Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Question: Should I Believe in Aliens?

  1. May 13, 2012 #1
    So here is the setup: I know a bunch of people who think it is the dumbest thing ever or absolutely ridiculous to say, "I don't believe aliens exist."

    What is your stance on that question?

    Here is what I currently know:
    +I have seen no evidence for alien existence

    Therefore, I don't believe in aliens. Now, if there is some evidence, I would change my tune. That is partly why I'm making this thread, to make sure there is no evidence as I have encountered.

    Here are some common arguments for alien existence:

    +Drakes equation
    Giving names to unknown probabilities does not mean we know them. Don't make me laugh.

    +"Pyramids! Therefore, aliens visited us, and by extension, aliens exist (since non-existent beings cannot visit us).
    First off, arguments of this flavor basically say, "We have no idea how [...]. Therefore, we do know how [...]." Ridiculous! The conclusion and premise are exact 180s of each other. As a demonstration of the insanity of this argument, consider the possibility of ultra-advanced humans coexisting with "tribal" humans, oh, for example how Americans coexist with small tribes in the middle of the Amazon jungle.

    +"Space is SOOO huge! Therefore, aliens must exist."
    This is a funny one. To this, I ask, "What is the probability of life spontaneously generating per unit of space"?" Without that probability, the number of trials for spontaneous generation mean nothing. In other words, (unknown probability of life generation per unit volume)*(known volume) = unknown expected value of instances of generated life.

    +"Space is INFINITE. Therefore, aliens must exist."
    This one tickles me more than the prior. It is extra misleading, because it is a valid argument. Given any nonzero probability of spontaneous generation of life and an infinite number of trials, life must have come about elsewhere. However, the premise that the universe is infinite is not known to be true as of now! So the conclusion based on it is dubious. I would go so far as to believe that premise is unprovable since it would take an infinite observation to verify something is infinite.

    Please help me not be an idiot. I have way too many people telling me I am. Thank you! I have even seen astrophysicists and astronomers on T.V. (albeit possibly sensationalists) say "OF COURSE there are aliens out there." When they say this, it makes me wonder how they know so steadfastly.
  2. jcsd
  3. May 13, 2012 #2
    What is the probability of finding H2O on other planets? Zero?? life must exist if water is found, that's why NASA is spending billions of dollars just to find water on other planets.
  4. May 13, 2012 #3


    User Avatar
    Staff Emeritus
    Science Advisor

    In the absence of direct evidence, we don't know if aliens exist or not. Even if they did, it doesn't necessarily imply that aliens would be humanoid.

    We do know that there are other planets that have oxygen and water, and possible the other elements/compounds that are requisite for life similar to that found on earth. However, that only indicates a potential.

    It would be amazing to find life on another planet in this galaxy, but most stars are beyond our reach. Life in other galaxies is even more beyond our reach.
  5. May 13, 2012 #4
    That Aliens exist somewhere in the Universe probability approaching one, chances of communicating with said Aliens probability approaching zero, that Aliens have visited Earth probability zero.
  6. May 13, 2012 #5


    User Avatar
    Gold Member

    +1 on that
  7. May 13, 2012 #6
    Ummmm ... ? Why must life exist if water is found? Water's necessary for life, but that doesn't mean other requirements are met, and even if all requirements are met, that doesn't mean life will exist.

    Anyways, I have some suspicion that they might not be primarily water as most earth species are if they exist.

    This is almost my argument. You did point out that there is no way to know (which I agree with), but due to the sheer size of the Universe, any probability other than a ridiculously small one of life being on a random planet will likely result in at least a few planets with life. I do, however, highly doubt they were ever on this planet. Note that I do not claim aliens exist, I do claim there is a good possibility they exist.

    At the moment, we have no evidence for aliens' existence (History Channel's Ancient Aliens basically just takes a few things we don't think ancient cultures had the technology to do, not all of which are valid, that they clearly did, and say it was aliens. Or just say "there's an uncanny resemblance between the Ark of the Covenant and a Nuclear Reactor." Hogswash.), but the only evidence we have for their nonexistence is the fact that we haven't found any. So it's all a bit uncertain. Those that claim that they definitely do exist have absolutely ridiculous arguments, and those that claim they don't just have to say "we haven't found any yet." So one must just come up with one's own opinion on how likely we are to find alien life and hope they're right. :smile:
  8. May 13, 2012 #7


    User Avatar
    Gold Member

    I assume you mean only that it would be amazing for us to IDENTIFY such life, not amazing that it would exist. Given the billions of stars in the Milky way, I'd say it would be quite amazing if there were no life other than us.
  9. May 13, 2012 #8
    It looks like it's happening here too. Can you guys tell me why you believe there are aliens? Astronuc seems to be on my page, though, that there is no evidence of alien existence.
  10. May 13, 2012 #9
    I'd say us believing there are aliens is too bold a statement, we believe that there are quite probably aliens.
  11. May 13, 2012 #10


    User Avatar
    2017 Award

    Staff: Mentor

    Well, our knowledge is quite limited:

    We know that there are a lot of planets, and some planets have conditions similar to earth (similar star, similar distance, mass and chemical composition). The estimates about the numbers are quite rough today, but that should get improved within the next decade.
    The big unknown number is the probability that life evolves on planets which can support it.

    However, there is an anthropic argument that some other planets should have developed intelligent (!) life. Let's assume 10^10 earth-like planets in the observable universe - this is some orders of magnitude below the real number, as observations showed.

    Now, what could the probability that intelligent life on a specific earth-like planet developes?

    We don't know. However, I would expect that 10^(-10) (one planet with intelligent life) is not 100.000 times more likely than 10^(-5) (10^5 planets with intelligent life). Therefore, if we follow bayesian statistics for a while, the probability of being one of 10^5 intelligent species is higher than the probability of being the only one.
  12. May 13, 2012 #11
    "It looks like it's happening here too. Can you guys tell me why you believe there are aliens? Astronuc seems to be on my page, though, that there is no evidence of alien existence."

    There is no direct evidence of alien existence, however there is growing evidence that Earth like planets exist in abundance in our galaxy making it an almost certainty that they exist in other galaxies.
    We have managed to produce ribonucleotides in the laboratory by simulating conditions found in on a primitive Earth the fact that this was possible suggests that the basic building blocks of life are relatively easy to make making life in other parts of the Universe far more likely.
    The combination of a great number of possible life supporting planets plus the apparent ease at which the basis of life can be created makes the probability of alien life very very high.
  13. May 13, 2012 #12


    User Avatar
    Staff Emeritus
    Science Advisor

    This is easy to answer. We do not know if there are aliens out there. Since we do not know, we can only say that we either believe that they exist, or do not believe that they exist. Whether you believe aliens exist or not will depend on your own reasons.

    So, in the end, YOU will have to decide whether you believe in aliens or not. You already have most of the most common reasons for believing in them.

    Edit: Perhaps a third option is needed. Believing they exist, not believing they exist, and neither believing nor disbelieving.
    Last edited: May 13, 2012
  14. May 13, 2012 #13


    User Avatar
    2017 Award

    Staff: Mentor

    This is not a binary decision. You can think of it as more or less probable (with a lot of freedom to choose). Recent discoveries of exoplanets shift it towards the "more probable" region, and an observation of extraterrestrial life would change the whole situation, of course.
  15. May 13, 2012 #14


    User Avatar
    Staff Emeritus
    Science Advisor

    You are correct. I will amend my previous post with a third option. Neither believing nor disbelieving.
  16. May 13, 2012 #15
    This part is based on the fact that life on Earth appeared not long after the late heavy bombardment, with evidence that life was present 100-500 million years after the end of it, about 3.9-3.5 billion years ago.
    There's something called the argument to the mean, where we can say that if we have one instance of something, then it is most likely to be close to the average value.
    Using this we can say that if the time taken for life to appear on Earth is typical, then the probability of life arising must by necessity be quite high, in the right circumstances.
    Hence if the probability of life arising is large, then there probably is extra-terrestrial life elsewhere in the universe, as it seems that Earth-like planets are common, as we have begun to see them, despite only just being able to detect Earth-sized planets.

    There are problems with this conclusion though, one of which is the Rare Earth Hypothesis, which says that the conditions for life to occur are rare. Another issue is we don't know whether assuming the argument to the mean is valid in this case as we only have one example of life occuring.
  17. May 13, 2012 #16
    Your argument should have stopped there. And as for your probability argument, you're going to have to state it a bit more clearly, perhaps symbolically at first. There is no reason to disguise a simple probability relation by calling upon an arbitrary name without even defining the probabilities associated in that relation clearly.

    The in bold is quite remarkable. You state in the same conjoined sentence that there is no evidence for A and that A is almost certainly true.

    Now, from what I can extract, you are stating our ability to manufacture ribonucleotides on planets 'like ours' combined with an abundance of planets 'like ours' means alien life almost certainly exists. However, you haven't cited any source saying how likely ribonucleotides spontaneously generate, or how likely it is that once they spawn, life will follow (which is sort of an important step in the equation... because correct me if I'm wrong, but ribonucleotides are not living).
    The in bold is a plain fact about anything -- that is, we can believe it or not believe it due to our own reasons. The qualifier to your observation ("Since we don't know...") is an unnecessary partition of the set of all possibilities. That is, it applies equally to things we "do know."

    The first thing you stated was you sizing up how much evidence there currently is, which you admitted was naught. Hence, you should (as I do) not believe in alien existence.

    You have made an awful mistake by playing this word game. What you are stating is a complete falsehood. You basically side-stepped the question. Let me explain:

    There are four possibilities:
    1.) "I believe aliens exist" & "I believe it is likely aliens exist"
    2.) "I believe aliens exist" & "I do not believe it is likely aliens exist"
    3.) "I do not believe aliens exist" & "I do believe it is likely aliens exist"
    4.) "I do not believe aliens exist" & "I do not believe it is likely aliens exist"

    In other words, the belief of whether aliens exist and of whether it is likely aliens exist are two different beliefs. It is unimportant that they are related (as in, no one should take on case 2). The proof that they are different is that case 3 is perfectly logical for some circumstances. We are talking about the former whereas you have pulled a red herring by bringing in the latter.

    And despite what you say, belief is binary. You cannot neither believe nor not believe something. The union of these possibilities contains all.

    To paraphrase, you stated, "A is a typical argument, but it is not a good argument (in bold)." Can I infer you are implying we should not believe in alien existence?
  18. May 13, 2012 #17
    Not long ago we thought the Earth was the center of the Universe, and the Sun was revolving around it. It also made perfect sense for most people, while the fact the Earth was just a planet seemed ridiculous.

    Actually, until very recently, just years ago, most people didn't even believe planets are a normal occurrence outside of our own solar system. Until technology evolved enough to find such planets around other stars.
    Last edited by a moderator: May 14, 2012
  19. May 13, 2012 #18


    User Avatar

    i'm pretty sure that ET aliens have never visited this planet (although it makes for and interesting premise in science fiction), simply because of the known distance between stars and the known speed of light and the known facts regarding special relativity. but i also think it unlikely that there are no other planets even in our galaxy that have never supported life. and once any kind of life emerges, i doubt that, once you give it a billion years or two (and assuming their sun doesn't burn out or go supernova on them), that more sophisticated life will not evolve from it.

    in other words, i am picking up on this:

    ask yourself what is the probability, knowing that life can emerge somewhere (because it has, at least at one place) in the galaxy, what is the probability that it has never emerged anywhere else in the galaxy. 100 billion stars out there. leaving our sun out of it (because we know what the answer is for that star), if the probability of life emerging on some planet around any particular star is very small, but not zero since we exist, then the probability of life not emerging on a planet around any particular star is not quite equal to 1. so it's 0.9999999999999999999999999999999999 or something like that. now multiply that probability times itself 100 billion times and see how close to 1 it remains and if it is still so likely that no where (else) life has ever emerged.

    it doesn't take a very large probability coming out of the Drake equation for it to be more likely than not that life has emerged somewhere else at some time in the past or the future. not terribly likely to be within 10 or 100 lightyears from us. and not terribly likely that they would become intelligent enough to send out radio signals that would be detected by us in the sliver of time our species would be listening. and very unlikely that we'll ever detect evidence of their presence since we will not measure any radio signal from them if they live halfway across the Milky Way (they would have to be within 100 lightyears, unless they send Morse code by detonating very large H-bombs in space - they gotta compete with the radiant output of stars).
  20. May 13, 2012 #19
    I think the word belief would be very difficult to justify in science, given the nature of science that it should be verified by evidence. science grows stronger in confidence when evidence grows stronger. Ex : Higgs boson - evidence for its existence grows stronger.Belief has very little use in science.
  21. May 13, 2012 #20
    What's wrong with saying "I don't know"?

    I remember there was a conversation in which someone was asking me whether I thought there were aliens or not, and they had enormous difficulty accepting the fact that "I don't know, and since I don't know, I don't have an opinion."
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook