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ETpro's avatar

What's your best guess of the probability that intelligent aliens are currently visiting Earth?

Asked by ETpro (34594points) September 19th, 2013

There are as many as 400 billion stars in our own Milky Way Galaxy, and many of them have planetary systems. Some subset of those billions of stars are sure to have water bearing planets orbiting them within their habitable zone (where temperatures allow for liquid water). Deep space scans by the Hubble Space Telescope tell us there are about 500 billion galaxies out there, some smaller than ours, but many larger.

Since we do not understand abiogenesis, we cannot fix any real probability for it happening anywhere. We can only say for certain that it either happened in our Earth’s case, or somewhere else then got transported somehow to Earth, because we couldn’t be here to say so if it had not. A reasonable guess (SWAG) is that the probability for life elsewhere in the Universe is extremely high, but not exactly 100%. If and when we figure out how abiogenesis occurs, we will be more able to fix a probability on its happening elsewhere, and have a better idea of the conditions necessary for it to occur.

The probability for intelligent life with advanced technologies would be much lower, though. For that to arise, a planet would need a stable, life-friendly environment lasting billions of years. Any nearby supernova, quasar, pulsar or gamma ray burst would bring the whole adventure to an end before intelligent life could evolve. A collision with a large space object, or such an object hitting the life-supporting planet’s star and causing a massive coronal ejection would also end life’s development there. The parent star can’t be a supermassive one, because it would supernova too quickly for life to begin. It has to be a main sequence star that will live many billions or ever trillions of years. Due to fluctuations in their parent star, many planets probably have environments capable of supporting simple single-cell life, but environments too extreme to support complex life-forms.

Then there is distance. Consider that Voyager 1 is now traveling at 35,000 MPH away from our Sun, and has been since 1977. At that speed, it will still take it another 40,000 years to reach the halfway point between the Sun and Centauri Proxima, our closest neighboring star at just 4.24 light years away. Our Milky Way is between 100,000 and 120,000 light years across. The known Universe is currently 94 billion light years across. Due to the accelerating expansion of empty space, distant parts of our Universe are now receding relative to us at speeds faster than light. If there are life forms out there, what is the mathematical probability that life developed advanced technology but did not destroy themselves with it, that they instead learned to travel thousands or billions of light years in a single lifetime, and that having managed all that, they set out to visit Earth of all possible places?

It would seem to me that given all that, the probabilities fall from near certain to near vanishingly small. Am I wrong? If I am, please convince me, because I would love to meet and interview another ET.

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36 Answers

downtide's avatar

If there is life out there smart enough to travel all this way they’re also smart enough not to bother. If they’re after natural resources they’ll be better off mining a planet that hasn’t already been stripped nearly bare by it’s inhabitants.

ragingloli's avatar

Can not give you that, because there are important questions that need to be answered first.
Apart from the Drake equation, these questions are:
1. Am I to ignore all the UFO sightings, or Abduction reports?
2. Am I allowed to assume that an alien civilisation is capable of faster than light travel?

Sueanne_Tremendous's avatar

I don’t know for certain of course, but we have a newscaster here in Milwaukee who sure looks like an almond-eyed alien, and I am betting he found a wormhole and he used it to sling-shoot himself right into the anchor chair.

Aster's avatar

I’m guessing 100% .

Seek's avatar

I’m bad with numbers. Let’s say ten to the power of eleventy zillion four hundred and three point blue against.

Jaxk's avatar

I have little doubt that some lower life forms have evolved elsewhere. Intelligent life capable of tachnologies equal to ours seems much less likely. It may very well be that we are the pinnacle of intelligent life in the galaxy. A depressing thought at best.

Mr_Paradox's avatar

I doubt they’re even interested in a relatively primitive species like ours.

Strauss's avatar

Does the OP assume that any alien life form is “life as we know it”?

Lightlyseared's avatar

100% sure – slime moulds.

talljasperman's avatar

@ragingloli I though you were an alien?

ucme's avatar

I don’t know about now or in the past, but some time in the far distant future they’ll turn up.
Clearly that’s a mahoosive, big arsed space out there, would be ignorant to suggest our little rock is the only place that supports life.
I have to laugh when everyone says they’ll be of a vastly superior intelligence, maybe the dumb bastards just got lost & showed up by chance & assumed Earth was a huge beach ball.

DWW25921's avatar

Why would an intelligent alien want to visit this dump? I mean, Earth has it’s scenic bits and all but the people will drive you mad!

Rarebear's avatar

Relativity is a bitch. It’ll never happen.

philosopher's avatar

I think they have observed us. Buzz Aldrin said, he was observed in space.

KNOWITALL's avatar

I’m with ucme, I think it’s probable. Don’t any of you watch Ancient Aliens? lol

Linda_Owl's avatar

An alien might be studying us, but I am sure that our behavior (especially the religious differences) they would find infinitely puzzling. Far too many people on this planet we call Earth, clearly do not have intelligent thoughts.

snowberry's avatar

Seriously, the more I listen to the news, the more I feel like I’m in an alien movie. Only it’s not a movie, it’s real life. Yeeech!

Paradox25's avatar

I’m not sure if there’s any reasonable way to determine this. I do think it’s highly arrogant to think that our knowledge of physics is top notch, that our theories are infallible or that we should limit what advanced aliens can do or how they travel based upon our very limited understanding of physics. I highly doubt that we’ll be able to communicate with aliens using SETI protocols either.

The best estimates seem to come from the Drake equation, though it’s concerned more with the likelyhood of life outside of Earth than the likelyhood of travel to here. I really would not be surprised if there are other intelligent entities on other planets/moons whom wonder if they’re alone as well (less advanced intelligences like us according to Kaku).

ETpro's avatar

@downtide The only reason that I can imagine that a civilization at Type III on the Kardashev Scale (the minimum level of technology I would expect to ba able to pull of superluminal travel) would visit Earth is the same reason we sent the Voyager Probes out into space. Curiosity.

@ragingloli As you know, the Drake Equation relies on Bayesian analysis where none of the probabilities are even close to well known. It was never intended to state a real probability, just to stimulate interest.

Regarding alien abductions and sightings, interestingly they now occur with almost exactly the same frequency that witch and warlock abductions and demonic possessions occurred before the UFO craze began. And guess what, in areas exposed to press coverage of stories like the Roswell crash and such, witches, warlocks and demons suddenly quit bothering mankind while wicked little grey aliens took up the slack. I leave you to guess what conclusions to draw from that.

As to superluminal travel, assume as you wish. It’s clearly a requirement for travel to even the nearest stars in a single lifetime. Can it be done? Not now, but maybe when we figure out how to merge gravity, relativity and quantum mechanics into a theory of quantum gravity it can. All I know about that is that I don’t know.

@Sueanne_Tremendous Ha! Outstanding. You suspect a newscaster and ETpro slides by without raising any suspicion among Earthlings. Is it the beard? :-)

@Aster Flunk on statistics 101. It can’t be 100% till we actually find intelligent, space-traveling life out there, or around here. And despite all the Alien stories on the History HisFiction Channel, there is no credible evidence any alien has actually visited Earth.

@Pachyderm_In_The_Room I like Bill Nye and I’m pretty sure he has a long-form birth certificate proving he’s not an alien. :-)

@Seek_Kolinahr That’s pretty close to my rough estimate of almost vanishingly small.

@Jaxk One more of those rare moments when we totally agree. Break out the Grand Marnier.

@Mr_Paradox One more good reason to place the probability quite low.

@Yetanotheruser No assumptions whatsoever. As far as I am concerned, we cannot make any rational pronouncements about this till we fully understand abiogenesis. Even on Earth, extremophiles show us that life, once going, is incredibly adaptable. For all I know there are self-replicating life-forms in the Sun’s radiative zone and its photosphere or chromosphere, formed from quantum entangled particles generated in the core’s fusion reactions. Maybe there are self-replicating things in the acidic clouds of the gas giants like Jupiter and Saturn. We have no evidence there are. It they are there, they don’t appear to be showing any interest in is. But I am not prepared to interpret that as categorical proof they don’t exist.

@”: as a man of science, how do you justify that conclusion?

@Lightlyseared As discussed in the OP. 100% is not a logically supportable answer. And since when did we discover that slime molds are capable designing and building interstellar spacecraft? If some are, then Earth definitely got cheated in slime-mold IQ.

@talljasperman I’ll leave @ragingloli to clarify that. I have my suspicions, but she hasn’t given me the green light to confirm them.

@ucme Believe me, if a species masters interstellar space travel in a single lifetime, they will definitely not be dumbasses. They will be so far beyond us in technology that their abilities would be to us indistinguishable from magic.

@DWW25921 That’s a damned good question that I do not have a damned good answer for. Hell, I don’t even know why you shouldn’t end a sentence with a preposition.

@“Rarebear”; What happens when relativity is reconciled with quantum mechanics? We know it has to be. There has to be a theory of quantum gravity, because it works. But we haven’t a clue how to two can be reconciled. Obviously, we are missing a major part of the puzzle, and who knows what falls out of the equations of the accurate theory of quantum gravity?

@philosopher Pop culture said…

@Rarebear Thank you. Saved me the trouble.

@KNOWITALL The Ancient Aliens shows are just another test of modern culture credulity. It you give them any weight as evidence, you fail the test. They trot out “evidence” that is absurd and would only fool those completely unaware of the scientific method. All they prove is how incredibly gullible the American public at large is. That’s a dangerous thing when we are governed by democracy.

@Linda_Owl Yes, that’s come out in this thread and many others.

@snowberry My sympathies. Try the tinfoil hat. Works every time. The aliens can’t penetrate aluminum despite all their technology. :-)

@Paradox25 I don’t know any top-notch physicists that think our knowledge of physics is top notch. They, far-far more than the general public, are painfully aware of all that we do not know.

If I had to hazard a guess, though, I’d be right with you in betting there are other intelligent life-forms out there gazing up at the immensity of the Universe and guessing they must not be alone.

philosopher's avatar

The Universe and our own galaxy have shown signs of life. If there is water in any form there could be life. Some where in our Universe there is probably other sentient life. M theory makes it more interesting and difficult. Since there probably are other Universes.
I believe based on what some Astronauts have said, that they have been observed in space. Our governments do not wish to alarm us by telling us this.

Aster's avatar

@ETpro I don’t mean I think they’ve visited us like they’re walkng down Park Avenue. I mean I am 100% certain they are observing us . And they have their reasons, of course. One reason is to create humanoids. Why do they want humanoids? I have no idea. Several astronauts discuss UFO’s on youtube. I doubt all of them are liars knowing they would be laughed at. An astronaut telling about UFO’s is not something people like you would call proof. You would need them to land on your yard then float through your walls and even then you’d dismiss it as a dream. I have a fantastic video by a very convincing, intelligent man whose entire family were taken aboard a UFO that will be made into a movie. HIs name is Matthew REED . He’s on youtube and has subjected himself to public ridicule to tell the truth .

Lightlyseared's avatar

@ETpro slime moulds are a single cell life form that can transform into a multicellular life form in order to move to a new area to feed. Compared to that interstellar space travel is childs play.

ETpro's avatar

@philosopher There are no credible, peer reviewable signs of extraterrestrial life yet. It’s true that the absence of evidence is not the evidence of absence; but it’s also true that in the absence of evidence, we court grievous error when we claim to know what the evidence will show if and when it’s found. Astronauts have seen odd things around spacecraft. All we can say with any certainty is they were unidentified flying objects or visual phenomena approximating UFOs. The emphasis on unidentified is an important one. It is an enormous and unsupported logical leap to conclude that because we saw something appear in the viewscreen of a spacecraft, and we are unable to identify what it was, it was obviously a flying saucer piloted by extraterrestrials. There are a whole host of far more mundane and potentially likely explanations. Paint chipping off the capsule, water vapor frozen on the craft and now flaking off, and so on. Even if we rule all those out, which has not been done, we still can’t then say these were spacecraft piloted by intelligent beings from a distant star system. They may be some perfectly natural phenomenon we are just not yet aware of.

As to government suppression of all knowledge of extraterrestrials, I find that idea preposterous on its merits. It asks us to believe that while the US government could not keep the lid on its most sensitive secret, NSA spying, for a few years; all the governments of the world have had tens of thousands of personnel at all levels aware ET is here for over 70 years now and they have never suffered a leak.

@Aster That’s the kind of credulity that scares me. The same sort of credulity led to centuries of witch trials and the inquisition;s killing of millions for demonic possession. All of this was done by the good holy men of the church. Some of its most prominent, honest believers were eyewitness to skies filled with witches flying on brooms. Does that mean it really happened?

@Lightlyseared “Compared to that interstellar space travel is childs play.” Umm, no.

Funny, I’ve yet to see a slime mold colony blast of for happier hunting grounds on planets orbiting nearby stars.

Aster's avatar

@ETpro I assume there were eyewitnesses to airplanes flying around decades ago
and the people claiming to have seen them were laughed at for a brief time. But now we have eyewitness testimonies in many countries, videos from all over the world, under the skin implants being removed and analyzed and those videos are on tv. How can you possibly compare that to witches seen on broomsticks? In fact, I have never once heard that people saw witches on broomsticks so thanks for telling us. The Spanish Inquisition killings were a brutal reality far removed from what we know about UFO’s. Where is the comparison ? The US government has , in fact, destroyed documentation of UFO sightings but not “tens of thousands” of documents. I find it to be very naive and narrow to think that we are the only planet inhabited by advanced humans and there could not be a planet with beings thousands of years more developed than we are. After the 1940? Roswell, New Mexico UFO crash the US Army rushed to the scene and cleaned up every single sliver of evidence. They were that paranoid and terrified that someone might find something that we would not be able to explain . In fact, I think some people would feel quite threatened if they saw Matthew Reed’s youtube video where he describes his entire family’s abduction experience. It doesn’t scare me one bit and I have kept it on my DVR. People should be afraid of floods, sinkholes, anarchy and earthquakes if they want something to be afraid of. Look up.

philosopher's avatar

I have seen a video with Buzz previously saying he believes he was observed by aliens in space. No we do not have conclusive documentation. I just found this.
I wish I could find the video. I do not see why Buzz would lie. What I found now is more difficult to believe.
The truth is we do not know. I believe the US government and others know much more than they will tell us. People would panic.

ETpro's avatar

@philosopher I also meant to not that while the postulate of a multiverse is widely called M Theory or Multiverse Theory and seems to arise out of what even professors of Physics call String Theory, none of those things are legitimate theories or even hypotheses, because at present we have no way to test them, no way to falsify them. Till we do, in truth they remain only postulates. They are terrifically interesting and if we some day develop ways of testing them and they prove to be true, that proof will probably lead to an explosion of scientific knowledge similar to what the Theory of Relativity did.

@Aster I find it informative that the very first reported alien abduction case came after dirigible flight began. In 1897, a Colonel H. G. Shaw reported that a silvery disk-like craft tried but failed to abduct him. It wasn’t until human aircraft and then the Russian Sputnik launch occurred that people began to routinely report abductions, generally with claims they were sexually probed. Curiously, although these aliens have mastered superluminal travel, have shields to protect their craft from space dust and asteroid like debris, and the technology to float through bedroom walls and float human bodies back out through them; they strangely all use medical instruments like you would find in an ordinary or even rather primitive hospital examining room.

Before manned flight, people were taken in their beds by incubi and succubi. They witnessed witches possessing them. But none of that started till Christianity made its debut.

Before Christianity, they were visited by the gods and the demigods, and guess what, they were obsessed with sexual contact with humans as well.

No chance that dreams, waking dreams, sleep paralysis and hallucinations could possibly play a rile, though. All these many abductions and supernatural with human mating rituals are clearly to be believed. Well not by me. I can see plenty of mundane explanations. Truth is not established by how many people claim something. The world did not transform itself from flat to round when humans finally figured out how it was shaped.

@philosopher I certainly don’t think the Astronauts lied. I just think we need to wait for clear evidence before reaching conclusions.

philosopher's avatar

I enjoy reading about all kinds of Science.
Scientist may be able to prove more hypnotize if,
we have Quantum computers.
I read Dr. Kaku’s books. I watch Science channel and learn.

ETpro's avatar

@philosopher You and I enjoy the same sort of TV and reading, then. Dr. Michio Kaku has quite a bibliography to his credit. Which of his books are you referring to?

philosopher's avatar

I have read a few. The last one was Psychics of the Future.
I like when he wrote about a computer program that will read our thoughts. I think we should subject Congress to weekly testing. I know they will try to prevent this.
They are all trying to tell us that genetically modified food is safe. If we could make them say this and see what they are thinking. It would be clear that they are lying.
I also watch Through The Wormhole. I use to watch Brink. That was a great show.
I know ET that your are a thinker. Sadly, most people are not thinkers.

ETpro's avatar

I already had Physics of the Impossible on my reading list. Just added Physics of the Future to my list.

Interesting how the NSA and all the other alphabet soup is so profoundly interested in what we all do and say, but they want absolute secrecy when it comes to what they are up to. Technology is giving them an increasing ability to snoop, but it works both ways. Little brother is increasingly watching big brother too.

I think it would be great if more citizens embraced rationality and critical thinking.

Tinbobtina's avatar

I think that we won’t find life on other planets by trying to travel there with our space ships. I think we will find life if we discover some new technology like the internet connection but on a massive scale so that we can use the equivalent of face time and interpretation and share knowledge using gamma wave technology or radio signals but obviously the technology is there but maybe won’t be accessed during our lifetime.

VenusFanelli's avatar

If life exists on distant planets, it can’t visit us. The distances between stars is vast, so a spaceship would have to travel very, very fast to go from one star to another in a feasible amount of time. The problem is that the Theory of Relativity shows that matter has a severe limit upon how fast it can travel. Also, the energy requirements can never be met for interstellar travel. How can we ever contain and direct hydrogen fusion or matter-antimatter reaction?

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