Endnotes
Note 1: Relativity and the Cosmic Microwave Background
- Quote: There’s no grid crossing the universe, no array of cosmic streets, that would allow us to state or even define the spatial address of a galaxy, or of anything else.
- Endnote: Readers familiar with astronomy may wonder about the Cosmic Microwave Background, the diffuse leftover glow from the Big Bang at the universe’s birth. One can indeed specify one’s motion (though not location) relative to this bath of ancient light. But this bath is no more stationary than anything else, even though it is more widespread. Moreover, it would be absent from an isolated bubble, so its existence leaves Galileo’s principle intact. I’ll say more about these issues later.
- Discussion
Note 3: The Sun and the Earth
- Quote: . . . as Kepler’s precise measurements confirmed, our planet circles the Sun at 20 miles per second. This faster, steadier motion also goes unnoticed thanks to Galileo’s principle.
- Endnote: There is a common misunderstanding that Einstein, in his theory of gravity, claimed that whether the Earth orbits the Sun or the Sun orbits the Earth is just a matter of perspective. This is not so if one speaks carefully about how motion and gravity work.
- Discussion: Ah, now this is a subject that touches on all sorts of important issues about what is and isn’t real! It motivated me, back in 2022, to write a whole series of articles, which sparked a variety of interesting conversation with readers. I originally posed the question here, and ended the series by giving a clear answer in this post (with more precise details in this one). Other posts along the way dealt with potential confusions and how to avoid them: #1, #2, #3, #4.
