Do You Need to Explain the Fermi Paradox?

[RJM Corbet]

No. Although there is some 'you-must-give-credibility-to-your-SF-story' that permeates more strongly than in Fantasy, they are both FICTION. Made up. Basing it on the most relevant thepory is all fine and dandy, but it is just a theory.

And the surest sign that there's intelligent life in the Universe is that none of it has visited here... Calvin and Hobbes rule!

Ha! Ha!

But there may be the truth.

Why do we assume that aliens will visit us in visible form?

 

[Ursa major]

But DNA is so complex (it goes way beyond just the simple double helix generally portrayed) that surely the chances of two DNA like systems emerging independently and being able to "exchange components" is less likely than all the atoms of my body jumping two feet to the left at exactly the same instant.

Organs of sight, and the ability to perceive based on the data from those organs, have emerged more than once (and many exist to this day). It strikes me that sight (the organs plus the perception) is a very complex system.

As for DNA systems being similar enough to exchange components: I don't see that as an insuperable problem. As with the round wheel, perhaps, in spite of its flexibility, the DNA system has to have certain identical component parts (not the components you mentioned ) because the system can't work at all without them. So, for instance, perhaps DNA only really works properly with Adenine, Thymine, Guanine and Cytosine. Perhaps there's only one way that certain parts of the system can come into existence because even though there may be better ways, there's no route to them that would ever be viable. And if those parts include how you read and interpret sequences of ATGC, plugging in strands containing ATGC sequences will work (i.e. be interpreted as identically as they are in practice**).

Let's face it, the DNA system is almost unbelievable in itself; we know it works so we believe it can. I'm not sure I'd be as confident that it would work if it was only a theoretical example of how an inheritance system might work.


** - This assumes that they always do, which may not be true, at least not with 100% effectiveness.

 

[Interference]

I wondered if someone would come up with that!

My forename is "Predictable".

Yup.

I am the original Predictable Interference.

 

[Vertigo]

I agree that DNA is wonderfully and almost unbelievably complex. But that's just it, what are the chances of two totally independent forms of life emerging that result in exactly the same complex molecule with only the bases changing. Surely this is what is being proposed by the multiple ancestry hypothesis and it just seems to me to be impossibly unlikely. We're not just talking about being able to swop the bases of two lifeforms but whole genes which, if I understand it correctly, are complete sections of DNA.

My other problem with the multiple ancestry hypothesis is that if life has emerged more than once then I would have expected it to happen millions of times. If you like it is the same argument as saying life has emerged here on Earth therefore it is going to happen anywhere it can in the universe. In the same way you could argue that if it has emerged once on Earth it should have happened thousands/millions of times on Earth... or just the once; anything in between doesn't make a lot of sense to me. But I don't believe the multiple ancestry hypothesis claims that; just "several times".

In the end I'm just saying that when you string together all the unlikely things that have to happen for life to emerge it begins to look, to me at least, that it may be a very very rare thing even on the scale of the Universe or at least on the scale of the galaxy.

I am the original Predictable Interference

I never would have said you of all people were predictable Inter!

 

[RJM Corbet]

... I am the original Predictable Interference ...

Is that an Italian name?

 

[Ursa major]

You could turn that on its head, Vertigo, and ask why, if something can happen once, why it can't happen twice. Or four times. And why do its other occurrences have to be on other planets? Is there anything about the emergence of the DNA system that prevents it occurring in the next pool, on the next island, on the next continent?

In fact, one could argue that for something as complex as the DNA system to emerge, there must be something about the chemistry involved that makes its emergence almost inevitable. It's either that, divine intervention, or a long sequence of ever-more unlikely, coincidences.

 

[Vertigo]

You could turn that on its head, Vertigo, and ask why, if something can happen once, why it can't happen twice. Or four times. And why do its other occurrences have to be on other planets? Is there anything about the emergence of the DNA system that prevents it occurring in the next pool, on the next island, on the next continent?

In fact, one could argue that for something as complex as the DNA system to emerge, there must be something about the chemistry involved that makes its emergence almost inevitable. It's either that, divine intervention, or a long sequence of ever-more unlikely, coincidences.

But that's my point Ursa if it can happen twice then over the lifetime of this planet it should have happened thousands of times.

But lets assume you are correct and it has happened many times and apparently all carbon based DNA. That now suggests we should find similar life out in the stars. But then we come to the other problems. First the galactic habitable zone. If all life is carbon based DNA or something very similar then it's not going to survive the radiation and gravitational stresses of the galactic centres (I have also seen it stated that the radiation levels would be too high even deeper into the spiral arms). Nor is it likely to have emerged in the galactic fringes due to the paucity of heavier elements there. I'm not sure just what percentage of the available systems that removes but I guessing a good 3/4, since there are so many more stars in the centre than further out. Then we elliminate all systems without nice rocky planets in the goldilocks zone. Then, though I'm not so sure about this, but I think we get to elliminate all planets that don't have magnetospheres stong enough to protect their atmospheres, and ones that don't have a thin enough mantle to have tectonics, and ones that don't have a suitable moon to stabilise their axial wobble.

However I look at it, I just don't see a universe that is going to be teeming with life. I'm not saying none; it is a big place and I'm pretty sure there is going to be other life out there. But I suspect that it will not be very common. I also think it will be surprisingly similar to terrestial life; parallel evolution and all that.

 

[J Riff]

Life will adapt to increased gamma rays, no problem, given a few billion years. It will be much more complex and varied than life on earth, where we only get second-hand gamma rays.
ONE advanced alien race could seed thousands or millions of planets, and gamma rays be damned.

DNA itself is deceptive. It has a pattern, irreducible complexity,a sequence......so? Of course it does, it has to, nothing doesn't. It may be older than the earth by far, no way to test for that.
Fibonachi sequence (sp?) had people postulating Creation a few years ago.
Different lifeforms could evolve - given billions of years. We can't test for that either.
Most of the stars back towards galactic central are, in fact, millions or billions of years older than Earth, aren't they? There's probably a trillion planets that have gone thru the insect/reptile/mammal business with infinite variations.
I'll bet five bucks that life turns out to be dirt cheap across the Universe, existing everywhere that it is possible for it to do so.
Advanced spaceship life, not so common, but then it will spread like a fungus anyway.

 

[RJM Corbet]

Life will adapt to increased gamma rays, no problem ... Different lifeforms could evolve ... I'll bet five bucks that life turns out to be dirt cheap across the Universe, existing everywhere that it is possible for it to do so.
Advanced spaceship life, not so common ...

Man searches for carbon or silicon based life forms similar to our own that depend on liquid water, or perhaps liquid methane -- but the universe is a big place; 96% is dark matter and dark energy, and other life forms may not be visible or perceivable to us. An intelligence that can hop between galaxies is unlikely to do so in any form that we could recognize -- or to reveal themselves to us unless they choose to ...

 

[Vertigo]

Life will adapt to increased gamma rays, no problem, given a few billion years. It will be much more complex and varied than life on earth, where we only get second-hand gamma rays.
ONE advanced alien race could seed thousands or millions of planets, and gamma rays be damned.

DNA itself is deceptive. It has a pattern, irreducible complexity,a sequence......so? Of course it does, it has to, nothing doesn't. It may be older than the earth by far, no way to test for that.
Fibonachi sequence (sp?) had people postulating Creation a few years ago.
Different lifeforms could evolve - given billions of years. We can't test for that either.
Most of the stars back towards galactic central are, in fact, millions or billions of years older than Earth, aren't they? There's probably a trillion planets that have gone thru the insect/reptile/mammal business with infinite variations.
I'll bet five bucks that life turns out to be dirt cheap across the Universe, existing everywhere that it is possible for it to do so.
Advanced spaceship life, not so common, but then it will spread like a fungus anyway.

Not when you are talking about the radiation levels present at galactic cores, they really are extremely high and the general consensus amongst even the optimistic scientists is that there will be no life there, certainly not any kind of complex life.

It would also have to survive planets having massively erratic orbits due to the gravitational pulls of so many nearby stars, with much much higher incidences of bombardment by comets and asteroids due to their erratic orbits for the same reason. And the gravitational stresses would probably result in massive tectonic activity.

All told life evolution in galactic cores would be extremely unlikely, certainly any kind of complex life.

 

[Ursa major]

But that's my point Ursa if it can happen twice then over the lifetime of this planet it should have happened thousands of times.

My example of the next pool was meant to indicate that if the conditions were right in one pool, they could very well have been right in the other. But once the development gets going, I'm quite prepared to believe that the environment becomes unhelpful to new starters: the chemistry of the environment may change due to the early starters; new starters may be just the sort of nutritious input the early starters are seeking. But then, if the process continued for a long time but ended with indistinguishable results, how could we tell which animal resulted from which start up? I'm not sure we could, not without looking for it (which might require a greater understanding of how the system came into being over time to work out where variation would be possible and what it would spawn in the way of evidence.)

But lets assume you are correct...

I stopped reading there.

...and it has happened many times and apparently all carbon based DNA. That now suggests we should find similar life out in the stars. But then we come to the other problems. First the galactic habitable zone. If all life is carbon based DNA or something very similar then it's not going to survive the radiation and gravitational stresses of the galactic centres (I have also seen it stated that the radiation levels would be too high even deeper into the spiral arms). Nor is it likely to have emerged in the galactic fringes due to the paucity of heavier elements there. I'm not sure just what percentage of the available systems that removes but I guessing a good 3/4, since there are so many more stars in the centre than further out. Then we elliminate all systems without nice rocky planets in the goldilocks zone. Then, though I'm not so sure about this, but I think we get to elliminate all planets that don't have magnetospheres stong enough to protect their atmospheres, and ones that don't have a thin enough mantle to have tectonics, and ones that don't have a suitable moon to stabilise their axial wobble.

However I look at it, I just don't see a universe that is going to be teeming with life. I'm not saying none; it is a big place and I'm pretty sure there is going to be other life out there. But I suspect that it will not be very common. I also think it will be surprisingly similar to terrestial life; parallel evolution and all that.[/QUOTE]
I'd be surprised if there wasn't a lot of proto-life out there, but whether the conditions were quite right and whether they persisted for long enough (or, perhaps, changed to the right set of new conditions quick enough) to get the hereditary system up and running, it's hard to say. For myself, I'm not a big supporter of the galaxy teeming with many different types of intelligent life, if only because intelligence seems to equip organisms with the ability to wipe themselves out (accidentally or otherwise). However, I have a sneaking suspicion that there are aliens out there suggesting that there's no way life could form so far from the galactic centre, as there isn't enough radiation to stimulate the required amount of variation in the passing on of genes (always assuming that their heredity system works at all like ours).

 

[Vertigo]

However, I have a sneaking suspicion that there are aliens out there suggesting that there's no way life could form so far from the galactic centre, as there isn't enough radiation to stimulate the required amount of variation in the passing on of genes (always assuming that their heredity system works at all like ours).

I couldn't quite understand your last statement Ursa but I think it looks like our conclusions are not so very far apart even if we got there by slightly different routes (I also have strong doubts about how long a technological civilisation is likely to last and therefore the odds being against overlap)

 

[Ursa major]

All I meant is that we're discussing this in glorious ignorance (a position in which we're likely to remain), and that we're probably not the first (as a species), and probably won't be the last (as a species), to do so. And all these species will know that the environment in which they're discussing the issue will generate and support life but will have doubts about others being able to do so.

 

[paranoid marvin]

This thread reminds me of The Galaxy Song from The Meaning of Life.

 

[Ursa major]

Because it's spiralling out of control, you mean...?

 

[paranoid marvin]

That's certainly a universal truth.

 

[Vertigo]

I would certainly agree with you there Ursa; for the forseeable future it seems likely that any discussion such as this will remain purely speculative.

 

[J-WO]

This thread reminds me of The Galaxy Song from The Meaning of Life.

So, er, you gonna give us your liver then?

 

[J Riff]

Gah. People still can't figure out whether there was life on Mars or not.
The more radiation, the faster the mutation. There's a thousand different situations
a planet could be shielded, life starts underground, develops a radiation shield in order to survive, etc. etc.- just like on Earth, they adapt to whatever, and go on.
What makes sense is more lifeforms where there is more planets. Makes space travel easier too, and means they aren't going to be hanging out in the western spiral arm where we are.
Life develops from....germs... bugs, microorganisms. They will develop everywhere and they will not be stopped by details like radiation or lack of liquid water.
Cockroaches have little difficulty with atomic radiation. I see bug worlds that make Starship Troopers look like a day at Disneyland. )

 

[Vertigo]

I would still have to disagree with you there J. It is not as simple as "more radiation more mutation". Yes cockroaches can take a lot of radiation but not the sort of quantities that you get in the galactic centre.

However by your statement:

They will develop everywhere and they will not be stopped by details like radiation or lack of liquid water.

Then every planet in our solar system should be teeming with life but even if there is, or has been, some life on Mars or wherever, the solar system is clearly not teeming with life. So I'm afraid that argument falls down rather.