How far outward can we rule out intelligent life?

[Chronos]

This is not the place for speculation, or personal theories. Discussion should be constrained to science as we know it, or reasonable extensions thereof.

 

[phinds]

45 billion light years, that's the definition of the Hubble Radius.

Odd that no one has caught this. Your answer is sort of correct when answering "how far away are those object NOW. I say "sort of" because "now" is a bit ambiguous in this context. However, the actual question you were specifically answering was "how far away were they when they emitted the light that we see now?" and 45Billon light years is too large by at least a factor of 1000.

 

[Alltimegreat1]

I thought the response provided by newjerseyrunner couldn't possibly be correct, but I'm not a trained scientist so I didn't challenge it. Would you mind taking a crack at this question: With regard to the most distant objects at the edge of our observable universe, approximately how far away from the Earth were they when they emitted the light that we see today?

 

[rootone]

... With regard to the most distant objects at the edge of our observable universe, approximately how far away from the Earth were they when they emitted the light that we see today?

The expansion rate appears to have varied over time so it's not easy to be precise, but the ball-park figure is as phinds says a factor of around 1000x.
So that would be about 45 million light years (as opposed to billions).

 

[irenebaron]

The variable of a planet harboring intelligent life comparable to or greater than ours, in my opinion, would make no difference as to how close one would be to Earth.

Note: The NASA opinion is that EVERY STAR HAS AT LEAST ONE PLANET.

When you consider (a) the Hubble Telescope spending ten-days photographing one long time exposure a "straw-sized" segment of dark space and (b) coming up with a photograph of over 10,000 galaxies, you begin to realize that the number of planets possible in our known universe is most likely beyond our comprehension. Consider what the visible light Hubble Telescope or variable wavelength Webb Telescope (such as infrared) would find in between those galaxies. The "edge" of the known universe as we know it of under 20-billion light years in distance from Earth will be expanded infinitely. The quantity of galaxies and their billions of stars and their increasing number of planets will be beyond our concept of quantity. Every known bit of knowledge about space as we understand it today is nanoinfinitesimal compared to what is going to be learned in the future with advance technology. Welcome that information to expand your concepts of what is beyond our system of Sol and current known universe.

Interesting question and one which I will address in a post to my blog later this week. You may check it out later at: www.irenebaron.com.

 

[|Glitch|]

Let's assume there is a planet out there with life equally intelligent as humans that is putting in the exact same amount of effort to detect alien life that we are. Their science and technology also developed in line with human technology. Given that we're looking and they're looking, what is the closest this planet could be to us given that we don't know about them (yet)? Any guesses?

That is an almost impossible question to answer. If a nearby civilization evolved and produced radio waves for a few hundred years ten thousand years ago, we would never know about it. However, if that civilization evolved ten thousand light years away, we would just be detecting those radio signals today, assuming they were strong enough to be detected. The odds of any civilization developing the same technology at the same time is astronomically small. If we ever do detect radio signals from a distant civilization, they will most likely already be extinct by the time we detect them.

 

[Loren]

The short answer, it's unlikely there are any ETI's with our level of development or greater within 100 light years of Earth. That's about the distance we could detect a powerful military radar with the square kilometer array.

Edit: I now see that russ_watters answered this question above. Note that since our Galaxy is so large, there could easily be 100's of civilizations more advanced than ours, but just outside of our current range of detection. Just to elaborate, if the Universe is infinite, or even near infinite, it's probable that there would be a near infinite number of civilizations more advanced than ours.

Radio is not the only signature we have to detect life. We are just at the cusp of using technology to look for signs of life's footprint on the atmosphere of other worlds.

But to answer the original question, we are just getting into the game with our search and we don't know very much about life given we only have a sample size of one.

 

[IllyaKuryakin]

Loren, I was responding to the original question that was a thought experiment based on intelligent life like ours. We could branch out from there in any number of directions with different forms of life that existed in the past or in the possible future, or speculative methods of communications and detection, but just to keep the discussion within some sort of bounds, I'll stick with my original parameters and estimate. There are probably no creatures like us or more advanced than us within 100 light years of Earth, or we would have picked up their signals. If there were ETI's just like us within 100 LY of earth, we'd still have to account for transmission delays which means they would actually have needed to be broadcasting 100 years earlier, or be 100 years more advanced than us. Even so, we would only be able to pick up powerful beamed military radars and such to detect their presence with our current level of technology. We wouldn't be able to listen to their omnidirectional radio and TV programs even from the distance of the nearest star, about 4.24 LY away, as those signals are far too weak.

Since our Galaxy is about 100,000 light years across, that's still a very small sample of our local neighborhood. It wasn't the original premise of the question, but as you say, in the very near future we may have methods that can detect some forms of life at much greater distances, like resolving the spectra of chlorophyll or even modern industrial pollution on a distant planet.

 

[IllyaKuryakin]

OK, but as for intelligent creatures like us living on a planet 100 light years away from Earth the chance is slim. If there are 5000 ( a guess) suns within 100 light years of us, let's assume maybe 100 have life. But a civilization? Thats rare and its possible there's one but I doubt it. On the other hand, if each galaxy has 100 civilizations and there are say 10^9 galaxies, that's 10^11 civilizations. Regardless our species is very special and hopefully will rise above the shallow predator mentality.

I agree. The possibility of other advanced civilizations is discussed at length in the book, Rare Earth, by Peter D. Ward (Author), Donald Brownlee (Author). It's a great book on the subject. The conclusion is we are very rare and special. I also hope we someday act like it.

 

[write4u]

IllyaKuryakin,
I agree. The possibility of other advanced civilizations is discussed at length in the book, Rare Earth, by Peter D. Ward (Author), Donald Brownlee (Author). It's a great book on the subject. The conclusion is we are very rare and special. I also hope we someday act like it.

I guess you did not see the lecture on the origins of life, by Robert Hazen at the Carnegie Institute of Science, which proposes that the probability for other forms of life throughout the universe is almost a certainty. Human type (highly intelligent) life may be rare, but not necessarily unique.
(the actual lecture starts at 25:00)

 

[IllyaKuryakin]

I guess you did not see the lecture on the origins of life, by Robert Hazen at the Carnegie Institute of Science, which proposes that the probability for other forms of life throughout the universe is almost a certainty. Human type (highly intelligent) life may be rare, but not necessarily unique.

Oh, I agree completely. It seems very unlikely, given the vastness of the Universe, that we would be the only intelligent life. Most estimates predict very many occurrences of simpler forms of life, but very few occurrences of intelligent life, i.e. life capable of building a radio. That's essentially the conclusion of the book, Rare Earth.

Consider the only real example we have, the Earth. About 5 billion species of life have lived on Earth. About 99 percent of those are now extinct. Out of all those 5 billion lifeforms, only one is known to ever have evolved to the point that they could build a radio. Extending that observation outward, there could be thousands of locations with simple forms of life near the Earth, and even a few with more advanced forms, like whales and dolphins or primates, but the odds of an advanced form of life that can build a radio existing near the Earth might be much less than one in a thousand. In science, when something has less than a 1 in 1,000 chance of occurring, we generally assume that it wont. Of course, it's all a game of probabilities. Just because something is highly improbable, that doesn't mean it's impossible, especially considering the long time and large number of possible locations for such an event to occur, as Dr. Hazen pointed out in his lecture. Indeed, we are an example of that improbable event occurring, so we are sure it's at least possible. Good discussion. Thanks for that link!

 

[phinds]

but the odds of an advanced form of life that can build a radio existing near the Earth might be much less than one in a thousand. In science, when something has less than a 1 in 1,000 chance of occurring...

Sure, maybe one in a thousand over some large amount of the cosmos, perhaps even over a significant portion of the Milky Way (though I doubt it) but over the whole universe? Even just the observable universe (which is, of course, all that can really matter to us)? How can you come up with such a number?

 

[mgkii]

I'm thinking, all the way up to Donald Trump's apartment door.

So will the world actually end when he's President in charge of the big red BOOM button... or will it just seem like it?

To give much narrower answer to the OPs question; if you take the opening line from the wiki page on SETI history as an arbitrary date for when we started to actively look for ET, then anything communicating from further than 120 light years away** would still not have reached us by any light-speed comms method.
(** +/- corrections for relativity, expansion, dilation, tri-lation, saturation, one-nation,,,,,, and a host of other things I don't even know I don't know about!)

As early as 1896, Nikola Tesla suggested that an extreme version of his wireless electrical transmission system could be used to contact beings on Mars.[5] In 1899 while conducting experiments at his Colorado Springs experimental station, he thought he had detected a signal from the planet since an odd repetitive static signal seemed to cut off when Mars set in the night sky

 

[write4u]

Oh, I agree completely. It seems very unlikely, given the vastness of the Universe, that we would be the only intelligent life. Most estimates predict very many occurrences of simpler forms of life, but very few occurrences of intelligent life, i.e. life capable of building a radio. That's essentially the conclusion of the book, Rare Earth.

Sure, maybe one in a thousand over some large amount of the cosmos, perhaps even over a significant portion of the Milky Way (though I doubt it) but over the whole universe? Even just the observable universe (which is, of course, all that can really matter to us)? How can you come up with such a number?

Well, to my knowledge, human intelligence is one of those *rare* (low probability) events* Hazen speaks of.

As I understand it our brain is due to a drastic mutation in hominid chromosomal evolution. While we are descendent from a common ancestor, humans have one less chromosome than other hominids, but the missing chromosomes was due to the accidental fusion of two chromosomes into one larger chromosome, which might well be the cause for our divergence from the other hominid species.

All great apes have 24 pairs of chromosomes, whereas humans have 23 chromosomes. There is a hypothesis that the common ancestor of all great apes also had 24 pairs of chromosomes and that the fusion of two of the ancestor's chromosomes created chromosome 2 in humans. The evidence for this hypothesis is very strong

http://www.evolutionpages.com/chromosome_2.htm

I like the philosophy of *necessity and sufficiency* as a fundamental concept of evolutionary adaptation to the environment.

Almost all species have extraordinary abilities in one area or another. Many animals posess extraordinary abilities far advanced over human physical abilities in such areas as strength, speed, flight, smell, hearing, unassisted short range communication, sight (ability to see infrared or ultraviolet colors) beyond our ability to see. All sufficient to assure a good chance to survive the test of natural selection for those species.
.
It is clear that all great apes have sufficient intelligence to have made it this far, whereas human intelligence seems to far outstrip our need and is more than sufficient than is necessary for our survival. In fact our brain may well have evolved too soon, in view of our lack of wisdom in our use of this extraordinary ability for advanced abstract thought.

 

[nikkkom]

My baseline is the earth, where insects had mastered flight 600 million years ago. We need only look at the variety of surface, aquatic, and flight capable organisms very early on to get an idea of what is not only possible, but probable

You are looking at a wrong time interval. What's important is not how old insects are now, but how long did it take for them to appear.

The answer is: more than 3 billion years.

There is evidence that simple (unicellular) life on Earth appeared fairly soon, within first 0.5 billion years. This taking into account that it wasn't the calmest period in geologic history, by a long shot.

But multicellular life, especially differentiated one (i.e. not cell mats), took very long to appear: 3.5 billion years.

It's possible that this was a very unlikely fluke, and most other planets with life in the Universe are populated by their analogs of cyanobacteria.

 

[write4u]

You are looking at a wrong time interval. What's important is not how old insects are now, but how long did it take for them to appear.
The answer is: more than 3 billion years.

I see no major conflict in our position. I was addressing a special ability (flight)practised by insects 10-15 million years ahead of the appearance of birds.

There is evidence that simple (unicellular) life on Earth appeared fairly soon, within first 0.5 billion years. This taking into account that it wasn't the calmest period in geologic history, by a long shot.

Watch the Robert Hazen lecture, which I linked in previous posts.

But multicellular life, especially differentiated one (i.e. not cell mats), took very long to appear: 3.5 billion years.

I see no major conflict in our position.

It's possible that this was a very unlikely fluke, and most other planets with life in the Universe are populated by their analogs of cyanobacteria.

Robert Hazen proposes that biochemicals are abundant in the universe and that the Earth is not a special planet, but that it requires only an average rocky planet with oxygen and water to eventually (inevitably) produce bio-chemistry and the beginning of bio-molecules, which then evolved into complex bio-organisms. The exact times are not important, all that matters is that complex bio-molecules almost inevitably will form, given enough time and under the right conditions.

In the Hazen lecture one scientist proposes that, given our knowledge of universal chemistry and minerology, life itself (in one form or another) was a universal imperative.

 

[IllyaKuryakin]

Sure, maybe one in a thousand over some large amount of the cosmos, perhaps even over a significant portion of the Milky Way (though I doubt it) but over the whole universe? Even just the observable universe (which is, of course, all that can really matter to us)? How can you come up with such a number?

Sorry, I can't understand your question. I gave the reasoning for my numbers in my post. Five billion species have evolved on earth, but only one could build a radio. By that reasoning, species of life capable of building a radio seem to be very rare, and others are very unlikely to have occurred near Earth at the same time as we are able to detect them. I would call something that occurs in less than 1 in 1000 opportunities rare, but here we have an event that has occurred in only one of many millions of opportunities, so it might be fair to call it extremely rare.

I agree that if you are willing to search half way across the Galaxy, you are likely to find another "radio making" species, simply because of the very large number of locations available for such species to evolve, but the original premise of the question was the likelihood of being able to detect another ETI within 100 LY of Earth. As others have stated in this thread, we probably have the technology to detect those signals now, if they exist. I'm making the case here that the reason we haven't detected such signals is that they do not exist within our current range of detection. Depending on how you want to calculate the Drake Equation, one might need to go ten's of thousands of light years to find another radio building species. If that's the case, it's unlikely we would ever detect it with our current technology. Now, if we photograph a star at 10,000 light years surrounded by a Dyson Sphere in the near future, I'll gladly eat those words.

 

[rootone]

Then again, a civilization existing inside a perfect Dyson sphere might not be detectable anyway unless it's close enough to be detectable gravitationally.

 

[phinds]

Sorry, I can't understand your question. I gave the reasoning for my numbers in my post. Five billion species have evolved on earth, but only one could build a radio...

You're right, I was not focused on that part of your reasoning. I do tend to forget about that aspect of things. BUT ... given that so many species have evolved on Earth, to some point, and then died off, why would it not be reasonable that just as many would have evolved on exoplanets, including one that builds radios.

Also, as you pointed out, your response was concerning a very small area of the cosmos and my thinking went much further out so my response to you was off base.

 

[write4u]

You're right, I was not focused on that part of your reasoning. I do tend to forget about that aspect of things. BUT ... given that so many species have evolved on Earth, to some point, and then died off, why would it not be reasonable that just as many would have evolved on exoplanets, including one that builds radios.

Also, as you pointed out, your response was concerning a very small area of the cosmos and my thinking went much further out so my response to you was off base.

Acording to Hazen, he estimates that the number of chemical reactions in the life of Earth is somewhere in the neighborhood of : 4 trillion, quadrillion, quadrillion, quadrillion chemical interactions.

That's just on earth. And complex organisms can form through a host of different chemical models. So intelligent life does not necessarily have to evolve exactly as it did for humans. There may be many different pathways to form complex biological organisms.

 

[Alltimegreat1]

I just disovered today the term "radio bubble," which extends 110 LY from the Earth in all directions. This bubble around the Earth contains 15,000 stars.

 

[nikkkom]

I see no major conflict in our position. I was addressing a special ability (flight)practised by insects 10-15 million years ahead of the appearance of birds. Watch the Robert Hazen lecture, which I linked in previous posts. I see no major conflict in our position. Robert Hazen proposes that biochemicals are abundant in the universe and that the Earth is not a special planet, but that it requires only an average rocky planet with oxygen and water to eventually (inevitably) produce bio-chemistry and the beginning of bio-molecules, which then evolved into complex bio-organisms. The exact times are not important, all that matters is that complex bio-molecules almost inevitably will form, given enough time and under the right conditions.

My point is, average "enough time" for appearance of differentiated multicellular life may be very large. Say, much larger than current age of the Universe. It's possible that we are a very unlikely statistical fluke.

"Something is bound to eventually happen" does not equal practically meaningful probability above zero. Example: a neutrino can scatter off other particles via gravitational interaction. But its probability is so astoundingly tiny that even if human civilization will spend the rest of eternity (until heat death of the Universe) trying to detect such an event, it will never be seen.

 

[Dr Barkus]

Let's assume there is a planet out there with life equally intelligent as humans that is putting in the exact same amount of effort to detect alien life that we are. Their science and technology also developed in line with human technology. Given that we're looking and they're looking, what is the closest this planet could be to us given that we don't know about them (yet)? Any guesses?

One overlooked question is could intelligent life evolve on planets that are unsuitable for us? If it transpires that only Earth type planets can evolve intelligent life then there maybe only a few of these per galaxy hence the quietness

 

[|Glitch|]

One overlooked question is could intelligent life evolve on planets that are unsuitable for us? If it transpires that only Earth type planets can evolve intelligent life then there maybe only a few of these per galaxy hence the quietness

intelligent life can certainly evolve on planets that are unsuitable to humans. Intelligent life has evolved on Earth in environments that are totally unsuitable to humans, so why not elsewhere?

 

[Rx7man]

I think the timeframes we're looking at here are SO NARROW.. we've had technology for what.. 100 years?.. Perhaps in another few hundred years we'll have wiped ourselves out.. If that is a pattern that happens on other planets that could or have had intelligent life, the timeframe is so small there's a good chance we'd never witness it, even if we were looking in the right place.

And the definition of intelligent life seems a little narrowminded in itself.. Perhaps if we defined it as radio-capable intelligent life it would be more accurate. For billions of years we've had intelligent life on earth, though it never broadcasted any radio signals.
For the Fermi paradox.. I think we ought to worry more about what perils we're setting ourselves up for at our own hand than the slight chance that an alien will pick up our signals and come destroy us... Yes, it makes for (debateably) good sci-fi movies, but trivializes what we're doing ourselves