Call Went to Voicemail

This week's episode of Big Picture Science is titled Calling All Aliens, which is naturally enough, about recent SETI and METI efforts.  By chance, I was asked by a friend earlier this week about my opinion on the general topic.  The three thoughts I had on the matter were:

1. 
   Imagine our galaxy as a pizza – a really big pizza – one meter across and one centimeter thick.  Now imagine a bubble of space radiating out from Earth in this pizza-galaxy.  A bubble big enough for our first powerful radio signals to have reached another civilization, and for them to have sent a reply back.  At the one meter pizza scale, that bubble would be about the size of a sesame seed.  Would we really expect to have reached anyone in such a small sample?
2. More quantitatively, take a current credible guesstimate at Drake's Number – about 86,400 contactable civilizations in our galaxy.  Seems a little high in comparison with numbers I've previously seen, but let's roll with it.  Given the speed of light, expect about a 50-50 chance of that bubble in Item 1 to encompass another civilization in about 330 years.  What's more, these Drake Equation results are all over the place, and numbers as low as 100 are reasonable.  That puts the expected time to a 50-50 chance of contact out around 3200 years.  Frankly,* it's just too soon to reasonably expect any return replies.
3. However, we should still keep listening, especially given the continuing and amazing increases in signal processing power.  Don't let those two-way contact numbers in the previous item discourage you.  Unlikely as it seems, a random alien signal could come crashing in any given day – and we'd best be listening.
4. Finally, if aliens ever do find us, they'll probably view us about the same way we view the Sentinelese (see inset picture): present, but violent and not worth contacting.  Best left alone.

On that note, time for a bike ride.  Anyway, the above-linked podcast is well worth an hour's listen, and one of the more noteworthy recent episodes  at Big Picture Science.

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*10 Internet Points if you caught that one.