IM Egdall

More detail on accelerator experiments and testing length contraction: "a spherical bunch of particles coming at you looks like a flattened ellipsoid due to relativistic shortening, and the detection probabilities and expected directions of ejecta are affected." Physicists must take this into account in their experiments. REF: SelfAdjoint Mar 9, 2004 07:08 PM. See My link Also "coulomb attraction between a stationary electron and a stationary proton are judged to increase when viewed from an inertial frame that moves in the direction of separation" (Ref: Relativity: Special, General, and Cosmological, Oxford University Press, 2001).

I think it goes like this. One of the virtual pair particles has to be negative energy so the resultant collision doesn't produce energy. This is invoked in Hawking radiation: a particle, antiparticle pair appears out of the vacuum at the edge of a black hole event horizon. The negative energy virtual particle falls into a black hole, but the positive energy particle escapes.

I don't think gravity has anything to do with non-locality, per se. This action at a distance of gravity is an issue with Newton's theory of gravity. But Einstein resolved it in his theory of general relativity. The Sun, for example. causes space and time (spacetime) outside the Sun to curve (warp or change). The key is this so-called curvature of spacetime has energy. And this energy in turn curves spacetime a little further out. And so on, so that spacetime curvature spreads out from one local region to another till it reaches the Earth. This now diluted spacetime curvature holds the Earth in its orbit about the Sun. So Einstein's general relativity says gravity is spacetime curvature and is not action at a distance. (REF: John Archibald Wheeler, A Journey into Gravity and Spacetime, p. 12)

Ya, good point. It occurred to me as I read this that two colliding photons can (and do) produce matter particles if their energy is high enough. So, as you point out, the charge and half-integer spin are much better arguments.

Assume a single electron (or any particle) passes through a double-slit. Per quantum field theory, the electron's wave function travels through both slits. The results is the electron is detected in one location at the detector screen. But over time with a number of electrons passing through the apparatus one at as time, you get an interference pattern at the detector screen. So here is my question: Per general relativity, the electron (or any other particle) is a source of spacetime curvature (gravity). So could a sensitive-enough gravity detector placed near one slit tell in principle which slit the electron went through? Or maybe a better question is: Is a particle's wave function a source of spacetime curvature?

And here is another thing that comes to mind. Photons have no mass. Matter particles (electrons, neutrinos, quarks) do have mass. So how can particles which have no mass make up particles that do have mass? So it appears from this that photons cannot build up to make matter particles.

You are talking about virtual particles, which appear out of "empty" space and collide. They are a particle and antiparticle pair. One has positive energy and the other has negative energy. So when they collide, no energy is released. The amount of time a pair exists is determined by the HUP, as you note. I was talking about real particles. Here they are a particle and antiparticle pair. But they both have positive energy. So when they collide, they release energy.

As I understand it, the big bang was the expansion of space. And the universe at time zero may have been finite or infinite. Inflation theory says a tiny moment after the big bang, the universe expanded exponentially. So couldn't we say this was an explosion of space.

Here's how I think it works. A photon is not a particle with "very little mass". It is a particle with zero mass. The conservation law is conservation of mass/energy. Mass is converted to energy by E = mc^2. So say an electron and anitelectron(positron) collide, annihilate each , and produce photons. The total mass/ energy of the electron and positron before the collision equals the total energy of the photons after the collision. Mass/energy is conserved. And of two photons have enough energy, when they collide, they can produce an electron and a positron. Again the energy of the photons before collision has to be enough to equal the mass/energy of the electron and positron after. This mass/energy consrevation works for all particle interactions.

Good stuff here. Thanks. But again what does the 12 miles refer to and how is it calculated?

Are you saying the event horizon is about 12 miles in diameter? And if there is no space between the particles at the black hole center, then isn't the center infinitely dense?

Oh. I guess I take things too literally.

boy, this is getting tough to sort out. I think rotating the bucket is technicallly equivalent to rotating the rest of the universe. This is Einstein's Principle of General Covariance -- there is no "preferred" frame of reference. Any reference frame is as valid as any other one. So the bucket spins in the universe frame, and the universe spins in the bucket frame. And both ways of looking at it produce identical physical results. I also think your talk of moving through space for the bucket but not moving through space for the universe is not quite right. There is no absolute space in relativity -- so space doesn't move along with the universe. Both the bucket and universe are moving though space and through time or spacetime.

Sure it does. This is demonstrated in particle accelerators all the time. The faster the particles move, the longer they live on average. This is because of time dilation -- time for the particles rus slower than time for the laboratory. So from out point-of-view in the laboratory reference frame, the particles live longer than the same particles at rest. Fro example, see link: http://www.physlink....perts/ae611.cfm

Do you have a link for this infinite singularity? I think whether the universe is finite or infinite is still an open question in cosmology.

Yes in your reference frame, that dizzy feeling you get when you spin around is caused by the frame dragging produced by the rotation of the rest of the universe. And yes, when you spin around, from your point-of-view, stars that are far enough away are moving faster than the speed of light. But you can not use this effect to send a signal faster than the speed of light -- so relativity rules are not violated.

The distance between your eyes and your nose are always the same to you, because you are moving at the same velocity as your eyes and nose. BUT another observer moving relative to you will measure the distance as shortened (along the direction of motion.) And the greater the speed, the more the shortening. That is why we say space is relative. But the speed of light is the same for all observers, no matter what their uniform motion. So it is absolute.

Welcome to the club.

I think we are getting into semantics here. No matter what your uniform motion with respect to a beam of light, you will always measure that light's speed (in a vacuum) as the same value, c. This is what is meant by the speed of light is absolute. (If the speed of light were relative, then observers moving at different speeds would measure different values for the speed of light. )

Frame dragging is accepted science -- a recognized prediction of general relativity. Testing it, however, has been a challenge because iti s a very small effect for the rotating Earth. NASA launched Gravity Probe B in 2004 to measure frame dragging. After lots of problems, the team says they have confirmed Einstein's prediction to 15%. (NASA Science Report - Dec. 2008).

Wht paradoxes contradict relativity? What superluninal experiments (outside of recent CERN neutrino issue)? Experiments with light stopped, as I understand it, do not contradict relativity - do you have a reference that says it does? I am not familiar with Magueijo and Grusenick -- are their claims recognized by mainstream science? Outside of the CERN neutrino measurements, I think relativity is on very solid ground. and that could be a measurement issue. Please provide links to the above questions.

Good arguments. Let me try to answer them: As to reason 1 -- I think you are rediscovering the equivalence of gravity and inertia. See link: http://philsci-archive.pitt.edu/1287/1/A1085285 As to reason 2 -- I believe if the bucket rotates to match the rotation of the universe, then there is no relative rotation between the two. This is equivalent to a reference frame where the bucket and universe are at rest. I think you have to consider only relative rotation. There is no absolute rotation in Einstein's construct.

Nice!

I agree with Iggy. Well said.

I got the idea that a spinning universe with no other mass/energy besides the water bucket would still cause the water to become concave from Brian Greene, The Fabric of the Cosmos, p .417: " whereas standard Machian reasoning would claim that the water would stay flat in the bucket spun in an infinite, empty universe, general relativity diagrees. What Pfister and Braun results show is that a sufficiently massive rotating sphere is able to completely block the usual influence of the space that lies beyond the sphere itself." Again, I do not get this last part. A sufficiently massive rotating sphere implies a universe WITH mass/energy, doesn't it? The idea of this thought-experiment is to show one effect of Einstein's Principle of General Covariance. Per general relativity, any reference frame will do. Newton says the only legitimate reference frame is absolute space itself. The bucket is spinning with respect to absolute space. Einstein says there is no absolute space. The bucket itself is a legitimate reference frame, per the Principle of General Covariance. But in this frame, the bucket is at rest. So what makes the water go concave" From this point-of-view, the rest of the universe is rotating in the opposite direction. And through frame-dragging, this causes the water to go concave! I learned this from Brian Greene's The Fabric of the Cosmos, beginning of Chapter 14. He also gives references in the endnotes: D. Brill and J. Cohen, Phys. Rev. vol 143, no. 4, 1011 (1966) and H. Pfister and K. Braun, Class. Quantum Grav. 2, 909 (1985).