The Universe
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Off With Their Heads
Member # 4045
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written Tuesday, March 29 2005 05:18
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As I understand it, there are some problems with absolute zero. Particles need not have mass. Photons don't. They have energy, which can sort of be thought of as mass, but it's more reasonable to say they have energy. Ultimately, the problem in talking about this is that the Newtonian ideas that are easy to discuss don't quite work in quantum or relativity. Quantum mechanics is by far the most proven scientific theory in history, though. It is bizarre, and you are not the first one to say that it is bizarre, and many people have tried to disprove it, and they can't. But here: if photons actually had mass, then by going at the speed of light, they'd have INFINITE mass, because one of the relativistic laws is that objects with mass gain mass as they travel faster. It's much less logically contradictory to say that photons have zero rest mass, and this works fine because photons can never be at rest anyway. -------------------- Arancaytar: Every time you ask people to compare TM and Kel, you endanger the poor, fluffy kittens. Kelandon's Pink and Pretty Page!!: the authorized location for all things by me The Archive of all released BoE scenarios ever Posts: 7968 | Registered: Saturday, February 28 2004 08:00 |
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...b10010b...
Member # 869
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written Tuesday, March 29 2005 05:46
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Frankly, it's quite surprising that photons manage to avoid fouling up the laws of physics as artfully as they do. They have momentum, which is about as close to having mass as you can get without actually having mass. -------------------- My BoE Page Bandwagons are fun! Roots Hunted! Posts: 9973 | Registered: Saturday, March 30 2002 08:00 |
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Shock Trooper
Member # 4214
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written Tuesday, March 29 2005 07:38
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quote:I am not even thinking about trying to disprove the quantum-theory, but some of its minor aspects confuse my defective mind. quote:I think - although I am, most-probably, mistaken - it is vice versa; An object which moves, loses some of its matter, which is converted into kinetic energy. An object which moves also keeps moving in the same way until something affects its movement. However, it would take nearly infinite energy to make a photon match the speed of light if it would have mass. At least, that is what I have read. quote:Which laws are you referring to? quote:Can particles consist of other energy than matter? I doubt it. My ignorance is not only irritating you, but me as well. Please keep that in mind. [ Tuesday, March 29, 2005 07:41: Message edited by: Mind ] Posts: 356 | Registered: Tuesday, April 6 2004 07:00 |
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Off With Their Heads
Member # 4045
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written Tuesday, March 29 2005 07:55
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You really just need to buy a textbook on this. quote:No, not at all. If that were true, then objects could start moving spontaneously without violating conservation of energy. Objects need to acquire energy in order to start moving, and at relativistic speeds, some of that energy goes into increasing the object's mass. quote:Eh, close, but not quite. It's not that it would take "nearly" infinite energy; it would take EXACTLY infinite energy. You end up dividing by zero when you're trying to figure out the kinetic energy of a particle that has mass that's going the speed of light. The only reason that photons can go the speed of light is that they have no mass. quote:It's not that they consist of it, per se; it's that they have it. An object may not consist of velocity, but it can have velocity. Similarly, photons can have momentum (and I think here we're talking about quantum momentum, which doesn't require mass -- this is still a few weeks ahead in the course that I'm taking, so I can't explain it quite yet), but photons do not have mass. Let me repeat that: photons have energy but no rest mass. The funny thing is that I literally just came back from a class lecture on this. -------------------- Arancaytar: Every time you ask people to compare TM and Kel, you endanger the poor, fluffy kittens. Kelandon's Pink and Pretty Page!!: the authorized location for all things by me The Archive of all released BoE scenarios ever Posts: 7968 | Registered: Saturday, February 28 2004 08:00 |
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Shock Trooper
Member # 4214
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written Tuesday, March 29 2005 08:53
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quote:I am reading a book concerning the quantum mechanics, as I said, but the majority of its contents is uninteresting and irrelevant. Specific theories such as "If protons and neutrons collide with enough kinetic energy, they can form pions and mesons." concerning the quantum mechanics do not interest me at all. In fact, I'm no longer about to seek another, more interesting book concerning this subject. It's hopeless. [ Tuesday, March 29, 2005 08:56: Message edited by: Mind ] Posts: 356 | Registered: Tuesday, April 6 2004 07:00 |
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Electric Sheep One
Member # 3431
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written Thursday, March 31 2005 05:12
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Energy is not an alternative kind of stuff. It is a property. You have energy in the way that you have height, not in the way that you have blood. So things are never 'made out of energy'. Anything massless must always move at the speed of light; anything moving at the speed of light must be massless. The two properties necessarily go together. It's quite true that photons have momentum but no rest mass. This is not quite the same thing as having no mass, though. A box full of light (for instance a box with very reflective insides, or a hot box that was glowing) would actually have slightly higher mass because of the energy of all the light inside: For a motionless object, like the box, E = mc^2 cuts both ways. Heat is not only vibration of molecules. Heat is the amount of energy that is tied up in random motion or vibration or whatever. It's the randomness that makes it count as heat. Randomly bouncing light waves carry heat; a laser beam does not. Exactly what counts as 'random' is a very subtle question, though. Extreme cases are easy to classify, and it is fortunate that practically every case of practical importance is either extremely random or extremely non-random. As an issue of principle, though, the nature of heat is still rather puzzling. -------------------- It is not enough to discover how things seem to seem. We must discover how things really seem. Posts: 3335 | Registered: Thursday, September 4 2003 07:00 |
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Off With Their Heads
Member # 4045
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written Thursday, March 31 2005 05:20
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I was under the impression that E=mc^2 didn't have a lot of relevance here, because we're really talking about E^2 = p^2*c^2 + m^2*c^4, and m=0. That is, E=pc is the more relevant equation -- so the photons have momentum but no mass. [ Thursday, March 31, 2005 05:21: Message edited by: Kelandon ] -------------------- Arancaytar: Every time you ask people to compare TM and Kel, you endanger the poor, fluffy kittens. Kelandon's Pink and Pretty Page!!: the authorized location for all things by me The Archive of all released BoE scenarios ever Posts: 7968 | Registered: Saturday, February 28 2004 08:00 |
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Electric Sheep One
Member # 3431
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written Thursday, March 31 2005 09:29
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But the photons do contribute to the energy of the box as whole, which has zero momentum (by assumption). The individual photons are massless; yet the aggregate of all of them does have a mass, correctly given by the formula you quote, but with p = 0 because the aggregate has no net momentum. Of course, with the huge c^2 factor now in the denominator, the mass of the energy of any reasonable intensity of light is very small. But a boxful of light does weigh something. -------------------- It is not enough to discover how things seem to seem. We must discover how things really seem. Posts: 3335 | Registered: Thursday, September 4 2003 07:00 |
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Triad Mage
Member # 7
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written Friday, April 1 2005 00:54
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p = mv - if it has no mass and has momentum, then there's another conundrum. -------------------- "At times discretion should be thrown aside, and with the foolish we should play the fool." - Menander ==== Drakefyre's Demesne - Happy Happy Joy Joy desperance.net - We're Everywhere ==== You can take my Mac when you pry my cold, dead fingers off the mouse! Posts: 9436 | Registered: Wednesday, September 19 2001 07:00 |
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Off With Their Heads
Member # 4045
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written Friday, April 1 2005 04:50
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quote:As I said. The equation p=mv holds up in higher-level physics just about as well as F=ma. -------------------- Arancaytar: Every time you ask people to compare TM and Kel, you endanger the poor, fluffy kittens. Kelandon's Pink and Pretty Page!!: the authorized location for all things by me The Archive of all released BoE scenarios ever Posts: 7968 | Registered: Saturday, February 28 2004 08:00 |
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Electric Sheep One
Member # 3431
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written Friday, April 1 2005 05:29
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p = mv does not hold in special relativity, at least not if 'm' is the rest mass. In terms of the rest mass, the relativistic particle momentum is p = m (1-v^2/c^2)^(-1/2) v. One alternative notation is to define M = m (1-v^2/c^2)^(-1/2) as the velocity-dependent mass, in which case one can preserve the form of the equation p = M v. This is just playing with notation conventions, and all the relativists I know prefer to use 'mass' to mean 'rest mass' always, and let the relationship between momentum and velocity be different from Newton's. In neither case does the formula make sense for the case of zero rest mass, because then v is always c, and one has p = 0/0 = ?. The resolution is to work from the alternative formula for momentum, p = (E^2/c^2 - m^2 c^2)^(1/2). This gives p = E/c if m = 0, with no ambiguity at all. Quantum mechanics does change the notion of momentum in one sense: it makes momentum the primary quantity, rather than velocity. One very rarely writes v in quantum mechanics, but p is everywhere. So one is more likely to write p/m instead of v. But apart from this subtle shift of perspective, Kelandon is right that the relationship between velocity and momentum is not changed by quantum mechanics. That's in nonrelativistic quantum mechanics. It is possible to combine relativity and quantum mechanics, but the startling consequence is that it becomes impossible to restrict oneself to considering only a single particle. Photons appear and disappear all the time, for instance. Relativity plus quantum mechanics automatically creates the possibility that particles can appear or disappear, and this means one must use quantum field theory. Quantum field theory is an appallingly complicated subject. It is notorious that there are no really good textbooks on quantum field theory, but the best ones are all massive great tomes. So QFT is usually reserved for graduate school. Kelandon's comment that F = ma survives in quantum mechanics is also interesting. (It isn't true in special relativity; what remains true is F = dp/dt, but p now depends on v in a more complicated way than in Newtonian physics.) F=ma could certainly be preserved in nonrelativistic quantum mechanics. But nobody ever uses it. In quantum mechanics one works directly with potentials, rather than with forces. It would be a pointless appendix to a completed quantum calculation, to go back and work out what all the forces were, just so that you could have something to say to a Newtonian who really wanted to know them. It would be just about as pointless to work out what all the accelerations were, because the point of a quantum calculation is to find the wave function, not the trajectory of a particle. But if you did both these things, just for the hell of it, you would indeed find that F = ma, in nonrelativistic quantum mechanics. -------------------- It is not enough to discover how things seem to seem. We must discover how things really seem. Posts: 3335 | Registered: Thursday, September 4 2003 07:00 |
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Off With Their Heads
Member # 4045
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written Friday, April 1 2005 05:35
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What I was saying is that two of them don't particularly hold up in relativity or quantum. (Particularly relativity; I haven't done enough quantum yet to really see what's going on with it.) [ Friday, April 01, 2005 05:37: Message edited by: Kelandon ] -------------------- Arancaytar: Every time you ask people to compare TM and Kel, you endanger the poor, fluffy kittens. Kelandon's Pink and Pretty Page!!: the authorized location for all things by me The Archive of all released BoE scenarios ever Posts: 7968 | Registered: Saturday, February 28 2004 08:00 |
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Shock Trooper
Member # 4214
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written Wednesday, April 6 2005 11:57
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I've read an intriguing theory which explains how the singularity could explode, despite its absolute gravity; Atoms constantly move 300 km per second, colliding with other nearby atoms. Because they collide so frequently with other atoms, their speed is reduced to 1 mm per minute. When subatomic particles collide with enough kinetic energy, they create new subatomic particles. The atoms of the singularity were colliding so frequently - considering its density - that they caused enormous explosions of countless subatomic particles. Posts: 356 | Registered: Tuesday, April 6 2004 07:00 |
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Apprentice
Member # 5662
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written Wednesday, April 6 2005 14:23
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i think that if colisions between atoms are very frequent, their speed should increase, because there is an increase in temperature. this gradual increase in speed and temperature would eventually cause singularity to blow up what i do find wierd is that singularity can explode when there is endless gravity to hold it together but my knowledge of physics is very limited. correct me if i am wrong [ Wednesday, April 06, 2005 14:23: Message edited by: imho ] Posts: 38 | Registered: Sunday, April 3 2005 08:00 |
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Off With Their Heads
Member # 4045
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written Wednesday, April 6 2005 14:31
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Well, even though there is a ridiculous amount of gravity involved in a black hole, it's not an infinite amount -- there is a very definite limit. From what I've heard, our understanding of singularities is somewhat limited at the moment, so while there are many interesting and compelling theories, we need a lot more research before we can know the details of what's going on inside. -------------------- Arancaytar: Every time you ask people to compare TM and Kel, you endanger the poor, fluffy kittens. Kelandon's Pink and Pretty Page!!: the authorized location for all things by me The Archive of all released BoE scenarios ever Posts: 7968 | Registered: Saturday, February 28 2004 08:00 |
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Electric Sheep One
Member # 3431
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written Wednesday, April 6 2005 15:37
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Yeah, air molecules at room temperature are going at around the speed of sound (not a coincidence), but hit each other so often that they don't actually get very far very fast. (I don't see much sense in the mm/s figure, though. Diffusion is not described by any steady speed, and average drift speed of air molecules can be as fast as the wind blows.) Even the productive collisions of high energy particles still conserve energy, though. Collisions per se do not produce energy, so neither temperatures nor speeds increase. Chemical or nuclear reactions are another story, of course; they conserve total energy, but release a lot of potential energy into heat and light. There are nuclear reactions that can occur at enormous temperatures and densities, which can release a lot of energy. One of the two types of supernovas happens this way. Black holes are even more of another story, though, I'm afraid. Our current theory of spacetime, Einstein's general theory of relativity, prescribes a singularity at the center of a black hole. Probably the theory is wrong at this point, and in reality there is no singularity; but we have no idea what there might be instead. As far as current theory goes, though, none of the ideas mentioned in the posts above make any sense for a singularity. A singularity has finite mass, but infinite spacetime curvature, and hence I think one could fairly say that the force of gravity is infinite there. But even referring to a singularity as 'there' is misleading. The singularity in an Einsteinian black hole is not an infinitely dense object. It is not an object at all, and it is not composed of any kind of particles. It is not even a place. The singularity in the heart of a black hole is an instant in time. (In technical language, a spacelike hypersurface.) It isn't heaven or hell, it's judgement day. That's why, once anyone crosses the event horizon, they cannot resist moving inwards to the singularity: if you are inside the event horizon, then the singularity is your future, and it is the flow of time itself that moves you towards it. The theory of Hawking radiation, as it has been developed so far, does not really deal with singularities. It could well be that this is reckoning without our host, and the Hawking effect fails because of some singularity feature. [ Wednesday, April 06, 2005 15:38: Message edited by: Student of Trinity ] -------------------- It is not enough to discover how things seem to seem. We must discover how things really seem. Posts: 3335 | Registered: Thursday, September 4 2003 07:00 |
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Warrior
Member # 4590
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written Thursday, April 7 2005 05:56
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Just FYI, incase you didn't already know about it, check out the sci.physics FAQ, it talks about some of this stuff http://math.ucr.edu/home/baez/physics/. Also, some stuff about particle physics http://particleadventure.org/particleadventure/. I don't think anyone's mentioned these links already. -------------------- I often quote myself. It adds spice to my conversation. - George Bernard Shaw Posts: 103 | Registered: Sunday, June 20 2004 07:00 |
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Apprentice
Member # 5662
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written Friday, April 8 2005 09:09
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so, the best definiton for singularity is basically something where there is neither time, nor space? cool it is like before the universe appeared. maybe our universe is the result of, lets say, the "explosion" of a singularity? what about that? Posts: 38 | Registered: Sunday, April 3 2005 08:00 |
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Warrior
Member # 2711
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written Friday, April 8 2005 12:36
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I only read te first few posts, but I have my own theory about this. The universe is said to be ever-expanding, think of another thing that keeps expanding for an indefinite amout of time. That's right, we're a tumor. -------------------- spiderweb soft make an mmorpg! Posts: 126 | Registered: Wednesday, February 26 2003 08:00 |
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...b10010b...
Member # 869
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written Friday, April 8 2005 15:09
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quote:It sure did, at least as far as we can tell. If you read a few books about cosmology, you'll find a lot of them talk about the "Big Bang singularity". -------------------- My BoE Page Bandwagons are fun! Roots Hunted! Posts: 9973 | Registered: Saturday, March 30 2002 08:00 |
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Shake Before Using
Member # 75
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written Friday, April 8 2005 15:39
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Midknight Warrior> Lava and strong acid can both be fatal to humans when applied to their skin, but this does not mean that lava is a strong acid. Posts: 3234 | Registered: Thursday, October 4 2001 07:00 |
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...b10010b...
Member # 869
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written Friday, April 8 2005 15:53
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quote:Actually, the sulphates in lava decompose to sulphur dioxide at high temperatures and react with water vapour in the air to produce sulphuric acid, so your example is poor, even if your point is good. :P [ Friday, April 08, 2005 15:54: Message edited by: Levitating Netherlander ] -------------------- My BoE Page Bandwagons are fun! Roots Hunted! Posts: 9973 | Registered: Saturday, March 30 2002 08:00 |
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Law Bringer
Member # 335
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written Friday, April 8 2005 22:14
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Gas in vacuum expands infinitely, too, much like the universe. We're gas! —Alorael, who wouldn't like to get either lava or strong acid on his face. Cold lava wouldn't be so bad, though, though it might hurt if thrown with enough force or dropped from a significant height. Weak acid is only bad when it's in your eyes, unless it's very hot weak acid, which may cause burns. Posts: 14579 | Registered: Saturday, December 1 2001 08:00 |
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Bob's Big Date
Member # 3151
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written Friday, April 8 2005 22:36
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quote:Weak acid and strong acids don't differ in corrosiveness. What you are thinking of is molarity. -------------------- The biggest, the baddest, and the fattest. Posts: 2367 | Registered: Friday, June 27 2003 07:00 |
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...b10010b...
Member # 869
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written Friday, April 8 2005 22:46
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quote:Depends on what it's corroding. Human tissue isn't strongly acidic or alkaline, so a strong acid will damage it more severely than a weak one. With a metal or base, though, a weak acid will work almost as well as a strong one, although probably more slowly. -------------------- My BoE Page Bandwagons are fun! Roots Hunted! Posts: 9973 | Registered: Saturday, March 30 2002 08:00 |