Ignoring 500 Billion Galaxies: Mathematics vs Common Sense in the Debate About the Probability of Extraterrestrial Life
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February 23, 2012

Ignoring 500 Billion Galaxies: Mathematics vs Common Sense in the Debate About the Probability of Extraterrestrial Life

 

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Carl Sagan said that "extraordinary claims, require extraordinary evidence." In a stunning display of mathematical logic vs common sense, David Spiegel of Princeton University and Edwin Turner from the University of Tokyo published a paper last summer that turns the Drake equation upside down using Bayesian reasoning to show that just because we evolved on Earth, doesn’t mean that the same occurrence would necessarily happen elsewhere; "using evidence of our own existence doesn’t show anything" they argue, "other than that we are here."

What Bayesian reasoning overlooks, of course, is the inconvenient fact that there are some one trillion galaxies in the known universe and some 50 billion planets estimated to exist in the Milky Way alone and some 500,000,000 predicted to exist in a habitable zone.

Spiegel and Turner point out that basing our expectations of life existing on other planets, for no better reason that it exists here, is really only proof that were are more than capable of deceiving ourselves into thinking that things are much more likely than they really are.

They argue that other unknown factors exist that could have contributed to us being here that we don’t yet understand. So, they conclude that, deriving numbers from an equation such as that put forth by Drake, only serves to underscore our belief in the existence of other alien life forms, rather than the actual chances of it being so.

We think evidence will be discovered in the next 20 years: The Kepler mission has discovered 1,235 exoplanets that revolve around a sun, in an area that represents around 1/400th of the Milky Way. By extrapolating these numbers, the Kepler team has estimated that there are at least 50 billion exoplanets in our galaxy — 500 million of which sit inside the habitable "Goldilocks" zones of their suns, the area that it is neither too hot nor too cold to support life.

Astronomers estimate that there are 100 billion galaxies in the universe. If you want to extrapolate those numbers, that means there are around 50,000,000,000,000,000,000 (50 quintillion) potentially habitable planets in the universe.

As Arthur C. Clarke, physicist and author of 2001: A Space Odyssey wrote, "The idea that we are the only intelligent creatures in a cosmos of a hundred billion galaxies is so preposterous that there are very few astronomers today who would take it seriously. It is safest to assume therefore, that they are out there and to consider the manner in which this may impinge upon human society."To an objectivist, empirical view, the rules of Bayesian statistics can be justified by requirements of rationality and consistency and interpreted as an extension of logic. Using a subjectivist view, however, the state of knowledge measures a "personal belief".

More information: "Life might be rare despite its early emergence on Earth: a Bayesian analysis of the probability of abiogenesis" http://arxiv.org/abs/1107.3835 and physorg.com


Image credit: Fahad Sulehna

Comments

Mysterious hidden factors? Like what? Magic? Stats are irrelevant as so far we have only one data point (Earth). Drake's equation is a starting point, an a priori stab at thinking rationally about a subject which is brand new as opposed to an offshoot of a preexisting field of study (look at philosophy which spun off mathematics, physics, chemistry etc). Did Drake get it right? Not very likely! But it is a start, we will get better numbers for the parameters, we may eliminate some, add others, maybe come up with totally different ways of thinking about this. But these jokers sound a lot more like Fundamentalist Creationists than statisticians. I (one data point) am a sub 6 foot tall white male, therefore the population as a whole is male, white and short?

Mysterious hidden factors? Sounds like the creationists have had a hand in the "edits" religion is terrified of the truth. ironic, no?

The inference (there are lots of galaxies) -> (therefore life exists in more than 1 of them) is as horribad an inference as ever there was.

I eagerly await replies from people who don't know what "bad inference" means.

How pessimistic would one have to be to believe that life hasn't developed on any of those other 50 quintillion planets in the habitable zone? It is of course a slam sunk just using logic--intuitively, it is even more of a certainty.

I love Arthur C, but I agree with David Spiegel of Princeton University and Edwin Turner from the University of Tokyo that there is a fault in his thinking: "using evidence of our own existence doesn’t show anything", they argue.

I am *not* a creationist!! and religion plays no role in my thinking about the nature of the Universe. Certainly it's possible that intelligent life exists on other planets - there are some really weird "alien" species right here on Earth.

All I'm saying is that logic does not lead inevitably to the conclusion that x number of planets = intelligent life.

This is a philosophical question, not a mathematical one.

Peace :))

It is ignorant to deny that there are many other intelligent life in this galaxy alone. The universe... come on now, isn't it obvious? You say this is a philosophical question and not a mathematical one? Can't those somewhat play hand in hand? Anyways ignoring the immense numbers that proves it.. I don't see how any ones philosophy can block the idea of intelligent life elsewhere. That would have to be one shitty philosophy in my opinion. I believe GOD created the universe and those other stars aren't out there just for the fun of it... we are not alone in the universe. And certainly can't be the most intelligent form either.

I'll wager there's lots of life out there, but the percentage of planets with intelligent, tool-using, technologically communicating life is probably very small, giving what we know about the completely unpredictable (and essentially random) accidents resulting in our own evolution, is probably small in comparison.

But small in comparison is still pretty big.

And the optimist in me wants to believe that one in a million chances crop up nine times out of ten.

Apologies. Didn't edit this properly the first time.

I'll wager there's lots of life out there, but the percentage of planets with intelligent, tool-using, technologically communicating life, giving what we know about the completely unpredictable (and essentially random) accidents resulting in our own evolution, is probably small in comparison.

But small in comparison is still pretty big.

And the optimist in me wants to believe that one in a million chances crop up nine times out of ten.

If we start thinking that life has not evolved anywhere else in this Universe, then we are simply Ignorant - I must say.

Clarke was correct in his idea of it being preposterous for us to assume we are alone. His views serve science justice in face of a terracentric agenda.

At one time it was commonly that the Earth was flat, the heavens revolved around it.

Oh and then guess what? WRONG.

I think it is entirley mathematically possible that other living worlds exist.

Matter exists in various states due to heat, magnetism and gravity. It's entirely possible that other intelligent biological creatures exist, but with a different set of materials, molecular structures and evolution.

"What Bayesian reasoning overlooks, of course, is the inconvenient fact that there are some one trillion galaxies in the known universe "

"Astronomers estimate that there are 100 billion galaxies in the universe."

which is it?

Don't any of these scientists understand that the information needed for producing life is inherent in the source field? Of course there is life out there. As a matter of fact, i guarantee you that the universe is teeming with life; both similar to what is on earth, and WILDLY alien. And who is to say that only the planets in the "habitable" zones are the only ones capable of supporting life? I bet you there is life that has adapted to just about ANY condition out there. Heck, the universe itself is alive.

A 15th century Indian says to the other "I think there may be people elsewhere in this land"
The other replies " I don't see their smoke signals..."

Just because we can't yet detect them, does not prove that they are not there.

Well, let's take this a little further. Yes the chance of evolution on a planet is extremely low. So low that we must consider our own existence a miracle, that is if we, as most scientist of our time do, assume that random chance lead to our own existence. But with so many inhabitable planets out there, why should we assume that we are unique in our evolutionary path, or that it is in fact random at all? An option that should be considered is that life forms elsewhere had the motives and means to spread this beautiful thing we call life. I mean, billions of years ago there were roughly as many inhabitable planets as now. Scientists seem to think that we need more direct evidence to lead to a conclusion of extraterrestrial help, and they are right.

For one, fossil records do not support darwins ideas of evolution fully, as every so often (300,000 years-ish) there is a great burst of species. And intelligent life, that some say have a soul, cannot really be traced to a specific origin. One possibility is someone out there has goals for an evolving planet, one of which seems to be letting nature run its course, while still providing gentle nudges on the 'right' direction, like sending the pattern of life our way, and providing us with organs necessary for perceiving certain forms of energy, and finally what some would label a soul and conscious. Sorry for the run- ons and grammar, on an iPad.

Once our Solar System was created out of a molecular cloud that contained a certain amount of gasses; liquids and particles that created life on Earth.

How big are the odds for finding a similar precise cloud otherwhere that can create excatly the very same life as here on Earth?

NB: Mathematics has the same weakness as with other cosmological consensus "constants" ideas: It can only be used measuring static stages. Even measuring a wooden board fails matematically when the board is either cooled or heated up.

The only real constant is that nothing is constant.

We can debate until the sun goes nova and solve nothing.
1. At one time people of learning thought that Homo sapiens was the only sentient species on this planet - now we know better
2. At one time people thought the planet was flat – now we know better.
3. At one time we did not know what the far side of the moon looked like – now we know better.
4. At one time some of the scientists at the Hadron Collider thought they had made a particle go faster than light. Then they found it was a computer ghost caused by a loose connection. So now we know better.
5. At one time scientists thought they had devised a method to produce cold fusion. But since the experiment has never been duplicated – now we know better.

Hmm – there seems to be a pattern here.

Statistics says there must be life do the vastness of the universe, not even counting parallel universes allowed by quantum mechanics.
It is also possible prove, or disprove, almost anything with statistics.

All we can really say – right now we just don't know.

according to Ezekiel, and his record of strange visitors, I think we are not alone, his record is in the Christian holy bible.

who was it who quoted, "there are leis, damned lies, and statistics" ?

I believe that intelligent life isn't even on earth yet !!!

What if, indeed, we (earth) are the only life in the universe? What a sobering thought. We should ponder this though, we might arrive at a paradigm shift that will save us.

Due to many planets being in the habitable zone, and the chemical seeds of life being all over, life may be ubiquitous. Intelligent, technological life, seems to be rare. If you think otherwise, show me :-) SETI has been going for a while, they have zilch to show.

David Spiegel acts a little like a blind preteen who grew up with only a Daddy. He only has what he knows. Big boobs don't exist even though his father may be a plastic surgeon.

All those saying they "wager," or "believe," or "there has to be," or even the statistical formulas is great, but realize that those are merely hypotheses (more likely, conjectures). As long as you continue to keep your thoughts constrained to that realm, that's fine. In fact, without those conjectures, there wouldn't be any motive to pursue scientific discovery (which involves testing).

However, there is only one data point--earth. Until the is at least another data point, all other comments remain conjecture. You can scream until you're blue in the face there are other inhabited worlds, but it will be you against the data. The one data point.

Just realize when you go against the data, you are exercising faith--faith in your beliefs.

What people fail to realize is the number of ancient books in just about every religion that speak of Lords or Gods from the heavens. Heaven is also the same word to describe the sky or outer space and not some place when you die.. Most ancient cultures speak of a creator responsible for the advancement of mankind. All of this makes sence when you consider that the word God means 'judge' for which there are many. We may not see the presence of these beings daily but it's obvious that they made there presence known throughout history. Unfortunately religion has avoided the fact that God is actually a being of some kind and not a jini in your pocket to call on. Unfortunately most religions also speak about these heavenly being coming back to judge mankind, so we might want to wake up and take care of our issues here on Earth.


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