Will we ever communicate with extraterrestial life in a reasonable time frame?

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  • #1
KurtLudwig
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Granted that life exists somewhere. Just by stating that are 200 billion stars in the Milky Way galaxy tends to make us believe that intelligent life is close by.

We need to set a limit of 100 years to send and receive one answer. This necessary requirement will greatly reduce the possibility of any contact.
How many planets similar to Earth are within 50 light years?
What are the energy requirements to send that message?
What is the lowest signal we can reliably detect?

Many star systems contain two and three stars. Will planets in such systems have stable orbits to allow life billions of years to evolve?
Even if we find planets that can harbor life today, what was the history of such planets? We do not know.
 
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  • #2
Since this list piles speculation on top of speculation, how do you expect a scientific answer?
 
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  • #3
No.
Humans are too primitive and do not have the intelligence necessary to understand or communicate with ET life.
 
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  • #4
Let me rephrase. Since this list piles speculation on top of speculation, how do you expect a scientific answer? Furthermore, a lot of these are thing you could look up yourself, like how many stars are within a given radius. If it's not important enough to you to do it, why should it be important enough for us yp do it for you?
 
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  • #5
KurtLudwig said:
How many planets similar to Earth are within 50 light years?
That depends on how similar you want them to be. Rocky and in the habitable zone: Should be well over 100.
KurtLudwig said:
What are the energy requirements to send that message?
Existing telescopes on Earth could communicate with equivalent telescopes on the other planets within ~100 light years (with some limited capability beyond that) - if we send a directed signal there and they look in our direction and vice versa.
KurtLudwig said:
Many star systems contain two and three stars. Will planets in such systems have stable orbits to allow life billions of years to evolve?
We have found many exoplanets in stable orbits in multi-star systems.

"Reasonable time frame" is not a physical constant. You probably chose 100 years because that's of the order of a current human lifespan. An animal that only lives for a year would conclude that there are no stars in range for a reasonable time frame. What if future technology increases our lifespan to 1000 years? Or make us almost immortal?
 
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  • #6
mfb said:
What if future technology increases our lifespan to 1000 years? Or make us almost immortal?
The nightmare scenario!
 
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  • #7
Vanadium 50 said:
Let me rephrase. Since this list piles speculation on top of speculation, how do you expect a scientific answer? Furthermore, a lot of these are thing you could look up yourself, like how many stars are within a given radius. If it's not important enough to you to do it, why should it be important enough for us yp do it for you?
I had researched the number of stars and possible exoplanets around those stars at various distances from Earth. At 5,000 light years a two way conversation would take 10,000 years. Then I set a limit for a two way communication at 100 years, more than an average person's lifetime.
At Atlasoftheuniverse.com, it was stated that there are 133 visible stars and over 1000 within 50 light years, resulting in 4,000 exoplanets. in my opinion, not that many at all.
 
  • #8
Of great concern is the reception of a signal from an exoplanet. Is it even possible? On Earth, how can we receive a signal by pointing a telescope at a distant star with a circling exoplanet. The star emits electromagnetic radiation in all frequencies. How powerful could the signal be - a quadrillionth of its star's emission? The signal to noise ratio is all noise!
 
  • #9
You gain a factor ~1 million from a directional emission, and another factor ~1 billion from emitting in a narrow frequency range, and another factor ~1 billion from emitting far away from the Sun's peak, and suddenly your emitter outshines the Sun.
PeroK said:
The nightmare scenario!
If it happens it'll change our perspective on time.
 
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  • #10
Something no one has even mentioned so far is that if it takes 100 years for a signal to get somewhere and another 100 years for the response to get back, political and/or societal upheaval could well be such that no one will be listening for a response after 200 years.
 
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  • #11
Well, when you looked it up on Wikipedia, you would have discovered there are 130 K, G and F type stars within 50 light years. You also, when you looked it up on Wikipedia, learned that estimates from Kepler are that 1.4-2.7% of such stars have planets in their habitable zones. That's 2-3, one of which is the sun.

So, there are 1 or 2 candidate stars. To have a civilization, this requires that the star not only has planets in the habitable zone, but that these planets are habitable. The sun has, arguably four: Venus, the Earth, the Moon, and Mars. Only one is habitable.

The rest is speculation, but I point out:
  • For half of earth's history, there were no eukaryotes
  • For 75% of eukaryote history, there were no multicelluar organisms
  • For 99.5% of multicelluar life history, there were no people (genus homo)
  • For 99.5% of human (genus homo again) existence, there was no civilization.
  • For 99% of civilization, radios did not exist.
Give all that, 1 or 2 candidate stars does not seem like a lot.
 
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  • #12
Oh, @Vanadium 50 there you go again, bringing logic and facts into a nonsense discussion. You spoilsport. :smile:
 
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  • #13
Guilty.
 
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  • #14
Vanadium 50 said:
Well, when you looked it up on Wikipedia, you would have discovered there are 130 K, G and F type stars within 50 light years. You also, when you looked it up on Wikipedia, learned that estimates from Kepler are that 1.4-2.7% of such stars have planets in their habitable zones. That's 2-3, one of which is the sun.

So, there are 1 or 2 candidate stars. To have a civilization, this requires that the star not only has planets in the habitable zone, but that these planets are habitable. The sun has, arguably four: Venus, the Earth, the Moon, and Mars. Only one is habitable.

The rest is speculation, but I point out:
  • For half of earth's history, there were no eukaryotes
  • For 75% of eukaryote history, there were no multicelluar organisms
  • For 99.5% of multicelluar life history, there were no people (genus homo)
  • For 99.5% of human (genus homo again) existence, there was no civilization.
  • For 99% of civilization, radios did not exist.
Give all that, 1 or 2 candidate stars does not seem like a lot.
Thank you for your reply. I did learn something.
Therefore the probability is that there is no intelligent and technically advanced life within 50 light years. So the distance has to be increased to increase the probability of finding intelligent and technically advanced life on a planet.
Increasing the distance to 250 light years, will increase the response time to 500 years. It will increase the probability by the cube. 5 times the distance results in 125 times the volume. 1.5 candidates within 50 light years, results in a probability of 188 candidates within 250 light years. Will we and they still be watching for a signal or is the time frame just too long? The monitoring will need to be automated, which I assume has been done.
 
  • #15
mfb said:
You gain a factor ~1 million from a directional emission, and another factor ~1 billion from emitting in a narrow frequency range, and another factor ~1 billion from emitting far away from the Sun's peak, and suddenly your emitter outshines the Sun.
If it happens it'll change our perspective on time.
From your reply, I assume that this is being done by SETI in the radio frequency band.
Thanks for your answer.
I am always trying to learn when reading threads on physics forums.
 
  • #16
Vanadium 50 said:
Well, when you looked it up on Wikipedia, you would have discovered there are 130 K, G and F type stars within 50 light years. You also, when you looked it up on Wikipedia, learned that estimates from Kepler are that 1.4-2.7% of such stars have planets in their habitable zones. That's 2-3, one of which is the sun.

So, there are 1 or 2 candidate stars. To have a civilization, this requires that the star not only has planets in the habitable zone, but that these planets are habitable. The sun has, arguably four: Venus, the Earth, the Moon, and Mars. Only one is habitable.

The rest is speculation, but I point out:
  • For half of earth's history, there were no eukaryotes
  • For 75% of eukaryote history, there were no multicelluar organisms
  • For 99.5% of multicelluar life history, there were no people (genus homo)
  • For 99.5% of human (genus homo again) existence, there was no civilization.
  • For 99% of civilization, radios did not exist.
Give all that, 1 or 2 candidate stars does not seem like a lot.
See: "Drake Equation," THE speculator's speculation.
 
  • #17
All of what I wrote down is maybe two terms in the Drake Equation.

Extrapolating from a single data point is, well, better than from zero data points, but not much. And there are things we just don't know - multicelluarlsm (is that a word?) evolved two dozen times, but was lost in most instances. Why? It also appears to have evolved late. Again, why?

One could argue that you don't get intelligence without a metabolism based on oxidation rather than photosynthesis and reduction, so you need to wait until the atmosphere is mostly plant poop. Maybe so. But this will reduce the probability a given planet will ever develop intelligence. Probably lots of planets evolve cyanobacteria, who then eat all the CO2 and possibly water in the atmosphere, causing the planet to freeze and that, as they say, is that.

I would not be surprised if pond scum (or at least extinct pond scun) is common, but anything beyond that is rare. But what do I know? This thread isn't about science - it's about guesswork.
 
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  • #18
There's an enlightening video on line by a British professor explaining why the sheer number of stars and exoplanets does not guarantee an abundance of intelligent life. The issue, in a nutshell, is that however many plantets there are, the probability of the evolution of an intelligent civilisation could be correspondingly small.

For that reason it's not possible to estimate whether:

a) We are the only advanced civilisation in the galaxy.

b) There are 1-10 other advanced civilisations.

c) 11-100

d) 100+

You can't even make an intelligent guess in that multiple choice.
 
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  • #19
Vanadium 50 said:
Well, when you looked it up on Wikipedia, you would have discovered there are 130 K, G and F type stars within 50 light years.
And many more M type stars.
Vanadium 50 said:
You also, when you looked it up on Wikipedia, learned that estimates from Kepler are that 1.4-2.7% of such stars have planets in their habitable zones. That's 2-3, one of which is the sun.
I don't know where you get that number from. "from Wikipedia" is neither a clear nor a good reference and the number is far too low. Maybe it's just planets discovered by Kepler? That requires a line of sight which makes most planets unobservable for Kepler. This study predicts ~0.5 terrestrial planets in the habitable zone per star. Combine that with the point from above and we get more than 100 terrestrial planets in the habitable zone within 50 light years.
You shouldn't subtract the Sun because our perspective is necessarily from a habitable planet, by the way.
Vanadium 50 said:
The sun has, arguably four: Venus, the Earth, the Moon, and Mars. Only one is habitable.
The Moon is not a planet and Venus is not in the habitable zone, so we only have two. One has life, one looks like it had favorable conditions for life in the past.

The chance to find another civilization at the same technological level is absurdly tiny, but it's possible civilizations will stay around for a while. Maybe we can receive and transmit radio waves for a million years or longer. I don't know, and I don't want to assign a probability to that either.
 
  • #20
mfb said:
I don't know where you get that number from
Catanzar1 et al. ApJ 738 151 (2011)

mfb said:
Venus is not in the habitable zone
If Earth were on Venus orbit, the mean temperature would be 150 F. Too hot? Maybe, maybe not. But this won't make any difference - if I shrink the habitable zone, the fraction of habitable planets goes up, but the number of candidates goes down by the same factor.
mfb said:
The Moon is not a planet
It would be if it were in its own orbit. And if there were intelligent life on a moon, it would "count" as far as the OP is concerned.

However, I question the entire premise of your post. I reported this as speculation untethered by science, and the Mentors elected to keep this thread going. Fine. Your call. But you can't then turn around and complain my speculations don't match your speculations.
 
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  • #21
KurtLudwig said:
From your reply, I assume that this is being done by SETI in the radio frequency band.
Thanks for your answer.
I am always trying to learn when reading threads on physics forums.
Are you kidding? But of course the extra-terrestrial beings will speak English!


(please interpret properly; I am joking.)
 
  • #22
My guess is that this topic will make no more progress than has already been posted, so readers may like to be reminded of the Twilight Zone episode, To Serve Man.
 
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  • #23
Or The Sinpsons take on it in one of the (possibly the very first) Treehouse of Horror episodes.

 
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  • #24
I'm reading a book titled "The Third Chimpanzee," by Jared Diamond, who also wrote "Guns, Germs, and Steel." BTW, "third chimpanzee" refers to us Homo Sapiens, whose DNA is closer to common chimps and pygmy chimps than to any other animals.

In the chimpanzee book Diamond reaches pretty much the same conclusion as have many in this thread, that since we haven't heard from any beings elsewhere in the universe, there aren't a whole lot of them out there. OTOH, if there are others who are sufficiently advanced to be able to send a signal strong enough to reach us, it's likely that they are way more advanced than we are, and we should not encourage them to come here. This conclusion is reached by comparing how we humans have treated other species not advanced as we are, even those species like the chimps whose DNA is so close to ours.
 
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  • #25
And of and to Vanadium 50, about post #23 the Simpsons video,
See, they really do speak English!
 
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  • #26
A technological civilization needs a first, easily obtainable energy source. Another interesting wrinkle is that it took very particular conditions to create Earth’s vast coal deposits - plant matter in wetlands needs to be buried quickly in peat. A planet that developed without these phenomena would then have its hydrocarbons predominantly in harder to extract oil and natural gas. Difficult to imagine industrialization without this easy energy source and equally difficult to think about drilling for oil or natural gas with early 18th century metallurgy.
 
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  • #27
BWV said:
A technological civilization needs a first, easily obtainable energy source.
Whale oil. Peat. Charcoal. Alien-bovine gas emissions.

I don't see this as an insurmountable problem, although it might slow things down quite a bit. I think the bigger issue is to support a high enough rate of metabolism (see "plant poop" above) as it took the Earth a very long time to get past.

Another is our DNA fidelity. The error rate during reproduction is about one in a million. It's checked twice - if it were checked once it would be 1:1000 which is too high for survival most of the time, and if it were checked three times, evolution would grind to a halt. It may have taken a very long time to get this working right.

There's also the issue of "how intelligent is intelligent". Intelligence evolved three times - arthropods, cephalopods, and chordates. But it's energy intensive, and the first two are constrained by the availability of oxygen.
 
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  • #28
Vanadium 50 said:
Whale oil. Peat. Charcoal.
A planet with abundant peat that had been around long enough would have coal, the others do not scale. A living forest cannot compete with millions of years of dead forest as a sustainable energy source

The US consumed 1,100 petajoules of coal in 1870 vs about 1 PJ of whale oil (source). Coal was a miracle energy source compared with other options available
 
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  • #29
Vanadium 50 said:
The rest is speculation, but I point out:
  • For half of earth's history, there were no eukaryotes
  • For 75% of eukaryote history, there were no multicelluar organisms
  • For 99.5% of multicelluar life history, there were no people (genus homo)
  • For 99.5% of human (genus homo again) existence, there was no civilization.
  • For 99% of civilization, radios did not exist.
So you're telling me there's a chance!

 
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  • #30
I save that for special occasions, along with Billy Madison and "I award you no points, and may God have mercy on your soul."
 
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  • #31
Vanadium 50 said:
Catanzar1 et al. ApJ 738 151 (2011)
Online
That's based on the first four months of Kepler data, it's only looking at Sun-like stars, and only considering "Earth analog" planets. Kepler had no chance to observe three transits for habitable planets around Sun-like stars in that time so there is a huge amount of extrapolation involved as well.

Edit: Wikipedia's article explicitly references this as "older study" for historic context, it has a much larger more recent estimate in the previous paragraph.
Vanadium 50 said:
But this won't make any difference - if I shrink the habitable zone, the fraction of habitable planets goes up, but the number of candidates goes down by the same factor.
It does make a difference because the references count planets in the habitable zone, not some much larger area. Venus-like planets and moons are not included in the numbers for planets in the habitable zone, so you shouldn't include them in your comparison either.
Vanadium 50 said:
However, I question the entire premise of your post. I reported this as speculation untethered by science, and the Mentors elected to keep this thread going. Fine. Your call. But you can't then turn around and complain my speculations don't match your speculations.
There are published numbers and reliable estimates we can discuss.
 
  • #32
Vanadium 50 said:
Well, when you looked it up on Wikipedia, you would have discovered there are 130 K, G and F type stars within 50 light years. You also, when you looked it up on Wikipedia, learned that estimates from Kepler are that 1.4-2.7% of such stars have planets in their habitable zones. That's 2-3, one of which is the sun.

So, there are 1 or 2 candidate stars. To have a civilization, this requires that the star not only has planets in the habitable zone, but that these planets are habitable. The sun has, arguably four: Venus, the Earth, the Moon, and Mars. Only one is habitable.

The rest is speculation, but I point out:
  • For half of earth's history, there were no eukaryotes
  • For 75% of eukaryote history, there were no multicelluar organisms
  • For 99.5% of multicelluar life history, there were no people (genus homo)
  • For 99.5% of human (genus homo again) existence, there was no civilization.
  • For 99% of civilization, radios did not exist.
Give all that, 1 or 2 candidate stars does not seem like a lot.
It comes back to Arthur C. Clarke's argument about Apes or Angles..
 
  • #33
I didn't read it. Lots of extraneous stuff on that link, and when he says the Earth will last a (US) trillion more years, he's using outdated information. How outdated? Could it be "jungles of Venus" outdated? Maybe, maybe not.

There is certainly a lot we don't know, such as how long technological civilizations last. We do know that the scientific method could have taken root in at least four cultures, but did not.

I suspect - but certainly do not know - that energetics plays an important role. That's not good for intelligent life, because K class stars are far more common than G and F's and the brighter the star, the shorter its life. It may well be that dim stars never get going, and bright stars usually don't last long enough. Or not. How would you know?
 
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  • #34
@sbrothy : Did you really mean "Angles"? I'm just a midwestern boy.....but.....that sounds wrong to me.
 
  • #35
Yup. Follow the link and press pgdwn once. In my opinion he makes a compelling argument.
 

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