Sean Carroll of Cosmic Variance made his way to Pittsburgh on Friday. Sean and I managed to solve the problems of the Universe over lunch (more or less), before his…
Soul Physics Meets Cosmic Variance
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How Time Really Passes
We all experience the passage of time. This is not an illusion. We agree on the serial delivery of moments, and it is very hard to dislocate us from this…
Get Started Playing Ehrenfeucht-Fraisse Games
Ehrenfeucht-Fraisse games are a very useful method in logic, when you’re trying to figure out if two models are elementarily (logically) equivalent or not. This may be of special interest…
Another Unexpectedly Simple Failure of Determinism
Here’s a simple Newtonian system that fails to determine a unique Cauchy evolution, in the spirit of Norton’s dome. In the system I will describe, one begins with a mass…
Why does matter follow geodesics?
In the very first lessons on General Relativity, we learn that free particles follow geodesics — the equivalent of straight lines in curved spacetimes. Why? Well, it’s easy to show…