theres a fair size doubt both of these statements
me I dont know 50:50 each way
if there are space faring aliens we're already discovered due to the fermi paradox, I suppose we could be in quarantine (which is a definite possibility)
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me I dont know 50:50 each way
if there are space faring aliens we're already discovered due to the fermi paradox, I suppose we could be in quarantine (which is a definite possibility)
Really?
As far as I'm aware we have two <direct observational> constraints on the probability of life existing on any given exoplanet of interest:
- it's not zero
- it's not one
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Agreed. We don't know the probability of life forming. Arguing that there's gotta be life out there is like seeing this equation and asserting that y gotta be pretty large, without knowing x.
10^100 * x = y
Well, my reasoning is thus:
1. What we know of life here on Earth seems to indicate that it's probably very, very likely to appear once the conditions are right.
2. Our star is not a terribly exceptional one.
3. Planets are very common, and thus we expect reasonably Earth-like planets to not be that rare either.
4. Earth-like planets may even appear around binary star systems, significantly expanding the range.
Now, there may be additional issues, such as tectonics, that prevent life from being common, but most signs point towards it. Granted, the evidence really isn't in yet, but there are many tantalizing hints that life is quite common out there.
However, let me state that one thing we currently know nothing about is just how commonplace technological life is. I think we can expect bacterial life to be very common, but multicellular or technological might be similarly common, or exceedingly rare. We just don't know yet.
Well, that's just not the case, though. We aren't the result of any extra-terrestrial intervention.
Yes, because there is nothing about our biology that is in any way surprising. Evolution and related fields don't see anything that would suggest an external "guiding hand".Wow you seem so sure of yourself.
But I'll bet you could come up with a reasonable estimate of the probability of Earth like conditions existing out there.
And Life formed pretty early on Earth suggesting that given the right conditions it will form relatively easily elsewhere as well.
Taking those two pieces of information together it seems pretty likely there will be other life out there somewhere. Yes there are still elements of the equation we don't know for certain but which evidence suggests would be high enough to produce life elsewhere.
Considering the age of the universe, if high technological life was common, I'd say we'd have to have been visited by it fairly often by now. However ...
1. I thought the contrary is true. There's a lot of unique conditions going on here in the "vicinity" of our planet that allow life, and only just.
2. Yes, again, it sort of is.
3 (+4). Define rare.
You have to add, no, actually multiply all those odds too. It has to be a planet that allows life to form, it has to be a planet that allows life to develop, it has to be a planet that allows and stimulates life to form intelligently, it has to be a planet that is around long enough for this to happen, it has to be a planet that isn't bombarded with meteor strikes too often or too little to allow or force life to evolve further whenever some form of stability is reached (consider the dinosaurs, fairly intelligent but not likely to board a space-ship any time soon). Then once something develops that actually wants to leave the planet and search around for other planets for any other reason than needing it to survive (in which case it may well just kill us on sight, or by accident), it still needs to be close enough and develop space travel at a high speed. Even if light-speeds were physically attainable by intelligent life-forms it takes ages to get anywhere in this universe at all, and then find our tiny little dot in that gigantic vastness of space.
Even just calculating the amount of space travel in this universe needed even at light-speeds to find anything like our planet using any kind of clever tracking solution all by itself shows that the chance of us being discovered by alien life-forms is almost depressingly small. Never mind multiplying this with all the other odds stacked up against alien life even reaching the point where it starts looking.
The chance that we start looking ourselves and then split up in different directions and rediscover old branches at a later time that have evolved into different directions enough to look alien is already a lot more likely imho, because they'd start from the same location. Compare that with how the Earth was populated with human beings.
Depends upon what you mean by "common", and there are a large number of other unknowns when you had technology to the equation. For example, it may be that it's just so incredibly difficult to travel between the stars that there could be intelligent organisms orbiting Alpha Centauri, and they'd never be able to get here. Or it may be that technological civilizations tend to kill themselves off before they reach the level of technology where they can travel across the stars. Or it may be that life is sufficiently rare that there is, on average, only one intelligent species in any given galaxy, at which point there would still be around a hundred billion intelligent species within the visible universe.
I guess my point is that we don't yet know much about how common or uncommon intelligent life is. I think we know more about how common life in general is, and we don't know much about that.
The best limits we have on extra-terrestrial technology, at the moment, come from SETI, where we've basically ruled out extra-terrestrial technology for a small number of stars near Earth.
I guess my point is that we don't yet know much about how common or uncommon intelligent life is. I think we know more about how common life in general is, and we don't know much about that.
The best limits we have on extra-terrestrial technology, at the moment, come from SETI, where we've basically ruled out extra-terrestrial technology for a small number of stars near Earth.
To my mind the fun starts when we start detecting rocky planets in the habitable zone. This could come within the next year or three (Kepler may find one though just as likely not), a good statistical sample is still a decade or more away as far as I know. Detecting biomarkers in their atmospheres, maybe another decade who knows.
Until then it's all guesswork and, in my opinion, no small amount of wishful thinking.
Until then it's all guesswork and, in my opinion, no small amount of wishful thinking.
We already have. Only problem is it's around a low-mass star, and they tend to be very hot when they're young, which likely means that any planets that are now in the habitable zone would likely have had all of their light elements evaporated away during formation.
http://www.dailymail.co.uk/sciencetech/article-450467/Found-20-light-years-away-New-Earth.html
However, what I find particularly exciting about this is it's only 20 light years away. That's obscenely close in galactic terms. So when we get the instruments up that can detect planets around more Sun-like stars, well, I'm expecting we'll find tremendous numbers of them.
Msini?
The mass estimates are from radial velocity measurements of the reflex motion of the host star, but the inclination of the planet orbit wrt the line-of-sight is unknown. They represent lower limits on the mass of the planet(s). So they're quoted as M * sin(inclination). The real mass could well be twice that quoted in that article, and a 10 Earth mass planet gets into ice-giant territory.
That's why transiting systems are worth the hassle, 'cos you get tight constraints on the inclination, hence mass, density and all the other goodies
That's why transiting systems are worth the hassle, 'cos you get tight constraints on the inclination, hence mass, density and all the other goodies
Like what?
Well, it seems so, although we haven't actually observed too many yet.
That's anecdotal evidence at best. You're making a conclusion from a single sample of data.
