[lisa_henderson]

It's also important to think about the implications of articles such as "What's 96 Percent of the Universe Made Of? Astronomers Don't Know"

http://www.space.com/11642-dark-matter-dark-energy-4-percent...

If 96% of the universe consists of dark matter, we should start with the assumption that 96% of life is built of dark matter. Disproving that becomes the work of exploration, but that is the obvious default starting assumption.

[cperciva]

Dark matter is estimated at 23% of the universe, not 96%. The other 73% is dark energy.

And I'd argue that it's reasonable to presume that life would be "normal" matter, simply because life requires structure, which requires both attractive and repulsive forces over nontrivial distances. Dark matter, by definition, does not interact electromagnetically; the strong and weak nuclear forces are too short-range to give rise to meaningful structures; and gravity provides only attractive force, not repulsive force.

[jerf]

More generally, a certain amount of humility and skepticism about these issues is good, but I have almost a pet peeve sort of relationship with people who think we must profess total ignorance. We really don't. If they live in this universe, they play by the same rules we do, and that will shape them every bit as much as it does them. While I have no reason to believe that in the style of pulp sci-fi we will stroll out into the universe to find a universe of interbreedable humanoids, there's really no reason to believe that we will understand nothing about the aliens.

In fact it's sort of a violation of the general Copernican principle... we are not so special that we will be uniquely unable to understand anybody else. We are, probably, fairly normal.

[calgoo]

I had this stray thought the other day, that dark matter is really the rest of civilizations shielding and hiding themselves from us and other unevolved civilizations. That's why we cant find life in the galaxy, and once its unblocked we will see all of the 1000s of civilizations that exist.

[gizmo686]

It is possible that dark matter interacts with forces that we have not discovered.

We have been able to make some inferences about the structure of dark matter, but I believe our methods are not precise enough to detect small features.

[gizmo686]

If we had no prior knowledge, then that would be a safe assumption. However, we have the prior knowledge that we exist as life of normal matter, which biases the probabilities to normal matter being more supportive of life.