timo

No, the two opposite charges simply reflect conservation of charge.

iNow, what do the labels on the axes of the diagram mean?

No, but sound is directed motion of moelcules (air, water or whatever the sound travels through). Motion of molecules is kinetic energy. No, but they are quite similar to sound in also being directed motion of molecules. They also have energy. Quite a lot, actually. There's attempts to harness the energy of ocean waves comercially. Light is not energy. Dunno, but it's related for sure. Depends. For everyday-physics I'd say test it on a nice summer day. In more advanced applications light can also cool down -> laser cooling. No. The electrically charged constituents of something react with the light or not. Depends on your definition of mass and the something. "No" imho is the better choice, the "yes" crowd uses a definition of mass that I simply call energy. A biker can overtake a car in a traffic jam. Yes, that's why you should take important photos at a studio of a professional photographer. Yes -> Gravitational lensing. dunno Depends on the band. Yes. Neither of the three waves has an infinite range and neither is completely stopped, they dimish gradually.

Who's gonna judge? Do you have to accept that you're wrong or is it enough if someone with a credible background in physics plays the judge (and what would a credible background/person be for you)?

Not sure if I really understand what you say/want. Are you looking for an example where diff.eqs. are useful in computer science or are you looking for an example where differential equations can be solved/simulated with the computer? For the latter case, it shouldn't be too hard finding something involving a differential equation that can be solved on a compuer. Simplemost case probably is movement in a jump&run game where, as soon as you're in the air and not on the floor, the movement would -in first approximation- follow [math]\frac{ d^2 P }{dt^2} = \vec g [/math] with P being position and g being the gravitational field. The computer implementation is pretty simple: Each frame you alter the position according to the current velocity (P += v*dt) and the velocity by the gravitational field (v += g*dt).

From the mathematical term "equivalence relation" and the resulting equivalence classes. I can call/define two vectors or R² equivalent if they have the same x-coordinate. But I can as well call them equivalent if they have the same y-coordiante or if they have the same length. That's already three different meanings of equivalence for one very specific class of objects.

The human females are always so concerned with laying their eggs, they don't find the time browsing the internet.

Closest I've done was presenting my project in the "computational physics" course which was about GR simulations (the project where e.g. this picture comes from). T'was a 5-10 minute crash-course presenting the relevant formulas to 3rd-4th year physics students. That's probably not comparable, but I had the feeling that it was way too much for them, even though I only really needed the equation of motion and the Schwarzschild-metric (which I didn't even motivate but simply stated). An idea would be consistently showing the concepts on a visualizable manifold, where 2D manifold in 3D are probably the best/only choice. E.g. you can nicely show the parallel-transport of vectors using a pencil and moving it around an apple (or an arrow on earth if you're doing it on a diagram). And blowing up a balloon if you're covering that, of course. You should probably not be afraid using stone-old analogies. If people saw them before that might actually help since they can then put them in context. Nucleosynthesis or dark matter might be easier topics for that you can cheat a lot of understanding by showing Feynman diagrams. Especially modern experiments on dark matter searches might be interesting to hobby astronomers. Keeping things as simple as possible of course is the default-advice. You hopefully do that in all your talks. Would probably interesting if you'd post your talk here on sfn, afterwards.

. . . . . . . . . . . . . . Not sure about the "test"-part, though.

A wave equation is a differential equation describing/modelling waves. What you're talking about is the wave function. Consider the seriousity of your judgement about quantum mechanics in the light that you cannot tell an equation from a function.

Errr .... let's say "now that you mention it, yes I remember" . So thx for reminding me of which way round it was. Doesn't change the problem that if BH production can indeed not be measured and detected/determined experimentally it's not a test, neither a test for predictions nor a falsification test.

Try a search for "division by zero" on the math subforums. Should at least give similar tricks.

I seriously hope that SFN doesn't try to please everyone (e.g. astrologers, witches,...). The site is targeted at people interested in science. To what extent which non-scientific topics (and let's face it, assuming discussions in a religious forum would be even remotely scientific -theology or religious science- is illusionary) add to the overall pleasure of those people is the big question. Personally, I'd favor to also cut out the politics section (no need to cry out, it seems pretty clear that the sfn staff has a different attitude towards that and I can/do accept that). Initially, I have a similar attitude towards a religious forum. However, there's two potential problems I have (others might have some others or none): (1) A religious forum is a breeding pool for antipathies that might swap over to the scientific fora if people participate in both sections. (2) I don't want people posting in the scientific sections with a religious background (note that this is not the same as people with a religious background posting in the scientific sections). If there's no religious debate on the site at all, the chance of this happening seems smaller to me. I'd say that's not the right attitude to start participating in a religious subforum. Considering religious and moral issues I do not believe in verificable objective truth and hence not in any possible backup more solid than "I think..." or "I feel that...". Though it might well be my erroneous view of reality, that statement is not up for debate with strangers on the internet. ... like a purely scientific forum? Yep. Problems: The large grey-zone and that the ultimate reason for mod-interference being "we mods feel that..." . Luckily, that's the problem of the admins and moderators, not ours (and especially not mine). For my own opinion: I am against reopening the religious and the philosophy (other reasons there) forum. I'm not gonna cry out loud or even bother too much if it happens. But I think it'll do sfn more harm than good.

But that's all part of the SM already so it does, in my eyes, not contribute to testable predictions (it's rather a sanity-check). For these, there had to be a testable feature that is not part of the SM. A testable prediction would be something in the lines of a Z' peak in ILC-range (which then had to compete with other models proposing Z' peaks). As a matter of fact, "testable" strictly speaking goes down not only to the level that something different from the SM must happen but also that it must be measurable experimentally. I remember that some time ago Martin advocated a paper on black hole production at LHC claiming it was a testable prediction for LQG. Incidently and uncorrelatedly, around the same time (same week) I had a Skype conversation with the guy I shared the office with who was in ... think it was Belgium ... at that time. He told me that he had lunch with some phenomenologists (the kind of pheno people that actually work together with the experimentalists) who were making fun of black hole production at LHC because it gave no distinguishable signal in the detector (e.g. no preferred direction of energy disposition). Now, I neither claim to have enough knowledge of either strings or lqg or even experimental physics. I just wanted to point out that the understanding of the term "testable prediction" might differ from person to person. And to grab a seemingly widespread prejudice: Stringers are notorious for having a very lax understanding of the term. A question on gauge coupling unification: --------------------------------------- Do the couplings of "pure SUSY" (whatever that would mean, say the particle content of the MSSM) actually meet at the GUT scale? I always see these statements in conjecture with sidenotes saying "if you consider a GUT-factor of ..." ... errr ... I think it is "3/5". Do the couplings meet in SU(5), in SO(10), in all GUTs (not sure how many there are) or is it really a general feature of SUSY alone? Or asked the other way 'round: What does the statement about the GUT factor (e.g. in the SUSY-primer by Steven Martin at the place where the graph with the meeting couplings is shown) mean? Making three lines meet by shifting one is not that much of a trick from a purely geometric point of view (although admittedly the factor might come from somewhere else and not from the demand to make the lines meet).

It doesn't explicitely break the rules stated in the OP and is also mentioned in the link given by River_rat which sais "some people have a trick to get around the problem: they send a gas, water, or electric line through one of the houses".

A unit-sphere and a unit-circle are the respective objects of [math] \{ \vec x \, : \, \| \vec x \| = 1 \} [/math] for [math] \vec x \, \in R^3 [/math] and [math] \vec x \, \in R^2 [/math], that's a similarity but not "the equivalence". There is no universal mathematical definition of the term "equivalence", therefore the answer to the thread-title is "depends on what 'equivalence' means". I do not agree that "almost every three-dimensional shape we know of [...examples...] can be formed simply by extending their two-dimensional equivalents": Looking around I spontaneously see exactly no 3D-shape for which an obviously similar 2D shape exists. Examples: Telephone, car, computer, bottle of water, cup of coffee.

I tend towards thinking there is no solution. If you take 2 squares and three circles, then I think there's only one solution, the one in the picture I attached (solutions which are created out of each other by moving around the objects and/or bending the lines are assumed equivalent, so you could move the upper square down without a problem). This solution divides the total area into three subareas 1, 2 and 3. The 3rd square had to lie in one of those areas but for each area, one of the circles is unreachable (1:C, 2:A, 3:B).

If you have some experimental data (not a sketch of the setup, that seems pretty clear) at hand then I'd be interested in taking a look at it.

Slower than lightspeed, lightspeed, faster than lightspeed.

Typo beats spellchecker, I guess. EDIT: As always, I'm not sure to what extend you (Martin) were serious or joking, so: The letters "s" and "d" are next to each other on a keyboard, that's why I'm guessing a typo - but of course I'm not a native english speaker, so I might have gotten it completely wrong.

Darn, blew my cover.

http://www.khalisi.com/jokes/physiker/newmatter.jpg

I'm gonna leave out the details here for simplification: Probably g = 9.81 m/s² which is the gravitational acceleration for all bodies here on earth (as an approximation at least). Yes. Since g is the acceleration all objects dropped from a height H will move according to h(t) = H - gt²/2, where h(t) is the height at time t. The reason for this behaviour is that the masses cancel out: The gravitational force is Fg = m*g. Acceleration is a=F/m = Fg/m => a = g, when Fg is the only force working. Friction only depends on geometry and velocity, i.e. FF = FF(geometry, v). Then, mass does not cancel out in calculating the acceleration and you instead have a = F/m = (Fg + FF)/m = (mg + FF(geometry,v))/m = g + FF(geometry,v)/m. Note that FF and Fg will have opposite directions, hence the acceleration will be reduced. But the heavier the particle, the less the reduction. EDIT: Perhaps I should stop posting when Klaynos is online .

I dunno what Asimov said, but it strongly sounds like the pseudo-norm for vectors - 4-velocity in this case. With the signature of the metric tensor chosen to (-1,+1,+1,+1), this value would be =0 for lightspeed, <0 for velocities below lightspeed and >0 for velocities faster than the speed of light. The 4-velocities only give directions (note that a direction in 4D has the same amount of degrees of freedom as a vector in 3D) and are usually normalized to -1 and +1, respectively (except where the value was 0 in the first place, you cannot normalize that to anything else). Note: In the signature-choice that appears more common to me, namely (+1,-1,-1,-1), the signs are inverted, so don't run around telling people that all sub-lightspeed velocities are negative (not a good idea anyways, unless you can answer the follow-up question "what does that mean?").

Explains why I never really found an answer to the mystical question "what's the opposite of my telephone" (I was tending to "a well-working ultra-modern technical device", btw).