Where is Everybody? Fifty solutions to the Fermi Paradox, by Stephen Webb

[Nik]

"...build an optical interferometry telescope array in orbit ..."

Yup, one's planned. IIRC, it could, in theory, resolve continents and oceans (!!) on terrestial planets out to a dozen light years, piccy-quality equivalent to Mars seen by 'amateur' telescope...

Snags are *money* and *will*. If current and soon-launching instruments find wonders, then the next generation of instruments may be planned.

Also, if 'truly re-useable' launchers like Alan Bond's Skylon fly, assembling monster, multi-component optical interferometers is much more feasible.

Unfortunately, the forthcoming Euro-launch puts two *very* expensive and potentially irreplaceable astronomy sats at risk. Cruelly, they could not afford to build spares or launch them separately...

 

[Moonbat]

Is it possible that Aliens have visited Earth but just not in the last few hundred years, and so any tales of them are regarded as myths.

With the time scales we're talking about, Aliens could have visited over 50'000yrs ago and so there is no record of them. If it was several million years ago, still less information.

I think to assume that any advanced race would continue to grow (in population size) to the point where they collonise the enitre galaxy is a little pretentious. The difference between developed and developing nation's birthrates should show a decline as the society advances. (don't quote me on that, I'm clutching at straws)

For all we nkow there are other intelligent species in our own solar system but we don't recognise them as life yet. I heard a rumour that there were Women on Venus!

 

[Nik]

"Women on Venus!"

They must be really, really HotBabes.

(Sorry, been a bad day, could not resist that one... ;-)

 

[Hilarious Joke]

Very interesting thread!

 

[skeptical]

My arguments on this topic tend to begin with the assumption that many people have - that is : that there are a lot of intelligent and civilised aliens. Projecting that over several billion years into the past, and there must have been an awful lot of aliens.

If we look at the obvious outcomes of there being a large number of alien civilisations (Drs Drake and Sagan calculated 1 million at any one time!), then we see that such a large number must have left traces. If the number is small, on the other hand, the logical outcomes are very different.

If there are many such aliens, there will be enormous variability. Thus, we cannot use arguments of the kind that go : 'perhaps they are stay at home philosophers.' While some may conform to such a stereotype, some will not. At least some will be highly expansionist.

Even assuming a maximum travel speed of 10% of light speed, and relatively slow reproduction and social development, an advanced and expansionist species will colonise the entire galaxy to the point of overpopulation in no more than 10 million years. If intelligent aliens are common, then, over the past 2 billion years, at least one, and probably thousands, of such species will already have overpopulated the galaxy.

In spite of arguments suggesting that such species will be the ultimate greens, and recycle everything, I cannot believe they could live on Earth (as opposed to a mere temporary camp) and not leave traces. As I said, even such ephemeral beasts as jellyfish have left fossil traces.

And when you get down to it, if an expansionist and colonising species got to Earth 400 million or more years in the past, why would they not colonise? Why would they not reproduce in numbers? It is the basic biological drive, after all.

The only good explanation for the lack of any traces of any intelligent alien, either here on Earth, or in a manner receivable by SETI, is that intelligent and civilised aliens must be in very small numbers.

 

[ManTimeForgot]

So we are supposed to be able to recognize the consequences of bio-technology at least 500 years more advanced than us? Not a chance, especially not if they didn't want us to.

60 years ago we could have flown a stealth bomber over the middle of the US and it would not have gone detected in the slightest. If 50-60 years of tech difference results in an almost complete lack of detection what do you suppose several thousand years would do? You fly an F15 over some primitive's island and you get "the gods visited us today." Expose Man of 3,000 years ago to alien tech and basically nothing gets noticed: work of the gods.


Why would aliens waste resources by leaving it in space? Even assuming it happened why would it be probable for it to have gotten to where we could find it? We live in a fairly remote portion of the Milky Way. And assuming we have been visited why would aliens stick around long enough for us to become advanced enough to recognize them for what they are?

MTF

 

[Anthony G Williams]

Re: Planet hunter speaks out...

The Crowded Universe

quote:
"If this bold assertion is proved correct by Kepler and CoRoT, the implications will be staggering indeed: it will suggest that life on other worlds is not only inevitable but widespread. We will know that we cannot be alone in the universe."
/quote

The problem with this kind of statement is that many people will read the last sentence as meaning "there are other intelligent, technological civilisations with whom we can communicate".

If Earthlike planets complete with liquid water and oxygenated atmospheres are found, I would be surprised if they were lifeless. But "life" may just mean bacteria....after all, that's all that lived on Earth for billions of years.

 

[Anthony G Williams]

So we are supposed to be able to recognize the consequences of bio-technology at least 500 years more advanced than us? Not a chance, especially not if they didn't want us to.

You may postulate almost anything as being possible, but without evidence that is just so much hot air.

Given that no kind of evidence for the existence of extra-terrestrial civilisations has ever been found, it's a bit pointless speculating whether or not these theoretical beings might have visited Earth, if they ever existed.

 

[Urlik]

Even assuming a maximum travel speed of 10% of light speed, and relatively slow reproduction and social development, an advanced and expansionist species will colonise the entire galaxy to the point of overpopulation in no more than 10 million years. If intelligent aliens are common, then, over the past 2 billion years, at least one, and probably thousands, of such species will already have overpopulated the galaxy.

given that it has taken life on Earth around 3.5 billion years to get from single cells to intelligent life, I find your estimate of 10 million years to completely colonise the galaxy as a trifle optomistic.

You may postulate almost anything as being possible, but without evidence that is just so much hot air.

Given that no kind of evidence for the existence of extra-terrestrial civilisations has ever been found, it's a bit pointless speculating whether or not these theoretical beings might have visited Earth, if they ever existed.

what if we have got the evidence for a vist from ETs but haven't recognised it as such?
I know most of Von Daniken's "evidence" has been disproved but his basic premise that ancient texts describing visitors from the heavens might be records of meetings with ETs isn't impossible.

Von Daniken's theories have been ridiculed because a lot of his "evidence" was dodgy, but that doesn't rule out the possibility that the ancients wrote what they saw and if the estimates for ETIs is close to accurate, then it is quite likely that that is what they did and that we have a written record of 1 or more visits but written by people who didn't fully comprehend what they saw

 

[Nik]

IIRC, there was a 'Golden Age' SF tale that explained life on Earth as beginning with a leak in a long-ago visitor's waste-recycling system...
"Nothing to see here, move along, move along..."

IIRC, AC Clarke used a similar ploy to accidentally kill off the *only* ET-lifeform found within considerable search radius. The protean beastie raided the explorers' trash and was poisoned...

But seriously...

IIRC, our Sun / Solar Nebula mix is turning out to be of exceptionally high 'metallicity'. Having a leaner mix would really, really stack the odds against developing to space-faring ...

By rare happenstance, our Moon's formation by skew collision may have gifted the Earth with an unusually large core and thin crust, keeping the continents moving and 'dynamo' warm, while the Lunar tide kept the 'dynamo' wound. Active geology means a lot of minerals are rotated through our environment-- To where we can get at them...

I've hunted about, can't find the reference for this next possibility, so take it as speculation for now...

IIRC, Jupiter *eats* comets etc, and sweeps them from inner system. Our near-binary Moon has stopped a few in its time, especially around the 'Late Heavy Bombardment' stage...

Although tidal-stirred terrestial 'mega-moons' around gas giants in 'habitable zone' may be much more common than free-standing terrestial planets, those gas-giants may draw trouble upon their moons...

By this argument, 'Mega Moons' may make good brew-houses for primitive life, but they're not safe for long enough to evolve better. On the other hand, the safer terrestial planets tend to grind to a halt without tidal input...

---

Hopefully, the success of the new space telescopes and planet-finding techniques will help to unravel the extra-solar planets' zoo...

 

[skeptical]

To Urlik, who thinks that 10 million years to colonise the galaxy is hopelessly optimistic.

On the contrary, that is my most conservative estimate - the upper limit.

If I were to get really optimistic, and suggest the fastest possible colonising of the galaxy, my reasoning would be as follows.

The NASA scientists I quoted earlier said that humanity, within 1000 years, will be able to travel between the stars at 0.1 to 0.2C. Optimistically assume that our expansionist alien or human civilisation can travel at 0.2C.

Now assume that, starting with a technology equivalent to humanity in 10,000 years, over a period of another 10,000 years, this highly advanced civilisation makes 100 billion space craft. Each is controlled by computers and robots of advanced design, and carries a cargo of frozen embryos along with all the equipment and software to thaw them, incubate them in artifical wombs, and raise them to an educated adulthood. Granted that such an effort would require a civilisation totally obsessed with galactic colonisation - but I am going here for the most rapid expansion possible.

The space craft are fired off to all the stars in the galaxy. The slowest trip would be to the opposite side of the galaxy. Assuming a 'direct' route was followed, that journey would take 350,000 years approximately. Once arrived, the computers/robots would need to be able to manufacture habitats for people from the detritus of the star system - asteroids, comets, small moons etc. This because habitable planets would be few and far between, most likely.

Assume 'normal' reproductive rates, allowing a doubling of the population each 50 years. If the colonising vessel holds 1000 embryos (fewer would carry the risk of later inbreeding) then the population would be more than 100 billion in 1500 years.

Thus, the galaxy could, in theory, be colonised to the point of overpopulation in less than 400,000 years.

I am not seriously suggesting this, of course. Many of the assumptions for such rapid colonisation are a bit questionable. Thus, I present the very conservative figure of 10 million years. The reality is that total galactic colonisation most likely would take a period somewhere between those extremes.

 

[Urlik]

skeptical, I suggest that 10 million years is optomistic because other life forms aren't starting out with a tech level 1000 years more advanced than ours.
they'd start out the same as life on Earth and take 3 or 4 billion years to get to that level.

so regardless of how fast they can travel across space, it would still take them in excess of 3 billion years

 

[Anthony G Williams]

what if we have got the evidence for a vist from ETs but haven't recognised it as such?

If we haven't recognised it, then by definition it can't be evidence.

Evidence is what you can show to other people to convince them of its reality.

I suggest that 10 million years is optomistic because other life forms aren't starting out with a tech level 1000 years more advanced than ours.
they'd start out the same as life on Earth and take 3 or 4 billion years to get to that level. so regardless of how fast they can travel across space, it would still take them in excess of 3 billion years

As I pointed out in the first post of this thread, the stars in our galaxy are, on average 6.5 billion years old. Our sun is 4.5 billion. So if it takes 4.5 billion years to develop a technological civilisation, other star systems have on average a 2 billion year advantage over us (some will of course be far older - the oldest star in our galaxy is about 13 billion years). So there has been plenty of time for any extraterrestrial civilisations to develop and colonise the galaxy - thousands of times over. The fact that no evidence has so far been found anywhere (in space or on Earth) for any such civilisation raises some fundamental questions, which I address in the final part of the first post.

 

[Urlik]

If we haven't recognised it, then by definition it can't be evidence.

Evidence is what you can show to other people to convince them of its reality.

ok, I should have said "potential evidence".
as an example, until the late 19th century fingerprints were not recognised as evidence but that doesn't mean that criminals prior to this time left no fingerprints. they did but they weren't recognised as evidence.
we may have evidence of ETI visits all around us but because it has always been there we fail to recognise it for what it is.

As I pointed out in the first post of this thread, the stars in our galaxy are, on average 6.5 billion years old. Our sun is 4.5 billion. So if it takes 4.5 billion years to develop a technological civilisation, other star systems have on average a 2 billion year advantage over us (some will of course be far older - the oldest star in our galaxy is about 13 billion years). So there has been plenty of time for any extraterrestrial civilisations to develop and colonise the galaxy - thousands of times over. The fact that no evidence has so far been found anywhere (in space or on Earth) for any such civilisation raises some fundamental questions, which I address in the final part of the first post.

that is similar to what I was saying.
a civilisation capable of exploring the galaxy isn't going to do it in 10 million years. it is going to take 3 or 4 billion years longer than that for the planet to form and life to evolve to the point where galactic exploration is possible.

another point to consider is what size planet is most likely to support life?
if the Earth is towards the lower limit, many potential galactic voyagers might never get off their planet due to the greater effect of gravity.

 

[Anthony G Williams]

a civilisation capable of exploring the galaxy isn't going to do it in 10 million years. it is going to take 3 or 4 billion years longer than that for the planet to form and life to evolve to the point where galactic exploration is possible.

I took the "10 million years" as starting from the beginning of interstellar travel - in other words, an advanced technological civilisation would already have to be in place.

 

[Urlik]

fair enough

another point to consider is what type of star is most likely to have planets capable of life?
would they be the older stars that have several billion years head start on us or would they be the younger stars like our Sun?

 

[Anthony G Williams]

A very difficult question to answer, as we only have one example of a planet which has developed a technological civilisation!

Some stars are not stable enough, for long enough, to allow the billions of years of reasonably consistent planetary conditions necessary to develop advanced life. That seems to be the main limitation, although there may well be others.

 

[Urlik]

after having a bit of a read, it appears that many of the older stars aren't metal rich like the Sun and are unlikely to have formed accretion disks.
the majority of these older stars also occupy a region close to the Galactic Hub and would be heavily dosed with radiation.
if this is the case, then stars capable of forming Earth like planets are likely to be among the younger stars like our Sun.
this would reduce the head start of any potential ETIs in colonising/exploring the galaxy.

 

[zachariah]

There ain't no justice
There's just us.

I'm amazed nobody's motivated to go to the expense of making a real generation ship, with the prize of your own planet waiting at the other end (for your descendants). I'd sign up!

 

[Urlik]

well it is a huge expense and until we find at least a few likely candidate planets, firing a generation ship off into the void isn't practical.
the ship will need a lot of fuel to go into orbit around any planets they pass, then if that planet isn't suitable, they will need to get back out of orbit and up to a reasonable velocity again.
this will require, for a ship large enough to class as a generation ship, a huge amount of fuel.
get the fuel allocation wrong and, instead of a ship and crew colonising the galaxy, we end up with an artificial comet with an organic core.