Severian

Could someone recommend to me a good free start up manager for Window XP? I am getting sick of all the crap my pc starts when I switch it on.

He is not completely 'off base'. Lattice QCD is a way of simulating Quantum Chromodynamics (a gauge theory) on a space-time lattice of points (which included discrete time). If fact the discretization is a valid regularization of the divergences in the theory, and lattice QCD is a very valid (most valid?) way of looking at QCD theoretically. These simulations are also probabilistic and very often involve Markov Chains. http://en.wikipedia.org/wiki/Lattice_gauge_theory

To be honest, I don't understand how a physics teacher could be confused about this. Work is done - the runner has exerted a force in order to overcome the frictional/disapative forces in his muscles and joints. Now if your marathon runner were on perfect, frictionless rollerskates, and is pulled by a friend then the total work done in moving the rollerskater from the start of the marathon to the end is just [math]mgh[/math] where [math]m[/math] is his mass, [math]g[/math] is acceleration due to gravity and [math]h=h_{\rm finish}-h_{\rm start}[/math] is the height difference between the start and finish. So even if he is frictionless, there will probably be work done. To have no work done, he would have to be frictionless, and finish at the same height. To put it another way, work done = Force x distance. Ignoring friction, moving along a completely horizontal track requires no force (because there is no force opposing his motion). If the track slopes upwards, you have to apply a force to oppose gravity, and the work done will be [math]mgh[/math]. If the track slopes downwards, you are given acceleration by gravity and the work done is negative - he will end up with kinetic energy equal to [math]-mgh[/math]. When a frictional force is present you always need to overcome this force in order to move him - lets say the force is [math]F_f[/math] - so you do work [math]F_f s + mgh[/math] (where s is the distance he moves).

I have no problem with any of these things. Why not specify a kids hair colour? Why not have them brighter? None of these sorts of traits are things which are 'unnatural' - they all have a chance of happening in a 'natural' birth, so why would a baby having these traits be bad? The only possible objection could be that the definition of 'bad' is arbitrary. For example, I am sure many gay people would object to a 'gay gene' being removed. But I think that there are enough difference of opinion in possible parents that this would not be a problem, and if everyone were agreed that something is bad, hey, that's democratic evolution! Also, we already have this artificial distinction of 'good' and 'bad'. For example, most people would have no qualms about genetically ensuring kids don't have Down's syndrome. But kids with Down's can lead perfectly happy lives, so why should they be selected against?

Sure it is. Just because we are not technologically advanced enough to distinguish two different theories doesn't make them indistinguishable in principle. String theory, for example, can't be tested at the moment, but it can be tested in principle, so it is valid science.

I think the original premise is wrong. Our theories are not getting more complicated - they are actually getting simpler. By this I mean that the mathematics is becoming more elegant - we drive our theory forward by making statements of principle rather than saying parameter x=y. The theories (like string theory) are only difficult when you try to calculate something with them, but that is essentially only because the approximations which we have used elsewhere break down and can't be used anymore, not because the theory is complicated. Also, we are used to looking at the world through low energy, slow moving eyes, so it is natural for the Newtonian description of the world to be 'simpler' in our eyes than (say) the description of Einstein's relativity. But relativity is a very elegant theory (much more so than Newtonian physics).

This is not an experimental statement - it is a statement of principle. If different theories do not predict different outcomes then they cannot be distinguished. I do not need to verify this experimentally because I can prove it mathematically.

If you can't tell the difference between them by experiment (and you can't) then it is not science. Please take non-scientific discussions elsewhere.

Dark matter is matter, but since matter has energy (like mass) it generates a gravitational force.

I think I agree with everything that Glashow said in that interview (except for the bit about us 'proper' physicists being too old for the LHC).

Why is this more historical than, say, Loops '04?

It is good that this is shown not to be needed because it is very hard to get most dark matter candidates to clump in this way (although, like Tycho, I don't believe this new result for a second). However, this astrophysical need for dark matter is far outwieghed by the cosmological arguments. If you look at experiments like WMAP, to explain the data you need to have lots of dark matter spread throughout the universe.

It is this. The solid line is an electron 9or really any charged particle, while the wavy line is the photon.

I know where you are coming from arkain101. I have my own theory of quantum gravity which explains all the unanswered questions in physics, unifies all the forces, solves the baryon asymmetry problem and brings me a nice cup of tea in bed every morning. Unfortunately I am not willing to share it with you at this point.

Light doesn't have mass, but it more definitely has structure. There are even workshops on it, e.g. http://www.hep.lu.se/workshop/twogam/twogam9809.html Also see http://www.cerncourier.com/main/article/39/7/11

There was even a crank(ish) paper that got passed the hep-ph screening the other day ( http://www.arxiv.org/ftp/hep-ph/papers/0510/0510086.pdf ), so you would be in good company...

Sorry, I don't know any physicists :/

I suspect "insane IQ" is only half right.....

Since you don't have an affiliation with a research group, if you send it to a journal, they will just throw it in the trash. If you are serious, you should go along to your local university and approach someone in the physics department. If you can convince them that your idea has merit (which I personally doubt) then they may let you send it to a journal under their affliation name.

No' date=' the four-vector is a four-component vector whose zeroth (or fouth, depending on your notation) component is the Energy (over c) and the rest are the momentum. So i is (E/c,px,py,pz). The length of this four vector is [math']E^2/c^2 - p_x^2-p_y^2-p_z^2[/math] (the minus signs are because of the weird Minkowski metric). Under a Lorentz boost the energy and momentum change, but you can show that the length remains fixed, and is called the "mass". It has nothing to do with the Photoelectric effect. It was derived by Einstein from the postulate that light has the same speed in all inertial reference frames. (Although I think it was first written down by Lorentz.)

E=mc2 is also just a unit thing. I usually use units where E=m.

Why 3? Why not 4, or 5, or 573689.4?