Get your fill of sci-fi, science, and mockery of stupid ideas
http://stardestroyer.dyndns-home.com/
http://stardestroyer.dyndns-home.com/viewtopic.php?f=18&t=108743
Starships that lose engine power just come to a halt, which might be caused by the mass lightening field shutting down.If the Starship is done accelerating and is at a constant velocity and the mass lighteners are turned off what happens.
Hum that shouldn't work after all there has to be a force exerted in order for decelleration to occur. And with no power their inertail dampeners will also be down, which means they would get squished if they just stop.Bounty wrote:Starships that lose engine power just come to a halt, which might be caused by the mass lightening field shutting down.If the Starship is done accelerating and is at a constant velocity and the mass lighteners are turned off what happens.
Presumably, the ship's velocity would drop in proportion to its mass increase in order to conserve momentum. Any imbalance in the ship's kinetic energy would have to be converted to heat, raising or lowering the ship's temperature accordingly.dragon wrote:I have a question on mass lighting. If the Starship is done accelerating and is at a constant velocity and the mass lighteners are turned off what happens.
The force needed to accelerate them was never applied in the first place under mass lightening. The ship would simply revert to the status it should be in if real world physics had been in force.dragon wrote:Hum that shouldn't work after all there has to be a force exerted in order for decelleration to occur.Bounty wrote:Starships that lose engine power just come to a halt, which might be caused by the mass lightening field shutting down.If the Starship is done accelerating and is at a constant velocity and the mass lighteners are turned off what happens.
How about no? No engine power /= no power, period. Notice how outside TUC which involved a DELIBERATE attack on that subsystem they NEVER lose artificial gravity?And with no power their inertial dampeners will also be down, which means they would get squished if they just stop.
Isn't conservation of momentum just another way of saying conservation of KE and direction?Starglider wrote:Conservation of momentum suggests that the ship's velocity vector would change to be the vector it would have had if the mass lightening system had not been operating (ignoring the effects of gravity, which complicate the analysis). However this violates conservation of energy, unless you have the mass lightening system pumping in and removing energy in the right quantities to match the change in KE. You could directly conserve KE by slowing the ship so that its effective KE (relative to when the mass lightening field was turned on) remains constant whether the field is on or off, but that breaks conservation of momentum. Personally I'd rather have conservation of energy than conservation of momentum, but it depends on the exact physical realisation of the system. The only major sci-fi setting I designed had a hybrid STL/FTL drive system that worked as an effective combined mass lightener/antigravity system/warp drive strictly limited by conservation of energy (extra energy had to be pumped in or removed through the drive to balance things, particularly when traversing gravitational PE gradients). I tried to set this up as carefully as possible to give the tactical environment I wanted (and no easy relativistic planet smashing) while being as physically consistent as possible (though with completely invented fantasy physics).
It's not an either-or proposition. One will always fail to conserve momentum. In the instantaneously comoving inertial frame before the mass operation, there must be no momentum change. However, the momentum is already zero in that frame, so the change in velocity must also be zero, and therefore zero in every other inertial frame. Thus, there always exist frames in which CoM fails (in fact, almost every frame). On the other hand, CoE fails as well, as increasing the mass amounts to conjuring energy. Perhaps one can hand-wave that away by blaming subspace--the standard Trek pseudo-answer.Starglider wrote:Conservation of momentum suggests that the ship's velocity vector would change to be the vector it would have had if the mass lightening system had not been operating (ignoring the effects of gravity, which complicate the analysis). However this violates conservation of energy, unless you have the mass lightening system pumping in and removing energy in the right quantities to match the change in KE. You could directly conserve KE by slowing the ship so that its effective KE (relative to when the mass lightening field was turned on) remains constant whether the field is on or off, but that breaks conservation of momentum.
I've been thinking about this, and I've realized that, if the mass lightening field actually works as its name suggests —that is, in the comoving frame, the ship appears to gain mass and not change velocity— then in all other frames, the action of turning off the field must result in the velocity in that frame not changing if both CoE and CoM apply. Here's why:Kuroneko wrote:At first I thought it adjust the velocity as well, but it simply doesn't work.
It's not an either-or proposition. One will always fail to conserve momentum. In the instantaneously comoving inertial frame before the mass operation, there must be no momentum change. However, the momentum is already zero in that frame, so the change in velocity must also be zero, and therefore zero in every other inertial frame. Thus, there always exist frames in which CoM fails (in fact, almost every frame). On the other hand, CoE fails as well, as increasing the mass amounts to conjuring energy. Perhaps one can hand-wave that away by blaming subspace--the standard Trek pseudo-answer.Starglider wrote:Conservation of momentum suggests that the ship's velocity vector would change to be the vector it would have had if the mass lightening system had not been operating (ignoring the effects of gravity, which complicate the analysis). However this violates conservation of energy, unless you have the mass lightening system pumping in and removing energy in the right quantities to match the change in KE. You could directly conserve KE by slowing the ship so that its effective KE (relative to when the mass lightening field was turned on) remains constant whether the field is on or off, but that breaks conservation of momentum.
Because without it you cannot guarantee that the universe will work the same way tomorrow as it did today. It's called "Noether's theorem" — for every continuous symmetry (time translation being one), you can derive one conservation law. From time symmetry (the guarantee that you can perform a physics experiment at any time and come up with the same result) you get the conservation of energy. Wihtout conservation of energy, if you turn on a light today and illuminate the room today, you can't guarantee that turning on the same light tomorrow would not cover the entire room in cocoa butter.bz249 wrote:Sorry why the conservation of energy is so critical question?
Kinetic energy is just the excess in internal energy resulting from projecting the moving object's four-momentum onto your own time basis vector. It's a trick of coordinate systems, so it shouldn't be surprising that it isn't conserved. Four-momentum, on the other hand, is conserved. Always.bz249 wrote:In this case we only talk about the conservation of kinetic energy, and as far as I know there is no conservation law for that (oh sorry there is a weak one, that conservative fields conserve the total mechanical energy).
Dead stop relative to whom, bz249? If in one reference frame, the ship goes from traveling at a certain velocity v to a dead stop, then I can always find a frame such that, in this frame, the ship goes from dead stop to traveling at an equal and opposite velocity, -v. Whence did this kinetic energy come from, dearheart? Futhermore, you say that the ship goes to a dead stop and dissipates the kinetic energy (presumably as heat) which is radiated. In the frame where the ship goes from dead stop to -v, the ship also radiates energy. Where did this energy come from?bz249 wrote:So the simpliest answer to the question that the mass lightening conserve the linear momentum, but not the kinetic energy. It uses some external energy source (to pump in the required energy) during accelaration and the excess energy simply dissipates during a deadstop.
Yes, that's exactly what I said. Although you don't actually need both CoE and CoM for the conclusion that the change in velocity is zero in every inertial frame.Wyrm wrote:I've been thinking about this, and I've realized that, if the mass lightening field actually works as its name suggests —that is, in the comoving frame, the ship appears to gain mass and not change velocity— then in all other frames, the action of turning off the field must result in the velocity in that frame not changing if both CoE and CoM apply.
Those statements are contradictory... perhaps you mean to ignore the intermediate steps of the subsequent scenario (as you do later), but at this point your meaning is rather unclear. There is a violation of momentum conservation at several steps in the experiment (e.g., between events 2 and 3); your invocation of an external field is necessary not to just conserve angular momentum, but also momentum and energy.Wyrm wrote:In comoving frames, the ship would stay still, and in frames where the ship moves, the ship would receive just enough momentum to keep it going at the same speed with the increased mass. ... The problem with mass lightening fields in general is more subtle than merely CoE or CoM problems. Both conserve fine.
Well, it seems to work on a formal level, but it also makes mass lightening completely unnecessary. One could just as easily extract an arbitrary amount of four-momentum and put it back later, according to this scheme.Wyrm wrote:We propose that spacetime is filled with a field that acts as a reservoir of four-momentum (I call it the "mass reservoir", 'mass' because "four-momentum reservoir" is unwieldy), and the transfer of four-momentum is controlled by the mass lightening field ...
Although not on a curved spacetime.Wyrm wrote:Let us suppose that the mass reservoir is a four-momentum field where each point in space has a defined four-momentum density, π(x). We may integrate this over a region of space to get a four-momentum for that region, p(R), from which we can extract a mass and a four-velocity for that region of the mass reservoir. ...
Just dropping in, but if I understand this correctly, Wyrrn is just describing a rocket and a net. That's how the math works out for me, at least.Kuroneko wrote:Well, it seems to work on a formal level, but it also makes mass lightening completely unnecessary. One could just as easily extract an arbitrary amount of four-momentum and put it back later, according to this scheme.Wyrm wrote:We propose that spacetime is filled with a field that acts as a reservoir of four-momentum (I call it the "mass reservoir", 'mass' because "four-momentum reservoir" is unwieldy), and the transfer of four-momentum is controlled by the mass lightening field ...
Yes, I see that now.Kuroneko wrote:Yes, that's exactly what I said. Although you don't actually need both CoE and CoM for the conclusion that the change in velocity is zero in every inertial frame.
I admit to some clunky wording. However, I protest that there were "several" violations of CoM. There were only two, when the field was turned on and when the field was turned off. And the second was an undoing of the first violation; when the field turned off, all of the missing momentum should be accounted for.Kuroneko wrote:Those statements are contradictory... perhaps you mean to ignore the intermediate steps of the subsequent scenario (as you do later), but at this point your meaning is rather unclear. There is a violation of momentum conservation at several steps in the experiment (e.g., between events 2 and 3); your invocation of an external field is necessary not to just conserve angular momentum, but also momentum and energy.
The ship's lighter with the field on, right?Kuroneko wrote:Well, it seems to work on a formal level, but it also makes mass lightening completely unnecessary. One could just as easily extract an arbitrary amount of four-momentum and put it back later, according to this scheme.
'Ey, if I wanted to bring curved spacetime into the discussion, I would've at least mentioned the metric.Kuroneko wrote:Although not on a curved spacetime.Wyrm wrote:Let us suppose that the mass reservoir is a four-momentum field where each point in space has a defined four-momentum density, π(x). We may integrate this over a region of space to get a four-momentum for that region, p(R), from which we can extract a mass and a four-velocity for that region of the mass reservoir. ...
Like with the first calculation involving the angular momentum not taking account of the angular momentum of the mass reservoir, I'm glossing over the dynamics of the reservoir itself. I wouldn't be surprised if the mass reservoir extracted an energy premium for being torqued. (Just as long as it's not too big.)Kuroneko wrote:It is more than a little bit disconcerting to have a reservoir of `stuff' that has energy and momentum but that either does not move itself at all or one that costs no energy to accelerate.
True, but the neutrino was proposed for similar reasons, wasn't it? Physicists didn't want to give up on CoM and CoE for beta decay? The assumption of CoM, CoE, and conservation of angular momentum, plus an assumption of energy savings as a function of the proportion of mass hidden leads us to this conclusion.Kuroneko wrote:In the end, what's being "shunted" is not the mass or four-momentum but the all conservation problems in the physical universe.
Not quite. It's more like leaving a large ballast behind at your start point, then picking up an identical ballast at your destination to restore your original mass.metavac wrote:Just dropping in, but if I understand this correctly, Wyrrn is just describing a rocket and a net. That's how the math works out for me, at least.
I don't think that dog hunts. A ballast analogy places a massive body in a massive scalar field coupled to a repulsive electrostatic one. An action in which ballast is release at t = t_0, r = r_0 and is recovered some t = T, r = R later will result in the body returning to r = r_0. You want to recover less mass at r = R so that r'(t) = 0 relative to the field at r = R.Wyrm wrote:Not quite. It's more like leaving a large ballast behind at your start point, then picking up an identical ballast at your destination to restore your original mass.metavac wrote:Just dropping in, but if I understand this correctly, Wyrrn is just describing a rocket and a net. That's how the math works out for me, at least.
You do know that analogies fail at some point, do you not? And that's why you shouldn't reason with them and only use as a tool to intuitive understanding.metavac wrote:I don't think that dog hunts. A ballast analogy places a massive body in a massive scalar field coupled to a repulsive electrostatic one. An action in which ballast is release at t = t_0, r = r_0 and is recovered some t = T, r = R later will result in the body returning to r = r_0. You want to recover less mass at r = R so that r'(t) = 0 relative to the field at r = R.
Mea culpa--yes, there are exactly two in that scenario.Wyrm wrote:I admit to some clunky wording. However, I protest that there were "several" violations of CoM. There were only two, when the field was turned on and when the field was turned off.
Yes, but that's not at all what I was alluding to. How about simply extracting four-momentum from the field and putting it back when one is done? Such an operation would be for most practical purposes equivalent to the above scenario, just in opposite order.Wyrm wrote:The ship's lighter with the field on, right? I would say that making the ship mass that is lost actually disappear completely from our reckoning is beside the point and a completely unnecessary requirement.
Yes. That's why I was proposing to simply skip that step. The name would be nothing but a fanciful analogy.Wyrm wrote:You must admit that a field that makes everything inside appear less massive is fanciful enough already, ...
In this case, the gap is too large, and has other problems as well. For example, the most obvious application of mass-lightening technology is to use on a gas reservoir, thus decreasing its temperature and pressure. If turning off the field restores original energy and momentum of the gas particles, this allows us to simply destroy entropy, since there we do not need to do any work to compress a gas. If the operation is affected by volume, we can keep the same volume and still use the lightened gas as a heat sink, still violating the second law.Wyrm wrote:True, but the neutrino was proposed for similar reasons, wasn't it? Physicists didn't want to give up on CoM and CoE for beta decay?
Yes, I do, and I suspect the reason you went with that analogy is to get the reader to think of a spaceship shedding its mass imparted with negligible momentum with respect to hull. Problem is that there's another piece of the system in play, that electrostatic field, that will now do work on the ship. By the way, the ballast analogy works best with a solar or laser sail.Wyrm wrote:You do know that analogies fail at some point, do you not? And that's why you shouldn't reason with them and only use as a tool to intuitive understanding.metavac wrote:I don't think that dog hunts. A ballast analogy places a massive body in a massive scalar field coupled to a repulsive electrostatic one. An action in which ballast is release at t = t_0, r = r_0 and is recovered some t = T, r = R later will result in the body returning to r = r_0. You want to recover less mass at r = R so that r'(t) = 0 relative to the field at r = R.
Which, like I pointed out, would lead to the ship circuiting B right back to A, provided the analogy holds. We can modify it by eliminating the coupled potential gravitational and electrostatic fields, but now you're just hurling mass out (a rocket) and hoping to run into another body with the right momentum (a net) to stop. That is, of course, unless we simply accept the violation in energy-momentum conservation that you and kuroneko pointed out.Anyway, you're even using the wrong analogy. There are two distinct but identical ballasts, one at A and another at B. You drop one ballast at A, move to B, and pick up the one sitting at B. Clear?
That is more or less how Star Trek treats subspace. It even offers the beginning of a an explanation to the myriad "sub-space anaomalies" that crop up in Star Trek. Let's suppose that one can usually hurl mass out to accelerate and find the corresponding mass to stop at one's destination. Occasionally one would come across an area of space where the corresponding subspace did not allow you to "pick up your ballast". In those situations the ship would move faster of slower or sideways, or would heat up or cool down, or suffer numerous other effects.Metavac wrote:We can modify it by eliminating the coupled potential gravitational and electrostatic fields, but now you're just hurling mass out (a rocket) and hoping to run into another body with the right momentum (a net) to stop.
Um, first, please go into more detail on how such a strategy is to work. How does borrowing energy from the reservoir reduce the amount of energy total that the ship has to spend to get from A to B?Kuroneko wrote:Yes, but that's not at all what I was alluding to. How about simply extracting four-momentum from the field and putting it back when one is done? Such an operation would be for most practical purposes equivalent to the above scenario, just in opposite order.
And if all gasses are affected similarly, then the crew would be surrounded by supercooled air and freeze to death, if not experience a temperature drop in their own bodies. Either way, they're crewcicles. This makes the field useless for its intended purpose, carting ship and crew around a solar system cheeply.Kuroneko wrote:In this case, the gap is too large, and has other problems as well. For example, the most obvious application of mass-lightening technology is to use on a gas reservoir, thus decreasing its temperature and pressure. If turning off the field restores original energy and momentum of the gas particles, this allows us to simply destroy entropy, since there we do not need to do any work to compress a gas. If the operation is affected by volume, we can keep the same volume and still use the lightened gas as a heat sink, still violating the second law.
I don't think we're talking about the same kind of ballast, dearheart. You seem to be talking about ballast as used in electrical engineering, especially in flourecent lights where the "ballast" is indeed an induction coil. I'm talking about "ballast" as used in the shipboard sense.metavac wrote:Yes, I do, and I suspect the reason you went with that analogy is to get the reader to think of a spaceship shedding its mass imparted with negligible momentum with respect to hull. Problem is that there's another piece of the system in play, that electrostatic field, that will now do work on the ship.Wyrm wrote:You do know that analogies fail at some point, do you not? And that's why you shouldn't reason with them and only use as a tool to intuitive understanding.
Ie, I when I say "ballast," I mean a chunk of lead, or a stone. And if you think a real spaceship wouldn't need ballast, think again. Ballast on a spaceship would keep the center of mass right smack where it should be, along the axis of thrust. Otherwise, your ship will spin about as a lever arm forms.The Free Dictionary wrote: bal·last (blst)
n.
- Heavy material that is placed in the hold of a ship or the gondola of a balloon to enhance stability.
- Coarse gravel or crushed rock laid to form a bed for roads or railroads.
- The gravel ingredient of concrete.
- Something that gives stability, especially in character.
No. Read the example again. We don't "hurl" mass into the reservoir or "run into" it. In the comoving frame, shunting mass to and from the field gives no acceleration, and therefore change in speed, as it would for a net or rocket.We can modify it by eliminating the coupled potential gravitational and electrostatic fields, but now you're just hurling mass out (a rocket) and hoping to run into another body with the right momentum (a net) to stop.
Yes, and we were talking about similar things, although I was talking about ballast to control buoyancy and I have no idea why anyone would think a sailing ballast analogy has much of anything to do with changes in motion along a desired axis.Wyrm wrote:I don't think we're talking about the same kind of ballast, dearheart. You seem to be talking about ballast as used in electrical engineering, especially in flourecent lights where the "ballast" is indeed an induction coil. I'm talking about "ballast" as used in the shipboard sense.metavac wrote:Yes, I do, and I suspect the reason you went with that analogy is to get the reader to think of a spaceship shedding its mass imparted with negligible momentum with respect to hull. Problem is that there's another piece of the system in play, that electrostatic field, that will now do work on the ship.
Ie, I when I say "ballast," I mean a chunk of lead, or a stone. And if you think a real spaceship wouldn't need ballast, think again. Ballast on a spaceship would keep the center of mass right smack where it should be, along the axis of thrust. Otherwise, your ship will spin about as a lever arm forms.
Is that clearer?
It doesn't, except that dropping the ballast makes your ship easier to move. That's the point.metavac wrote:Yes, and we were talking about similar things, although I was talking about ballast to control buoyancy and I have no idea why anyone would think a sailing ballast analogy has much of anything to do with changes in motion along a desired axis.
Except the field doesn't actually provide acceleration, as would be required for a rocket. The shedding of mass/4-momentum by way of the field and the acceleration that moves the ship are accomplied with two different mechanisms. Activating and deactivating the field here yields no change in velocity in any frame.metavac wrote:Here's the problem as I understand it. You're looking a ship whose captain wants to change velocity relative to the comoving frame you're in. You can do this by adding or shedding mass-energy, but to conserve the 4-current, the energy-momentum of the shed mass-energy must sum with the energy momentum of the ship after the field is turned on to give you what you measured before you turned the field on. That, my friend, is exactly what a rocket does.
Irrelevant, because the operation of the field does nothing to the ship but scale its 4-momentum. It therefore does not cause acceleration in the ship and therefore the analogy with the field operation with a rocket fails hard.metavac wrote:Now as I understand it, kuroneko (and Hinson) for that matter, argue that global spacetime is foliated by a bundle such that the product of any tangent vector at a given point with a vector in the corresponding space is non-zero. That's to say, there exists at every point in spacetime a space of vectors with non-zero momentum.