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

[Tanya Li]

I was recently reading about Earth analogues like Kepler-452b and considering the real probability of life on these worlds. Given that these exoplanets reside within the habitable zone where liquid water can exist, it seems highly plausible that microbial lifeforms could thrive there completely undetected by our current technology.

Because we are currently limited to atmospheric spectroscopy, we can only search for broad biosignatures rather than directly observing surface biology. If an exoplanet does possess the exact baseline conditions of Earth, what are the primary astronomical constraints preventing us from confirming the presence of microbial ecosystems, and how varied could those ecosystems realistically be?

 

[javisot]

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.

Or not.

In this regard, the only thing we know with relative certainty is that wherever there is complex, intelligent life, there is microbial life; however, the existence of complex, intelligent life is not a prerequisite for the existence of microbial life.

 

[haruspex]

What's the probability that string theory and that number are valid assumptions?

As I indicated in post #22, the answer is predicated on those assumptions. What odds one ascribes to them is another matter.

 

[256bits]

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

As well as the "I" in "We" being a Boltamann brain.

 

[FactChecker]

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).

I like NASA's idea of requiring the ability to evolve. I hadn't considered that.

 

[DaveC426913]

I like NASA's idea of requiring the ability to evolve. I hadn't considered that.

I do not see that page as containing a list of "requirements". It's a list of "Earthly characteristics", not a definition of life.

I'm not sure why evolution would be on a list of requirements. If we came across a walking, talking, radio-adept lifeform that had, for some previous reason, reached a stage where its copying mechanism was now perfect (the copy process, not the lifeform) and did not change further, would we label it as non-living? What if they recently switched from sexual reproduction to mitosis or (natural) cloning? etc.

 

[BillTre]

The ability for a planet to spawn life and the ability for us to detect it are two different things.

A NASA view of a good candidate for an origin site would include: liquid water, water plus basalt-like rock (to cause serpentinization reactions), a pre-existing mechanism to isolate potential reactions from its environment (to prevent reaction products from diffusing away, prior to membranes). This is all based on organic based life, not other possible chemistries. The liquid water could be due to residing in the goldilocks zone of being in some other place. The key issue is the serpentinization reactions between the water and rock. This produces a low level of localized production of simple organic compounds that considered to be feedstock for possible pre-life chemical systems. The isolation prevents products from freely diffusing away, so it could accumulate to levels more favorable to reactions occurring.

When it comes to detecting, the assembly theory approach is currently a popular option. It is based on finding lots of copies of specific kinds of molecules while lacking lots of others. Non-biological chemical production is considered to be more random (chemistry not directed by biological processes). This is like to organic sludge of chemicals found in some meteorites (Murchison meteor) where there are not so many copies of lots of different compounds (rather than lots of copies of a few compounds).
Finding an oxygen atmosphere like on Earth would probably be considered a strong indicator since it would probably be considered something produced by life's terraforming processes.

WRT definitions, The NASA definition although popular, has some problems. By that definition, a non-reproductive animal would not be considered alive because it does not reproduce. There are many such animals, such as: mules, many castes of social insects, or a heavily irradiated but not yet metabolically dead organism.

 

[FactChecker]

I do not see that page as containing a list of "requirements". It's a list of "Earthly characteristics", not a definition of life.

I'm not sure why evolution would be on a list of requirements.

Above the list of characteristics of terran life, in the third paragraph:
The NASA definition of life, “Life is a self-sustaining chemical system capable of Darwinian evolution”

 

[Tanya Li]

With the James Webb telescope actively probing around the atmospheres of distant exoplanets, scientists are no longer guessing if habitable worlds are existing. For instance, the ongoing observations and debates regarding planets like K2-18b, where data hints at carbon, breaking molecules and potential biosignatures, show exactly how we might first prove life exists elsewhere in the universe. While finding an atmosphere with an unexplainable equilibrium of gases (like oxygen and methane together, since they are chemical enemies) isn't a definitive 'smoking gun' of intelligent life, it represents the most tangible data we've ever had in the search of extraterrestrial biology.

 

[WWGD]

This is the thinking hope.

So you envision whatever life we run into will be well disposed towards us?

 

[WWGD]

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

Yes, losing their religion.

 

[DaveC426913]

So you envision whatever life we run into will be well disposed towards us?

? The question I was addressing was 'can the subsurface oceans support life'.

I suspect it won't be more advanced than plankton, so disposition is likely moot.