Severian

Agreed.

Sorry - Newton's first law then. Pedant.

Not true. Gluons and presumably gravitons are also massless.

I think you may be thinking about a torque as only originating from one force, which is incorrect and can lead to confusion. If I apply a force to an object and it doesn't move that must mean that there is a force pushing back (Newton's third law). Now that force is pushing exactly opposite to the force I am applying (ie. along the same line). But what would happen if they weren't along the same line? Imagine a table in your office. If I push it I can overcome the fristion and move it about. Now imagine a 'friend' pushing it in the opposite direction - if he pushes from exactly opposite you the table will stay still. But if you are pushing in slightly different directions, the table will turn. The two forces acting in slightly different directions are applying a torque to the table making it turn. You actually don't need the friend to see this - friction will do the job for you. Imagine you push the table from off centre (so you are not pushing towards the centre-of-mass). The frictional force opposing the move does act towards the centre of mass, so your forces are not aligned, you are applying a torque and the table will turn. Alternatively, for a pedal on a bike, you are applying a force to move the pedal and the bit of metal attaching it to the bike. But the bike is holding the pivot - it applies a force to keep the pedal from falling off, but the force is not in line with the force you are applying (since it is at the pivot) and you have an unbalanced torque. Just like an unbalanced force produces a change in linear momentum, an unbalanced torque causes a change in angular momentum and the thing turns.

Have you had experience of our healthcare systems. I have lived in the UK, Germany, France and Switzerland and been in hospitals (and at many doctors) in each (a little brain problem). Compared to the other three the UK's NHS is a pile of steaming doggy poo. In fact, this was so severe that in returning to the UK I took out private health insurance for my entire family so we wouldn't have to rely on the NHS. It is so shit that I don't want it even when it is free!

Really? Is this how it works in the US? I am very surprised. In the UK, you only pay the higher rate on the amount you are over the threshold. So in this case you would only pay the 30% on $1.

Yes, it is. But there is a reason for it - the only point interaction in QED is a photon interacting with an electron.

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What about other bits of the body? If you get a good price for your kidney, could you also get a good price for your retina? How about selling portions of your scalp for hair replacemnet surgery? Or your teeth? Can we transplant limbs or appendages from one person to another yet? Maybe in a few years, these spam emails offering larger penises will have a different angle...

At least it is not completely shit like the UK one.

Note to self: don't read forum posts in reverse order.

I would like: A theory of everything A cheap limitless source of energy which could be generated from the universe itself (ie. no need to refuel with anything) and provide limitless power on nanoscale sizes. A cure for cancer Wormholes which allow you to make gates providing instantaneous passage between two points The fountain of youth - a pill you take that repairs your body back to how you would be in your late twenties or so. An AI that can pass the Turing test (to provide us with artificial sentient life that we can persecute at our leisure)

If you want to do that, the most interesting paper in Friday's list is arXiv:0711.2473, Parton Distributions for LO Generators, A. Sherstnev, R.S. Thorne But maybe I am just boring...

I think the biggest problem with progressive taxes is that they don't tax the rich the most. They tax the middle classes the most. The rich can pay for tax lawyers to find tax loopholes.

As Mr Skeptic said, you don't need to go into the 'void' where the big bang is expanding into (which would be a little hard anyway since it doesn't exist - the Big Bang happened everywhere at once). In principle, even sitting on the Earth, if you look far enough away you will look right back to the big bang, since anything 13.7 billion light years away must have emitted the light you are seeing now at the big bang. In principle this is not quite true since at the big bang and for a while afterwards the universe was so dense and hot that it was opaque to photons. So you can't 'see' earlier than that time. And this 'surface of last scattering' (which is fancy name for the boundary at which the universe became transparent to light) is exactly what the COBE and WMAP satellites were looking at when they examine the CMBR (Cosmic Microwave Background Radiation).

To expand on ajb's answer, as an example, the Lagrangian for QED is: [math] {\cal L} = -\frac{1}{4}F^{\mu \nu} F_{\mu \nu} + \bar \psi \left( i \gamma^\mu \partial_\mu +m \right) \psi [/math] In principle, everything you need for QED is in that formula (once you define the notation) - it completely specifies the theory (which is quite neat I think). Edit: the link works fine for me.

I suppose it depends on what you are used to. I find the traditional form much more intuitive.

It is just a matter of perspective. There exists a frame in which the orbit is the straight line, so is exactly what Newton would tell you happens with no gravitational force.

Can't we have a 'None of the above' option?

One could certainly argue that you are perfectly weightless when in freefall. Since GR is all about making all frames of reference (inertial and non-inertial) equivalent, then in the frame co-moving with you, there is no gravitational force, so you are weightless. Massless is rather different. Most of your mass comes about from the strong interaction binding quarks into protons and neutrons in your body. So to become massless you would need to switch off the strong force, which may be rather unhealthy...

I was somewhat bemused by a paragraph in the article: "The film also depicts the personal lives of some of the people behind Hell House, such as the father of four whose wife has run off with a man she met over the Internet (a similar situation is played out in Hell House)." Is this somehow passing judgement on this father? Is the article implying that one cannot/shouldnot be a Christian if your wife runs off with another man? I suppose the important question is, are the children who go to the 'Hell House' forced to go?

I was amused to discover recently that one of our departments now has a zero fail rate. Their assessment has two possible outcomes: 'passed' and 'not yet passed'.

It really depends what you mean by 'size'. Normally one applies the word 'size' to macroscopic objects, like a table - we define its size by touch, or by bouncing light off it. Both of these are simply interactions with the atoms in the table, and in fact we never make comntact between the atoms in our fingers and the atoms in the table - they are repelled by electromagnetism before we get there. So, 'size' is difficult to define. Does it mean the distance at which you start to interact with the object? In that case, and electron for example has infinite size because its electromagnetic field extends forever (though getting very small). A photon is neutral so generates no such electromagnetic charge, but in principle if you get really close you will start to distinguish it converting into electron-positron pairs and back again. The electrons and positrons are charged but very close together. So it still looks neutral from a distance, but if you get up really close you will start to feel an electromagnetic force. In other words, the photon does have a size, since you start to feel it pushing back against you if you go to close. This happens at about half a fermi, or roughly [math]0.5 \times 10^{-15}[/math]m.

More interesting is what happens if you add an extra dimension and try and use Maxwell's equations in 5d. Then you find that you get a theory which looks very much like electromagnetism+gravity. This was first developed by Kaluza and Klein way back in the early 20th centuary. Edit: And looking at your webpage, how do you justify e.g. x1 depending on only t1 and not t2 or t3?

But it should be.