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About K^2

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  1. Absolutely. You pick your favorite boson field, preferably one with a zero rest mass. Then you polarize the vacuum in that field, flip the polarization, and repel from vacuum. Easy. For example, lets pick electromagnetic field. Vacuum is a dielectric, so you can apply electric polarization. Start alternating the electric field in your generator, and you will get a reaction force propelling the craft forward. Of course, you'll be producing electromagnetic waves, but you have to have something carry away momentum, so that makes perfect sense. Congratulations, you just invented a photon drive, AKA, pushing yourself with a flashlight. It has best-in-class ISP of over 30,000,000s, or nearly 100,000x better than kerlox! The only problem is that it does take a bit of power. 300MW per 1N of thrust, to be specific. So you better bring some matter/anti-matter fuel or a black hole to power this thing. There's a reason why we don't discuss propellant-less thrusters outside of science fiction topics. Energy-momentum is a conserved current, which means you either bring mass to propel yourself with, or you waste an enormous amount of energy to stand in for that mass. Anything else violates the most fundamental of underlying principles - local symmetries. You can think of it as being geometrically impossible to do better than this. That said, there are ideas out there that involve moving yourself places without actually accelerating. Warp drives, wormholes, etc. Sadly, nobody figured out yet how to do any of this without negative energy densities and enormous amounts of ordinary energy. A black hole drive is way more realistic at this point, and that's all that needs to be said on the matter.
  2. Solar is poor substitute for nuclear with current limitations on energy storage. The nice thing about nuclear plants is that just like coal and gas plants, they rely on a rather heavy turbine, which can store quite a bit of kinetic energy. For chemical burning plants, that energy is enough to increase/decrease power output to meet the demand. With a nuclear power plant, it doesn't quite get you there, as reactors take a good while to change the output, but it certainly helps even out the load, letting you rely on nuclear as your primary energy source. Solar doesn't have that built in. What solar does give you is peak power during peak use. So a combination of nuclear and solar can get you 90%+ of typical usage, with the remaining power coming from gas burning plants that are just above idle load, but can be throttled up to full output in a matter of minutes if you suddenly get a high usage spike. Naturally, every one wants to go 100% renewable. That's a great goal. But it is a longer term goal and should be treated as such. Going 90% nuclear/renewable can be achieved in a matter of years on existing and proven technology if we put resources into it, and that would make a huge difference. Going 100% solar in 20-30 years might be too late if we spend most of that time burning 70% coal, and that's the trajectory the countries with renewables-only plan are on right now.
  3. In pure GR, yes. In Quantum Gravity, I'm not sure. I don't think there's a problem, because neither time nor space are actually quantized in Standard Model. There's Planck length, which is the shortest wavelength you can have, but that merely sets the limit on how thin the shockwave can be, not how rapidly it can travel, or how fine of time resolution you have on interaction. Things don't actually jump from state to state in quantum physics, despite what poorly-written chemistry text books might be trying to convince you of. All of the physics we know are some flavor of field theory, and time and space is continuous in these models. So while I'm by no means an expert in Quantum Gravity, and given that no solutions to equations of Quantum Gravity are known, so I have nothing concrete to reference, I don't think that will be a problem. Of course, if laws of physics we know are merely approximations and fall apart at relevant energy scales, *giant shrug*.
  4. I don't approve of his publicity strategy for getting funding, but that aside, I'm kind of impressed, and wished him all the best in his endeavors, because there is nothing more Kerbal than strapping yourself to a water heater with safety valve welded shut just to see how high you can make it go. Edit: Just wish he got someone with better engineering to help him with his stuff. Just read that last link. Edit2: There's a video now, and I cannot think of a more Kerbal way to go. His parachute fired together with his engine.
  5. USA is a bit different. I'm not sure it would deter everyone, and I don't know how much impact this still has on younger generations, but the fear of nuclear war and everything associated with it that was put into people during the 70s and 80s still resonates with many. I was born in USSR, grew up in a research town next to a military base, two of my grandparents did work on uranium refinement for reactors, one served in the military, and my father's reserve training involved ICBM navigation. People I grew up around didn't have half as much respect or fear of the radiation hazard sign as I see from a lot of people a little older than me in US who had no association with any related field of work. There's also a lot of completely irrational fear of anything that has words "radiation" or "nuclear" in it, but that's a separate story.
  6. Plausible. The most hazardous thing that comes to mind is MMH the orbiter used both in the main thrusters and RCS. In a pinch, if you wanted to make sure people stayed out, radiation hazard markings might be just the thing to post to keep people from nosing around. I mean, how many people even know what chem hazard symbols look like, and what they mean? Radiation, though, people know to stay away from. Though, misusing warning signs like that does diminish their impact somewhat, so I don't necessarily agree with the decision. And yeah, human remains are definitely classified as biohazard. There might have been any number of experiments aboard as well that would, technically, be classified as such following the crash. Whether they'd present an actual danger is another matter.
  7. You might have missed the lowest point. It looks like it's starting to brighten again. It's hard to say for sure with publicly available data, but it looks like the minimum was a few days ago. It also kind of looks like it might be cooling, because the B band isn't recovering quite as rapidly as V band, but I'm going from single observer on that one, so this is all well within error bars. Can't wait until we get published data on the whole event. Hopefully, there will be more ESO images as well.
  8. Well, mostly meaningless. Speed of light is a local limit, not a global one. Space-time curvature can allow for an object to travel much faster than speed of light relative to anything that's not in its immediate neighborhood. That's why our universe is allowed to be less than 14 bilion years old and over 90 billion light years wide. While energies required would be entirely absurd and non-physical, purely from perspective of mathematics of General Relativity, one can construct such space-time curvature as to allow an object to approach Earth at many times the speed of light, and also to have transition be sharp enough that the object has no chance of slowing down despite immense gravitational gradients this is sure to result in. That will result in the incoming projectile creating a shockwave in space-time itself, frame-dragging a region of space-time that allows it to continue at FTL speeds relative to whatever's in front of the shockwave. Anything the shockwave encounters will be turned into gamma radiation, because any mass the matter has is absolutely meaningless compared to the energies involved. Naturally, no two particles collide at FTL speeds in this scenario, because that would actually violate locality and causality, but the boundary across the shockwave can be pretty thin, so you can think of it as something punching a hole through Earth at FTL speeds. In terms of an outcome, the difference between this and simply encountering a sub-light object with similar kinetic energy is entirely academic. In both cases, Earth gets blasted into rapidly expanding hyper-relativistic particle soup which will probably produce many new galaxies as it cools down.
  9. Yeah, I should have clarified that by "launch into space," I mean establishing an orbit. Thank you for that correction.
  10. Yeah, which just involves iteratively solving an integral equation for the integrated form of the diff eqs governing the bullet's motion. It's still the same physics, and if one struggles to produce good results in the sight tracking, they probably wouldn't be able to write good bullet simulation either. That said, the engine and gameplay team are usually distinct. And it's probably the engine guys who wrote the simulation and gameplay who wrote the sight. Hence my comment. It's not that I expected gameplay guys to just know how to write it. I expected them to talk to the engine guys or somebody else who knows relevant physics. If that happened right away, it'd be done correctly right away. This is something that's pretty straight forward to implement if you've encountered it before and know methods used to solve these sorts of problems. But if you're just a good programmer who has been given this as a task without having relevant background in numerical methods, your first few attempts are going to be pretty far off, and probably far more computationally expensive than they need to be.
  11. Firework rockets and most hobby model rocket engines are based on gunpowder or something similar, and have exhaust velocity around the speed of sound. You'll notice that they have no bell on their nozzle, because the later only makes sense with supersonic exhaust. Exhaust from SRB is 5-6 times faster, which also means they operate with way higher pressure. Outside of both being solid fuel motors, they are actually very, very different rockets. You can launch an SRB into space. You cannot launch a firework rocket into space, no matter how big you make it. Tetens formula is another empirical formula, which is also just a result of fitting. Except, you can clearly see that they are using Buck's parameters, which might actually make the resulting equation they give not only empirical, but also incorrect. Though, it's probably within error bars, anyways. In order for formula to be anything but empirical, and for the constants within to have meaning, it has to be derived from first principles, with only numbers present being either fundamental constants or unit conversions. For example, the ideal gas constant is just Boltzman constant per mole. Both of these are just unit conversions, and basically relate temperature to kinetic energy of a mole of gas. In natural units, R = 1. That makes Ideal Gas Law an actual first principles equation. If you take observational data, fit it to an arbitrary formula, and get the parameters that way, no matter how much derivation and manipulation you do afterwards, it's just an empirical formula. And the parameters in it are just as arbitrary as the initial fitting parameters were. There is no hidden meaning behind any of them. Empirical formulas are useful. I don't mean to knock them. But when somebody asks what the numbers in the formula mean, the answer is nothing. They are just fitting parameters to make the observation data fit the equation. No matter how much additional massaging of them you've done to fit your particular use case.
  12. If you mean the one in January, it was refined to be from a different part of space, IIRC.
  13. Because the original empirical equations were derived in Kelvin, because, obviously. Then somebody combined these empirical relationships and converted the units to get a convenient humidity formula, which is why you get a few familiar looking numbers in there mixed in with the rest. But these start with Buck's relations, and the numbers in these are purely from data. You cannot derive these from fundamental properties of materials involved. The fact that you later did a bunch of math on them to convert to a different set of units doesn't magically make this formula less empirical.
  14. That sort of thing always makes me sad. I don't expect gameplay engineers to just know how to write this sort of thing. But then it really doesn't take much effort to find someone who does. Two things always make me really sad in games. Bad physics and bad networking. Both are always very easily fixable by somebody who knows what they are doing.