Severian

Once energy is not a problem, then gravity won't be either. If you are going on a long journey, just keep the ship accelerating at 1g and you will have normal 'gravity'. Half way to your destination, flip the ship around and decelerate at 1g. Constant acceleration is the fastest way to get to your destination - the only problem is that it takes a lot of energy.

Didn't you ever bother to ask your wife what she believes before getting married and having a child?

To paraphrase the tree, I'd be grateful if you could source that claim.

When I was a student we used to have a Cannabis plant sitting on top of our fridge. We actually gat raided by the cops once during a party - they were looking for drugs, but didn't find any, miraculously missing the plant sitting in full view.

Actually, I get irritated by the opposite: people who use the expression 'multiverse' to denote 'multiple universes'. If the 'universes' in question in a 'multiverse' are casually connected (ie. events in one can effect the other) in what sense are they separate universes? After all, I don't count London and New York as being in separate universes just because they are on opposite sides of the Atlantic. The only justification for classifying two regions of space as being in different universes, is if events in one cannot in principle affect events in the other. But in this case, we can never ever test the existence of the other 'universe', so what is the point? The 'universe' is by definition everything we can experience/measure, so there is only one.

That is presumably because people have stopped getting married.

If he is as rich as you say, and yours sister gets 'dumped' at age 40, she will never have to work again in her life. I have a BMW and a Longine watch - does this make me a bad person? I personally think an appreciation for beauty is a good thing. It is just that one should be able to see inner beuaty as well as outer beauty, but I see no indication in your post that he appreciates one and not the other (on the other hand, it is obvious that you do appreciate one and not the other). I think you should leave well alone.

This isn't unique to Left Behind. You cannot complete Half Life 2 for example without killing lots and lots of (virtual) people, therefore, by definition, the 'right thing to do' in the game is to kill. I have never played GTA, so I am not sure that you have to commit acts of violence to win the game, but I am fairly sure that you do need to steal cars. So are you claiming that FTA is fine because stealing cars is the 'right thing to do'? I think consideration should be taken of context. GTA happens in (allegedly) the 'real world', so it presents a rather poor role model for teenagers who must function in that real world. In contrast, Left Behind is set in a world after the second coming, so it is hardly a real life situation. I really don't see how it is any different from HL2 or say Doom 3 (which had demons in it, if your objection is any form of religion protrayed in games).

I hope you remember that principle when discussing the political views of particular groups on the right, rather than just "the right"

There is still a gravitational potential difference between the ships if they are accelerating at different rates.

I think your original question and your example are both very amibiguous. The Casimir effect is normally examined under conditions of zero 'background field', ie a true vacuum with no sources. Obviously if you put a charge on the plates, they will feel an electromagnetic attraction or repulsion, but that is not what we are after. In your example, you have applied a field between the plates in one experiment and not in the other. The accelerating ship is sitting in a gravitational potential, so obviously the force between the plates will be different. But this is also true if I apply an electromagnetic field, so nothing new there. I think what you are really trying to ask is, examining a pair of plates infinitely far from any gravitational source (impossible of course, but nevermind that), if I could switch off gravity (altogether, no gravitons of any form) would the casimir force between the plates change? This is a bit difficult to say, since the Casimir effect is a quantum effect but we don't have a quantum theory of gravity. My gut feeling is that it would in principle change the force. After all, the Casimir effect happens by plucking out vitural particle anti-particle pairs from the vacuum and pulling them towards the plate. In principle, since the plates have mass (or more precisely energy) this can happen using gravitons. If those gravitons are missing, then there is no effect from them. However, this effect would be very very small. Gravity (we think) is many many orders of magnitude weaker than the other forces, so I very much doubt this would be measurable unless you had very very big plates! What does this have to do with the value of the zero point energy? (This is another difficult topic, since we don't undestand it either!) Well, the zero point energy provides a cosmological constant, which you can think of as a uniform curvature of space. So, if there is a cosmological constant, the true vacuum (without any gravitational sources) already has a gravitational field, so the casimir force will change. However, that is cheating since the casimir force is supposed to be in zero field (a true vacuum), so to be fair you would need to place gravitational sources in such a way that the effect of the cosmo constant is cancelled out...

Could you please explain the mechanism for this creation of 'new universes' from black holes? I am not even very sure what you mean by 'universe' in this context.

Which land? Obviously the arabs who were displaced must have owned land before, and didn't own it afterwards. So who got this land? They were refugees running away from a war, who were then prevented from returning to their homes at the end of the war. This is hardly 'self-created', and quite frankly to say it is is a lot more inflammatory than the Iranian ambassador's remarks. By refusing to let the palestinians return to their homes, it was instantly a country of exclusion.

I thought you might be interested in Polchinski's review of Woit's and Smolin's books: http://cosmicvariance.com/2006/12/07/guest-blogger-joe-polchinski-on-the-string-debates/ Rather predictably, he doesn't like them much, but he brings up some interesting points.

Dark energy is needed to explain why the expansion of the universe is as it is. Dark matter is needed to explain rotation curves of the galaxies and the variations observed in the CMBR. So Dark matter is more of a local matter like phenomenon, while dark energy is more a global, structure of space-time sort of thing. because it has no electric charge (that is just the definition of 'dark' in this context). They do! (I am not quite sure what you are meaning here.)

This looks wrong to me. The elastic potential energy is [math]E_E = \frac{1}{2}kx^2[/math] where k is the spring constant, and x is the extension of the spring beyond its natural length. Usually one would write the gravitational potential energy of an object is [math]E_G = mgh[/math] where m is its mass, g is the acceleration due to gravity and h is the height from some arbitrary ground level. Then, taking the zero of the gravitational potential at the height of natural extension of the string, [math]E_G = -mgx[/math] which is clearly not inversely proportional to [math]E_E = \frac{1}{2}kx^2[/math]. However, this gravitational potential is just an approximation, so maybe they want you to use [math]E_G = -G\frac{Mm}{r}[/math], where M and m are the mass of the Earth and object respectively, r is its distance from the centre of the Earth and G is the gravitational constant. (This reduces to the previous example for small deviations form the zero point.) But again, this isn't inversely proportional to the elastic case.

Well, you are talking at cross purposes. If you keep the density fixed and increase the volume then clearly the mass changes (this is the sense in which "So it's the "m" part of mc2 that changes, not the "c" part"). But obviously the mass of an object is fixed, so really, if you 'stretch' it into an extra dimension, its volume increases and its density decreases to compensate. E=mc2 still. In other words, the energy is always proportional to the mass (for an object at rest), but is not necessarily proportional to the density.

I think I see your problem. You are getting confused by the difference between mass and density. An object of fixed density would clearly have more mass if it was extended into another dimension (since it has more volume), and thus it would store more energy. However, an object of fixed mass obviously doesn't have more mass, so doesn't have any more energy either. To put this is equations: In 3D, for a cube of length L, mass m = d L3 where d is the density. So the enrgy contained in the mass is E = mc2 = d L3c2 In 4D, for a cube of length L, mass m = d L4 where d is the density. So the enrgy contained in the mass is E = mc2 = d L4c2

I am not sure about that. Why use polonium. Why not just use cyanide? Cyanide is easier to get, a lot less tracable, would kill just as surely and wouldn't attract so much media attention. It seems like a particularly inconvenient way to kill someone...

Well, John Ellis is the ultimate fanboy of supersymmetry. But I was being tongue in cheek - I know John very well, and have a lot of respect for him. He has a bit of a reputation of overpublishing - he publishes a huge amount of papers, most of which don't have much content, but his work still contains more constructive results on susy than pretty much anyone else. There is this joke in particle theory, that every published phenomenologist is at most one collaboration removed from John, i.e. Everyone has written a paper with someone who has written a paper with John. The scary thing is, that it is true!

No - that isn't true. Even in a 2d world (one time dimension, one space dimension) we would still have E=mc2.

I am tempted to add: John Ellis needs supersymmetry more than supersymmetry needs John Ellis.

Well, it is not terribly clear what you are trying to say. You seem to be saying that momentum is not conserved, which really would be a crackpot notion, but I suspect you are being deliberately obtuse. Conservation of momentum is a very simple concept and is required for space-translation-invariance of the laws of physics. You can't just throw it away. As I said before, the only effect that you could have of the kind you describe would be from the internal motion of the fuel changing the centre-of-mass such that the fuel is ejected in a different direction. Since I had this in my previous post and you ignored it I can only assume that you disagree. So please tell me why you disagree with conservation of momentum?

*sigh* You don't seem to be understanding this, do you? Which bit aren't you following? The rate of change of momentum is given by the net force. If the momentum of the fuel is in one direction the rocket goes in the other, period. You can't change that - as Scotty would say 'you cannie change the laws of physics'. The effect that you are claiming is probably due to you changing the direction of the fuel flow by changing where the exhaust is in relation to the centre-of-mass of the rocket and remaining fuel. Obviously if you change the direction that you eject the fuel, the rocket will change directions, but that is hardly... rocket science... and is completely not the point of the discussion here.

It makes no difference where the back of the rocket is compared to the centre-of-mass. As long as the fuel leaves the rocket in a constant direction, there is no change, since the only important thing is the change in momentum.