100 Billion: "The Great Silence" -A Galaxy Classic

"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."

Arthur C. Clarke, physicist and author of 2001: A Space Odyssey

One of the greatest philosophical and scientific challenges that currently confronts humanity is the unsolved question of the existence of extraterrestrial intelligence.

The Fermi paradox is the apparent contradiction between high estimates of the probability of the existence of extraterrestrial civilizations and the lack of evidence for or contact with such civilizations.

The 14-billion-year age of the universe and its 130 billion galaxies and a Milky Way Galaxy with some 400 billion stars suggest that if the Earth is typical,  should be common. Nobel laureate Enrico Fermi, discussing this observation with colleagues over lunch in 1950, asked, logically: "Where are they?" Why, if advanced extraterrestrial civilizations exist in our Milky Way galaxy, hasn't evidence such as probes, spacecraft, or radio transmissions been found?

As our technologies become ever more sophisticated and the search for extraterrestrial intelligence continues to fail, the "Great Silence" becomes louder than ever. The seemingly empty cosmos is screaming out to us that something is amiss. Or is it?

Using a computer simulation of our own galaxy, the Milky Way, Rasmus Bjork, a physicist at the Niels Bohr Institute in Copenhagen, proposed an answer to the Fermi Paradox. Bjork proposed that an alien civilization might build intergalactic probes and launch them on missions to search for life.

He found, however, that even if the alien ships could hurtle through space at a tenth of the speed of light, or 30,000km a second, - NASA's current Cassini mission to Saturn is gliding along at 32km a second - it would take 10 billion years, roughly half the age of the universe, to explore a mere four percent of the galaxy.

Like humans, alien civilizations could shorten the time to find extra-terrestrials by picking up television and radio broadcasts that might leak from colonized planets. "Even then," he reported in the New Scientist, "unless they can develop an exotic form of transport that gets them across the galaxy in two weeks it's still going to take millions of years to find us. There are so many stars in the galaxy that probably life could exist elsewhere, but will we ever get in contact with them? Not in our lifetime."

The problem of distance is compounded by the fact that timescales that provide a "window of opportunity" for detection or contact might be quite small. Advanced civilizations may periodically arise and fall throughout our galaxy as they do here, on Earth, but this may be such a rare event, relatively speaking, that the odds of two or more such civilizations existing at the same time are low.

In short, there may have been intelligent civilizations in the galaxy before the emergence of intelligence on Earth, and there may be intelligent civilizations after its extinction, but it is possible that human beings are the only intelligent civilization in existence "now." "Now"  assumes that an extraterrestrial intelligence is not able to travel to our vicinity at faster-than-light speeds, in order to detect an intelligence 1,000 light-years distant, that intelligence will need to have been active 1,000 years ago.

There is also a possibility that archaeological evidence of past civilizations may be detected through deep space observations — especially if they left behind large artifacts such as Dyson spheres.

Perhaps...but in our search for life and intelligence we have to keep in mind that the Milky Way  Galaxy is two or three times the age of our Solar System, so there are going to be some societies out there that are millions of years, maybe more, beyond ours, which may have proceeded beyond biology—that have invented intelligent, self-replicating machines and it could be that what we first find is something that's artificially constructed if we have the ability to recognize it as such. It may very well be that our greatest discovery will be that the very nature of alien communication will prevent our being able to communicate with it.

Posted by Casey Kazan.

Related Galaxy posts:

James Cameron & Arthur C Clarke on 2001 A Space Odyssey
New Technologies & the Search for  -A Galaxy Insight
Lonely Hearts of the Cosmos Revisited -NASA's Phoenix Probe & the Search for
Eyes on the Cosmos -European Space Agency's Hawk 1 & Hubble's Successor
New Phoenix Mission Technology to Search for Life
Cruising the Goldilocks Zone -The Search for "Super-Earths"
Adventures of a Planet Hunter
Non-Carbon Lifeforms -Why We May Overlook
The Milky Way Enigma -How Galactic Forces May Control Life on Earth
Astro-Engineering Artifacts as Evidence of
The Biological Universe -A New Copernican Revolution? 
Jupiter's Europa & the Search for
Earth's Twin Habitable?
Search for Extraterrestrial Genomes

Comments

[Daniel Appleton]

Un - manned / crewed space probes like Pioneer, Voyager would perhaps be more successful at gathering data & sending it back to whatever civilization ( s ) sent them. I remember reading a Star Trek novel " Strangers From The Sky " where the ubiquitous Vulcans observed us with automated probes - apparently using tachyon transmissions somehow - before sending living observers, that way, no cultural contamination is involved.

Also, even if extra - terrestrial civilizations were out there just pumping out radio transmissions every hour of every day, how would we recognize them, especially when time, distance, & interference from other interstellar phenomena would garble them ? How many civilizations out there would recognize transmissions from the early days of 20th century radio, the Apollo 11 landing, Martin Luther King's " I Have a Dream " speech, the razing of the Berlin Wall, any of earth history's high points ? Uncounted trillions & trillions of miles & several hundred thousand light years would possibly garble any message to or from earth.

Just a few thoughts.

[Naturyl]

I think the concept of the Singularity explains the Fermi paradox. Specifically, civilizations that survive their "adolescence" develop technologies which allow them to transfer their consciousness to media other than biological. Computer circuitry is the obvious first step, possibly followed by transference of consciousness to photons (light) or a similar subtle medium.

Basically, we don't see or hear anybody because the biological period of an intelligent civilization is relatively short. At any given time we choose to look, we will find that everyone else blew themselves up or took it to "the next level."

[John]

There's another non-mainstream(?) view; that of religious fundamentalists. They say that we will never communicate with alien beings because the earth is under quarantine. We are just a mess, under Satan's control, and God, or the Q for ST fans, just has forbade any contact.

Far fetched? Sure, but completely logical within its own construct.

[Nate D.]

Some people have raised the concern that constantly babbling out so much information about ourselves is not a very wise thing to do. Perhaps a nearby civilization, only slightly ahead of us in the scheme of things, has some time ago developed a communications network on their world that is closed-circuit so to speak. It doesn't leak. We might of had a window to detect their earlier communications, but it may have only just passed us by when we first started waving around antennas such a short while ago. Perhaps we ourselves are only a relatively short while off from developing new exotic forms of long-distance communication that creatures with simple RF antennas would never detect. That would mean that our era of rampant RF babble might only be a few centuries long. That might be an easy window to miss. I see no paradox at all.

[peter jones]

Hi great blog, must check out much more of yr content.

I wondered if I could please use the image at:

http://www.dailygalaxy.com/my_weblog/2007/09/you-create-th-3.html

- in a blog post?

My favourite book is CETI ed. by Carl Sagan from about 1977. I've some astro links that may be of interest:

http://www.p-jones.demon.co.uk/linksTwo.htm

I crunch 4 seti at home too.

All the best for 2009....
pj
hodges model

[Scott]

As of this date there is an equal amount of data to support the existance of GOD and life in the universe other than on our planet.......NONE...... I repeat.....NONE.... all the rest is the type of mental masterbation we all performed stoned, drunk or crazy. There is no proof of either.

[Adrian Clare]

Intelligent detectable life on Earth has only been around for about 100 years. The first man-made transmissions coming from Marconi. So, if your intelligent civilization is more than 100 light years from the Earth, they will have no knowledge of intelligent life on Earth. In addition, most of the early signals would have been weak and thus extremely difficult to detect. We might just be detectable fifty light years from here, which is a minute volume even of the Milky Way, let alone the Universe. There may well be thousands of civilizations out there, but finding them is always going to be the problem.

[robert]

read "the quantum sausage machine" for insight on interaction with new species

[Ian G.]

This doesn't take into account that civilizations wouldn't explore blindly. We can detect exo planets and discover specific details, such as temperature and content of the atmospheres. Surely an advanced civilization would be able to do the same. Even just taking the earth back to the dinosaurs, 65 million years, means that the light of a living eath has been broadcast across the galaxy for some time and if there were civilizations out there looking, they would be able to detect it with technology only slightly better than our own. Meaning, if they were going to send probes they wouldn't need to explore the whole galaxy, just the important spots they could see from afar. So any civilizations out there that could see Earth and felt like exploring would logically have sent probes here. The best place to start looking for evidence of interstellar civilizations is right in our own solar system.

[claudio]

The article proposes a good old dilemma : are we alone ??
As matter of facts except for the usual 'metropolitan legends' we have NO 'known signs' yet of alien civilizations.

Then the question remains : are we alone ??

Radio transmission-reception of 'intelligent signals' is impeded by the physics laws.......

Simple formulas would tell many (including some scientist) that Transmitting from Arecibo (a 300m diametre dish ) a 100KW signal at 4 GHz it would be submerged by the noise at a mere 1 light year (1LY= 67000 AU) and that signal with only 10Hz bandwidth would NOT be detectable from another Arecibo (300m receiving parabolic dish) at 1LY distance.

I am quite expert in these thgings.....by the way.

Then the question is even more simple of those above :
FAQ : 'What SETI scientists are doing' ?????

Likely (only by inference ) we can say that they are either looking at nearby stars ...or at much shorter distances....

In fact 'Intelligent radio signals' emitted by nearby stars (say within 40LY) are NOT detectable on this planet: Nor from the 'large array' and not even from the gigantic Arecibo antenna.

I leave to You (NOT expert.... but intelligent) to understand what is a TV transmitter or even a music channel transmitter signal at 1LY....: Submerged by thermal noise...lost ...gone....NOTHING of detectable.

We are talking physics and NOT Holliwood moovies....with VEGA based civilization having received the Germany TV signals of Year 1938... : ....RIDICOLOUS.

This does NOT impede to space ships like ours (e.g. the aging Voyagers) and made by 'others' ...in principle to be able to exchange 'intelligent signals'.....from a much shorter distance....than that of nearby stars.

Voyager 1 is now within the Heliopause at a mere say 1/10 of a LY...and believe me they at NASA & Co are doing miracles to receive its weak telemetry signals.

Then the question remains intact are we alone and what are doing (paid by the US citizen taxes) those at SETI ??

At the end of the day ...'ONLY using my inference'...
I can presume by deduction that those 'metropolitan legends' (i.e. the greys and greens....or the like) are NOT so stupid....and these alien guys may have in place ships orbiting the sun at distances past Neptune ....or beyond....or the like.

Regards

[o-dish-es]

I'm hoping that French will become the official language of the inhabited universe. Also, I am pretty sure that soccer is the universe's most played sport.

[Mifkin]

Who says that aliens use Radio waves?

Its very arrogant to assume that "intelligence" automatically means "same technology as us"

[Bill Lin]

If we view the cosmos with nowadays knowledge.It's always impossible to realize the truth.Why we can't fly above light speed?Is Einstein's theory always true?It should be not.Human's science is so childish compared to whole cosmos.Aliens are always around of us....But we can't believe it even somebody see them.Other can't believe it.

[Bill Lin]

Yeah,agree with you.We don't need radio wave and language to communicate in the future.The world would be quiet...

[BoT]

A sample of 1 cannot be meaningfully interpreted. Unless and until another civilization is discovered, the odds that life is unique to the earth can't be known. But I grant you it's fun to talk about.

[MarkMark]

The Drake equation might be utterly wrong, too.

[Steppenwolf]

Don't think we're ready for something or someone to "find" us for our species can't even deal with itself and has some real issues waiting...
Why would we rather travel millions of light years (if we could), fight hundreds of wars, watch people die on a large scale, find thousands of excuses why exactly this is still happening, than finally face ourselves????

[Seth]

"He found, however, that even if the alien ships could hurtle through space at a tenth of the speed of light, or 30,000km a second, - NASA's current Cassini mission to Saturn is gliding along at 32km a second - it would take 10 billion years, roughly half the age of the universe, to explore a mere four percent of the galaxy."

That math does not make sense. The Milky Way is 100,000 light years across. In that example the probes would cover a sphere of space 1 billion light years in radius. Since when does 4% * 100,000 = 2,000,000,000?

[Saganite]

Another possibility, and I suspect a highly likely one, is that the period of time a civilization uses known mediums like RF, laser and other light speed limited variations etc, to communicate is probably a very short window indeed. Already we, ourselves, are looking at the ability to transmit data via quantum entanglement hardly a 100 years after the development of radio...just one example.

[bitirim]

thank you

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