Hi all, Suppose we have a closed quantum mechanical system which evolves (in the Heisenberg picture) such that all the required canonical commutation relations (e.g.,...

Birkhoff's theorem says that any vacuum solution of Einstein's equations must be static, and asymptotically flat. One of the consequences of Birkhoff's theorem is that the...

How would you answer this: What good are the Maurer-Cartan equations for a Lie group (other than just sitting there being true)?

18-JUN-2006 In the context of a Lornetz boost in the x,x' dimension, and in dimensionless terms where the velocity of light is given as c = 1, I've found for parameter 0 v...

A future gun physics question. Simply stated, what is the maximum practical speed of a bullet in air at (roughly) sea level? Ignore the acceleration mechanism. I assume...

I wrote: One way to see why the products of some rotations will be boosts is as follows. Suppose that for a pair of linearly independent vectors u and v in R^3 we...

John Baez wrote: So one thing you're saying is that a product of rotations in two different rest frames can be a boost?? One way to see why the products of some...

Hi: Has the use of x-rays for telecommuncations ever been considered? I imagine that x-ray photons would have more bandwidth than visible-spectrum photons. Other than...

About 30 years ago, terrestrial GW detectors were only sensitive enough to observe "hammer blow" radiation of indeterminate origin. I would like to know; have modern...

hi all, I am an adjunct instructor at St. John's reading my texts again in hopes of pasing a qualifier so I may continue to persue a PhD in Quantum Gravity. I started about...

Folks - This is my first post. My name is Ty Drago, and I'm a published novelist. I have a new hard SF novel in the works that deals with quantum physics in what I...

Also available at http://math.ucr.edu/home/baez/week232.html May 18, 2006 This Week's Finds in Mathematical Physics (Week 232) John Baez I'm at the Perimeter Institute now....

With any luck, sometime soon you can read this paper on the arXiv: Aristide Baratin and Laurent Freidel Hidden quantum gravity in 4d Feynman diagrams: emergence of spin...

I've been thinking about a cool model concerning quantum gravity, by assuming two elementary particles can get quantum gravitational entangled, after they have exchanged two...

The following (probably) dumb question has recently occurred to me: Is the velocity of light in water a) constant b) dependent on the velocity of the water relative to the...

John Baez and others have discussed on this newsgroup the fact that Einstein's equation can be nicely encapsulated in the relationship between the second time derivative of...

Hi, The question is as the title : When water is supercooled it can suddenly transition between the water and ice phases. Presumeably this phase change propogates as a...

I previously described some numerical calculations of the total group-valued momentum of N particles of equal rest mass and speed, and a uniform angular distribution of...

John Baez wrote: In article , Greg Egan wrote: So, are the geodesics through B and B' being made to diverge? ...

My son was boiling 6 eggs, and we noticed that the eggs formed a kind of close packing, but pentagonal, instead of hexagonal. Very vaguely, a bit like this: ...