PeterDonis's latest activity

In QFT (Quantum Field Theory) photons are described by the quantized EM field. Or, perhaps it's better to say that the Quantum Field...

Simply changing the "zero" of time changes nothing about physics. You can, however, do mathematical modelling, which I would describe...

@Julian_M YouTube videos are not valid references here. The paper you have cited does not support any of the claims you are making, and...

If there's energy present, it isn't the true vacuum state.

The number of independent components of the Riemann tensor in a general curved spacetime is 20. In spacetimes with symmetries, the...

Actually including the spin-up or spin-down would cost an enormous amount. Fluid dynamics are messy, especially when you have to include...

There is no such thing; it's not a well-defined concept. It's only well-defined between observers that can exchange round-trip light...

The spatial geometry changes with time, yes, but that doesn't produce any time dilation between one point in space and another, because...

That's because the spatial geometry of the universe (including the Einstein static universe) is homogeneous--it's the same everywhere...

Yes, it has ##a(t)## constant in FLRW coordinates. The difference is that the spatial part is a hypersphere, i.e., positive curvature...

Of course you can look at it either way. Another statement is that Minkowski spacetime is the analytic continuation of the geodesically...

I see what you're saying. I'm just not sure it's a slam dunk that the two cases you describe must count as "putting a different metric"...

Technically, yes, I suppose this is true. But this formulation lacks a key property of all other FLRW metrics: it's impossible to take a...

Invention is a process, not an event. There is no instant of time when an invention "comes into existence". You are trying to draw sharp...

In the sense that humans formed the concept and explicitly recognized its properties, sure. But at least one of those properties--the...