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I have to agree with the professor that it is unlikely that there is sentient life out there.

Life is rare. It's rare in the solar system. It's rare even on Earth if something like a mass ratio is used to measure it (a few parts in 10 billion).

On the extremely rare occasion that we find life it will most likely be single cell organisms.

It's possible that life once existed on Mars and Venus. Simple life seems to appear within millions of years given the right conditions.

While there are probably an incredible number of planets in the Universe, the probability for conditions and the sequence of events needed for intelligent life is incredibly small.

While there are probably an incredible number of planets in the Universe, the probability for conditions and the sequence of events needed for intelligent life is incredibly small.

One way to look at it is basic life vs intelligent life. We have had a good loo at 8 planets and their moons. Of those we have one direct hit (Earth) one near miss (Mars) and one probable (Europa). 2.5 out of 8 for doesn't seem like bad odds. But two could never develop advanced life. Life on Europa (if it exists) can't get out of the oceans. Life on Mars (if it ever existed) was snuffed out when the planet lost its atmosphere due to a lack of plate tectonics and strong magnetic field.

Besides in evolutionary terms being smart isn't much of an advantage. Ants are a much more successful animal group than hominids. All the tool using hominid species except one have gone extinct. And we came within a few individuals of going away after the Toba eruption There are thousands of species of ants. And none are even threatened despite our best efforts to wipe some of them out.

From an evolutionary standpoint hominids are a dead end. Always just one catastrophe from the big dark. Sponges, crabs, ants, termites and cockroaches. Now those are some serious success stories right there. Asteroids, ice ages, super volcanoes, nothing stops the bugs. Brains, in evolution it turns out they aren't all that necessary for success. In fact their requirement for high metabolism and lots of protein make them a definite liability.