# Is the solar system special?



## Venusian Broon (Nov 13, 2021)

A very nice video on the subject. Could also be interesting for those writing interstellar SF!


----------



## HareBrain (Nov 13, 2021)

It's the only one with me in it.


----------



## Venusian Broon (Nov 13, 2021)

HareBrain said:


> It's the only one with me in it.



Oddly the Harebrain in Lambda Serpentis told me this too.


----------



## hitmouse (Nov 13, 2021)

HareBrain said:


> It's the only one with me in it.


Yeah exactly. It is pretty feckin special to me too, no matter what those influencers in Ursa Major may say.


----------



## Fiberglass Cyborg (Nov 14, 2021)

I feel like it's more "particular" than "special." 

Both from this video and wider reading, I get the impression that planetary systems are extremely diverse. Elsewhere in the cosmos, people may be smugly proclaiming: "I don't see how life could /possibly/ arise on any world that is not a carbon-rich mini hot Neptune in a binary relationship with an exposed iron planetary core, orbiting an orange dwarf star alongside several super-Earths, the star itself being in a distant binary relationship with a Wolf-Rayet star that gives out life-producing gamma radiation yet is orbited by a sub-brown dwarf that hoovers up rogue comets. Anything else is inconcievable."

I read a book a few years ago which also argued that the Mediocrity Principle can be seriously misleading at times. Think it was "The Copernicus Complex" by Caleb Sharf (it was a a library book, so I'm not certain.) My favourite source on exoplanets is "The Planet Factory" by Elizabeth Tasker- her focus is theories of planet formation, and she covers a lot of the more exotic stuff.


----------



## Venusian Broon (Nov 15, 2021)

Fiberglass Cyborg said:


> I feel like it's more "particular" than "special."
> 
> Both from this video and wider reading, I get the impression that planetary systems are extremely diverse. Elsewhere in the cosmos, people may be smugly proclaiming: "I don't see how life could /possibly/ arise on any world that is not a carbon-rich mini hot Neptune in a binary relationship with an exposed iron planetary core, orbiting an orange dwarf star alongside several super-Earths, the star itself being in a distant binary relationship with a Wolf-Rayet star that gives out life-producing gamma radiation yet is orbited by a sub-brown dwarf that hoovers up rogue comets. Anything else is inconcievable."



I totally agree with you that we have no conception of the 'range of parameters' that will allow life on alien systems (hell, even on our own solar system), and furthermore what causes intelligent life to flourish in our universe. We are working, essentially, with a sample of one. Who knows? We need more data!

And, the Copernican principle is useful in tempering our hubris. Let it be our 'base case'. However, the lack of "signals" from alien civilisations re: Fermi Paradox is somewhat perplexing. 

Better I feel, however, a universe with mysteries than one with a fixed sterile robotic "purpose".


----------



## Ursa major (Nov 15, 2021)

hitmouse said:


> no matter what those influencers in Ursa Major may say


Oi!

Your solar system is not special until I say it's special. (I haven't said so, and may never do so.)


----------



## M. Robert Gibson (Nov 15, 2021)

Have you been watching Brian Cox's Universe?








						Universe
					

Professor Brian Cox reveals epic moments of sheer drama that changed the universe forever.




					www.bbc.co.uk
				




The second episode explores the possibility of alien life


----------



## Vertigo (Nov 15, 2021)

Interesting video. I've been suggesting for some time now that the conditions that have favoured life on Earth might (and I do stress _might_) be unusual or even rare. I've also been suggesting that the more we learn the more this seems to be the case.

From the point of view of life that raises the question; does this matter? If it is true that life will appear wherever conditions make it possible then no it probably doesn't; there will still be lots of stellar systems out there with planets that might possibly support life and so it is likely that life is at least moderately abundant out there. However, I am getting steadily less optimistic that that is the case. I would suggest that it is wrong to say that we have a data sample of only one. I would rather say we have a sample of several planets or moons that could theoretically have, or have had, life on them. And yet we haven't found any signs yet; nothing on Mars, the only one we've had a realtively close look at, but also no tell tale signs of life on any of the others we have looked at. Obviously that still doesn't mean there are none but as we look ever closer and find nothing I do think the probability of life being common wherever it is possible does seem to be diminishing. Not vanished, of course, but definitely, in my view lessening rather than increasing.

This is not the conclusion I want to come to but I find little to persuade me that new discoveries and contradicting it.

And incidentally I just want to say how nice it is to see a presentation like this that doesn't talk about all the solar systems out there. There is only one star called Sol so there is only one solar system and lots of stellar systems. This video made the piont of always talking about other solar system-like systems. Hooray!!


----------



## paranoid marvin (Nov 15, 2021)

The chances for the development of life are incredibly small. But the fact that we know it is possible, even if those odds are tiny, means that that in a Universe as vast - perhaps even infinite - as ours, there is a good possibility of life developing elsewhere than Earth.

The problem is that the time for life to exist (in Universal time) is tiny, and the distances between everything so vast, that two lifeforms having the chance to have any kind of meaningful communication in the same place and at the same place are quite possibly zero.

I do think that we will find some form of life - either past or present - on one of our planets or moons. We haven't found it yet, but if the right conditions are (or have been) there then logically and scientifically it should be there, as there is nothing special about Earth that Mars didn't have a long time ago.

The fact that whilst the equipment we have is (for us) at the forefront of scientific skill and knowledge, it still amounts to a Big Trak (remember those?) in the middle of a desert wasteland trying to find it. If we find life on Mars with current technology, I would be very surprised. I think it will need a concerted human-led mission and perhaps many years of building , exploring and excavating to find what we are looking for. More likely we may find some very basic form of life in the water/ice of one of the moons of the other planets.

The key thing for me is that whole point of a Universe is to generate life. If it didn't, then it would serve no purpose. And we know that in nature, everything has a reason to be where it is.

What is a great pity for me is that we are not making a more concerted effort to escape our world and reach out to other planets. We all know that even if we manage not to ruin our ecosystem that at some point a rock will come floating by and reset the clock to give another lifeform a chance on the Earth. Although colonisation of Mars is still beyond our means, a base of operations on the Moon should have happened decades ago.


----------



## Vertigo (Nov 16, 2021)

paranoid marvin said:


> What is a great pity for me is that we are not making a more concerted effort to escape our world and reach out to other planets. We all know that even if we manage not to ruin our ecosystem that at some point a rock will come floating by and reset the clock to give another lifeform a chance on the Earth. Although colonisation of Mars is still beyond our means, a base of operations on the Moon should have happened decades ago.


Funnily enough I've just (last night) finished the second of Mary Robinette Kowal's Lady Astronaut books about an alternative future in which we have been hit by just such a rock in 1952 providing the impetus to get into space much faster than we have actually done. Really very good and very solidly based hard science fiction addressing how this could have been achieved in the '50s and '60s.


----------



## Wayne Mack (Nov 16, 2021)

I suspect that this might be more of a discussion of semantics than of science. I suggest that special is not a yes-no attribute, but one of degree. Our solar system is both special and not special depending on the specific attributes identified. I also believe that observation has not identified any attributes that could not be explained via naturally occurring forces.


----------



## paranoid marvin (Nov 17, 2021)

Wayne Mack said:


> I suspect that this might be more of a discussion of semantics than of science. I suggest that special is not a yes-no attribute, but one of degree. Our solar system is both special and not special depending on the specific attributes identified. I also believe that observation has not identified any attributes that could not be explained via naturally occurring forces.




The circumstances for life to occur in our solar system and on our planet required quite a number of very specific things to happen at a very specific time. Anything that interrupted it - say a stray asteroid or anyone of a million other things - could have put paid to it. And it needed for the same specific things to keep occurring for a very long time , with no outside interference.

But as I mentioned above, the fact it _has_ happened means that we know  it _can_ happen. And if it's happened once, it can happen again.

As you say, every thing that has led to the build up of life can be scientifically explained. But what can't be explained is how something can come from nothing or just why nature is so intricate and beautiful.


----------



## Vertigo (Nov 17, 2021)

paranoid marvin said:


> The circumstances for life to occur in our solar system and on our planet required quite a number of very specific things to happen at a very specific time. Anything that interrupted it - say a stray asteroid or anyone of a million other things - could have put paid to it. And it needed for the same specific things to keep occurring for a very long time , with no outside interference.
> 
> But as I mentioned above, the fact it _has_ happened means that we know  it _can_ happen. And if it's happened once, it can happen again.


This is absolutely right! What's often wrong (not that you are suggesting it!) and is specifically what that video addresses is that just because it has happened once it is not necessarily a common occurrence. And in fact the video suggests quite the opposite. Going from that, as some will do, to talk about the almost infinite number of star systems in the universe making abiogenesis frequent is, I think, a little meaningless. The intergalactic distances are so great that it is really only sensible to think about our place in our own galaxy. From that I conclude that there is almost certainly other life out there but the indications are that it might not be all that common, and it's possible that anything more complex than microbial life might be even less common. That jump from prokaryote to eukaryote was a pretty staggering evolutionary leap and there is no evidence that it (or the original abiogenesis for that matter) happened more than once.


----------



## Venusian Broon (Nov 17, 2021)

Vertigo said:


> This is absolutely right! What's often wrong (not that you are suggesting it!) and is specifically what that video addresses is that just because it has happened once it is not necessarily a common occurrence. And in fact the video suggests quite the opposite. Going from that, as some will do, to talk about the almost infinite number of star systems in the universe making abiogenesis frequent is, I think, a little meaningless. The intergalactic distances are so great that it is really only sensible to think about our place in our own galaxy. From that I conclude that there is almost certainly other life out there but the indications are that it might not be all that common, and it's possible that anything more complex than microbial life might be even less common. That jump from prokaryote to eukaryote was a pretty staggering evolutionary leap and there is no evidence that it (or the original abiogenesis for that matter) happened more than once.



I more optimistic that microbial life will be 'common'; that we have not observed any evidence of it outside the Earth's biosphere speaks more of the inability of our technology to perform little more than rudimentary (but quickly improving!) observations and simple experiments with our probes. Europa is enticing in our prediction that there could be liquid water there...but trying to get a probe down there to have a look, through 100km of ice seems like long-term science fiction. (I guess look at the cracks or geyers to see if organic material is being ejected too, perhaps....) 

One must remember that not only are we seperated by vast distances, we are seperated by the vast scales of time. We are talking about looking at a 'snapshot' of time in the universe. Mars and Venus may have been a paradise for bacterial life billions of years ago and we may find the fossilised remains if we dig deep enough in the Martian regolith (I fear Venus's surface has long baked away any evidence and trying to get anything down there to dig into it - forget it!). Titan may just be far too cold for complex chemistry to spur on Abiogenesis now, but in a billion years time, as the sun's output steadily increases, that may change. 

I remember pre-1987 when you could hold a viewpoint that perhaps planets are not common at all around stars, but our observations since then have exploded as technology has gone to places I didn't think was possible, and shown a dazzling array of worlds and situations that really we did not think might exist. I think it will be the same for microbes.  We just need to get out there and explore and observe.


----------



## Vertigo (Nov 17, 2021)

Venusian Broon said:


> I more optimistic that microbial life will be 'common'; that we have not observed any evidence of it outside the Earth's biosphere speaks more of the inability of our technology to perform little more than rudimentary (but quickly improving!) observations and simple experiments with our probes. Europa is enticing in our prediction that there could be liquid water there...but trying to get a probe down there to have a look, through 100km of ice seems like long-term science fiction. (I guess look at the cracks or geyers to see if organic material is being ejected too, perhaps....)
> 
> One must remember that not only are we seperated by vast distances, we are seperated by the vast scales of time. We are talking about looking at a 'snapshot' of time in the universe. Mars and Venus may have been a paradise for bacterial life billions of years ago and we may find the fossilised remains if we dig deep enough in the Martian regolith (I fear Venus's surface has long baked away any evidence and trying to get anything down there to dig into it - forget it!). Titan may just be far too cold for complex chemistry to spur on Abiogenesis now, but in a billion years time, as the sun's output steadily increases, that may change.
> 
> I remember pre-1987 when you could hold a viewpoint that perhaps planets are not common at all around stars, but our observations since then have exploded as technology has gone to places I didn't think was possible, and shown a dazzling array of worlds and situations that really we did not think might exist. I think it will be the same for microbes.  We just need to get out there and explore and observe.


It will be hugely interesting to see if the hoped for resolution of the James Webb telescope will allow the analysis of exoplanetary atmospheres. Reading between the lines I have the impression this is hoped for but by no means certain.


----------



## Venusian Broon (Nov 17, 2021)

Vertigo said:


> It will be hugely interesting to see if the hoped for resolution of the James Webb telescope will allow the analysis of exoplanetary atmospheres. Reading between the lines I have the impression this is hoped for but by no means certain.


And by no means a hit if we find somethung like an oxygen rich atmosphere or methane, say, there could be chemical atmospheric & geological processes that might give such a signal, rather than biological.


----------



## Vertigo (Nov 17, 2021)

There are other atmospheric indicators though: 
Biosignature - Wikipedia 
Down the page a little there is a section on atmospheric.


----------



## Venusian Broon (Nov 17, 2021)

Vertigo said:


> There are other atmospheric indicators though:
> Biosignature - Wikipedia
> Down the page a little there is a section on atmospheric.


I heard that it might be possible for James Webb to pick up light on the dark side of planets (if close enough of course), therefore potentially picking up 'civilisational' signatures.


----------



## Vertigo (Nov 17, 2021)

Venusian Broon said:


> I heard that it might be possible for James Webb to pick up light on the dark side of planets (if close enough of course), therefore potentially picking up 'civilisational' signatures.


Whoa, that would represent some serious levels of sensitivity!


----------



## Venusian Broon (Nov 17, 2021)

Vertigo said:


> Whoa, that would represent some serious levels of sensitivity!


Well, one is full of hope for such a telescope, it has loads of lnteresting targets other than planets, saggitarius A*, the first stars etc....but no doubt as soon as it goes up, they will find something wrong with it that hinders it a 'la Hubble


----------



## Vertigo (Nov 17, 2021)

Venusian Broon said:


> Well, one is full of hope for such a telescope, it has loads of lnteresting targets other than planets, saggitarius A*, the first stars etc....but no doubt as soon as it goes up, they will find something wrong with it that hinders it a 'la Hubble


I thought you were the optimist a few posts back!


----------



## Venusian Broon (Nov 17, 2021)

Vertigo said:


> I thought you were the optimist a few posts back!


About the cosmos, humans are naturally error prone.


----------



## RJM Corbet (Nov 17, 2021)

@Venusian Broon
Thanks for the video

I think life is far more subtle than the carbon or silicon based, liquid water dependent  life forms that we as humans are looking for. I think perhaps life exists pretty much everywhere in the universe, including our solar system, but we don't even know what to start to look for. I mean, we couldn't recognize it as living by the terms we understand?

Our truly brilliant science is still just always an ingenious way of extending the perception of our natural senses of sight, hearing and so in, to an jncredible degree. Watching that Mars lander sequence was to be blown away by the imagination and capablity of these scientific people to calculate and design and engineer to the Nth degree. Wonderful.

But IMO there may be senses and dimensions beyond our ability even to conceive.

Perhaps our stunning 21st century technology is indeed starting to demonstrate just how scarce may be the fine-tuning parameters for life as we know it to originate, at least within any range of ourselves that we can ever hope to test.

Holding breath for the James Webb, finally set to go after all the years. More nail biting stuff ...


----------



## RJM Corbet (Nov 17, 2021)

Repeat posting. Mods please delete


----------



## paranoid marvin (Nov 18, 2021)

RJM Corbet said:


> @Venusian Broon
> Thanks for the video
> 
> I think life is far more subtle than the carbon or silicon based, liquid water dependent  life forms that we as humans are looking for. I think perhaps life exists pretty much everywhere in the universe, including our solar system, but we don't even know what to start to look for. I mean, we couldn't recognize it as living by the terms we understand?
> ...




I agree. Our criteria for what we deem as 'life' and what conditions are possible for life to exist in are far from definitive. I think not long ago creatures found living at the bottom of the ocean existed in conditions which thought impossible for life; and that is on our own planet!

In terms of exploring the galaxy (never mind the universe) we are still at the stage of sticking a sand into the desert and hoping to discover buried treasure. Though I suspect that the human race, in the brief moment of time allotted to us, will never expand beyond our home here on Earth, and many of the mysteries of the Universe will never be revealed to us. Which is a shame.


----------



## RJM Corbet (Nov 18, 2021)

paranoid marvin said:


> I agree. Our criteria for what we deem as 'life' and what conditions are possible for life to exist in are far from definitive. I think not long ago creatures found living at the bottom of the ocean existed in conditions which thought impossible for life; and that is on our own planet!
> 
> In terms of exploring the galaxy (never mind the universe) we are still at the stage of sticking a sand into the desert and hoping to discover buried treasure. Though I suspect that the human race, in the brief moment of time allotted to us, will never expand beyond our home here on Earth, and many of the mysteries of the Universe will never be revealed to us. Which is a shame.


And possibly other life-forms would look right past us, as we would them, unable to recognise one another as living entities?

Why should man be unable to regard or recognise the Earth and other planets as living entities? Do fleas recognise the dog they're on, lol?


----------



## Justin Swanton (Nov 18, 2021)

Another way of looking at the solar system is to see it as it is rather than as we hope it will be. What it is, is a dramatic contrast between Earth and everything else. On Earth life can exist from about 2km underground to about 6km above the surface. That's a sliver 8km thick. Everything outside of that sliver is intensely hostile to life. In space a human can hope to survive, unprotected, for about 90 seconds. The most resilient organism, the tardigrad, might last a week. No planet lengthens that survival time and most shorten it. The delicate and fantastically complex structure of carbon-base life forms requires some very specific conditions to exist and only the surface of the Earth supplies those conditions. The universe as a near-total whole is not for us. But it is very beautiful.


----------



## M. Robert Gibson (Nov 18, 2021)

Obligatory Douglas Adams quote

“It is known that there are an infinite number of worlds, simply because there is an infinite amount of space for them to be in. However, not every one of them is inhabited. Therefore, there must be a finite number of inhabited worlds. Any finite number divided by infinity is as near to nothing as makes no odds, so the average population of all the planets in the Universe can be said to be zero. From this it follows that the population of the whole Universe is also zero, and that any people you may meet from time to time are merely the products of a deranged imagination.”


----------



## paranoid marvin (Nov 19, 2021)

I also like his other quote 

'Space is big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist's, but that's just peanuts to space.'

I miss Douglas Adams.


----------



## Extollager (Nov 19, 2021)

What will be the social consequences if civilization persists on this planet, even space exploration continues, but in 50 years there is still zero evidence for life anywhere else?


----------



## Justin Swanton (Nov 19, 2021)

Extollager said:


> What will be the social consequences if civilization persists on this planet, even space exploration continues, but in 50 years there is still zero evidence for life anywhere else?


Nothing will change. We'll still be convinced there's life out there somewhere. Personally I'm not convinced, but it's easy to argue that humanity could continue another million years on Earth and *never* become aware of life on other planets since the distances are just too great, even for signals.


----------



## Elckerlyc (Nov 19, 2021)

Hardly any, I would think. A lot less anyway than would be the case if evidence for alien life were actually found. "Be patient," they'll say, "Give it another 50 years, when we are able to leave our own solar system." The universe is too unimaginable vast to allow anyone to say at any one point, "We searched everywhere, without result. Now we're certain we're alone."

For most of human history the notion of alien life was totally... alien. Until about 100 years ago. Since then the awareness of the possibility has slowly grown more common, but hardly generally accepted. Is all highly hypothetical and will remain just that as along as evidence is lacking.


----------



## Extollager (Nov 19, 2021)

I do wonder about how the stubborn non-appearance of evidence for extraterrestrial life might affect large numbers of people, most of whom will not have a firm grasp of the vast distances, etc.  The fact is that popular entertainments and so on endlessly reiterate the idea that the discovery of an advanced civilization is only a matter of time.  

For example, a poll from four years ago:









						Poll Shows What Americans Think About Life On Other Planets
					

Poll Shows What Americans Think About Life On Other Planets




					www.huffpost.com
				




That's a lot of people who believe that there is some sort of scientific evidence for extraterrestrial life.  So it's a part of popular consciousness.

Thus I do wonder what might be the situation in 50 years if there's no more real evidence then than there is now for "life."  Will people have been prepared to accept this by, say, their high school teachers, to counterbalance the common notion?

It would seem that popular entertainment would stick with the theme as long as it sells movies, games, TV shows, and so on.  On the other hand, wouldn't it seem strange to us if, in 10 or 20 years, nobody was producing such material?  If all of the familiar productions about extraterrestrial life were as dated as, say, Western movies seem to be today?  

When the Western was king, sf was really pretty marginal.


----------



## paranoid marvin (Nov 20, 2021)

There will always be speculation of the 'what if' of extraterrestrial life. The world of sci-fi fiction is safe; look at  War of the Worlds - over 100 years old, and long since disproven that life exists on that remote, forbidding planet. Yet the story is still going strong with tv series and movies.

But as has been said, the universe is too vast and our methods of determining life too inadequate to determine the possibility of life - or not - on worlds thousands of light years away.


----------



## paranoid marvin (Nov 20, 2021)

Justin Swanton said:


> Nothing will change. We'll still be convinced there's life out there somewhere. Personally I'm not convinced, but it's easy to argue that humanity could continue another million years on Earth and *never* become aware of life on other planets since the distances are just too great, even for signals.




Distance is a definite factor, but perhaps moreso is time. Due to the age of the universe, galaxy, planets and stars I'm not sure how many signs of life could be easily traced several billion years after it lived, thrived and then died out. Perhaps up close, but certainly not from telescopes or satellites light years away.

I agree though, that even if we exist for another million years, meaningful contact with an alien species is a remote possibility. I still do think though that we will (eventually) find basic forms of life on one of the water-based moons of our solar system, and even the fossilised remains of life beneath the surface of Mars. Although I don't think we'll find evidence on Mars unless/until we send a manned mission there.


----------



## Justin Swanton (Nov 20, 2021)

paranoid marvin said:


> I still do think though that we will (eventually) find basic forms of life on one of the water-based moons of our solar system, and even the fossilised remains of life beneath the surface of Mars. Although I don't think we'll find evidence on Mars unless/until we send a manned mission there.



I know, we're all hoping for something from Europa. But the idea that the moon has a subsurface ocean of water is speculation and not proved. Besides water, life would need a source of energy and there is nothing on Europa that would demonstrably fit the bill. The temperature on the surface varies between -160 degrees and -220 degrees C, so life could not get anything from there. The only chance is subsurface volcanic activity and we still need evidence that Europa has a sufficiently hot core. Given that the surface ice may be 10-30km deep (presuming there is water below it) we may never be able to determine if there is life underneath.

For Mars we don't have any proof that surface conditions could ever accommodate life. There is evidence water flowed on the surface some time in the past but under what conditions (a cataclysmic upheaval that melted subsurface ice and drove it to the surface?) and for how long is unknown. I prefer Occam's Razor: Mars doesn't have a magnetic field hence gamma rays and solar flares would be a huge problem for anything on the surface.  Its lighter gravity combined with solar wind was enough to strip most of its atmosphere a long time ago. I see no reason to suppose it ever supported life.


----------



## Vertigo (Nov 20, 2021)

Justin Swanton said:


> since the distances are just too great, even for signals.


I can never understand why so many people ignore this fact. Everyone seems to think that after we started broadcasting radio and tv it was only a matter of time before the signals get picked up by alien civilisations. however these signals were/are not focused they are omnidirectional broadcasts and not particularly strong ones at that. This means that they are subject  to the inverse square law and so their strength diminishes incredibly quickly. I looked into this a few years ago and found multiple sources showing that, beyond something like a light day or two (never mind light years), our signals were tiny compared to the background radiation and were already pretty much undetectable. Note this is in complete contrast to our ability to receive signals from, say, Voyager; although its transmission is incredibly low power it is focused and directed back to Earth using parabolic dishes. So the only way our signals would stand any chance of being detected over interstellar distances is for them to be focused and directed at exactly the right stellar system at exactly the right time for Mr Alien to be pointing their incredibly sensitive receiver directly at our solar system also at exactly the right time. The chances of that happening make winning the lottery look like a certainty.

Of course exactly the same principle applies to us detecting any alien broadcasts.

Then of course there's the other possibility that any aliens out there are sensible enough to keep their heads down anyway and not go announcing their presence to the rest of the galaxy!


----------



## Extollager (Nov 20, 2021)

Vertigo, that long paragraph is one of the most instructive things I've ever read on this topic -- thanks.


----------



## Vertigo (Nov 20, 2021)

Let's hope my facts are right. I seem to recall when I was investigating it that about the only thing we have that would realistically communicate across interstellar space is high power radar - but again this is highly directional.

A quick bit of googling seems a little more optimistic than me with 4-5 light years before it is undetectable ie. the signal is less than 1db above background noise.

I just removed one bit that I think was a mistake where I stated that a signal focused by a parabolic dish is not subject to the inverse square law. I think this is incorrect; it's just that such a signal has all it's available power directed in one vector rather than being spread all around in every direction making it relatively more powerful.

Incidentally the Three Body Problem gets around this issue by effectively modulating the sun's output. Now that's one seriously powerful radio transmitter!


----------



## paranoid marvin (Nov 21, 2021)

Of course the other issue we have is that being such a vulnerable species, having limited technology and living on a planet still full of rare, natural resources do we really want to advertise to the rest of the universe 'here we are?' Anyone who picks up our signal, and is capable of reacting to it, will obviously be far more advanced than ourselves, and we would very likely be no match for it if it wasn't benevolent. 

It probably also doesn't help that we are actively demonstrating that we are not very good custodians of such valuable resources. I'm really not sure how any intelligent alien species would regard us in this respect.


----------

