Severian

Yes. The Casimir effect is mainly (quantum) electromagnetism.

From the article: That sort of statement just makes me angry. They have not "systematically establish[ed] its existence". They have shown that in certain theoretical frameworks such a scenario is possible.

In that case you need to ask someone who is not a particle physicist. Atheist and I both are, so we will give you the particle physicist answer.

It is a matter (no pun intended) of definition. We call certain fundamental particles 'matter' and others not. As Atheist said the fundamental quarks and leptons are the matter while the gauge bosons were not. Historically this came about because the photon is its own antiparticle, so when you have a reaction like [math]\gamma \to e^+e^-[/math] this definition of matter allows us to say that 'matter is conserved'. It would be better to say 'fermion number is conserved'. This historic reasoning breaks down though as we include more forces. The gluon is the strong force analogue to the photon, but since the gluon has color it is not its own antiparticle (a [math]R\bar G[/math] gluon is not the same as a [math]\bar R G[/math] one). Nevertheless we still regard it as not-matter to allow us to say 'matter' and 'anti-matter' rather than 'fermion' and 'anti-fermion'.

I don't think it even has to be an evil dictator. If the average person is asked before conception "Do you want your child to be homosexual or hetrosexual?" they will pick hetro. Its only natural because then they will be more likely to have grandchildren. Or if they are asked "Do you want your son to look like Brad Pit or Homer Simpson?", which do you think they would choose? In these cases, the availability of choice will be enough to lead to eugenics.

Are you implying that the US didn't sign up to Kyoto because they want more stringent measures to be taken?

I agree with Martin. Quantum Mechanics only allows predictability in large statistical samples. The wavefunction collapses would be different so we would end up with a different universe.

It's hardly a designer baby. Normally in IVF more than one embryo is made, and the (usually) two healthiest are implanted. The rest are thrown away. This is simply an alternative quantification of 'healthiest' by screening for inheritable diseases. This is just another example of the British press blowing things out of all proportion.

Phew! Thank God it wasn't just me

I don't think there is anything wrong with mentioning that great people in history were gay, but to imply that their greatness was caused by their sexual orientation (without proof - it may be in some cases) would be wrong. PS: Is it just me or does Sayonara3's new avatar look incredibly dodgy?

No - that's not true. Virtual particles are always virtual. I think what you mean is that if we have enough energy, a real particle-antiparticle pair can be produced. Below the threshold for their production they can only be created as virtual particles which have a short life time. So in principle, if you have enough high energy photons, say, you could turn them into matter and antimatter, separate them and create a planet and an 'antiplanet'. Just make sure they don't collide!

Dak: As a matter of interest, where are you from (I mean originally). I am guessing you are French, right?

Sorry, I think you are right with that solution. My mistake.

Edit: I just checked and do agree with [math] \frac{d\theta}{dt} = -1 [/math] Yes, that's better.

A quantization of time or space would cause a breaking of Lorentz invariance. Since Lorentz invariance has been tested extremely well by now, we know it is not broken up to roughly the Planck scale. So if space is quantized, its indivisible unit is smaller than a Planck length 1.61624(12)x10-35m.

That depends on the theory. There are some (reasonable) theories which predict black holes will be formed at the LHC when it switches on next year. The biggest problem I can see would be stability. Small black holes evapourate very quickly, while big black holes gobble you up. I haven't lloked into it, but I imagine keeping a black hole the right size would be very difficult.

There is a flaw in that argument..... There is no 'Law of conservation of mass'. We convert mass into energy and back again every day. Fission power is an example of mass->energy and particle colliders are an example of energy->mass.

Sarahisme: where do you go to school? You seem to get a lot of homework.

This looks right. but this isn't (you screwed up the algebra after the integration I think). Also' date=' be careful of your intergration endpoints. You started with 2 equations and converted them into r and theta. This must have given you two equations which you solved for dr/dt to get the dr/dt equation you have above. Now you can put this dr/dt back in and solve for dtheta/dt. (The point of this exercise is to show you how problems can be made much much simpler by choosing the correct reference frame.)

As has been already mentioned, there is nothing in SR or GR which forces a finite universe. I am not sure what you mena by the second part - if you mean 'does the curvature change?' then yes, the curvature changes in response to the energy/mass present. The crucial point is that the measurment of time and distance are not universal - they are different for different observers. The length of an object for example is not a well defined quantity unless you specify the frame you are observing from. I am not going to rederive this here, but it is a logical consequence of the speed of light being the same in all reference frames. It is either. Usually it is expressed in terms of one particle because that is the simplest case. But when one has multiparticle systems one still has an uncertainty. notice that this is not an uncertainty inherent in measurement - this is an uncertainty inherent to the particle itself. If the energy of a particle is fixed to one value then the particle is spread out - it doesn't have a definite position, and so we cannot meanure a definite position.

First of all, there is nothing 'unnatural' about the particles made in particle colliders. They all exist in the everyday world - we just don't see them very often. For example, electrons have mass because of the Higgs mechanism (we think), and mass is a fundamental property of the electron. So although we don't see Higgs bosons in our cornflakes, they are there - they just don't live long enough for us to see them. Anyway, the point is not to see what particles exist in everyday matter, but to investigate the fundamental nature of the forces. The intent is that if we understand what makes them work we will be able to better explain the everyday world.

Describe to us how you got your 'complete solution'. (Hint: your equation [math] x + \frac{y^2+1}{x} = c [/math] is not a solution of [math] \frac{dy}{dx} = \frac{1-x^2+y^2}{2xy} [/math]. To see why, solve our solution for y and differentiate. )

I agree with Cap'n, Ecoli and Hades. Kids should be protected from certain things on the internet. The internet has some pretty sick content, and I am sometimes a bit shocked when I stumble apon some of that stuff accidentally. (I am not talking about a seeing a pair of breasts.) I imagine that viewing that sort of thing could seriously disturb a child, maybe even to the point of thinking that behaviour is normal.