias comes in and we have to ask ourselves if there's any good reason that the universe would be almost, but not exactly, flat? The answer is sure, we can come up with reasons, but justifying the actual numbers involved is a posterior exercise. Instead, the preference is for the simpler model, flatness, until the data improves.

Do you see why I might have stated that both statements are so arguable that they're close to meaningless? I could have phrased it better, and I apologise for sounding brusque, but I stand by it.

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!

sooo....

[xaoslaad]

I didn't rtfa but if these explosions prevented life for billions of years, does this mean things are settling down? Over the many years will it be possible for life to develop in the other galaxies? Does this make us one of the elder races? If so I feel bad for the universe.

Re:sooo....

[Arancaytar]

In the time between these bursts, maybe a few species got lucky and made it almost to space colonization before getting scrubbed.

Maybe we're one of them.

Re:sooo....

[pla]

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

Re:sooo....

[jbolden]

Yes things are settling down. The universe was much more energetic 10b years ago and will be much less energetic 100b years hence.

Re:That's Life...

[__aaclcg7560]

"I dunno what the hell's [out] there, but it's weird and pissed off, whatever it is." The Thing, 1982.

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.

Re:Relativistic Species

[lgw]

That's why it isn't useful. You can't use it for anything interesting to anyone but you

And if the only problem remaining to you in life is boredom?

So, what would a star moving at near-C look like to the rest of us?

Get it going fast enough and it would look somewhat like a gamma ray burst, to those directly ahead of it, and be invisible from most directions. But there's probably not enough energy in a star to get it up to that sort of speed, at least with any sort of "stellar engine" anyone has yet imagined.

I blame the Inhibitors and their devices

[enjar]

If only there hadn't been a Dawn War.

Light takes a long time to get here

[Streetlight]

Most of the galaxies are likely to be so far away that the light - including gamma rays which are made up of high energy photons - has been in transit for billions of years. What's the situation now in those billions of gamma ray emitting galaxies we are now observing in the intervening years since the light was produced? They may have settled down making life possible.

Um, can't life just evolve under water?

[Dr. Spork]

...the gamma rays would set off a chain of chemical reactions that would destroy the ozone layer in a planet's atmosphere. With that protective gas gone, deadly ultraviolet radiation from a planet’s sun would rain down for months or years

Yeah, because it's impossible that complex life could be protected by a different (better!) kind of UV shield like... water. From my understanding, it's not exactly rare in the universe.

Re:Um, can't life just evolve under water?

[Firethorn]

How likely is complex life to evolve under those circumstances? Besides, I got the idea that only microbes with their extremely high radiation resistance would survive even in the deep ocean, as enough would penetrate to kill even things like ocean vent crabs.

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...

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.