Recent content by Cusp

Recent post on this issue: http://xxx.lanl.gov/abs/1001.4795 Interestingly (and I say so as an author), the time average of the deceleration parameter appears to be very close to zero. Through the Looking Glass: Why the "Cosmic Horizon" is not a horizon Authors: Pim van Oirschot...

F=ma does work in both SR and GR as long as you are using the 4-vector (tensorial) version.

Point taken - but the key point is that the "uniform" gravitational field has a zero Riemann tensor, just the same as uniform acceleration in Minkowski space, and the surface of the Earth is not a uniform gravitational field.

I've been looking at this issue in a little detail recently, and some aspects of the opening post are incorrect. The metric for a uniform gravitational field can be written as ds^2 = -(1+gz)^2 dt^2 + dx^2 + dy^2 + dz^2 (e.g. Principle of Equivalence, F. Rohrlich, Ann. Phys. 22, 169-191...

Thanks George - will check it out.

The Kretschmann scalar (the full contraction of the Reimann tensor K = R_abcd R^abcd) is often used to identify singularities - i.e. for a Schwarzschild black hole, K \propto 1/r^6, so we have a singularity at r=0, but not at the Schwarzschild horizon). Clearly, as r->\infinity, K->0. Is K=0...

>> I'm really starting to hate science/physics. And what is left to resort to? Absolutely nothing. I think threads like this are heralding the TRUE death of physics. Physicists are arguing over words, not concepts. The concepts don't make sense. But they are so engrossed with the...

no - you can't travel (locally) fast than light (in a vacuum)

The problem with workholes is that they are generally found by metric mechanics - you specify the spacetime structure you want and then invert to find the required energy distribution - generally finding it to be "wierd" and hence you are unsure if it's a physically valid description.

Why does there have to be a why? Things interact - all interactions occur at points so all interactions (including observations) collapse wavefunctions.

Tine is defined so that all event don't happen at once. That's all you need. I agree that most philosophy of science has no baring on science itself. From what I have seen, most of it stems from the philosophers inability to properly understand quantum mechanics.

Just like the wavefunction and the magnetic field, spacetime is a construct. You can never devise a test (within relativity) to *prove* its existence. If you ant to think this implies existence, then be prepared for it to vanish in a future model of the universe.

This is not a "scatter-shot" of citations, but part of a recent set of ongoing discussions on the nature of spacetime. As noted in these paper, in relativity spacetime is not a thing - it's a mathematical construct

In 1939, Einstein wrote that black holes cannot exist (Einstein, A. 1939, AnMat, 40, 922) and in 1936 said that there can be no gravitational waves (http://www.physicstoday.org/vol-58/iss-9/p43.html ). Appealing to authority is not the way to have a discussion. As for the nature of spacetime...

No - empty space is not a something in relativity.