$P(H/E) = \frac{P(E/H) \times P(H)}{P(E)}$

Since we know so little about aliens — RogueAI

Do we know anything about aliens?

Do we know anything about aliens? — Tom Storm

They're illegal, I think.

Is the guy that maintains my pool from alpha centauri?

What is the probability some aliens are here now AND they are homeless?

P=1

(ask Gov. Abbott)

Yeah, but what it Pr(E/h)?

That's one of the fundamental problems with probability. How to assign values to probabilities. It's easy for simple stuff like coin tosses and dice throws, but the real world is a different story altogether.

Welcome to the real world, Neo. — Morpheus

Do we know anything about aliens? — Tom Storm

Yes. One thing. That we don't know anything about them.

Do we know anything about aliens? — Tom Storm

We immediately jump into the conclusion that they must be human-like, except more intelligent, less sexy, and peace-loving or else warmongers, but never in-between.

Whereas aliens have reached our planet, in the form of protein formation, maybe not exactly viruses, but simple proteins such as amino acids. Travelling on meteorites and other space debris that fall to earth on Earth. I don't know if this is still just theory or it's proven.

So what we know about aliens that reached the Earth is that they are simple organic compounds.

Watch the tabloids next week. "GOD ON WEBSITE SPAKE: ALIENS THAT REACHED THE EARTH ARE REAL AND THE PENTAGON KNOWS ABOUT IT."

I think you are running ahead too fast. Before we think about conditional probability we need to think about probability. For the kind of calculation you have in mind, probability is one number on top of another to make a proportion. The number on the top is (let's suppose) the number of times that aliens are seen in the next ten years. That number can be 1 to begin with, for example, because that's the least that we're interested in; later, we would be interested in whether aliens are seen more than once. Now how about the denominator on the bottom? We want to know whether we see aliens exactly once out of ..... what? Well, I suppose, out of all the times we don't see aliens plus all the times we do - that makes all the times we see or we don't see aliens. OK, how do we count that number of times? Take today, for example. How many times have I seen aliens? That's easy: it's zero. Now how many times have I not seen aliens? The question doesn't seem to make sense. But until we can make sense of that denominator and so hypothesise a proportion, then we cannot even talk about probability, let alone conditional probability.

The problem is that you are not talking about probability in a mathematical sense at all. You are talking about plausibility. That is, do we think it's credible that we might see aliens, given that we've never seen them before? Well, that depends partly upon whether there are aliens.

@RogueAI

H = Aliens will contact us in the next 10 years
E = Aliens have never contacted us in the past

$P(E/H) = \frac{P(H \land E)}{P(H)}$ (i)

Consider.

1. Do aliens have favorites?

If they don't, E and H are dependent on each other. They might not want to visit a place they've already been to. P(E/H) decreases.

If they do, E and H are still dependent on each other. May be they like the place and want to see it again even if what they liked about earth is long gone. P(E/H) increases.

---

Refreshing me memory ...

$P(H/E) = \frac{P(H \land E)}{P(E)}$ (ii)

From (i) and (ii)

$P(E/H) \times P(H) = P(H/E) \times P(E)$

$P(E/H) = \frac{P(H/E) \times P(E)}{P(H)}$

I'm also having similar problems with Pr(E). Since we know so little about aliens and the odds of abiogenesis, I can't justify anything for Pr(E) other than .5. — RogueAI

The odds of abiogenesis occurring are 1. Because here we are talking about it lol.

As for the odds of abiogenesis occurring multiple times? A little bit trickier. We could assume our planet and its conditions are an extremely rare phenomenon.

However, sun's are extremely common. In the trillions. 400 billion alone in our own galaxy. Solar systems are almost just as common if not as. Let's say 100 trillion for arguments sake.

Then if we take earth to be in a goldilocks zone that's not too close not too far. And that is around 1-1.5 astronomical units, the entire solar system being around 40 Au thats about 3% of the span of a basic solar system give or take thats ripe for life "as we know it".

So out of trillions we can cut it down by a factor of 97% which is 3 trillion.

2 of the four solid planets in our system have magnetic fields. If that runs true in general that's 50% and if they have magnetic fields they're likely to have both liquid water and an atmosphere.

That's 1.5 trillion planets.

Other variables need to be considered but as you can see, even with Conservative estimates the basic conditions for life appear to be pretty common given the massive quantities involved.

If life is a natural progression of the laws of physics and some probabilities of them interacting in the right way. Then abiogensis is almost a certainty.

If life was created by a creator. Which seems to have an obsession with just earth out of all of the universe, then multiple life sustaining planets is unlikely.

Mathematical probabilities are calculated. Empirical probabilities can at times be theoretically estimated based on looking at the actual world. Probabilities of fictional events are meaningless.

One issue with empirical theoretical estimates is that they require biased philosophical presuppositions prior to any personal experience or possible futuristic scientific observations. Another is that cosmological speculations require cosmological presuppositions, not fictional ones.

To my estimate, even if there ever was any extraterrestrial intelligence, their signals will never cross our timelines, therefore whether there are or ever were aliens out there we remain thankfully alone and free forever.

Yep, some presuppositions are made.

Here's my problem if we can't assign a value for Pr(E/H): any hypothesis about alien contact in future time t we have to be agnostic about. Will aliens contact us in ten thousand years? Maybe. In a thousand years? Maybe. 10 years? Maybe. The next ten seconds. Maybe? The ten microseconds. Maybe???

We've reached an absurdity.

I'm sorry but I don't see any absurdity.

$P(E/H) = \frac{P(E) \times P(H/E)}{P(H)}$

Each one of these probabilities (use the variable p) can be such that
1. p = 50% (agnostic)
2. p < 50% (unlikely)
3. p > 50% (likely)

Note that $0\% \leq p \leq 100\%$

There are 3 values to consider [p is P(E) or P(H/E) or P(H)] to calculate P(E/H) and so there should be $3^3 = 27$ possibilities to calculate. Lemme calculate two of these possibilities (vide infra)

1. P(E) = 50%; P(H/E) = 50%; P(H) = 50%

$P(E/H) = \frac{50\% \times 50\%}{50\%} = 50\%$ i.e. we have to be agnostic about it.

2. P(E) = 50%; P(H/E) < 50% (let's say it's 40%); P(H) = 50%

$P(E/H) = \frac{50\% \times 40\%}{50\%} = 40\%$ i.e. its unlikely.

So on and so forth ...

For different time frames e.g. in the next 10,000 years, in the next microsecond, etc. we can scale up/down the probability we assign to P(H) = aliens will contact us in the next 10 years. For example the suppose P(H) = 20%. Then the probability that aliens will contact us in the next 5 years will be 10% [5 years is half of 10 years; I'm assuming that the probability of contact increases with time].

N. B. Scaling up can sometimes lead to percentage probabilities > 100%. These should all be made = 100%.

For example, given that the probability of contact within the next 10 years is 70%, what is the probability of contact in the next 100 years? 70% × 10 = 700%. Probabilities can't be > 100%. You'll have to go with 100%.

I'm also having similar problems with Pr(E). Since we know so little about aliens and the odds of abiogenesis, I can't justify anything for Pr(E) other than .5. — RogueAI

Let E = "there has been no indisputable contact with advanced aliens so far" — RogueAI

I don't get this. There is a 100% chance that we've had indisputable contact with aliens. For each item of evidence, it is disputed.

I'm assuming that the probability of contact increases with time]. — Agent Smith

You're assumption is twofold: (1) there are aliens and (2) the probability of contact with them increases with time.

Once you've assumed #1, you've got your proof of aliens, with or without contact.

Consider these 2 questions:

1. What is the likelihood we'll send a man to Mars in 10 years?

2. What is the likelihood we'll find bigfoot in 10 years?

#1 is something we can compute because it doesn't assume an unsupportable fact. There are men, spacecraft, and Mars.

#2 is asking the chances that something occur for something that may not even exist.

RogueAI is quite specific about his question.

I'm assuming that the probability of contact increases with time — Agent Smith

You can't assume this! In order to assume it, you would have to know that aliens, in fact, exist, and will contact us at some point in the future.

You can't assume this! In order to assume it, you would have to know that aliens, in fact, exist, and will contact us at some point in the future — RogueAI

:chin: Then we have to factor that into our calculations:

What is the probability that aliens have contacted us in the past given that aliens exist & Aliens will contact us in the next 10 years?

. . . given that aliens exist & Aliens will contact us in the next 10 years? — Agent Smith

This turns the whole conversation into probababble. :roll:

This turns the whole conversation into probababble — jgill

Why?

E = aliens exist
V = aliens will visit us in the next 10 years
C = aliens have visited earth

$P(C/(E \land V)) = \frac{P(E \land ~ V) \land P(C)}{P(E \land V)}$

Why? — Agent Smith

Because the hypotheses are nonsense. You're just playing with math equations.

But if it pleases you to do so by all means continue.

Why are the hypotheses nonsense?

Hypotheses -> Conclusion

The old CS adage, garbage in = garbage out.

G'nite :smile:

There's nothing wrong with the hypotheses. RogueAI is asking an interesting question. What are the chances that aliens have visited us given they will in the next 10 years. Basically, if we make contact, is it the first time for planet earth or is it not? Preliminary examination of the question shows that the two (contact in the next x years and past contact) are dependent events (check my posts where I explain why).

@Hanover then kindly pointed out I'm making an unfounded assumption assumptiom (aliens exist). I then tried to include that into the formula and you (resident mathematician) declare me analysis "probabble" :snicker:

What is the probability of this happening to a guy like me? :lol:

Why are the hypotheses nonsense? — Agent Smith

Because a probability (in maths) is a proportion and a proportion has a numerator and denominator. In the case of the OP the denominator is not defined. https://thephilosophyforum.com/discussion/comment/766026

No defined denominator -> no measure of probability.
No measure of probability -> no conditional probability.

Each one of these probabilities (use the variable p) can be such that
1. p = 50% (agnostic)
2. p < 50% (unlikely)
3. p > 50% (likely) — Agent Smith

50% means, for example, 1 out of 2 or 500 out of 1,000. '1' and '500' would perhaps refer to the number of times an alien is spotted. What does '2' refer to? Impossible to say. You are trying to fit a non-mathematical concept of probability into mathematical terms.

Magnifique!

I need some kind of reason or justification for assigning probability to the value P(H), P(E/H) or P(H/E). I have no good reasons or justifications for any of them - so I would just be fumbling in the dark blind. I can't even attempt a rough estimate.

About the only one of your probabilities I could attempt is P(E), which as an above poster said is 100%. Every potential contact with aliens so far has been disputed, so the probability that there has been no undisputed contact with aliens so far is 100%.

To try to put it succintly, it's reasonable to be agnostic about alien contact ten years from now, but not ten minutes from now. But I can't see what's driving that intuition. Is it (k), background knowledge, bleeding through into the Bayesian calculus?