Strange

Plus what is biologically feasible in terms of lenses and sensor pigments. A lot of people would argue with that! (It can look yellow, e.g. at sunset)

Of course.

It is used when it is a reasonable approximation (as the results in the paper you quote from shows it to be). Accounting for all the stars in the galaxy (and all the toehr galaxies in the universe?) would be infeasibly hard. And, we know, from Newton's work, that it wouldn't make a significant difference. The shell theorem, as you can see, is derived from Newton's laws. Go on then.

It was: no one has said the clock doesn't stop. For the obvious reason that it does (under any reasonable interpretation of the very slightly ambiguous description). In all frames of reference.

Does it? Where does it say that? That doesn't make any sense (I mean, literally, I cannot extract any meaning from it): what does "gravitating away from" mean? Voids are not points. They are (very) large areas of (relatively) empty space.

I see what you mean: because we observe (and use) antimatter all the time, it can't be travelling backwards in time.

Sorry, I can't understand that. Voids don't cause gravitational lensing, mass does. And that still has nothing to do with white holes (which, if they existed, would be spewing out matter and energy).

I thought everyone agreed that the clock stops (as seen from all frames of reference) but people disagree about why (i.e. whether the flashes were simultaneous or not).

I don't know enough to comment on that. But I wouldn't put too much faith in one unpublished (as far as I can tell) paper. BTW: this is a slightly better link: http://arxiv.org/abs/physics/9812021v2 But that isn't by Barbour, so ... That doesn't sound anything like what is in that paper (which takes the time-reversal symmetry of antimatter as real).

Do you have a reference for this? I don't really understand what it means. Does he present any evidence for this idea? Well, no. Time is one of the dimensions of space-time (the clue is in the name ). They would annihilate, producing distinctive radiation (which is being actively looked for). Acceleration would no prevent this. A void is nothing like a white hole (it is more like nothing). How can our universe be travelling throuigh space when it is space. There is no evidence for it. Surprisingly large amounts (i.e. minute amounts) have been found, for example in our galaxy, but there is no evidence that there is a similar amount as there is matter.

Just to be clear, the velocity doesn't need to be near the speed of light, this happens at all speeds. It is just that it doesn't become noticeable at "everyday" speeds. Also, describing this as "increasing mass" is not very accurate (even though it is often used) and can lead to misunderstandings. It is really the total energy that has increased - but as we know, mass and energy are equivalent so we can talk about a "relativistic mass" made up of the rest mass (the real mass) plus the kinetic energy. From the point of view of the person in the craft, there is no change in (relative) speed either. They are still stationary wrt the craft. So there is no increase in kinetic energy. Energy is not an absolute thing, it depends on the observer. The stationary observer sees the spacecraft increasing in kinetic energy; the observer on the craft doesn't.

Just like in Einstein's thought experiment. He doesn't. No specifed. The "stationary" observers external to the train. (Just like in Einstein's thought experiment). No it isn't. It must be the same distance as the clocks are equidistant from the centre. Yes, in different times because (from her perspective) the train is moving towards one flash and away from the other. And at the same speed (of light). Hence they must have occurred non-simultaneously. But they were simultaneous for the observer on the train.

If it was a ring then we could not. If it was a reasonably even, spherical distribution of stars (which it is) then it is a useful approximation. Once could try and calculate the effect of ever star in the galaxy but this would be (a) impossible and (b) would not make a significant difference. Science deals with approximations like this all the time. http://en.wikipedia.org/wiki/Spherical_cow No. They are indivudal stars. The cluster can be approximated as a spherically symmetrical body. Perhaps you can show your calculations to support this, as it appears to disagree with everyone else's.

As I say, the problem seems to be with your understanding.

The error appears to be in your understanding of it.

Journalists do it all the time. (Not that that is any justification. )

No. I am telling you what Newton actually said (proved): http://en.wikipedia.org/wiki/Shell_theorem Yes. As stated in the paper that you quoted from. Because your expectation is wrong? Just gravity and orbital velocity. This is the case. (Except there are not two objects, there are thousands) The paper says that the stars in the cluster and the black hole all orbit the barycenter (i.e. their common center of mass).

In a variety of ways. The article linked in post 2 has some examples.

In semiconductors they can be created in many ways, for example by "doping" the semiconductor (adding atoms of another element with fewer electrons than the bulk material). Or the application of energy (e.g. photons) can cause an electron to be freed from the lattice leaving a hole: then you have two current carriers, positive and negative. They can go in any direction. Holes, like free electrons, will just drift around slowly in the absence of something forcing them to move in a particular direction. Which is why I said: This is in the process of being tested by the CERN ALPHA experiment - when they can generate enough anti-hydrogen to measure the effect of gravity on it.

In that case, the objects are moving apart and so the space between them will be changing for that reason. There doesn't need to be: we are just talking about the distance that is measured. You can measure distance in space without a substance present. Don't be rdiculous.

Off the top of my head, I think the answer is that relativity of simultaneity means that from the external (stationary) perspective, the front and back of the train accelerate at different times and so one clock ends up lagging the other. (A variant of Bell's spaceship paradox.)

And I have tried to use it to explain Newton's Shell Theorem. To understand the orbit of S2, all that matters is the mass of the central black hole. The mass of S2 is much smaller and can be ignored. The gravitational forces of the surrounding stars cancel out. This is all described in the paper you quoted from. It is a dense cluster of stars at the centre of the galaxy (it seems that most spiral galaxies have a central nucleus like this). It is about 3 parsecs in radius (I think, I can't be bothered to go and read the paper again right now) surrounding the balck hole. Because it is a globular cluster. The stars are all orbiting around the black hole (or, more accurately, the centre of mass of the balck hole and the cluster). They have different speeds and directions but the overall rotation is parallel to the plane of the galaxy.

This is a variant of the train/lightning example that Einstein used in his book to explain relativity of simultaneity. The bit you are missing in your description is the meaning of "at the same time". The people external to the train will not see the flashes light emitted simultaneously. This must be true, because they will see the flash from the middle clock, they know the distances and speed of light are the same therefore they see the flash at the back occur first in order for it to reach the middle at the same time.

To add to that, we have three differnt (overlapping) receptors. Some birds have four, for example, and some of these extend into the ultra-violet. As such, it seems clear that they would see things that we can't (and, perhaps, vice versa). But we certainly can't get inside their heads to know what the experience is like. But then we can't do that with other humans either (see also: qualia). One of the articles I read on this subject included demonstrations of creating "impossible" colours such as yellow-blue. It's a weird experience to see somethign which is not quite blue and not quite yellow!

It certainly sounds like a sample from a random text generator.