BDanielMayfield wrote:So, since we can take this as evidence that the universe has been cranking out new planetary systems for well over 10 billion years, Fermi's paradox is stronger now than when he first asked:(By "everybody" he meant alien civilizations.)Where is everybody?
That's a reasonable question Mike. But there were many very massive stars popping off as supernovae in those early times when these planets formed, so plenty of metals (elements heavier than helium) where being injected into interstellar space back then. Probably too many SN in fact for wide spread habitability that far back, I would think.FloridaMike wrote:I am wondering if a planetary system this old has the necessary chemistry to support life. That is, were there enough supernovas nearby to provide the necessary elements before this system formed?
An add up to that.BDanielMayfield wrote:That's a reasonable question Mike. But there were many very massive stars popping off as supernovae in those early times when these planets formed, so plenty of metals (elements heavier than helium) where being injected into interstellar space back then. Probably too many SN in fact for wide spread habitability that far back, I would think.FloridaMike wrote:I am wondering if a planetary system this old has the necessary chemistry to support life. That is, were there enough supernovas nearby to provide the necessary elements before this system formed?
I'm skeptical. If Earth is any indicator, life is very robust. Major extinction events still leave plenty of life, possibly stimulate mutations, and certainly open up lots of new niches. Sea life in particular should be quite resilient to GRBs.BDanielMayfield wrote:I have to admit that what Doum has just shared about the GRB hazard in the early universe sort of cancels out the point I was attempting to make. Fermi's Paradox asks us to find reasons why we appear to be alone in the universe. Even though planets have been around for a very long time, SAFE planets evidently are a more recent development.
I'm still of the completely subjective opinion that advanced life is rare in the universe. The reason for my belief is that there are so many factors that have gone into making advanced life possible on the Earth. There is the well-behaved (and more-massive-than average) star, there are the nice relatively circular orbits of the major planets, there is the fact that the Sun has no companion, the fact that it is a slow rotator and has a very adequate but not violently flaring magnetic field, there is the fact that the Earth has its own robust magnetic field (in contrast to similarly-sized and almost similarly-massive Venus) to protect its atmosphere, there is the fact that the axis of the Earth is tilted by about 25 degrees, so that our planet has seasons and escapes the fate of getting relentlessly hot in certain places and incredibly cold in others, there is the fact that the Earth has plate tectonics that continually recycle material on its surface, there is the fact that the Earth has the perfect amount of liquid surface water (which means that the Earth has both oceans and land masses), there is the fact that the Earth has a water precipitation cycle, there is the fact that the Earth has maintained a relatively constant temperature and the presence of liquid surface water (except during its Snowball Earth phase) for most of its four and a half billion year existence.Chris Peterson wrote:I'm skeptical. If Earth is any indicator, life is very robust. Major extinction events still leave plenty of life, possibly stimulate mutations, and certainly open up lots of new niches. Sea life in particular should be quite resilient to GRBs.BDanielMayfield wrote:I have to admit that what Doum has just shared about the GRB hazard in the early universe sort of cancels out the point I was attempting to make. Fermi's Paradox asks us to find reasons why we appear to be alone in the universe. Even though planets have been around for a very long time, SAFE planets evidently are a more recent development.
I suspect that the resolution to the Fermi Paradox has a lot more to do with the incidence of technological species than of life itself.
All true, but it's a big universe out there, and even a big galaxy. With multiple planets likely around most of the 200 billion or so stars in the Milky Way, I find it absolutely compelling that life, intelligent tool-wielding life, has certainly occurred in many places. The trouble is, it's a big galaxy! So those intelligent beings may still be much too far away to communicate with, let alone visit. Even if I'm right, and there's lots of other species out there, it's going to remain a lonely galaxy.Ann wrote:... So many things could have gone wrong here. I still think it is very unusual that all these positive factors are present at the same time in any planetary system to create such benign conditions for life and, not least, for fragile advanced life. But I agree with Chris that simple life forms are likely to form much, much more easily, and that they may be present on (or more likely below the surfaces of) many planets.
I suspect simple life is common (like that which was on Earth for more than a billion years). Complex life is much less common, but still numerous for the reason you suggest: it's a big galaxy. If even a fraction of a percent of systems have complex life, it still amounts to a large number in absolute terms. I think complex life may frequently produce highly intelligent life, but where that life is tool-using, I think it is rare in the galaxy because it may be inherently unstable. If a technological civilization only has a lifetime measured in a few thousand years, we're not going to find very many at any one time.rstevenson wrote:All true, but it's a big universe out there, and even a big galaxy. With multiple planets likely around most of the 200 billion or so stars in the Milky Way, I find it absolutely compelling that life, intelligent tool-wielding life, has certainly occurred in many places. The trouble is, it's a big galaxy! So those intelligent beings may still be much too far away to communicate with, let alone visit. Even if I'm right, and there's lots of other species out there, it's going to remain a lonely galaxy.
To Ann's nice long list of things that have made our Earth so nice for us I would add the presence of our large Moon that stabilizes Earth's axial tilt and helps to keep our oceans in motion, and the fact that we have a gas giant in the right orbit to reduce the threat of major impacts.Ann wrote:I'm still of the completely subjective opinion that advanced life is rare in the universe. The reason for my belief is that there are so many factors that have gone into making advanced life possible on the Earth. There is the well-behaved (and more-massive-than average) star, there are the nice relatively circular orbits of the major planets, there is the fact that the Sun has no companion, the fact that it is a slow rotator and has a very adequate but not violently flaring magnetic field, there is the fact that the Earth has its own robust magnetic field (in contrast to similarly-sized and almost similarly-massive Venus) to protect its atmosphere, there is the fact that the axis of the Earth is tilted by about 25 degrees, so that our planet has seasons and escapes the fate of getting relentlessly hot in certain places and incredibly cold in others, there is the fact that the Earth has plate tectonics that continually recycle material on its surface, there is the fact that the Earth has the perfect amount of liquid surface water (which means that the Earth has both oceans and land masses), there is the fact that the Earth has a water precipitation cycle, there is the fact that the Earth has maintained a relatively constant temperature and the presence of liquid surface water (except during its Snowball Earth phase) for most of its four and a half billion year existence.
Ah, the Cambrian Explosion of multicellular, complex life. There is an explanation that doesn't involve luck or random chance for these things, and for ...And of course, there is the unexplained and perhaps just lucky or random emergence of complex life forms some 650 million years ago or so.
But stating the explanaton is not permitted here.... the perhaps equally lucky or random much later emergence of a species that could both think, speak, cooperate and manipulate its surroundings with its own body.
No Ann, it wasn't, for either myself or Enrico Fermi.Then again, I don't think it was these little critters that BDanielMayfield was talking about, or that it was bacteria-like life forms that Fermi referred to when he formulated his paradox.
Ann
Of course it is, the planet had just emerged from an extreme extinction event. See Snowball earthBDanielMayfield wrote: ....Ah, the Cambrian Explosion of multicellular, complex life. There is an explanation that doesn't involve luck or random chance for these things, and for ...
...But stating the explanaton is not permitted here...
Loved that youtube clip John. Looked like Earth isn't the only planet suffering from "Glow Ball" warming.JohnD wrote:BBC TV Horizon programme last night was about the origins of planets, and how those gas/ice giants in our Solar System cannot have started where they are now.
http://www.bbc.co.uk/iplayer/episode/b0 ... lar-system for those of you who can watch it on iPlayer.
The programme used Kepler's Orrery, a video display of all (many?) of the extrasolar planets discovered by Kepler, all on screen at once, animated in scale to show their orbits.
It's on YouTube: https://www.youtube.com/watch?v=gnZVvYm6KKM
If you haven't seen it before, the Solar System is top left, showing only the Inner Planets.
And the point, of the Orrery and the Horizon, is that there are so many Hot Jupiters!
This would be a great APOD!
John
I don't understand your comment.Ron-Astro Pharmacist wrote: Loved that youtube clip John. Looked like Earth isn't the only planet suffering from "Glow Ball" warming.
Understand your sentiment. I was attempting to make the statement that Earth is going the way of the Hot Jupiters unless we change our ways with respect to our atmosphere. Humor and seriousness often mix like oil and water and you are correct to point that out.JohnD wrote:I don't understand your comment.Ron-Astro Pharmacist wrote: Loved that youtube clip John. Looked like Earth isn't the only planet suffering from "Glow Ball" warming.
New theories suggest that in our very distant past, Jupiter and the other giant planets formed close to the Sun, and then moved outwards to their present orbits.
The Kepler data show systems where that didn't happen.
What has that to do with "Glow Balls"? Which mean nothing in this context or any other, certainly not astronomical.
Not helpful, Ron.
JOhn
I mean – I am getting older. Truth is - most everyone else here knows recess was over long ago. 
Lucky for me there are some new jungle gyms just being built. 