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> Let's say the origin of life is a million to one filter, and the successful development of sentience is another million to one filter. Those are actually pretty high odds for those two events, and the combination of those two togehter is enough to make it likely we're alone in the Milky Way.

I mean, not really? Doesn't the Milky Way have ~100 billion stars?

(million: 1)^2 * 100 billion gives an estimate of ~0.1 stars in the Milky Way that host life.

Indeed. But then developed it hitch hikes a ride on asteroids and spreads virally. See Dr Zubrin’s recent discussions https://www.centauri-dreams.org/2017/12/21/interstellar-comm...

> Since most of the star's energy is emitted in the infrared ... does this limit the potential of photosynthetic organisms ... ?

I'm not any sort of biologist or chemist, so somebody please correct me if I'm wrong, but...

If you specifically meant photosynthesis by terran chlorophyll, then yes, I suppose it would be less effective. However, I could imagine photosynthetic life to evolve under those conditions that uses some other compound to capture and convert the energy.

Also to consider is the amount of radiation (light, etc.) available on the surface, which can be figured as a formula of the radiation emitted by the sun, distance from the sun to the planet, and attenuation of radiation by the atmosphere. Much of the light (and other energy) emitted by a sun does not reach the surface of a planet with an atmosphere. The particulars are, of course, dependent on the atmospheric composition, but generally I would expect infrared light, with longer wavelengths than visible light, to better penetrate the atmosphere and be more available to life on the surface.

>Let's say the origin of life is a million to one filter, and the successful development of sentience is another million to one filter. Those are actually pretty high odds for those two events, and the combination of those two togehter is enough to make it likely we're alone in the Milky Way.

The Drake equation has 7 terms. When it was first proposed, all but the first were complete unknowns. We're just barely starting to gather enough data to start tightening our guesses for the next two. The rest (which include the two you used) are complete unknowns. You say "those are actually pretty high odds", but by whose measure? There's exactly one data point to support that assertion, and right now that data point suggests that the odds are 100% (with an uncertainty also approaching 100%). We're still decades away from really having the data to assert anything at all about the presence of life outside of our solar system with confidence.

We should be able to make some approximations regarding sentience. If we only consider Homo Sapiens Sapiens, then yeah we only have one data point. If we consider other extinct hominid species, we have more. If we consider dolphins, ravens, etc - we start to have a fuller picture and can make some (at least slightly) informed estimates to that term

You're still extrapolating from a single life-creation event. Until we find a second planet that evolved life entirely separately from Earth, we have exactly zero meaningful information about the genesis of life. Without knowing what percentage of life is roughly similar to life on Earth, we have exactly zero meaningful information about how valid Earth-centric extrapolations are.