No opportunity to arise in an empty galaxy at the present cosmic time, t=13.8Gyr. If the appearance rate of expansionistic civs is too high, every galaxy is already packed.

Self-indication says we should re-weight probabilities according to the relative number of observers who have anthropic information like ours (arising in an empty galaxy at t=13.8Gyr).

So, self-indication rules out super-low appearance rates (it wants more life), but also rules out super-high appearance rates (since that would imply dramatically fewer empty corners of the universe at the present cosmic time).

Thus, it squeezes our uncertainty about the appearance rate into a just few orders of magnitude.

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I definitely see a net benefit from the POV of credibility.

As I see it, we have a subject that is one of the few remaining "really, really big questions" on the basic nature of the universe, but which has been avoided by a lot of science, due to the impossible-to-navigate proliferation of wild "what if" scenarios. That can create a massive, self-reinforcing problem for credibility.

But, then you get two independent lines of research that find a way to simplify the picture on a very large scale. They use different analytical methods, but the same basic postulates are returning a big set of nearly-identical conclusions.

That's got to be worth something.

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Normally, this modeling is set up to take advantage of the large-scale homogeneity of the universe -- this scale appears at just above the size of superclusters and voids. That's where the geometry gets really simple.

Within a single galaxy, they would have to appear at *exactly* the same time for one not to have an enormous first-mover advantage over the other. And if they did, it may be that small, otherwise-minor differences (in tech used, in location within the galaxy, etc) would also have huge effects on the competitive grab for resources.

But from the outside, from across a cosmological distance and time, this scenario would look just like a single expanding civilization. Geometrically the same as if two or three competing nations initiated aggressive expansion from the same planet, on the same day.

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It almost sounds as though you think there were some benefits to your analyses having been independent. Is that the case, and if so, do you think there was *net* benefit?

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Is it possible to use your model to the situation when several civilizations appear almost simultaneously in a one galaxy because of panspermia and all other galaxies are empty? They will start colonisation waves in that galaxy which will collide relatively soon.

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Olson and we both explicitly calculate angles and agree that we find aliens appear as large disks. Yes you could assume that no planets longer-lived than Earth can be habitable, but that's a pretty extreme assumptions w.r.t. the literature.

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I have a beginner's question.

OK, how far could commercial or military radio signals carry?

That is, if there were an advanced civilization, say, 200 light-years from earth, but which never targeted earth for communications, would we be able to pick up their signals? That is, we could Intercept their "ordinary" radio traffic.

How about 500 light years?

I am assuming, rightly or wrongly, that nothing can exceed the speed of light.

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Via email.

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Where did Olson make those comments you end this post with?

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