Where is everyone?

[QED]

In the topic: Is Stephen Hawking correct about moving into space? the subject of other life in the universe came up. In response to my question about why our Galaxy does not seem to already be colonised Harvey introduced an idea that interested me...

...it does seem inescapable that some sort of exponential colonisation pattern should emerge to fill every available habitat in a trivial timescale. This presents us with the niggling question "where is everyone then?". So from a simple logical imperative we might have a reason to wonder at the fact that we seem to be alone in the universe.

My (optimistic) view is that we are like kids in a family growing up in a retirement village (the stars are the adults in this retirement village). We are the only kids in the village from what we can see, and we begin to ask ourselves why no other family has kids since the retirement village has been here a long time. I think the answer would be obvious in that example. There were kids of these other resisdents, but they grew up and no longer live with their parents. I prefer this view because that means that some great things are ahead of us, and that this home we call the universe is just a place that we are spending our childhood and adolescence. Perhaps we'll eventually meet others on the block who are around our age, and we'll all leave home together...

This seems to suggest that all life naturally reaches a point where is transcends the physical realm and comes to reside in some other realm that has no connection with the physical. Is this reasonable? Is it supported in some measure by any of the religious faiths? Is there any logic we could call upon to dismiss it as an explanation for why we seem to be the only kids in the village?

[Bugmaster]

We keep coming up with the disappointment that people have about the time/distance problems, but isn't it naive to put this forward as a limit to what might be achieved? Surely there are other timescales that apply, not just our own pathetic three-score and ten?

Yes, but there are all kinds of other questions that this assumption raises. For example, what is the maximum constant acceleration which the aliens can endure ? If they're anything like us, the answer is "1g". But, even if the answer was "10g", the resulting speed of the alien sleeper-ship would be so slow that traveling from their distant planet to ours would likely take longer than the lifetime of the Universe.

You might reply by saying, "well, what if the alien life is radically different from anything we know ? What if the aliens are energy-based life-forms ?" Well, that's possible, but just not very likely; I find it highly improbable that aliens that are immune to acceleration could exist at all. Furthermore, the more different alien life is from ours, the harder it will be for us to recognize it as life at all (let alone intelligent life). If you've played Civilization: Alpha Centauri, you have an idea of what I mean.

The main obstacle to all these enterprises is money. Money has a habit of buying you things that you couldn't dream of affording ten years or so ago.

No, another such obstacle is relevance. Should we send a longship out to a distant stars, if we know for a fact that signals from it won't reach Earth for billions of years ? What would be the point ?

[CJK]

Perhaps the visible universe is a membrane floating within a higher-dimensional space? Rather than little green men with space ships, there are beings operating on a different wave-length?

Just a thought.

[Bugmaster]

That's as good a sci-fi plot as any other :-)

[QED]

Yes, but there are all kinds of other questions that this assumption raises. For example, what is the maximum constant acceleration which the aliens can endure ? If they're anything like us, the answer is "1g". But, even if the answer was "10g", the resulting speed of the alien sleeper-ship would be so slow that traveling from their distant planet to ours would likely take longer than the lifetime of the Universe.

I haven't done any actual calcs, but I would have thought a solid-state sleeper mechanism ought to be able to withstand far higher G's than you mention, and make the span of our galaxy accessible within its lifetime.

I find it highly improbable that aliens that are immune to acceleration could exist at all. Furthermore, the more different alien life is from ours, the harder it will be for us to recognize it as life at all (let alone intelligent life). If you've played Civilization: Alpha Centauri, you have an idea of what I mean.

This is essentially a robotic mission though, and the sleeping life component is purely an expression of our collective drive to spread as far and wide as possible. The point is that this pattern is one which has the potential to get into every niche once technology reaches the level of self-reproduction. This is the sort of watershed that would have the capability of reshaping the galaxy in ways that couldn't be missed. This coupled with the observational evidence we have now raises the question in the OP.

No, another such obstacle is relevance. Should we send a longship out to a distant stars, if we know for a fact that signals from it won't reach Earth for billions of years ? What would be the point ?

Like Everest -- because it's there

[Bugmaster]

I haven't done any actual calcs, but I would have thought a solid-state sleeper mechanism ought to be able to withstand far higher G's than you mention, and make the span of our galaxy accessible within its lifetime.

Solid state doesn't mean indestructible, though; if you don't believe me, drop your CPU off your roof and see what happens to it :-) In fact, I have worked on military-grade accelerometers before (solid state), which had to withstand (IIRC) 25g continuously for 50ms (and I hope I didn't just disclose a state secret). This was already pretty difficult to achieve, and we're talking of enduring much more for much longer

The point is that this pattern is one which has the potential to get into every niche once technology reaches the level of self-reproduction.

Whoa there ! You'd first have to convince me that a). self-reproducing nano is possible at all, and b). such nano could survive extreme accelerations, as above. I am not convinced that either point is true. As it happens, we know of at least one kind of self-reproducing machinery -- our own cells -- but they're pretty squishy.

No, another such obstacle is relevance. Should we send a longship out to a distant stars, if we know for a fact that signals from it won't reach Earth for billions of years ? What would be the point ?

Like Everest -- because it's there :D

Forget it. I am not paying for a robotic probe whose signals won't reach Earth for billions of years. The Sun is scheduled to turn into a red dwarf by then, anyway. The probe is a waste of resources. Things would be different if I was traveling myself, of course -- in that case, I'd be willing to pay my own way, but I wouldn't expect anyone else to chip in, for the same reason that I wouldn't pay for the probe.

[Cathar1950]

I enjoy sci-fi. I am a sucker for anything to do with time travel.
I did read some place that people that are interested in time travel are dysfunctional at some level. I don't recall the details because it is not going to make me stop enjoying time travel just because there is something wrong with me.
But It would not stop me from imagining space travel to other planets.
What about spooky action at a distance?
What if there are 11 or 14 dimensions?
Anything might be possible, almost.
What if we encounter beings that just think of us as food?
What if we are the nice folks in the universe?

[ENIGMA]

Yeah, like you said, it's a neat story, but it's just not very likely. For example, the closest star to us is Alpha Centauri; IIRC, light takes 4.5 years to get there. This is already too far away for any practical conversation; and it is much too far away for a starship maintaining a constant 1g acceleration to visit. And, as far as we can tell, there aren't any habitable worlds there, either

Not necessarily. The key is that if you can maintain such an acceleration long enough to get close to the speed of light, then time-dialation effects will greatly shorten the intermediate journey, at least for the perspective of the people/stuff on the ship.

A few quick calculations:

Assuming 10 m/s^2 acceleration, starting from rest.

vf-v0=at
3*10^8 m/s=10 m/s^2 * t
t=3*10^7 s

3*10^7 s = 500000 minutes
500000 minutes = 8333 hours
8333 hours = 347.2 days which is just under a year.
Not Star Trek, but not too shabby either.

So, basically do 1g acceleration for a year, kill the engines. Wait until you are equidistant to your destination as you were to home when you killed the engines and apply a 1g thrust to decelerate. It would then take a bit over 2 years from the perspective of the people on the ship, 1 to accelerate, 1 to decelerate, and the bit is the part in the middle.

[QED]

The point is that this pattern is one which has the potential to get into every niche once technology reaches the level of self-reproduction.

Whoa there ! You'd first have to convince me that a). self-reproducing nano is possible at all, and b). such nano could survive extreme accelerations, as above. I am not convinced that either point is true. As it happens, we know of at least one kind of self-reproducing machinery -- our own cells -- but they're pretty squishy.

Squishy Formula 1 racing driver David Purley managed to survive a crash which subjected him to 179.8g when his car came to rest from 107mph in just 26 inches! I'm sorry you don't like this line of argumentation. I find it pretty convincing myself. It's along the same lines as time-travel tourism: with the whole of eternity ahead of us (good as) if at any time in the future time travel is invented then we would expect to see flocks of tourists all heading back to a single interesting event (like the resurrection of Christ perhaps). It's a one to many mapping that works in both directions. It only takes one "pyramid" colonization effort to fill the galaxy.

Forget it. I am not paying for a robotic probe whose signals won't reach Earth for billions of years. The Sun is scheduled to turn into a red dwarf by then, anyway. The probe is a waste of resources. Things would be different if I was traveling myself, of course -- in that case, I'd be willing to pay my own way, but I wouldn't expect anyone else to chip in, for the same reason that I wouldn't pay for the probe.

Yes, well I mentioned the shift in affordability that technology undergoes over time. But the key to the scheme really lies in the ability to reproduce by making use of the natural resources available in each solar system visited. As for the technology, it needn't be nano. The University of Bath is not alone in working on Universal Constructors. The range of physical devices that can be fabricated by such machines is already quite impressive. I don't think we have to use too much imagination to see how this sort of development could turn UC's into commodity items that change the face of manufacturing and industry. Once unshackled from the ways of the industrial revolution I think it's only natural for this to extend into space to make use of greater reserves of material resources.

Even if ENIGMA'a direct approach to exploration doesn't work for us I think there's still something to be said for extending the experience to future (sleeper) generations in the spirit of adventure. After all what else is life about?

[harvey1]

So, basically do 1g acceleration for a year, kill the engines. Wait until you are equidistant to your destination as you were to home when you killed the engines and apply a 1g thrust to decelerate. It would then take a bit over 2 years from the perspective of the people on the ship, 1 to accelerate, 1 to decelerate, and the bit is the part in the middle.

All of this of course assumes that a quantum gravity device won't be able to generate a gravitational equalizer such that the inhabitants on board do not experience any Gs at all. Also, fusion reactors could generate much more than 1g of force, so I think space travel to remote stars is conceivable. I think, however, until we have a full understanding of quantum gravity and the nature of spacetime, it is very premature to put a limitation on space travel utilizing new physics.