Aliens...why do so many just assume?

Great Debates
41

You’re assuming that because there’s no way to travel faster than light, there’s basically no reasonable way to explore space. That’s true only for certain definitions of “reasonable”; a spacecraft capable of maintaining .01 gravities (that’s .1 m/s/s) could reach the nearest visible star system in about forty years. To get a good hundred light years out, it’s about 200 years with that acceleration. If we increase the thrusting power of the spacecraft to 1 gravity, those times start looking a lot better: three years and nine years, at least for the people on board. Granted, we have no way to get that kind of acceleration (well, continuous acceleration, anyway) right now, but it’s not theoretically impossible- we just don’t have a method to do it yet. If we make any kind of theoretical breakthrough that can allow significant continuous thrust (much better than the ion drives that we’re testing now, I mean), we’ll reach the stars. Considering the way that science keep accelerating and making new discoveries, I think it’s possible that we’ll figure out some way to do this. We certainly haven’t hit many “insurmountable” barriers that stayed insurmountable thus far.

I grant you, I’m not holding my breath either. I think we’ll get there. Eventually.

Other galaxies, though? Shoot, I’d be astounded if we ever even built a transmitter that could reasonably transmit a signal that distance without fading completely into background noise, let alone went there.

42

As I understand it, there is no edge. No “cosmic event horizon”, except in the sense of the edge of the observable universe, which is only an “edge” from our perspective. My understanding has been that the universe is believed to be either a finite hypersphere, flat, or hyperbolic; with no edge in any of those possible shapes.

43

I’m not arguing with you on any of those points… I was simply stating that within our lifetime, and perhaps well beyond, we won’t be getting to another star system. Aside from landing on a planet, there’s no way to be completely sure there’s not life there (excluding some miraculous invention in the future). And developing a smart enough automated probe that will be capable of that kind of adaptability will take another long while.

Also, one problem with reaching that sort of acceleration might be any kind of impact from even a microscopic piece of space-dust. Not saying we won’t solve the problem (or an alien species), but perhaps eliminating that sort of danger never gets below acceptable risk for traveling at that speed for extended, interstellar durations.

All that’s moot, if you simply want to send a probe into the nearest system to just see what’s there… although you’ll still need to reach 18,620 per second to get there in just over forty years. Plus the 4.5 year trip for the probe to broadcast the data back. What a bummer if something goes wrong 35 years into the trip! I guess redundancy would be where it’s at for a trip like that.

44

Not aliens…Quaggarrz…its a name he made up. They look like Roast Chickens.

45

Or they could be here now, watching us. Maybe they don’t want to interfere. Maybe UFO sightings are just the spacemen playing around, seeing how we’d react.

46

If there was 1 intelligent civilization per galaxy, there would be hundreds of billions of civilizations in existence - and Id expect we’d be so far apart there would be no practical hope of communicating unless we manage to make some pretty amazing jumps in technology. Let alone if you have only one place with life in the galaxy, with X galaxies needed per civilization.

‘Space is big’ both makes life seem awfully likely to be more than 1 and make it so theres a fair chance we’d never see it anywhere but here.

Otara

47

Quagaars! Double A, actually.

48

There is certainly a cosmic event horizon (or cosmological horizon) beyond which objects are redshifted below detectable radio frequencies (corresponding with a cosmological redshift factor z~1100). We can’t say anything about spacetime beyond this veil except in base speculation. This isn’t an “edge” but a (presumably) spherical bounding surface centered around our particular reference frame. (I suppose you could call it a “hyperedge” but I’ve never seen such terminology used in technical literature.) Note that there are objects even within the observable universe that are still fleeing away at a relative speed greater than c, and if in fact if I recall correctly the bounding condition is z~1.4 for objects receeding at c, owing to the fact that the space between these objects is expanding at a rate proportional to the distance between them, meaning that the light we see today was emitted by the object when it was much, much closer. Since the light is traveling away from the object, the space between it (the light) and our reference frame is expanding less slowly than the distance between the two objects themselves.

Anyway, this tells us nothing about the current or ultimate size of the universe. The lower bound on the diameter of the universe is currently estimated to be 78 billion light years (based on analysis of WMAP data). It could be infinite in volume, or could, in fact, be smaller and merely overlapping (although to date no comparison of data has shown similarity between different sections, but of course we might be observing them from different directions). Regardless, it is an understatement that the observable universe is obscenely, rudely, obnoxiously large, and unless sentient life is as common and widely distributed as Mormon missionaries on a Saturday morning it is statistically unlikely that we would just incidently run into it. It may in fact be very common and we’re just out in the unfashionable end of the galaxy, or vary rare and we’re screaming across the hilltops from Kansas City to Cairo with no hope of being heard. Lacking, as we do, any data beyond our own existence (and not even having a good understanding of abiogenesis on Earth), we can’t say anything statistically meaningful about the likelihood of life aside from speculation about the incidence of organic molecules and occurence of primordial environments on other worlds.

Stranger

49

Space is far from empty, but that aside, the idea is that you send one probe out to the nearest star system at 0.1c. When it reaches alpha centauri (or wherever), it explores the system, and harvests enough material from the asteroids/planets to build two or more duplicate copies of itself, which it sends to the nearest unexplored stars.

If for some reason you think that is unfeasible, replace “self-replicating probe” with “colony ship” , and you get roughly the same result. 50-or-so years of travel time, maybe 10 years in-system to build two more ships.

50

That’s a big assumption. I’d say, intelligent life within the parameters you believe it is constrained to.

51

I see no problem with the Drake equation, remembering that it is a quantification of our ignorance – not in the insulting sense, but in the sense that we do not know the values for the parameters. (Note also that Drake confined his figures to this galaxy; add another parameter for the number of potentially-inhabitable (i.e., non-Seyfert, non-quasar) galaxies in the Universe.

I believe that it was Arthur C. Clarke who commented, “Either we are the only intelligent life form in the Universe, or there are others. Either way, the implications are staggering.”

52

You must have a different definition of infinity than the rest of us. Please let me know what an infinite universe at time t =0+epsilon does to inflation theories. You have a cite for this assertion? This would require infinite energy after the singularity, which I suspect would make the CBR a bit higher than it is.

The universe is definitely big enough for any number of other civilizations. What it is not big enough for is the “there is a planet just like Earth somewhere else” hypothesis.

53

Maybe when t = infinity. Remember, the expansion is creating space, it is not that the universe is expanding into an already created infinite space. (Created used very loosely.) If a subset of the natural numbers is defined as the set of numbers counted, and you start with 0 and keep adding 1 to it every nanosecond, you will have a very big number very soon, but you will not reach infinity until t = infinity.

54

Sounds like a good way to end up with Cylons.

55

In the simplest (i.e., topologically trivial) models of the Universe, a flat universe (such as ours appears to be) must necessarily be infinite, and have always been infinite. It was already infinite at t = 0+epsilon, and will always be infinite. In such simple models, it is just plain not possible for the Universe to be finite.

Now, to be fair, there are more complicated models which are topologically nontrivial. In those models, it is still possible for a flat (or even open) universe to be finite. We cannot currently confirm nor rule out such models, and it appears that we will never be able to. But we can at least say that if the Universe is finite, it is very, very large indeed: There are at least tens or hundreds of billions of galaxies in the Universe.

But of course, one could argue that maybe the chances of intelligent life developing are just so small that even that astronomically huge number fades into insignificance. What can we say about the other factors in the Drake equation? Well, we only have one data point for life arising, but we can say that it happened very, very soon in our planet’s history. Nearly as far back as the Earth’s crust solidifying, we have evidence of life existing. This suggests (though it does not prove) that it’s reasonably likely for an Earthlike planet to develop life.

But that just gives us pond scum. What about intelligent life? Here, actually, we do have multiple data points, for almost every step of the process. Everything that needed to happen to get from pond scum to ape-level intelligence has happened at least twice in Earth’s evolutionary history. Prokaryotic organisms absorbed and incorporated other prokaryotes to form eukaryotes: This happened with both the things that became mitochondria, and the things that became chloroplasts. Single-celled eukaryotes joined together to form multicellular organisms: This happened with both the lineages which became plants and animals. Differentiation of multicellular organisms into discrete organs happened multiple times, if nothing else with the plants and the animals, and I’m pretty sure multiple times in the animal lineage, too. Once you get to the point of discrete organs, you get intelligence on the order of the proto-mammals evolving multiple times, completely independently (octopodes are at least as smart as shrews). From something like a shrew, you ultimately get the cetaceans, the elephants, and the apes. Since all of these steps occured multiple times on our planet alone, it’s reasonable to say that none of those should be all that unlikely. So we should expect plenty of other examples of ape-level intelligence elsewhere in the Universe. How big of a step is it from ape-like intelligence to human-like intelligence? I don’t know, but I doubt that it’s 1 in a billion.

56

I’d say you are vastly overestimating the ease with which a probe like that (or colony ship) could self-replicate. Do you know how many different industries are involved in making the robots we have today? One little robot represents the end result of a huge amount of infrastructure. And star systems probably have vastly different environmental conditions with very diverse compositions with hard to reach resources. I seriously doubt it is physically possible to create a self replicating robot in any mechanical sense. The only way it would be possible is if we had some sort of transporter/replicator technology similar to Star Trek that could manipulate matter on the quantum level.

57

Any self-replicating autonomous probe would not be manufactured of formed and welded steel chassis bolted together with threaded connectors, but would instead be self-constructed from materials readily available in planetary space (i.e. hydrogen, nitrogen, carbon, oxygen, et cetera), built on a framework of silicates or long-chain carbon molecules. We don’t have the kind of technology that lets us make machines like this today, of course, but we do have a wide range of excellent examples in nature to draw from: living organisms. These don’t require any kind of indistinguishable-from-magic methods of fabrication beyond basic (if very complex in arrangement) chemical reactions, and have evolved to exist in the harshest terrestrial environments.

Given a reasonable extrapolation of molecular engineering ability to mimic the functions of living organisms, such a device is barely even science fiction, and it makes a lot more sense than Spandex-leotarded heros zapping around the galaxy in large but highly vulnerable metal cans. However, barring some kind of unknown-to-modern-physics method of propulsion, even these organisms are going to be limited to hundreds or thousands of years just to travel to a nearby star, much less explore a significant portion of the galaxy.

Stranger

58

Nuclear pulse propulsion ? Good old 1960’s technology.

59

Nuclear pulse propulsion is adequate for tooling around a planetary system, but for interstellar distances it still produces too little specific impulse (at ~I[sub]sp[/sub]10,000s it falls short by about an order of magnitude) for the practical minimum for interstellar travel. This is essentially independent of what speed you wish to obtain (within reasonable, non-relativistic speeds over timeframes of decades to tens of centuries), as it predicates how much propellant–in this case, nuclear bomblets–needs to be accelerated and carried to slow the craft down as it approaches the target. (This isn’t a problem if you don’t care about decelerating, but then you end up flying past uselessly.) There is also the problem of keeping nuclear fuel/bomblets stable over century timeframes; as nuclear material decays (even material with long half-lives like [sup]239[/sup]Pu) subtle changes occur in the structure of the material which may make it unreliable and/or unsafe for use; this is currently a problem which occupies much research effort in aging and surveillance for stewardship of the US Enduring Stockpile of nuclear weapons. [thread=441422]Here[/thread] and [thread=398234]here[/thread] are a couple of old threads on the topic.

And it goes without saying that any self-replicating probes are not going to use Project ORION-type nuclear pulse propulsion, given that efficiency scales up in mass but has a definite lower limit.

Stranger

60

Well, that’s the thing people always seem to forget. Unless you’ve got antigravity or some other such magic technology, you’re going to have to travel by rocket.

And that means sitting in a canoe and throwing rocks off the back to make you go forward. You can get a bigger pile of rocks, but that just means that you need an even bigger pile of rocks to move the first pile of rocks. Then you can improve your throwing arm. But once you reach .99999c, you can’t get any better. Even if you have unlimited power due to a ultratech energy source, you still can’t just turn the engines on full and head for Alpha Centauri at 1g, because you’ve only got so much delta-v, and that’s that. You can improve your specific impulse to 99.999% efficiency, but when you’re looking at interstellar distances that doesn’t do you as much good as you might hope.