Severian

I think it is despicable. They are putting the lives of innocent people at risk to satisfy their own greed. I would have no problem with limited strikes at some other time to aire their greivances, but not at Christmas time. Academics went on strike last year (about tution fees) and no-one noticed. It was discussed at the time whether we should have stuck during the exam period - this would have meant that final exams could not be done and everyone would have to resit in September. We decided that this would be too unfair on the students (who we were trying to help with the strike) so we didn't do it and struck at a different time of year.

That is all very well, but I could imagine an untrained person coming to the same conclusion about string theory.

The thing which annoys me about creationists/ID is the unwillingness to accept that what they believe is a belief and not a scientific theory. But if they do accept that, then I have no problem with them. They can even point out that the definition of 'scientific' is a bit arbitrary and I would have no problem. For example, if the universe was constructed instantaneously 6000 years ago, with every particle in exactly the same position (and with the same properties) that it would have been in after 13.7 billion years of evolution, then one could not perform any experiment which would be able to distinguish between creation and more usual post-BB evolution. The difference is that the ID/creationist pov is non-predictive - its entire content is in a boundary condition. So while standard cosmology can explain many features of the universe we see around us, ID can only state them as prerequisites of a boundary condition. Since one of the definitions of a scientific theory is predictivity, ID is not science. Having said that, predictivity is a human placed constraint on science. There is absolutely no reason why the universe couldn't be non-predictive (ie. contain features which cannot be predicted) so our restriction of 'science' to predictive phenomena is an arbitrary restriction designed to enable us to actually do something useful (make predictions). I think ID has been so successful in subverting minds (even some 'scientists' minds) because many 'sciences' seem to have forgottten this requirement for predictivity. This is particularly true in fields like evolutionary biology because it is so difficult to make predictions which can actually be tested. So you can make a prediction that two specied have a common ancestor, but finding fossil evidence for that common ancester is very difficult.

I agree with the decision, but not on the method by which is was decided. I don't think a judge should be deciding what should or should not be taught in schools. I don't think a judge is clever/trained enough to be able to distinguish a legitimate scientific theory from a hole in the ground. Lets face it, most judges are as thick as mince, and should leave science well alone.

So how do you transfer momentum between two particles without a mediating particle?

This is then similar to the situation in the second diagram, just moving the initial state electron into the final state (making it a positron) and having it hit by another photon. The magnetic field is photons too, so you just produce the electron-positron pair and each interacts with a photon. In fact, this is the basis of electromagnetic colorimeters in particle physics detectors.

Electromagnetic radiation is made up of photons, which are not classified as 'matter'. Whether something is 'matter' has nothing to do with whether or not it has mass. The photon has no mass, and is not matter, but the Z boson does have mass, and is not matter either. It just so happens that all matter particles we have observed do have mass, but even if the neutrinos had been found to be massless, they would still have been matter. And do answer the second question, all four forces are the interaction of matter with non-matter.

Interestingly this will probably be how we show the Higgs boson is spin-0 (or at least not spin-1). If we see it decay into two photons we know that it cannot be spin-1. (Showing it is not spin-2 is a little more difficult.)

Normally I would draw the internal electron/positron line as vertical, so that it would represent both an electron moving backwards in time (i.e. a positron) or an electron moving forwards in time. I just drew it this way because of the original context of the question. Also, on Feynman diagrams, the arrow only denotes the direction of the fermion number flow (in this case, the direction of an electron).

Even without using any maths it is pretty obvious. If you are in the centre of the sphere, you will be pulled in all directions at the smae time, so no net force. (I don't think anyone is disputing that.) Now, if you move closer to one of the edges, then you are closer to the side in front of you and it will therefore pull you more strongly towards it (gravity gets stronger as you approach the source). But now there is more mass behind you (most of the sphere is behind you now), and since gravity increases with mass, the part of sphere behind you will also be pulling you more strongly. Since the area of a sphere increases as r2 and the gravitational force behaves as 1/r2 these two effects are exactly balanced, and you feel zero net force.

I concur with Sisyphus. Its a simple application of Gauss' Law.

These aren't really Christmas logos though - more winter logos.... ... they look good though.

Buy a hat?

If fact, any force based on a non-abelian symmetry do. So photons are the exception - they are the only force carriers which do not self-interact (there is also no triple-Z vertex, but you could argue that the ZW+W- vertex is a sort-of self-interaction). To take the original question further, even if you discount gravity, the interactions will not be entirely absent. Imagine a neutrino which has no charge (so doesn't feel electromagnetism) and is 'colorless' so doesn't feel the strong interaction. All it feels is the weak interaction. Also imagine a particle which feels electromagnetism and the strong interaction but not the weak interaction (it doesn't exist, but never mind). At first order they do not interact, but since the neutrino has a weak interaction, it can split into a virtual electron and W-boson, and then the charged electron or W-boson can inteact with the hypothetical particle before annihilating again to reform the neutrino. This would be a very very very small interaction, but not zero. This is true of all particles. The only way to prevent them from interacting with each other is to prevent them from having any interactions with common particles. But then, we (who are made of quarks, etc) would never be able to observe with these particles in any way, so as far as science is concerned they do not exist.

Philia is the word that was used in ancient Greek. We don't really have a modern equivalent. Edit: Or are you meaning a divine love, which would be Agape?

Energy is conjugate to time and momentum is conjugate to distance. The important thing to realise is that a state with a definite position is a superposition of lots of states of different momentum. This is simply a Fourier transform: [math]f(x) = \frac{1}{(2 \pi)^4} \int F(p) e^{ipx} d^4p [/math] f(x) is the distribution of the object in position, while F(p) is the distribution in momentum. Now if F(p) is a delta function, ie. the particle has a definite momentum, then f(x) will be spread over all space - it won't have a definite value for the momentum. Similarly (via the inverse transform) if the particle is at one point, its momentum distribution will be spread out. So basically, the HUP is just a statement about Fourier transformations....

No it doesn't. Please don't just make things up.

5614: Well, presumably, but then I am not really sure what the worry was. Even if it is a prefered state the transition rate is incredibly small (since it is a weak process), so it would take millions of years to convert even a small amount of mass into these stranglets. I don't see what the gravitational attraction has to do with it since gravitational forces are tiny on a quantum scale. insane_alien: As far as gravity is concerned, it is the energy of the system which is important, not the mass (although the energy includes the mass - for slow moving objects it is dominated by the mass, which is why Newton's gravity is based on mass). Presumably the saving in energy of the configuration is enough to make up for the mass difference since the statement was that it is a lower energy state. But if it is a lower energy state then it should have less gravitational pull...

It shouldn't go anywhere. The schools should teach what they like and the parents should be able to decide which schools to send their kids to. The schools would pretty soon learn that if they teach the kids this rubbish that the kids won't get places at college or get jobs, and the parents won't send them there. I suspect this sort of thing would only effect a tiny minority of schools, which would very quickly gain a bad reputation.

I don't understand why the gravitational pull would be greater either. If they are a lower energy state, their gravitational pull should be less surely?

I was actually rather disappointed by that transcript. The professor was reasonably consistant in his answers. He took a definition of 'science' which was way out there and claimed it was the definition used in the scientific community (when it is not). But then, within his definition he correctly argued that ID is a science. The lawyer harped on about astrology, which the witness (perfectly correctly) said was included as a scientific theory in his definition. He accepted the definition and pressed on to see what that definition implied. What the lawyer should have done was attack the veracity of the claim that the definition was standard. He did not do this! (In fact, astrology is more of a science than ID is because it at least claims to make predictions.) The problem with letting this sort of thing go to the courts is that the lawyers don't have the faintest clue what they are talking about...

Strange matter is a bit misnamed, since it isn't just strange. There are six different types of quark (up, down, charm, strange, top and bottom) and each comes in 3 different colors (red, green and blue). Because the strong interaction grows with increasing distance, quarks are confined into composite particles like the proton, which are color neutral (have the same amount of all three colors). You can make a color neutral state in 2 ways: 1. You can have a quark and antiquark bound state of opposite color (they need not be the same quark type). This is known as a meson. The [math]\pi^+[/math] for example is a bound state of an up quark with an anti-down quark. 2. You can have a bound state of three quarks, all with different colors. This is known as a baryon. The proton, for example, has two up quarks and a down quark. Strange matter (or 'strangelets') is a bound state of an up quark, a down quark and a strange quark (again all with different colors). It is therefore a baryon. The interesting thing about this state is that it potentially requires less energy to make because the three quarks are all of different types (fermi-dirac statistics). There was then a worry that the strangelets would be the prefered form of matter, and creating strange matter would cause a catastophic decay of all normal protons etc into strangelets, thereby destroying the universe...

So the 'boundary condition' in your example is that the endpoints of the string in one case are restricted to lie on the brane, while in the other case, they are not. But saying that the graviton is restricted to the brane is not a prediction of string theory itself, since I could equally well set up the string theory with different boundary conditions. It is a prediction of the boundary condition. Equally, I could have a non-string theory with a boundary condition such that the gravitons are allowed to propagate in the bulk, which would also dilute gravity. Indeed, the first suggestion of this was the Randall-Sundrum model, which is not a string theory.