I also found interesting that we were able to go one magnitude further in our instruments (into 10^-16) than the smallest know object (neutrons and protons at 10^-15) and we have yet to find anything.

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- 02-03-2013Mario F.
I also found interesting that we were able to go one magnitude further in our instruments (into 10^-16) than the smallest know object (neutrons and protons at 10^-15) and we have yet to find anything.

- 02-03-2013megafiddle
- 02-03-2013Mario F.
From my understanding you cannot produce the probability of life on Earth because there is only one Earth. There are no other Earths to play the lottery and it can only be played once. Without any number of events, without different possible results, there are no probabilities. in this context life on Earth appeared exactly because it had to. Life on earth has a probability of 1:1.

But you can entertain the thought of discussing the probability of life in the universe because there's more than one planet to play the lottery. We use the Drake equation to entertain ourselves. After that you can finally extend that result to life on earth. So, in order to understand the probability of life on earth, you need to first understand the probability of life on the universe. - 02-03-2013megafiddle
That is the probability that life

*has*occured, not the probability that it*might*occur.

The probability or certainty of something that has already occured is always 1.

If you are saying that life is inevitable on an earthlike planet, then the probability would be close to 1.

But has that been demonstrated?

The Drake equation does not try to determine the probability of life on an earthlike planet. It tries to determine the

number of civilizations that might be within communication range of earth.

The probability of life on an earthlike planet is a given, assumed value, and is therefore on the right of the equal

sign. The value N on the left is what the equation is trying to determine.

I think that's true. There's no reason to think that only earthlike planets could generate or support life. Still though,

there's the matter of determining the probability of such non-carbon life occuring. It could very well be more probable. - 02-04-2013Subsonics
Yes I agree and that was my point, we have a sample size of 1, therefore we can not say anything about the probability as far as I can tell. We need to be here to be able to comment on it, but that doesn't mean that we are here by necessity or by a 1:1 probability.

- 02-04-2013Mario F.
Ah! Now I see where your initial question comes from. There's a bit of a misunderstanding here.

That's not correct. It's true it makes mention to our Galaxy. It's true it had a specific purpose of trying to establish the likelihood of extraterrestrial life in range of our instruments, but if you look carefully at its variables, it can (and has been) applied anywhere to our universe. It couldn't be any other way. The intention of the equation is irrelevant. It's the formulation that matters.

Because it can be applied anywhere it answers too the likelihood of life on Earth. We don't need to first find the probability of life on earth because that's what the Drake equation is trying to establish. See my last post.

Yeah. I made a mess there. You are correct. What I meant is that it should be on the left side. I was unconsciously exchanging the expressions positions relative to the equal sign. blabla = N, instead of the more correct N = blabla.

Case in point, N is the likelihood of life on earth too. That's what the drake equation answers due to its formulation (again look carefully at its terms). For which reason we don't expect to need to somehow calculate the probability of life on earth by different methods and apply that result to the Drake equation. - 02-04-2013Mario F.
Indeed! But now imagine we needed to somehow include the probability of life on Earth as a new term or a new factor to the existing terms. Remember that was the context of the discussion. i.e. The probability of life on Earth would be a necessary factor to the Drake equation.

We only have one outcome and one possible event. There's no real probability. A ratio of 1:1 would fit the description and thus your factor would be 1, you agree? Which, incidentally would be incorrect and immediately demonstrate there are gremlins here. Because as you correctly assume that's almost certainly not the probability of us being in this universe (all and any anthropic principles should be banned at gun point, if you ask me).

But that would still be the only thing we would have to work with. Think carefully, by trying to calculate the probability of life on planet Earth to include that in a formulation about life on other planets, we were effectively ignoring other planets in our life-on-earth probability calculation. As incorrect as 1:1 is, that would be the only possible factor to the equation asking for a non probability.

Edit:

So, going back to the initial post where I make that assertion, my understanding of Probabilities Theory is that the absence of a probability reads as 1:1 (or 0:1 if it didn't happen). - 02-04-2013megafiddle
It seems to me that using our own presence here as an indication of something, is analagous to seeking out the winner of a lottery

and drawing some conclusion based on the fact that he has won. Of course he has won. Of course we are here. It would be a very

different matter if we selected someone at random. Or selected an earthlike planet at random.

That is why I mention the*weak*anthropic principle, and only in a limited sense: everything must have been perfect here on earth

for the generation of life, no matter how unlikely, else we wouldn't be here talking about it.

I can see that it could be applied to the universe in general.

But isn't the probability of life on an earthlike planet still one of the terms? (f sub l in the equation)?

How can you possibly know that, if that's what you're trying to determine?

It's sort of a "circular" or reiterative equation (like a circular argument).

Could you explain that better. Interesting stuff. - 02-05-2013Mario F.
I think what we are trying to do is more or less this. We throw a dice once and the number 42 came up. We don't know how many sides the dice has (or even if its loaded), but are still trying to find what were the odds of that number having come up. Inevitably we will need to incorporate the knowledge we already have (42, or the fact Earth harbors life) even though that obviously creates a circular reference that invariably invalidates the result.

Try to think, with the knowledge we have today, how could we speculate about life on other planets without speculating about the possibility of life on ours? It just couldn't happen. So, you would be right apparently. We would first need to know about the probability of life on Earth. But then, how can we know that? We would need other samples (a large number of planets with and without life) to make compelling statistical evidence. The problem is of course we don't have those samples. They are exactly what we are trying to determine. So we speculate. But in order to speculate we need to take our reality into account. We embroil ourselves into conjecture.

The actual Fl term isn't about earth. It's simply about the possibility of life on another planet. Doesn't even need to be an earth-like planet. In fact shouldn't even need to be a planet. A moon is a perfectly good place to harbor life if the right conditions are met. But that's besides the point. What matters is that there's no real circular reference here that invalidates the equation. I'd say that the equation is sound in mathematical terms. It's just that to speculate about it we need to incorporate what limited knowledge we have of Earth to fill Fl (and in fact all other terms except R). - 02-05-2013megafiddle
Ok, that makes sense.

Pretty neat scale video. - 02-05-2013C_ntua
The Drake equation is nonsense in my opinion. First it is not mathematically correct, you assume that you have one civilization per planet which we don't even consider for earth. Or that one civilization cannot inhabit multiple planets. But the bad part is how it is broken down. Getting NE for example, the number that can potentially support life, is harder than answering the actual question. Even if you can see all the planets and get your answer, you still don't have a way to determine the "potential" of a planet supporting life (see below...)

Lets say we could see 10,000 planets that have life out of 20,000 observable planets. What good would it do us? It is like having statistical evidence that in a neighborhood there are 90% women. Does that tell you anything for the whole city? Claiming that the city might have high percentage of women might be wrong, there could be another neighborhood with 90% men. So you would first need to see the whole universe. Well, in that case you don't need to calculate any probabilities, you know the answer. So finally you probably need to see*most*of the universe. So lets say we actually could see most of the universe and we could get statistical data that there is 70% of the planets with life. Now we discover a new planet. Is there 70% probabilities to have life? No, we don't know if life occurring in a planet is completely random. It is like saying there is 1/X chances to get 1 in an X sided dice. It is only true if the sides are even.

So we need something more that just statistical evidence. We can simplify the question on "similar to us life". Then we can make an educated guess and say that the planet that could have life would need to have some elements that sustain our life or help create it. But if you kind of think about it we are asking the opposite question. What are the possibilities of having life in earth. So if we were to repeat the earth story, what are the possibilities we would end up with life? It is like throwing a X sided dice. You cannot see the possibilities. But if you throw 1,000 X sided dice and you see that 25% of them have a 1, 25% of them have a 2 and 50% of them have a 3 you can make an educated guess that it has 3 sides and one side is bigger. So if you are seeing a 1 on the X sided dice you can say that it had 25% chance to happen (for example). The same way we could say that life in this particular earth had X% to happen.

We still would need to assume that life only happens to earth-like planets and get the ratio between earth-like planets and not earth-like planets to get an answer. - 02-06-2013whiteflagsQuote:

Lets say we could see 10,000 planets that have life out of 20,000 observable planets. What good would it do us?

From here you went on in great detail about margin of error. I have a problem with the way you framed your explanation. Why would you ever need to compile statistics on the entire Universe or most of the Universe in order for such statistics to have an acceptable error margin? To begin with, the Universe is too big. We don't have enough time. Furthermore information on "the neighborhood" can be incredibly important and those statistics can be well done. We do not want to do a lazy iterative search on every far away galaxy in order to find life. We should be looking for Goldilocks zones if we want to find water. If you can work out reasonable, helpful statistics for a solar system I would be glad to have them.

Quote:

So we need something more that just statistical evidence. We can simplify the question on "similar to us life". Then we can make an educated guess and say that the planet that could have life would need to have some elements that sustain our life or help create it. But if you kind of think about it we are asking the opposite question. What are the possibilities of having life in earth.

Currently the search for life is very boring, because there is no such thing as deep space travel, and even in our solar system I feel like we are answering basic questions. Part of the reason I think scientists are still interested in Mars, for example, is because finding out why a planet doesn't support life necessarily answers questions about the science of our Earth. It informs us, and if statistics on the entire Universe were ever reasonable we would at least know what the variables are better. So I am all for studying interesting planets. We might bump into life on the way, living in some extreme environment, but it isn't terribly important.

So, I at least hope I get what everyone is saying but the more I try to read this discussion, I just get demoralized. If the number you discover is disappointingly low, what do we do? I still kinda want to meet Mork. And I simply cannot separate the search for extra-terrestrials with the exploration of space. For a long time, we will be doing double duty.

And that's all this moron has to say. :o - 02-06-2013Mario F.
Don't even consider the Drake equation. It was meant simply as a discussion starter for a conference somewhere about something. Of course the naivety of its creator of thinking that such a thing wouldn't immediately become a meme, is worth a debate of it own on how attracted supposedly learned men are to bad ideas :p

That said, the best work on the Drake equation is in my opinion the book I mentioned before. It's a full exploration of every of the terms in the equation. Sagan and Shklovsky are quick however to produce the disclaimer that this isn't how we should be finding about life in other planets. It's all a ridiculous exercise and it serves instead as a great teaser to talk about real science and what we know or don't know about life. They actually end up with a range that goes from a near zero possibility to an encouraging high number where our galaxy is teeming with life. Well... hmm, thanks I suppose.

In my opinion you are absolutely right. It's currently a boring, I'd even say unimaginative, enterprise what we are doing concerning the search for extra-terrestrial life. Despite the enormity of such finding, I confess I look down at programs like SETI as trying to find the atom by slicing an apple in ever smaller bits with a kitchen knife. There's better things we could probably be doing with that telescope array. Extra-terrestrial life will most probably be found exactly like you say: We are doing our business mining off-world planets and have this directive that we should inform of any potential signs of life during our travels. And that will depend really on our spaceships range.

If someone asked my opinion (I know, I know...) I say we should just forget about the damn thing. As exciting as it is, it's really the equivalent of a children dreaming with live dinosaurs. The real exciting enterprise, the one that gets me real pumped, is space exploration. It won't be in my lifetime unfortunately that I will see a shift in direction and humanity starts undertaking that epic adventure of exploring, studying and colonizing other planets and moons. And that really bums me a lot. Life that we so much value, that we are so eager to find elsewhere, and so marveled by in our own planet, is after all as flickering and weak as a candle. It goes fast by and won't let you see much of this universe. Damn you, you overrated jerk!