Intelegent life in the Universe, how common is it?

[Last Conformist]

I don't see why travel times is such an issue.

Imagine that some alien planet sends out a spaceship that needs a million years to reach the next star. Once there, it establishes an outpost, and builds a new ship. The mother planet does likewise (after watching reruns of Family Guy for a million years). In a further million years, these two ships arrive at two new systems. Repeat.

In less than eighteen million years, there'll be an outpost at every star in the galaxy (except for some recently formed stars, and a few that will have gone supernova and blasted it's associated outpost to bits, but that's marginal).

Eighteen million years is, of course, well little on the galactic timescale. And this assuming pretty slow interstellar travel - in a million years, Voyager 1 will have reached 50-60 ly out, or some ten times the average distance between stars in this part of the galaxy.

So, if even one civilization in the galaxy has embarked on a such project, we should expect they've got an outpost in the Solar System.

Now, if that outpost would contact us, or be easily contactable, is a whole 'nother question.

[Dauphin]

Originally posted by Last Conformist
I don't see why travel times is such an issue.

Imagine that some alien planet sends out a spaceship that needs a million years to reach the next star. Once there, it establishes an outpost, and builds a new ship. The mother planet does likewise (after watching reruns of Family Guy for a million years). In a further million years, these two ships arrive at two new systems. Repeat.

In less than eighteen million years, there'll be an outpost at every star in the galaxy (except for some recently formed stars, and a few that will have gone supernova and blasted it's associated outpost to bits, but that's marginal).

I don't disagree with the potential of the principle but you do have a flaw in your method of calculating reproduction of colonies. Quickest way to demonstrate there is a flaw is to take the assumption that it takes 1 million years to reach the next star system, say that the distance is 5 light years, and the radius of the galaxy is 35,000 light years. It would therefore take 7,000 million years to travel the radius of the galaxy, which is considerably longer than your estimate of complete galactic colonization.

You have to remember that only colonies on the periphery of colonized space will be able to replicate and find new planets to colonize, and that will only be a small proportion of the whole.

[Boris Godunov]

Originally posted by Darkstar
BS. There *are* no experts in interstellar travel here.

Um, but we have experts in in physics. They're called physicists. Might want to read something from them sometime.

What we know is that, for us, the economics are against it. But so was a direct China-Spain exchange of goods at one point on our *little* planet.

The economics are certainly considerable, but that's nothing compared to the physical possibility. Again, talk to the physicists. If, as DanS mentioned, the theoretical max speed of an unmanned object is 1/10 c., then at that speed, things will take a long time to get anywhere and longer still to relay information back.

[Last Conformist]

I did oversimplify a bit, I admit; the one million years should be seen not as the duration of any given trip, but as the average between all trips. A million years between two stars 5 ly apart is very slow, as I think my voyager comparison made clear. If the commonly accepted limit of 0.1c is accepted, one million years is enough to reach any system in the galaxy.

Furthermore, there's no reason that the "old" planets couldn't send ou new colonies. They'd just have to go further and further. (Max range isn't an issue, since the could refuel at older colonies.)

Third, note that I inflated the time estimate by the assumption that the planets would wait one million years between sending out new expeditions. Family guy might be good, but I think you'll agree that this is a very conservative estimation; in practice they'd probably be able to send them out in much more rapid succession.

[Last Conformist]

Originally posted by Boris Godunov

The economics are certainly considerable, but that's nothing compared to the physical possibility. Again, talk to the physicists. If, as DanS mentioned, the theoretical max speed of an unmanned object is 1/10 c., then at that speed, things will take a long time to get anywhere and longer still to relay information back.

At 0.1c, you can reach anywhere in the galaxy within a million years. On the galactic timescale, that's simply not a long time.

[Boris Godunov]

Originally posted by Last Conformist
At 0.1c, you can reach anywhere in the galaxy within a million years. On the galactic timescale, that's simply not a long time.

Except that we have no reason to assume that there was a sentient species sending out probes a million years ago, or that their probe happened to come across us, or that their probe reached us at a point where we could detect them and vice-versa.

A million years may not be long on the galactic time scale, but it's long enough to make our knowing about other life--which is the key issue here--problematic, if such a probe came nearby.

[Dauphin]

There is no reason to assume there is a sentient species now. If there are none now there were probably none then, and if there are others now, then there were probably others then.

Any scenario that explains lack of communication despite their existence has to presume that they existed in the past, and so travel time and distance is not the primary issue.

[reds4ever]

Originally posted by Dauphin
And, there is nothing wrong with the Drake Equation except that its margin of error is so huge its of no practiucal use. Pin down the variables and you are getting somewhere useful.

The fact that is of no pratical use means theres nothing wrong with it?

The equation may or may not hold water when the right numbers are plugged in, the thing that annoys ne is that people use it as mathematical proof that intelligent life must exist.

When your first variable is such a large number (ie stars in the galaxy), all the other numbers can be pretty much anything you like (>1) and you'll get an answer that tells you the gaxaxy is teeming with life!

[Boris Godunov]

Originally posted by Dauphin
Any scenario that explains lack of communication despite their existence has to presume that they existed in the past, and so travel time and distance is not the primary issue.

Not necessarily. Why is it inconceivable that any other sentient species in the galaxy out there, far away, that is either at about the same tech level as ourselves, or more primitive? For all we know, we were one of the very first systems in the galaxy to produce an intelligent species.

Travel time and distance is still an issue even if there is a more advanced species sending out probed, because even if they sent a probe that passed our sun to find a life-bearing planet, what are the odds we would know about that probe?

[Dauphin]

Originally posted by Boris Godunov


Not necessarily. Why is it inconceivable that any other sentient species in the galaxy out there, far away, that is either at about the same tech level as ourselves, or more primitive?

Not inconceivable, just unlikely. Why would two unrelated planets develop sentient life at the same time in cosmological timescale terms? If there is another sentient life out there it is likely there are several, and so what reason is that all would develop at the same time in cosmological timescales?

[Dauphin]

Originally posted by reds4ever


The fact that is of no pratical use means theres nothing wrong with it?

There is nothing wrong with a simple statement that a straight line has the equation y = mx + c. The fact that you don't know what m, x or c is doesn't make it wrong.

[Dauphin]

Originally posted by Boris Godunov
Travel time and distance is still an issue even if there is a more advanced species sending out probed, because even if they sent a probe that passed our sun to find a life-bearing planet, what are the odds we would know about that probe?

Thats not an issue of distance to other planets, thats an issue of our technical ability to detect something like a probe in our solar system, and looking at the right place and the right time.

[reds4ever]

Originally posted by Dauphin


There is nothing wrong with a simple statement that a straight line has the equation y = mx + c. The fact that you don't know what m, x or c is doesn't make it wrong.

y=mx+c has been *PROVEN* to be true, Drakes 'equation' has not.

[Dauphin]

Originally posted by reds4ever


y=mx+c has been *PROVEN* to be true, Drakes 'equation' has not.

Drake's equation is not a disprovable equation. Its a probablity statement.

Put garbage in you get garbage out.

[Boris Godunov]

Originally posted by Dauphin
Thats not an issue of distance to other planets, thats an issue of our technical ability to detect something like a probe in our solar system, and looking at the right place and the right time.

It is an issue of distance. If the sentient species was in the next star system over, then yes, we'd be teeming with their probes, probably. If they were even 20 ly away, we'd probably be teeming with them. But if it's 10,000 ly (which is far more likely, given that very special conditions seem to be needed for life, not to mention intelligent life), then the likelihood for them to have sent a bunch of probes our way in a time frame where they probes could detect our sentience (which is a very small window, relatively speaking) is remote, not to mention their ability, once the info got back to them, to actually do anything about it.