Severian

Well, its better than 'Tracy'...

He was working for CERN at the time. CERN should have slapped on a $0.0000001 charge per internet click for using the web, and we would have no problems funding particle physics research....

So we have gotten rid of one terrorist. Who is up for bumping off the other one? Sharon looks fat enough for a massive heart attack, no?

Nothing stops it. In principle the orbit will decay eventually. It is just that space is so empty and the Earth is so big (compared to objects which would steal its momentum in collisions) that it will take an incredibly long time to decay - longer than the lifetime of the sun. That is why satelittes have finite lifetimes: they are no so big, so collisions with small dust particles steal a sizable chuck of their momentum and energy, and eventually down they come. Edit: incidentally, in a perfect vacuum, with no other forces involved, the orbit would last 'forever'. It is interesting that this is only true for a law of gravity which is 1/r2. No other distance law gives stable orbits, so it is fortunate indeed.

Yes, you are right I think. You would have two photon exchange processes: the electron emits a photon, becoming virtual (ie. having borrowed energy) and then would have to emit/absorb another photon before the [math]\Delta t[/math] was up. It is interesting that that is a higher order process though, so will have a smaller probability of happening. That means that this should be testable: reduce the temperature to 'near' zero and see if the effective charge is reduced. I doubt it is actually visable though since you also have the change in effective charge coming from the variation in [math]\alpha_{em}[/math] from the change of the energy scale.

Well, it is all very well for them to say that they will attack neutral targets in space, but if they actually do it I would have thought they would be in big trouble. The US legal system is presumably sufficiently robust that the owner of the satelitte would be able to sue the USAF for billions and billions of dollars. No?

I think we are arguing semantics here, or in other words reading the question differently. The question was: I read this the first time as meaning that you throw the bal off the back into the air while travelling at 70mph. I assume TWJian read it this way too. In this case the ball would continue at 70mph, with a little bit of a reduction from air resistance as TJWian said. However, I think the rest of you are reading it as throwing the ball backwards with a velocity relative to the thrower of -70mph. (Rereading the question I think this is what was intended.) In this case, as you all say, the ball would just drop straight down.

Hmmmm.... but that isn't free energy. They are not allowed to drop into lower energy states if they are already filled.

I think I see where you are coming from now 1veedo..... ...although I still disagree. The confusion is arising because of the analytic continuation from a Minkowski metric to a Euclidean metric. The time dimension is converted into a 'space' dimension by analytic continuation into the complex plane. But this is just a mathematical trick in order to solve the mathematics - it isn't really being turned into a space dimension. They just do this to solve the maths and then continue back again to the usual 3+1 Minkowski metric.

Yes, you are right - in order to transfer energy from one to the other, there has to be energy there in the first place. But each photon is transmitting such a small amount of energy that it can just take it from the matter particles which is feeling the force (which will have plenty energy of its own). For example, the electromagnetic interation between two electrons is the exchange of a photon. One of the electrons emits a photon, whose energy is thus coming from the electron itself, and the photon travels over to the other electron who absorbs it and its energy. This will be happening all the time, with energy passed backward and forwards between the two electrons. PS: This also answers the question in the other thread about whether or not one could still have gravity at zero temperature. If zero temperature were really possible, no particle in the object could emit a graviton since it has no energy to give it and there would be no gravitational force. Since zero temp is impossible, this is a bit academic though...

Why would you need 2 time dimensions to have colliding branes? One is enough. You can have 2 surfaces in a higher dimensional space collide with only one time dimension - it is just the higher dimensional analogue of dropping a piece of paper on a table. I don't need two time dimensions to do that - do you?

Yes and no. You are right in saying that the photons or gravitons transfer energy between the two bodies which are interacting, but it is a two way process. There is no energy being 'used up' and it can be transfered back and forwards as often as you like. So the Earth and the Sun are presumably exchanging gravitons (and thus energy) backwards and forward between each other (I say 'presumably' since gravitons have not yet been observed). You can find a lot of information sites about particle physics on the web. For example: http://particleadventure.org/index.html http://public.web.cern.ch/Public/Content/Chapters/AboutCERN/WhyStudyPrtcles/WhyStudyPrtcles-en.html http://www.cpepweb.org/ http://www.aps.org/units/dpf/quarks_unbound/

Why do you say this? Our theories explain how gravity and magnetism work very well. Magnetism for example is caused by the universe having a local U(1) symmetry. Why the universe has a local U(1) symmetry is of course not yet clear, but if one accepts that it has, electromagnetism is a natural consequence.

Publishing a book is not a test of scientific merit. Shall we look and see how many science papers Mr McCutcheon has published in scientific journals: http://www.slac.stanford.edu/spires/find/hep/www?rawcmd=FIND+A+MCCUTCHEON%2C+m Doesn't inspire much confidence, does it?

You appear to suggest that I believe there is no time dimesnion at all. I am sorry but I don't believe any of this. Could you please provide links to Guth's papers on his 'multiverse' theories where he has multiple dimensions, and links to papers describing M-theory with 2+ time dimensions. Because every M-theory paper I have ever read has 1 time dimension; the branes are separated in space, not time.

Defining x as the distance up the ramp and calling the angle of the ramp [math]\theta[/math], you have: The force in the x direction: [math]F=-mg \sin \theta=m a[/math] Integrate this to get: [math]v=u-g \sin \theta t[/math] Integrate again: [math]x=ut-\frac{g}{2} \sin \theta t^2[/math] At the maximum, [math]v=0=u-g \sin \theta t[/math] so [math]t=\frac{u}{g \sin \theta}[/math] (this is what Swantson said) Putting this into the equation for x: [math]x=\frac{u^2}{g \sin \theta} - \frac{u^2}{2g \sin \theta} = \frac{u^2}{2g \sin \theta} = \frac{60^2 m^2s^{-2}}{2 \times 9.81 ms^{-2} \sin 60^o} = 212m[/math]

Yes, we do understand pretty well how gravity works, just not in special cases (very small distances and very high energies). And we understand how magnetism works extremely well - amazingly so that there has never ever been an experimental observation of magnetism which we cannot explain with the theory. The website you quote (as Swantson points out) is written by an utter moron. This guy knows nothing about science, and the descriptions of 'science mistakes' are so bad I was getting embarressed reading them. Avoid at all costs.

That book is truely amazing. How could anyone possibly get that published!??

Sorry - I misread your post. I agree that we need to have at least one dimension of time, so I think it was your statement which was the strawman - to suggest that there be no time dimension is jsut silly. Fair enough, so justify the statement. I just posted a review on inflationary cosmology by Guth himself, who you cited as having invented cosmologies which require multiple time dimensions. He does not mention multiple time dimensions! If the alleged creator of the theories of multiple time dimensions does not deem them fit to mention in a review article, it does not seem justified to suggest that 'most cosmologies' include multiple time dimensions.

No - I am happy to entertain new ideas. I was objecting to your statement that most theories have multiple time dimensions, or that multiple time dimensions was somehow natural.

No! Inflation does not have two time dimensions. Look at astro-ph/0404546 which is a review (by Guth) of inflation. There is most certainly only one time dimension - look at the signature of the metric after Eq.(1.4). No it isn't. The branes are separated in space, not time. Oh, there may be one or two bizarre models out there which do have multiple time dimensions but they are the sort of theories which do not get good receptions at conferences....

1veedo: I will repeat, theories with multiple time dimensions are not conventional. They exist but are certainly not mainstream. M-theory for example, does not have multiple time dimensions. Your claim that there are 2 time dimensions is just nonsense. In fact, there is even a well known proof that the number of time dimensions must be odd! Furthermore, constraints on extra time dimensions have been shown to be prohibitive. Unfortunately I was unable to find an M-theory text which explicitly says that there is pnly one time dimension (it is just assumed, because of the causality problem). However here is an M-theory basics (very basic!) page. It explicitly states that "A p-brane spacetime whose metric solves the equations of motion for a (p+2)-form field strength in d spacetime dimensions can be described using p space coordinates {yi} along the p-brane and (d-1-p) space coordinates {xa} orthogonal to the p-brane." which implicitly supposes that there are d-1 space dimesnions and thus 1 time dimension. (It is quite a nice site actually.)

Yes. It is the conjugate (antiparticle) of the W-, the W+. so you have [math]u \to W^{+}d\to e^+ \nu_e d[/math] PS: Notice that is a neutrino which is emitted, not an anti-neutrino, since in this case it is the e+ which is the anti-particle. PPS: CP invariance tells us that the matrix element for this decay is the same as the previous decay (of the d). So the only reason why this only happens in special cases is because of the restricted phase space (as Swanston pointed out earlier).