Walter
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 Oct 8 comment Could there be dark matter black holes? @questionhang As I've said 'since DM cannot lose its excess energy and angular momentum as easily as gas'. It can only lose it via gravitational interactions (with anything), but that is very inefficient. Oct 6 comment What will happen to life on Earth when the Andromeda and Milky Way galaxies collide? I was not asking for a comment, but for improvement to your answer, and I was not asking because I doubted it, but to give you a chance to improve your answer (though I was a bit surprised at the time scale of only 1Gyr). Oct 5 comment What will happen to life on Earth when the Andromeda and Milky Way galaxies collide? The only remotely sensible answer here. Oct 5 comment What will happen to life on Earth when the Andromeda and Milky Way galaxies collide? You should provide evidence (via links to respectable sources) for your claims that in 1-2 billion years water on Earth will be evaporated. Oct 5 comment What will happen to life on Earth when the Andromeda and Milky Way galaxies collide? Why do you assume that any humans or even any observing life forms will be around on Earth in 4billion years? Oct 5 comment When will all eight planets in our solar system align? Ignoring [...] interference from any bodies [...] interfering with their orbits -- this obviously includes the Sun, and without the Sun, the planets orbits are not well defined. Hence your question is unclear. Oct 5 answered When will all eight planets in our solar system align? Oct 5 comment When will all eight planets in our solar system align? There are several blunders in this answer. First, using all digits in your tables (which implies converting to centidgrees and centidays) I actually get $x\approx1.698\times10^{42}$ (from the same online tool), which amounts to $1.29\times10^{33}$yr. I don't know how you obtained the lower value, but I strongly suspect you omited some digits. Secondly this shows that when adding more digits the solution tends to infinity: the correct answer is: radial alignment never occurs. Finally, assuming that the planets' orbits are following this simple motion is just wrong. Oct 5 comment When will all eight planets in our solar system align? Never even if they were co-planar. Oct 5 revised How special is the Solar system compared with other planetary systems? edited title Oct 1 comment Could there be dark matter black holes? @questionhang As I've said a 'small fraction of matter accreted into the supermassive BHs (SMBHs) at galactic centres was likely dark', I'd be surprised if its much more than 1%, likely much less. Sep 30 comment Why is the Solar Helical (Vortex) model wrong? Nowhere was the (a) definition of vortex used/provided. Sep 30 answered What would happen if we stepped on the Sun? Sep 30 comment Could there be dark matter black holes? The term dark-matter black holes makes little sense, see also my answer. Sep 30 answered Could there be dark matter black holes? Sep 14 comment Is it just coincidence that the Moon follows the ecliptic? I don't think that tides with the Sun will necessarily bring an inclined moon into the ecliptic. Do you have any reference/evidence for this? Sep 14 revised Is it just coincidence that the Moon follows the ecliptic? deleted 6 characters in body Sep 14 comment Is it just coincidence that the Moon follows the ecliptic? @LocalFluff No, only the total angular momentum is conserved, i.e. the inclination of the combined Moon-Earth system is about the same as that of the (mass-weighted) mean inclination of the pre-Earth and Theia. But the orientation of the resulting Moon-Earth orbit is not contrained by angular momentum conservation (the angular momentum in the relative orbit is tiny compared to the orbit of the Earth-Moon system around the Sun). Sep 14 answered Is it just coincidence that the Moon follows the ecliptic? Sep 14 comment Could we estimate the age of the universe based on the planar property of the Solar System? The Solar system formed well after the BB, but, of course, its age (which we can meaure from isotope ratios) is a lower limit for the age of the universe, though not a very useful one.