What is "Earth-like"?

[pErvinalia]

I've heard "earth like' mentioned. Rainbow is going to be perturbed. A bit like the stars that the earth-like planets are orbiting..

[rainbow]

[rainbow]

NASA says 'we are not alone' as it reveals 10 new Earth-like planets which could sustain life

NASA announced its Kepler telescope had identified 219 new planets on Monday, 10 of which are believed to be able to support life.

http://www.cnbc.com/2017/06/20/nasa-kep ... -life.html

[pErvinalia]

Earth like.

[Forty Two]

We don't have any verifiable evidence of life on other planets, but on the assumption that life arose naturally here on Earth, it can be reasonably concluded that life could arise naturally on other planets given the same or similar circumstances. We don't know how likely those circumstances are, but given that planets somewhat similar to Earth appear to be something of a banality in our galaxy, it appears at least possible that some of those other planets also had life arise naturally.

That being said, it would appear to me to be expected that on some portion of planets on which life arose, that life would be fleeting and very temporary. Others would last longer. Evolution, it seems, does not have a direction, and for most of the 4 billion or so year history of life on Earth, all but the very last tiny fraction of a tiny fraction of a percent of that time involved "intelligent" life and even less involved "technological" life.

So, we can, perhaps, be living in a galaxy where technological life is exceedingly rare, but life more plentiful than that. Maybe it's common to have microbial life, but not quite as common to have it evolve much past that. Maybe it's common to have had animal life, but they tend to get wiped out by asteroid impacts, and only in very rare cases do the pieces fall into place for higher intelligence life, developing tools and transportation, to evolve.

We need to view this not in just a 3 dimensional perspective, but a four dimensional perspective. Humans have been on Earth for what? 100,000 years? 200,000? Let's call it 250,000 years. We've only had writing for like 10,000. We've had space flight for something going on 68 years. 1949. How many creatures could have evolved to do that, and are long gone? How many have not yet evolved? Are we among the first? I.e., does it take this long for any life of our kind to evolve in a universe like ours? Or, are we at the end, with most such life forms evolving much earlier, and already dying out? Are we on the ends of the parabolic statistical curve, or in the middle?

It seems to me that we just don't know enough to say "get over it, we're alone." And, that statement involves an ambiguous definition of being alone. Does alone mean no life at all? Does it mean no animal life? Does it mean no life similar to humans?

We just don't know, and the equation that we all see that estimates the number of civilizations in the universe is just arbitrary - it's a thought experiment. We have no basis for any of the numbers included - we can say "if only 1% of the stars have planets and only 1% of the planets have life....then billions of planets have life..." but, we can't know that 1% is close to the probability or worlds away. Maybe it's .1% or .01% or .0000001%. On what basis do we pick any of those numbers? The only answer is wishful thinking and presuppositions about what's a big and small number.

If we live in a universe where life arises on about 1 in the number of planets in the universe, then that's the actual fact. As much as we wouldn't like it, then that's way it is, and we are likely alone. If we live in a universe where life arises in approximately 1 planet in every solar system, then we live in a universe that is positively teaming with life. And, that's the fact that we'll have to deal with. If it's somewhere in between, it's somewhere in between.

The fact that we view the universe as so big, that it would be an awful waste of space not have life in it, is just, basically, human solipsism. We seem to have this tendency to look at the universe and think that the reason it must be here is for us, or at least life in general. But, if you look at the universe has not being here "for" anything, then we really can't look at it as a waste of space without life. It's the universe. It is what it is. Even if life is in it, it's not here "for" life. The universe is not here "for" anything.

In sum, it's not known if there is any life in the universe besides us, and we have so much more to learn that right now we simply cannot calculate the probability of there being any life in the universe. However, that lack of knowledge now is not a reason to "disbelieve" in the existence of life on other worlds either. Like gods, this life on other planets issue is one about which people seem to have a hard time just saying "I don't know, maybe. Let's go find out."

I don't know, maybe. Let's go find out. Breathe in, breathe out. Doesn't that feel good?

[mistermack]

The way it's looking, I would be amazed if there isn't abundant life around the Milky Way.

There are two possibilities for the explanation of life on Earth. Either it was seeded by deep frozen primitive life from previous planets or moons, or, it started spontaneously here on Earth.
The first would of course mean other instances of life going back a long time.
The second would be one example, one instance of life self-starting. A 100% record.

Either way, the odds are very high for lots of life around.

The odds for intelligent life, or more importantly technological life, have to be an order of magnitude longer.

We humans are complete freaks in the animal world. Our brains are 3 x the size of those of our nearest cousins. And the reasoning part is probably more like 20 x the size. It might be that we are the only techy creature in the galaxy.

Intelligence might be common, but there might be a natural limit beyond which it doesn't normally evolve.
Chimps ancestors seven or eight million years ago were the same as ours. Our brains have evolved spectacularly. Theirs haven't changed in any noticable way.

So how often freaks like us would evolve is the question. I think it would be very very rare, maybe never.