Is Extra Terrestrial Life Possible in This Universe?

[Stephanus]

Sentient life, or life that is self-aware, is a completely different matter...Assuming homo sapiens do not become extinct (which is defying the odds), the most time we can expect to have on Earth is another ≈500 million years. By then the luminosity of the sun will be 10% higher...

So it's 500 millions years. I thought it would be another 2 billions years for sun to become red giant.
It takes 2 millions years for Homo Erectus to develop civilization.
And it takes 5000 years for Homo Sapiens to develop advanced technology.
100 years for Space Travel, since Wright, Goddard and ISS.
But, pardon me. There are some setback civilization such as bushmen tribe in Africa. They live like they were at 70 thousands years ago.
I think if we repeat the process once more from Homo Erectus, I doubt that they will develop civilization in 2 millions years. Considering US has sent Curiousity to Mars but bushmen still live like 70 thousands years ago.

 

[Stephanus]

On purely probablistic ground, we have a pretty good idea there are about 11,000,000,000 earthlike [i.e., similar size, composition, and of a similar age] planets orbiting a sunlike star [class G] in the MW.How many of these earthlike planet develop complex [multicellular life]? Let's just say1 in 4, or about 3,000,000,000. Of that number, how many host life forms that possesses technological intelligence? Let's just be conservative and call it 1 in 100,000, or 30,000. And how many of these civilizations might still exist to this day. About 1 in 1,000 sounds reasonably pessimistic. That suggests about 30 tech savvy species currently residing in the MW scattered across 100,000 light years. If you include planets orbiting stars lower on the food chain than sol, you can pretty much quadruple that number to 120, so our nearest tech savvy neighbor is conceiveably within a thousand or so light years. No wonder we haven't heard from ET. You can tweak the assigned numbers as you please, but, IMO, it is unrealistic to push the odds down to just one present earthlike civilization in the MW.

You're not talking about Drake equation are you?

Of that number, how many host life forms that possesses technological intelligence? ...call it ... 30,000. And how many of these civilizations might still exist to this day. About 1 in 1,000 sounds reasonably pessimistic.

1 in 1000? I think it's very, very pessimistic. I think if we add another 500 years to Earth civilization, we will be able to save our civilization even if there's a neutron star heading in our way.
Michio Kaku says that a Type 2 civilization can save themselves from any nature disaster.

That suggests about 30 tech savvy species currently residing in the MW scattered across 100,000 light years.

Only 30? Hmmh.., it's better than none. Or it just an awful waste of space.

 

[Stephanus]

On purely probablistic ground, we have a pretty good idea there are about 11,000,000,000 earthlike [i.e., similar size, composition, and of a similar age] planets orbiting a sunlike star [class G] in the MW.

I'm sorry, did you say 11 billions Earth like with class G star in Milky way? But I heard that there are about 100 billions star in MW. Do you thing 11 billions is too much of a figure for class G star and Earth like planet?

 

[Chronos]

The figure is based on this paper http://arxiv.org/abs/1510.03902, Prevalence of Earth-size Planets Orbiting Sun-like Stars

 

[|Glitch|]

So it's 500 millions years. I thought it would be another 2 billions years for sun to become red giant.
It takes 2 millions years for Homo Erectus to develop civilization.
And it takes 5000 years for Homo Sapiens to develop advanced technology.
100 years for Space Travel, since Wright, Goddard and ISS.
But, pardon me. There are some setback civilization such as bushmen tribe in Africa. They live like they were at 70 thousands years ago.
I think if we repeat the process once more from Homo Erectus, I doubt that they will develop civilization in 2 millions years. Considering US has sent Curiousity to Mars but bushmen still live like 70 thousands years ago.

It is indeed at least another two billion years before Sol starts its red giant phase. However, between now and then the luminosity of Sol will steadily increase. Our star has just barely reached middle-age, but complex life forms on this planet will cease to exist long before our sun reaches maturity. Extremophiles will still be around, probably for billions of years, but the plants, the herbivores that require those plants, and the omnivores/carnivores that require the plants and herbivores will cease to exist in approximately another 500 million years.

That may not seem like a long time, but as you pointed out we have already accomplished quite a lot in a very short period of time. We were almost completely wiped out after the Tambora eruption ≈75,000 year ago, and for humans to develop civilization and advanced technology in just one third of an interglacial period is quite an accomplishment. We will be put to the test as a species when this interglacial period ends and we are facing another 100,000 years of glaciation. One day this 2.58 million year old ice-age will end and the mean surface temperature of the planet will increase by ≈8°C, and we will be put to the test again. If we can do as well as the dinosaurs and last ≈165 million years we will be doing very well indeed.

 

[|Glitch|]

I'm sorry, did you say 11 billions Earth like with class G star in Milky way? But I heard that there are about 100 billions star in MW. Do you thing 11 billions is too much of a figure for class G star and Earth like planet?

According to NASA 100 billion stars in the Milky Way galaxy is the low-end. On the high-end they estimate 400 billion are in the Milky Way galaxy. Since ≈7.6% of the stars in the Milky Way galaxy are spectral type G stars, that would place the range at 19 billion ± 11.4 billion spectral type G stars. Approximately 60% of those spectral type G stars will have planets. Which brings us back down to 11.4 billion ± 6.84 billion spectral type G stars that have planets. When you factor in the spectral type M, K, and F stars, those stars in the Milky Way galaxy that could hold an Earth-like planet increases significantly.

Source:
How Many Stars in the Milky Way? - NASA

 

[Stephanus]

Extremophiles will still be around, probably for billions of years,

Exremophiles, is it bacteria? How many celsius do you think they can stand?

We were almost completely wiped out after the Tambora eruption ≈75,000 year ago

do yo mean "TOBA"?

Do you see the "island" Samosir, in the middle of the lake?
When the volcanoes erupted it gutted the crater, now you'll see the lake.
https://en.wikipedia.org/wiki/Toba_catastrophe_theory
I know this. I live in Indonesia!

, and for humans to develop civilization and advanced technology in just one third of an interglacial period is quite an accomplishment.

An accomplishment, indeed!

...the mean surface temperature of the planet will increase by ≈8°C, and we will be put to the test again. If we can do as well as the dinosaurs and last ≈165 million years we will be doing very well indeed.

Come on, dinosaurs weren't wiped out because of temperature rise ≈8°C.
Do you mean the last 65 millions years, not 165 millions years?
And why should we do as well as those dinosaurs. They didn't do well! They're gone!

 

[Stephanus]

Since ≈7.6% of the stars in the Milky Way galaxy are spectral type G stars...

Wow, that high?

Approximately 60% of those spectral type G stars will have planets.

Also high.
I expect, at least in Milky way alone, we are teeming with life. Just how many of those planets have sufficient carbon, oxygen, nitrogen and all the essential elements. And in habitable zone, and sufficient mass to hold atmosphere.

 

[Simon Bridge]

Exremophiles, is it bacteria? How many celsius do you think they can stand?

Strain 121 manages to do well at 120C and can go as high as 130C. Beats out P. Fumarii which lives at 113C.
The lowest temperature for terrestrial life seems to be -20C (below which the organisms stop reproducing) but we can imagine a frozen planet that undergoes periodic thaws allowing life to flourish breifly then go into hybernation (or just deep freeze).

And why should we do as well as those dinosaurs. They didn't do well! They're gone!

The Dinosaurs did well enough to have lasted as a type for 165 million years (see below) - by comparison, how long have Primates been around? Mammals?
The oldest species still around is the Nautilus, at 500 milllion years old. Dinosaurs just get the mention because they are famous.

Technically modern birds are a kind of dinosaur ... so they are kinda still around.
The ones you are thinking about arrive about 230 million years ago and left about 65 million years ago: which is 165mya.

 

[Simon Bridge]

But how can two civilization in this universe can be said similar?

It's an example being used to illustrate the vast distances involved and the difficulty of getting in touch ... I put it forward as a response to your question about how come we havn't met any yet.

Supposed this civilization is more advanced, say... 300 years from us.
I'm not talking about 300 years like Alexander the Great vs Julius Caesar,
but 300 years like us vs Star Trek, Than the technology different would be very, very big.

Star Trek would be an unrealistically optimistic model for technological development.
eg. By the ST:TOS timeline, we had hybernation ships by the 1980's so Khan Singh could be exiled in the 90's at the end of the Eugenics wars.
IRL we have just managed to get probes through the solar system and we are nowhere near manipulating human dna enough to build supermen to order.
Actual technological development is usually slower than science fiction.

When we do this sort of thing we need to be careful about how we speculate ... we have to start out with "to the best of our knowledge to date" and modify our speculations as new information comes in. To the best of our knowledge, no matter how long an intelligence has to grow, they are still going to be restricted by the speed of light for any kind of communication. There is no known reason why this should change - and lots of reasons (i.e. causality violations) as to why it won't.

What I want you to pay attention to is the vast distances involved: this is the major barrier to intellegent life, with the means and the desire, to make contact.

When you get to the 1000's and 10000 year time frames ... your should realize that a typical civilisation lasts 100's of years.
So SETI is looking for signals sent from one such sometime during it's high-tech and curious stage at a time in history sufficiently distant that the signals are coincidentally just arriving now. These signals will have been spending centuries traveling from a close neighbour ... and that is an optimistic estimate. Their whole civilization could have risen and collapsed in the time it took for us to get their "we are here" ... which is all it could be.
Those timeframes may be nothing to the Universe - but they are really long for a species.

Maybe humans will break the rule - we are good at breaking things.

 

[Stephanus]

The Dinosaurs did well enough to have lasted as a type for 165 million years (see below) - by ...

Yeah you're right! I missunderstood @|Glitch| replies. I thought he wrote "dinosarus extinct 165 millions years ago. ". They extinct 65 millions years ago. By an asteroid? Yucatan Peninsula?
Then all my responses regarding @|Glitch| were invalid. Yes, dinosaurs did manage from 230 mya to 65 mya. It's 165 millions years.
Mammals just 65 millions year, right after dinosaurs were gone.
Nautilus. Squid?

Yep, I read Crichton books. He mentioned that dinosarus were warm blooded.
Dinosaurs: Ovipar, terrestrial,??
Reptiles: Ovipar, terrestrial, cold blooded
Birds: ovipar, terrestrial, warm blooded.
So, if dinosaurs were warm blooded, yes they were closer to birds. T-Rex and raptor are examples.

 

[|Glitch|]

Exremophiles, is it bacteria? How many celsius do you think they can stand?

Extremophiles are indeed bacteria, and also life.

Upper limits of existence for carbon based lifeforms appear to be about 150 degrees Celsius, based upon inherent thermal stabilities of amino acids and polypeptides essential to DNA manufacture. Source: Extremophile

do yo mean "TOBA"?
View attachment 96867

View attachment 96868
Do you see the "island" Samosir, in the middle of the lake?
When the volcanoes erupted it gutted the crater, now you'll see the lake.
https://en.wikipedia.org/wiki/Toba_catastrophe_theory
I know this. I live in Indonesia!

I did indeed mean Toba. Thank you for correcting my mistake.

An accomplishment, indeed!

Come on, dinosaurs weren't wiped out because of temperature rise ≈8°C.
Do you mean the last 65 millions years, not 165 millions years?
And why should we do as well as those dinosaurs. They didn't do well! They're gone!

I never said the dinosaurs were wiped out by a temperature increase. I said dinosaurs were around for ≈165 million years. Dinosaurs first appeared ≈230 million years ago and were around until 65 million years ago. With regard to Earth's mean surface temperature, except for the five ice-ages (of which were are currently experiencing the fifth ice-age), and the last 20 million years of the Permian (270 to 250 million years ago), has been 22°C ± 1°C for the last 500+ million years. Currently Earth's mean surface temperature is 14.8°C. So that would be an ≈8°C increase when this current ice-age ends.

 

[rootone]

Carbon is very likely to the basis of lifeforms other than on Earth because of it's unique abilities to combine with itself and with other commonly present elements in an uncountable number of different ways.
There are other high valency elements such as you mentioned, (Silicon, Germanium) which can do this to some extent, but they are nowhere near as versatile as Carbon, and also they are also more rare.
Carbon combines with Oxygen to make CO2, a gas which is soluble in water, and that means that carbon chemistry can be mobile and thus highly complex.
Oxides of silicon are insoluble solids, and Germanuim is so rare it's barely worth considering.
So the odds are strongly in favour of Carbon based life as opposed to anything else, but that does not necessarily mean DNA, and it certainly doesn't imply that highly evolved alien life would be anything like human.

 

[Stephanus]

Star Trek would be an unrealistically optimistic model for technological development.

Claims that Star Trek was scientifically serious or accurate are totally lunatic. I have never seen any serious person claim such a thing. Krauss's book on the science of star trek largely concludes it was all nonsense, ...

And all this time I believe every word Data says.

 

[Stephanus]

I never said the dinosaurs were wiped out by a temperature increase. I said dinosaurs were around for ≈165 million years. Dinosaurs first appeared ≈230 million years ago and were around until 65 million years ago.

See my post.

Yeah you're right! I missunderstood @|Glitch| replies. I thought he wrote "dinosarus extinct 165 millions years ago. ". They extinct 65 millions years ago. By an asteroid? Yucatan Peninsula?
Then all my responses regarding @|Glitch| were invalid.

 

[Stephanus]

Carbon is very likely to the basis of lifeforms other than on Earth because of it's unique abilities to combine with itself and with other commonly present elements in an uncountable number of different ways.

Yes

There are other high valency elements such as you mentioned, (Silicon, Germanium) which can do this to some extent, but they are nowhere near as versatile as Carbon.

Yes.

and also they are also more rare.

Yes

So the odds are strongly in favour of Carbon based life as opposed to anything else,

Yes

but that does not necessarily mean DNA, and it certainly doesn't imply that highly evolved alien life would be anything like human.

Why?
I just spend time reading about DNA.
Guanine C₅H₅N₅O,
Thymine C₅H₆N₂O₂,
Cytosine C₄H₅N₃O,
and Adenine C₅H₅N₅,
they are all carbon compound, looks like hydrocarbon or sugar I think
If there's a carbon base life, would it by high chance develop DNA for their reproduction means?
Do you have any other means for replicating method other than DNA?

 

[rootone]

DNA is a long chain molecule (actually two long chains which are 'mirror images' of each other).
Because one chain is the complement to the other chain this provides the mechanism for DNA to reproduce itself. Each chain can re-build it's opposite chain.
The actual process is highly complex though and involves a lot of other chemistry as well as the DNA itself.
In sexual reproduction, DNA from two individual ogansims of the same species can also recombine to make a new and unique DNA and therefore a unique individual organism.
The four bases which encode the instructions to make proteins (and this builds an organism), are arranged along a skeleton chain of phosphates and sugars.
Although the four bases you mentioned are present in all DNA on Earth, there are similar compounds which could play the same role as those four, and even the backbone chains could be different.
It's conceivable (to me anyway),that there could also be self replicating complex organic molecules that are not even analogs of DNA.
We just don't know what is possible until we find an example of non-Earth life.

 

[Stephanus]

...It's conceivable (to me anyway),that there could also be self replicating complex organic molecules that are not even analogs of DNA.
We just don't know what is possible until we find an example of non-Earth life.

Oh

 

[Simon Bridge]

[dinosaurs] extinct 65 millions years ago. By an asteroid? Yucatan Peninsula?

Asteroid impact is the dominant theory - but the extinction was only sudden in geological terms. Note: modern birds are dinosauria.

Mammals just 65 millions year, right after dinosaurs were gone.

... depends what you are calling a mammal.
https://en.wikipedia.org/wiki/Evolution_of_mammals

Nautilus. Squid?

https://en.wikipedia.org/wiki/Nautilus

Yep, I read Crichton books. He mentioned that dinosarus were warm blooded.

You can't take Crichton books for science either.
In Jurassic Park he managed to confuse velociraptor with deinonychus.
http://www.smithsonianmag.com/ist/?next=/science-nature/you-say-velociraptor-i-say-deinonychus-33789870/
... as well as many other mistakes in the books and then the film...

Dinosaurs: Ovipar, terrestrial,??
Reptiles: Ovipar, terrestrial, cold blooded
Birds: ovipar, terrestrial, warm blooded.
So, if dinosaurs were warm blooded, yes they were closer to birds. T-Rex and raptor are examples.

Those are not identifying characteristics of dinosaurs.
http://www.ucmp.berkeley.edu/taxa/verts/dinosauria/

If only there was some sort of online resource you could consult to check these ideas before asking about them?

 

[Simon Bridge]

Replicators without RNA/DNA ... answered in another forum:
https://www.quora.com/Are-there-molecules-besides-RNA-and-DNA-that-can-self-replicate

Not many people are looking at the question, possibly because there is so much more money to be made researching Earth biology and biochemistry. Still, the odd paper comes out under "artificail life research".
http://www.cc.gatech.edu/~turk/bio_sim/articles/hutton_rep_molecules.pdf

... you could see this as a template for exo-life research: life appearing in exotic chemistries.
I imagine it could get as weird as you like ... once more the caveat on speculation: you need some reason to believe the chemistry in question is one that will occur on exoplanets where we can check.

That is why so much effort is on terrestrial planets (besides better press) ... we know more about the possible outcomes and we can tell what to look for.

 

[Chronos]

My money is on nanobots as our most likely first contact experience. It makes sense that biological life elsewhere would find interstellar travel impractical and opt for robotic missions, not unlike our current efforts. The big plusses for nanobots are cheap, robust and disposable. Advanced nanobots could conceivably construct outposts and even initiate life on suitable planets. Plus, it's a technology realistically within our scientific grasp.

 

[Simon Bridge]

Nanobots could also be used as a deliberate way to distribute the species - you'd have to assume others may try to so some would be anti-nanobot-bots ... oooh... nanobot berserker wars...

 

[Chronos]

It would, of course, most likely be life as 'they' know it.

 

[Mark Harder]

Before we can answer this question intelligently, I think we need to answer another one: How would you decide if a thing is a form of life, or not? Suppose you are walking along the beach, and there's this purple blob lying in the surf. Is it alive? I submit that the phenomenon must be examined over a suitable duration. That's because life is characterized by processes, not mere static structures, that occur in time. Ingestion of matter/energy, growth, reproduction, all take time. There's an arrow in time for all living processes. It's as though living things are moving toward some goal. The material components exist and take their properties from the need to 'function', i.e. to support the essential processes of life. The best you can do by merely inspecting or dissecting the structure of the purple blob is to determine if it once was living. Perhaps, try a thought experiment. You are exploring and exoplanet and you come across something like the purple blob, how would you know if it is alive or not?

Life, the thing and the process, has to take in energy and matter in order to create more of itself. Just guaranteeing that genetic information is faithfully copied imposes costs in energy on systems that correct the errors that inevitably occur during replication of that information. The growth of information, which is what replication is, is equivalent to loss of entropy. The highly ordered, information-containing and propagating structures of living organisms cannot exist for very long if entropy holds sway. The entropy of a system can only decrease if energy is added to it, which requires influxes from the environment. Thus, living organisms must be open systems, thermodynamically speaking, in order to defeat the second law. And of course reproduction of an organism requires that it increase in mass between reproductive events.

We don't have to go to exoplanets to confront the question. There are the viruses. You can sample a batch of viruses to see if it creates more of them. It won't. So are viruses alive? Not by themselves. You can only uncover evidence they are alive when the viruses are exposed to the right kinds of living cells. In order to exhibit a living process, viruses must steal matter and energy from other life forms to carry to grow and reproduce. Regardless of how and where they do it, I would consider viruses living. But again, I would have to spend time with viruses before I could answer the question. The other candidates I have in mind are the prions. Prions are protein molecules that reproduce themselves inside living organisms which, like viruses, die from the internal buildup of these molecules. Are prions living? I"m not sure...

 

[ogg]

So many problems with this thread...but there's a LOT of great information also! I'll focus on the problems. Life. We can't even define it, we certainly shouldn't pretend to know where it might exist. We mean LAWKI, life-as-we-know-it. It is, imho, a tautology to then claim life needs "Earth-like" environments. One thing we do know is that life requires an energy source, as well as sufficiently complex chemistry, and, virtually certainly, variation in the energy gradient as well as variation in the chemical environment. It is massively arrogant to claim that life can't exist under the surface of planets without a star (as long as, say, geothermal energy is available, or perhaps even gravitational energy).Evolution of life: it requires a hospitable environment. Any planet which has 'frequent' extinction level bombardments, or collisions which strip the atmosphere (or hydrosphere) may not allow life to evolve. Add cosmic radiation (supernovae, black holes, etc.) and the number of 'Earth-like' planets might be much less than the numbers thrown around here. We just don't know; nor do we understand star system evolution well enough to be say what fraction of Earth-sized planets are "Earth-like". Based on history, our civilization won't last another 500 years. StarTrek is FICTION. There ARE limits to technology. Or perhaps you can point to a new energy source we've discovered since 1933? We already have nanobots: they're called bacteria. No life exists alone, lawki exists in a complex living environment, its not likely, imho, that nanobots will be any different. What reason do you have to suppose in 500 years that civilization will be technological? Why not back to ox carts and feudalism? It isn't about intelligence, imho, its about our ability (or lack of) to control our individual emotional responses to address existential dangers. Are we capable of it? IDK, but I fear we aren't. Also, be aware that DNA from Earth has made its way to all of the inner and probably some of the outer solar system. We can't say definitively how many different trees of life developed on (or now exist on or under) Earth. At least one, but we have established no upper limit. We don't know whether RNA/DNA was enevitable or one of several likely possibilities. (but AFAIK, no other good choices (for lawki) exist.)

 

[Stephanus]

So many problems with this thread...but there's a LOT of great information ..

Yeah, especially when it hit Arecibo message. Life is beautiful.

...We don't know whether RNA/DNA was enevitable or one of several likely possibilities. (but AFAIK, no other good choices (for lawki) exist.)

I don't know about the "inevitable", but...

Replicators without RNA/DNA ... answered in another forum:
https://www.quora.com/Are-there-molecules-besides-RNA-and-DNA-that-can-self-replicate
...

 

[Chronos]

Unfortunately, we are unavoidably constrained by our existing knowledge of biology, so, RNA based life is the only form we can speak about with any scientific authority.

 

[Simon Bridge]

In these discussions, someone usually points out the issue of "how do we identify life?" ... there is currently no problem identifying what counts as life and lots of discussion about the boundary/borderline cases that have been identified in the biology literature. It is clearly possible to have a study of a group that is incompletely defined - and we can talk about the possibility of other places supporting members of the group.

It is implicit to these discussions that the "life" would be what we would be able to identify using our existing knowledge. We may want to extend the definition later as we make more discoveries - but right now, biologists have no trouble identifying objects within their field of study.

 

[Buzz Bloom]

Prions are protein molecules that reproduce themselves

Hi Mark:

I wonder if you can clarify this for me. My understanding is that prions do reproduce in any sense other than the way proteins are reproduced. Rather a priion converts a different form of the same protein molecule into it's own form. If this is correct, why does that qualify as "reproduction"? Surely this is just a stretch of semantics.

The reproductive process is still: DNA->DNA followed by DNA->T-RNA->protein. Then this particular protein happens to be able to form itself into two different shapes, and one of these two shapes can subsequently change the other shape into its own shape.

Regards,
Buzz

 

[newjerseyrunner]

We will have a much better understanding on biology in the next few decades. As we explore worlds that may harbor life, both finding it and not finding it would provide more information about the likelihood of life. I'm partial to the idea that if you put all of the raw materials and water in something that'll mix it, you'll eventually get life. Planets are really really big mixing bowls and have long long times to mix.