Severian

Hardly any fundamental particles are directly observed. What does 'directly observed' even mean? I suppose the only particle you ever really directly observe is the photon....

It really depends on what you regard as 'the same particle'. Even before the Higgs boson comes along, the electron and neutrino and different components of an 'isospin vector'. This means that they have exactly the same quantum numbers as each other apart from 'isospin'. So they are not (in my opinion) ever the same particle (although one could in principle claim they are because you could regard the ispospin doublet as the 'particle' and the electron and neutrino as different facets of the same particle). When you include the Higgs into the picture, they get a further difference - they have different couplings to the Higgs boson. We still don't know why different particles have different couplings. They are just added to the theory by hand.

http://pdg.lbl.gov/2004/listings/contents_listings.html Gluons are experimentally proven by the way, as are virtual particles (as 5614 said).

Try http://webphysics.davidson.edu/mjb/qcd.html and http://particleadventure.org

I have seen a prototype of a car with spherical wheels. It allowed the car to move sideways (well, at any angle I suppose) which looked really handy for parking. I have no idea how they worked though. (Didn't the Audi in 'I Robot' also have spherical wheels?)

http://imagine.gsfc.nasa.gov/docs/features/news/20may99.html

I think this is the only bit I agree with.

You are almost correct. Imagine first a not quite rigid body. The system cannot sit in this completely up-down symmetric position. What will happen is that the body will move down very slightly, so that the rail pushes the wheels outwards. but since we are slightly off the central point (ie. the height where the distance between the rails is smallest) the rails are at a very slight angle. So part of this force is pushing upwards and it will balance out the force of gravity. Where this point is depends on how rigid the body is. Now for a rigid body. If the body is entirely rigid then the wheels cannot turn (since they are rigid) and the body cannot move. If you allow the wheels and rod to be separately rigid, then you need to say that the wheel is running frictionlessly, but as the rod moves down it will exert an increasing sideways force on the wheel and any definition of 'frictionless' will at some point break down (otherwise the rod would pass throught the wheel!). In other words, the premises of 'rigid' and 'frictionless' don't work in the case you demonstrate because they would require the object to fall apart.

I think the moderators of these forums have a moral responsibility. People who are genuinely interested in science come here to ask questions, and often don't know much about the subject they are asking about. They are not at a level to be able to tell who is an expert and who is not. That is why the 'expert' tag was introduced. It is the moderator's responsibility to ensure that any really bad science (not so much minor errors, but real flaws of understanding) are visibly challenged so that any casual readers do not go away with wrong ideas. We do not want SFN to become a "crackpot" site. Now, Johnny5's problem was that he believed himself to be an expert when he very clearly was not. Therefore, no matter what the logic of the argument presented to him, he would continue to insist that his original idea was correct, and would spam the thread until the person opposing his view gave up out of sheer exhaustion. I personally just stopped posting in his threads. What should the moderators have done? Should they just have followed him about, closing threads which got out of hand? This was what they originally did, but the mods have a finite amount of time, and it is better spent doing something else. Johnny5 really didn't contribute anything to this forum, and I support the decision to ban him. If he wanted to learn about physics, he should have asked questions and discussed topics in a modest and moderated fashion, instead of going on egotistical rants.

I look a bit like Brad Pitt when he was younger (before the shaved head thing), except I am better looking and slightly more muscular.

Lol - they have Albert Einstein in there! I hope Oprah Winfrey wins, just for a good chuckle at our American friends' expense....

this is an entirely semantic argument (as usual). It simply depends on your definition of 'time'. The way Janus defined time, it does become imaginary, so his comment was completely appropriate. The obvious question to you is, why would you define time differently from Janus' definition? What insight of FTL travel do you have that we do not? Do you have personal experience? I suspect you don't, so any alternate definition you can come up with will be just as arbitrary.

"Bunch of light" gave me a giggle at least...

I remember coming home with exam results one time and telling my Dad I had 99% for my exam. His reaction was 'What happened to the 1%? Work harder next time!'.

The wild-west thing can get a bit tedious though....

It is harder to accelerate because momentum (which is linked to energy) increases non-linearly with velocity. [math]p = \frac{mv}{\sqrt{1-v^2/c^2}}[/math] Even if you put in really huge amounts of momentum (p) you will never get velocity (v) to equal c. But how do you measure that 'quantity'? Is it the volume it contains, the downward force it exerts on a set of scales, or what?

No. (It depends on your definition of 'mass' of course, but with the definition that physicists use, no.)

My weight seems to vary quite often. Just yesterday, one of our secretaries commented that I had lost weight recently.

Well, it is still expanding, but that is a different thing....

Yes it is. First of all, unless your friend who is not on the train plans on running around with the gold at light-like speeds then it's 'mass' (as you quaintly call it) will revert to the mass it had before getting on the train, since the important quantity is its velocity with respect to the observer. Alternatively, if you ask your banker onto the train, he will weigh the gold and find that it is exactly the same weight as normal, because his velocity with respect to the gold is zero. Secondly, rest mass (which is the correct quantity here) doesn't change. In relativity the relation between velocity and momentum is non-linear. It is the desire to keep it linear which has lead some books to 'redefine' mass as momentum divided by the velocity. This is a silly redefinition, and certainly has no equivalence with gravitational mass (which is used to price gold).

I know its not a book, but I must say that I am rather enjoying Firefly on TV. I like how thay at least pay lip service to physics, by for example having no sound in space.

And why is that? Have you actually met him? I have.... He is a reasonably good physicist but is by no means a genius. I would even dispute that he is good enough for the Lucasian chair at Cambridge.

There has been some interesting work on Black holes recently by Bena at al (http://arxiv.org/abs/hep-th/0402144 etc) which suggest that black holes may not be singularities at all. They were able to build objects which look like black holes out of more normal geometries. So there is really no experimental evidence to suggest that physics has problems beyond the Planck scale either.

Relativity tells us that only relative speed is important. Since the laws of physics are applicable in all frames of reference (all inertial frames for SR, all frames for GR) there is no notion of any particular frame being more special than any other. Since the elctron has mass and travels <c then it does have a rest frame, and your argument breaks down. It makes no difference how fast an electron actually goes since it is still infinitely far away from travelling at c (ie. you would have to put an infinite amount of energy in). Secondly, this deosn't even work for phtons which have no mass and travel at c, since the collapse of the wavefunction is non-local. So the wavefunction collapses everywhere at once, quicker than you could send a photon across it. This sounds paradoxical, since it seems like some parts of the wavefunction actually collapse before you measure it (in certain frames) but is not when worked out in detail.

Just a clarification here. It's Schrödinger's cat, or alternatively Schroedinger's cat, but not Schrodinger's cat.