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

Life in the universe.

  1. Jun 21, 2011 #1
    Hello PF.

    I will give you my thoughts about the chance of there being life in the universe and I would like you too write what you think and maybe come with arguments against me. I am not very pro in any way at all so I may be incorrect in some things and if I am I would be happy if you can correct me. Most of this knowledge I have learned come from Neil deGrasse Tyson I should say and I share his beliefs.

    I should say I talk about intelligent life and my definition of intelligent life in this thread is the knowledge too send radio waves, communicate and send objects into space.

    Our atoms are made of hydrogen,oxygen,nitrogen and carbon. Our body is 60 percent water = H2O = 2 H atoms and 1 O atom our DNA is based on Carbon and Nitrogen occurs in all living organisms we know. If we look at the most common atoms in the universe we find the exact same atoms; hydrogen,oxygen,nitrogen and carbon. We know, because of modern astrophysics, how those atoms are made they are traceable to the crucibles that cooked light elements into heavy elements in their core under extreme temperatures and pressures. These stars exploded, what we would call a supernova i guess, scattering their atoms across the galaxy.
    These ingredients become part of gas clouds that condense, collapse, form the next generation of solar systems stars with orbiting planets. And those planets now have the ingredients for life itself.

    IMHO the universe is too vast, there is way too many stars, way too many planets throughout the universe with those ingredients for life itself, that life would not drive of one of those planets would be very ego too suggest.

    One could argument that, yes we haven't found life yet but IMO that argument is not really valid when we consider how big the universe is contra how much we have looked.

    In my very humble opinion life is just an invertible consequence of complex chemistry.

    Now;

    Do you agree with me or do you think I am completely wrong?

    /WeW/

    By the way sorry for my bad English but I am from Denmark and don't get too write or talk English that much.
     
    Last edited: Jun 21, 2011
  2. jcsd
  3. Jun 21, 2011 #2

    Drakkith

    User Avatar
    Staff Emeritus
    Science Advisor

    I mostly agree. When you look at the simply enormous scale of the universe it seems almost silly that there isn't any other life out there.
     
  4. Jun 21, 2011 #3

    Nabeshin

    User Avatar
    Science Advisor

    The thing is, it really isn't a question of opinion or how you feel or anything like that. The rate of star formation, the rate of planet formation, the fraction of planets within the habitable zone, the fraction of those which have water etc. are all well defined quantities. That is to say, all the terms in the drake equation are perfectly well defined -- we simply do not know their values (and hence, the variations of those values).

    Space is, of course, inhumanly big, so it is no wonder that many of us 'feel' that there 'must' be other life out there. However, us humans are also notoriously bad with large and small numbers, and it could be the case that the formation of, say, planetary bodies within the habitable zone is an extraordinarily rare event such that, probabilistically, there is next to no chance of life. (Disregard for a moment what we actually know about this process -- The point is that people have been making the claim that surely life 'must' be out there for much longer than we've had any idea about such things!)

    My point is that it's a question of facts and data, and one should not appeal to intuition for any kind of answer to this question.
     
  5. Jun 21, 2011 #4

    Drakkith

    User Avatar
    Staff Emeritus
    Science Advisor

    I understand you Nabeshin, but unfortunantly the facts and available data are woefully inadequate to form an informed opinion either way really. All we can look at is the sheer size of the universe and take a guess and form an opinion.
     
  6. Jun 21, 2011 #5

    marcus

    User Avatar
    Science Advisor
    Gold Member
    Dearly Missed

    I agree with Drakkith. I mostly agree with WeW.

    One must have carefully reviewed opinions and hunches (intuitive suspicions) in order to decide on questions like exoplanet research budget. It is rational to have guesses about stuff we don't know in order to set scientific priorities. In a democracy (like Denmark) there is a role to be played by informed public opinion. That includes informed opinion about what is still unknown, and only a possibility. Scientists form opinions about what could be and what might be interesting to discover. So must also the Public be able to form opinion of probabilities about what is still unknown. Or so I think. If it is a real democracy.

    WeW, you should say "incontrovertible" for undeniable, something you cannot argue against.
    I hope you practice your English with us. Your ideas are good. You just need more practice---then you will be indistinguishable from a native English-speaker.

    Also the words "to" and "too" are different. They sound the same but mean different things.

    "to" forms the infinitive and also expresses motion towards. I go to school. I want to learn.

    "too" expresses the idea of "in addition" "more of the same added on" and sometimes "excess" (like "too much" is more than you need or want).
     
  7. Jun 21, 2011 #6

    DaveC426913

    User Avatar
    Gold Member

    Note that there are two critical factors that are very important to us where those probabilities fall short, and, if not in our favour, makes the rest moot.

    These one-or-many extraterrestrial lifeforms must occur frequently enough to raise the probablities that at least some of them are:
    a] near enough in space for us to locate them (let alone study or communicate with)
    b] near enough in time that they are here when we are.

    If life is not so common that either of the above fall below some threshold (lots of lifeforms - but they're 10,000 light years away - or - lots of lifeforms but shortlived, and all died out a billion years ago), then the mere probability of life in the whole universe is meaningless.

    What we concern ourselves with is the vanishingly tinier probability of life within observational distance anid at this time in the univers's lifetime.
     
  8. Jun 21, 2011 #7

    marcus

    User Avatar
    Science Advisor
    Gold Member
    Dearly Missed

    WeW why don't you ask two separate questions both restricted to LIFE IN OUR GALAXY? Restricting the question just to our galaxy makes it more practical to address.

    A. is there some other life in our milkyway galaxy?

    B. is there some other life in our galaxy that builds radios?

    It is more practical to address questions like this, because we know how many stars, we know what they are like (numbers of different types of stars) we have a sample of planetary systems. We have rough estimates of planets with liquid water etc etc. IN OUR GALAXY limits the numbers so you are more able to calculate probabilities.

    It is also more practical because there are more real decisions to make based on the information, if it becomes available.

    Life in a distant galaxy 100 million lightyears away we don't have to take seriously. Sure there might be. But we could never hold a radio conversation, or send a robot visitor to them. It is an abstract question whether there is some radio-able life in a distant galaxy.
    Probably there is, but so what? The information has no practical consequences and is not very easy to test.
     
  9. Jun 21, 2011 #8

    DaveC426913

    User Avatar
    Gold Member

    More to the point, it is not merely unknown, it is virtually unknowable. You might as well go looking for God.
     
  10. Jun 21, 2011 #9

    bcrowell

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Well, to go to another galaxy you have to get to like warp factor 13, and also you have to break through the energy barrier at the edge of the galaxy.

    But in the meantime, this book is pretty interesting:

    Ward and Brownlee, Rare Earth: Why Complex Life Is Uncommon in the Universe
     
  11. Jun 21, 2011 #10

    DaveC426913

    User Avatar
    Gold Member

    Ah yes, the Energy Barrier. :uhh:

    Ever get the feeling they were sitting around in the writer's war room and said to themselves "What's the dumbest sci-fi techno-nonsense we can get away with and still get the fans to swallow it?"

    But back to the thread, before it gets derailed...
     
  12. Jun 21, 2011 #11

    Drakkith

    User Avatar
    Staff Emeritus
    Science Advisor

    Probably the fact there are hundreds if not thousands of species in about 1/4 of the galaxy that looks 90% just like humans.
     
  13. Jun 21, 2011 #12

    bcrowell

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    You're telling me there's no Energy Barrier??
     
  14. Jun 21, 2011 #13

    bcrowell

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    I complained to my running buddy the other day about Vulcans being able to interbreed with humans, etc. He launched into an intense explanation of why this is actually possible in the Star Trek universe. Sometimes it's good to know that you aren't the biggest geek in the whole world.

    But if I really wanted to derail the thread, I'd mention how Klingon babes are totally hot.
     
  15. Jun 22, 2011 #14

    Drakkith

    User Avatar
    Staff Emeritus
    Science Advisor

    I always liked the depiction of strong and decisive women lol.
    Too bad it wont be like that for real. :frown:
     
  16. Jun 22, 2011 #15

    Ryan_m_b

    User Avatar
    Staff Emeritus
    Science Advisor

    For the most part I don't think it is reasonable to assert that it is probable that there is life anywhere else but Earth, especially so for intelligent life. Obviously it's happened once so it could happen again but we have very little idea of how abiogenesis works and consequently no idea of how likely it would be that given another primordial Earth abiogenesis and evolution would occur. It could be that the odds are incredibly high and once you have the right chemical mix/temp etc it is only a matter of time, it could also be that Earth was extremely lucky.

    You can ditto that for the evolution of multicellular life, development of central nervous systems, evolution of social animals and evolution of tool-using animals. Looking at it from an Evo-Bio stance we have nothing to base our probabilities on and so cannot really guess at an answer.
     
  17. Jun 22, 2011 #16
    I will practice English and quite frankly' I did not know the difference between "to" and "too" so thank you for clearing that out.


    I totally agree with you Marcus. The question about life in our galaxy or a nearby galaxy would definitely be the most relevant question to impose given that the data we have on those galaxy's is of course more reliable than galaxy's we have little or no data off.

    I of course agree with you Drakkith.

    Yes there could be anything, something or nothing we simply do not know and probably we'll never figure it out. So all that's left is "empty" guessing.

    /WeW/
     
  18. Jun 22, 2011 #17

    Ryan_m_b

    User Avatar
    Staff Emeritus
    Science Advisor

    No all that is left is to methodically design and implement research :wink:
     
  19. Jun 22, 2011 #18

    DaveC426913

    User Avatar
    Gold Member

    Well, I'm not really sure it's a total mystery, but maybe I'm optimistic.

    Lipids tend to form naturally, which tend to form closed self-contained bubbles. Amino acids tend to form naturally. From amino acids you get proteins and you're at least on your way toward chemical complexity.
     
  20. Jun 22, 2011 #19

    Ryan_m_b

    User Avatar
    Staff Emeritus
    Science Advisor

    I agree it's not a total mystery, the field of http://en.wikipedia.org/wiki/Abiogenesis" [Broken] is far from square one but I don't think we have a good enough understanding of the processes to presume the likely hood that they will give rise to life. This combined with the lack of data as to the number of planets where abiogenesis conditions could arise means I am always sceptical about estimations for the prevalence of life.
     
    Last edited by a moderator: May 5, 2017
  21. Jun 22, 2011 #20
    Time in life cycle is very important also. Intelligent life, as defined by WeW, has only been around on Earth for 100 years or less out of the 5 billion years of Earth's existence. Who knows how long it will continue to be on Earth. If each of the billions of stars in our galaxy had one planet in the right place to support life, how many would support "intelligent life?" And then how many of those would be at the same life cycle as us, such that we could communicate?

    I agree that life probably exists, has existed or will exist at some future time, but the probability that will ever communicate with them is very very remote. IMHO.
     
  22. Jun 22, 2011 #21

    bcrowell

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Nice post. I'll sketch a counter-argument.

    Suppose I watch a black box whose inner workings are unknown to me. After I've watched for one hour, the top of the box springs open and a jack-in-the-box pops out. Later, I come across another black box that looks identical to the first. What should I guess for the probability that the new jack-in-the-box will pop out within one hour? I could say that there's no way to answer that, because I have no idea at all how the mechanism works. Maybe the average time it takes before it opens is a million years, and I just happen to have been extremely lucky to see the first box open in only an hour. Or maybe the average time it takes is only one minute, in which case it was extraordinarily improbable that it would have taken as much as an hour to open. But basically, my guess is going to be that this type of box has a half-life of somewhere on the order of an hour, so I'm going to guess a probability of roughly 50% that the second box will open within an hour.

    There is a flaw in this argument because of the anthropic principle. If life had never evolved on earth, then I wouldn't be here to think about it. This means that out of all possible outcomes of the black box, we never get to observe outcomes in which the box never opens at all. That biases the observation. But the argument can be modified to deal with that. Our planet will probably end up having spent about 5 byr in a state where it's reasonably hospitable to life. Suppose that a large sample of the mysterious black boxes are observed, each for 5 hours. If the box doesn't open at all, then the observer doesn't record it. If the box does open, then the observer posts a 5-hour video of the box on you-tube. We randomly pick one of the you-tube videos to watch, and the box opens 0.5 hours from the start. If the half-life was a month, then the time at which the box opened in one of the videos would be almost uniformly distributed from 0 to 5 hours. The fact that we observe t=0.5 hr in the only video we have access to suggests that this is not the case. Probably the half-life is more like 0.5 hr. This is essentially what happened on earth. Earth has been capable of supporting life for something like 5 byr, and it appears that life got started something like 0.5 byr into that period. That suggests that on an earthlike planet, the half-life for abiogenesis is something like 0.5 byr, and therefore the probability of abiogenesis is extremely high.

    All of these events (multicellular life, etc.) happened relatively late in the game on earth. This suggests that the half-life for them to evolve is at least billions of years, and maybe much longer, i.e., their occurrence may have been very unlikely -- but they all happened on our lucky planet, and that's why we're here to think about them.

    So IMO the most likely hypothesis is that bacteria are present in lots and lots of solar systems throughout the galaxy, but that multicellular life is extremely rare. This hypothesis is supported by the fact that SETI has failed so far.
     
  23. Jun 22, 2011 #22

    DaveC426913

    User Avatar
    Gold Member

    Agreed. I've always considered the fact that life got started here relatively quickly after things became hospitable to be a very encouraging sign.

    On the other hand, despite life starting within .5by, multicelled life didn't come along for another 2by after that.
     
  24. Jun 22, 2011 #23
    I note much of the discussion on the development of life in this post resolves around earthlike environments - which is obviously justifiable in that we know the chances for life on earth like planets is greater than 1.

    There is also the possibility of life developing in other environments, which maybe inhospitable to us - possibly even complex life in these environments, and given the limitations the OP placed on technological capabilities we may be failing to include a broad spectrum of possibilities.

    It could be that multicellular complex life is very rare on planets and actually much more common in nebula or gas giants - obviously speculative just worth a thought when discussing the entire Universe as the questing ground!

    WhateverWorks - if not already familiar with then I would recommend you to do some reading on the fermi paradox as I think this has some significant bearing on the original questions you posed and I think you would find it interesting.
     
  25. Jun 22, 2011 #24

    DaveC426913

    User Avatar
    Gold Member

    Problem is, there are precious few combinations of chemicals that even form large molecules at all, and they don't exist in concentratrions high enough to provide building blocks - all that let alone getting them to do anything spontaneously.

    Remember, there are only a few dozen useful elements in the universe, and they behave here in our labs the same way they behave out there. And we just don't see much in the way of contenders.

    Here's a question to all:

    C O and H form molecules of millions of atoms. What is the largest molecule known that is not composed of some combination of C O and H? (There are some inorganic compounds that use carbon but still, they are no more than a handful of atoms.)
     
    Last edited: Jun 22, 2011
  26. Jun 23, 2011 #25
    The development of complex life would never be an easy route - are there many environments we struggle to recreate in a lab?

    I am in no way saying development of life in unearthlike places is likely or even possible, just speculating that we have to consider the possibility of life developing in other environments considering the scale of the U.

    However I was simply playing devils advocate, personally I would expect simple celled life to be quite commonplace across the cosmos but would expect the development of multicellular intelligent life to be very restricted based on the complexities required. That being said, while I stipulate multicellular complex life is restricted in its development - I would still think given the scale of U and sheer probability life would be varied throughout the cosmos, BUT if life does prove it can survive or even thrive in totally different environments then the argument must be extended even further.

    Dave I think your previous question on inorganic molecule composition is an interesting one! Hopefully someone knowledgeable can comment on this :)
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook