Rare Earth

[otseng]

Imagine there's no spacemen except the ones we launch
No alien rock n' rollers to listen to Sagan's hunch
Imagine we're all stuck here and must confront ourselves

.. uh oh!

Imagine now that Star Trek is just a TV show
No cosmos full of life forms just earthlings here below
Imagine there's no 'contact' to make 'cause no one's there

... uh oh!

You may say I'm a realist but I'm not the only one
Who knows there's zero data from SETI - or anyone!
Imagine your dream's over no Yoda to soothe you
And your only choices left then boil down to two
Imagine you're unique here and must opt for love or hate

... uh oh!

You may say I'm religious but I'm not the only one to say if you seek communion
it's the heart that must be won!

From the Rare Earth Song

In the book Rare Earth, the authors make two main points:
- Microbial life is common in planetary systems.
- Advanced life (animals) is rare in the Universe.

The arguments they give can be found at wikipedia.

But, in the book, they don't really explore the implications of their hypothesis.

So, what I'd like to ask is:

What are the implications if earth is the only planet with advanced life on it?

[olivergringold]

That's a pretty strong statement. Do you have any empirical evidence that we are not alone?

Probability. You and I apparently disagree on that much. I'm working on that.

Actually, it would be quite a leap. Actually, several large leaps. Yes, we can detect Jupiter-size planets in other solar systems, but we have not detected any Earth-sized planets in other solar systems. That doesn't mean they might not be out there, but from current observations, we have no evidence of them.

In our solar system there are eight planets as well as numerous smaller, planetoid objects beyond Pluto. They come in many sizes and are both rocky and gaseous. Even if we weren't able to live on Earth, the fact that eight planets and numerous planetoids can exist in a sustainable solar system well disproves the notion that Jupiter-sized planets are the only planets out there. The only reason we have no evidence for planets our size is because the distances we're dealing with are so vast that the light those planets, even large ones, emit simply don't get picked up. We can only detect the vibrations of larger planets.

Saying that not directly seeing with our devices a planet our size excludes the possibility that planets our size exist is outright nonsense. When we conduct galactic surveys outside our local region, many elliptical and irregular galaxies don't show up because the light they emit isn't as strong as the light coming from spiral galaxies. When we study our local group, however, we find that spiral galaxies are a very small proportion. Is this because our local group is anomalous, and spiral galaxies really are far more common? Nope! Spiral galaxies just emit the most light, and so are far easier to detect. That doesn't make the elliptical or irregular galaxies go away. By limiting your sample by gravitational detection you're ignoring huge portions of the sample we know exist. Within this very solar system, we have very sound reasons to suspect that Mars once hosted water. That's a twofer: two planets in one solar system, both with water. That's not because our solar system is special, it's because solar systems such as ours are prone to supporting liquid water within certain ranges of distance, depending on the planet's atmosphere.

Also, just because there might be a planet the size of ours, it doesn't mean it will have the same characteristics as ours. Size is only one factor. There are several other factors in the Drake equation that also needs to be considered.

And you managed to bungle up almost all of them. A pause, whilst I grumble beneath my sighs.

Where:

N* is the number of stars in the Milky Way. This number is not well-estimated, because the Milky Way's mass is not well estimated. Moreover, there is little information about the number of very small stars. N* is at least 100 billion, and may be as high as 500 billion, if there are many low visibility stars.

No arguments here.

ne is the average number of planets in a star's habitable zone. This zone is fairly narrow, because constrained by the requirement that the average planetary temperature be consistent with water remaining liquid throughout the time required for complex life to evolve. Thus ne = 1 is a likely upper bound.

Who says that ne = 1 is an upward bound? If there is a finite distance between a star and an object between which said object could engage in stable orbit about said star, and if there is a particular position within that range in which planets could be considered habitable, ne would be equal to the proportion of possible orbital locations in relation to the desired orbital location, multiplied by the number of stars sampled. Let's pretend that the desired orbital location only represents a 0.00000000001 fraction of all possible orbital locations. Multiply that by the average of our two star numbers (100,000,000,000 + 500,000,000,000 / 2 = 300,000,000,000) and you get a 300-to-1 chance that a star in our galaxy would host a habitable planet. Even though that ought've set you straight, go ahead and, just for kicks, multiply it by the number of known galaxies. Not even the number of possible galaxies in our Universe, just the number of known ones. Go ahead. Get back to me on that. It'll be fun.

fg is the fraction of stars in the galactic habitable zone. 0.1 at most.

Bull. Stars which are in the galactic habitable zone are named as such because they are already capable of hosting life. Read that very carefully: We are not capable of hosting life because of where we are, but we are where we are because we are capable of hosting life. If you look in the galactic center, what you're going to find is a bunch of very old, very big stars. The reason all the dust is in the galactic disk is because that's where the exploded remains of galactic center stars wind up. The dust makes the young stars, the young stars make the planets. If we existed in an elliptical galaxy, or in a spiral galaxy's bulge you might have a point, as they're almost exclusively made of large, old stars. We're not, however. We're between two spirals in a late-stage spiral galaxy. That's pretty dang standard news for potential life. In irregular galaxies, or colliding galaxies, virtually 100% of all stars would be within a "galactic habitable zone."

fp is the fraction of stars in the Milky Way with planets.

Studying our immediate surroundings we've already found some with planets. I'm not clear on the proportion, however.

fpm is the fraction of planets that are rocky ("metallic") rather than gaseous.

Looking at what we've got, I'd say life has more than its fair shake, especially when you get closer to the stars, in the habitable zone.

fi is the fraction of habitable planets where microbial life arises. W&B believe this fraction is unlikely to be small.

It doesn't have to be likely. We know it has happened at least once. When the probability is applied over an area as vast as the universe the odds against "no second genesis" are staggering.

fc is the fraction of planets where complex life evolves. For 80% of the time since microbial life first appeared on the Earth, there was only bacterial life. Hence W&B argue that this fraction may be very small. Moreover, the Cambrian Explosion, when complex life really got off the ground, may have been triggered by extraordinary climatic and geological events.

Evolution is triggered by the necessity to evolve. There are many points in the geologic record which indicate that for periods of up to millions of years long, very little happened within some genus. Evolutionary splits, causing speciation, generally happened around the times of large climactic or migratory shifts. The "Cambrian Explosion" was a singular event...that wasn't what got us to where we are today. Given a rocky planet with an oxygen-rich atmosphere and large bodies of water, varying weather conditions are just about a gimme. Put a self-replicating microbe, subject to mutation, on an Earth-like planet, and then wait a couple hundred million years...game, set, match.

fl is the fraction of the total lifespan of a planet during which complex life is present. This fraction cannot be high because complex life takes so long to evolve. Complex life cannot endure indefinitely, because the energy put out by the sort of star that allows complex life to emerge gradually rises, and the central star eventually becomes a red giant, engulfing all planets in the planetary habitable zone. Also, given enough time, a catastrophic extinction of all complex life becomes ever more likely.

Yet we know that our star has about 500,000,000 years of juice left in it. Plenty of time for us to defy the second law of thermodynamics and figure out sunless self-sustainance in space. It only took us 100,000 years from Africa-to-present to come up with computer networks that possess more computing capability than the human brain.

fm is the fraction of habitable planets with a large moon. If the giant impact theory of the Moon's origin is correct, this fraction is small.

There are other things that could affect tides and weather conditions, such that life would not require a moon. Besides which, there are plenty of creatures which live at levels far beneath sea level which aren't particularly hindered by whether the moon decides to show up or not. We know almost nothing about fish beyond a certain depth. We know enough, however, to suspect that they're probably there, and have been for some time.

fj is the fraction of planetary systems with large Jovian planets. This fraction could be large.

If it's not too much trouble, could you please clarify the relevance of this figure?

fme is the fraction of planets with a sufficiently low number of extinction events. W&B argue that the low number of such events the Earth has experienced since the Cambrian explosion may be unusual, in which case this fraction would be small. Such a low number again requires a very stable planetary system, with outer planets having nearly circular orbits, no gravitational perturbations from passing stars, and no nearby supernovas, quasars, or gamma ray bursts.

Stable planets might have creatures, but said planets would not be nearly as conducive to speciation as those with extinction events. Life is not a fluffy, cotton-soft fairy tale. It's natural selection: survival of the fittest and unmarked graves for the rest. If not for mass extinction events, we would not be here.

Too zealous to fully appreciate for all their magnificence?

Apparently. While you do a good job of analyzing how rare life may be, the scope of the universe around us utterly eludes you.

Just one question, if so many intelligent civilizations exist, why have we not been able to detect even one of them?

The nearest star to us is about eight light years or so away. If there were intelligent life orbiting about said star, and they attempted to send us a care package, but misfired by a single arc-second, Mr. Trigonometry says we probably wouldn't even notice it passing by. Our radio and television waves dissipate over a finite distance, well before reaching the nearest stars, and sending a manned crew would be a disastrous waste of time, resources, and human life. Any other bright ideas?

(Also, could you resize the graphic in your signature to about half its current size? The large size makes the page too wide. Thanks.)

I already reduced it to half its original size
What resolution is your monitor set to?

[otseng]

That's a pretty strong statement. Do you have any empirical evidence that we are not alone?

Probability.

You stated "we are not alone". You did not state "we are probably not alone".

And you managed to bungle up almost all of them. A pause, whilst I grumble beneath my sighs.

Bungle? All I did was quote the Wikipedia, which in turn referenced the book Rare Earth.

ne is the average number of planets in a star's habitable zone. This zone is fairly narrow, because constrained by the requirement that the average planetary temperature be consistent with water remaining liquid throughout the time required for complex life to evolve. Thus ne = 1 is a likely upper bound.

Who says that ne = 1 is an upward bound? If there is a finite distance between a star and an object between which said object could engage in stable orbit about said star, and if there is a particular position within that range in which planets could be considered habitable, ne would be equal to the proportion of possible orbital locations in relation to the desired orbital location, multiplied by the number of stars sampled. Let's pretend that the desired orbital location only represents a 0.00000000001 fraction of all possible orbital locations.

Ne would be for the number of planets around a single star. 1 would be gracious estimate. But, I like your number better - 0.00000000001.

fg is the fraction of stars in the galactic habitable zone. 0.1 at most.

Bull. Stars which are in the galactic habitable zone are named as such because they are already capable of hosting life.

Too close to the galactic center would be too dangerous for life. It emits too much gamma rays, X-rays, and other ionizing radiation. Supernova explosions are also more common near the center. The outer regions would not have enough concentration of higher elements necessary to form life.

fi is the fraction of habitable planets where microbial life arises. W&B believe this fraction is unlikely to be small.

It doesn't have to be likely. We know it has happened at least once. When the probability is applied over an area as vast as the universe the odds against "no second genesis" are staggering.

I would disagree that we know abiogenesis happened. It's equally as likely that life got placed here (either by a God or even by panspermia).

fl is the fraction of the total lifespan of a planet during which complex life is present. This fraction cannot be high because complex life takes so long to evolve. Complex life cannot endure indefinitely, because the energy put out by the sort of star that allows complex life to emerge gradually rises, and the central star eventually becomes a red giant, engulfing all planets in the planetary habitable zone. Also, given enough time, a catastrophic extinction of all complex life becomes ever more likely.

Plenty of time for us to defy the second law of thermodynamics and figure out sunless self-sustainance in space.

I think it's pretty safe to assume that the laws of thermodynamics will never be defied by us humans, no matter how technologically advanced we are.

fm is the fraction of habitable planets with a large moon. If the giant impact theory of the Moon's origin is correct, this fraction is small.

There are other things that could affect tides and weather conditions, such that life would not require a moon.

Besides tides, the moon also has a stabilizing effect on the tilt of the earth. Without the moon, the spin axis could vary as much as 90 degrees.

fj is the fraction of planetary systems with large Jovian planets. This fraction could be large.

If it's not too much trouble, could you please clarify the relevance of this figure?

"Because it cleans our solar system of dangerous Earth orbit-crossing asteroids and comets" (page 240, Rare Earth)

While you do a good job of analyzing how rare life may be, the scope of the universe around us utterly eludes you.

Actually, I can't get credit for any of this. Ward and Brownlee, authors of Rare Earth, deserve the credit. I'm merely restating what they've published.

Just one question, if so many intelligent civilizations exist, why have we not been able to detect even one of them?

The nearest star to us is about eight light years or so away. If there were intelligent life orbiting about said star, and they attempted to send us a care package, but misfired by a single arc-second, Mr. Trigonometry says we probably wouldn't even notice it passing by. Our radio and television waves dissipate over a finite distance, well before reaching the nearest stars, and sending a manned crew would be a disastrous waste of time, resources, and human life. Any other bright ideas?

So, in other words, even though there is not even one single empirical evidence to show that even one alien is out there, you believe that "1,000,000 to 1,000,000,000 intelligent civilizations" are out there.

Further, the SETI program is not looking for "care packages", but any EMR transmissions. These cannot be narrowed to a single arc-second, but are transmitted omni-directionally.

[olivergringold]

You stated "we are not alone". You did not state "we are probably not alone"

It is very improbable that the sun will detonate overnight. Therefore, I can safely say that the sun will come up tomorrow, even though in all honesty it is only highly probable that it will. This is a semantic argument, not a practical one.

Bungle? All I did was quote the Wikipedia, which in turn referenced the book Rare Earth.

Not every book in the non-fiction section can be instantly believed as true. The reason I scantly post sources is because I have lost count of the number of them which I have absorbed over time. Scientific consensus, then, is that the Rare Earth authors bungled it up.

Ne would be for the number of planets around a single star. 1 would be gracious estimate. But, I like your number better - 0.00000000001.

My figure of 0.00000000001 is not Ne...it is the fraction of all planets in the star's habitable zone. You neglected to consider, however, that when multiplied by the number of stars in a galaxy, Ne skyrockets. Furthermore 0.00000000001 was intentionally set to an absurdly low figure simply to illustrate a point. The actual fraction, though I'm not clear on precisely what it is, probably lends itself to your argument far less than this one does.

Too close to the galactic center would be too dangerous for life. It emits too much gamma rays, X-rays, and other ionizing radiation. Supernova explosions are also more common near the center. The outer regions would not have enough concentration of higher elements necessary to form life.

This was addressed later on in the paragraph which you quoted. Spiral galaxies and elliptical galaxies together represent a plurality of galaxies, but neither alone represents a majority. Furthermore spiral galaxies have very large disks in which a large number of stars (admittedly a small proportion) could be hosts for potential life. In the irregular or colliding galaxies you failed to take into account, nearly 100% of all stars would be within a habitable zone. If, then, you were referring to the unlikelihood of us appearing in a spiral galaxy, allow me to remind you that Ne is far higher than you give it credit for.

I would disagree that we know abiogenesis happened. It's equally as likely that life got placed here (either by a God or even by panspermia).

If the latter then it is highly unlikely that all seeds were placed here. If the former, then a great deal of explaining would be required. I notice you still haven't either recovered from or been able to respond to (one or the other, and I lack the insight to determine which) my elsewhere reference to The God of the Gaps' accuracy rating.

I think it's pretty safe to assume that the laws of thermodynamics will never be defied by us humans, no matter how technologically advanced we are.

Tell that to the folks at Steorn: www.steorn.com. The jury is still out, literally, but they've already received testing and confirmation from several scientists.

Besides tides, the moon also has a stabilizing effect on the tilt of the earth. Without the moon, the spin axis could vary as much as 90 degrees.

Again, deep sea creatures probably wouldn't be terribly affected by this.

"Because it cleans our solar system of dangerous Earth orbit-crossing asteroids and comets" (page 240, Rare Earth)

The large Jovian planets in our Solar system are at a sufficient distance, and the sun is of a sufficient gravitational pull, that any asteroid that intended to hit us will, indeed, hit us. And we have many, many reliable records of it happening in the past, as well as the knowledge that, save for our scientific intervention, it would have happened in the future. Exit Mundi did a clever article on the subject. I'd link you, but the entire site is worth exploring whenever you have a free minute. Just Google them.

Actually, I can't get credit for any of this. Ward and Brownlee, authors of Rare Earth, deserve the credit. I'm merely restating what they've published.

Fair enough.

So, in other words, even though there is not even one single empirical evidence to show that even one alien is out there, you believe that "1,000,000 to 1,000,000,000 intelligent civilizations" are out there.

Further, the SETI program is not looking for "care packages", but any EMR transmissions. These cannot be narrowed to a single arc-second, but are transmitted omni-directionally.

How we define intelligence is arbitrary as, of course, we are inclined to call ourselves intelligent. The deep sea life that would predominantly inhabit the planets without large moons probably has little interest in strapping giant radio wave emitters to the surfaces of their planets...if the change in pressure could even be survived as they ascend. Secondly, I mentioned that wave-versions of transmission dissipate over a finite space. To clarify, we receive tons of signals at SETI every day of the week...the trouble is that many of the signals are so weak having traveled so far a distance, that it's difficult to separate a potential communication from a solar flare. If SETI is the first to find intelligent extra-terrestrial life, I will be quite surprised. But just the same as the sun will come up tomorrow, even though I have no empirical evidence that something traveling at light speed couldn't hit it and cause it to die out, we are not alone.

[otseng]

You stated "we are not alone". You did not state "we are probably not alone"

It is very improbable that the sun will detonate overnight. Therefore, I can safely say that the sun will come up tomorrow, even though in all honesty it is only highly probable that it will. This is a semantic argument, not a practical one.

The sun rising and an alien on another planet are in two different categories. We have empirical evidence of the sun but none of aliens.

Bungle? All I did was quote the Wikipedia, which in turn referenced the book Rare Earth.

Not every book in the non-fiction section can be instantly believed as true. The reason I scantly post sources is because I have lost count of the number of them which I have absorbed over time. Scientific consensus, then, is that the Rare Earth authors bungled it up.

How do you know that scientific consensus shows that Ward and Brownlee bungled it up? Have you even read the book? Have you read any material that disproves the book?

Ne would be for the number of planets around a single star. 1 would be gracious estimate. But, I like your number better - 0.00000000001.

My figure of 0.00000000001 is not Ne...it is the fraction of all planets in the star's habitable zone.

Let me reiterate that "ne is the average number of planets in a star's habitable zone." It is only for a single star system.

You neglected to consider, however, that when multiplied by the number of stars in a galaxy, Ne skyrockets.

N* would be the number of stars in the Milky Way. The multiplication of the values is in the Drake formula, not combined in Ne.

Too close to the galactic center would be too dangerous for life. It emits too much gamma rays, X-rays, and other ionizing radiation. Supernova explosions are also more common near the center. The outer regions would not have enough concentration of higher elements necessary to form life.

This was addressed later on in the paragraph which you quoted. Spiral galaxies and elliptical galaxies together represent a plurality of galaxies, but neither alone represents a majority. Furthermore spiral galaxies have very large disks in which a large number of stars (admittedly a small proportion) could be hosts for potential life.

That small proportion is what fg is addressing.

In the irregular or colliding galaxies you failed to take into account, nearly 100% of all stars would be within a habitable zone.

If two galaxies are colliding together, I would guess it would be closer to 0% would be within a habitable zone. For an irregular galaxy, I would have no guess one way or the other.

I notice you still haven't either recovered from or been able to respond to (one or the other, and I lack the insight to determine which) my elsewhere reference to The God of the Gaps' accuracy rating.

There's no need to address that in this thread. And I believe I have debated about this before a while ago. If I could only find it though...

I think it's pretty safe to assume that the laws of thermodynamics will never be defied by us humans, no matter how technologically advanced we are.

Tell that to the folks at Steorn: www.steorn.com. The jury is still out, literally, but they've already received testing and confirmation from several scientists.

It would be interesting if one day we do have a true perpetual motion machine. But until the physics book are all rewritten, the laws of thermo stands.

Besides tides, the moon also has a stabilizing effect on the tilt of the earth. Without the moon, the spin axis could vary as much as 90 degrees.

Again, deep sea creatures probably wouldn't be terribly affected by this.

Even if a planet with a 90 degree axis could support seas and if life could evolve under those conditions, deep sea creatures cannot evolve into an advanced civilization.

"Because it cleans our solar system of dangerous Earth orbit-crossing asteroids and comets" (page 240, Rare Earth)

The large Jovian planets in our Solar system are at a sufficient distance, and the sun is of a sufficient gravitational pull, that any asteroid that intended to hit us will, indeed, hit us. And we have many, many reliable records of it happening in the past, as well as the knowledge that, save for our scientific intervention, it would have happened in the future.

Nobody is saying the the Jovian planets acts as an impenetrable force field of cataclysmic sized asteroids or comets. But that they act as a filter which reduce the chances of getting hit by one. And if the theory of the origin of the moon is correct, supposedly one was able to hit the Earth in order to create the moon.

The deep sea life that would predominantly inhabit the planets without large moons probably has little interest in strapping giant radio wave emitters to the surfaces of their planets.

Deep sea creatures could probably evolve no more than creatures that swim, eat, and replicate. Hardly enough to be able to be considered an advanced civilization.

If SETI is the first to find intelligent extra-terrestrial life, I will be quite surprised.

As far as I know, SETI is the only scientific program in the US that is searching for alien life. How else do you think it will first be detected?

But just the same as the sun will come up tomorrow, even though I have no empirical evidence that something traveling at light speed couldn't hit it and cause it to die out, we are not alone.

It's relatively easy to show that the sun will come up tomorrow. But, how can you show that we are not alone?

[Cathar1950]

I must admit I am over my head here despite how much I have studied over the decades.
So I am at best guessing and going with my gut feeling based mostly on what I don't understand. I guess I am not alone.
I have read where even the DNA and RNA of worms is like ours except for arrangements and what is being expressed. What ever life forms we have seem to have this same building blocks, It displays a great deal of diversity. Yet it also limits what can be even if we do not know the extent of the limits or possiblites.
It seems even on a planet hat spins at 90 degrees could have adaptable mechanisms that rapidly change or are so slow the rapidly changing environments promote a different species or forms of life. We only have what we see.
Worms use the same blocks as we have to make eyes. Until something is expressed we don't know what the outcome might be. If the outcomes help and are passed on it works.
There maybe other building blocks even crystals have been produced that were unpredictable.

[QED]

Rather than continue to argue whether we are alone or not, I think we should concentrate on the original question in the OP:

What are the implications if earth is the only planet with advanced life on it?

I would like to know why anyone would be justified in thinking it signified anything particular if it was true.

[otseng]

I would like to know why anyone would be justified in thinking it signified anything particular if it was true.

If complex life was only on Earth, then it would jeopardize the validity of the Mediocrity principle and the Copernican principle.

[Greatest I Am]

Rather than continue to argue whether we are alone or not, I think we should concentrate on the original question in the OP:

What are the implications if earth is the only planet with advanced life on it?

I would like to know why anyone would be justified in thinking it signified anything particular if it was true.

Alien's or not we will continue the same way.
I have wondered what would be different if we encountered another sentient species.
Once we caught up to their technology and became accustomed to space travel, we would treat aliens the same way that we now treat others who are well removed from our own race.
In the news, names and "faces" would change but the topics would all be the same.

In about five years the impact of the encounter would be absorbed and we would continue as we are. Tourism will eventually be the only work left for us.

Not to worry thought any alien would be stupid to visit earth at this point in time.
We are too unorganized. Take me to your leader would be meat with a blank stare.

Regards
DL