Ender wrote:Agemegos wrote:
You realize shields are one way, right?
Then they won't keep neutrinos and IR from reaching any detectors.
I'm curiosu as to this logic - they let things out, but stop things from coming in, therefor they will let things in. I just don't follow.
The ISD's shield lets its neutrinos out. Therefore the neutrinos are there to be detected.
Supposing that shields stop neutrinos from going in, my detectors will not be able to detect the ISD if they are inside my shield and if my shields are up. It is (by this hypothesis) my shields, not the ISDs shields, that make the ISD's neutrinos indetectable. But I, not the ISD, have control over my shields.
I could very easily put my detector on a pylon outside my shield, or on a drone outside my shield. Or I might be in a fleet with a sensor picket ship. I might even drop my shields for a sensor fix for a split second every now and again. In any of which cases I would be informed of the ISD's position.
The same is true of explanations of the drives and weapons that chew up the non-waste part of the power output: the engines, shields, and weapons.
Hence this thread.
Exactly so.
I realise that it is an official statement of some sort, and that it is offered as an explanation. But it only succeeds as an explanation if it is consistent with what we know of neutrions. If it isn't, for instance if it demands further explanation of why those neutrinos are not as detectable as neutrinos actually are, then it is at least insufficient.
Right, and if the sheilds block sensors (or where you would place the sensors) then the problem is neutralized. Then it just becomes a question of why they don't make them small enough to extend beyond the shields, and there you can wave it away by citing sensor tech limits.
Okay, but the sensor tech limits have to be plausible. And consistent with any canon statements about neutrino detection.
I suppose its possible they collaminate it into a beam
No, I don't think it is possible. We'd better ask someone whose physics background is in thermodynamics rather than electromagnetism,
*raises hand* AFAIK Mike and I have had the most training on the subject; though mine was abbreviated and more focused on what was relevent to nuclear reactors rather then thermodynamics on the whole.
Well, my physics training was aimed at making me an electrical engineer (except for second-year Modern Physics, which I did for fun). So you're ahead of me.
I raised this point a little over a year ago in discussion and the response was basically a big "I dunno". I'm thinking of writing a university that runs a neutrino generator and asking about their machine, but I'm not sure if those ae omni directional or focused.
Please do. I will be very interested in learning about it if a highly anisotropic beam of neutrinos is
not very low-entropy.
but I have a strong suspicion that such a beam would represent a lot of energy at very low entropy. In other words this would violate the Second Law of Thermodynamics.
I think it might depend on how it is done. Consider, a flashlight is an omnidirectional release of light that is turned into a beam by cupping it in a mirror. The light that hits the mirror is reflected out so it only comes out through the opening.
Yes, and näively one might think (I used to) that this represented a way to turn waste heat into useful energy (a beam weapon, or at least a serachlight). But in discussions on the usenet group rec.arts.sf.science I was told by people who sounded as though they knew what they were talking about that it in not possible to run even an IR searchlight on waste heat. Apparently an anisotropic flood of radiation has low entropy, so that it costs energy to concentrate it into even a spreading conical beam. I never saw a detailed argument, but several of the more rational-seeming posters quoated a result that confining the radiation of waste heat to
pi steradians of sky was in principle possible only as a limit with an emitter of infinite size and with zero efficiency.
I figure that you are in a better position than I am to discover whether that is true and whether the principle applies to neutrinos as well as to photons. But if you would prefer to stick to the formalities of debating I guess I could eventually ferret out the facts.
Now we don't know if shields, assuming they are opaque to neutrinos, absorb them, or scatter them.
They must scatter of reflect them, I think. If shield absorbed neutrinos there ought to be a way to use shields themselves as neutrino-detectors. Especially considering the flux intensities we are talking about here.
They might possibly concentrate it into a cone, and point the cone away from know enemy sensors, I suppose. But I thinki thermodynmics requires that this would cost energy, and sets a fairly broad lower limit on the width of the cone.
Indeed. I have seen a few references to "neutrino lasers", I need to dig deeper.
You can't run a laser on waste heat. I would be very, very surprised if you could do so with a neutrino laser, because if you could you could use the neutrino laser to heat a target to a temperature higher than your engine, which is a definite no-no.
Exhaust you should get scattered gamma flashes from collisions, particularily when it is turning. But you need not get thermal reading from the exhaust plumes. I can have an ice cube moving at .99 C afterall.
Only if the process you use to accelerate the icecube is godawful efficent.
Lets say I toss it out the airlock. This was meant solely as an example.
Well, if you toss it out the airlock it won't be a very efficient rocket exhaust. To be an efficient rocket exhaust it needs to have a very high velocity compared to the ship.
Besides which, kinetic energy tends to degrade to heat. I expect that an icecube whipping through the interplanetary medium at 0.99c is going to heat itself by friction, and explode into a puff of incandescent vapour. Lets say that the interplanetary medium consists of five million hydrogen attoms per cubic metre. The cross-sectional area of the icecube will sweep out 3E8 cubic metres per square metre per second, so from the point of view of the icecube the interstellar medium is a beam delivering 1.5E15 hydrogen atoms per square metre per second. At 0.99c those atoms have a kinetic energy of (gamma-1)mc^2. Gamma is 6.08 we calculated before. The mass of a hydrogen atom is about 1.7E-27 kg. c^2 is 9E16. That's 1.4E6 Wm^-2, which is about a thousand times as bright as sunshine. It will evaporate 700 metres of ice a second.
Dude, you are digging ay too deep. My only point was that there is a major difference between kinetic energy and thermal energy and that one can have a high kinetic energy with a low thermal energy.
You can. But not, I contend in the exhaust plume of a rocket unless either the exhaust velocity is low or the engine is implausibly efficient.
Temperature is relative, and a low temperature is going to have very little emissions.
No, temperature is an absolute.
No. Don't let the term "absolute zero" fool you. Temperature is the average random molecular kinetic energy of a substance. Kinetic energy is proportional to velocity, and velocity is relative.
I think we are drifting off on a tangent here. But I don't think this is right. The heat of a parcel of molecules is the energy of their random motion with respect to their collective centre of mass, not the whole of their kinetic energy. The velocity of each molecule is decomposible into the velocity of the centre of mass with respect to the observer and the velocity of the molecule with respect to the centre of mass. The square of the first (times half the mass of the molecule) is that individual molecule's share of the kinetic energy of the parcel, the square of the second (times half its mass) its that molecule's share of the heat. I recoil from teh relativistic case, but I think it is pretty easy to see that under the Galileian transformations the total heat of the parcel is independent of frame of reference.
Even in experiments on earth where they try to stop all motion in a substance to get it to absolute zero, the slow down is only realitive to the instruments as the substance is still moving at great velocity as earth orbits the sun.
Yes, of course. But that is not random thermal motion. The collection of supercooled atoms has high kinetic energy in the Sun's frame of reference, but not high heat.
In short, thermal energy depends not on a single velocity (that of the molecule) but on the difference between velocities (that of the molecule and that of the centre of mass of the object it is part of). Vector algebra assures that this difference is the same vector if the same vector is added to both.
And by the way, in every case except that of monatomic gases, some of the thermal energy is stored in rotational and vibrational modes, which are not relative.
If I had a magic device that let me measure the temperature of that substance from the moon I would get a different reading because the molecules would be moving at a different velocity relative to my instruments.
Well, rather than using a magical instrument, let's imagine that we calculate the heat of the object by observing the spectrum of its thermal radiation. The emitivity to an depends on its composition, and ought to be the same in all frames of reference, right? And the thermal emissions depend on the emitivity and the temperature. So we ought to be able to determine the temperature of an object by finding the peak of its thermal emission spectrum. Now, the object emits real photons, and different observers must surely agree on what photons are emitted. They can only disagree about their wavelength because of the Doppler effect. The thermal spectum of an approaching object will be 'warmed', but that of a retreating object 'cooled', even though both have
more kinetic energy.
There is a real difference between the kinetic energy of an object and its thermal energy. The second causes violent collisions between its molecules and leads to thermal radiation. The first does not. It is absolutely true that an object radiates particular photons as a result of its temperature. These photons are characteristic of the object's temperature. And therefore temperature is absolute.
We can look at this another way, by considering two objects with relative motion, as a wheel A rotating inside an evacuated shell B. An observer on object A performs experiments with the vapour pressures of various liquids, and determines that A is at the temperature of the triple point of water. B does the same, and determines that B is at the triple point of water. Now we go an determine whether heat actually flows from A to B or from B to A (by radiation). They can't both get hotter and they can't both get cooler. Either they both rmaintain a constant temperature (in which case they were both the same temperature to begin with) or one heats and teh other cools. But if one heated and theother cooled we would be able to determine which one was really moving and which really stationary, which would violate the postulate of relativity.
(Okay, perhaps a rotation wasn't a very good example, because you can detect that. Let's make A and B infinitely long, infinitely wide, thin plates ver close to each other, and each determined in its own frame of reference to be at uniform temperature are teh triple-point of water.
The tracers on the weapons
Actually, I was not thinking so much of the glow of the bolts. I was thinking in terms of incandescent wreckage from the targets.
Are you thinking of this from a neutral planetary observer position?
I hadn't thought specifically about who the observer was. Somebody (Darth Wong, I think) specified the scenario of an ISD accelerating at full bore and firing all possible weapons, and I immeditely thought that the weapons fire must be hitting something, even if it were only the interplanetary medium.