# What are the odds that other life exists?

That would mean that there is life on 1,000,000,000,000 planets in the observable universe. We just happen to be one of them.f
Summary:: Like how is it possible that Earth was just perfectly made for life?

It seems impossibly unlikely that Earth would be able to harvest life. I also heard that the moon is exactly 400 times smaller than the sun and 400 times the distance from each other, which makes solar eclipses possible.

It doesn't need to be exact. All that's necessary is for the angular diameter of the moon to be greater than or equal to the angular diameter of the Sun (or star in question). It can be "greater than." It doesn't need to be equal or "exact."

For example, here is a couple of simultaneous eclipses happening on Jupiter (eclipses happen on Jupiter very frequently; they're really nothing unusual). I took this photo last year with my backyard telescope.

Figure 1. Jupiter, Ganymede, and Io. 2020-08-15 04:33.7 UT

How could a coincidence this major even happen? I also heard that the moon is getting farther and farther away from the sun, so eventually solar eclipes won't even be possible, so what are the odds that the only time sentiment beings are on earth, is the time solar eclipes happen. Like just how could that even happen?

The Moon is not gradually getting farther away from the Sun any more than the Earth is getting farther away from the Sun. I think you mean that the Moon is getting farther away from the Earth. This is true, but only by a 3.8 centimeters (1.5 inches) per year.

Whatever the case, eclipses are not unusual, and more to the point, the existence of life on Earth almost certainly has nothing particularly to do with eclipses.

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On a different note, this might be a good time to introduce the Drake Equation into this thread.

The Drake Equation is a contrived equation to calculate the number of civilizations in our galaxy with which communication might be possible. Again, it's a contrived equation, not a derived one. So it's not particularly insightful on its own. But it does help with defining and compartmentalizing the different aspects involved, and should be relevant to this discussion.

$$N = R_* \cdot f_p \cdot n_e \cdot f_l \cdot f_i \cdot f_c \cdot L$$

where:

$N =$ the number of civilizations in the Milky Way galaxy with which communication might be possible.

and,

$R_* =$ the average rate of star formation in our galaxy
$f_p =$ the fraction of those stars that have planets
$n_e =$ the average number of planets that can potentially support life, per star that has planets
$f_l =$ the fraction of planets that could support life that actually develop life at some point
$f_i =$ the fraction of planets with life that actually go on to develop intelligent life (civilizations)
$f_c =$ 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

I won't go into the estimates for each component in this post. But I will say that our estimates of $f_p$ have gotten much larger within the last couple of decades.

valenumr, Hamiltonian, DennisN and 3 others
Of course, intelligent life exists elsewhere in the universe; AND THEY SPEAK ENGLISH! You had to have watched Star-Trek.

nuuskur and DennisN
Of course, intelligent life exists elsewhere in the universe; AND THEY SPEAK ENGLISH! You had to have watched Star-Trek.
Well, they can't be all that intelligent. They keep running up against Kirk, who talks like a moron, and they always lose.

DennisN
It doesn't need to be exact. All that's necessary is for the angular diameter of the moon to be greater than or equal to the angular diameter of the Sun (or star in question). It can be "greater than." It doesn't need to be equal or "exact."

For example, here is a couple of simultaneous eclipses happening on Jupiter (eclipses happen on Jupiter very frequently; they're really nothing unusual). I took this photo last year with my backyard telescope.

View attachment 292093
Figure 1. Jupiter, Ganymede, and Io. 2020-08-15 04:33.7 UT

The Moon is not gradually getting farther away from the Sun any more than the Earth is getting farther away from the Sun. I think you mean that the Moon is getting farther away from the Earth. This is true, but only by a 3.8 centimeters (1.5 inches) per year.

Whatever the case, eclipses are not unusual, and more to the point, the existence of life on Earth almost certainly has nothing particularly to do with eclipses.

--------------------------------------------

On a different note, this might be a good time to introduce the Drake Equation into this thread.
But you have the the Rare Earth version, which has a serious following:
(from the Wiki entry)
The following discussion is adapted from Cramer.[55] The Rare Earth equation is Ward and Brownlee's riposte to the Drake equation. It calculates
, the number of Earth-like planets in the Milky Way having complex life forms, as:

According to Rare Earth, the Cambrian explosion that saw extreme diversification of chordata from simple forms like Pikaia (pictured) was an improbable event

where:

• N* is the number of stars in the Milky Way. This number is not well-estimated, because the Milky Way's mass is not well estimated, with little information about the number of small stars. N* is at least 100 billion, and may be as high as 500 billion, if there are many low visibility stars.
• is the average number of planets in a star's habitable zone. This zone is fairly narrow, being constrained by the requirement that the average planetary temperature be consistent with water remaining liquid throughout the time required for complex life to evolve. Thus,
=1 is a likely upper bound.
We assume N* = 5*10^11. The Rare Earth hypothesis can then be viewed as asserting that the product of the other nine Rare Earth equation factors listed below, which are all fractions, is no greater than 10−10 and could plausibly be as small as 10−12. In the latter case, N could be as small as 0 or 1. Ward and Brownlee do not actually calculate the value of N, because the numerical values of quite a few of the factors below can only be conjectured. They cannot be estimated simply because we have but one data point: the Earth, a rocky planet orbiting a G2 star in a quiet suburb of a large barred spiral galaxy, and the home of the only intelligent species we know; namely, ourselves.

• is the fraction of stars in the galactic habitable zone (Ward, Brownlee, and Gonzalez estimate this factor as 0.1[6]).
• is the fraction of stars in the Milky Way with planets.
• is the fraction of planets that are rocky ("metallic") rather than gaseous.
• is the fraction of habitable planets where microbial life arises. Ward and Brownlee believe this fraction is unlikely to be small.
• is the fraction of planets where complex life evolves. For 80% of the time since microbial life first appeared on the Earth, there was only bacterial life. Hence Ward and Brownlee argue that this fraction may be small.
• is the fraction of the total lifespan of a planet during which complex life is present. Complex life cannot endure indefinitely, because the energy put out by the sort of star that allows complex life to emerge gradually rises, and the central star eventually becomes a red giant, engulfing all planets in the planetary habitable zone. Also, given enough time, a catastrophic extinction of all complex life becomes ever more likely.
• is the fraction of habitable planets with a large moon. If the giant impact theory of the Moon's origin is correct, this fraction is small.
• is the fraction of planetary systems with large Jovian planets. This fraction could be large.
• is the fraction of planets with a sufficiently low number of extinction events. Ward and Brownlee argue that the low number of such events the Earth has experienced since the Cambrian explosion may be unusual, in which case this fraction would be small.

It doesn't need to be exact. All that's necessary is for the angular diameter of the moon to be greater than or equal to the angular diameter of the Sun (or star in question). It can be "greater than." It doesn't need to be equal or "exact."

For example, here is a couple of simultaneous eclipses happening on Jupiter (eclipses happen on Jupiter very frequently; they're really nothing unusual). I took this photo last year with my backyard telescope.

View attachment 292093
Figure 1. Jupiter, Ganymede, and Io. 2020-08-15 04:33.7 UT

The Moon is not gradually getting farther away from the Sun any more than the Earth is getting farther away from the Sun. I think you mean that the Moon is getting farther away from the Earth. This is true, but only by a 3.8 centimeters (1.5 inches) per year.

Whatever the case, eclipses are not unusual, and more to the point, the existence of life on Earth almost certainly has nothing particularly to do with eclipses.

--------------------------------------------

On a different note, this might be a good time to introduce the Drake Equation into this thread.

The Drake Equation is a contrived equation to calculate the number of civilizations in our galaxy with which communication might be possible. Again, it's a contrived equation, not a derived one. So it's not particularly insightful on its own. But it does help with defining and compartmentalizing the different aspects involved, and should be relevant to this discussion.

$$N = R_* \cdot f_p \cdot n_e \cdot f_l \cdot f_i \cdot f_c \cdot L$$

where:

$N =$ the number of civilizations in the Milky Way galaxy with which communication might be possible.

and,

$R_* =$ the average rate of star formation in our galaxy
$f_p =$ the fraction of those stars that have planets
$n_e =$ the average number of planets that can potentially support life, per star that has planets
$f_l =$ the fraction of planets that could support life that actually develop life at some point
$f_i =$ the fraction of planets with life that actually go on to develop intelligent life (civilizations)
$f_c =$ 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

I won't go into the estimates for each component in this post. But I will say that our estimates of $f_p$ have gotten much larger within the last couple of decades.
Honestly, I'm not a huge fan of the drake equation. It is more like coffee table philosophy, and there is always the quarterly pop-sci article talking about it. The concept, and general question is interesting to me more than the idea of plugging in numbers to come up with an answer.

symbolipoint, BillTre and PeroK
@valenumr makes a strong point. Formulate an equation to use for predicting life occurring on other than our earth. Then the question naturally comes, How Do You Test The Theory?

How Do You Test The Theory?
You have to wait for the answer to come through.
There is a much more pertinent question to answer than Drake addresses. What is the probability that Mankind will avoid severely damaging itself in the next couple of decades. The variables are fairly easy to identify and many of them have relatively short error bars.

Dr. Becky's insight on the subject (video released just today, 2021-11-11):

DennisN
If we do find evidence of life previously existing on Mars or exotic bacteria in the oceans of Europa, I think a better question would be: can we extrapolate that life is abundant in the universe?
If life on Mars were found to be based on DNA, it just means we are martian in origin

We'll have no choice but to conclude that it must be.
At the same time, I think most people would be underwhelmed if the universe was teeming with bacterial life. What people really want to know is if intelligent life exists elsewhere in the universe.

russ_watters and symbolipoint
At the same time, I think most people would be underwhelmed if the universe was teeming with bacterial life. What people really want to know is if intelligent life exists elsewhere in the universe.
It would be surprising to find it anywhere.

It would be surprising to find it anywhere.
In the unlikely event of it being found (apart from in the solar system) and particularly if we got a 'message' from somewhere, the big problem would be to stop worldwide panic and misapprehension that 'they' could arrive here at any minute (despite the message coming from hundreds of thousands of light years away).

Still, the religions of the world would surely do well out of the news.

symbolipoint
In the unlikely event of it being found (apart from in the solar system) and particularly if we got a 'message' from somewhere, the big problem would be to stop worldwide panic and misapprehension that 'they' could arrive here at any minute (despite the message coming from hundreds of thousands of light years away).

Still, the religions of the world would surely do well out of the news.
Well, I was being snarky, as in, there is no intelligent life on earth.

Well, I was being snarky,
Heaven forbid - on PF of all places.

Heaven forbid - on PF of all places.
It would be crazy though, wouldn't it? I can't even imagine how the global world view would change.

I can't even imagine how the global world view would change.
It's amazing that it would get everyone off their backsides much quicker than the obvious potential disaster we already know about. Haha - Intelligent!

valenumr
It's amazing that it would get everyone off their backsides much quicker than the obvious potential disaster we already know about. Haha - Intelligent!
Would it though? We've been facing multiple existential crises for a while. I don't see too many people leaping from the couch!

sophiecentaur
Well, I was being snarky, as in, there is no intelligent life on earth.
CORRECTION: there is only slightly intelligent life on earth.

Given the millions of species that have ever existed on earth, there is only one that has been remotely capable of what humans can do. So add that as another 1 in a million factor. But I guess when we're on the order of 10^20 planets, maybe 1 in a million factored in really is meaningless.

If life on Mars were found to be based on DNA, it just means we are martian in origin
That's not necessarily the strongest assumption. DNA is very well suited for storing genetic information and might be a molecule selected in independent origin lineages.
I think it would be a stronger conclusion if the genetic code were drastically different from that on Earth.
Or if some of the important pillars of our metabolism, the ATP synthetase and the electron transport chain proteins that are both conserved among all Earth life. Both of these are very large complex proteins that depend upon a cell membrane for their function.

An alternative is that life on Earth might have gotten to Mars (however Mars has less of a gravity well to escape).

I don't think that life from another planet, when closely examined, would be all that difficult to identify.
This is because any life being shot off another planet (by an impact?), and then traveling through space for a (possibly) extended period of time, and then entering into our atmosphere to land on Earth, would probably require a pretty sophisticated outer coating (like a cell wall). They would also have to able to suspend life functions for the period of their trip. A strong cell coating that would not be found in the simple life forms that could possibly have lead to something LUCA (ancestor of all earthly life). This seems to be independantly derived traits of the bacterial and archaeal lineages.
If a life form came to Earth with these traits already established, those traits (independently derived by the alien life form before getting to Earth, and thus likely different in some way) would likely be revealing of them, as not be of our earthly lineage of life. If they did not have those traits, I doubt they could successfully make the journey.

there is only one that has been remotely capable of what humans can do.
The difference between humans and a number of intelligent species is much less than you claim. In another million years, a different species could be where we are now.
Although the assumption that "what humans can do" means 'what good they can do'. Human activity has not done a lot for their long term survival so it may not be the best benchmark to be judging success against.

The difference between humans and a number of intelligent species is much less than you claim. In another million years, a different species could be where we are now.
Although the assumption that "what humans can do" means 'what good they can do'. Human activity has not done a lot for their long term survival so it may not be the best benchmark to be judging success against.
I had a question similar to this. Does free will exist, and if not, does this mean something is controlling us?

I had a question similar to this. Does free will exist, and if not, does this mean something is controlling us?
No, no, the topic or thread should not be pushed into that direction.

BillTre and phinds
No, no, the topic or thread should not be pushed into that direction.
Sorry I thought that's where it was heading, it's been bothering me though. If our choices are predetermined isn't that evidence of a creator guiding us into doing something

PeroK