Sometimes a picture is worth thousands of words

[Skipjack]

Given a billion year head start, then an intelligence at our level would have spread quite readily through the galaxy. We would see signs of it. We do not. Therefore, it doesn't exist.

You do have a point here, one that I have heard from very reputable astro-physicists as well (e.g. Prof. Harald Lesch of "Centauri" fame).
His point and it is indeed a point worth discussing is: Where are they?
It would be very unlikely that all other intelligent species in the Galaxy are on the same developmental level as well are.
So if intelligent life was common, then there should alos be life forms that are millions of years ahead of us in there development. If these existed, they would most likely have conquerd the stars by now. So where are they?
I honestly do not have a satisfying answer to this question.
The evidence is very contradictive. On one hand, we find many systems that could have habitable planets and etrapolating from that there could be hundreds of millions of planets in the goldy locks zone in the miky way. Yet there is no hard evidence that other intelligent life forms exist, only a statistical likelyhood.
I do very much hope that we will find habitable planets one day and in that case, I also hope that at least a few of them are not inhabited by intelligent life. So we can seize them and collonize them.

[seedload]

Given a billion year head start, then an intelligence at our level would have spread quite readily through the galaxy. We would see signs of it. We do not. Therefore, it doesn't exist.

You do have a point here, one that I have heard from very reputable astro-physicists as well (e.g. Prof. Harald Lesch of "Centauri" fame).
His point and it is indeed a point worth discussing is: Where are they?
It would be very unlikely that all other intelligent species in the Galaxy are on the same developmental level as well are.
So if intelligent life was common, then there should alos be life forms that are millions of years ahead of us in there development. If these existed, they would most likely have conquerd the stars by now. So where are they?

I don't read enough. It's called the Fermi Paradox and has a really big wiki page. Interesting reading.

I honestly do not have a satisfying answer to this question.

I am adopting a pet theory. There is a hidden doomsday physics booby trap that every intelligent race runs into before it becomes interstellar. They all end up banging the wrong two particles together and their whole civilization gets sucked into a black hole.

Or maybe this. In a muti-universe, we MUST live on a branch where we are the first intelligent race or we wouldn't exist at all because our planet would have been colonized long before we had an opportunity to evolve.

Seriously, I actually hope it is something like that the window of use of radio signals by an expanding technological civilization is very very small thus there are no radio signals to detect.

Or maybe intelligent life is just really really really unlikely.

[Skipjack]

Yes, it is the Fermi paradox, indeed.
In any case, it makes sense to ask that question. Fermi might have mostly wondered about the lack of radio signals, but it also makes sense to Ask what Lesch was asking "why arent they right here, right now?" or rather "why havent they colonized earth a long time ago?".

[Scupperer]

It's because FTL is truly impossible, and interstellar distances are too far.

[choff]

I take the approach of "The Hitchhikers Guide To The Galaxy". There is no intelligent life in the universe and this can be proved mathematically. Number of galaxies infinite. Number of galaxies with intelligent life finite. A infinite number divided by a finite number gives a zero result.

[KitemanSA]

An infinite number divided by a finite number gives a zero result.

Backward, but an interesting consideration.

[hanelyp]

The 'Doomsday Physics' hypothesis sounds related to the Nuclear safety valve. This proposes that:
- interstellar travel requires nuclear power.
- any society that obtains nuclear technology without managing aggressive tendencies self destructs.
- any society lacking a degree of natural aggression may never bother to go to the stars.

As for radio, it appears that as we advance here on Earth, a growing portion of our radio transmissions use digital spread spectrum techniques that are difficult to distinguish from noise if you don't know the specific modulation.

[rj40]

I suggest this as quick reading:

http://www.amazon.com/Eerie-Silence-Ren ... 0547133243

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The Fermi Paradox is good. Fun to think about. And makes a good point.

Distance probably doesn't mean too much (I can't really know I suppose), but whose to say other life forms don't live for billions of years? Or, better still, are machines of some type that are effectively immortal?

Still worth looking I think. If we find nothing, it is still information we didn't have before. Sort of sets some limits. "We find no radio or laser signals to the limits of our equipment." That could be meaningful.

[Giorgio]

A infinite number divided by a finite number gives a zero result.

You probably mean the other way around. A Finite number divided by an Infinite number tends to zero.

[Giorgio]

Given a billion year head start, then an intelligence at our level would have spread quite readily through the galaxy. We would see signs of it. We do not. Therefore, it doesn't exist.

At a universal scale, I tend to think it is probably out there.

If there are (and I think there are) advanced civilization out there than their technological level will mostly be so advanced that we might as well live next door to them and simply don't recognize it.

Think to the tribes in living in the Amazonian forest that didn't know about the existence of our civilization even if they were living right in the middle of it.

[Betruger]

A halfway topical observation: Kurzweil's "universe waking up" is an interesting part of his predictions. Why haven't we seen any hint anywhere of such a wave sweeping the cosmos?

[chrismb]

I am interested enough in this to have given it some thought, as per my post above, and agree that life in some other galaxy seems probable. With an estimate of several hundred billion galaxies, I agree that it is difficult to come to any other conclusion.

But then we enter the realm of the truly philosophical and we can debate whether it is even a worthwhile topic to debate. With the nearest galaxy being over 2 million light years away, any observed evidence for life would not be evidence that life currently exists there. So in this way, we are truly stuck in a quandary with respect to life elsewhere in the universe.

In regards the pedantry of the point, the original post speculated 'are we alone'. Well, if I arrived on an otherwise barren planet next to a patch of mushrooms, sure, that is definitely life but I would most certainly still feel 'alone'!!!

It is surely an arguable point and the line at which someone draws it will be subjective, but for good reasons I would say that unless I found a species that farmed its own nutrients, rather than plucking them from the environment, then I would tend not to associate that with 'intelligent life'. In other words, I would feel alone if not in the company of people who understood the necessity of, and relied on, farming. I do not see any other useful delineations that uniquely describe the differences between 'animal life' and 'human life'. Does anyone have any other definitions that they think are meaningful delineations?

[Skipjack]

It's because FTL is truly impossible, and interstellar distances are too far.

You dont need FTL. All you need is generation ships and an energy source capable of keeping them going for a few decades. Which brings us to that other topic again...

Anyway, if we imagine a travel time of 150 years. At 0.1c you can travel 15 lightyears in that time. There are 40 star systems within that distance from us. It is not completely unlikely that there is a planet within the goldy locks zone in one of them.
Accelerating to 10% of lightspeed "only" takes a little more than a month at 1g constant acceleration.
So most of the travel time would be spent at the desired speed.
A constant one g acceleration for a month does not seem completely inconceivable to me. We would still need several technological break throughs, but it is not unimaginable technology.
So in theory the colonists of a very advanced civilization should be able to reach other stars and colonize them.
So if we were to spin this further. You travel 150 years, colonize the planet and repeat the traveling after another 200 years or so.
Then you cover a radius of 15 lightyears every 350 years. So you can "cover" a sphere of some 30,000 lightyears in diameter within "just" 350,000 years (of course the arm of the milky way is only 6000 lightyears wide). From a cosmic point of view 350,000 years is not a very long time. At that rate they could have colonized most of the galaxy within 1 million years. Double the time and make it 2 million years. That is still a very short time, in cosmic terms.

[seedload]

It's because FTL is truly impossible, and interstellar distances are too far.

You dont need FTL. All you need is generation ships and an energy source capable of keeping them going for a few decades. Which brings us to that other topic again...

Anyway, if we imagine a travel time of 150 years. At 0.1c you can travel 15 lightyears in that time. There are 40 star systems within that distance from us. It is not completely unlikely that there is a planet within the goldy locks zone in one of them.
Accelerating to 10% of lightspeed "only" takes a little more than a month at 1g constant acceleration.
So most of the travel time would be spent at the desired speed.
A constant one g acceleration for a month does not seem completely inconceivable to me. We would still need several technological break throughs, but it is not unimaginable technology.
So in theory the colonists of a very advanced civilization should be able to reach other stars and colonize them.
So if we were to spin this further. You travel 150 years, colonize the planet and repeat the traveling after another 200 years or so.
Then you cover a radius of 15 lightyears every 350 years. So you can "cover" a sphere of some 30,000 lightyears in diameter within "just" 350,000 years (of course the arm of the milky way is only 6000 lightyears wide). From a cosmic point of view 350,000 years is not a very long time. At that rate they could have colonized most of the galaxy within 1 million years. Double the time and make it 2 million years. That is still a very short time, in cosmic terms.

Agree or Embryo Colonization. There is no reason that an intelligence on our level could not easily colonize the galaxy within a few million years.

[chrismb]

Agree or Embryo Colonization. There is no reason that an intelligence on our level could not easily colonize the galaxy within a few million years.

Not sure how you come to that conclusion! The reason could be that it is practically impossible to generate enough energy to propel a spacecraft a sufficient distance. Seems a pretty substantial reason to me. Plus that anyone travelling a long way may require radiation shielding greater than that which is practical to put on board a spacecraft. Plus it may not be practical to grow enough nutrients to self-sustain those on board. Plus, &c. &c....

I think what you mean is; there is no reason, according to science fiction, that.... &c....