# Chance of life on other planets

Discussion in 'Astronomy, Exobiology, & Cosmology' started by James R, Sep 4, 2010.

1. ### James RJust this guy, you know?Staff Member

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I came up with the following thought experiment in another thread.

Suppose I line up 100 boxes in front of you. I open one box and you see that it contains an egg. I tell you that the other boxes may or may not contain eggs. You open another 9 boxes. None of them contain eggs.

The question:

On the basis of the data you have so far, what is your best estimate of the total number of boxes that contain an egg?

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Obviously, this is a crude analogy for estimating the probability of life on other planets. What similarities and differences do you see?

Last edited: Sep 4, 2010

3. ### Green DestinyBannedBanned

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There is a conceptual error, because we are assuming there are a finite amount of boxes. In all essense, the general consensus is that there are an infinite amount of planets, as it may well be regarded with an infinite amount of spacetime.

If atleast one planet has the capability of sustaining life, there needs to be another occurrance by laws of probability when you are dealing with such high numbers.

5. ### James RJust this guy, you know?Staff Member

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Green Destiny:

We will only ever be able to communicate with a finite number of other planets. So, maybe it's better to confine ourselves to considering the probability of life on the planets that can possibly communicate with us.

7. ### Green DestinyBannedBanned

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Oh I apologize. I did not realize you were actually looking for an answer - I thought it was just an anecdote.

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9. ### Green DestinyBannedBanned

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If i have opened 10 boxes, and I have found only 1 egg, then there is a ratio so far that 1 in 10 boxes have a probability of containing an egg. There is no way for me to know which box has definately got an egg, so its a guessing framework.

10. ### James RJust this guy, you know?Staff Member

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Yes. But I'm interested in other people's answers.

(Green Destiny: I have edited the egg question in the opening post to cast it in terms of expected numbers of eggs rather than probabilities.)

11. ### Green DestinyBannedBanned

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I say there is a 1 in 10 chance.

12. ### Green DestinyBannedBanned

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Hi James,

I just saw your message. Perhaps I will be going this around the wrong way.. But, here is my answer. If I use my ratio, that 1 in 10 boxes may contain an egg, then if I have a 100 boxes, I would statistically place that atleast 10 boxes may contain eggs.

13. ### tablariddimforexU2Valued Senior Member

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How do you define life? If bacteria is life then the general consensus seems to be that it is very probable that bacteria do exist outside of our planet.

I don't get your question with the boxes, it's nonsense, unless you said something like, you gave 100 people 1 box each and asked them to either place an egg in it or not then you check the first 10 boxes. The way your question is put we don't have enough information to hazard a valid guess. Even then, as an analogy to the universe and to your main question, 'is there life on other planets' (you don't define how many planets), the 100 box sub question is nonsense.

14. ### lightgiganticBannedBanned

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Do you assume that there is no more advancement to be made in the perception of life?

IOW whatever (current) standards we hold for deeming an environment to be possessed or bereft of life forms cannot be improved on?

15. ### Spud Emperorsolanaceous common taterRegistered Senior Member

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James, I'll have a crack at this (crap pun intended).

The one egg in ten or a hundred boxes means not much because it's only one egg and only ten boxes opened so far.
The probability of there only being one egg in a thousand boxes is probably much the same as there being one in twenty. I dunno, maths is not a strong point for me.

The chance of there being life on other planets in the universe?
Well I'd have to turn that around and say that the chance of us (on Earth) being the only form of life in the universe would be so close to zero that it just doesn't matter.
I see the universe as being life itself. I don't see it as being a series of cold or inanimate or lifeless forces.

And as far as sentient life, the chances are the same.
The idea of us being the only sentient beings out there is purely a human construct (we're a fairly flawed species).

Let's see, on the metaphorical speck of sand in the universe that we occupy, there are how many species (count them, start with the insects)?
To think that on the other squidbillion specks of sand nothing else exists, not a cracker; only a delusional, self absorbed human could believe that.

The elements are much the same throughout the universe (and if they're not, surely that would only increase the chances of more potential life forms), the conditions don't vary that much, heat sources, water, gases and the existence of super intelligent life creators (sorry, red herring to see if you're still reading).

Chances, odds, numbers,...forget it, There is life, we are life, it's universal.

16. ### D HSome other guyValued Senior Member

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What is this, 100 box monte? For all I know, you planted an egg in exactly one box, leaving the other 99 empty. You knew where you planted the egg, so showing that one special box was no mean feat on your part.

You are implicitly asking us to apply the principle of indifference here, James. Using this principle leads one to the conclusion that there is a 50-50 chance that the sun will rise tomorrow. An assumption of equiprobability needs to be justified. The right answer, in my mind, to the question "We don't know anything about situation X. What is the probability that situation X will occur?" is "We don't know (yet)."

17. ### nietzschefanThread KillerValued Senior Member

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James get a clue. 100 boxes? Try Trillions, just in our galaxy.

18. ### D HSome other guyValued Senior Member

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He's trying to make an analogy. My thoughts on the analogy: We need to exclude the one box that we know has an egg in it because (a) we *know* a-priori that it has an egg in it and (b) we don't know if the selection of that initial box was random. So, based on a sample set of nine out of nine empty boxes, the best guess regarding the other 90 boxes is that all are all empty, but the uncertainty is rather large due to the small sample size.

We don't even have nine boxes yet. The Kepler mission data has only started to trickle out. The data released to date is not all that promising regarding life in other solar systems. That might just be selection bias based on the bunch of empty boxes shown to us so far. The principal investigators have withheld he data for 400 of the systems. The set we are able to see is not a random sample.

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.

first, did you forgot the already boxes that have been discovered and still didnt opened yet?
what about the hall garages, that each garage have sections, and each section have boxes, while you still in a small shop in a town, and you opened the existing 10 boxed, and you finded an egg, in a one box only, and you didnt see all of the other garages and boxes, infact, you don't even know about them, you still in a shop, in a small section of a garage, does that means that there's 10 boxes in the existence? and 1 boc contain an egg?
also, this is a stupid way to compare to the univerce and what's in it. dude, it's the univerce, that we don't even our own univerce..

20. ### nietzschefanThread KillerValued Senior Member

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Well his analogy stinks. We have trillions of planets and have only seen 7-9 so far(gas giants mostly).

21. ### Michael歌舞伎Valued Senior Member

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1 in 10

There must be many billions of other planets with life in the universe.

22. ### DinosaurRational SkepticValued Senior Member

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As stated,I wonder about implications relating to the person opening the ten boxes.

If the problem stated that ten boxes were opened at random & one was found to contain an egg, it would seem that an estimate of 10% of the 100 boxes having an egg cannot be far off the mark.

Fooling with Poission probabilities indicates the following.
• If 10% have an egg, a sample of ten boxes is as likely to have no eggs as it is to have one egg. P(0) = .367 879; P(1) = .367 879; P(>1) = .264 241

• If there is only one egg in the 100 boxes, P(0 in sample of 10) = .990 050

• If 11 in 100, P(1 in a sample of 10) = .366 158

• if 9 in 100, P(1 in a sample of 10) = .365 913
Using a binomial distribution.
• P(0 in a sample of 10) = .348 678

• P(1 in a sample of 10) = .387 420

• P(>1 in a sample of 10) = 263 901
Somebody who remembers more statistics than I would be able to put a confidence limit on the probability.

23. ### DoreenValued Senior Member

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The problem with this analogy to me is that it means that the eggs are not taking the test. We looked at Mars and found no life, let's say. Now we can give some ridiculously high statistic for the probability of life on other planets because we have looked at 2 planets and one had life. Sure we get humbled over time, or we don't if we never seen to get a handle on certain kinds of technology.

To use a not very fair counter-analogy. I find myself in my clothes and then go and look at my brother. He is not wearing my clothes. I then email my friends and say - it appears that 50% of the human race wears my clothes.

IOW, for statistics, it is probably best we say we have not found any, yet. At least until we find a large sample of planets.

This is, of course, working in this flat, let's not consider the conditions, kind of way.