Are we alone out there? The mystery of life in the Universe

[Tanya Li]

Hi everyone,
I wanted to start a discussion about one of the most fascinating questions in science: are we alone out there?

Given that there are billions of Earth-like exoplanets in our galaxy alone, the odds seem high that life could exist elsewhere. However, we haven't found any definitive evidence yet (the Fermi Paradox).

As a student interested in astrobiology, I wanted to ask the community: do you think we will find evidence of microbial life (like on Mars or Europa) in our lifetimes, or are we more likely to detect intelligent signals from deep space first?

I would love to hear your thoughts and theories!

 

[javisot]

As a student interested in astrobiology, I wanted to ask the community: do you think we will find evidence of microbial life (like on Mars or Europa) in our lifetimes, or are we more likely to detect intelligent signals from deep space first?

Greetings. If those are the two options, I personally choose the scenario where we first discover microbial life (assuming it exists), based on a very simple argument: microbial life is simpler than intelligent extraterrestrials, and therefore more likely to exist and be found.

 

[Tanya Li]

Greetings. If those are the two options, I personally choose the scenario where we first discover microbial life (assuming it exists), based on a very simple argument: microbial life is simpler than intelligent extraterrestrials, and therefore more likely to exist and be found.

Thanks for your input. I think that's a really logical argument. Even though finding microbes isn't as dramatic as receiving an intelligent signal from space, discovering even a single alien bacteria would still completely change our understanding of biology forever.

 

[FactChecker]

Greetings. If those are the two options, I personally choose the scenario where we first discover microbial life (assuming it exists), based on a very simple argument: microbial life is simpler than intelligent extraterrestrials, and therefore more likely to exist and be found.

On Earth, we seem to find life in places we long thought were impossible, as long as there is some source of energy. And the definition of "life" is getting more diverse. I think we will find some form of life within our Solar System, long before we get real proof from other star systems.
This is just the opinion of a casual amateur, but I'm not sure that expertise gives you much in answering this question.

 

[WWGD]

On Earth, we seem to find life in places we long thought were impossible, as long as there is some source of energy. And the definition of "life" is getting more diverse. I think we will find some form of life within our Solar System, long before we get real proof from other star systems.
This is just the opinion of a casual amateur, but I'm not sure that expertise gives you much in answering this question.

I think there's a technical definition of life. @BillTre may know it.

 

[PeroK]

Hi everyone,
I wanted to start a discussion about one of the most fascinating questions in science: are we alone out there?

Given that there are billions of Earth-like exoplanets in our galaxy alone, the odds seem high that life could exist elsewhere. However, we haven't found any definitive evidence yet (the Fermi Paradox).

As a student interested in astrobiology, I wanted to ask the community: do you think we will find evidence of microbial life (like on Mars or Europa) in our lifetimes, or are we more likely to detect intelligent signals from deep space first?

I would love to hear your thoughts and theories!

The only valid answer at this stage is that we don't know. There are already some threads on here about this.

 

[loop quantum gravity]

Hi everyone,
I wanted to start a discussion about one of the most fascinating questions in science: are we alone out there?

Given that there are billions of Earth-like exoplanets in our galaxy alone, the odds seem high that life could exist elsewhere. However, we haven't found any definitive evidence yet (the Fermi Paradox).

As a student interested in astrobiology, I wanted to ask the community: do you think we will find evidence of microbial life (like on Mars or Europa) in our lifetimes, or are we more likely to detect intelligent signals from deep space first?

I would love to hear your thoughts and theories!

Probably if there are aliens they don't want to be detected.. (espiecally with a violent animal like us...
). Have you seen Men In Black, good movie! (some say it's a documentary... kiddin').

 

[pinball1970]

are we alone out there?

If we are alone, it seems like an awful waste of space.....

If it turns out there is a lot of life, say per galaxy I would not be surprised. The universe is good at making complex molecules and there may be more than one way of getting to "life."

A recent publication.

https://arxiv.org/abs/2608.14381

 

[FactChecker]

I think there's a technical definition of life. @BillTre may know it.

There seems to be a variety of definitions, some of which (IMO) would include things as basic as prion diseases, and others would require more complicated functions.

 

[BillTre]

I think there's a technical definition of life. @BillTre may know it.

There are many definitions of life. Non-reign supreme, but some are probably considered more useful, like the NASA definition (which has its problems) and Cronin's assembly theory (which doesn't say how life works).

 

[WWGD]

I was thinking of c) here: https://www.merriam-webster.com/dictionary/life

 

[DaveC426913]

I was thinking of c) here: https://www.merriam-webster.com/dictionary/life

Metabolism, growth, reaction to stimuli, reproduction.

That is the common one, yes.

 

[DaveC426913]

I had an idea lying around somewhere that, to a very rough degree, we might expect to find life out there whose complexity distribution is correlated with occurrence in Earth's timeline. A random sampling of a dataset should start to show frequency correlating with duration (i.e. time required to evolve).

eg.

• For every ten thousand planets with single celled organisms, we might find a thousand with multi-celled organisms.
• For every thousand of those, we might find a hundred with macro organisms (eg. insect, polyp, fish analogues)
• For every 100 of those we might find ten with reptiloid analogues.
• For every 10 of those we might find one with mammalian analogues.
• etc.

IOW, we could search our spiral arm and find a thousand planets of pond scum before we find just one with complex brains comparable to that of a shrew.

In fact, a snapshot of our findings would make it appear that our galaxy (the parts not barren) seems like it's pretty much all pond scum planets.


You might be able to refine it more than that simplistic 10:1 ratio. Life single-celled life appeared 4by ago, but multi-celled life appeared 2by ago. That's 2:1 not 10:1.

With this metric, we should expect to find only one human-level intelligence in a sample size of 35,000 life-bearing planets (3.5Gy / 100,000y). That's a LOT of searching.



This assumes a uniform search technique, like searching for telltale atmo chemistry. Obvs, a radio-capable civilization would change the odds dramatically. Still, that civilization would sit in sample size of (3.5Gy/75y) = 40 million pond-scum-bearing planets.

 

[Tanya Li]

Thanks for all the amazing responses and the breakdown of the evolutionary timeline! It makes a lot of sense that single-celled life would be significantly more common than intelligent civilizations.

Speaking of microbial life close by, I was recently reading about how scientists have found evidence of massive subsurface lakes trapped inside the icy shell of Jupiter's moon, Europa.

Given that basic organisms are more likely to exist, do you think these under-ice lakes are the most probable place in our solar system to find active alien microbes? Or would the extreme lack of sunlight and reliance on geothermal energy keep life from forming there?

 

[DaveC426913]

Given that basic organisms are more likely to exist, do you think these under-ice lakes are the most probable place in our solar system to find active alien microbes?

This is the thinking hope.

 

[WWGD]

I had an idea lying around somewhere that, to a very rough degree, we might expect to find life out there whose complexity distribution is correlated with occurrence in Earth's timeline. A random sampling of a dataset should start to show frequency correlating with duration (i.e. time required to evolve).

eg.

• For every ten thousand planets with single celled organisms, we might find a thousand with multi-celled organisms.
• For every thousand of those, we might find a hundred with macro organisms (eg. insect, polyp, fish analogues)
• For every 100 of those we might find ten with reptiloid analogues.
• For every 10 of those we might find one with mammalian analogues.
• etc.

IOW, we could search our spiral arm and find a thousand planets of pond scum before we find just one with complex brains comparable to that of a shrew.

In fact, a snapshot of our findings would make it appear that our galaxy (the parts not barren) seems like it's pretty much all pond scum planets.


You might be able to refine it more than that simplistic 10:1 ratio. Life single-celled life appeared 4by ago, but multi-celled life appeared 2by ago. That's 2:1 not 10:1.

With this metric, we should expect to find only one human-level intelligence in a sample size of 35,000 life-bearing planets (3.5Gy / 100,000y). That's a LOT of searching.



This assumes a uniform search technique, like searching for telltale atmo chemistry. Obvs, a radio-capable civilization would change the odds dramatically. Still, that civilization would sit in sample size of (3.5Gy/75y) = 40 million pond-scum-bearing planets.

Are we talking Organic /Carbon- based life here?

 

[Klystron]

Given that basic organisms are more likely to exist, do you think these under-ice lakes are the most probable place in our solar system to find active alien microbes? Or would the extreme lack of sunlight and reliance on geothermal energy keep life from forming there?

If (microbial) lifeforms are discovered in Jovian moons, Jupiter itself could harbor life forms. Consider Io, a very active satellite containing and distributing sulphur within Jovian system. Jupiter's massive gravity attracts passing asteroids and icy objects providing water as we observe on Europa, Ganymede and Calisto; not to mention Saturn's rings and moons.

Energy sources abound including solar, tidal gravity from Jove and orbital resonances among the larger moons, and truly amazing electromagnetic radiation (EMR) from Jupiter. I happened to look up recent fly-by probe EMR data for Ganymede surface last night, if memory serves, at ~5.4 rem. Add chemical energy from vast subsurface saltwater oceans on several moons churned by tidal forces and prospects for life appear profound.

 

[PeroK]

If (microbial) lifeforms are discovered in Jovian moons, Jupiter itself could harbor life forms.

Do you have a source for the probability of finding life on Jupiter?

 

[DaveC426913]

Are we talking Organic /Carbon- based life here?

Not necessarily.

 

[Tanya Li]

If (microbial) lifeforms are discovered in Jovian moons, Jupiter itself could harbor life forms. Consider Io, a very active satellite containing and distributing sulphur within Jovian system. Jupiter's massive gravity attracts passing asteroids and icy objects providing water as we observe on Europa, Ganymede and Calisto; not to mention Saturn's rings and moons.

Energy sources abound including solar, tidal gravity from Jove and orbital resonances among the larger moons, and truly amazing electromagnetic radiation (EMR) from Jupiter. I happened to look up recent fly-by probe EMR data for Ganymede surface last night, if memory serves, at ~5.4 rem. Add chemical energy from vast subsurface saltwater oceans on several moons churned by tidal forces and prospects for life appear profound.

This is an excellent point regarding the role of tidal forces and the distribution of sulfur from Io. The dynamic where Jupiter's gravitational pull acts as a tidal engine—actively churning the interiors of these moons to generate geothermal heat—is critical, especially where solar radiation is negligible. If tidal energy and abundant chemistry are indeed the primary requirements for abiogenesis, the Jovian system is arguably the most promising target in our solar system for finding microbial life.

 

[PeroK]

the Jovian system is arguably the most promising target in our solar system for finding microbial life.

This is not a science-fiction forum! This is from the following NASA webpage:

Jupiter’s environment is probably not conducive to life as we know it. The temperatures, pressures, and materials that characterize this planet are most likely too extreme and volatile for organisms to adapt to.

https://science.nasa.gov/jupiter/jupiter-facts/

Here is a NASA webpage on the subject of life on Europa:

https://science.nasa.gov/solar-system/new-findings-support-prospect-of-life-on-jupiters-moon-europa/

 

[haruspex]

Greetings. If those are the two options, I personally choose the scenario where we first discover microbial life (assuming it exists), based on a very simple argument: microbial life is simpler than intelligent extraterrestrials, and therefore more likely to exist and be found.

I think you are overlooking the detection requirement. There may be vastly more places where there is just primordial life than anything more advanced, but an industrialised intelligent life would be detectable from a lot further way.

As to the Fermi paradox, one answer is based on the anthropic principle and the notion that our Universe is just one in a Multiverse of all possible universes. We may guess that the vast majority of universes produce nothing of much complexity; that an overwhelming proportion of those that do are quite inimical to life; that in all but a tiny fraction of those where life could arise, it remains so unlikely that it only happens once; and so forth.
On that basis, the odds are that we find ourselves in a universe of the third kind.

 

[javisot]

I think you are overlooking the detection requirement. There may be vastly more places where there is just primordial life than anything more advanced, but an industrialised intelligent life would be detectable from a lot further way.

You, on the other hand, seem to assume that if both microbial life and complex intelligent life exist in the universe, their abundance would be the same, and therefore it would be easier to find signs of complex intelligent life.

The fact that microbial life is simpler than complex intelligent life reasonably leads one to think that its abundance in the universe would be greater.

 

[PeroK]

On that basis, the odds are that we find ourselves in a universe of the third kind.

To flesh out the Bayesian argument:

Assume as a prior that there are three types of universe:

a) The laws of physics prohibit life.
b) The laws of physics make life rare.
c) The laws of physics allow life in abundance.

Given that we have life on Earth, the overwhelming probability is that we are in universe c).

The two problems are: First, we do not know the relative frequency of a, b and c. If b is much more frequent than c, then this disrupts the argument. Second, there may not be a multiverse in the first place.

Bayesian statistics may give you an answer. But, whether that answer is more than just an abstract number is not clear.

 

[gmax137]

I happened to look up recent fly-by probe EMR data for Ganymede surface last night, if memory serves, at ~5.4 rem.

5.4 rem per hour? ... per day? ...

 

[javisot]

As to the Fermi paradox, one answer is based on the anthropic principle and the notion that our Universe is just one in a Multiverse of all possible universes.

The multiverse is not part of the scientific consensus; we operate based on the idea of a single universe.

Consequently, the concept of "inter-universal panspermia" is invalid; life in this universe does not originate from another universe. We know that this universe transitioned from states lacking matter to states containing matter; therefore, life within the universe necessarily began through abiogenesis.

We do not know whether the origin of life in the universe coincides with the origin of life on Earth. If life on Earth is the only life in the universe, then yes, speaking of the origin of life in the universe and on Earth amounts to the same thing.

(If we assume that life on Earth is the only life in the universe, then there is not much to say. We assume that life is abundant in the universe—not because it is necessarily true, but simply as an initial premise to develop a line of reasoning)

 

[haruspex]

The multiverse is not part of the scientific consensus; we operate based on the idea of a single universe.

True, but coupled with the anthropic principle it has the advantage of solving the "goldilocks universe" puzzle.

Consequently, the concept of "inter-universal panspermia" is invalid;

I don't know why you mention that. It has nothing to do with my post.

 

[haruspex]

First, we do not know the relative frequency of a, b and c. If b is much more frequent than c, then this disrupts the argument.

My basis is the string theory landscape of around $10^500$ equally possible universes. Amongst those, I feel sure b would vastly outnumber c.

 

[haruspex]

You, on the other hand, seem to assume that if both microbial life and complex intelligent life exist in the universe, their abundance would be the same,

Not at all. I am suggesting that while microbial life only examples might be ten million times as common as advanced civilisations it could also be that the distance at which we might be able to detect the latter could be a thousand times the distance at which we could detect the former. That would make finding advanced life the easier by a hundred times.

 

[PeroK]

My basis is the string theory landscape of around $10^500$ equally possible universes. Amongst those, I feel sure b would vastly outnumber c.

What's the probability that string theory and that number are valid assumptions? You can add this additional (first) step in your conditional probability tree, which changes things significantly.

In any case, until you have evidence for your assumptions, the resulting calculations may not be physically meaningful.

For example, using the same Bayesian approach, some people have concluded that we are almost certainly living in a simulation!