Are Aliens Listening? Evidence for Intelligent Life in Space

[Schnellmann]

To date we have not picked up any signals from aliens. Some take this as a sign that we are alone in the universe or that intelligent life and culture, if it exists elsewhere, is rare.

What I am not clear on is what we are expecting to find.

Reversing the argument, if aliens were searching the heavens for us how close would they have to be to be able to deduct the electromagnetic radiation we have been inadvertently sending over the past 100 years or so?

 

[phinds]

To date we have not picked up any signals from aliens. Some take this as a sign that we are alone in the universe or that intelligent life and culture, if it exists elsewhere, is rare.

What I am not clear on is what we are expecting to find.

Reversing the argument, if aliens were searching the heavens for us how close would they have to be to be able to deduct the electromagnetic radiation we have been inadvertently sending over the past 100 years or so?

Well, how far do radio waves travel in 100 years?

 

[Ernest S Walton]

There is no possibility they could detect e.g our television signals, these become indistinguishable from background noise within a few light years. Signals such as military radar are more powerful, but they exist within such a narrow beam that the aliens would have to be in exactly the right place and time to detect them.

So the chances of detecting us electromagnetically are almost nil. But if biospheres are rare, then we have already been sticking out like a sore thumb for millions of years, and aliens with sufficiently powerful telescopes will know of our planet's unusual properties. How they choose to respond to that is a matter of pure speculation.

 

[Schnellmann]

Well, how far do radio waves travel in 100 years?

So you are saying that aliens would be able to detect our signals at 100 light years?

 

[Schnellmann]

This is what I've suspected. So our only realistic chance of picking up a signal is if aliens are deliberately beaming a powerful signal at stars they think could have planets that are home to civilisations. So absence of signals could also be a deliberate policy of non communication.

 

[phinds]

So you are saying that aliens would be able to detect our signals at 100 light years?

Not exactly. What I am saying is that there is NO possibility if they are farther away. Although I think Walton overstates the case regarding the difficulty of radio waves being detected at various ranges, I absolutely agree w/ him that there is likely about zero chance at the full range of our signals. Normal radio/TV signals are not DESIGNED to be detected much beyond their designed broadcast range which is, after all, right here on Earth.

 

[BenAS]

This is what I've suspected. So our only realistic chance of picking up a signal is if aliens are deliberately beaming a powerful signal at stars they think could have planets that are home to civilisations. So absence of signals could also be a deliberate policy of non communication.

We could in principle develop telescopes that could filter out the background noise.

 

[tech99]

We could in principle develop telescopes that could filter out the background noise.

Analogue transmission lasted for only about 100 years, the Twentieth Century, which is negligible in the timescales of the universe. Digital transmissions are designed to be noise-like, because that is the most efficient way. Without knowing the code, digital transmissions are difficult to distinguish from noise.
My rough figures (may be wrong) tell me that, using a 100m receiving dish, signals from a UHF TV station with 1 MW ERP would fall to the noise level in about 100 hours. This assumes 1 deg K for the Cosmic Microwave Background at 1 GHz and 10 kHz B/W.

 

[BL4CKB0X97]

To date we have not picked up any signals from aliens. Some take this as a sign that we are alone in the universe or that intelligent life and culture, if it exists elsewhere, is rare.

What I am not clear on is what we are expecting to find.

Reversing the argument, if aliens were searching the heavens for us how close would they have to be to be able to deduct the electromagnetic radiation we have been inadvertently sending over the past 100 years or so?

Don't forget, even if they did get a signal distinguishable from the background noise,they may not see it as it is. As it is very possible they communicate in different ways. Sound(speech)is a human form of communication,what is to say they don't communicate by colour,taste or touch,even pheromones like hive insects such as ants? I am no xenobiologist but I'm sure the old of means of communication will be the same. They might even talk outside of the pitch(right word?) we are capable of hearing.

 

[russ_watters]

Not exactly. What I am saying is that there is NO possibility if they are farther away.

I'm pretty sure you are answering the wrong question. The OP isn't asking how far away our radio signals could be detected by now, he is just asking how far away our radio signals could be detected...as a way to judge if we could detect an alien species with a similar level of technology to what we posess today.

 

[russ_watters]

There is no possibility they could detect e.g our television signals, these become indistinguishable from background noise within a few light years. Signals such as military radar are more powerful, but they exist within such a narrow beam that the aliens would have to be in exactly the right place and time to detect them.

So the chances of detecting us electromagnetically are almost nil. But if biospheres are rare, then we have already been sticking out like a sore thumb for millions of years, and aliens with sufficiently powerful telescopes will know of our planet's unusual properties. How they choose to respond to that is a matter of pure speculation.

There is also the Arecibo message, which demonstrates that it is possible in principle to send a signal, with meaningfule data, that has a chance of being detected and disciphered at 25,000 light years, with 1970s technology.

https://en.m.wikipedia.org/wiki/Arecibo_message

The Aricebo message was a one-shot deal, but using some game theory logic, one could examine the possibility that a civilization might be sending such a message our way.

 

[russ_watters]

Don't forget, even if they did get a signal distinguishable from the background noise,they may not see it as it is. As it is very possible they communicate in different ways. Sound(speech)is a human form of communication,what is to say they don't communicate by colour,taste or touch,even pheromones like hive insects such as ants? I am no xenobiologist but I'm sure the old of means of communication will be the same. They might even talk outside of the pitch(right word?) we are capable of hearing.

While more or less true (but extremely unlikely), no such society would be of a sufficient level of technology to pique our interest in the context of the question.

 

[phinds]

I'm pretty sure you are answering the wrong question. The OP isn't asking how far away our radio signals could be detected by now, he is just asking how far away our radio signals could be detected...as a way to judge if we could detect an alien species with a similar level of technology to what we posess today.

Fair point, but double-check the last sentence in the OP

 

[Schnellmann]

Yes this is exactly what I was asking

 

[russ_watters]

Fair point, but double-check the last sentence in the OP

Yes - I think you are reading something in the last sentence that isn't there; Timeframe of emission is mentioned, but timeframe of receipt is not.

 

[velocity_boy]

To date we have not picked up any signals from aliens. Some take this as a sign that we are alone in the universe or that intelligent life and culture, if it exists elsewhere, is rare.

What I am not clear on is what we are expecting to find.

Reversing the argument, if aliens were searching the heavens for us how close would they have to be to be able to deduct the electromagnetic radiation we have been inadvertently sending over the past 100 years or so?

There has been much speculation on what sort of signal or code we could send that would be discernible by ET intelligence. Prime numbers are a very popular idea and I also think it is a good bet. If there is one universal science that can be transmitted and probably understood by a vastly different culture or civilization I think it would be mathematics. So, yeah: pulses at intervals or maybe duration (in seconds?) that reflect prime numbers.

As far as how long for them to hear us, we must remember the vast distances involved. Any intelligent life is going to come from outside of our own solar system, so that means the nearest star system is the binary Alpha Proxima/Centauri system, which is some 4.3 light years away. So even if the ET's were this close (which is a small chance) you're looking at close to nine years for us to receive a message that they got ours and then decided to respond. I personally am of the opinion that the Universe is teeming with intelligent life. But I also do not believe that we have been visited, like these UFO apologists do, becasue of, again, those mind-numbingly vast distances. Just think: our own little MIlky Way galaxy is about 100,000 light years across! And this is only ONE of billions of galaxies. So even if there was Intelligence in our own "Local Group" of galaxies, it could take longer than your entire lifetime for us to receive ans answer to a signal we transmitted.

For this reason, the "needle in the haystack" dynamic, the US government canceled the SETI program a few years ago. It is not that they don't think there's no life out there, it's just that they know the distances make the chances of contacting them while anybody here is still around very small. I tend to think the odds are better that we one day receive a signal or even get visited by a very advanced civilization than they are of somebody out there getting one of our signals.

This latter idea of course opens up a whole new debate: would it be a good thing for us to be visited by ET's? Many Cosmologists don't think so. Including Stephen Hawking.

 

[JLowe]

I think life is relatively common in the universe, but intelligent life? I'm not so convinced. And to take that one step further, intelligent life with sufficient technology to make themselves known to us? And yet further, intelligent life with the technology, thought pattern, that can make themselves known to us, WANT and TRY to make themselves known to us, and exist in their technological age in timespans comparable to ours, at distances close enough to be relevant and detectable? Yea...no. These chances IMO are so close to zero they can be considered zero.

Think about what all has to go right for this scenario. A suitable planet close enough to us with a star similar in age to our own, a planet in the habitable zone with a stellar environment stable enough to allow life the chance to evolve for billions of years, an environment similar enough to our own for that life to have evolved similar thought patterns to our own, a planet with sufficient resources to develop electrical technology, a stable neighborhood free of an over abundance of asteroid impacts, a possible need for them to be aligned in such a way to detect us by transit, and have this occur in nearly the exact same miniscule timeframe as our ability to receive, understand, and acknowledge a signal? This seems a near impossibility.

 

[Schnellmann]

Much as I would like to believe that instellar travel is possible and that we will be visited by ET I think the distances involved are just too far for living beings. Despite the incredible technological advances of the last fifty years the reality is that those advances have been predominantly about computing and control of the small scale. There were BMW adverts boasting about how the 7 series had more computing power than the Apollo space craft. True but what was not said is that the 50 year old Saturn 5 rocket is still the most powerful rocket ever launched and the fastest aircraft is still the Blackbird from the 1960s. Despite our advances we are not at all close to visiting the stars. I think ET will face the same problem. If we are ever visited it will be, in my view, by inorganic AIs for whom thousands or millions of years traveling between stars is no problem.

 

[JLowe]

[QUOTE="Schnellmann, post: 5752935, member: 596904]If we are ever visited it will be, in my view, by inorganic AIs for whom thousands or millions of years traveling between stars is no problem.[/QUOTE]

And even that has its own significant technological and circumstantial hurdles.

 

[TinHelmet]

Our universe is almost 14,000,000,000 years old. Humans have existed maybe approx. 200,000 years. We have been using radio waves for just over 100 years. I think it is somewhat pointless to try to figure out what the other intelligent species (if any) can see, hear or do, as they have most likely been existing and communicating much much longer than us. Speculating is always fun, though!

 

[Fervent Freyja]

If aliens were searching for other life forms, then they wouldn't rely on any signal we've broadcasted. Instead, they would determine whether or not our location is habitable and go from there before paying us a visit. If another life-form has already predicted that life would exist on Earth and has been traveling for a very long period of time, then they could arrive at any moment. That's the only way I can see the time discrepancy being resolved from very far distances. They would need to have already been on their way to Earth before humans even evolved in order for this to work. Who knows? They may have had the knowledge and technology in order to be certain that we would be here when they arrived much later.

 

[Schnellmann]

Even if their technology and knowledge is much more advanced than ours they still face the problems of vast distances, time necessary to travel those distances and the energy required to accelerate and decelerate a spaceship. Those problems get wished away in Sci Fi with warp drives or just brushed over. In reality those are problems that better technology can't remove. Even if you could develop a way of accelerating a spacecraft to a meaningful percentage of the speed of light such that time dilation comes into play and the journey doesn't take as long from the viewpoint of those travelling, from those staying behind it would be just as long.

 

[John d Marano]

If there is intelligent life out there they're ignoring us. For the same reason the USA has never invaded has never invaded South Sudan there's just nothing there the USA wants.

Its hard to admit humans are not wanted but its true. What would aliens want from us
To dig up and burn our coal/oil; if they can travel the universe they have a better power source
To colonize; our biology and gravitates would be so different that our planet would be hazardous to them
As a pit stop; we're on the edge of the galaxy in the middle of nowhere
To enslave humans; We're so unproductive we can barely feed ourselves

They only reason I can think that aliens would visit us is that they're curious. If that's the case they'd come, see the Earth is a primitive dump and leave . . .

 

[stefan r]

Don't forget, even if they did get a signal distinguishable from the background noise,they may not see it as it is. As it is very possible they communicate in different ways. Sound(speech)is a human form of communication,what is to say they don't communicate by colour,taste or touch,even pheromones like hive insects such as ants? I am no xenobiologist but I'm sure the old of means of communication will be the same. They might even talk outside of the pitch(right word?) we are capable of hearing.

That will not matter. For the classic analog record you just change the rotation speed and the pitch changes. It is a bumpy piece of vinyl regardless of how you listen. Digital mediums like a CD can be images or sound. You can recognized that digital or analog signals are information without being able to read or interpret it.

You can recognize Chinese, cuneiform, hieroglyphs and Greek as forms of writing without decoding the text. A deaf person might read Chinese characters and then communicate the message to another deaf person without ever using sound.

 

[bahamagreen]

The distances and other issues involved may not be an issue for our older brothers...

Kepler 444 is estimated to be 11.2 billion years old with rocky exoplanets, so the oldest population 1 systems look to be about that age. That gives them a 6 to 7 billion year head start compared to the Earth, which consumed 3 billion years to go from the initiation of life to forming multi-cellular tiny worms... but just one more billion to produce man.

For our older brothers out there 2 to 3 billion years ahead of us, I strongly suspect that the travel distances and virtually all other intractable technical problems of all kinds have been successfully entertained and overcome in ways we cannot even begin to grasp... :)

 

[nikkkom]

Much as I would like to believe that instellar travel is possible and that we will be visited by ET I think the distances involved are just too far for living beings.

It's just a failure of imagination on your part. Off the top of my head:
(1) a single living being does not have to survive the entire trip - generation ship would work.
(2) medical advances can make hibernation or life extension possible.
(3) aliens may evolve from animals who have natural hibernation.
(4) after a few more thousand years of advances in science and medicine, I am almost certain our descendants would not classify as "living beings". Why would anyone want to have this unreliable, fragile mess of organic nanomachinery as a body?!

 

[stefan r]

The distances and other issues involved may not be an issue for our older brothers...

Kepler 444 is estimated to be 11.2 billion years old with rocky exoplanets, so the oldest population 1 systems look to be about that age. That gives them a 6 to 7 billion year head start compared to the Earth, which consumed 3 billion years to go from the initiation of life to forming multi-cellular tiny worms... but just one more billion to produce man.

For our older brothers out there 2 to 3 billion years ahead of us, I strongly suspect that the travel distances and virtually all other intractable technical problems of all kinds have been successfully entertained and overcome in ways we cannot even begin to grasp... :)

If they can move at 30 kilometers per second they can cross the milky way in one billion years. Would be a lot less if you factor in galaxy rotation. If they migrate in or out from center then the rotation smears civilization around. Escaping from stars requires higher velocity. Any interstellar colonizers should swamp the whole thing in much less time.

Colonizing the Kuiper belt includes all the problems that could block colonizing the Milky Way.

 

[Mark Harder]

I won't even attempt to answer the question, but it's often useful to examine the assumptions. So far, we have been constrained to live on our rock circling around our star, and we tend to expect that other civilizations are similarly stuck in place. What if an alien species, with sufficiently advanced technology, is traveling about? What would it take, or is it even possible, for maybe a few thousand beings to sustain an existence over many generations aboard a large vessel containing some sort of self-renewing environment? I'm not an SF reader, but surely this is a premise of many speculative tales.

 

[stefan r]

I won't even attempt to answer the question, but it's often useful to examine the assumptions. So far, we have been constrained to live on our rock circling around our star, and we tend to expect that other civilizations are similarly stuck in place. What if an alien species, with sufficiently advanced technology, is traveling about? What would it take, or is it even possible, for maybe a few thousand beings to sustain an existence over many generations aboard a large vessel containing some sort of self-renewing environment? I'm not an SF reader, but surely this is a premise of many speculative tales.

Kim Stanley-robinson wrote a full novel focused on that topic. https://en.wikipedia.org/wiki/Aurora_(novel)

Karl Sagan is mostly non-fiction but https://en.wikipedia.org/wiki/Comet_(book) has a chapter on life in the Kuiper belt. The science history chapters are also among the best I have read.

 

[Ernest S Walton]

What if an alien species, with sufficiently advanced technology, is traveling about? What would it take, or is it even possible, for maybe a few thousand beings to sustain an existence over many generations aboard a large vessel containing some sort of self-renewing environment?

But what if they encountered superior technology, which didn't take kindly to them? I would think a prime consideration before embarking on an interstellar voyage is to make sure the coast is clear. And how do we prove that, since advanced technology would be able to camouflage itself? That's why I favour a Paranoid Universe theory, where there are many intelligent species but each confines itself to its own quarters, as discretion is deemed to be more intelligent than valour.

 

[Chronos]

Even assuming aliens have the same sensory capabilities as humans - which seems fairly reasonable. There is an unbounded parameter space for language to emerge. How many languages exist, much less have ever existed, on this planet; hundreds, thousands, more? Each language has a unique history of development. They all began with a few basic sounds or gestures followed by subtle manipulations thereof, all based on the unique culture heritage of its native speakers. And this does not even address the issue of interpreting written language We have enough trouble figuring out other human languages; e.g., WWII Japanese v Navajo language, and almost no clue how to interpret the language of other animals: after all, they don't make noises or engage in ritual behaviors because of the survival value in alerting predators to their presence. It would be incredibly difficult to translate an ET language, or even recognize it as language - and vice versa. A pattern recognition algorithm may suggest data content in a message, but little else. I understand the hostile universe concept, as does Stephen Hawking, but risk taking cannot be eliminated from any effort to advance and prosper.

 

[lpetrich]

I'll now consider analog vs. digital reverse engineering.

Analog signals are fairly easy to reverse engineer, since their content parallels the original content, and since video signals have horizontal and vertical synchronization signals that stand out from the content signals.

Digital signals are much more difficult to reverse engineer for these reasons:

• Data compression. In summary, it gets rid of redundancy. But while it reduces the number of bits to transmit, it also deprives the signal of clues that reverse engineers could use.
• Error-correction coding. That involves adding extra bits so that if some of the bits get corrupted, there will still be enough to reconstruct the signal.
• Encryption. Without knowledge of the encryption algorithm, breaking it will be VERY hard.

So all that an extraterrestrial eavesdropper will be able to tell about digital broadcasts is that those broadcasts are present. That's true not only of radio and TV, but also of the Internet.

 

[sophiecentaur]

We could in principle develop telescopes that could filter out the background noise.

There are some very practical limits to this. You can use very directive receiving arrays (telescopes) but diffraction is a fundamental limit. You cannot necessarily distinguish between a wanted signal (with an unknown format) and the random signals from the same direction. By reducing the bandwidth of a receiver, you can improve the signal to noise ratio but you very soon get down to a bandwidth of fractions of a Hz and the information content of such a signal would be of not much use for making sense of your received signals. Imagine taking a Megawatt analogueTV signal and trying to make sense of what's in a 1Hz bandwidth part of the signal. You could perhaps recognise the frame repeat rate if you swept it very slowly with a spectrum analyser set to 1Hz b/w. There is an even greater problem spotting signals used in modern communication systems. Digital signals are deliberately profiled to maximise the rate of information transfer and such signals are very random looking and hard to distinguish from random noise.
The probability becomes very low of spotting a likely looking source when you are effectively scanning the whole of space with a pencil (if you are lucky) beam and taking days and days to scan the received signal in each beam position.
Now we have spotted many planets in Goldilocks Zones, we could avoid aimless scanning in all directions by looking just at them with our radio telescopes but success would require their civilisations would need to be only a thousand years (or less) out of step with ours for us to miss each other.
If a channel could be identified in one direction (i.e. we hear them or they hear us) then the recipient would find it very interesting (and throw them into blind panic, no doubt). But how many years / generations / millennia would be involved in a meaningful two way conversation? That puts a maximum limit on the 'relevance' of anything we (or they) could receive.
Scifi media have explored so many possibilities of communication. At present, I think the more likely scenario would be a more advanced civilisation spotting us (the basic OP scenario) but what if they are not very far away - near enough to come and have a look within a few centuries? That is one of the scariest scenarios I could ever contemplate. "Independence Day' with no happy ending.
Edit: I see that @lpetrich has made my point about the difference between various signalling systems; a cross post and very well put.

 

[nikkkom]

Diffraction limit problem can be overcome with interferometric telescopes. In space, there are no hard limits how large your baseline can be. Millions or even billions of kilometers are possible.
Space-based antennae are also not limited to diameters of about ~150m for steerable and ~500m fixed antennas, as they are on Earth.

 

[stefan r]

Diffraction limit problem can be overcome with interferometric telescopes. In space, there are no hard limits how large your baseline can be. Millions or even billions of kilometers are possible.
Space-based antennae are also not limited to diameters of about ~150m for steerable and ~500m fixed antennas, as they are on Earth.

When the source signal is less than 1 photon you have a hard limit. A Dyson sphere sized dish would probably nice long range. They could also use a longer exposure time.

If single photons are appearing occasionally you still lose the message. I suspect that would foil an interferometer too.