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1. New Twin Paradox

Suppose you have two people who are in identical orbits around a large star. The only difference between them is the direction they are traveling. At a certain point where they meet ( there are two such points ), they sync clocks. After a few orbits, they meet again and again compare clocks...
2. Number of unknowns - Coordinate Transforms

I made a mistake in my question. I know that functions have an unlimited number of degrees of freedom, I meant to ask how many functions are involved in a generic coordinate transform in R^4. My guess is 16, since there are two indexes in the transformation matrix, each running over 4 values...
3. Number of unknowns - Coordinate Transforms

In general relativity, what are the total number of unknowns for a generic coordinate transform? Is it just 4 * 4 = 16? Is there a way to break those down into combinations of types, such as boosts, rotations, reflections (parity?), etc, or is it just left wide open from an interpretive...
4. Closed Dimensions

Ok cool. Are there any decent references you know of so I can read about this? Surely the closed nature of the space would manifest somewhere in the equations...
5. Closed Dimensions

If we assumed an empty space, but also assumed space dimensions are closed ( repeat after some distance D ), what would the metric tensor look like? Is this just equivalent to a space with a constant curvature R? If so, how does R relate to D? Would the time dimension also necessarily be...
6. Conservation of Particle Number

Sure that would make sense since curvature means the space is filled with non-zero energy ( Energy Momentum tensor non-zero ). That, I would guess, acts like an interaction and thus particles can be created as the interaction occurs.
7. Conservation of Particle Number

Yes, and like I said, it's not relevant to my question. Thank you however for the commentary. I'll make a note to not use relativistic mass anymore. Semantics. Ok, sounds like the answer to my question is that particle number in invariant under coordinate change. So, despite the extra...
8. How do black holes grow?

Yes, it happens in one particular coordinate system. I never said it happened in all coordinate systems. This particular coordinate system is used, however, to show what the event horizon is and to do an easy calculation for it. It is HARDLY just an "artifact". Fair enough, but I think it...
9. Conservation of Particle Number

Well, actually that's not true. m changes when it's in motion, as does E. Regardless of that, you're not answering my question. Since the energy of the particle in the moving reference frame is significantly higher, do particles appear? Is the particle number conserved under coordinate...
10. Conservation of Particle Number

Because E=mc^2, when we increase the energy of a system we can introduce new particles. What about accomplishing this simply via a change of coordinates via Special (or even General) Relativity? If I have a system of one electron sitting still (E = E0), then I change to a coordinate system...
11. How do black holes grow?

The event horizon is a place where the metric tensor contains an infinity. Thus, there are no null geodesics (light paths) that cross this "line". This gets quite sticky, as infinities pose a whole host of mathematical problems that most physicists just choose to ignore (not all). I am of the...
12. Co-variant Derivative of a Complex Vector

What is the form of the co-variant derivative for a vector with complex elements (such as the Electromagnetic field vector A)?
13. Differential Geometry in C^2

Are there any good papers or books that go over our current understanding of differential geometry for 2-dimensional complex spaces? Hermitian vs anti-symmetric metric tensors, dealing with complex conjugates, and defining affine connections? Yes, I've already hit up Google, so I was hoping...
14. Gravitational Redshift really verification of GR?

If we assume: E = mc^{2} and for photons: E = hv Then we can derive an effective mass: m = \frac{hv}{c^{2}} And using simple classical gravity obtain: hv - \frac{GMm}{r} = hv - \frac{GMhv}{c^{2}r} = Constant You can derive the constant by evaluating the equation above at...
15. Spacetime, physical or not really?

First is right, second is only half right. GR is an extension of the principal of relativity to all frame, not just inertial. This is accomplished by replacing all equations with tensor equations. It was via thought experiment that once can conclude gravity = warped space-time if you assume...
16. Non-Tensors in GR

I know that GR deals exclusively with tensors (at least, in every book I have), but how does the same concepts of affine connection etc extend to non-tensor entities? Example would be a spinor, or even a mix of spinor / tensor. Are there different affine connections? Something different yet...
17. Constant Curvature

If a certain space-time region has a constant curvature (caused by, say, an even distribution of energy over the region) how would radiation be effected by the curvature? Would it create a red-shift / blue-shift as the radiation moved through the region or would it be un-effected? Has anyone...
18. Covariant Derivative

The covariant derivative is different in form for different tensors, depending on their rank. What about other mathematical entities? The electromagnetic field A is a vector, but it has complex values. Is the covariant derivative different for complex valued vectors? And what about...
19. Geometric shape of Minkowski space

Not donuts. Stupid iPhone autocorrect. "it's" ...
20. Geometric shape of Minkowski space

Thank you. This makes complete sense. Donuts really just a flat plane like Euclid had, but a different formula for distances. Couldn't you transform one to the other by making time real / vs imaginary?
21. Geometric shape of Minkowski space

Ok. Thank you all for your help. One thing I was thinking about was to take the proper time and use that as a "third" dimension so I could visualize things. If you do that, then eucledian space is just a cone. z^2 = x^2 + y^2. Minkowski space would just be the curve z^2 = x^2 - y^2.
22. Geometric shape of Minkowski space

So, suppose for visualization there are only two dimensions: ct and x. Now if the metric where Euclidean, we could visualize this space is a simple plane. What would be the shape of the "plane" when the metric is +1, -1 (Minkowski)? Is it somehow hyperbolic?
23. Hermitian Metric - Calculating Christoffel Symbols

Ben Thank you for the reply. I am aware of what you are talking about, but honestly I'm not concerned with creating a "real only" metric. I guess my question is more of a pure mathematical question than physics, and i was hoping that someone out here could point me to some references that...
24. Hermitian Metric - Calculating Christoffel Symbols

While tempting to debate this statement, it's really off topic. I'm more asking about how the other components of differential geometry change when we change the symmetry condition on the metric tensor.
25. Hermitian Metric - Calculating Christoffel Symbols

Here is the equation using the editor: \frac{\partial g_{\mu \nu}}{\partial x^{\tau}} - g_{\alpha \nu} \Gamma^{\alpha}_{\mu \tau} - g_{\mu \alpha} \Gamma^{\alpha}_{\tau \nu} = 0 which I propose changing to: \frac{\partial g_{\mu \nu}}{\partial x^{\tau}} - g_{\alpha \nu}...
26. Hermitian Metric - Calculating Christoffel Symbols

Yes I know, but that assumes the metric has only real values. I am not assuming that, so in essence the metric, Christoffel Sybols, and Ricci tensor would all allow complex values. Solving for the Christoffel symbols (from examples I've seen) involves writing out the equation for a zero...
27. Hermitian Metric - Calculating Christoffel Symbols

Hello, I am trying to understand what the differences would be in replacing the symmetry equation: g_mn = g_nm with the Hermitian version: g_mn = (g_nm)* In essence, what would happen if we allowed the metric to contain complex elements but be hermitian? I am not talking about...
28. How do black holes gain mass?

It's related directly to the last question of the original post.
29. How do black holes gain mass?

Oh absolutely this is all based on a thought experiment and an ideal case. In reality, as the body gets within a Plank length of the event horizon, particles can begin to tunnel in, and it gets sucked in (finite time). The full reality of this is more complicated then just the application of...
30. How do black holes gain mass?

That is true, but I think it's important to note that the black hole radius isn't effected by that. It's only effected by the mass inside the event horizon.