Comments on: How Common Is Life in the Universe

By: Doctorrick

Doctorrick — Mon, 12 Nov 2012 23:08:59 +0000

I echo what a few have already said. Based on extremophiles found here on Earth, I think life is probably relatively common in the universe. Perhaps even “complex” (i.e. multicellular) life. What I am far less certain about, is how common intelligent life is. It doesn’t seem to me that intelligence is that huge an evolutionary advantage, especially in terms of its biological cost. A number of different events have brought human to near extinction, and intelligence really didn’t help much (asteroids, ice age, pandemic). At this point in our intelligence development, we like to think our intelligence would help with survival, and that is probably true. However not sure how true that is for most of our history on the planet.

By: Christopher Newell

Christopher Newell — Mon, 12 Nov 2012 05:17:23 +0000

An often over looked factor in discussions of this kind is distribution of life in the universe and how it might be effected by interstellar migration. It could be that even in a universe where life seldom emerges and where that life seldom develops advanced enough technology to travel to nearby stars, that the total population of the universe would be quite high due to this sort of technological panspermia. Once a civilization passes through the bottleneck it would become tenacious enough to persist almost indefinitely due to the low probability of interstellar disasters and by sheer numbers. In a universe of this kind, we might expect to see a kind of large scale clumpiness where whole galaxies or even galactic clusters are populated by life which originated from a single point, while other areas would be devoid of life. There would be the equivalent of urban areas, rural areas and wilderness. Given enough time, this sort of universe might mature into a more homogeneous one, but with most life stemming from a handful of planets. This alludes to the Fermi paradox, which isn’t really a paradox because due to our limited knowledge, we could be right in the middle of a cosmic “downtown” and not even realize it. Alternatively, if we’re in the desert, it might be very difficult for SETI searches to turn up anything, even with improved methods; because of the great distances of these “cities” and even if the populated areas are quite large.

By: Aardwark

Aardwark — Mon, 05 Nov 2012 08:28:49 +0000

The most important thing, when life in the Universe is concerned, is not to jump to any conclusions based on fragmentary data.

However, to say that we ‘just don’t know’ would be equally unfair and ultimately untrue. There is a lot of data that could help drive the investigation of various hypotheses. And plenty of room for the unexpected, of course.

The ongoing astrobiological revolution is based on integrating the knowledge gained by various disciplines investigating various fields by various methods and applying some creative (but highly critical) thinking to it all. In this sense, it becomes the most exciting and gratifying scientific endeavour of all times.

But if we are to jump to our feet and shout every time there is a new piece of the puzzle brought to the table (such as ‘methane on Mars’, or ‘no methane on Mars’) and be drowned under a vast mountain of senseless media sensationalism, than crucial points will likely begin to fade from the picture. So will the interest of serious people for the, otherwise fascinating, subject.

Specifically, since this article mainly discusses Rare Earth Hypotheses (REH), which include, but are not limited to ‘Rare Jupiter’, ‘Rare Moon’, and ‘Rare Asteroid Belt’, I would like to bring to the attention of this community a recently published book. It is titled “The Astrobiological Landscape” and one chapter is specifically devoted to discussing REH. It is the most clear, concise, comprehensive and well-written treatment of the subject that I personally have had the chance to encounter so far (although I admit there may be some ‘observation selection effect’ at play).

In the same book you will also find highly enlightened review of other astrobiological ‘big questions’ and the underlying philosophical foundations – in brief, I highly recommend the book. I also apologize to all who are already aware of it, or have read it.

http://www.amazon.com/Astrobiological-Landscape-Cambridge-Astrobiology-ebook/dp/B008CDSB30

By: Alex Clark

Alex Clark — Sun, 04 Nov 2012 16:49:16 +0000

“There almost certainly is life elsewhere in the universe”. This is just a guess — we don’t have an N of 1, we have an N of 0. The solar system we know about is not a random one, but one that has life in, so its existence doesn’t tell us anything about the probability of life other than that it is nonzero. If the probability of life is 10^{-100} on a given planet, then there will still be intelligent life on the planet that we live on.

As a result there is no argument that says there is likely to be other life in the universe, since we have absolutely no way of estimating the quantities in the Drake equation, which lends a spurious air of precision to what is basically just an exercise in handwaving.

By: Jared Olsen

Jared Olsen — Sun, 04 Nov 2012 10:48:27 +0000

Even though I SO want to believe there are other civilizations out there, I think it’s unlikely. I’m pretty sure that the universe is teeming with micro-life, but intelligent life? not so sure. Intelligence is just one of the myriad ways an organism evolves to deal with it’s environment, not the teleological end goal that it’s sometimes made out to be. Amongst our 50 million or so organisms only one (us) developed high end smarts.

By: norrisL

norrisL — Sat, 03 Nov 2012 21:50:45 +0000

Historical estimates of the parameters

Considerable disagreement on the values of most of these parameters exists, but the values used by Drake and his colleagues in 1961 were:[8][9]
R* = 1/year (1 stars formed per year, on the average over the life of the galaxy; this was regarded as conservative)
fp = 0.2-0.5 (one fifth to one half of all stars formed will have planets)
ne = 1-5 (stars with planets will have between 1 and 5 planets capable of developing life)
fl = 1 (100% of these planets will develop life)
fi = 1 (100% of which will develop intelligent life)
fc = 0.1-0.2 (10-20% of which will be able to communicate)
L = 1000-100,000,000 years (which will last somewhere between 1000 and 100,000,000 years)
Drake states that given the uncertainties, the original meeting concluded that N ≈ L, and there were probably between 1000 and 100,000,000 civilizations in the galaxy.

The above info comes from that “wonderful source of scientific information”, Wikipedia.

Given that, as of this morning we still have an N of 1, I still believe the above estimates can be nothing much more than pure speculation.

By: norrisL

norrisL — Sat, 03 Nov 2012 21:43:35 +0000

The Drake Equation is an estimate of the probability of there being a technological civilisation that releases detectable signals into space.

The Drake equation states that:

where:
N = the number of civilizations in our galaxy with which communication might be possible;
and
R* = the average rate of star formation per year in our galaxy
fp = the fraction of those stars that have planets
ne = the average number of planets that can potentially support life per star that has planets
fℓ = the fraction of the above that actually go on to develop life at some point
fi = the fraction of the above that actually go on to develop intelligent life
fc = the fraction of civilizations that develop a technology that releases detectable signs of their existence into space
L = the length of time for which such civilizations release detectable signals into space

This is all very well, but the thing is we have no real idea of what any of the actual numbers pertaining to the above equation may be.

As Steven has said, we have an N of 1. While this may change tomorrow, it may also never ever change. That would be quite sad.

By: locutusbrg

locutusbrg — Sat, 03 Nov 2012 04:10:22 +0000

Our relatively large satellite does more than sweep life killing asteroids from the sky. It stabilizes the earths axis which in turn helps keep climate stable. There is also the relative tidal effect due to its large size. This probably contributed to the evolution of life outside of the sea. That is just one small part of the complexities of finding a similar world as a livable planet.
Life and evolution of “advanced life on earth” is also subject to time. Given our N-1 example, we are just a “Planck Length” second of the history of the universe. Given a finite life to our star, and current lack of faster than light travel we”humans” in some form will have a short finite existence on a galactic scale. It took us one third of our stars life to appear and if we don’t figure out how to leave or prolong the life of our solar system we will only be around a tiny fraction of the remaining life of the universe. That is also assuming we don’t kill ourselves some other way. Even if we make maximum solar life of our system it will be unlivable well before the collapse of our star into a dwarf star. My point is that I am sure that there is life somewhere in the universe but finding even simple life is a lottery ticket win within our short lives. Little chance we will ever see evidence of “Advanced” life resembling ours. If we say there are 1.6 trillion Goldilocks’s earths in our “local” part of the universe, it is entirely possible that 2/3 are either in early formation or late life resulting in unlivable conditions. Given factors of time, distance and our short lifespan odds weigh heavily against us. For all we know we are the fruit flies of the universe with ridiculously short lifespans.

By: hoebywan

hoebywan — Fri, 02 Nov 2012 22:32:17 +0000

If I was to bet money on it In would say there have to be many civilisations more advanced technologically than us. Why? Just sheer enormously, stupendous numbers and for me we seem to have an over inflated opinion about how well we have done with what we have. We could have done better and probably should have and with better conditions it is likely we would have too.

By: Karl Withakay

Karl Withakay — Fri, 02 Nov 2012 18:45:59 +0000

How common is life? I suspect that it’s probably extraordinarily rare (that is, you’d have to look at an exceptionally large number of star systems and planets before you found another one with life*), but in a universe with on the order of 10,000 billion billion stars, the number of planets in the universe with life on them is probably quite large.

Consider that if there is only one planet with life for every one hundred billion stars (which would make life extremely rare), that would still mean there would be on the order of 100 billion planets with life in the universe, though probably only around one per galaxy.

Life is likely both abundant and rare at the same time, depending on how you look at it.

* At least life that does not have a common origin with life on Earth. Discovering life on Mars that shared a common origin with Earth’s organisms wouldn’t change my opinion on this matter at all. Finding life on Mars with an origin distinct from that of earth’s life would cause me to reverse my opinion.