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Tuesday, March 27, 2007

The Fermi Paradox

The story goes that, one day back on the 1940's, a group of atomic scientists, including the famous Enrico Fermi, were sitting around talking, when the subject turned to extraterrestrial life. Fermi is supposed to have then asked, "So? Where is everybody?" What he meant was: If there are all these billions of planets in the universe that are capable of supporting life, and millions of intelligent species out there, then how come none has visited earth? This has come to be known as The Fermi Paradox.

Fermi realized that any civilization with a modest amount of rocket technology and an immodest amount of imperial incentive could rapidly colonize the entire Galaxy. Within a few million years, every star system could be brought under the wing of empire. A few million years may sound long, but in fact it's quite short compared with the age of the Galaxy, which is roughly ten thousand million years. Colonization of the Milky Way should be a quick exercise.

So what Fermi immediately realized was that the aliens have had more than enough time to pepper the Galaxy with their presence. But looking around, he didn't see any clear indication that they're out and about. This prompted Fermi to ask what was (to him) an obvious question: "where is everybody?"

Also, if one considers the amount of time the Galaxy has been around (over 10 billion years) and the speed of technological advancement in our own culture, then a more relevant point is where are all the super-advanced alien civilizations. Russian astrophysicist Nikolai Kardashev proposed a useful scheme to classify advanced civilizations, he argues that ET would posses one of three levels of technology. A Type I civilization is similar to our own, one that uses the energy resources of a planet. A Type II civilization would use the energy resources of a star, such as a Dyson sphere. A Type III civilization would employ the energy resources of an entire galaxy. A Type III civilization would be easy to detect, even at vast distances.

This sounds a bit silly at first. The fact that aliens don't seem to be walking our planet apparently implies that there are no extraterrestrial anywhere among the vast tracts of the Galaxy. Many researchers consider this to be a radical conclusion to draw from such a simple observation. Surely there is a straightforward explanation for what has become known as the Fermi Paradox. There must be some way to account for our apparent loneliness in a galaxy that we assume is filled with other clever beings.

While interstellar distances are vast, perhaps to vast to be conquered by living creatures with finite lifetimes, it should be possible for an advanced civilization to construct self-reproducing, autonomous robots to colonize the Galaxy. The idea of self-reproducing automaton was proposed by mathematician John von Neumann in the 1950's. The idea is that a device could 1) perform tasks in the real world and 2) make copies of itself (like bacteria). The fastest, and cheapest, way to explore and learn about the Galaxy is to construct Bracewell-von Neumann probes. A Bracewell-von Neumann probe is simply a payload that is a self-reproducing automaton with an intelligent program (AI) and plans to build more of itself.

Attached to a basic propulsion system, such as a Bussard RamJet, such a probe could travel between the stars at a very slow pace. When it reaches a target system, it finds suitable material (like asteroids) and makes copies of itself. Growth of the number of probes would occur exponentially and the Galaxy could be explored in 4 million years. While this time span seems long compared to the age of human civilization, remember the Galaxy is over 10 billion years old and any past extraterrestrial civilization could have explored the Galaxy 250 times over.

Thus, the question arises, if it so easy to build Bracewell-Von Neumann probes, and they has been so much time in the past, where are the aliens or at least evidence of their past explorations (old probes). So Fermi Paradox becomes not only where are They, but why can we not hear Them and where are their Bracewell-von Neumann probes?

- Rohan Warnmallya


Tom said...

Thanks. What if there was no "beginning" to the universe? And what if there is no life off outside of earth?

RG said...

The statement that there is "no life outside of Earth" is very much out of favor with the theories of probability.

At most, you can ask, "what if there is no intelligent life outside of Earth" - which again, is nearly impossible - but not so much as the previous statement.

There is, indeed, no tangible concept of the "birth" of the universe itself, but because the universe's boundaries are being defined by the points where the farthest celestial objects exist, the big bang is taken as the origin.

Gr81 said...

I agree with RG... we cant state that there's no life outside Earth..

There could be so many planets which could sustain life... and maybe they actually do have life. But it isnt necessary that they have "intelligent" life.
Looking at our space voyages, what if the other civilization is about a thousand years "behind" us... mayb they are yet to develop spaceships etc.

But the biggest problem is that this topic has lots of "May bes"
But till we can actually get a strong proof, i dont think we should ignore any possibilty.
coz u never know wat may lie in the future.....

Tom said...

Thank you for the comments. It seems that the questions of the origin of the universe and "life" outside of earth are rendered suppositional by the availability of hard science to determine the answer.

Varun Khetarpal said...

Theories and experiments together help in predicting the state of the universe. Theory of relativity is partially applicable for understanding the origin of the universe. Hence, we cant depend on it.

The farthest celestial object of the universe is yet unknown and alongside we are aware that universe is continuously expanding. Therefore, it we can't say that it is finite or has a well-defined boundary.

As we know, if we start from one point on earth, we reach the same point again. According to one of the three Fredmann models, space is considered to wrap itself in a shape just like the earth. It is therefore considered to be infinite. But this model has various drawbacks of its own.

The universe has to have a start. It has to have a beginning. Universe is said to have 4 dimensions. The 4th dimension is time. The beginning of Time is taken from the same point as the beginning of the universe. If the universe doesn’t have a start, time doesn’t have a start either and the existing state of the universe cant be as it is.

The universe would either end up into a black hole region or a big bang crunch. Equal possibilities of both.

Varun Khetarpal said...

The reasons we haven't come across intelligent life maybe the following :-

1) Our earth is not even of the size of a dust particle in this universe.Even if life exists, it is difficult to come across.

2) Life might be present outside earth but not intelligent enough to build a communication link with us.

3) The conditions of life might be totally opposite to what is required on earth. So it will not be 'life' for us.

4) Life might be present in earlier stages of the universe but its gradual destruction decreased the probability of finding life now at this point of time. Same as something which happened with dinosaurs.

5) UFO incidents, Face on mars etc. - none of them is a success till now.

This is science !

When you are speaking to technically illiterate people you must resort to the plausible falsehood instead of the difficult truth.

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Astro-photographer? Send your photos to pics@exploreuniverse.com and have them featured on this blog with your name. Comet Mcnaught : Pictures taken with Nikon D100 on 19/1/07 from Manning Point, northern NSW, Australia by Mr. Peter Enright.
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