Doktor S wrote:Great post, but I have a few contentions.
You ain't the only one.
Quote:1:Somewhere I read a thesis by a mathematician that given the age of the universe, and the fact that life can exist, the odds point to life being literally everywhere. I can't support this at the moment, being that I can't remember the name of the author, but I'll see if I can't dig it up..
Actually, i've seen several variants on this theme. I even wondered for a moment if you were playing a game here, but i'm just going to assume that you don't recall well what you read, or that it was not well expressed.
Leaving aside intergalactic travel, for reasons which i will get to a bit later, one would consider the probability of space-faring civilizations arising in this galaxy. As i recall reading, there are a few tens of billions of stars in this galaxy. For sake of
speculation (which is all, in the end, this engages), i'll assign a probability of one tenth to each level of consideration.
Before proceeding, however, fully half of all stars can be eliminated. At the galactic center, tidal forces would preclude the probability of life arsing in complex forms on planets--not impossible, but improbable on an order approaching impossibility; in dual-star systems and multi-star gas clouds, other considerations produce the same "unlikelihood" of complex life arising on planets, if any planets even exist in such conditions.
Therefore, we are considering at least a few tens of billions of stars. Stipulating that organic chemicals are as common in the cosmos as dirt on the surface of our planet--not at all an unreasonable stipulation--let's suppose that the probability of the
potential of life arising is high, whenever greater cosmic forces do not preclude (center of the galaxy, near "black holes," in multi-star gas clouds, etc.). How many of those few tens of billions of stars, then, have planetary systems? Abandoning in this one case the "one tenth" rule, i'll stipulate about half, and say ten billion stars. Of these, how many have planets suitable for the rise and sustained prevelance of replicating life forms? One billion . . . How many such life sustaining planets remain in a reasonably stable state for long enough that evolutionary forces to create "higher" life forms? One hundred million . . . Of those planets with higher life forms, how many produce sentient, "mechanic" creatures (mechanic in the sense of being able to "manipulate" their environment--whether or not they have "hands")? Ten million . . . Of those planets with such sentient, mechanic life forms, how many produce stable civilizations which do not decay or self-destruct before acheiving space-faring technology? One million . . .
I don't consider the probability that the cosmos is rife with life forms to be an unreasonable proposition. Nevertheless, i consider that i've been unreasonably generous in the casual computation i just went through. However, even with one million potential space-faring civilizations in this galaxy, we would still be at least several hundred light years from the nearest one, considering a more or less even distribution of said planets. It would only be chance which would put us "next door," or hopelessly far away. This brings us down to my original thesis, which comes in the form of a question: why would they want to come here, in particular? At even a hundred light years, they are well beyond the range at which they could have picked up evidence of microwave radiation from this star system, let alone to have found it, interpreted it and responded by immediately coming to investigate.
So in fact, simply positing that life may literally be everywhere, in no way addresses the questions i raised about the probability that we've been visited.
Quote:2: Your post seems to assume things based on our current understanding of technology, ie the speed at which they would probably travel.
No, it assumes that 299,792,458 meters per second is the cosmic speed limit. You're going to have to do much better than that. I know people don't like speed limits--but unless and until you can
plausibly speculate on how a mass of matter ran reach 300,000 kilometers per second without vaporizing into energy, i intend to insist upon it. Science fiction is an interesting genre--i read lots of it when i was young. It is not a basis upon which to speculate upon what can or has happened in fact on this planet. It is for this reason that i won't even canvas the possibility of inter-galactic travel.
For someone who rejects the fictions of religious scripture, it is ironic to see you indulge something like this.
Quote:It is possible and reasonable that a species far more advanced than us may have technology that would to us seem like magic, ie instantaneous or at least far faster than light travel.
Horsie poop--see the condition required above. Being so advanced technologically as to seem to us to have magical power (Isaac Azimov, by the way) will not permit such a putative species to make silk purses of sows' ears. The limitations to which i referred placed on interstellar travel on a large scale by the marshalling of resources and energy apply to magic wands and warp drives just as much as they do to hydrogen converters.
Quote:3: Your post seems to assume that we would recognize aliens should we see them, or detect their microwaves with our instruments.
My post neither assumes as much, nor even seems to. At no time did i speculate on whether or not we would know if the little green men had been here--a possiblity which i consider ludicrous for other reasons in addition to what i've already mentioned. However, my post makes no such assumptions. As for detecting microwaves, we've got that one licked.
Quote:What if these 'aliens' are truely alien, so far from what we 'expect' that one could pass under our nose without us realizing.
What if we are the first civilization to approach the threshold of space-faring? What if we are the last, and all the others are gone, or have left the building? Such speculation does not at all relate to the objections i raised, which have to do with the likelihood that anyone would come
here in particular.
Quote:Personally I think alien visitation is reasonable, but only given a vastly superior technology.
You are entitled, of course, to think what you like. I do not see you offering any valid objections to my thesis, which concerns itself with the probability that any other species capable of space-faring would have come here in particular.
