There Have Probably Been Aliens

The probability that God exists depends entirely on your priors. After all we have no observable evidence to consider. I would give it a very low prior, because it's such a weirdly specific belief, considering all the possible origins of the universe.

The probability we are in a simulation depends on a bunch of assumptions. Assuming specifically we are asking about a "historical simulation", that the parent universe is identical to ours, we can change the question. Instead ask what is the probability we will someday create historical simulations of our past.

Technology certainly seems to advance over time, and the upper limits on computational power are extremely generous. So it's possible we could someday have the technology to do it. Assuming that, then it just depends on the probability you think we will want to make simulated beings. Something about that seems kind of sick and immoral, so I am skeptical of that assumption.

But if it is true, then the probability you are in a simulation is extremely high. Because the number of simulated beings could easily be orders of magnitude higher than the number of actual 2016 Earth inhabitants. Provided that many different simulations are run.

>To assume that a collection of beings which have obtained the ability to travel amongst the stars would focus their attention on a single species on a single planet is fundamentally selfish.

The "focus their attention" implies some total devotion. They could just study us or just come visit for the experience.

Like we "focus our attention" to thousands of wild life, with documentaries and shelters and various research, despite having obtaining the ability to travel among the continents (and even to the moon) and being much smarter than them.

Second, who said they have "obtained the ability to travel amongst the stars" in the first place? If they exist, they could be just like us, or even like us back in ancient times. And in that case, one would imagine they'd totally "care" for us, if they only could find us (like we care as to whether others exist or not).

>Science requires a theory and experimental validation.

You'd be surprised. That's 19th century thinking about science, and not really how science works in practice most of the time.

The universe is so big, that I think it's very likely that somewhere out there are, there are many other intelligent civilisations, in distant galaxies–but so far away we'll never be able to visit them, never be able to communicate with them, we'll likely never even know of their existence (not in a million years–and I mean that literally.)

In the long-run (of millions of years), the two most likely outcomes for humanity are extinction or galactic colonisation. If we do colonise the galaxy, we'll prevent any other intelligent species from evolving within it (by fully occupying that ecological niche.) If we go extinct, we'll leave that niche open for another species to maybe one day occupy as we would have failed to do. The galaxy is likely a natural hard limit for our species, since while interstellar travel is difficult it is arguably possible (not with present day technology and economics, but potentially within a few centuries from now), but intergalactic travel is likely never going to be possible.

Even if these authors are right that other intelligent life once existed in this galaxy, it's almost surely extinct by now. If that's true, it makes their conclusion profoundly pessimistic – the more ruins of dead civilisations this galaxy contains, the greater the likelihood that we'll meet the same fate as they did.

I think we'll always be alone in the universe. And it's probably better that way.