How Do Extraterrestrials Know We Exist?

[HAZZARD]

How could "they" find us...!??

Lets set aside the question of whether advanced galactic societies would have the slightest interest in our wars, WMD, our pollution problems, our reproductive systems or our cows butts.

The real question is, how would they know about us at all?

There is only one way that they can tell from interstellar distance that intelligent creatures inhabit this planet...RADIO. Our radio signals travel at the speed of light, and this means that even with infinitely fast spacecraft , the aliens can't be much farther off than 15 light-years to have reached our lovely planet by 1947,(Rosswell).

The number of star systems within 15 light-years is about three dozen. There would have to be 10 billion technically sophisticated societies in the Galaxy to have a reasonable chance of finding one camped out among the nearest three dozen stars. Thats optimism of a high level indeed.

What about warp drive...? Lightspeed...? Maybe the aliens can create wormholes and get here in essentially no time...?

It doesn't matter.

Ill worry about how they got here once I am convinced that theyve really made the scene.

To get here they need to know were we are.

Approximately half the U.S. population suspects that extraterrestrials have come to our planet. This is such a controversial (and emotional) topic that its mere mention guarantees a storm of Web chat and high-voltage PMs.

In the end, of course, the matter of alien visitation will be decided by the evidence, not by the intensity of opinion.

While I certainly expect that the Galaxy is home to many advanced societies, the quality of the evidence has so far failed to convince me that any of them have emissaries on our planet.


PS:... I would find myself extremely self centric if I said that there are no other intelligent civilizations out there... I am convinced there are many. But I highly doubt that any of them happened to be so close that they have discovered us in our little, private corner of the galaxy.

 

[whybother]

Approximately half the U.S. population suspects that extraterrestrials have come to our planet.

Morbid curiosity, but where did you get that statistic from?

And I'm not totally sure what your question is... if intelligent life existed elsewhere, how could they find us? And you sort of answer it yourself with 'radio waves', so yes, that seems like a valid method, many frequencies of man-made EM transmit through the atmosphere and into space, they could notice.

And as a slight note:

even with infinitely fast spacecraft

This implies they could be here instantly. I think you meant "near light speed ships" to mainstain some sense of physics.

 

[mgb_phys]

It's from an (in)famous CNN poll that said

While nearly three-quarters of the 1,024 adults questioned for the poll said they had never seen or known anyone who saw a UFO, 54 percent believe intelligent life exists outside Earth.

Sixty-four percent of the respondents said that aliens have contacted humans, half said they've abducted humans, and 37 percent said they have contacted the U.S. government.

Not clear how only 54% believe in ET but 64% believe in a coverup!

 

[whybother]

It's from an (in)famous CNN poll that said

Not clear how only 54% believe in ET but 64% believe in a coverup!

That is horrifying... for several reasons...

 

[junglebeast]

There is only one way that they can tell from interstellar distance that intelligent creatures inhabit this planet...RADIO. Our radio signals travel at the speed of light, and this means that even with infinitely fast spacecraft , the aliens can't be much farther off than 15 light-years to have reached our lovely planet by 1947,(Rosswell).

People will believe what they want to believe regardless of how irrational it is. Just look at religion. At least the people who believe in alien's have latched onto a concept that probably does exist somewhere in the universe, unlike the concept of a god.

 

[moose]

An idea is that they just searched some planets they felt could support life.

 

[mgb_phys]

Teasers are usually rich kids with nothing to do. They cruise around
looking for planets which haven't made interstellar contact yet and buzz them.'

'Buzz them?' Arthur began to feel that Ford was enjoying making life difficult
for him.

'Yeah,' said Ford, 'they buzz them. They find some isolated spot with very few
people around, then land right by some poor unsuspecting soul whom no one's ever
going to believe and them strut up and down in front of him wearing silly antennae
on their head and making beep beep noises. Rather childish really.'

"Hitch-hiker's guide to Galaxy" by Douglas Adams (but you all knew that)

 

[junglebeast]

The big bang occurred 13.73 ± 0.12 billion years ago.
300 million years after the big bang stars and galaxies started to form.
5 billion years ago the Sun was formed.
3.8 billion years ago the first life forms evolved on earth.
700 million years ago animals have evolved.
600,000 years ago homo-sapiens evolve.

After each mass extinction, evolution rapidly converges to a stable-state global ecosystem, and then minor changes progressively follow. If it weren't for the mass extinctions during the days of the dinosaurs, that stable state might have persisted forever without a highly intelligent race like man ever evolving at all.

On an alternate world, highly intelligent life could have evolved during the "first wave", so let's assume the Earth time for the first wave of animals was typical, and that it takes about 4.3 billion years after a star is formed for the first advanced life forms to evolve on a planet (best case scenario). Then, perhaps the first intelligent life forms evolved in the universe 9.25 billion years ago.

Let's give them another 1 million years to develop space travel, and let's assume they have some very advanced craft that can travel at 5% of the speed of light (this is at the upward end of some theorized future spacecraft speeds).

(9.25 billion years) * (31556926 seconds / 1 year) * (3x10^8 meters/sec * 0.05 ) * (1 km / 1000 m) ( 1 light year / 9,460,730,472,580.8 km ) = 462 million light years

That means the maximum possible radius that an alien could have come from to visit Earth (if they randomly flew straight for us) would be roughly 462 million light years away -- which is significantly larger than the diameter of our galaxy ;)

 

[HAZZARD]

The big bang occurred 13.73 ± 0.12 billion years ago.
300 million years after the big bang stars and galaxies started to form.
5 billion years ago the Sun was formed.
3.8 billion years ago the first life forms evolved on earth.
700 million years ago animals have evolved.
600,000 years ago homo-sapiens evolve.

After each mass extinction, evolution rapidly converges to a stable-state global ecosystem, and then minor changes progressively follow. If it weren't for the mass extinctions during the days of the dinosaurs, that stable state might have persisted forever without a highly intelligent race like man ever evolving at all.

On an alternate world, highly intelligent life could have evolved during the "first wave", so let's assume the Earth time for the first wave of animals was typical, and that it takes about 4.3 billion years after a star is formed for the first advanced life forms to evolve on a planet (best case scenario). Then, perhaps the first intelligent life forms evolved in the universe 9.25 billion years ago.

Let's give them another 1 million years to develop space travel, and let's assume they have some very advanced craft that can travel at 5% of the speed of light (this is at the upward end of some theorized future spacecraft speeds).

(9.25 billion years) * (31556926 seconds / 1 year) * (3x10^8 meters/sec * 0.05 ) * (1 km / 1000 m) ( 1 light year / 9,460,730,472,580.8 km ) = 462 million light years

That means the maximum possible radius that an alien could have come from to visit Earth (if they randomly flew straight for us) would be roughly 462 million light years away -- which is significantly larger than the diameter of our galaxy ;)

I agree, (and sorry for sometimes rambling on/thinking out loud)... We don't know much about the average lifetime of technological societies, other than the fact that ours has, so far, managed to survive for a century. We also don't know at what rate sentient societies spring up in the Galaxy. But we do know that this rate is surely tied to the frequency with which stars are born. Clearly, a greater flux of new stars will ultimately produce a larger number of planets with thinking beings.

What is the star formation rate? Well, there are roughly 200 billion stars in the Milky Way, and that means that the average rate over the last 13 billion years has been about 15 new stars per year. Anyone whos used a radio telescope to study galaxies knows that when you examine a big spiral like the Milky Way, you find that the total amount of interstellar gas is typically a few percent of the mass of all the stars. Since interstellar gas is the stuff from which stars are built, its obvious that there's little material around today for constructing new ones. Clearly, this must affect the number members for our club of intelligent beings. And not to the possitive.



And about this "cover up" mentality. It is dismaying that many people assume proof that were not alone would cause governments to cover up the facts. I don't believe this for a second.

Consider the 1938 radio broadcast of War of the Worlds. Some Americans mistook the fictional Martian invasion for news, and fled their homes. Would a real discovery of extraterrestrials occasion a breakdown in public order?

This seems highly unlikely. Picking up a signal from space is different from watching aggressive aliens land in the pastures. Its difficult to imagine galactic beings would ever charge across the dark deserts between the stars merely to harass the inhabitants of a small planet.

I think that IF we ever detect a signal from other worlds would be wondrous. It would show that the appearance of life on this world and its slow, uncertain path to us - creatures that can comprehend their own existence - is not some improbable miracle, but a frequent occurrence.

In the 17th century, when early telescopes were revealing great clouds of stars, French mathematician and philosopher Blaise Pascal wrote that the enormity of space terrified him.

Space is enormous. To learn that others are out there would be a comfort.

 

[junglebeast]

Well, there are roughly 200 billion stars in the Milky Way, and that means that the average rate over the last 13 billion years has been about 15 new stars per year.

Although stars are being born and die all the time, a galaxy does not just grow linearly with time like that. In the same way that our solar system formed from a large nebula of gas, causing all the planets to accrete simultaneously, I think the galaxy itself would have formed all the stars in it simultaneously to start with.

 

[Anticitizen]

The big bang occurred 13.73 ± 0.12 billion years ago.
300 million years after the big bang stars and galaxies started to form.
5 billion years ago the Sun was formed.
3.8 billion years ago the first life forms evolved on earth.
700 million years ago animals have evolved.
600,000 years ago homo-sapiens evolve.

After each mass extinction, evolution rapidly converges to a stable-state global ecosystem, and then minor changes progressively follow. If it weren't for the mass extinctions during the days of the dinosaurs, that stable state might have persisted forever without a highly intelligent race like man ever evolving at all.

On an alternate world, highly intelligent life could have evolved during the "first wave", so let's assume the Earth time for the first wave of animals was typical, and that it takes about 4.3 billion years after a star is formed for the first advanced life forms to evolve on a planet (best case scenario). Then, perhaps the first intelligent life forms evolved in the universe 9.25 billion years ago.

Let's give them another 1 million years to develop space travel, and let's assume they have some very advanced craft that can travel at 5% of the speed of light (this is at the upward end of some theorized future spacecraft speeds).

(9.25 billion years) * (31556926 seconds / 1 year) * (3x10^8 meters/sec * 0.05 ) * (1 km / 1000 m) ( 1 light year / 9,460,730,472,580.8 km ) = 462 million light years

That means the maximum possible radius that an alien could have come from to visit Earth (if they randomly flew straight for us) would be roughly 462 million light years away -- which is significantly larger than the diameter of our galaxy ;)

There's also acceleration times to consider, and deceleration times, if we assume they bothered to slow down and not just zoom by at 5% C. That shortens the radius quite a bit.

 

[DaveC426913]

Lets set aside the question of whether advanced galactic societies would have the slightest interest in our wars, WMD, our pollution problems, our reproductive systems or our cows butts.

The real question is, how would they know about us at all?

There is only one way that they can tell from interstellar distance that intelligent creatures inhabit this planet...RADIO.

Your premises go awry here. We don't search for intelligent life, we search for signs of any life, and explore. Why would they be any different?

So, they detected our oxygen atmo, which pushes out the timeline to more than a billion years.

 

[junglebeast]

Your premises go awry here. We don't search for intelligent life, we search for signs of any life, and explore. Why would they be any different?

So, they detected our oxygen atmo, which pushes out the timeline to more than a billion years.

Good point...and just look how excited scientists are to discover exoplanets of roughly the correct size and distance from their stars. If we had the technology for interstellar travel, we would be interested in visiting almost all of those exoplanets even before knowing their atmospheric composition. So..this could give motivation to aliens to start heading in our direction even before photosynthesizing plants start oxygenating our atmosphere.

 

[DaveC426913]

Good point...and just look how excited scientists are to discover exoplanets of roughly the correct size and distance from their stars. If we had the technology for interstellar travel, we would be interested in visiting almost all of those exoplanets even before knowing their atmospheric composition. So..this could give motivation to aliens to start heading in our direction even before photosynthesizing plants start oxygenating our atmosphere.

That was kind of what I was suggesting, but I think you may be carrying it too far.

If we presume an level of technology capable of getting them across interstellar distances, we should be able to presume that they've got planet-spotting down pat (where as we are in the infancy of both). Only really unique planets (such as ones supporting life) would stand out of the crowd.

 

[junglebeast]

If we presume an level of technology capable of getting them across interstellar distances, we should be able to presume that they've got planet-spotting down pat (where as we are in the infancy of both). Only really unique planets (such as ones supporting life) would stand out of the crowd.

Planet spotting isn't without it's own fundamental limitations. If the interference and scattering of light waves makes the signal to noise ratio small enough beyond some distance that, by Shannon's theory, it would be impossible to detect the relevant information from beyond a certain distance.

 

[HAZZARD]

Your premises go awry here. We don't search for intelligent life, we search for signs of any life, and explore. Why would they be any different?

So, they detected our oxygen atmo, which pushes out the timeline to more than a billion years.

Sure, any advanced ET could spectroscopically sample the light reflected from our atmosphere, and learn that it has large quantities of oxygen and methane, tell-tale markers of biology. If biology is common in the universe, then Earth might be just another entry in a long list of "living worlds" compiled by ET.

Its discovery might not excite them very much?

But let's say they have some kick a** planet-finding telescopes, they could find our planet from hundreds or even thousands of light-years distance. For them to see the Great Wall of China, the lights from our cities, or even the cities themselves, would be extremely difficult.

Not to mention that the light carrying the immage would be hundreds or even thousands of years old. And that meens no Great Wall of China and no light from our citys, right.

If they exist at all...?

Who knows, we might be the only intelligent life in the entire universe?

 

[DaveC426913]

The big bang occurred 13.73 ± 0.12 billion years ago.
300 million years after the big bang stars and galaxies started to form.
5 billion years ago the Sun was formed.
3.8 billion years ago the first life forms evolved on earth.
700 million years ago animals have evolved.
600,000 years ago homo-sapiens evolve.

After each mass extinction, evolution rapidly converges to a stable-state global ecosystem, and then minor changes progressively follow. If it weren't for the mass extinctions during the days of the dinosaurs, that stable state might have persisted forever without a highly intelligent race like man ever evolving at all.

On an alternate world, highly intelligent life could have evolved during the "first wave", so let's assume the Earth time for the first wave of animals was typical, and that it takes about 4.3 billion years after a star is formed for the first advanced life forms to evolve on a planet (best case scenario). Then, perhaps the first intelligent life forms evolved in the universe 9.25 billion years ago.

If I read your logic correctly, you're assuming these guys are evolving around a Population III (first gen) star, which is virtually impossible. I think we have to assume a Population I star, which greatly shortens the time available.

 

[junglebeast]

An interesting article just came out describing how it's literally possible to analyze the light reflected off a planet and detect if it contains a large number of life forms, without actually being able to resolve any kind of a detailed image

http://www.eurekalert.org/pub_releases/2009-04/nios-sga042309.php

 

[HAZZARD]

Long story short... The simple factor that extraordinary claims require, and in fact demand, extraordinary evidence.

Whats being offered by the believers in the ETH doesn't even bear a passing resemblance to such...their assertion falls far short of any standard of scientific proof.

The hypothesis of alien visitations is rendered nonfalsifiable either by the invocation of a worldwide conspiracy/coverup, or, by saying that the aliens are so advanced technologically that there is no way for us mortals to prove their presence among us.

If UFO buffs want to believe in alien visitations as a kind of religion, and some of them do, fair enough. Everybody has the right to believe any religion he chooses.

But please, believers, let's stop pretending that the belief in alien visitations is real science.

 

[Ivan Seeking]

Long story short... The simple factor that extraordinary claims require, and in fact demand, extraordinary evidence.

Whats being offered by the believers in the ETH doesn't even bear a passing resemblance to such...their assertion falls far short of any standard of scientific proof.

The hypothesis of alien visitations is rendered nonfalsifiable either by the invocation of a worldwide conspiracy/coverup, or, by saying that the aliens are so advanced technologically that there is no way for us mortals to prove their presence among us.

If UFO buffs want to believe in alien visitations as a kind of religion, and some of them do, fair enough. Everybody has the right to believe any religion he chooses.

But please, believers, let's stop pretending that the belief in alien visitations is real science.

I don't know what you're talking about, but we don't discuss such theories or beliefs here. Are you blowing off steam or addressing something specific?

 

[junglebeast]

If I read your logic correctly, you're assuming these guys are evolving around a Population III (first gen) star, which is virtually impossible. I think we have to assume a Population I star, which greatly shortens the time available.

Good point!

 

[darkhorror]

Maybe instead of seeing "us" they instead just see a planet that could have life on it. Just as if we were to find a planet that could have life on it we would want to go and check it out. Also let's say they are able to move to different planets and live there. How many of these aliens would we find? Looking at what we see on Earth and population growth, now if this wasn't so limited by the land we had on Earth how many people would be here in hundreds, thousands, or millions of years?

Then the problem is that is life going to be anywhere near what we see on earth? Or is it going to be so different that what we look at on Earth has very little to do with what another civilization would do.

 

[gambit7]

"They" found us because they were here first.
You can't find something you haven't lost.

 

[Ivan Seeking]

The last post constitutes a personal theory, which is not allowed. It is true that some people believe that the alleged ETs have been here all along - based mostly on ancient religions and stories - but that is not a topic that can be pursued here.

 

[gambit7]

The last post constitutes a personal theory, which is not allowed. It is true that some people believe that the alleged ETs have been here all along, but that is not a topic that can be pursued here.

The OP posed a question, I proposed a possible answer. It is not a personal theory, merely a thought experiment (as was intended with this thread).

Anyways, the question assumes we as Humans are "God's gift to the Solar system." As if Sol can only have been "found" whilst we Humans were part of it. That's pretty egotistical and hence nonsensisal in the larger scheme of things.

If we take ourselves out of the picture, the light-year distance that an alien intelligence could've seen our vibrant world/system expands tremendously. You see today how our meagre technology is growing day-by-day with regards to the detection of planets around other systems, therefore assuming a culture with interstellar capability was "looking up" it's not that far-fetched for our system to be attractive (at many points in its history)... as has been discussed in this thread already.

Any of these similar "personal theories" which have already been stated all lead back to the simple fact that it's more likely any alien intelligence that has ever visitied Earth likely did so way before we were here or at best "civilized." The caveat is, assuming the same race of aliens visits us to this day, then it's likely that race would've destroyed itself long before ever getting here while Humans dominated the planet.

We've been civilized all of what? 12,000 yrs.? What's the expected evolutionary timeframe before a civilization destroys itself? I'd take that number and use it to formulate a radius for finding E.T. Of course, you'd have to factor in many other variables that I won't go into right now (a bit tired).

 

[junglebeast]

Any of these similar "personal theories" which have already been stated all lead back to the simple fact that it's more likely any alien intelligence that has ever visitied Earth likely did so way before we were here or at best "civilized."

That doesn't more likely to me. What is your justification

We've been civilized all of what? 12,000 yrs.? What's the expected evolutionary timeframe before a civilization destroys itself?

The expected value given 0 samples is undefined

 

[flatmaster]

THis could be an interesting alteration to the Drake equation. You could simply multiply by the probability that the given solar system is within the expanding sphere of man-made radio waves.
http://en.wikipedia.org/wiki/Drake_equation

 

[DaveC426913]

The expected value given 0 samples is undefined

The sample size is one.

One civilization has survived at least 12,000 years.

 

[HAZZARD]

I don't know what you're talking about, but we don't discuss such theories or beliefs here. Are you blowing off steam or addressing something specific?

Mostly the first... sense there seems to be no believers in the ETH here.

Have you guys here ever seen one jot of proof that any of what's been sighted, reported, filmed, or photographed has ever, in any way, been shown to be alien?? I do not deny that some things might be alien. I am all for that. What I do deny is that there has been any irrefutable scientific proof of it.

As believers begin to build the case about UFO = Aliens, the foundation of this is built on hear say, speculations, theories, guess work, assumptions, beliefs and emotions.

But there are no real scientific evidence...


...is there?

 

[HAZZARD]

THis could be an interesting alteration to the Drake equation. You could simply multiply by the probability that the given solar system is within the expanding sphere of man-made radio waves.
http://en.wikipedia.org/wiki/Drake_equation

Exactly.

There is only one way that they can tell from interstellar distance that intelligent creatures inhabit this planet...RADIO. Our radio signals travel at the speed of light, and this means that even with infinitely fast spacecraft , the aliens can't be much farther off than about 15 light-years to have reached our lovely planet by 1947,(Rosswell).

The number of star systems within 15 light-years is about three dozen. There would have to be 10 billion technically sophisticated societies in the Galaxy to have a reasonable chance of finding one camped out among the nearest three dozen stars. Thats optimism of a high level indeed.

 

[junglebeast]

The sample size is one.

One civilization has survived at least 12,000 years.

The question was, "What's the expected evolutionary timeframe before a civilization destroys itself?" Since our civilization hasn't destroyed itself yet, we have zero observed samples of the amount of time it takes for a civilization to destroy itself. All we know is that the first sample is >= 12,000 years. It could be 14,000 or 100,000 or 100,000,000...it doesn't allow even a crude estimate of the mean of the distribution.

 

[DaveC426913]

There is only one way that they can tell from interstellar distance that intelligent creatures inhabit this planet...RADIO.
...
The number of star systems within 15 light-years is about three dozen. There would have to be 10 billion technically sophisticated societies in the Galaxy to have a reasonable chance of finding one camped out among the nearest three dozen stars. Thats optimism of a high level indeed.

There are a number of assumptions in your assertion that I'm not willing to take at face-value.

1] Just because they didn't have proof-positive of intelligent life does not mean they would be completely uninterested in our planet. We humans are currently raving about the first planets with oxygen because of the potential for life - and any kind of life at that. It is not unreasonable that alien species might be doing the same thing. That pushes back their theoretical departure time by billions of years, which is a large fraction of the age and breadth of the universe.

2] You assume a randomly-distributed incidence of alien life across the galaxy. If one puts any truck at all in the panspermia theory, it is far, far more likely that incidences of life cluster.

 

[Vanadium 50]

It's from an (in)famous CNN poll that said

Not clear how only 54% believe in ET but 64% believe in a coverup!

I read this as 54% believe in ET and 64% believe ET has visited: meaning that 10% believe ET doesn't exist: but has visited!

 

[Belzy]

Well we do know of at least one tech society.

Nice little pocket in the outer rim.

Well on another note we have a lot of room in our own solar system to conquer first. So if ET is out there maybe it will find us before our sun grows and consumes us.

 

[Kalibr]

If "they" are at the sort of technological level we are at, it's be easier to just send out a signal instead of attempting to master intersolar travel. I'm guessing some sort of pulse, similar to the modern day EM Pulse would be used, but on a massive scale.

This is all assuming they don't follow the pessimistic prediction that all civilisations will destroy themselves before they attain the sort of technological level required for communications across the stars. I have a few even more outlandish theories, but they say simple is better, and making a pulse signal will certainly be the easiest to produce. It also works as a handy filter so that only civilisations that can actually intercept the signal and understand it for what it is will respond.

Of course, they'll have to repeat the pulse at some sort of rate in case a civ happened to miss the first. Of course, if they'd had made the pulse cycle once every 3.14 years that'd really hammer the point across, in case the observers think it's a natural event.