First summary

In the last post, I finally finished the first "thread" about galaxy rotation curves. My dad (who apparently also reads this blog, although not as consistently as my mom) wasn't quite sure how everything tied together (I believe he missed some entries in the middle). So to briefly recap: I started by explaining the Doppler effect, which was then followed by a series of posts on the wave/particle nature of light. I then discussed the Bohr model of the atom, because it provides a nice framework for understanding the emission of light by atoms. Combining all those posts, we can now understand how to measure the speed of rotation of a galaxy - hydrogen in stars emits light at known wavelengths/frequencies which are then shifted by the Doppler effect. Knowing the math behind the Doppler effect, we can determine how fast the galaxy is rotating. Next, we talked about Newtonian gravity, which led to a prediction for what we expect the rotation of galaxies to look like. In the last post, I described what we actually see, providing evidence for dark matter.

This is the goal of this blog - to try and describe all the pieces that go into a physics argument in a way that's understandable. My hope is that interested readers will see that while specific parts of physics may be esoteric or complicated (i.e. high level math), in a general sense we're making deductions in a way that is very similar to those made in almost any other field of study.