K^2

That's stupid. Converting energy directly to heat is way, way more efficient than electrolyzing water and burning the mix to generate the heat. If you are trying to use water as propellant, an NTR is going to be several times more efficient than what you are proposing. Rockets aren't magic. They don't get ISP from some mystical reaction between fuel and oxidizer. Fuel and oxidizer burn, generating heat. Nozzle allows heated exhaust gas to expand and converts internal heat energy of the gas into thrust. If you can generate the same heat without bothering with a chemical reaction, you've just saved yourself some trouble.

Lexus Hoverboard is a cheap publicity stunt. People have been riding magrails on type II HTSC boards in labs for years before that. Nobody made a big deal of it, because its not in the least practical without somebody laying down a rail for the thing to ride on. So no, there are no exceptions. Technology is lead by science. Every once in a while, a new piece of tech gets name from science fiction. Robotics is the most widely known example. Another good example is warp drive. It might be called after the Star Trek counterpart, but it works nothing like the one in the show, and has been derived as a mathematical formula first and foremost. If it ever becomes practical technology, it'd owe nothing but the name to the show. And this is the case with every piece of technology we have. The inspiration of technology is from pure science. The inspiration for names or how it's presented visually can come from other sources.

You are missing the point. In order to improve efficiency, you have to bring reaction mass. It's the only way to reduce ∂E/∂p. Ion drive brings very little reaction mass and is limited primarily by energy supply. Chemical drive brings a lot of reaction mass and that's your only limitation. Photon drive has no reaction mass and is purely energy-limited. Cannae drive is non-physical, and is limited by suspension of disbelief. It's entirely your call on which of these you want to be your limiting factors for a particular mission. They all fit along the same curve of the energy vs mass, give or take a chunk for efficiency. Up to a point, we can play around energy limits with a nuclear reactor. But mass defect of ~1% fundamentally limits you to a rocket with effective ISP of ~0.1c/g. For Solar System, that is plenty. For interstellar, it might as well be useless. Your next step up is an antimatter or a black hole drive. Again, your call on where the limitations of that are going to be, but you're still a prisoner of E² = p²c² + (mc²)². You can't get around that with a reaction drive. It's fundamentally impossible. The only way to go further in any reasonable time frame is to alter the geometry of space-time. It's wormholes, warp drives, or bust.

No, and pretty much the entire thread has been about why it would not.

Compared to energy required to put the craft into orbit or transfer trajectory, energy/fuel required to make it spin is negligible. Inertial forces thus generated are going to be an order of magnitude gentler than these generated during liftoff, or even softer than a typical insertion burn. The only good reason to have non-rotating section is in the case of ISS, where the rotating section is just an additional module used for experiments. If we are going to go for centrifugal gravity on something like interplanetary ship, we are way better off spinning the whole thing. In fact, tethered counterweights might be a good idea there.

P.S. Take that, IPB editor.

I would not put solar collectors on a tug. It'd be terribly inefficient. Solar collectors will keep fixed orbits at a location tugs come to visit and refuel at. The solar collector will break water into oxygen and hydrogen. These will either be used by tugs directly as fuel, or be used to synthesize a more convenient fuel. Alternatively, keep oxygen for the life support, and use hydrogen with NTRs on tugs.

E² = p²c² + (mc²)² This is the mass shell. It is a requirement for a particle that can propagate as a free (non-virtual) particle. We are interested in how much the energy changes as we change momentum. In other words, we wish to compute ∂E/∂p. ∂E/∂p = pc²/E Which tells you that to propel yourself efficiently, you want reaction mass with high E at low p. If you can come up with something other than increasing m in the equation for energy to achieve that, please, let me know. Otherwise, that's all there is to the limits. Note that in the limit of the photon drive, m = 0, the above reads ∂E/∂p = c. In other words, you need almost exactly 300MW of power for every 1N of thrust if you don't have reaction mass. The most important fact to keep in mind is that vacuum fields are taken into the account with above. In order for a quantum field to absorb momentum, you must create an excitation in it. For that excitation to propagate, it must have a mass pole. That mass pole is on the shell and obeys E² = p²c² + (mc²)². Like any other excitation that can propagate in space. There's your limit.

Same exact problem persists if you try to put a shell "in orbit" around a planet/star. It's not about shell vs. ring, but about what happens the moment it becomes slightly off center. And while shell theorem does tell you that there is equilibrium, both for ring and the sphere, that equilibrium is unstable. Which means that tiniest deviation from center would result in that deviation increasing, until one end of the ring/shell comes crashing down into the planet/star. This will happen regardless of whether the structure rotates or not. There are some really cool orbits where statically unstable equilibria can still be dynamically stable*. Unfortunately, the amount of symmetry exhibited by both rings and shells is the very thing that prevents you from doing anything creative. For a shell, absolutely any rotation makes no difference whatsoever. For a ring, rotating on axis perpendicular to axis of symmetry could be interesting, but still won't prevent the ring from crashing into the planet. * Lissajous Orbit is a cool example of dynamic stability at statically unstable equilibrium.

Which is fine, because communication via entanglement always relies on a classical channel of some sort, so if classical channels preserve causality, then QM channels preserve causality. But if you happen to have a wormhole that causes a time loop, or something along these lines, classical channels no longer preserve causality, and classical physics runs crying back to QM to save the day. Whether or not QM actually saves the day when causality is violated depends on some of the aspects of underlying field theory. I really hope it does, though, because there are no real mechanisms to prevent CTCs, at least on a small scale, and that would mean we'd be in for bad times if causality does get violated somewhere in the universe. Which is a big place. So even if it's very, very hard to build a time loop, you know someone out there is going to manage it.

This is an example of Quantum Teleportation, which uses entanglement to send information, but it's not using just entanglement. Basically, you can leverage entanglement to send along a lot more data than you would otherwise, or send very different data than you thought you were sending. But there still has to be a classical communication channel that obeys speed of light limits. It is extremely exciting to see this done with actual packets of data, rather than individual particle states. Experiments like this bring us a step closer to real, practical teleportation. It may be one step out of millions, and I would absolutely not hold one's breath for having it in our life time, but exciting nonetheless. Causality is also a softer subject in QM. There is still a notion of overall causality, but it's very different from what you normally picture in classical mechanics. Energy arriving at destination before leaving origin, for example, is totally kosher. Information arriving before it left, not so much. Not without CTCs, anyways. Which, of course, are a feature of underlying Field Theory. At any rate, I wouldn't put too much stock in Causality. It's a comfortable notion, but not one as strictly enforced in actual physics as some people seem to think.

I think it was The Ringworld Engineers that introduces fusion rockets around the perimeter. Here is the thing, though, a rigid ring around a planet/star is gravitationally unstable. If the ring is flexible, interesting things can happen, depending on how flexible it is. Larry Niven ran into the problem because he needed a world built on the inner side of the ring. That required something that's pretty rigid if he didn't want terrain being constantly devastated by flex of the ring. In fact, it required material which was impossibly strong and impossibly rigid, which he invented. But that's why he needed the fusion rockets. Something built from more realistic materials, however, would behave more like a swarm with tethers. Such a structure can be made to have a dynamically stable orbit. Of course, if you put jets on that thing and try to change its angular velocity, it will either be torn apart by centrifugal forces or collapse inward. Either way, it's not a good idea.

Two ships coming together from different orbits is called high velocity collision, not docking. You have to match velocities almost perfectly to successfully dock, and that means that orbits of two objects also match right before docking.

Highly dependent on experiment. There's a bunch of stuff where you really just care about low pressure. But yeah, that's precisely why there's an entire industry of super low vapor pressure lubricants for experiments. Sometimes you really care about the quality of that vacuum. I've never had to work with anything remotely that needy, but I'm told the high end pressure chambers actually have a turbine stage to get rid of these last traces of molecules when gas is basically just in ballistic mode.

Same problem is found in vacuum pumps, and a whole bunch of other applications where you need moving parts that have to move past each other smoothly, but must not allow gases to leak, and must be vacuum-safe. The solution is various mineral oils with absurdly low vapor pressures. They form an air-tight seal and lubricate the moving parts. At the same time, they evaporate only very, very slowly even in vacuum. In some applications, where you need really high quality vacuum, ionic fluids are used instead of regular oils. These are fluids that consist of two kinds of ions with opposite charges. As a result, they have almost zero vapor pressure. If a molecule tries to leave ionic fluid, it's pulled right back in by the resulting electric charge. So they effectively do not evaporate in vacuum. They are, however, more expensive and have narrower temperature range. I think it's going to be simpler and cheaper to just refresh the mineral oil in the seal every once in a while on a space station.

They should also make violins simple enough that anyone can play them. That's not how the real world works. It's not enough that you want something. There is also a factor of training and even natural capability. You can't understand Quantum Mechanics, let alone Quantum Field Theory. You lack training for it. Why do you insist that things you can't understand get dumbed down until you do? This kind of attitude is precisely the problem we are constantly facing in trying to prevent education system from completely collapsing. Everyone demands to make things understandable to them, which leads to entire education system devolving to a common denominator. This is bad. It's bad for you, because you simply need to get over it, it's bad for people who are actually trying to learn something and are willing to put in necessary effort, and it's really bad for society, because we simply end up lacking sufficient quantity of skilled individuals. And I honestly don't give a crap about your problems, but you are exhibiting the attitude that's destructive and you should at least have the common sense to stop. If you don't understand something, and you are actually willing to learn it, I can point you to a course on linear algebra that will get you started. Keep working at it, and in just a year or two, you'll have a pretty good grasp on basic QM. In a decade, you might start understanding basics of field theory. If you aren't willing to put in that sort of effort, not understanding is your fault and nobody else's. If you can't understand even that, then you really have a problem.

There are tons and tons of indirect measurements that would have revealed tiniest of discrepancies. The transition energies can be measured extremely precisely. You can use EPR to correct these and get many decimal places on your charge estimate. You could get q/M ratio directly by shooting charged particles past a magnet. You can look for excess electrons in conductive materials to prove that the proton/electron ratio in neutral materials is 1:1. I could probably go on. Direct measurements are hard, but we very rarely need them. My grandmother is perfectly happy with "God made it that way." Fortunately, this wasn't an acceptable standard of understanding for people who actually advanced our knowledge and gave us medicine and technology. People are perfectly happy to accept that they aren't as strong as someone else. Or not as rich. But the moment the subject touches intelligence, every fool seems to take a position that if they can't understand something, than neither can anybody else. So if you can't explain it to them, it's the fault of the person who does the explaining. Obviously, it can't possibly be insufficient education or insufficient mental capacity. That's the reason we still have people trying to ban evolution being taught in schools. That is not a good company to be in.

Exactly. We usually think of planets as if moving in vacuum, but over billions of years, a star system really works more like a really, really thin gas. Over long enough time frames, planets actually experience an equivalent of drag from all of the collisions and fly-bys. The net result of these interactions is that orbits tend towards more circular ones. Total energy remains roughly the same, meaning the semi-major axis stays almost as large as it was originally. But eccentricity decreases, raising the periapsis and lowering the apoapsis.

You disagree with Field Theory? Bold. I'm sure it's based on decades spent in the field and results of colossal research effort on your part, and not on total ignorance of the theory. Because, you know, that would be kind of dumb.

I think, some presets come with scaling predefined. You'll need to dig through the settings and see if you can find the actual fields that define it.

The only interaction that can change the charge of a particle is the weak interaction via the weak isospin flip. That is restricted to 1e by the SU(2) symmetry. Change by another increment would require a new fundamental force to be discovered. And not just any force, but one that fits a list of criteria that will make a profound impact on a host of known phenomena, making it incredibly unlikely to have been undetected to this day. I won't say impossible, of course, but this is not "Oh, we just don't know any better," type of thing. It's something with a known cause, well-understood mechanism, and very little in terms of possible loopholes. I am objectively confident in saying that 1e is the quantum of electric charge.

It's not a quantum of charge. Whoever called it a quantum was wrong. The quantum is still 1e. It's the same as with spin. Electron's spin is ±1/2ћ, but the quantum of angular momentum is always 1ћ. So the spin can only change by 1ћ. Example, spin flips from +1/2ћ to -1/2ћ. As it does that, it will emit a photon (possibly a virtual one), that will carry angular momentum of +1ћ. Which you can picture as EM vacuum going from 0ћ to +1ћ as that photon is created. You should note similarities with the process I described for a weak interaction in my previous post. The only weird thing about quarks is an offset of +1/6 e, due to the weak hypercharge of +1/3. So instead of -1/2 e and +1/2 e, you end up with -1/3 e and +2/3 e. Likewise, offset for leptons is +1/2 e, due to weak hypercharge of +1.

You either got confused with weak hypercharge, or got led astray all together. This is not how quanta work in QM. The quantum of something is the smallest amount of change, and the quantum of electromagnetic charge is 1e. No interaction can change charge by less than 1e. A good example is a weak interaction between electron and an up quark, which can produce an electron neutrino and a down quark. The lepton's charge went up by 1e, and quark's dropped by 1e, despite the fact that quark's charge is fractional. There is still no interaction that will change a charge of something by 1/3 e. The problem with electrical charge is that we observe it as a single quantity, but it's really a composite. It goes back to the whole mixing of U(1) and SU(2) symmetries that Higgs Boson is involved in. The quantity corresponding to the U(1) is the weak hypercharge, YW, which works the way you'd expect charges to work. The other quantity, corresponding to SU(2), is the weak isospin, T. And like any isospin, it has three components, giving us, finally, the formula for total electric charge, Q = T3 + YW / 2. This is where things get really interesting. I'm not really aware of any constraints on YW. I have no idea why it's +1/3 e for all quarks, and +1 e for all leptons. But the actual unit of charge at 1e comes from the weak isospin part. The weak interaction flips it between +1/2 e and -1/2 e, exactly like the electron's spin. Which means that the total change of charge is always 1e. Edit: Yeah, looking a bit more into literature, there is no reason in Standard Model for weak hypercharge to be quantized, since U(1) has a trivial generator. Still if values for leptons and quarks were anything else, we simply wouldn't have chemistry, and that'd be kind of bad. I suppose, that's the underlying appeal of Supersymmetry.

That looks like it would re-enter like a lawn dart, in which case, that sharp nose makes me worried. Actually, it makes me worried even on ascent. It'd need to be really large to be viable. I was picturing something way smaller and way flatter.

I'm picturing a shuttle-like design that goes up nose-first, and comes down on the belly. That should create enough of the shock to protect the intakes.