Is Extra Terrestrial Life Possible in This Universe?

[Stephanus]

Dear PF Forum,
I would like to know if LIFE in exoplanet is possible. And if it is, how?
When I drove my Pastor to my mother funeral, he asked me out of the blue while I was driving my car.
"Do you believe there is another earth?"
My immediate response would be, in parallel universe where there are Nicole Kidman, Megan Fox, Linday Lohan OR in this universe.
"In this universe," he said.
So there were the following problems I think.
First, life should be in a planet or moon (as in Avatar).
This planet must be supported by a nearby star.
And for this star:
I think the star cannot be too massive. I read that the comparisson between the mass of the star and its lifespan in main sequence is to the power of 3.
For example, a 2 solar mass star will have 1/8 lifespan of our sun.
10 solar mass star will have 1/1000 lifespan of the sun. That is: 10 million years.
Earth develop life form in 3.9 billion years. "Only" in 600 million years ago (Cambrium) there were many multilcellular organism blooming in the ocean. Trilobite, nautilus, etc...
And it takes 4.5 billion years for Earth to develop intelligence.
And the star cannot be too light, because if it's too cold, then the planet should be closer to the sun, then there are tidal lock problem, and radiaton.
So how is the chance for this universe to have, IMHO, stars that are 0.8 - 1.2 solar mass?
For these stars to have planet in their habitable zone?
I'm not trying to bring Drake Equation, just want to lay out the facts.

And after all those...
What would that lifeform be?
Will it be carbon compound? Since carbon has 4 valence and

Carbon is abundance in the universe. I don't know if this number represents carbon in outer space nebulae, or locked in white dwarf stars.
Silicon and Germanium have 4 valence, too. But since they are more complex than carbon, I think carbon is easier to build element compound rather than Si/Ge. And Carbon is more abundance than Si/Ge.
And IF the lifeform in exoplanet is carbon based, would they develop DNA as their method to replicate?
So my summary questions are these:
1. Given those conditions, would extra terrestrial life be possible?
2. IF it is possible, would it be carbon based?
3. IF it is carbon based, would it develop DNA as their replication method?

Thank you very much.

 

[Simon Bridge]

Dear PF Forum,
I would like to know if LIFE in exoplanet is possible. And if it is, how?

Is "LIFE" different from "life"?

When I drove my Pastor to my mother funeral, he asked me out of the blue while I was driving my car.
"Do you believe there is another earth?"

That's actually a different question: it seems very unlikely that there will be a duplicate Earth out there.
Calculations based on the probability of getting life as in a duplicate Earth biosphere are misplaced.

What would that lifeform be?
Will it be carbon compound?

You mean "carbon based" ... few biologists would consider any carbon compound to be living.
You should think of "live" as a class of emergent properties or behaviours arising from complicated processes.

Carbon is abundance in the universe.

Carbon is abundant - it is the 4th most common element in the Universe.
Life on Earth is built mainly from 5 of the 6 most abundant elements ...

I don't know if this number represents carbon in outer space nebulae, or locked in white dwarf stars.

1. Given those conditions, would extra terrestrial life be possible?

Id life possible off the Earth: almost certainly yes.

2. IF it is possible, would it be carbon based?

There would almost certainly be carbon based life off the Earth somewhere.

3. IF it is carbon based, would it develop DNA as their replication method?

Among other approaches, there will almost certainly be DNA based life elsewhere in the Universe. You are probably thinking of "reproduction" rather than replication ... DNA is not the only replicating molecule: there are many.
Look up "RNA world".

Basically, we'd expect the stuff we identify as "life" to be really common and turns up pretty much wherever it can possibly happen. The basic molecules are common, and you have to try hard not to get life to happen. Organisms do not have to use DNA to pass heredity, they do not need to be carbon-based. As we explore our own solar system more closely we should be able to get clues that will give us an idea of how common life is. Whatever the future outcome, the lesson of history is that treating humans as somehow special in the Universe is not the way to go. Scientific progress is made when humans are removed from the central role in Creation: it's a fundamental and important humility in Science.

 

[Stephanus]

Thanks Simon.

Is "LIFE" different from "life"?

Of course not. It's just an emphasis

That's actually a different question: it seems very unlikely that there will be a duplicate Earth out there.

Yes, unlikely. That's why my immediate respond was

My immediate response would be, in parallel universe where there are Nicole Kidman, Megan Fox, Linday Lohan OR in this universe.

"Do you believe there is another earth?"

Calculations based on the probability of getting life as in a duplicate Earth biosphere are misplaced.

I believe what my Pastor meant was "Do you think there is life in exoplanet?". But I think he's not much of a scientist, it's just a figure of speech.

You mean "carbon based" ... few biologists would consider any carbon compound to be living.
You should think of "live" as a class of emergent properties or behaviours arising from complicated processes.

Oh

Id life possible off the Earth: almost certainly yes.

Thank you

There would almost certainly be carbon based life off the Earth somewhere.

Thank you

... there will almost certainly be DNA based life elsewhere in the Universe...

Thank you

Certain? So the possibility will be very high.
And was just wondering if the intelligence creature there would be humanoid.
In the ocean, dolphin (and whales) and the extinct ichtyosaurs are fish like. Perhaps advanced life form under water is fish like.
Perhaps intelligence life is humanoid? Although they may only have four fingers like ET.

There would almost certainly be carbon based life off the Earth somewhere.
Among other approaches, there will almost certainly be DNA based life elsewhere in the Universe. You are probably thinking of "reproduction" rather than replication ... DNA is not the only replicating molecule: there are many.
Look up "RNA world".

Basically, we'd expect the stuff we identify as "life" to be really common and turns up pretty much wherever it can possibly happen. The basic molecules are common, and you have to try hard not to get life to happen. Organisms do not have to use DNA to pass heredity, they do not need to be carbon-based. As we explore our own solar system more closely we should be able to get clues that will give us an idea of how common life is. Whatever the future outcome, the lesson of history is that treating humans as somehow special in the Universe is not the way to go. Scientific progress is made when humans are removed from the central role in Creation: it's a fundamental and important humility in Science.

Thank you very much for your opinion Simon.

 

[Simon Bridge]

Certain? So the possibility will be very high.

I said: "almost certain" ... but yes, it is reasonable to expect the probability of there being life other than on the Earth to be very high.
You should be careful when religious people ask you about the probability if life, it is a common argument against evolution.

And was just wondering if the intelligence creature there would be humanoid.

The "humanoid" bodyplan is basically that of fish.
There are many more bodyplans possible - iirc most of the bodyplans that have ever emerged on the Earth went extinct through being unlucky rather than being slowly selected out. So it would be unreasonable to expect this bodyplan to be strikingly present on exoplanets. The only reason it is so noticable on the Earth is that we have it too.

We have to be careful about what we mean by "intelligence" too: we tend to define this term to suit ourselves and we may be a bit too smug about it.
Looking around us even today there are many strikingly bright animals - maybe even some that are self-aware. Expecting a human-like intellegence, if it should occur, to appear in a human-like body plan seems like too much.

In the ocean, dolphin (and whales) and the extinct ichtyosaurs are fish like. Perhaps advanced life form under water is fish like.

Perhaps sure - but that's just empty speculation. The way to go is to ask if there is any special reason to suppose that intellegence prefers to appear in fish-like forms. You got to realize that the humanoid body plan is not even all that common on the Earth.

 

[Drakkith]

Certain? So the possibility will be very high.

We really have no idea. But, have you ever taken a look at the Hubble Ultra Deep Field? There are somewhere around 10,000 galaxies in that picture. And it covers an area of the sky smaller than the full moon. So, given incomprehensible number of star systems in the billions upon billions of galaxies just in the observable universe alone, I think it would be extremely unlikely that life exists solely here on Earth and nowhere else.

 

[Stephanus]

I said: "almost certain" ... but yes, it is reasonable to expect the probability of there being life other than on the Earth to be very high.
You should be careful when religious people ask you about the probability if life, it is a common argument against evolution.

Yes Simon. But it's not the religious side that I want to discuss here in PF. It's just that I've never given thought of what would extra terrestrial life be. I often watch Startrek, Star wars, alien, etc. But never gave it a thought. It's just that last week I analyze.
IF there is a life in exoplanet, what would that be. Carbon based, DNA, mass of the star, etc... It's really not about religion

 

[Simon Bridge]

It's really not about religion

Didn't think it was - just raising awareness of an issue that plagues all too many of us.

It's not a very big "IF".
Like if you rolled 10 dice and got something other than 10 6's, you wouldn't be all that surprised right? Life is more likely than that. Much much more.
So if someone said: "IF I don't roll all sixes..." ... well you'd wonder why the emphasis.

Space is big, really big...

 

[Ophiolite]

One thing to keep in mind, Stephanus, that Simon Bridge has touched on: we only have one example of a biosphere. We are strongly influenced in our perspective on the nature of life by what we see on Earth. We talk of the Goldilocks zone, Earth like planets, carbon based lifeforms, water as the active solvent and present well reasoned arguments to support this focus.

This may turn out to be the truth. However, I always caution about extrapolating from a sample size of one. The fact is that we do not know how common life may be, or how common intelligent life may be, or even if we might be the only planet with life in the entire universe. That just makes it interesting.

If you would like to explore the topic more you might consider reading Rare Earth by Ward and Brownlee. Their conclusion: life is common, intelligent life very rare.

 

[Stephanus]

Didn't think it was - just raising awareness of an issue that plagues all too many of us.

It's not a very big "IF".
Like if you rolled 10 dice and got something other than 10 6's, you wouldn't be all that surprised right? Life is more likely than that. Much much more.
So if someone said: "IF I don't roll all sixes..." ... well you'd wonder why the emphasis.

Space is big, really big...

So, the reason why ET haven't phoned us yet is that space is really big.
I'm just wondering. Supposed, just supposed there's a civilization, say 100 thousands years more advanced than us, (star trek is only 300 years). They would have conquered any galaxies I think.
And 100 thousands years are not really that much.
But carbon based and DNA is enough for my curiosity. I just want to know that if there's life out there, how is the chance that it's carbon based. And if it is, how is the chance that it develops DNA.
Thank you guys.

 

[russ_watters]

Dear PF Forum,
I would like to know if LIFE in exoplanet is possible. And if it is, how?

I'm not sure what exactly you mean by "how", but if life is possible here, why wouldn't it be possible on another planet with similar conditions?

 

[Stephanus]

The "humanoid" bodyplan is basically that of fish.
There are many more bodyplans possible - ...

So, humanoid is not common. Okay

 

[Stephanus]

I'm not sure what exactly you mean by "how", but if life is possible here, why wouldn't it be possible on another planet with similar conditions?

That's what I want to know. Not in biological term but in mathematic point of view.
How big is this "similar conditions" chance.
And even if it's not "similar", just as @Simon Bridge says, it's likely carbon based and DNA. Thanks.

 

[|Glitch|]

Dear PF Forum,
I would like to know if LIFE in exoplanet is possible. And if it is, how?
When I drove my Pastor to my mother funeral, he asked me out of the blue while I was driving my car.
"Do you believe there is another earth?"
My immediate response would be, in parallel universe where there are Nicole Kidman, Megan Fox, Linday Lohan OR in this universe.
"In this universe," he said.
So there were the following problems I think.
First, life should be in a planet or moon (as in Avatar).
This planet must be supported by a nearby star.
And for this star:
I think the star cannot be too massive. I read that the comparisson between the mass of the star and its lifespan in main sequence is to the power of 3.
For example, a 2 solar mass star will have 1/8 lifespan of our sun.
10 solar mass star will have 1/1000 lifespan of the sun. That is: 10 million years.
Earth develop life form in 3.9 billion years. "Only" in 600 million years ago (Cambrium) there were many multilcellular organism blooming in the ocean. Trilobite, nautilus, etc...
And it takes 4.5 billion years for Earth to develop intelligence.
And the star cannot be too light, because if it's too cold, then the planet should be closer to the sun, then there are tidal lock problem, and radiaton.
So how is the chance for this universe to have, IMHO, stars that are 0.8 - 1.2 solar mass?
For these stars to have planet in their habitable zone?
I'm not trying to bring Drake Equation, just want to lay out the facts.

And after all those...
What would that lifeform be?
Will it be carbon compound? Since carbon has 4 valence and
View attachment 96801
Carbon is abundance in the universe. I don't know if this number represents carbon in outer space nebulae, or locked in white dwarf stars.
Silicon and Germanium have 4 valence, too. But since they are more complex than carbon, I think carbon is easier to build element compound rather than Si/Ge. And Carbon is more abundance than Si/Ge.
And IF the lifeform in exoplanet is carbon based, would they develop DNA as their method to replicate?
So my summary questions are these:
1. Given those conditions, would extra terrestrial life be possible?
2. IF it is possible, would it be carbon based?
3. IF it is carbon based, would it develop DNA as their replication method?

Thank you very much.

Without actual empirical proof nobody can say with absolute certainty that life exists beyond the planet Earth. However, as others have already noted, the odds are so statistically high that some form of life exists beyond the planet Earth that it can be said to be "almost certain." Consider that we have discovered evidence of life on Earth as far back as ≈3.8 billion years ago. There does not need to be an identical Earth out there, just one that is close. Obviously the planet needs to be within the habitable zone of its star and have a sufficiently dense enough atmosphere to support liquid water on its surface. However, the atmospheric pressure could vary significantly, and there does not necessarily need to be a moon, or there may be more than one moon.

Most of the main sequence stars (at least in the Milky Way) are spectral type M (76.45%), 12.1% are spectral type K stars, 7.6% are spectral type G stars, and 3% are spectral type F stars. Ideally, a main sequence star should be somewhere between 0.75 M_☉ and 1.25 M_☉ to give life the best opportunity to evolve for long periods, but as we discovered on Earth it does not take life very long before it gets started. In just under a billion years after the formation of Earth life had already begun. Therefore, it is possible for life to begin even under much higher mass stars, and thus stars with shorter life-spans.

Approximately 60% of the main sequence stars in the Milky Way galaxy have planets. A much smaller fraction of these planets will fall within the habitable zone of their star. However, considering the number of stars in the Milky Way galaxy alone, a reasonable estimate would be ≈40 billion Earth-size planets within the habitable zone of their star. That would seem to stack the odds rather heavily in favor of life existing beyond Earth just in the Milky Way galaxy, and there are billions of other galaxies that we are not even including.

There were multicellular lifeforms prior to the Cambrian. The Cambrian marks when arthropods evolved and a real diversity of life began, thus the phrase the "Cambrian Explosion." However, jelly fish and other soft-bodied multicellular lifeforms (including some forms of multicellular algae) existed for millions of years prior to the Cambrian.

Therefore, while no one can say with absolute certainty - until definitive irrefutable proof is eventually found - one can say with "almost certainty" that life must exist somewhere in the Milky Way galaxy.

Source:
http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?2001JRASC..95...32L&data_type=PDF_HIGH&whole_paper=YES&type=PRINTER&filetype=.pdf - Journal of the Royal Astronomical Society of Canada, Vol. 95, p.32, published February 2001.

 

[Stephanus]

One thing to keep in mind, Stephanus, that Simon Bridge has touched on: we only have one example of a biosphere. We are strongly influenced in our perspective on the nature of life by what we see on Earth. We talk of the Goldilocks zone, Earth like planets, carbon based lifeforms, water as the active solvent and present well reasoned arguments to support this focus.

Well, hydrogen, oxygen, carbon are abundant elements in this universe:
https://en.wikipedia.org/wiki/Abundance_of_the_chemical_elements

Their conclusion: life is common, intelligent life very rare.

I like it!

 

[russ_watters]

That's what I want to know. Not in biological term but in mathematic point of view.
How big is this "similar conditions" chance.

Are you familiar with the Drake equation?
https://en.wikipedia.org/wiki/Drake_equation

Even 20 years ago it was so wildly speculative that it was utterly useless (it is mostly a thought exercise), but since then we have learned a lot more about the universe. Including:
1. 20 years ago, the Hubble Deep Field revealed that the entire universe is utterly filled with galaxies.
2. We've learned that life seems to have arisen on Earth very soon after it became hospitable to our form of life.
3. In the past 5 years, we've discovered that most stars have planets around them. We've only been capable of detecting the large ones, but it stands to reason that there are a lot of solar systems similar to ours.

The one thing standing in the way of intelligent life that I can see is the fact that simple life existed on Earth for billions of years before complex life arose. So the jump from bacteria to animals may be more difficult than the start of life itself.

 

[russ_watters]

Without actual empirical proof nobody can say with absolute certainty that life exists beyond the planet Earth. However, as others have already noted, the odds are so statistically high that some form of life exists beyond the planet Earth that it can be said to be "almost certain."

I watched a pretty decent TV documentary on the Webb space telescope and it appears to be the general conclusion of the scientists working on it that life elsewhere in the galaxy - and relatively nearby - is near inevitable.

 

[Simon Bridge]

That's what I want to know. Not in biological term but in mathematic point of view.

Nobody knows any reason life should not be almost certain someplace.
As to the maths:

I don't think anyone knows enough to put a number on the odds ... it's just that the odds would have to be extremely long indeed for there to be even odds that we are the only ones in the whole visible Universe ever. That's the sort of calculation you can do.

You can also work out how likely the sort of life that the SETI project would have to be to give them an even chance of finding some.

Using just statistics, this is the best you can do ... you need data from things like biology and astrophysics to get a better guess.
See post #15 for examples.

 

[Stephanus]

Are you familiar with the Drake equation?
https://en.wikipedia.org/wiki/Drake_equation

Read it yes. Understand it, no. But many people thought that Drake equation has too many unexplained variables. It's like Ferim problem in space.

1. 20 years ago, the Hubble Deep Field revealed that the entire universe is utterly filled with galaxies.

Carl Sagan once said that there are 100 billions galaxies in this observable universe. Care to tell me what is the estimate now?

2. We've learned that life seems to have arisen on Earth very soon after it became hospitable to our form of life.

Yes. @|Glitch| says it's 3.8 billions years. But lately I heard that, as you say, life arose very soon after Earth became hospitable, perhaps after heavy bombardment period? But I just let his statement goes.

The one thing standing in the way of intelligent life that I can see is the fact that simple life existed on Earth for billions of years before complex life arose. So the jump from bacteria to animals may be more difficult than the start of life itself.

Please confirm:
From bacteria to animal is more difficult than from raw material to a single living cell? Because of statement number 2?

Thanks

 

[Stephanus]

I watched a pretty decent TV documentary on the Webb space telescope and it appears to be the general conclusion of the scientists working on it that life elsewhere in the galaxy - and relatively nearby - is near inevitable.

Wow!

 

[|Glitch|]

I watched a pretty decent TV documentary on the Webb space telescope and it appears to be the general conclusion of the scientists working on it that life elsewhere in the galaxy - and relatively nearby - is near inevitable.

I don't know how "near by," but I would not consider it unreasonable to say that the percentage is better than 99.9% in favor of life existing somewhere within the Milky Way presently, and much higher if you consider the 13+ billion years the Milky Way has been around. We have a tendency to only look at life in its present context. If we consider the 9+ billion years before our solar system even existed, the odds of life forming increase significantly.

 

[Stephanus]

...but I would not consider it unreasonable to say that the percentage is better than 99.9% in favor of life existing somewhere within the Milky Way...

99%. But why haven't ET phoned home? Or we can only capture EM wave? Perhaps much intelligence life communicates with something else?
I think it just like a primitive tribes trying to search smoke sign, while every body communicates with radio frequency.

 

[russ_watters]

Carl Sagan once said that there are 100 billions galaxies in this observable universe. Care to tell me what is the estimate now?

I'm not sure when he said that, but he may have been referring to the Hubble Deep Field. See the below video:



He points to a picture 30 seconds in that looks somewhat like the Hubble Deep Field (maybe a zoomed in piece of it?), but may not be. Later, at 1:20 there is a shot that definitely is the Hubble Deep Field, but it may have been edited in. In any case, googling, 100 billion seems to be about the accepted number.

I once calculated it myself (it is on my website) and came up with 150 billion...

 

[russ_watters]

99%. But why haven't ET phoned home? Or we can only capture EM wave? Perhaps much intelligence life communicates with something else?

See this recent thread:
https://www.physicsforums.com/threads/how-far-outward-can-we-rule-out-intelligent-life.856376/

Several problems:
1. "Life" doesn't necessarily mean intelligent life.
2. Radio signals aren't necessarily a great way to communicate.
3. Really, in order to be detectable a long way off, it almost has to be done on purpose and if we haven't tried it but once, briefly, why would ET?

Details:
I think it is possible we will detect radio signals from other intelligent life, but there are a number of barriers, not the least of which is that radio, as it was originally used, was horribly inefficient. We now transmit less than we did 20 years ago because of improvements in efficiency.

Even with strong signals such as military radar, we'd probably only be able to detect them out to a few hundred light years. Only if someone was actively transmitting along a narrow beam, would it be possible more than about 1,000 light years.

See, the Aricebo message, directed at the M13 star cluster, 25,000 light years away:
https://en.wikipedia.org/wiki/Arecibo_message

 

[Simon Bridge]

Compared to the size of the visible Universe, pretty much anything in the local galactic cluster is relatively nearby.
The "near certainty" estimate is because of the vastness of the Universe ... the same reason is why ET has not called us.

You need to get a feel for these numbers ... I'll tell a story:
i.e. a really optimistic figure from ages ago meant that the average separation for the closest two intellegence-bearing systems would be was about 250-300 light years. If they were exactly us, then how would they have got a signal to us? For us to receive the signal today, it had to be sent 250 years ago ... what would they use: semaphore?
Lets say they were more advanced, had really advanced optics and were observing us, learning all about our culture etc, and they decided to send a greeting (anticipating that we'd have developed the technology to receive the message in 250 years) ... and we got that greeting from them today: what would they say? The message would be based on how we looked 500 years ago... what was human culture like then?
See why we haven't heard from any of them?

While life in the Universe is almost certain, the probability that it is close enough to talk to is going to be small.

 

[|Glitch|]

99%. But why haven't ET phoned home? Or we can only capture EM wave? Perhaps much intelligence life communicates with something else?
I think it just like a primitive tribes trying to search smoke sign, while every body communicates with radio frequency.

Sentient life, or life that is self-aware, is a completely different matter. I was simply referring to life, which would include single-cellular and multi-cellular non-intelligent life. From that evolves intelligent life, or life with a memory and able to solve simple problems. After that comes sentient life, or life that is aware of its own mortality. Each preceding form of life is more rare than the former. For such life to evolve takes an exceedingly rare set of circumstances.

The vast majority of life probably does not evolve to intelligence. Those rare forms of life that do evolve intelligence most likely never survive to evolve sentience. The small handful of life forms that do become sentient most likely do not evolve anywhere remotely near the same time period, and may be separated by so much space as to be effectively isolated. 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, the oceans will boil off, and no life on Earth will be possible. In the grand scheme of things, half a billion years is not very long. More than a dozen civilizations could have sprung up and died off, each separated by half a billion years, long before Earth ever formed.

 

[Chronos]

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.

 

[enorbet]

I think it is important to remember that our Universe is not only unimaginably vast in Size (and population of planets) but also vast in Time especially relative to the entire time anything remotely resembling humans or any other possibly "intelligent" lifeforms have existed in our experience. It is possible to miss communication since civilizations rarely last much more than a mere million years, and have the technology to communicate for a mere thousand.

Since you mentioned Carl Sagan, recall his Galactic Calendar and how on that scale all of any life on Earth takes place in a fraction of the last few minutes of the last day, iirc. Furthermore, Mr Sagan pointed out that one of the more important reasons for contacting ET is "How did you do it? How did you survive the Technology to destroy yourselves?". Hawking spoke of this also in Brief History of Time citing Langauge as accelerating one kind of Evolution while our base instincts evolve at a crawl. So nobody knows how long a civilization can last, let alone if any have.

Another thing to consider was touched on wisely by Simon regarding the difficulties of a sample of one combined with our egocentric nature. We mostly consider whales and dolphins, let alone parrots and octopi, as animals beneath us even if they have a higher concentration of neural connections. Just consider how surprised everyone was to discover lifeforms at extreme temperatures and pressures, such as deep within rock and at Black Smokers/HydroThermal Vents undersea. The definition of the conditions under which Life can flourish seem to widen all the time. Fred Hoyle postulated in fiction a space-ferring intelligent cloud and some scientists wonder if life is possible under frozen seas far from our Sun, or high in the atmospheres of even Gas Giants. We won't know much of anything until we begin to discover extraterrestrial life somewhere other than here, a relatively closed system.

Certainly the odds went up and it is very important that the building blocks of organic materials have been found in vast abundance essentially everywhere. However until we can actually examine (or communicate with) other lifeforms than Earth forms, we are stuck with a very limited perspective and speculation. This is likely why NASA has "homed in" on Mars and the possibility of microbial life there. If and when that is confirmed, that will be a very big day for Science.

 

[Stephanus]

I'm not sure when he said that, but he may have been referring to the Hubble Deep Field. See the below video:

He did say billions and billions. Billions stars in billions galaxies. I forgot about "100 billions". Too bad, Carl died not long after HST became operational.

I once calculated it myself (it is on my website) and came up with 150 billion...

Very interesting, attractive, educating site you have .

Several problems:

1. "Life" doesn't necessarily mean intelligent life.

Actually what I want to know in this thread are:
1. What is the probability that life can arise in this universe beyond earth. This thread has replied: Very, very high
2. Would it be carbon based? @Simon Bridge says "Yes". Good, because when I talked to my pastor, I just fired away "carbon based", I was afraid that I was wrong, but I'm not
3. If it is carbon based, would it be DNA? The answer is Yes

2. Radio signals aren't necessarily a great way to communicate.

Okay, perhaps I should rephrase my question:
Is electromagnetic wave a way to communicate and to search outer civilization?

3. Really, in order to be detectable a long way off, it almost has to be done on purpose and if we haven't tried it but once, briefly, why would ET?

Oh

See, the Aricebo message, directed at the M13 star cluster, 25,000 light years away:
https://en.wikipedia.org/wiki/Arecibo_message

Concerning this message:

1. The numbers one (1) to ten (10)
Okay... 1 through ten in binary.
1 - 7 in 1 column. 8 - 10 in 2 columns.

2. The atomic numbers of the elements hydrogen, carbon, nitrogen, oxygen, and phosphorus...
1, 6, 7, 8, 15. Okay...

3. The formulas for the sugars and bases in the nucleotides of DNA (green)
H₇C₅N₀O₁P₀ or C₅H₇O
Searching in Google it's 1-Cyclopenten-1-olate. I thought, I would find 4 sugars. Adenine, Cytosine, Guanine, Thymine.

6. A graphic of the Solar System indicating which of the planets the message is coming from (yellow)
There are 9 planets in this message
Carl would have risen from his grave if he knew that one if his pupil (Degrasse Tyson) erased Pluto in 2006

Wow, if this plate dropped in my backyard, without Wiki explanation, I wouldn't have any ide what it is. I hope those aliens in M13 can decipher it. And it's not a plate isn't it. It's a radio signal.
By the way, ist it Hydrogen times Pi frequency like in Contact?

 

[Stephanus]

Compared to the size of the visible Universe...
While life in the Universe is almost certain, the probability that it is close enough to talk to is going to be small.

I like it!
- Life is almost certain
- Communication is very difficult.
No one ever discuss it. I only read "The absent of proof is not the proof of absent" and things like that. At least I get a feeling that we're not alone.

 

[Stephanus]

You need to get a feel for these numbers ... I'll tell a story:
i.e. a really optimistic figure ...If they were exactly us, then how would they have got a signal to us? For us to receive the signal today, it had to be sent 250 years ago ... what would they use: semaphore?

But how can two civilization in this universe can be said similar?
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.
What about us vs something that is 3000 years advanced. It's just like us vs Star wars.
And even 30 thousands years is nothing 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.