Mr. Oragahn wrote:Moff Tarquin wrote:
But the whole point of the problem is that nobody has the right to say that Bob is moving and Alice is sitting still in a relativistic universe. It's just as fair to say that Alice is moving at 100 m/s as it is to say that Bob and the BDO are moving at 100 m/s.
The crux of the issue is that one value contributing to kinetic energy (the rest mass of an object) doesn't change with reference frame, where as the other (the velocity of an object) does.
Well, depending on the reference frame, you will be considered to weigh more if you begin to approach relativistic speeds.
Yeah, but in this case, we're (for the sake of argument) dealing with a device that only effects the rest mass of the object. At relative speeds of 100 m/s and 1000 m/s, nobody's going to see any "kinetic mass" showing up.
In a relativistic universe, it seems to be impossible to satisfy both conservation of energy and conservation of momentum while nevertheless allowing for "mass lightening." Even merely obeying conservation of momentum in all reference frames would require for it to accelerate in two different directions simultaneously!
But Bob's gun is going to produce recoil. No matter what, there is going to be a difference between the moment the gun kicks back and the moment the beam of magic it shoots, which will have mass I suspect, hits the BDO Bob is on.
Even if it's not a gun, no matter what the mass lightener device does, it's a machine that has to transmit something tangible first, strongly implying a change in motion.
Although, yes, that doesn't solve the problem with the values.
The problem with the values is, in my opinion, the biggest one.
For the sake of argument, we will assume that the mass-lightening ray fires massless particles that are absorbed by the massive object, transferring momentum equal to that which would be imparted by a laser beam of equal energy. Everybody will agree (or agree as much as we can hope them to in a relativistic universe) on the transfer of momentum.
But isn't the problem that we're using rather newtonian equations for what might very well involve seriously advanced physics?
Yeah, there's a part of me that worries that this whole discussion is equivalent to somebody trying to use the Twin Paradox as a reductio ad absurdum of Special Relativity. But at the same time, there's a reason why High-School level courses still use Newtonian Mechanics: it works almost all the time. It's only when you're dealing with ridiculously small or ridiculously large amounts of energy that it breaks down, and 50 MJ is a fairly reasonable amount of energy to be dealing with. The black box of the mass-lightener aside, the Newtonian approximation should work here.
Even if the speeds involved there are rather small, the process of mass lightening literally infringes on the relation between light and matter.
As far as we've gone in physics, the more (rest) mass is lost, the more is turned into almost massless particles with great energy. A point I'll return to later on.
But let's put a bit more of a point on this issue. Let's add a third person into the mix: Chris. From Chris's reference frame, the BDO is traveling at -100 m/s. When Bob uses the mass lightening device (which is still summoning 45 MJ out of the void, incidentally), the BDO ends up traveling at -1000 m/s.
Let's sum up what's going on so far (all of this depends on the fact that if A measures the velocity of B at 100 m/s, then B measures the velocity of A at -100 m/s):
From Bob's perspective:
Bob starts out near the BDO. Chris is moving at 100 m/s, and Alice is moving at -100 m/s.
Bob turns on the mass lightener, which uses up a negligible amount of energy to counteract the BDO's gravitational binding energy.
The BDO's mass decreases, and it remains stationary.
Bob ends up near the BDO. Chris and Alice continue to move at 100 m/s and -100 m/s respectively.
From Alice's perspective:
Bob and the BDO are both moving at 100 m/s. Chris is moving at 200 m/s.
Bob turns on the mass lightener, which uses up a negligible amount of energy.
The BDO's mass decreases, and it accelerates to 1000 m/s, gaining 45 MJ of kinetic energy from nowhere.
The BDO ends up moving at 1000 m/s, Bob ends up left in its wake. Chris continues to move at 200 m/s.
From Chris's perspective:
Bob and the BDO are both moving at -100 m/s. Alice is moving at -200 m/s.
Bob turns on the mass lightener, which uses up a negligible amount of energy.
The BDO's mass decreases, and it accelerates to -1000 m/s, gaining 45 MJ of kinetic energy from nowhere.
The BDO ends up moving at -1000 m/s, Bob ends up left in its wake. Alice continues to move at -200 m/s.
From this, we can try to piece together the BDO's perspective:
Bob begins near the BDO. Chris is moving at 100 m/s, and Alice is moving at -100 m/s.
Bob turns on the mass lightener, which uses up a negligible amount of energy to counteract the BDO's gravitational binding energy.
The BDO's mass decreases, and it remains stationary. Chris accelerates to 1000 m/s and Alice accelerates to -1000 m/s.
Bob ends up near the BDO. Chris and Alice suddenly recede into the distance for no readily apparent reason.
Of course, an absolute reference frame in space would solve the problem, and would also allow for
reactionless thrusters and
FTL travel without time-like loops.
There's perhaps a faulty assumption, that the kinetic energy is directly related to energy expenditure of the device.
Perhaps, but if the energy doesn't come from the device, then where does it come from?
Maybe some of the mass lost gets turned into kinetic energy. But what we'd get from 900 kg being turned into energy is some 8.1e19 J. On such a solution, we have two extremes: 1) all of that energy becomes kinetic energy. But in that case, Alice and Chris would say that the BDO suddenly accelerates to relativistic velocities (Alice saying it went one way, Chris saying it went the other way) breaking the law of conservation of momentum. And God alone would know what Bob would say happened, since from
his reference frame, the BDO has no kinetic energy to begin with! Or 2) 45 MJ of that becomes kinetic energy and the rest is emitted somehow from the BDO. On the simplest such option, the energy would be radiated omnidirectionally from the BDO, vaporizing Alice, Bob, Chris, and the Mass Lightener. And Alice's Ghost would say that the BDO went in one direction, Chris's ghost would say that it went in the other direction, and God alone would know what Bob's ghost would say (actually, unless there's a medium out there who isn't a complete fraud, God alone would know what
any of these ghosts would say, but that's neither here nor there). The rather more complicated idea of a cloud of phantom energy is interesting, and we'll return to it in a moment or two.
Returning to my former point, we're most likely dealing with relativistic physics. At which point calculations become weird.
Up to there be no point using the traditional Ek=0.5*m*v² formula, because they simply cannot combine.
Now, for the sake of this thread, should we really bother considering doing such math, when we don't even know what phenomenon would be going on for mass lightening to ever happen?
In universe, it works, and I think the safest assumption is to consider that the energy that's needed is directly related to the difference between rest mass and lightened mass that's being seeked, and that our little kinetic energy problem might be solved at a higher level of physics.
Okay, so perhaps the kinetic energy issue isn't so cut and dry. But we'd still have to determine which direction (if any) a mass lightened object accelerates - and it has to either accelerate in order to obey conservation of momentum.
Also, it might turn out that something needs to be ejected when mass is reduced. So if Bob is attached to the BDO and shoots his left foot with the fancy mass lightening gun, triggering an effect that spreads to the entire BDO plus Bob, maybe both leave a shadowy residue of mass, perhaps a bottled field that will take some time to be assimilated back into real space as local space averages the differences.
So basically you magically ditch the mass? It turns into photons or something? That's called a photon drive that you magically convinced to run using the rest mass of your spaceship instead of using a reactor.
I think it's going to be fairly more complicated than that and I have no intent to come up with a Nobel-worthy theoretical model for a science fiction trope. :)
Oh, of course. The "magic" is some uber complicated piece of equipment that, to us, must be regarded as a black box. I don't require that you open the black box, I'm willing to accept it and its functions for the sake of argument. All I want to know is how it fits in with the things that aren't black boxes - big dumb objects, Alice, Bob, and Chris.
The entire system depends on manipulating the very essence of mass, something which as of today cannot even be properly defined because we're dealing with a concept at a low fabric-of-the-universe level here.
It's quite interesting to consider what might happen though. Obviously, all elements become less massive, yet all known interactions between particles, atoms and whatever still work the same way.
In other words, the natural "solid" structure automatically occuring thanks to the universe's laws is replaced with a temporary simile, an artificial construction that, perhaps, binds light to behave like mass, but still abides by the same laws, obviously, although in a more arcane way.
In other words, mass lightning involves generating solid and totally autarchic partial holograms (a bit like our plasma friend from the other thread, not needing anything else but itself), that is, partially turning your ship into something which we might call hard light. 60% still solid, 40% woo-woo.
Or else. If a shadowy mass isn't ditched, or tugged in another dimension, at least it would need to be stored, perhaps within the object itself.
And this might result in a bigger kaboom if something goes wrong.
Okay, if I thought I understood what you're postulating, I'd break it into chunks and address your suggestions in detail. As it stands, however, I think I need a better holistic understanding of what you're trying to say.
Are you suggesting that a sort of "phantom copy" of the object is left behind, and that copy is what contains the extra mass? Or are you saying that a mass-lightened object becomes its own phantom copy, with the lightened mass either "masked" somehow or left behind altogether?
Of course, I don't expect you to defend either view as being what "actually happens." I recognize that these are intended as mere possibilities, alternatives to the seemingly paradoxical road my assumptions lead down. I just want to know which (if either) option is what you are suggesting.
Or perhaps it's impossible to do so, and the affected object needs to be detached from the device for a differential to exist.
But then no ship could ever achieve that upon themselves, unless again they leave something behind as they progressively lower their overall mass.
But what if you want to get your mass back? Or increase your mass?
You turn a knob ! I've seen McKay do it in a puddle jumper. Piece o' cake.
I literally laughed out loud when I read that. Literally.
There are some technologies that result in major modifications to physics (eg, the introduction of a privileged reference frame). This one just seems to break physics.
LOL. Science fiction anyone?
Well, I'm willing to accept that time travel occurs (in a relativistic universe where FTL travel is possible, it's practically impossible to avoid), there's any number of ways to deal with it - alternative universes, mutable timelines, etc. - that don't involve completely overhauling physics. Same thing with FTL that doesn't allow for time travel - all it takes is a privileged reference frame. Most of science fiction doesn't require us to do away with what we have discovered, it just needs us to wiggle it around a bit so that it fits in a larger picture - which is exactly what real science does. It's a little notion called a classical limit: any new theory that we come up with that explains exotic conditions makes predictions that agree with the old theories once it comes back to normal conditions.
But this mass lightener? It seems to require us to say that a macroscopic object ends up doing multiple mutually exclusive things at once (jet off in one direction, jet off in the opposite direction, and not jet anywhere) when all reference frames involved have relative motions of less than 0.001% of the speed of light. Which quite simply flies in the face of everything we
do know about macroscopic objects and slow reference frames. The classical world that we have very well mapped out isn't being eased into a new position in a larger tapestry, it's being chucked out the window. And that isn't just contrary to scientific methodology - it's contrary to all reason.