We are definitely not alone in the universe

How can you be certain?

It is very hard to make probabilistic arguments when your sample size is 1. Many researchers now believe that life as we know it is likely to exist elsewhere in the universe, but no-one in the field of astrobiology will make the unsupportable claim that it definitely does exist.

Basically, there is not enough evidence on which to base such a conclusion.

Personally, I think it highly likely that life resembling bacteria does exist elsewhere in the universe, but that is nothing more than a gut feeling, based on what we know about life and about the ubiquity of exoplanets. It is not science.

In any case, it does not at all change my conviction that we will almost certainly never make contact with other intelligent life. The distances are simply too vast, so unless intelligent life turns out to be remarkably common, we will never even make radio contact.

Both my optimism and pessimism stem from a recognition of the size of the universe. It’s just too big for me to believe we are alone. But it’s also too big to even find our nearest neighbors.

Also, if you missed SBS Big Show, you can rewatch the Tonight, What Is Right, and Cafe performances on Big Bang’s official Youtube channel.

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JT’s 4th Mini-album Big Bang VN
big bang
thoughts
I’m really impressed with this mini-album. It shows how much BB has grown in 2 years they’ve been away. I have to say, this whole mini-album was very J-Pop influenced, well considering “Hands Up” and “Somebody to Love” were originally Japanese songs.

Yes, Cafe deserves it’s own paragraph. Cafe is really an amazing song. It’s like there’s a bunch of upbeat J-Pop-ish K-pop then there’s this one chill song at the end. Just like on the “Stand Up” mini-album, all K-pop songs, then there’s “Oh My Friend.” It’s one song that completely stands out. Just like DaeSung said during SBS The Big Bang Show…

There is (IIUC) still debate about whether viruses should be counted as alive or not.

If an alien life form were to possess a radically different biochemistry from us, how would we recognise it?

Intelligence is a such a generalistic adaption that it is hard to imagine ANY environment where greater intelligence would not provide an advantage.

It is not hard. Any environment in which the nature of the selection pressures is constant will tend to develop highly successful specialists. Intelligence is most valuable to generalists in a changing environment.

And if a technological intelligence goes extinct, it leaves artifacts behind, and we don’t know what effect those artifacts will have on promoting or impeding the evolution of another technological intelligence.

One thing we do know is that our technological society has used up all of the most easily-accessible resources in developing technology from stone tools to indudstrialisation. For example, the extraction of iron ore now requires technology, as our forebears left so little of the easily-available stuff lying around.

Therefore, if our technological society becomes extinct, we have hindered the potential development of any successor technological society.

It seems reasonable to assume that a similar effect will pertain elsewhere, if technological societies have risen and gone extinct on other planets.

You’re assuming an intelligent species will never go extinct. All other species go extinct, I’m not convinced our intelligence will exempt us from that.

And if the odds are 1 in 10 quadrillion species, if you were to visit an average planet now, then the odds that all those billions of species will have an intelligent species at that moment are still quite low. You’re confusing ‘will evolve’ (which you claim is close to unity if you’re patient enough) with ‘has evolved.’

Assume a constant rate of star/planet formation, and let’s say, for the sake of argument, that the galaxy is churning out exact copies of the Earth at a constant rate. Then if we were to randomly visit one of these Earth clones the odds are going to be quite low that it is exactly the 4 billion years old it needs to be for intelligent life to be found on the surface.

even if it doesn’t take that long, cosmically, for an expansionist civilization to spread throughout the galaxy

If we conservatively assume that they use volatiles for chemical rockets (say, by electrolyzing water ices) because that is what we know is possible on a sustained basis, a migration wave random walk in roughly 2D on the galactic disk would take on the order of the age of the universe unless I am mistaken. (Random walk because, as I have argued, they would not stay in contact.)

If someone would have got started with the early star generations, and we now know metallicity isn’t a problem for making terrestrials, they would be about spread out now. Or it would take a few billion years to get started, and the coverage would be local as of yet.

@ 42:

It’s been figured that self-replicating probes could spread throughout a galaxy the size of the Milky Way in about a half-million years.

There is, as of yet, no technology for “self-replicating probes”.

Life is pretty efficient that way but it takes a lot of resources anyway – a growing cell uses ~ 10^6 times as much energy as minimum survivability. Either you have to lug around a large biosphere (as when you colonize) or use time to evolve a new one from a few cellular species (analogous to when you terraform).

So based on what best technology is capable of I would say forget it, utopian dreams have never made it to reality.