29 Comments

@Robin: The following link is a good one. Jason Wright at Penn State has written a paper on detecting Kardashev Type 3 Civs and has potential candidate galaxies where they might be found with potential evidence(!). Here is the original paper http://iopscience.iop.org/0...

and here is the new scientist article http://www.newscientist.com...

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Wouldn't it turn itself into paperclips, at the end?

If we ever find the paperclip planet...attempt no landing there.

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Supernova's aren't evenly distributed. You need to work out the proportion of potentially habitable worlds which do get zapped.

*Hint* Many will survive

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I know you're not a big believer in it, but foom lowers this bar substantially. In many foom scenarios, the entity that undergoes foom may end up controlling most or all of the subsequent civilization's resources, in effect reducing each civilization from a vast number of members to a single individual.

There may also be effects that cause end-state superintelligences to be quite similar to each other. For instance, if there is a single optimal architectural design for intelligence given the physics of our universe, every self-improving superintelligence will, presumably, eventually end up with that architecture.

In other words, instead of diversity both within and between civilizations, it's plausible that there may be neither.

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I didn't mean to imply we could now see a star-sized Dyson sphere five billion light years away.

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Good discussion! One quibble:From http://www.centauri-dreams....

"a Dyson Sphere, which is supposed to be several thousand times wider than a super-jupiter, would be detectable at 10000 – 20000 light-years as far as energy conservation isn’t broken and the energy output of the central star, after having been used by a type II civilisation, is re-emitted in thermal infrared. "

so we can rule out Dyson spheres from part of our galaxy, perhaps 10^8 stars or so - not from the whole 10^20 stars in the whole visible universe.

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Agreed: there is no way to know short of a time machine. I'm recalling a half baked memory from a textbook "Gene?" I read about ten years ago on Genetics 101 about Eukaryotes and Prokaryotes and which came first. There are arguments in both directions but with the biggest camp favoring a Prokaryotes came first and it was hard to go from Prokaryotes to Eukaryotes.

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"Point I was trying to make is that prokaryote -> eukaryote is significantly more difficult thant eukaryote-> multicellular eukaryote."

I agree, I just didn't agree we have enough evidence to point to prokaryote -> eukaryote being a great filter. A single line could be the result of a fusion of existing eukaryote lines before the first multicellular organisms existed.

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Agreed. It looks fairly straightforward for multicellular life to develop - it happened repeatedly and continues to happen today. The latest evidence is that the geology of the earth itself actively worked to remove oxygen form the atmosphere even after photosynthesis started so there was a see saw effect on the levels of oxygen. Maybe that's one of the great filters right there.

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Agreed, we don't. At the same time, however, there is one one lineage left in the remaining Eukaryotes whereas there are multiple derived lineages of multicellular organisms. We can even see yeast going from unicellular to multicellular almost in real time. Point I was trying to make is that prokaryote -> eukaryote is significantly more difficult thant eukaryote-> multicellular eukaryote.

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How would we know if eukaryotes only evolved once? They don't leave fossils with enough detail so for all we know there was competition between multiple kinds a billion years ago, it's even possible it wasn't so much competition as fusion: single celled organisms can exchange DNA with each other and receive DNA from viruses.

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Actually the blind watchmaker has independently evolved multicellular life at least 40 times. And it's still going on. The hard part is going from Prokyarotes to Eukyarotes. That only happened once. Every single Eukyarote there is today is a descendant of that original organism.

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To be precise: it's mostly about not detecting signs of extraterrestrial technology. We now barely have the ability to detect an ocean on nearby exoplanets so there may be a large number of planets with life on them in our galaxy that we simply have not discovered and/or examined at a level where signs of life on the planet can be detected. So the question really becomes why haven't we detected radio or laser signals, an abundance of terraformed planets or even alien spacecraft (or why hasn't Earth been taken over by replicating machines long ago). I think that last point has been addressed by Robin before (Earth might be an oasis in a desert-like patch of the galaxy that alien civilizations don't bother to exploit). Of course we don't know how hard it is to terraform a planet so perhaps even with their best efforts aliens have not really multiplied the number of life-bearing planets by a large number, or, if we are an oasis, they have not done so in close proximity to Earth which means our current technology simply won't detect planets. When it comes to the lack of signals: this may just indicate a lack of deliberate communication, if the nearest advanced planet is 200 lightyears away (a mere fraction of the galaxy's radius) it will be very hard to detect any signal that is not deliberately amplified in our direction (from our own experience here on Earth we also know that long range radiotraffic can decrease with increasing technological advancement). There could of course be lots of cultural and strategic reasons as well.

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It's not that all multicellular life is very complex (there are multicellular lifeforms that are basically only 4 kinds of different cells patched together only slightly more secure than colonies of cooperating single cell lifeforms), but on Earth the concentration of oxygen was very low until the cambrian explosion and this is most likely what kept multicellular life from thriving before then.

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To make a substantial contribution, it is not enough that some advanced folks get bored. It requires that most entire civilizations don't have *any members who aren't too bored to expand. That is a very high bar.

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I'm not sure the "Earth had life on it almost right away" story is that interesting. A more interesting data point is how long it took very simple life to become multicellular. About 3.5-Billion years? Clearly *that step* wasn't simple, even if basic life was. Three billion years is long enough that maybe most planets aren't stable that long and we truly are special. The Cambrian Explosion is probably the Great Filter in the past that I'm most optimistic about. My top five potential great filters, in no order:

1) Multicellular life is hard.2) The Universe is still very young. We are among the first technological civilizations.3) Our ancestors or nearby cohort civilizations were among the first and we are a simulation.4) AIs dominate the future and even relatively small super-AIs learn all there is to know surprisingly quickly and universally and quickly look inward.5) It's difficult to imagine a technological catastrophe that would wipe us out completely and do it to most civilizations. The timing is too hard. It has to happen consistently before almost all civilizations colonize other planets but we, who are getting close, haven't sniffed it yet? Instead, positive effective extinction. Within 1000 years or so, civilizations transcend in some way.

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