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The 1.8 Gigayear Gap -A Galaxy Classic

Double_helix_nebula_2_3_3 Are we the lone sentient life in the universe? So far, we have no evidence to the contrary, and yet the odds that not one single other planet has evolved intelligent life would appear, from a statistical standpoint, to be quite small. There are an estimated 250 billion (2.5 x 10¹¹ ) stars in the Milky Way alone, and over 70 sextillion (7 x 10²² ) in the visible universe, and many of them are surrounded by multiple planets. The shear size of the known universe is staggeringly and inconceivably vast.

The odds of there being only one single planet that evolved life among all that unfathomable vastness seems so incredible, that it is all but completely irrational to believe. But then "where are they?" asked physicist Enrico Fermi while having lunch with his colleagues in 1950.

Fermi questioned, if there are other advanced extraterrestrial civilizations, then why is there no evidence of such, like spacecraft or probes floating around the Milky Way. His question became famously known as the Fermi Paradox. The paradox is the contradiction between the high estimates of the probability of the existence of extraterrestrial civilizations and yet the lack of evidence for, or contact with, any such civilizations.

Given the extreme age of the universe, and its vast number of stars, if planets like Earth are at all typical, then there should be many advanced extraterrestrial civilizations out there, and at least a few in our own Milky Way. Another closely related question is the Great Silence, which poses the question: Even if space travel is too difficult, if life is out there, why don't we at least detect some sign of civilization like radio transmissions?

Milan Cirkovic of the Astronomical Observatory in Belgrade, points out that the median age of terrestrial planets in the Milky Way is about 1.8 gigayears (one billion years) greater than the age of the Earth and the Solar System, which means that the median age of technological civilizations should be greater than the age of human civilization by the same amount. The vastness of this interval indicates that one or more processes must suppress observability of extraterrestrial communities.

Since at this point, there is no direct and/or widely apparent evidence that extraterrestrial life exists, it likely means one of the following:

We are (A) the first intelligent beings ever to become capable of making our presence known, and leaving our planet. At this point, there are no other life forms out there as advanced as us. Or perhaps extraterrestrial life does exists, but for some reason extraterrestrial life is so very rare and so very far away we’ll never make contact anyway—making extraterrestrial life nonexistent in a practical sense at least.

Or is it (B) that many advanced civilizations have existed before us, but without exception, they have for some unknown reason, existed and/or expanded in such a way that they are completely undetectable by our instruments.

Or is it (C) There have been others, but they have all run into some sort of “cosmic roadblock” that eventually destroys them, or at least prevents their expansion beyond a small area.

Then ancients once believed that Earth was the center of the universe. We now know that Earth isn’t even at the center of the Solar System. The Solar System is not at the center of our galaxy, and our galaxy is not in any special position in contrast to the rest of the known universe. From a scientific viewpoint, there is no apparent reason to believe that Earth enjoys some privileged status.

Since Earth’s placement in space and time appears to be unremarkably random, proposition “A” seems fairly unlikely. Assuming humans evolved like other forms of life into our present state due to natural selection, then there's really nothing all that mystical, special or remarkable about our development as a species either. Due to the shear numbers, there are almost certainly other planets capable of supporting at least some form of life. If that is so, then for Earthlings to be the very first species ever to make a noticeable mark on the universe, from a statistical perspective, is incredibly unlikely.

For proposition “B” to be correct would defy all logic. If potentially thousands, or even millions of advanced extraterrestrial civilizations exist in the known universe, then why would all of them, without exception, choose to expand or exist in such a way that they are completely undetectable? It’s conceivable that some might, or perhaps even the majority, but for all of them to be completely undetectable civilizations does not seem likely either.

Proposition C in some ways, appears to be more likely than A or B. If “survival of the fittest” follows similar pathways on other worlds, then our own “civilized” nature could be somewhat typical of extraterrestrial civilizations that have, or do, exist. Somehow, we all get to the point where we end up killing ourselves in a natural course of technological development and thereby self-inflict our own “cosmic roadblock”.

“Perhaps the most disturbing aspect of the Fermi Paradox is what it suggests for the future of our human civilization. Namely, that we have no future beyond earthly confinement and, quite possibly, extinction. Could advanced nanotechnology play a role in preventing that extinction? Or, more darkly, is it destined to be instrumental in carrying out humanity's unavoidable death sentence?” wonders Mike Treder, executive director of the Center for Responsible Nanotechnology (CRN).

Treder believes that some of the little understood new technologies now being developed such as nanotech, and others, could well be either our salvation or just as likely end up causing our ultimate destruction.

“Whatever civilizations have come before us have been unable to surpass the cosmic roadblock. They are either destroyed or limited in such a way that absolutely precludes their expansion into the visible universe. If that is indeed the case—and it would seem to be the most logical explanation for Fermi's Paradox—then there is some immutable law that we too must expect to encounter at some point. We are, effectively, sentenced to death or, at best, life in the prison of a near-space bubble,” suggests Treder. “Atomically-precise exponential manufacturing could enable such concentrations of unprecedented power as to result in either terminal warfare or permanent enslavement of the human race. Of course, that sounds terribly apocalyptic, but it is worth considering that the warnings we heard at the start of the nuclear arms race, and the very real risks we faced in the height of the Cold War, were but precursors to a much greater threat posed by an arms race involving nano-built weaponry and its accompanying tools of surveillance and control.”

When we consider the chronological history of life on Earth, humans have only existed for a small fragment of time and our existence has always been precarious. The entire time we’ve existed, we been banding into various groups and attempting to kill each other—or at least are constantly in the process of developing more effective ways of killing each other—just in case. The US government, for example, spends on “Defense” (including “preemptive” warfare) and Homeland Security, 8 times what it spends on educating the next generation. There is enough nuclear weaponry in storage around the world to kill every living creature on the planet several times over. Clearly, we’re a species with poor odds of surviving indefinitely.

Our self-destructive natures aside, curiosity may end up killing more than the cats. The faster technology is advancing, the more our “leap now, look later” nature appears to grow as well. If evolution on Earth serves as a somewhat typical template for evolution of other life forms, then becoming a truly advanced civilization must be a very daunting task indeed and a very rare, if not impossible, achievement.

In fact, Sir Martin Rees, Great Britain's Astronomer Royal and respected professor of astrophysics at Cambridge University has estimated that humans have only a 50-50 shot of making it through the 21st century. If Rees is right, and our standing on the planet is as precarious as he and others believe it is, then we may be alone due to a built-in evolutionary self-destruct button. Others have come before and others will exist after, but the cosmic roadblock may be an innate, finite nature, which only allows sentient life forms to exist for a very small window of time—windows of life which may be too small for our civilization to match up with the small windows of other civilizations that have been before or will come after.

In a contrary point of view, Milan Cirkovic believes that highly efficient city-state type of advanced technological civilizations could easily pass unnoticed even by much more advanced SETI equipment, especially if located near the Milky Way rim or other remote locations.

Posted by Rebecca Sato with Casey Kazan.

NASA Image is the Double Helix Nebula near the center of the Milky Way.

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you might want to make a correction in your article when you wrote

"There are an estimated 250 billion (2.5 x 1011) stars in the Milky Way alone, and over 70 sextillion (7 x 1022) in the visible universe"

I think you actually ment to write (2.5 x 10^1011) and (2.5 x 10^1011)

(2.5 x 1011) isnt really that big of a number

There is an option (D) not listed above: That advanced civilizations -- very much more so than us, being as crudely developed as we are -- would NOT want to be detected. They would want to keep to themselves and their own global cultures and would be pursuing non-technological activities more than not. Space travel and search for other beings is a really pretty silly waste of resources when we don't have our own planetary act together. All non-earth bound endeavors should cease until population stabilization, alternative energy development and global warming are under "control" or there is no point in going forward into space. Tom Shelley, Ithaca NY

Actually the writer ment 2.5 x 10¹¹ (2.5e11) and 7 x 10²² (7e22) but superscripts got somehow screwed...

I think all the mathematicians trying to correct the writer wish they could spell.

I would also suggest that the 1.8 gigayear assumes that intelligent life needed 200 million years of dino domination. Forget about the Permian... Its all about the conditions and circumstances. If they are just right, it takes less than a blink of an eye for intelligent life to rise, apparantly.

I think the proposition A(2) is easily the most plausible. At least for us optimists... We arent the first, but we are few and far between. Plus the signals have probably been there for millions of years, we just arent quite there yet, in the recieving department..

We know that there have been multiple extinction events on the Earth, with at least one happening during the age of man that almost put an end to the human race. So, another option to consider is the stability of planets in hosting life, not just the estimated propensity for intelligent species to exterminate themselves.

why could there not be an (e) - Star Trek Scenario

Highly developed civilizations have developed and they monitoring, but due to our state of development have not made first contact (e.g. Star Trek).

Altho it may appear to be inconceivable that we're the only intelligent species in our viewing radius, it's not necessarily impossible.

What if we're indeed the ONLY intelligent lifeform in our viewing radius. That knowledge should impart a sort of reverence for humanity to latch on to. And I don't mean a religious reverence, but rather a reverence that this sector of the universe has only one self-aware portion of itself. That makes us stewards. That imparts responsibility.

After all, we have art, culture, language, history, knowledge of the past, the present and the ability to imagine the future. WE ARE THE CONSCIOUSNESS OF OUR DOMAIN.

Until proven otherwise!

Another possible reason we have not found evidence of another civilization is that they may no longer use broadcast radio wave communication. Perhaps they use quantum entanglement in communication or some other quantum phenomenon we have yet to discover, and have no means to detect.

The article does not address the probabilities involved in the spontaneous development of life. Even if you filled the universe with planets having earthlike orbits and Sol-like suns the step from non-life to life is still problematic. I am curious how would you even calculate the odds giving optimal conditions life would occur spontaneously?

I have wondered for quite a while just how rare a slow spinning magnetosphere planet with a moon as large in relation to earth is and that it's spin is exact enough to show the same side through out it's periodicity of rotation? How truly rare this might be with an ozone shield and plenty of carbon or silicon.

something that most havent thought of is that there is life out there but it has evolved to the point where it would not need the things we require to detect them.

2 scenarios:

1) hit the roadblock. die off. what will live on? i believe the US are about to unleash weapons capable of ethical decisions. if we can do this than other civilizations have done this. thus, their machines are what are left of their civilizations (war with machines is not implied here but may be one result of this scenario)

2) life sciences and mechanical engineering merge into something called cybernetics. humans slowly have more and more mechanical parts to replace frail organic ones. who starts? the military. bionic legs to run faster and jump taller. science. implant extra processors or ram to do more complex calculations which a normal brain cannot do. eventually, scenario 1 happens. machines do not need heat to survive. it would only be a bi-product of their mechanical parts. they would not need to live on any particular planet as all become habitable. reproduction is replication. communication becomes a form of complex quantum entanglement.

what is there left for us to measure?

they are out there. all around. but we will not find them until we find out their unique signature. and this will not happen until we become just like them

Option F, not discussed, is that radio signals of artificial origin do not propagate well at interstellar distances.

This is nitpicking and off topic but the word is "sheer" as in "sheer size", not "shear size", of the universe.

I think the article is flawed in many assumptions and missing a number of possibilities. First off this self annihilating complex that many have is flawed. It basically the same as I think therefore I am. Because we do think, because we are self aware and because of popular culture we are acutely aware of our ability to destroy ourselves we will not destroy our selves. Even in humanities short violent filled history more often than not we have not predicated massive near apocalyptic destruction. Even with the means to do so we have shown great restraint and with the trend towards nuclear de-armament and stopping nuclear proliferation that possibility becomes far less. Secondly what the theories above don't include are the possibility of a highly advanced conglomeration of civilizations purposefully not making contact and rather waiting for a "primitive" civilization to reach the gap to being able to travel space in earnest rather than just send out probes as that would show 1. showing restraint toward self destruction 2. planetary unity to taking on such a massive undertaking. The second is important because when dealing with other civilizations this idea that we have of nation state vs nation state in negotiations and dealings are gone it would become planetary vs planetary and species vs species. Additionally in regards to detecting a highly developed civilization any such civilization would surely have moved beyond radio signals long ago.

I think, along with a couple of other posters, that A should not be so easily discounted. I don't believe that there is a universally accepted mechanism that generated life on this planet. So while the chain of evolution may seem probable (although that is also debatable) the sequence of events that started life may be so improbable that it occurs say less than 10 times in the length of the universe. I just don't think you can rule out (A) without a more finite set of probabilities for prelife at least.

Maybe we are expecting, "beacon lights". But nobody uses it anymore. Consider yourself as a 'babarian' in the modern time. In his lonely island near New York, he tries to find anyone 'outthere'. All he know about communication is beacon lights, so he fires up his torches everyday, and watch for the sign. How ever, he won't be able to find it. Cause we are using our cellphone and satelites....

Maybe for "something outthere" radio-wave is not very efficient, just like beacon lights are not. Maybe they just change some position in the some circuit, the ripple of "graviton" changes very subtly and anywhere can read the status of the circuit... or something like that. Or maybe they are all using "ansible"... you name what.

IMO, all those A) - C) cases are so "humane". And the problem is, what ever out there is, not human. not ever close to something we know of.

All three assumptions are based on the one assumption that we humans are viewing a significant part of "everything that exists in all dimensions". If what we see is only one trillionth of what is and if living is more pleasant in "some other part" of "what is", then we shouldn't expect any visitors. To make an analogy, perhaps we are at the equivalent of the north pole and other intelligence is 'relaxing on the beach in the sun'.

We are also assuming that we are sufficiently intelligent to be interesting to creatures which may be a billion times more intelligent. Since we are not interested in communicating with ants because we are a billion times more intelligent, why should creatures superior to us pay us any mind?

Proposition C seems plausible in the sense our planet will eventually run out of resources. Maybe other civilizations encounter a resource block. That would be something every civilization would encounter.

Earth as the center of the universe is just one example of thought process.

Its possible that our ability to listen for alien signal is roughly equivalent to that of a cave man cupping his ear. It could be that our technology is a primitive joke and what we think of as our great ability to detect alien transmissions is a laugh, and essentially no more effective than the cave man's approach.

Why has no one has yet brought up the idea that it is the unthinkable size of the universe that's keeping us from making contact with other civilizations?

The author brings the size of the universe up as proof that other life must, statistically speaking, exist. But he fails to bring home the point that the distances between us and and 99.999% of everything else is measured in the 1000's of light years or more.

If another civilization identical to us was in another galaxy, we would have NO IDEA they even exist! The chance of a stray radio wave traveling for hundreds of thousands of years and sweeping by this planet are slimmer than me winning the lottery.

Intelligent life is out there, but we're not going to have much luck finding it just sitting around on earth, peering out into the abyss.

We'll have to find a way to travel around the universe at a speed much faster than light in order to meet other sentient beings.

The real answer is D) Other civilizations exist or have existed, but exist a very great distance from earth and, like us, they are unable to travel at the speed required to make contact.

I can think of a couple more possibilities why we haven't seen solid evidence of extraterrestrial life:

It's possible that other civilizations have developed long-range space travel and simply haven't come here. Since the universe is huge, this seems reasonably probable.

Maybe more advanced civilizations just haven't wanted to visit us. Just because we exist, I don't see why that would mean that other civilizations would automatically want to visit us, even if the likelihood of intelligent life in the universe is small. And perhaps some civilizations have rules like Star Trek's Prime Directive which would prevent them from interfering with less advanced cultures.

And from what I've read of recent theoretical physics, here's wild thought: A different species may not perceive time the way we do, or may exist in different spacial dimensions. Theoretical physicist Michio Kaku and others speculate that there may be as many as 10 dimensions or even more, and if another species exists at least partially in some other dimensions that we don't perceive, then we wouldn't know they're there, even if they're all around us right now. With the infiniteness of the universe, species may come in infinite variety, and for all we know, another species may be vastly different from us.

On the other hand, what about the many UFO sightings and abduction stories that have been reported? I know some are hoaxes, but maybe not all of them are hoaxes. Maybe we've already seen proof that extraterrestrial beings exist and have not taken the proof seriously.

Why do people insist on making the requirements for life exactly what we have here on Earth? Of course, life on Earth couldn't exist if the planet were X degrees hotter or tilted this way or that because those are the conditions under which life here evolved.

Maybe I have read too much bad sf, but I believe it's possible that Earth is the only planet with intelligent life in this universe. There are strongly supported scientific theories that open the possibility for an infinite set of universes. Consider quantum theory at the same time, and consciousness may be the action which crystallizes a single universe into "existence" from the infinite possibilities. This really is "I think therefore I am."

I think its option B - civilizations expand in a direction undetectable to us. This is also known as "death by internet" - it's much cheaper to expand computationally into "paradise" than into the physical universe and if the laws of physics are the same everywhere.... why bother?

Or failing this, it is the anthropic principle at work saying that there are many more crappy possible universes with only one observing civilization that ones chalk full of space faring life. And we are this universe's lone observing civilization.

Geez, now I'm depressed. Let's hope it turns out to be none of the above.


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