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Here's a video I made a while back that tries to explain "The Great Filter".  I'm still not totally happy with it and will probably do another one, but it's good background for what I talk about briefly in this week's SFN.

Let me know what you think!
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Nice explanation of the Great Filter.
I am now subscribed, and eagerly awaiting your next masterpiece +Tony Darnell  ; - ) Thank you for sharing this again. It not only was a fantastic listen, but a good view as well on my Big screen HDTV.

  I feel we must be quickly closing in on our next filter possibility (meteor impact not withstanding). Population growth will eventually create another possible barrier. 
Good video.  I'd suggest this the on the GF: Either it occurs before a civilization hypothesizes a 'great filter', or after.  If before, then we've passed it.  If after, then knowing about it does not prevent it, and we're still going to be filtered.
I suppose we have to bear in mind that we're only here because of a series of mass extinction events which eventually enabled mammals to evolve beyond rather small and insignificant creatures. In fact, we very nearly went extinct ourselves ~75,000 years ago. Life seems to be pretty resilient once it gets started but there may only be a slim chance of intelligent life evolving and a similarly slim chance of intelligent life continuing for a long period of time. Sooner or later another cataclysmic event will befall this planet and we could easily be wiped out... Sorry for being pessimistic but you only have to look back in history to see that it's inevitable that apocalyptic catastrophes happen on earth, at least, every now and again. Maybe there are other planets that are more stable but it seems that instability is a driver of evolution. 
Love the video! I really like your thought-provoking style. The "most important photo ever taken" video of yours still haunts me (in a good way) to this day. 
Tony, just to clarify, because you don't seem to have drawn attention to this limitation elsewhere: The reason that we will never intercept signals SETI-style from alien worlds, even accepting the assumption that life is everywhere (which I do), is that the investment required to send a signal is prohibitively humungous, with no profitable return. Time scales, risks associated with regime changes, distances for profitable exploitation, etc. Quite simply, it will never happen. We need to think in terms of business, investments and returns. Pumping out a costly broadcast of the scale of the 3-minute Arecebo broadcast in 1974, with the intention of receiving a reply in 50,000 years (globular cluster M13 is 25,000 light years away), is not a sensible, realistic investment. Maybe there's another technology waiting to be discovered, but it ain't going to happen with what we have now. We wait in vain to receive a signal (SETI) in the misguided belief that another alien culture will invest what we never will. Just sayin'   :)
I guess my thinking on this is that if life is ubiquitous, then there must be at least some instances that have reached a pretty advanced level - advanced enough to make it outside their solar system or, even if they didn't, had been around long enough for their natural signals to have propagated in our direction for detection.

Using Earth as an example, in 100,000 years our first signals would have made it to the other side of the galaxy so we don't need to make special transmissions.

So, civilizations don't need to make a huge investment, we should be able to detect they natural footprints (signals) if they've been around long enough.

The galaxy has certainly been around long enough to allow civilizations to fill the galaxy with extraneous signals, where are they?
Maybe they're simply not there! It's easy to be seduced by the numbers but I don't think one can assume there's lots of intelligent life out there simply because there are a large number of suitable stars maybe with suitable planets. The dinosaurs were around for a long time (~160m years) and it's only chance events that resulted in their extinction allowing the rise of the mammals and eventually to us.Of course, it's always nice to think there could be comparable civilisations somewhere in our galaxy - so long as they're friendly, lol 
To prove my case that alien contact is extremely unlikely, I did a google search on 3 terms - SETI signal strength - Here's what I found:
1) This post by Mag6inMinnesota says almost word-for-word what I was trying to say:
2) As per above link (and a couple of arbitrary opinions stumbled across in my google search), a reasonable guesstimate for the maximum distance at which our planet's random radio chatter (tv, radio, etc) would be picked up by an equivalent SETI program on another planet is about 20 light-years. What this means is that for distances longer than that, the transmissions would need to be deliberate and directed, and this raises the point in my previous post... such a directed effort, implemented with serious intent, would be prohibitively expensive with negligible return. It would not be a sound investment decision regardless of the alien civilization implementing it.
3) The following site goes into more depressing specifics:
Bottom line? Quite simply, contact with aliens will never ever happen... unless an alternative technology can be found, probably something implementing the principles of nonlocality.
I will show that link to the spaceship, hovering over my cornfield. As is phase shifts in & out of sight. 
+Tony Darnell Our natural signals at great distances would become extremely weak.  The same would naturally happen to any other civilization.  Assuming they were even sending signals, the way in which we normally transmit information is in packets that the receiving end pieces back together (to counter-act any possible interference).  Any noise could wind up looking like random background noise if it's weak and seems random to us.

There's also a possibility that even if there are other developing civilizations, we could be the first or most advanced  (although, that ruins all my sci-fi kinda fantasies about finding intelligent life LOL).  Someone ALWAYS has to be first at something.  It took evolution a VERY long time in order to get to us, the very first species on our planet to develop to this level.  Even then, our simplest radio technology isn't even all that old, in comparison to that time that it took us to develop.  We have a tendency to think of aliens as being some supra-genius, technological species from some utopian society from the future, but in fact, they may be just as slow or slower to develop than us, even if they have the same capabilities as us.  (and to tell the truth, the amount of time human beings have been around compared to many species, and the leaps and bounds we have made in technological achievements in that very short time, have been at an extremely fast pace, on an evolutionary timescale) shrugs
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