How likely are we to find extraterrestrial life?

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How likely are we to find extraterrestrial life?

Post #1

Post by otseng »

Many NASA scientists think we're on the verge of finding alien life.

Ellen Stofan, NASA's former chief scientist, said in 2015 that she believes we'll get "strong indications of life beyond Earth in the next decade and definitive evidence in the next 10 to 20 years."

Many astrophysicists and astronomers are convinced that it's not a matter of if we'll find life — it's when.
https://www.businessinsider.com/nasa-pl ... de-2019-11

Questions for debate:
- How likely are we to find extraterrestrial life?
- What empirical evidence is there that any extraterrestrial life exists?
- What are the implications if extraterrestrial life exists or do not exist?

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Re: How likely are we to find extraterrestrial life?

Post #2

Post by DrNoGods »

[Replying to post 1 by otseng]
- How likely are we to find extraterrestrial life?


I think the primary support for this (in favor of finding life) is the sheer number of planets that we now know are out there. Some 4,500 exoplanets have now been found and the implication from these relatively recent findings (first exoplanet found was in 1992) is that there must be many billions of planets out there. This, combined with the fact that we do have one planet that supports life, suggests a high likelihood that life exists elsewhere in the universe. Statistically, the probability is very high.
- What empirical evidence is there that any extraterrestrial life exists?


To my knowledge there is none at the moment. But we are so severely limited in what we can see and study. Although we've identified exoplanets and can get limited information on the possible composition from their mass and orbital periods, we don't yet have the capability to really study the spectroscopy of these exoplanets and their atmospheres. The Cheops mission that just launched this week will help in that effort:

https://www.space.com/europe-launches-c ... llite.html

We've only directly visited the few planets in our tiny little solar system, which is a completely insignificant number just within our own galaxy. But I don't know of any empirical evidence yet discovered that could be categorized as actual evidence of extraterrestrial life. The primary argument for its possibility still seems to be a statistical one (ie. the likely existence of billions of planets, and the fact that there is one of them that is known to support life).
- What are the implications if extraterrestrial life exists or do not exist?


I would think this is mainly a religious issue as if life is found on another planet it would suggest that humans are not special creatures, and there are some religions that may not like that outcome. But it would be a super interesting science issue if life were found elsewhere as it may be completely different from the DNA-based life forms on this planet that all seem to work within that same basic framework. We have no idea how many different mechanisms there might be that could produce something that fits our definition of "life", and I for one would love to be around if and when extraterrestrial life is confirmed. Given the tiny speck of the universe that we occupy, and the extremely limited portion of even our own galaxy that we've been able to study, it could be many thousands of years or more before enough of the universe could be studied to bring the statistical probability of extraterrestrial life existing down to a small number.
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Re: How likely are we to find extraterrestrial life?

Post #3

Post by DrNoGods »

[Replying to post 2 by DrNoGods]
... it could be many thousands of years or more before enough of the universe could be studied to bring the statistical probability of extraterrestrial life existing down to a small number.
P.S. Assuming, of course, that it had not already been discovered during this time.
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Re: How likely are we to find extraterrestrial life?

Post #4

Post by otseng »

DrNoGods wrote:
- What empirical evidence is there that any extraterrestrial life exists?


To my knowledge there is none at the moment.
I agree there is no current empirical evidence for any extraterrestrial life (excluding UFO sightings and alien abductions). In particular, SETI has not come up with anything yet.

Given there is no empirical evidence, I found it striking in the article the certainty scientists have of the existence of alien life. "Many astrophysicists and astronomers are convinced that it's not a matter of if we'll find life — it's when."

So, a corollary question. If scientists can be convinced something exists when there is no empirical evidence for it, why would it be unreasonable for Christians to believe in something if there is (purportedly) no empirical evidence for it?

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Re: How likely are we to find extraterrestrial life?

Post #5

Post by DrNoGods »

[Replying to post 4 by otseng]
So, a corollary question. If scientists can be convinced something exists when there is no empirical evidence for it, why would it be unreasonable for Christians to believe in something if there is (purportedly) no empirical evidence for it?

I would personally not be as certain as the scientists in the article, but can accept the probability argument simply because we do have one planet with life, and we know there are likely many billions of additional planets out there. So from a pure statistical probability consideration it seems reasonable to expect that there may be life forms elsewhere in the universe if we could only figure out how to investigate the problem more efficiently.

But that is a real problem now because we have zero chance with current technology to actually get a space craft to a planet outside of our own solar system within a reasonable time. Even the closest star system to our solar system is 4.2 light years away (about 25 trillion miles), and with the fastest craft we have ever built it would take tens of thousands of years to get there. (about 70,000 years for a 40,000 MPH craft like the recent New Horizons probe to Pluto). So in the next 10-20 years there is certainly no way we can directly investigate any planet outside of your solar system with an actual probe to sample the atmosphere or surface. This leaves only remote sensing of the atmosphere as an investigative tool, and that can only suggest life from the resulting chemical composition. How convincing that would be is debatable, but maybe changes in the composition over time could be observed and lend further support for a hypothesis at least. We've only just recently been able to identify exoplanets positively, with very crude spectroscopy for some of them. We have a long way to go to be able to actually investigate the atmospheric chemistry on these exoplanets to see if there is any hint of biological activity, and as we have no idea of all the different forms life could take, conclusively proving that life exists on an exoplanet is a very tall order.

This leaves the only chance of directly finding extraterrestrial life within the next 10-20 years to a planet or moon in our own solar system where we can visit with a physical probe. Such an experiment on any exoplanet doesn't seem possible for a very long time, if ever (and certainly not within the next 1-2 decades). So the question is what is the probability that life exists on a planet or moon in our solar system, and there are more upcoming missions specifically designed to better investigate this:

https://www.space.com/15716-alien-life- ... ystem.html

But to address your question, I would assume that the probability argument for the existence of extraterrestrial life somewhere in the universe is still the best one given that we know life can exist on one planet, and we know there are likely many billions of planets out there. For the existence of a supreme being such as a god, we don't yet have even one example of such a being shown to exist through empirical evidence, and humans have invented literally thousands of gods and god concepts over the millennia. So it isn't quite the same analogy because we do at least have one planet with life to point to to confirm that it can happen at least once. If just one of the thousands of gods humans have invented would have made itself known in some way that could be considered empirical evidence for its existence, then the door is wide open to asking if any of the other gods exist, and how to confirm their existence. I would personally not be so sure as the scientists in the article that life will be found outside of Earth on a planet or moon within our solar system (the only prospects in the next 1-2 decades), but if the question is expanded to ask whether there is likely to be life elsewhere in the universe (existing now, or in the past) that seems much more probable even if our ability to directly investigate exoplanets might be centuries away, if ever.

Finally, the "radio bubble" around Earth (the distance travelled by human-generated electromagnetic signals) is only about 130 light years, while the distance to the center of our galaxy is about 26,000 light years. So if there are intelligent life forms elsewhere in the universe they would have to exist within this tiny 130 light year in radius bubble around Earth to "hear" us. There was another extensive thread here several months ago with a lot of discussion on SETI and the ability of systems like that (either on Earth, or elsewhere) to detect signals or transmit them over the distances needed to be useful for searching for intelligent life. Divergence has a lot to do with that issue, but I think most scientists expect that if life is found outside of Earth it would more likely be more like bacteria and archaea rather than more advanced, multicellular forms, and as such could never participate in any attempts to communicate via electromagnetic signals (at least intentionally). SETI can only hope to detect "patterned" signals originating from an intelligent extraterrestrial source (ie. they are looking specifically for intelligent life ... not just life in general ... as indicated by the "I" in their acronym).
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Re: How likely are we to find extraterrestrial life?

Post #6

Post by Divine Insight »

otseng wrote: - How likely are we to find extraterrestrial life?
I personally think there are good reasons to believe that we will find extraterrestrial life eventually. Although it may not be advanced enough to be technology. But keep in mind that humans existed for quite a very long time on earth before we became technological. In fact, we've only been seriously technology for a few hundred years. Prior to that time our "technologies" would not be noticeable from beyond our planet. The aliens would need actually come here and look up-close and in-person to notice that we were here. So potentially other intelligent civilizations could exist very nearby us and we simply can't see them because we are looking for signs of technology like radio communications, etc.

otseng wrote: - What empirical evidence is there that any extraterrestrial life exists?
For me the empirical evidence that extraterrestrial life most likely exists resides in the fact that living biological life on earth is made of common elements. There's nothing special about the earth that wouldn't be true for billions of other planets. Humans aren't made of anything special.

So the fact that the universe contains the same physics and elements as far as we can see is evidence that we should expect to see living creatures similar to what we see on earth throughout the universe.
otseng wrote: - What are the implications if extraterrestrial life exists or do not exist?
Well, to begin with, we can't really even talk about whether life exists in other galaxies. They are simply too far removed in both distance and time. So it would be next to impossible to rule them out as potentially having technological life. For example Andromeda, one of the closest galaxies to us, is 2.5 million light-years away. This means that it could be teaming with technological life today, but the signals from those civilizations wouldn't reach us for yet another 2.5 million years. So we can't tell by looking at other galaxies whether there is life there or not. At best all we can say is that there doesn't appear to have been a lot of activity 2.5 million years ago.

In short, we could never determine that extraterrestrial life does not exist elsewhere in the universe. All we can ever say is that we can't see any evidence for technological civilizations that it had existed in the distant past. It's also extremely difficult to measure technological signals from far away galaxies. And signals created by extra terrestrials are going to be extremely weak compared to the natural noise created by natural objects.

So we will never be able to determine that we are alone in the universe. It will forever be a one-way question. The only way we can ever get an answer is if the answer is yes and we actually find signs of other life.

What would it mean either way?

For me it wouldn't mean anything other than telling us something about the statics of how probably it is for life to spontaneously arise.

It certainly wouldn't cause me to jump to any conclusions about an intentional creator. After all, if there exists an intentional creator why not create life throughout the entire universe? The idea that a purposeful creator would have only created life on earth doesn't make any sense to me. Why bother creating such a huge universe if that was the original intent. As Carl Sagan once said, (I'm paraphrasing here) "The cosmic stage is far too large for a drama focused solely on life on Earth"
otseng wrote: If scientists can be convinced something exists when there is no empirical evidence for it, why would it be unreasonable for Christians to believe in something if there is (purportedly) no empirical evidence for it?
For me personally this idea is not even close to representing the actual situation.

Scientists have good reasons to suspect that life should emerge throughout the universe because there's nothing special about biology that should restrict it solely to Earth. So in a very real sense they do have evidence for the potential for life elsewhere. The universe is made of the same elements in the same abundance as far as our telescopes can see. And the laws of physics are also necessarily the same otherwise distance stars and galaxies wouldn't behave they way they do.

So scientists actually do have evidence to believe that life should be somewhat common in the universe. Precisely how common is yet to be understood.

However, Christian theology is not based on anything reasonable. It's very God is proclaimed to be a jealous God who becomes angry and wrathful with things don't go his way. Even if we ignore the myriad of problems with the mythology that the Christian Bible is based upon we still end up with a story about a God who has character flaws that even we as humans would like to improve upon.

So I don't see the comparison.

I think scientists have far more evidence that it's reasonable to expect to find other life forms in the universe, than Christian theologians have for justifying Hebrew mythology. So I see no comparison here at all.
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Re: How likely are we to find extraterrestrial life?

Post #7

Post by otseng »

DrNoGods wrote:This, combined with the fact that we do have one planet that supports life, suggests a high likelihood that life exists elsewhere in the universe. Statistically, the probability is very high.
Just because we are on a planet with life does not necessarily lead to a high probability life exists elsewhere. As we understand more about our planet and it's uniqueness, the odds of an exoplanet being able just to support life progresses lower.
The Rare Earth hypothesis argues that the evolution of biological complexity requires a host of fortuitous circumstances, such as a galactic habitable zone, a central star and planetary system having the requisite character, the circumstellar habitable zone, a right-sized terrestrial planet, the advantage of a gas giant guardian like Jupiter and a large natural satellite, conditions needed to ensure the planet has a magnetosphere and plate tectonics, the chemistry of the lithosphere, atmosphere, and oceans, the role of "evolutionary pumps" such as massive glaciation and rare bolide impacts ...
https://en.wikipedia.org/wiki/Rare_Earth_hypothesis

And the above conditions are just to have the environment that is necessary for life to begin. Once you factor in life actually trying to evolve, the odds become much smaller of any other life existing.

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Post #8

Post by Smythe »

From our sample size of one:

- Life began here on earth almost as soon as it possibly could have, given geological conditions (i.e. liquid water). Earth is 4.5 billion years old. Life began when the earth was somewhere around 0.7-1.0 billion years old.

Possible conclusion: Primitive life could be quite abundant.

- Life remained simple (bacteria-like) for another 1.5 billion years until complex cells (eukaryotes, with nuclei) evolved; and it took another billion years for multicellular life to evolve. And another half a billion years for the first relatively complex animals.

Possible conclusion: Complex life is not so easy to come by, and might be expected therefore to be rare.

- Estimates vary, but at least 1 billion species have existed over earth's history.
Only one has developed the intelligence to create complex technology. We've only had really powerful technology for a few hundred of those years, and sadly, the jury is still out on whether we will kill ourselves off with it.

Possible conclusion: There aren't many like us out there, and they are likely to be very few and very far between (which at least matches observations).

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Re: How likely are we to find extraterrestrial life?

Post #9

Post by DrNoGods »

[Replying to post 7 by otseng]
Just because we are on a planet with life does not necessarily lead to a high probability life exists elsewhere.


Right, but that is just part of the argument. The other part is that we can now infer from observations to date that the number of planets that exist orbiting other stars is in the many billions when the entire observable universe is considered. Earth is just one planet of 8 (after Pluto's demotion) orbing our star, so in our solar system the fraction of planets that support life is 12.5%.

There's no reason to expect anywhere near this fraction in some random solar system elsewhere in the universe, but from a statistical standpoint, if there are billions of prospects out there (ie. planets), and some of them are in the habitable zone where liquid water can exist (which we also know is true now), then the probability increases that at least one planet among the billions may support life of some sort. So it is not just that we are on a planet that supports life that is the probability argument ... it is the added inference (from observations to date) that many billions of planets exist and that some fraction of those are in the habitable zone where life may originate and evolve.
And the above conditions are just to have the environment that is necessary for life to begin. Once you factor in life actually trying to evolve, the odds become much smaller of any other life existing.


I'd argue that if life gets even a tiny foothold then the main problem is solved, and it would evolve from that point just as it did on Earth because the lion's share of the work has been done. We still don't know how life originated on this planet, and that fact (IMO) is what drives the huge interest in asking the question if life exists elsewhere in the universe. Those who are religious, and especially those who believe that human beings are special creatures made in the image of a god as in the Christian bible story, may have a hard time reconciling the discovery of life elsewhere with their fundamental beliefs, and it may call into question the validity of concepts like an afterlife in heaven (or hell).

If you (or anyone else reading this thread) are religious ... would your views change if life were found elsewhere in the universe? How would that impact the idea that humans are special creatures? Would it negate that? Or would it be just be another subject to try and analyze and explain within the framework of whatever religion one follows? That is probably a question for another section of the website, but I've always assumed that the great interest in the question of whether there is life elsewhere in the universe is driven in large part by this particular issue ... ie. are humans special in the grand scheme of things, or just creatures who evolved a highly complex and capable brain that allows them to ponder these kinds of questions.
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Re: How likely are we to find extraterrestrial life?

Post #10

Post by Menotu »

[Replying to post 1 by otseng]

Seems obvious to me that extra terrestrial life exists somewhere. I subscribe to the ancient alien theory that's seen today. I believe that there is likely already life here that is ET like, if not currently absolutely in the past.
Will we ever find it?
I believe, almost 100%, that some have. Will modern science admit to it? That may take some time, but it will happen (assuming humanity doesn't destroy itself in the coming decades, of course).

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