PlaidBastard t1_ixhxlal wrote on November 23, 2022 at 4:02 PM

Reply to comment by mfb- in Does dark matter have an influence on the earth orbit ? by CrDe

Woops, you were right about that velocity, but I don't think you not understanding my analogy for Newtonian gravitation really has anything to do with OP's question, either. You're absolutely right that dark matter isn't in clumps, but to detect it at all ever, it has to be less homogeneous than, say, the cosmic microwave background. I made the analogy to show how little distant, diffuse masses affect orbits.

Aseyhe t1_ixih6fa wrote on November 23, 2022 at 6:10 PM

> to detect it at all ever, it has to be less homogeneous than, say, the cosmic microwave background

That's not accurate: a uniform distribution exerts a nontrivial gravitational effect (and indeed this is something Newton got wrong, although with careful treatment, Newtonian gravity correctly predicts it).

PlaidBastard t1_iximnuc wrote on November 23, 2022 at 6:46 PM

Pardon the barely detectable difference in gravitational acceleration out of me. What is your problem?

Are you familiar with the hydraulic analogy in E&M? And how it's not perfect for all behavior in actual electrical circuits?

My analogy isn't perfect for the effect of many randomly dispersed tiny point masses (certainly <kg, we have to agree?) on the orbits of planets (10^20-25 kg?) around stars, but I get the intense impression that you're actively refusing to see how it might be useful in someone trying to understand undergrad-level astrophysics in spite of it not being a perfect analogous model for the nature and distribution of dark matter in and around our galaxy.

Yeesh.