The Drake Equation: Is there really other Life in the Universe?

[PhysicsPost]

The possibility of life on other planets has been one of our oldest doubts... and oldest hopes. Many believe that we are the only ones here in an infinite and lonely universe, but, as put so eloquently by in the film Contact, based on the novel by Carl Sagan, "If it is just us, it seems like an awful waste of space."

So, could life really exist elsewhere? Why haven't we found other civilizations by now? I hope to be able to provide you with a bit of understanding to the possibility of extraterrestrial life.

The way we can calculate the possibility of life is by the Drake Equation, created by Frank Drake in the early 1960s. It states:

N= [r* x fp x ne x fl x fi x fc] L where:

N= number of possible civilizations to communicate with

R* = is the rate at which stars capable of sustaining like are formed

fp = the fraction of these stars which have planets

ne = the number of planets similar to Earth in the planetary system

fl = the fraction of the Earth-like planets that hold life

fi = the fraction of life that becomes an intelligent civilization

fc = the fraction intelligent civilizations that attempt to communicate

L= the number of years the civilization remains able to communicate.

When these numbers are taken into consideration, we realize that there is a great possibility of life out there. There are about 400 billion stars in our galaxy, so there could be life right next door (relatively speaking, since that may be hundreds of thousands of light years away). Even if there is no life in the Milky Way, there are billions of other galaxies to turn to. We likely will not contact such civilizations in our lifetime, but it gives us a new kind of hope and dream for the future of our planet and the future of mankind.

 

[negru]

So how is L estimated? Based on how many years the dodo bird existed or what?

 

[Super Luminal]

The problem with the equation, in my opinion, is that the variables are TOO variable, that is to say the numbers applied to each variable are way too dependent on individual interpretations.

The more I consider this topic, which I find very interesting, the more I lean towards the rare Earth hypothesis. Also, the anthropic principle can be considered an answer to the Drake equation and why we haven't found bunk yet!

I do not agree with you, however, that many people think we're 'alone in the universe.' In fact, I believe most people think that there is intelligent life in the universe other than humans--I know I do. I think it is more probable that we're separated by such vast distances through space (and perhaps time as well) that contact remains difficult, but I hope not improbable!

 

[JeffKoch]

I never found this to be a useful equation. It's an obvious equation (though it assumes that life can only form on planets and that the planets must be Earth-like to sustain life), trouble is we can make reasonable estimates for only a few of the terms. Once we hit "fraction of Earth-like planets that hold life", we are guessing - absolutely guessing, with no foundational numbers to start with whatsoever. And so, we can come up with any final number we want.

 

[DaveC426913]

I never found this to be a useful equation.

It is useful for what it is. It defines the variables. It is up to the future to assign numbers.

It's an obvious equation

Most great ideas are obvious with 20/20 hindsight.

 

[Chronos]

The Drake equation suggests intelligent life is not unique to earth. I view it as an extension of the Copernican principle.

 

[JeffKoch]

Most great ideas are obvious with 20/20 hindsight.

But it's not a great or revolutionary idea, it's an obvious equation that must obviously be true within the constraints of life only on earth-like planets and several other implicit assumptions. It is alluring to some people, perhaps because it looks like an attempt to get at an answer, and in a sense it is - but breaking up the problem of estimating a number into a problem of estimating a half-dozen numbers does not illuminate anything unless those numbers are easier to estimate individually, and here is why the equation does not really advance anything.

Even a single, solitary data point of finding fossilized nanobacteria in a martian floodplain would make a huge improvement in our sense of what "fl" might be, but otherwise it could be anything from near unity to infinitesimally small with as many zeros after the decimal point as you like. We have no clue and can only guess, and your guess, my guess, and the guess of a three-year-old are all equally valid.

 

[DaveC426913]

But it's not a great or revolutionary idea, it's an obvious equation ...

And yet no one thought to define it until Drake came along. 20/20

It is alluring to some people, perhaps because it looks like an attempt to get at an answer, and in a sense it is

You're second-guessing the thoughts of others. You don't think it's an answer and I don't think it's an answer, so who are you claiming is more naive than us?

- but breaking up the problem of estimating a number into a problem of estimating a half-dozen numbers does not illuminate anything unless those numbers are easier to estimate individually, and here is why the equation does not really advance anything.

But it does. Before it came along, the answer to 'how many ETs might there be out there' was plain and simply 'your guess is as good as mine'.

The Drake equation demonstrates - in its first few terms if not the last few - that the fields that are ripe for the sewing of life are certainly myriad. Millions upon millions. And I think that actually brings a great degree of optimism to the search for ET.

 

[JeffKoch]

And yet no one thought to define it until Drake came along. 20/20.

Neither of us can say who first wrote it down as an equation. We know that someone named Drake wrote it down and popularized it, but it's not E= mc² - there is nothing profound about it, it's obvious.

You're second-guessing the thoughts of others. You don't think it's an answer and I don't think it's an answer, so who are you claiming is more naive than us?

Defensive, aren't we.

The Drake equation demonstrates...that the fields that are ripe for the sewing of life are certainly myriad. Millions upon millions. And I think that actually brings a great degree of optimism to the search for ET.

Ah, here is the crux of the issue - when you write it down this way, you can easily convince yourself that the number of Earth-ish planets with Earth-ish atmospheres and water must be vast, and that the number of civilizations with intelligent life out there must also be vast, and therefore that it makes sense to spend money to build equipment to search for it in a statistical way, which is appropriate for something that you have at least some statistical handle on but is not appropriate for a total unknown.

I'd personally rather spend the money on other pursuits. Even if the cost only adds up to an additional scientific experiment or capability for the next Mars lander, that seems to me to be money better spent - at least we have good reason to believe that we are looking at a planet that at one time shared Earth's most life-nurturing characteristic, liquid water, and so a careful search can shed some light on one of the totally unknown terms in the Drake equation, "fl", particularly if the search is fruitful.

 

[negru]

Someone should find the equation for computing the number of single hot women in the neighborhood, and name it after himself. Then the equation should be cited whenever discussing related topics. It should also be spelled with capital "E" due to its importance, unlike more trivial equations such as the Callan–Symanzik equation.

 

[epenguin]

I never found this to be a useful equation. It's an obvious equation (though it assumes that life can only form on planets and that the planets must be Earth-like to sustain life), trouble is we can make reasonable estimates for only a few of the terms. Once we hit "fraction of Earth-like planets that hold life", we are guessing - absolutely guessing, with no foundational numbers to start with whatsoever. And so, we can come up with any final number we want.

It depends maybe how earth-like is earth-like. I suggest this is one of the parameters that we can have the best idea of. When I last heard there has been life on Earth for at least 90% of its history, and we cannot exclude that it is near 100%. That suggests a reasonable estimate of this parameter is 1.

 

[Super Luminal]

Is it not naive of us to be looking almost exclusively for radio signals? Humans on planet Earth, our only point of reference on this matter, have been using radio for little more than 100 years in, what, approximately 200,000 years of 'existence?'

Will humans even be using radio type technology to communicate among ourselves in 50 years? Is radio and its variants already being replaced on Earth by "better" technology?

Perhaps radio is a particularly transient technology that technologically advanced civilizations abandon relatively quickly which is why we haven't heard anyone out there?

 

[mjacobsca]

The Drake equation is outdated and overly simplistic. Our knowledge of astrobiology, cosmology, and physics is far more advanced than it was 50 years ago. I'm not sure why people hang on to it so rigidly. The Rare Earth theory is far more convincing to me, and the formula far more sophisticated. It is likely that there are only a handful of civilization's in our galaxy, perhaps less.

 

[DaveC426913]

There is nothing profound about it, it's obvious.

You keep saying this. And I keep saying everything is obvious in hindsight.

Defensive, aren't we.

I'm not sure what you thought I meant but this is non sequitur. You should reread what I wrote.

I'm saying who exactly do you think is being fooled by [this equation claiming to answer more than it is]? You're not fooled. Neither am I.

So who exactly do you think you're protecting from misunderstanding?

Ah, here is the crux of the issue - when you write it down this way, you can easily convince yourself

Who can?

Again, you're not fooled. Why do you think you're the first person to realize that the Drake equation makes no predictions?

 

[DaleSwanson]

Is it not naive of us to be looking almost exclusively for radio signals?

What do you propose we look for instead? We don't have the technology to search for anything we produced prior to radio. And it doesn't seem we can search for things we may use in the future before we know what they are. In other words, searching for radio may have problems, but it's the only thing we can search for.

 

[Super Luminal]

Dale, I don't have a better proposition. I just meant to impart that perhaps we shouldn't deduce from the lack radio signals that we're necessarily alone, but rather that we (humans) aren't technologically on the same page as other more advanced civilizations, so to speak.

The Drake equation's power, IMHO, is in the wonderment and awe it inspires in some people, not in its scientific contribution. As far as I know, the Drake equation hasn't really expanded cosmology in any meaningful way but it probably has inspired some people that will make significant contributions one day.

 

[Super Luminal]

Dale, I don't have a better proposition. I just meant to impart that perhaps we shouldn't deduce from the lack radio signals that we're necessarily alone, but rather that we (humans) aren't technologically on the same page as other more advanced civilizations, so to speak.

The Drake equation's power, IMHO, is in the wonderment and awe it inspires in some people, not in its scientific contribution. As far as I know, the Drake equation hasn't really expanded cosmology in any meaningful way but it probably has inspired some people that will make significant contributions one day.

 

[DaveC426913]

...perhaps we shouldn't deduce from the lack radio signals that we're necessarily alone...

I think it is generally understood that our search of ET is in its infancy. No one's making any conclusions based on lack of data. (http://en.wikipedia.org/wiki/Fermi_paradox" [Broken]... )

 

[narrator]

I view it as an extension of the Copernican principle.

In a similar way, I prefer the mediocrity principle.. to quote http://en.wikipedia.org/wiki/Mediocrity_principle" [Broken]:

"The idea is to assume mediocrity, rather than starting with the assumption that a phenomenon is special or has somehow violated the laws of the universe."

 

[narrator]

Is it not naive of us to be looking almost exclusively for radio signals?

They're using more methods than that. For example, they look for signs of the right gasses for any planets found - nitrogen, ozone etc.

 

[Tanelorn]

Using this equation or similar has anyone computed the odds of another civilisation with technology as advanced as ours or greater, existing in our galaxy at the same time as us? I guess the odds are small.

I also wonder what the odds are for two independant civilisations to develop and survive long enough to actually make contact? There are enough galaxies in the universe to allow this two happen I suspect.


Sometimes when I see our world and its problems I can almost believe that civilisations seldom last more than a few millennia before they are destroyed hence they rarely if ever connect. Carl Sagan thought we had a 1% chance of making it another 100 years.

 

[DaveC426913]

Using this equation or similar has anyone computed the odds of another civilisatio with technology as advanced as ours or greater, existing in our galaxy at the same time as us? I guess the odds are small.

That's exactly what the equation defines. Have you looked at it?

Problem is, it's up to you to assign numbers, and each successive variable in the equation is increasingly less predictable. By the 7th, they just guesses.

I also wonder what the odds are for two independant civilisations to develop and survive long enough to actually make contact?

Again, that's exactly what the equation defines.

There are enough galaxies in the universe to allow this two happen I suspect.

Well no. Civilizations that are that far away from each other are cut off forever by the speed of light. At least, for two-way communication.

 

[Tanelorn]

Ah yes I see it includes a variable for the length of time a civilisation lasts. What if in the whole history of our galaxy (10B yrs?) there have been 10 advanced civilisations each lasting 1000 years (ours has lasted 80 years approx) the odds are not very promising that they could ever communicate let alone meet up for a coffee - or a war.

So all that ET, Close Encounters, and Star Wars stuff seems even more far fetched! Steven Hawking was concerned that we would get invaded by Riddick type parasite aliens, but I can't see it myself. Most "advanced" civilisations could fail even before they radio waves reach us!




Originally Posted by Tanelorn
There are enough galaxies in the universe to allow this two happen I suspect.

"Well no. Civilizations that are that far away from each other are cut off forever by the speed of light. At least, for two-way communication."


In this instance I meant two civilsations within the same galaxy. There are so many galaxies perhaps it did happen.

 

[DaveC426913]

In this instance I meant two civilsations within the same galaxy.

Even within the galaxy we are limited to our neighborhood. It's 100,000 light years across, so messages take 100,000 years one way.

 

[Super Luminal]

One thing that never seems to be seriously considered--and fallaciously so in my layman's opinion--is the possibility that WE are among the most advanced creatures in the galaxy and other civilizations might be relatively abundant but too primitive to communicate across interstellar distances.

 

[marcus]

The possibility of life on other planets has been one of our oldest doubts... and oldest hopes. ...
The way we can calculate the possibility of life is by the Drake Equation, created by Frank Drake in the early 1960s. It states:

N= [r* x fp x ne x fl x fi x fc] L where:...

... a new kind of hope and dream for the future of our planet and the future of mankind.

You know science changes. 40 or 50 years later they may have a different way to investigate.
This question is being handled differently now. A good focus of effort is finding Earth-like exoplanets. And understanding other solar systems. How they form. What kind of planets are most common? What sizes? What distances from star?

You can't do everything all at once. Now we are accumulating information about how common are planets that could have liquid water. Before too long I guess we will be detecting atmosphere.

back in 1960-1970 we were not detecting exoplanets SO RADIO SIGNALS WERE THE ONLY SIGNS OF LIFE WE COULD HOPE FOR. So naturally we focused on imagining civilizations that might send radio signals.
That is a very restricted idea of life-search. It led to Drake Equation.

Now the game has changed. We want to know how abundant are habitable planets. How good are the living conditions--typically? Hundreds of planets have been found. I guess you have read thru the lists.

So it is as if attention has focused on just one or two numbers in the Drake Equation, where we can get definite data, and we've temporarily forgotten about many of the other numbers.
Which is OK. It is OK just to focus on what you can get good information about.

 

[Chronos]

It appears improbable we are the only intelligent civilizations in this galaxy, much less the universe. Perhaps all intelligent civilizations are quarantined for the same reasons we are.

 

[narrator]

If time is a factor, for a viable planet to develop atmosphere, then organisms, then intelligent life, then advanced civilization... then we add the effect of gravity on time.. then perhaps the worlds closest to the gravity well at the centre of our galaxy would be further along the evolutionary/advancement scale.

 

[Chronos]

And let's not forget we are still focused on EM signals broadcast by life forms similar to us. That really narrows the field. It is not improbable the number of such intelligent, detectable civilizations in our galaxy is vanishingly small. We might have a shot at catching a signal from a juvenile ET messing with a science fair project on radio technology.

 

[Tanelorn]

I suspect that all stars have planets and most stars our size have planets like earth. My issue is that the progress and evolution of life could be derailed for a multitude of reasons at each stage from single celled onwards.

 

[DaveC426913]

If time is a factor, for a viable planet to develop atmosphere, then organisms, then intelligent life, then advanced civilization... then we add the effect of gravity on time.. then perhaps the worlds closest to the gravity well at the centre of our galaxy would be further along the evolutionary/advancement scale.

No. GR has a vanishingly small effect.

 

[Tanelorn]

I think I recall a discussion here that our galaxy has a habitability zone where the conditions are more friendly to life. I had suggested that the older stars near the central hub would have older civilisations but there are also much higher levels of radiation around there.

 

[DaveC426913]

I think I recall a discussion here that our galaxy has a habitability zone where the conditions are more friendly to life. I had suggested that the older stars near the central hub would have older civilisations but there are also much higher levels of radiation around there.

Also, all those Population III stars are much poorer in metals.