# Question: Should I Believe in Aliens?

• RoshanBBQ
In summary, I don't believe that there is evidence for alien existence. However, if there is some evidence, I would change my stance.
rbj said:
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 got to compete with the radiant output of stars).

RoshanBBQ said:
How on Earth are you coming up with these probabilities

Whovian said:
I think that was just a guess, for the sake of example

RoshanBBQ said:
Well, if it's just an arbitrary guess, what good is it?

it's good for framing questions. or re-framing questions. would you like me to do that?

so let's say that if you pick any star you see in the Milky Way at random (but leave out our sun, since we know what the outcome is for that particular star).

so the Drake equation (copied from Wikipedia) is:

$$N = R^{\ast} \cdot f_p \cdot n_e \cdot f_{\ell} \cdot f_i \cdot f_c \cdot L$$

where:

N = the number of civilizations in our galaxy with which communication might be possible;

and

R* = the average rate of star formation per year in the Milky Way
fp = the fraction of those stars that have planets
ne = the average number of planets that can potentially support life per star that has planets
f = the fraction of the above that actually go on to develop life at some point
fi = the fraction of the above that actually go on to develop intelligent life
fc = the fraction of civilizations that develop a technology that releases detectable signs of their existence into space
L = the length of time for which such civilizations release detectable signals into spaceso, just to keep the discussion simpler, i want to fold a bunch of probabilities together into a single probability:

$$p = f_p \cdot n_e \cdot f_{\ell} \cdot f_i$$

that appears to me to be about the right expression for the probability that if you pick any old star out there, there will be intelligent life at some time around it. let's all agree that this probability is very, very small. like, for the sake of illustration, it's 0.0000000000000000000000000000000001. i just pulled the number out of my butt.

this means that the probability that, if you pick some star outa the sky at random, the probability that no life has ever existed on any planet around that star is 1-p = 0.9999999999999999999999999999999999 which is less than 1.

now, how many times can you multiply (1-p) times itself to get below 1/2? that is when the likelihood that there are no ETs out there is less than the likelihood that there are. since there are 100 billion stars in the Milky Way, even if p is that small, the likelihood that there are ETs somewhere in the Milky Way still comes out pretty close to 1.

so then invert the question and ask what must p be in order to get the total probability to 1/2?

$$(1-p)^{100000000000} = \frac{1}{2}$$

p doesn't have to be very large for it to be more likely there are ETs than not.

jreelawg said:
Your use of the word belief, may be correct, but not consistent with that of most people in the context.

So you position more simply put is, I don't know. I think if you just said that in the first place, the people your referring to wouldn't have thought your position was ridiculous.

All this talk about probability is ridiculous in my opinion. I don't think many people know what probability is or how to calculate it. It is impossible to know the probability of aliens existing, or visiting Earth given the evidence we have to base this discussion on.

My position is I don't know, which means I do not believe aliens exist. As for the in bold portion, that is largely what I suspect, which is why I have the position I have. It is also why I opened up this thread -- to see if my concept of the current state of evidence on the topic was right.

jreelawg said:
I could say that I don't believe physics forums will exist in the morning. Would you take it that I think that will be the case, or just that there is some possibility of it? I think there certainly is the possibility physics forums could be wiped out no matter how unlikely. So I guess anyone who believes that physics forums won't be wiped out in the morning is full of it.

We have to be careful with your sentence structure. What exactly is "I don't believe physics forums will exist tomorrow" saying? It is the same as saying, "I lack the belief that the physics forums will exist tomorrow." In other words, you do not assign truth to the statement, "The physics forums will exist tomorrow."

Now, as far as I can tell, no probability enters into this equation. I would think you're saying exactly what you're saying. You do not assign truth to that statement. But I would be quite assuming to think you would assign false to the statement, "The physics will exist tomorrow." That is to say, you could be in a state of "I don't know."

So to answer your question in bold, you haven't stated any belief -- so I don't take it you believe in any particular thing with probability or no probability. I take it you lack belief in something.

Travis_King said:
No, to his credit, RoshanBBQ did say that his point has nothign to do with uncertainty. I agree with that, at least. Belief doesn't require certainty, that's why it isn't called knowledge.

You can recognize the potential for your belief to be wrong, and yet still have that belief, i.e. you can recognize that physics forums might exist in the morning, and still believe that they will not. The degree to which your belief clings to reality, and the probability of it being true describe how rational your belief is.

(1) I believe X will happen
(2) I do not believe X will happen
(3) I believe X will not happen
(4) I do not believe X will not happen (epistemically different than 1)

So you can have 1&3, 2&3, 2&4
These are three logically consistent and epistemically different combinations of stances on this matter. Thus, the issue is not binary.

As far as probabilities actually go, I agree with jreelawg. We cannot know the probability of life existing, or the probability of abiogenesis. But we know that it is non-zero, and that life is pretty darn resilient and can survive in incredibly hostile environments. We also know that there is a limited number of different kinds of stuff in this universe, and the stuff that makes up life (at least as we know it) are extremely abundant. Does the evidence suggest that life exists elsewhere? That's up for debate. But it surely doesn't pit against that notion.

Now I'm starting to like your posts. However, there is a small problem I detect. Belief with respect to a single statement is binary -- you can either belief it or lack belief in it. The reason you came up with 4 statements of belief (or lack of belief) is you analyzed two statements from each two statements (the binary ones of which I speak) derived. The two statements were: "X will happen" and "X will not happen." More concisely, X happening and X not happening are all possibilities. So you analyzed two statements: "X" and "Not X (The complement of X)".

As for the in bold, I agree we don't have the evidence as you put it. The only deviation I have is it's not up for debate. I feel ironclad with my lack of belief in alien existence.

rbj said:
it's good for framing questions. or re-framing questions. would you like me to do that?

so let's say that if you pick any star you see in the Milky Way at random (but leave out our sun, since we know what the outcome is for that particular star).

so the Drake equation (copied from Wikipedia) is:

$$N = R^{\ast} \cdot f_p \cdot n_e \cdot f_{\ell} \cdot f_i \cdot f_c \cdot L$$

where:

N = the number of civilizations in our galaxy with which communication might be possible;

and

R* = the average rate of star formation per year in the Milky Way
fp = the fraction of those stars that have planets
ne = the average number of planets that can potentially support life per star that has planets
f = the fraction of the above that actually go on to develop life at some point
fi = the fraction of the above that actually go on to develop intelligent life
fc = the fraction of civilizations that develop a technology that releases detectable signs of their existence into space
L = the length of time for which such civilizations release detectable signals into space

so, just to keep the discussion simpler, i want to fold a bunch of probabilities together into a single probability:

$$p = f_p \cdot n_e \cdot f_{\ell} \cdot f_i$$

that appears to me to be about the right expression for the probability that if you pick any old star out there, there will be intelligent life at some time around it. let's all agree that this probability is very, very small. like, for the sake of illustration, it's 0.0000000000000000000000000000000001. i just pulled the number out of my butt.

this means that the probability that, if you pick some star outa the sky at random, the probability that no life has ever existed on any planet around that star is 1-p = 0.9999999999999999999999999999999999 which is less than 1.

now, how many times can you multiply (1-p) times itself to get below 1/2? that is when the likelihood that there are no ETs out there is less than the likelihood that there are. since there are 100 billion stars in the Milky Way, even if p is that small, the likelihood that there are ETs somewhere in the Milky Way still comes out pretty close to 1.

so then invert the question and ask what must p be in order to get the total probability to 1/2?

$$(1-p)^{100000000000} = \frac{1}{2}$$

p doesn't have to be very large for it to be more likely there are ETs than not.

You're going to have to be a bit more reasonable than this. It seems the discussion of aliens is the only place some scientists accept completely made up numbers as evidence.

RoshanBBQ said:
You're going to have to be a bit more reasonable than this. It seems the discussion of aliens is the only place some scientists accept completely made up numbers as evidence.

you need to stop blowing smoke.

what's unreasonable? that the probability of no life circling either stars A or B is the product of the probability of no life circling star A times the probability of no life circling star B? is that unreasonable?

what number did i make up? that there are 100 billion stars in the Milky Way?

BBQ, do you know how to do math? in case the answer is "yes", here is a number i didn't just make up (i was going to let you calculate it but you didn't rise to the challenge):

7 × 10-12

that's 0.000000000007 , a helluva lot bigger than the number i pulled outa my butt.

if you pick at random any old star you see in the sky, if it is more probable than 0.000000000007 that around that star ET lives (or had lived or will live) and is looking up at his sky and asking the same question about you that you are asking about him/her/it, if the the probability is at least that, then it is more likely than not that there is (or was or will be) ET circling around some star in the galaxy.

can you do the math and tell us why?

rbj said:
you need to stop blowing smoke.

what's unreasonable? that the probability of no life circling either stars A or B is the product of the probability of no life circling star A times the probability of no life circling star B? is that unreasonable?

what number did i make up? that there are 100 billion stars in the Milky Way?

BBQ, do you know how to do math? in case the answer is "yes", here is a number i didn't just make up (i was going to let you calculate it but you didn't rise to the challenge):

7 × 10-12

that's 0.000000000007 , a helluva lot bigger than the number i pulled outa my butt.

if you pick at random any old star you see in the sky, if it is more probable than 0.000000000007 that around that star ET lives (or had lived or will live) and is looking up at his sky and asking the same question about you that you are asking about him/her/it, if the the probability is at least that, then it is more likely than not that there is (or was or will be) ET circling around some star in the galaxy.

can you do the math and tell us why?

That number doesn't matter, because we don't know what the actual number is. There is no reason to believe the number is anywhere close to what it needs to be to satisfy your 1/2 equation. The probability of life around a star could be 10^-500 for example. I'm also not well-versed enough on the spontaneous creation of life to suppose the events per sun are independent. Basically, we know almost nothing about the phenomena since we cannot observe it or recreate it.

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RoshanBBQ said:
I'm also not well-versed enough on the spontaneous creation of life to suppose the events per sun are independent.
Exactly. And the key point is that no one is that well versed, although some believe they are.

We may suspect certain values apply in the Drake equation. We may think that if the value differs radically from the one we suppose that we should be utterly amazed. We may ague eloquently as to why the value will fall with in a give range, but - as you say - we do not know. Therefore any estimates based upon wholly uncertain numbers are interesting, but they are meaningless - other than as a thought experiment.

RoshanBBQ said:
That number doesn't matter, because we don't know what the actual number is. There is no reason to believe the number is anywhere close to what it needs to be to satisfy your 1/2 equation. The probability of life around a star could be 10^-500 for example. I'm also not well-versed enough on the spontaneous creation of life to suppose the events per sun are independent. Basically, we know almost nothing about the phenomena since we cannot observe it or recreate it.

The point is that the universe is very, very large. There are so many places other than Earth in which there could be life. To assume Earth to be so rare as to be the only place where life has begun seams very ridiculous. We have found that on earth, life thrives all over the place. There is life deep deep underground, there is life at the bottom of the Ocean living without the need for sunlight. There is life living in extreme cold, in extreme heat. Life is very adaptable.

I think the question to ask, is why would there not be life in other places? Is it that Earth is an unimaginably rare place. I don't think so, do you? Why?

Rather than dancing around the semantics of what it means to believe; why not hold a position worth discussing? Do you suspect there exists life in other solar systems? How strongly do you suspect it? If not, how strongly do you suspect life does not exist?

rbj said:
if you pick at random any old star you see in the sky, if it is more probable than 0.000000000007 that around that star ET lives (or had lived or will live) and is looking up at his sky and asking the same question about you that you are asking about him/her/it, if the the probability is at least that, then it is more likely than not that there is (or was or will be) ET circling around some star in the galaxy.

RoshanBBQ said:
That number doesn't matter, because we don't know what the actual number is. There is no reason to believe the number is anywhere close to what it needs to be to satisfy your 1/2 equation. The probability of life around a star could be 10^-500 for example. I'm also not well-versed enough on the spontaneous creation of life to suppose the events per sun are independent. Basically, we know almost nothing about the phenomena since we cannot observe it or recreate it.

Ophiolite said:
Exactly. And the key point is that no one is that well versed, although some believe they are.

We may suspect certain values apply in the Drake equation. We may think that if the value differs radically from the one we suppose that we should be utterly amazed. We may ague eloquently as to why the value will fall with in a give range, but - as you say - we do not know. Therefore any estimates based upon wholly uncertain numbers are interesting, but they are meaningless - other than as a thought experiment.

i think that astrobiologists would disagree. take a different component of the Drake equation fp and ne. 2 or 3 decades ago they had no experimental evidence other than our own solar system what the values of those might be. now we see exoplanets all over the place and it begins to look like fp might be nearly unity and ne might be 1.6 . we, as a species with intelligence, are starting to get a grip on those parameters. there are several scientists that work in abiogenesis that have both discovered life on Earth that has no need of sunlight (it only requires water and an energy gradient in order to exist) and they have discovered evidence of H2O on other planets and moons in our solar system. they are working out the means to see if H2O on certain exoplanets will be detectable in the light reflected from them. there is the Miller–Urey experiment that demonstrates the possibility of the emergence of organic molecules out of inorganic precursors.

so, maybe what you need to think about is the Strong Anthropic Principle. i don't know if i buy into it or not (everybody buys into the Weak Anthropic Principle, since it is essentially a tautology). essentially, the SAP says that, if you shuffle an honest deck of cards and draw a single card offa the top, that eventually (if you repeat this experiment and give it a few billion years), you will draw the Ace of Spades. even if there are a helluva lot more cards in the deck than 52, eventually the "life-giving" card will be drawn, unless there is something physical that prevents it. but if you have the right kind of "petri dish" on the right kind of planet circling the right kind of sun, give it a billion years or so and the SAP says that eventually the right combination of molecules (and they have an idea what this combination may be) will fall together, chemical reactions will occur, organic molecules will emerge, complexity will increase, proteins, metabolism and self-replication emerge, etc. the probability of this cannot be zero because it happened here. as long as that Ace of Spades lies in the deck somewhere, eventually we will run the experiment and it will pop out.

i don't know why you think that the Copernican principle or Mediocrity principle is untrue. we got past the denial of that obviousness hundreds of years ago.

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jreelawg said:
The point is that the universe is very, very large. There are so many places other than Earth in which there could be life. To assume Earth to be so rare as to be the only place where life has begun seams very ridiculous. We have found that on earth, life thrives all over the place. There is life deep deep underground, there is life at the bottom of the Ocean living without the need for sunlight. There is life living in extreme cold, in extreme heat. Life is very adaptable.

I think the question to ask, is why would there not be life in other places? Is it that Earth is an unimaginably rare place. I don't think so, do you? Why?

Rather than dancing around the semantics of what it means to believe; why not hold a position worth discussing? Do you suspect there exists life in other solar systems? How strongly do you suspect it? If not, how strongly do you suspect life does not exist?
This is clearly a false dichotomy. You are positing I must either believe aliens exist or believe aliens do not exist. You forward this position through the question of why I would think life on Earth is so rare and so forth [Something I never said, nor would I say without backing].

The truth is a person has or lacks belief for these two statements:
There are aliens.
There are not aliens.

I lack the belief in both statements due to the lack of evidence for both of them. This action follows the foundations of science and induction.
rbj said:
i think that astrobiologists would disagree. take a different component of the Drake equation fp and ne. 2 or 3 decades ago they had no experimental evidence other than our own solar system what the values of those might be. now we see exoplanets all over the place and it begins to look like fp might be nearly unity and ne might be 1.6 . we, as a species with intelligence, are starting to get a grip on those parameters. there are several scientists that work in abiogenesis that have both discovered life on Earth that has no need of sunlight (it only requires water and an energy gradient in order to exist), they have discovered evidence of H2O on other planets and moons in our solar system. they are working out the means to see if H2O on certain exoplanets will be detectable in the light reflected from them. there is the Miller–Urey experiment that demonstrates the possibility of the emergence of organic molecules out of inorganic precursors.

so, maybe what you need to think about is the Strong Anthropic Principle. i don't know if i buy into it or not (everybody buys into the Weak Antrhopic Principle, since it is essentially a tautology). essentially, the SAP says that, if you shuffle an honest deck of cards and draw a single card offa the top, that eventually (if you give it a few billion years), you will draw the Ace of Spades. even if there are a helluva lot more cards in the deck than 52, eventually the "life-giving" card will be drawn, unless there is something physical that prevents it. but if you have the right kind of "petri dish" on the right kind of planet circling the right kind of sun, give it a billion years or so and the SAP says that eventually the right combination of molecules (and they have an idea what this combination may be) will fall together, chemical reactions will occur, organic molecules will emerge, complexity will increase, metabolism and self-replication emerge, etc. the probability of this cannot be zero because it happened here. as long as that Ace of Spades lies in the deck somewhere, eventually we will run the experiment and it will pop out.

i don't know why you think that the Copernican principle or Mediocrity principle is untrue. we got over the denial of that obviousness hundreds of years ago.
Drake's equation is merely a sequence of common sense probabilities with which a college student could come up if asked to do so for a project in his undergraduate probability class. It is basically a ploy to dress ignorance with a fancy name and fancy symbols for the purpose of giving an authoritative feeling as its user declares whatever he wants to declare with it. (It has been used, by the way, as 'evidence' for both sides of the argument.)

But that is beyond the point. The real point is in this sequence of n probabilities multiplied by the others, it wouldn't matter if we had accurately figured n - 1 of them. If there is but one unknown, it makes the entire product unknown. Your argument does not work.

And regarding this "anthropic principle", I have no idea what that is, and I don't intend to know what it is. If it says something evidentiary, go on and state it clearly instead of disguising the message with a fancy philosophical name. I will then judge it. But since no evidence exists as of now, I can assure you it is not a valid argument.

But the worst part of your post was its end, shown in bold. I never stated anything regarding these principles. I have no idea how you can transform my repeated, stated lack of belief in something into a belief in the complement of something else. That is logically impossible. I would appreciate if you staid away from the straw man fallacy, friend.

RoshanBBQ said:
This is clearly a false dichotomy. You are positing I must either believe aliens exist or believe aliens do not exist. You forward this position through the question of why I would think life on Earth is so rare and so forth [Something I never said, nor would I say without backing].

You misinterpreted what I said. I asked you what you think and why? Your position could be anything. Having no position one way or the other about a subject doesn't make for a very interesting discussion.

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This thread has gone way out of hand. It appears that the posters are just throwing around opinions and unverified claims. This is outside the scope of this forum.

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