[kaj_sotala]

My summary of the link:

Possible solution to the Fermi paradox: there is no paradox. The normal approaches find that there should be a very large number of civilizations by plugging point estimates into the Drake Equation, but multiplying point estimates (as opposed to probability distributions) with each other gives you misleading results.

As a toy example, if you multiply nine factors together to get a probability of life per star, each of the factors a random real number drawn uniformly from [0, 0.2] and the point estimate for each being 0.1, then the product of the point estimates is 1 in a billion. This would translate to an expected 100 life-bearing stars, given 100 billion stars. But if you instead combine the probability distributions, you get a median number of 8.7 life-bearing stars (the mean is still 100).

Going through the literature to estimate reasonable prior distributions for different values in the Drake Equation, you get much more pessimistic estimates for the probability of life in the universe; the priors chosen by the authors suggest a 40% a priori chance for life only emerging once. We really might just be alone.

[svachalek]

Thanks for the summary - the slides were a little hard to follow.

In a universe that's practically if not actually infinite in size, it seems to me that no species is ever big or strong enough to be safe from a bigger, stronger one. And thus any rational species interested in self-preservation (I hope this includes us) simply MUST hide. Forever. We're not very quiet but we're also extremely harmless at a galactic scale so I imagine if I were an alien species that noticed us, I'd just leave us alone as bait to reveal any less cautious species.

Following that line of thought, I'd be much happier to believe we're simply alone. :-)

[Retric]

Assuming the speed of light is absolute the odds of finding a civilization is vastly diminished. EX: Assume they are 1/2 the age of the universe and expand at the speed of light. From the 46.5 billion light-year radius observable sphere due to expansion. They have a bubble ~1/4 the size of the observable universe in size (less time for expansion of space/time). But, that's only ~(1/4)^3 = ~1/64th chance we see this super civilization even with such optimistic estimates.

Start plugging in more reasonable numbers for expansion say a smaller chunk of c and reasonable assumptions of requiring old rocky planets etc, and there could be 10^10th such civilizations and we just can't see them.

[lisper]

The slides become a lot easier to follow if you start with the actual definition of the mathematical terms in the Drake equation:

https://en.wikipedia.org/wiki/Drake_equation#Equation

This information really should have been in the first slide.

[sillysaurus3]

Another explanation, possibly unrelated to the slides:

It's hubris to (a) know the universe is probably infinite and (b) assume that life evolved anywhere within our slice of it.

Infinite! The universe seems to be infinite. If that's true, it seems just as likely that all intelligent life in the universe is completely alone.

[smilliken]

Consensus in physics is that the universe is finite[1]. Even if it weren't finite, it's likely still a moot question because the speed of light will inhibit us from every seeing outside a finite radius.

[1] https://en.m.wikipedia.org/wiki/Observable_universe

[sillysaurus3]

That's likely our observable portion of the infinite universe. It doesn't mean the universe is finite.

[oceanswave]

If your definition of infinite is also includes that the portion of the universe that actually has energy in it is 1/∞ then sure