Could 'aliens' already know there's life on Earth?

[Gondur]

We can indirectly measure the atmospheric composition of worlds outside our solar system.
Suppose there are aliens out there.
On their world, they use the same technique we use to measure the atmospheric composition of worlds.
Suppose they turn their telescope on Earth.
Is it possible they conclude Earth is an 'Earth-like' planet much like their own that may support life? In the same way we have concluded there are many Earth like planets out there that may support life?
So, at this point in time, could there actually be distant civilisations in the milky way who know that Earth is one of many planets they have observed that may sustain life by measuring Earth's atmospheric composition, but don't actually know about 'us'?

 

[Arman777]

So, at this point in time, could there actually be distant civilisations in the milky way who know that Earth may sustain life, but don't actually know about 'us'?

Yes, that is possible. The radius of the Milky Way is approximately 50.000 ly. So when an alien try to observe our planet, he will see the past of our planet which it is mostly (approximately) 76.000 year back. (due to position of the solar system in the Milky Way). And we can say that modern humans appeard on Earth around 100-200 thousand years ago. In that sense its possible that they don't know us.

 

[mfb]

Sure. The will need roughly the equivalent of our upcoming telescopes (JWST, ELT) to measure the atmosphere from tens of light years away, and better for larger distances.

The presence of methane and oxygen at the same time is a strong indication for life - without biological processes one of them would go away quickly.

 

[nikkkom]

A moderately advanced interplanetary civilization, one which uses only technologies already known to us, but which expanded from its home planet and is in the process of colonizing other planets, asteroids, etc, would be able to construct space telescopes of almost arbitrary size (think kilometers-size) - many problems of huge telescopes on Earth are due to gravity and air. Hooked up into an imaging interferometer (again, much easier in space), half a dozen of such monsters would be able to image Earth with resolution sufficient to see our cities at night.

 

[bland]

Sure. The will need roughly the equivalent of our upcoming telescopes (JWST, ELT) to measure the atmosphere from tens of light years away, and better for larger distances.

But if we postulate intelligent life at a distance of 10's of light years from us then we may as well postulate the Galaxy teeming with intelligent life and ergo intelligent life in existence for perhaps billions of years which leads us back to the Fermi paradox, where is everyone?

 

[Arman777]

But if we postulate intelligent life at a distance of 10's of light years from us then we may as well postulate the Galaxy teeming with intelligent life and ergo intelligent life in existence for perhaps billions of years which leads us back to the Fermi paradox, where is everyone?

For a similar discussion

https://www.physicsforums.com/index.php?threads/931857/

The thing is even they send signal to us it will take time to reach us. Also we have a radio telescopes for like 80 years. It's really short period of time. Maybe they sended but we have missed and then their civilization ended. Who knows ?

A discussion which has no conclusion.

 

[rootone]

Aliens at a similar technology level to us humans should certainly be able to see that Earth potentially could harbour life.
Oxygen rich atmosphere would be a big clue, indicating not only life, but evolving life.

 

[mfb]

Oxygen alone can have chemical origins - water with the hydrogen escaping, for example. Oxygen and methane together is something our atmosphere has that has no plausible geological origin. The methane has to be replenished constantly because it reacts with oxygen.

 

[osilmag]

I suppose you haven't read about the Fermi Paradox.

https://www.britannica.com/story/the-fermi-paradox-where-are-all-the-aliens

 

[Alloymouse]

We should also consider how other potential lifeforms search for "signs of life" - indeed, oxygen and carbon are essential indicators of life on earth, but that might not mean that this applies to other lifeforms. For instance, there are sulphur-based lifeforms that exist, and some scientists postulate that silicon-based life can exist due to similarities in chemistry (that I won't elaborate on here).

TLDR; provided these aliens are intelligent enough to understand that our environment can harbour life, we might not even be noticed by them.

 

[rootone]

Silicon does have similar properties to Carbon.
The problem is that Silicon dioxide is a solid at Earth like temperature and Carbon dioxide is not.
Also CO2 can dissolve in water, try doing that with sand.

 

[Alloymouse]

Silicon does have similar properties to Carbon.
The problem is that Silicon dioxide is a solid at Earth like temperature and Carbon dioxide is not.
Also CO2 can dissolve in water, try doing that with sand.

Well yes, that is true. However, since silicon is in the same chemical group as carbon, it can form bonds similar to that. Although physical properties may differ, there is still potential for molecules to develop that are similar in chemical properties as our organic molecules.

You could take a look at work done by scientists to prove that such stuff can exist too on google :)
http://www.caltech.edu/news/bringing-silicon-life-53049

 

[mfb]

@Alloymouse: Please give a reference for sulphur-based life forms on Earth. There is life using sulphur compounds as energy source, but they still use carbon-based DNA, proteins and so on.

Carbon is excellent for complex chemical molecules. The other elements are not.

 

[Alloymouse]

@Alloymouse: Please give a reference for sulphur-based life forms on Earth. There is life using sulphur compounds as energy source, but they still use carbon-based DNA, proteins and so on.

Carbon is excellent for complex chemical molecules. The other elements are not.

@mfb My bad, I kinda slipped there. I should've clarified between energy sources and "building blocks".

 

[stefan r]

But if we postulate intelligent life at a distance of 10's of light years from us then we may as well postulate the Galaxy teeming with intelligent life and ergo intelligent life in existence for perhaps billions of years which leads us back to the Fermi paradox, where is everyone?

I believe there are flatworms in my back yard because biology textbooks say most yards have lots of them. I know how to use a microscope and I have access to microscopes. However, I have not bothered to look at the flatworms. I have made no attempt to communicate with them.

 

[bubbleHZ]

I wrote a manuscript about the explanation of Fermi Paradox by applying the index of cvilization. Does anyone has interest to know about it?

 

My short answer is "definitely yes." It is possible.

We already have Hubble. It is in orbit outside the Earth's atmosphere. It has detected atmosphere in an exoplanet.

But we need to do much better than Hubble, as great as it is. I'm enthusiastic about project LUVOIR. We need the next step, whether it is LUVOIR or something even better.

I would definitely bet that our galaxy is teeming with intelligent life. I just can't prove it. I don't understand why people think intelligent life is to be found only on Earth. If the conditions for life arise on other planets, as they have on Earth, then why would there not be life? Also I think evolution would work the same way it does on Earth. There's nothing specifically terrestrial about it. Given how life evolved over billions of years, most of that time as one-celled creatures, why would we expect anything different elsewhere?

This leads, in my opinion, to the conclusion that not only are there intelligent aliens, but they are probably humanoid. My reason is that we developed the form we have as a result of the same evolutionary process which must exist everywhere. In other words, genetic mutations and natural selection. Why would Nature not come up with the same solutions to the problem of survival on another planet as it does on Earth, assuming that planet is Earth-like?

As for planets that are very different from Earth, how would life even survive there? Carbon is carbon, organic molecules are organic molecules, chemistry is chemistry, no matter where we are.

I would dare say that even their language would not be very different from our own. I am speaking of humanoids in their natural state. Soon we will be modifying ourselves thanks to technology. Who knows what we will create? Who knows what aliens have already created?

If aliens have visited us -- something I am not going to say I believe in at this time -- it could be in the form of intelligent human-like entities made in a laboratory, which are essentially immortal, and can do just fine as they cruise through the galaxy in search of other planets. If you are immortal, then you have a long time to discover other planets.

https://asd.gsfc.nasa.gov/luvoir/

 

[nikkkom]

My short answer is "definitely yes." It is possible.

We already have Hubble. It is in orbit outside the Earth's atmosphere. It has detected atmosphere in an exoplanet.

But we need to do much better than Hubble, as great as it is. I'm enthusiastic about project LUVOIR. We need the next step, whether it is LUVOIR or something even better.

I would definitely bet that our galaxy is teeming with intelligent life. I just can't prove it. I don't understand why people think intelligent life is to be found only on Earth.

The standard argument against it is "if so, why not even one alien starship was seen yet?"

If the conditions for life arise on other planets, as they have on Earth, then why would there not be life? Also I think evolution would work the same way it does on Earth. There's nothing specifically terrestrial about it. Given how life evolved over billions of years, most of that time as one-celled creatures

Exactly. On Earth, it was "most of that time as one-celled creatures". But the jump to complex life might be exceedingly rare - it took _billions_ of years here.

It's plausible one-celled life is ubiquitous. But "intelligent life" probably needs more than one-celled organism :)

 

[unusually_wrong]

Something else to consider: We've had 5 mass extinction events and we are the result of what is left over. It would be a little silly to think other life bearing planets haven't had any. However, who is to say what type of dominant life form emerged and thrived and how they may have evolved as well as their food.

 

[berkeman]

Thread closed for Moderation...

EDIT/UPDATE -- The high level of unsubstantiated speculation in this this thread is what has the Mentors uncomfortable. We are trying to decide if the thread is salvageable with some pruning. Feel free to PM me suggestions. Thanks.

And please always remember that the gold standard here at the PF is peer-reviewed journal articles and mainstream textbook references. Thanks.

 

[berkeman]

Final update -- after a Mentor discussion, this thread will remain closed as too speculative. Thanks folks.