# Thoughts on the Drake Equation

1. Jul 22, 2012

### Stu21

Personally I think the equation greatly overestimates the number of possible intelligent life in the universe... But then again all I have is a college level education.

Can any one explain?

2. Jul 22, 2012

### Staff: Mentor

The drake equation is...mostly meaningless. We don't have any numbers to substitute for the variables, so it's pretty useless. As far as I understand at least.

3. Jul 23, 2012

### Simon Bridge

Explain what?

The Drake equation?

What leads you to think that the equation is an over estimate?

Last edited by a moderator: Sep 25, 2014
4. Jul 23, 2012

### Chronos

The drake equation is a reasonable attempt to approximate the number of intelligent civilizations. Unfortunately, not all the variables are well defined, much less quantifiable.

5. Jul 23, 2012

### Stu21

what do you mean by reasonable? what about goldilocks zones for planets, or vital metals in the planets such as nickle and iron. I also think that stuff like water and meteors should be considered, as well as large planets like Jupiter within a system shielding inner planets from outer system phenomena. I also believe life in general arises easily, but intelligent life is another matter.

6. Jul 23, 2012

### jackmell

I personally prefer to use: n=iv where i represents the massively contingent nature of life, and v represents the large number of planets in a galaxy. When I plug-in those numbers I get n=1. And that number is consistent with our wonderful success at making contact, no offense to Carl.

7. Jul 23, 2012

### Staff: Mentor

I think you have a misunderstanding of what the Drake equation is. It simply puts in place some of the variables that should be taken into consideration when considering the prevelance of life (and intelligent, communicating life especially) in the galaxy. It doesn't propose an answer because we do not know the probabilities of any of those variables yet.

Increasingly complicated variables like "what is the average number of meteor impacts" aren't too much of a concern because they are covered by bigger considerations e.g. "what is the chance life arises" or "what is the chance life becomes tool using".

8. Jul 23, 2012

### Staff: Mentor

Well, the star formation rate has some number, and the fraction of stars with planets has reasonable estimates (and lower bounds), too, with significant improvements expected in the next years. The number of habitable planets per planetary system is something which can be estimated with current telescopes, too.
However, the remaining factors are guesswork, therefore the drake equation cannot give a reasonable number of intelligent+communicating civilisations at the moment.

@Stu21: All those things are part of "the fraction of the above that actually go on to develop life at some point". This fraction depends on everything which influences the development of life.

9. Jul 23, 2012

### Whovian

It states that

$$\dfrac ab=\dfrac ac\cdot\dfrac cb$$

a lot of times. No idea why it's that important. (When I saw the word Drake in the title, my first thought was, "Nice knowing you, Becky.")

10. Jul 23, 2012

### jackmell

I do not believe we can do that.

11. Jul 23, 2012

### Czcibor

Actually, there were not so bad studies with microlensing on that. (Maybe still a bit crude, but not a pure guessing)

I'd agree that it is within reach of contemporary tech, and only matter of gathering enough observations.

From lack of contact with other civilization I'd assume that there is something too optimistic in Drake Equation. Or it's enough that we don't have good enough technology to contact other civilization. Or maybe we're simply one of the first within region.

12. Jul 23, 2012

### Simon Bridge

I see, stu21 feels that the Drake equation is an over estimate because there are a bunch of parameters that are not included. But how does he know that including those parameters won't make the number come out higher? Or have no impact at all?

Since we don't know the values in question there is no reason to suppose that the effect is one way or the other. Like others have pointed out - it's not the job of the equation to estimate the amount of contactable intellegences out there - it's job is to paint in broad strokes what sort of things we need to know to carry out the calculation.

To paraphrase Pratchett: The equation doesn't so much illuminate, as outline the darkness.

13. Jul 23, 2012

### Staff: Mentor

The detection of habitable planets that are Earth sized cannot currently happen unless their orbital plane is nearly parallel to our line of sight, which allows us to use radial velocity measurements or transit observations to detect them. And even these methods are barely capable of detecting an Earth sized planet, let alone find out if it's habitable or not. So it isn't a matter of gathering enough observations, as we can't even do the observations to begin with yet.

14. Jul 23, 2012

### Simon Bridge

How does that follow when you don't know what the values of the terms are - for all you know the Drake equation predicts that contact is extremely unlikely.

The more optimistic figures suggest 182 million civilization-bearing stars in our galaxy (fulfilling the parameters) ... given a estimate 100-400 billion stars in our galaxy to start with, this gives 0.04-0.2% of stars with civilization.

0.122 stars per cubic parsec (around us) means an expectation of 16-27pc ... the long range being of the order of 100ly. Any signals they could be getting right now would have come from 100 years ago ... clearly it's not us sending them.

To put this in perspective - imagine they are us.
100 years ago we would not have been able to put out the kind of signals that a project like SETI would have spotted. The closer distance (16pc) would be getting whatever we put out in the mid 50s. They would conclude that our Sun did not have a civilization in it... even though the guess wasn't far off.

And then - this is deliberately a very optimistic guess indeed so the situation is more likely to be worse than that.

The most pessimistic guess makes us the only civilization in the galaxy - and probably in the observable Universe.

However, the Drake equation itself does not make these estimate big or small ... it does not say anything about the actual number of civilizations. The main reason we have not detected other civilizations so far can still be accounted for by the huge size of the galaxy.

Drakes own lower bound in the original conference suggests we still have some centuries to wait to find them.

http://en.wikipedia.org/wiki/Drake_equation#Equation_results

15. Jul 23, 2012

### Czcibor

http://exoplanet.eu/catalog/?f="microlensing"+IN+detection

On the above attached list of planet detected by microlensing there are already superearths. Is your point that with contemporary technology only superearths are possible to be detected, but exactly a bit lower that the method simply fails?

Knowing mass is possible to rule out gas giants and tiny planets. Knowing orbit and luminosity of the host star is possible to calculate whether the planet is within HZ. That's enough to roughly asses whether the planet is potentially habitable. (yes, I know a few of such "habitable" would be a nasty)

I also don't get here the argument concerning that planet orbit should be coplanar for purpose of statistical analysis. Knowing which is probability of finding a coplanar system you can extrapolate that to know how many systems are omitted because of different configuration and how many indeed lack planets within their HZ.

16. Jul 23, 2012

### Staff: Mentor

Microlensing is a rare occurrence that cannot be relied upon and does not tell you anything about whether the planet is habitable or not. (To be fair, currently no method does, only potential habitability can be assessed)

Most of such habitable planets would not support human life on a large scale without significant infrastructure. They would be "nasty".

Whether the orbit is coplanar only matters for detection purposes. We cannot detect planets whose orbits are not near-parallel to our line of sight with our most successful methods at this time. The radial-velocity method is by far our most successful method of detection and the orbits MUST be very close to coplanar or the method cannot be relied upon. The transit method is even more dependent on the orientation of the orbital plane.

17. Jul 23, 2012

### Staff: Mentor

Well, I understand the factor as "planets in the habitable zone" - and include other factors in the next fraction (probability that life evolves).

Kepler is able to find earth-sized planets. Earth-sized planets in the habitable zone are possible to find, just very rare (but with a well-known probability due to their orbits). With several years of observation and some hits, the number of those planets can be evaluated.

18. Jul 23, 2012

### Stu21

So I guess that in the end the Drake equation holds a lot of value in that it is giving us a reasonable estimate based on the reliable information we've so far managed to gather.

One thing i'd still like some clarification on though; out of all this i'm getting that the biggest problem with the Drake equation right now isn't the variables, its the lack of strong data about the variables, would i be right in assuming this?

A lot of good answers though, thanks to all.

19. Jul 23, 2012

### mjacobsca

Stu21, look into the Rare Earth Equation. It adds a ton of variables to the Drake equation. Whether you agree or disagree with its conclusion, it should give you more food for thought as to the rarity or lack thereof of the conditions needed for Earthlike conditions. It is by no means the end-all, final word on the subject, but it has some fascinating analysis. It's conclusion , as you might expect, is that Earth is rare indeed! You can find more info in the book "Rare Earth".

Last edited: Jul 23, 2012