K^2

You can get what, 10μN of thrust from square meter under optimal conditions? And you wouldn't be able to go much thinner than 0.01mm for foil. That's about 0.35mN/kg. Pound per pound of propulsion system mass, that's worse than a good ion thruster under the best condition. So solar sail only makes sense when propellant mass is several times heavier than your ion thruster, and that's a hell of a long mission. Since ion thrusters are only getting better and cheaper, the deciding factor is the mass to LEO, and ion gives you much lighter thing to drag to orbit than sails. Now, if we were to manufacture the probe already somewhere in space. Say, in the asteroid belt, then you really just want a cheap, reliable propulsion system, and solar sails might be a good option there.

I don't buy into orbital PV as near-future technology either, but to be fair, you don't need to refocus MW transmission. You just need the initial dish to be large enough to provide a beam that does not diverge. We are dealing with ~1cm waves. So if you want divergence on the order of the size of the dish from, say, ~1,000km, you need a dish ~100m across. Since it can be foil or chicken wire, that's probably not going to be the heaviest part of the equipment. With a bit of improvement on PVs themselves, it's the generator that will end up being heaviest, and consequently, the most expensive part of the setup.

Modern field theory has no problems with time travel. Only local causality is critical. Global causality can be violated left and right. And standard model is symmetry based. There are only a handful of "real" fields, corresponding to the fermions. All of the boson fields are gauge fields, and they are consequences of fundamental symmetries. Nothing we can do about it. These symmetries are really there. And yes, it's getting cluttered. The full symmetry group we are dealing with is: R1,3 ⋊SO+(1,3) × U(1) × SUL(2) × SU(3) × SU(2). The R1,3 ⋊SO+(1,3) part of it (Poincare group) corresponds to symmetries under translation, rotation, and boosts. In other words, movement in our 3+1 space. It's also the source of gravitational force. The rest correspond to internal degrees of freedom of particle fields, and are responsible for remainder of the forces. It's messy, but nowhere near as bad as some people seem to imply. And while there may be some structure to these symmetries, for the time being, that's all we've found.

That's why I'm mentioning rotating black holes. They've been around for a while. But yeah, if you want to go to the time just after Big Bang, you'd need to find another way.

A single AD ship in the mostly flat space-time does not make a time machine. In fact, AD by itself doesn't allow for time travel without two bubbles passing through each other, which is all sorts of trouble. If you travel at FTL speeds, the earliest you can get somewhere is right now. It did not. It's actually 13-something billion years old. The galaxies we see are now 90-something billion light years away, because universe expands faster than light. But light still travels at light speed. On the other hand, AD does allow to traverse otherwise untraversable wormholes and pass bellow event horizon of black holes. That opens up a whole list of time travel opportunities. The most obvious is in the Kerr metric, corresponding to a rotating black hole. It contains closed curves which allow for time travel. Unfortunately, Kerr solutions are suspect bellow event horizon. The exact solution for the interior is not known. So this isn't a guarantee. But arrangements that allow for time travel using an Alcubierre Drive do exist. So it's a theoretical possibility. If we build FTL Warp Drive, time travel would be something we'd have to eventually accept.

Sorry about the double-post, but in case anyone is still interested, I did run the numbers for sub-light Alcubierre drive. You end up with regions of negative energy density either way. However, the total amount of energy required scales with speed. So a "slow" moving warp bubble is going to be much easier to organize than an FTL one. I have seen a lot of literature mentioning that negative energy is only strictly required for FTL, though. I'll try to see if I can find a scheme that doesn't rely on negative energy for sub-light. There are a lot of parameters to play with. Perhaps, something as simple as a different shape for the bubble boundary could do it. And even if energy limits the top speed, the fact that ship experiences no acceleration as bubble accelerates still makes it worth investing research into.

Fair enough. I would still expect it to go full Milhouse for me, so I still don't feel comfortable recommending it to anyone else. But if you feel like you can walk someone through all of the safety steps, go for it.

No. Not at that magnitude. To get an idea of how much of an effect Earth's rotation has on pendulum, take a look at Foucault Pendulum. Gyros could redirect that effect, but not amplify it.

N_las is right. Swinging differently with gyros on/off means absolutely nothing. You have to show net deflection. Time-average of deflection angle is proportional to thrust (for small deflection angles).

I'm not talking about huge shards of glass flying out, as if a large petard went off inside. But small pieces of glass do end up flying everywhere if you just crack that thing. It's pretty much inevitable if you go with a brute force method. I suppose you could relieve the pressure gently, yeah. And then use glass cutter or heat stress fracturing to break off the relevant portion. But I've never been able to drill/break glass without it cracking in the wrong place. Maybe that's just me. But I'd definitely go for an already busted CRT tube if all I needed was the electron gun. It's just one less thing to go wrong. In any case, drilling/cutting into a CRT tube would not be on my list of general recommendations. If you feel comfortable working with glass, sure, go for it. You probably know what you're doing with that thing. I don't. And I doubt a random person just tinkering with things does either.

He said "open CRT monitor," which, to me, reads remove the housing. If OP wants to salvage an electron gun off a CRT tube, he'd have to take one apart. Best thing to do is find one that's already trashed. Still lots of sharp glass, but at least you aren't dealing with it flying all over the place as it implodes.

I don't think smoke detector source is sufficient to do this with a simple fluorescent screen. And anything that is is a bit too radioactive. It's sort of why I warn against it in my post above. You might be able to pull it off with a low intensity source using photo paper, which is a bit tricky to obtain and get developed these days. Might work with a roll of film, if you just do a 1D "cut" across the sphere around target. The advantage is that you can leave it for several days (might be useful to do an estimate of actual amount of time it should take) and get away with using a very weak source. Something you can either get from a smoke detector or even buy on eBay. This would actually be fun to try. I'll do some math to see how feasible it is with film.

Also, kind of tricky to set up. I know, it sounds easy, but the fact that it was first performed only in 1961 should tell you something. (Other than with light, of course. But that's boring.) In contrast, e/m was done at the very end of 19th century. And as a rule of thumb, any experiment they managed in 19th century, you can reproduce at home. Though, some of the early radiation experiments I would not recommend trying to reproduce. For example, Rutherford's Experiment (which is, technically 20th cen, but still very easy to set up.) requires a strong alpha source. You don't need a lot, so you can probably get away with something perfectly legal, but I still can't recommend it to someone as an at-home experiment, because radiation. A lot of particle physics experiments have radiation danger, of course. What's nice about e/m is that you can do it with energies on the order of keV, and that just produces some UV. If you go up to higher energies, working with an electron gun from CRT, for example, you'll start hitting dental X-Ray energies, and that's where you need to start worry about shielding. People have built cyclotrones at home, and you can get to hundreds of keV with that stuff. On one hand, it's really cool, because you can start doing some real particle physics at these energies. On another, safety requirements, as well as costs, are on a completely different level. I might be able to think of some other experiments that can be done with either a very weak radioactive source or an electron gun, but the reason e/m comes to mind is because it's simple, about as safe as these get, and very visual. So it's actually fun to do. Edit: Ah, speaking of visually interesting, simple, and still going after the same idea as double slit. So long as you are building/modifying an electron gun and a vacuum chamber, you can try doing electron crystallography. All you need is a target in front of your electron beam and a fluorescent screen a bit behind the target. You are a bit limited in choice of targets, compared to X-Ray or neutron source, but there are some fun ones. It's a bit hard to do this with a proper crystal at home, but if you do, say, powdered graphite, instead of dots, you'll get rings. Measuring radius of the rings will give you lattice constants of graphite. So this is a sort of 2 in 1 experiment. You do a solid state experiment, measuring lattice constants, but also confirming wave-particle duality of electrons, similar to double slit, which is a particle physics experiment.

IIRC, sub-light warp can be done with positive energy. But I'm not 100% sure that it follows Alcubierre's scheme. I really should sit down and run through the math on the sub-light warp. But even with FTL warp, there is no proof that negative energy is required. It is a requirement of every known scheme, however, so it might actually be a fundamental requirement, but we don't know for sure yet. (Same deal with traversable wormholes, by the way.) Fortunately, even if negative energy is a requirement, you really just have to have energy lower than vacuum energy. And you can achieve that by excluding field harmonics. Casimir Effect, etc. Think of it like a bubble in a liquid. It has positive mass, but lower than that of surrounding fluid, so it rises up, against gravity, as if it had negative mass. There are a whole lot of open questions there, but in principle, this should give us a loophole for building FTL warp drives and making wormholes traversable. There are a whole lot of new challenges with this approach, but at least we aren't dealing with total fiction here. We do have physics that describes "negative" energy we need, and we do have physics that tells us how to arrange that energy to form a warp bubble. So, to some degree, it is an engineering problem. Granted, it's the sort of engineering problem that dwarfs pretty much every other technological challenge we are facing, but it's nice to know that FTL is at least not impossible. Kind of lets you hope for a better future than being stuck in this star system until extinction. All of that said, FTL Warp is way, way out of our league right now. Hydrogen fusion (the slow, controlled kind), sub-light warp, and even some limited gravity manipulation are a short list of techs we'd have to hit long before we even seriously consider it. But limited experiments with sub-light could be done in our life-time. Not as a self-sustaining ship, but as tiny probes launched by enormous machines that will generate a warp bubble externally. I don't know about you, but for me, even a quantum dot moving along a particle accelerator beam at a turtle's pace, but under warp, without ever having to have undergone acceleration, would be an absolutely phenomenal achievement. Technically, we're further along with Quantum Teleportation than warp, but because of how the former scales, my money would still be on practical sub-light warp coming about first.

All that matters is getting the right space-time curvature. Until you have enough matter being transported to cause curvature of its own, it makes zero difference. But size is important. Larger bubble means larger volume of space that has to be filled with the right amount of energy to form the bubble. I don't know if scaling is actually going to be as bad as surface area. But you'll definitely have harder time forming and maintaining a larger bubble.

He can approach the ghost. Naturally, you'd first get yourself into "mostly" right place, then fast-forward the station. Otherwise, you are just denying it to a bunch of people who could have used it at a different time.

Because if you just make a measurement on your end, you can't possibly tell if what you measured was a state that has already been collapsed from the other end, or if you just collapsed it with your own measurement. And in the later case, the outcome is completely random. So you can't get any useful information out of it until you either look on the other side, or they send you a message with the results. But if you did get measurements from the other end first, and then did the measurements and compared results, that's where magic happens. In a nut shell, that's how quantum teleportation happens. It's a little more complicated than that, all in all, but this was the basic idea that paved the way to the actual algorithm. Edit: Just to clarify, if you just got results from the other end, and did the measurement with nothing in between, then you will just get a measurement that agrees with message that has been sent. The trick is to do the two measurements in different bases.

Larger bubble needs more energy. But unless you plan to haul neutron matter, actual mass of the ship or the drive doesn't matter.

Hm. Good point. That still doesn't exclude problems with two people trying to dock to it at the same time, though. Say, the time ordering is (station, ship 1, ship 2). Both ships want to dock to station. Naturally, if ship 1 fast-forwards the station to own time, it will start throwing things off for ship 2 who is trying to approach for docking. Or if ship 2 starts fast-forwarding station to own time while you are trying to dock with it. Of course, it's a fairly minor issue compared to everything else. And it results in inconvenience, rather than hard sync issues.

Just to clarify, that's called maximally entangled state. There are other ways to entangle states. You can't communicate via entanglement. It's a useful "filter" for communications, but you are still limited to classical channels. So it's never faster than light. There are some FTL effects in QM, but they all have some very interesting limitations. Tunneling is a fantastic example of that. Yeah, that's doable. You need a laser that does quantum state amplification to preserve entanglement, and a bunch of other requirements, but the concept is great. I've been looking into something similar in relation to communication and spectrum crunch. I have an algorithm that can do a 1000x "compression" using modern tech, and can be expanded up to 1Mx potentially. There are actually powerful enough solid state QCs to do rudimentary quantum information processing on a cell phone now. It's generating the signal that's the problem. So far, I've only figured out how to squish 400MHz worth of data into it, and you can do better than that with ordinary cell tower. I'm looking into EPR for an alt generator, though, which would bring me to 1012 Hz, potentially. And then I just need a signal amplifier that can go in place of a conventional tower. And yeah, it's all related to the concept of entanglement. Like I said, it doesn't let you communicate directly, but you can do awesome thing with a classical channel by throwing some entangled data at it. It's ok to break special relativity. It's already broken. What you should be careful with is general relativity. The difference is that in GR, the speed of light limit is local. What that means is that no signal can propagate faster than light relative to anything in its immediate neighborhood. QM gets around that limitation by having things not strictly speaking propagate. (Or, I should say, not propagate freely.) It's a tricky topic that I can get into with some examples, but it's all heavy on math.

Which is a huge problem. Ok, so lets say that any two players trying to dock together are always concurrent and on voice-chat. Trying to dock up with another player without comms is a suicide pact anyways. So accelerating ghosts won't matter there. But what of stations? Suppose, I want to dock to a station that another player is docking to at the same time, but his game time is several hours into the future. Any bump I make against the station during docking will send it tens of kilometers off course. But it gets worse. Suppose, another player docks to a station first, but in the future compared to my timeline. I dock to station and bump it off course. Should it move the station along with docked ship? Probably. According to game logic, they are one ship now, anyways. But what if the ship that docked to the station also gets interacted with in its past timeline? Who gets moved where? Technically, docking wouldn't even have happened. Honestly, this is a royal mess. Ghosting offers a lot of advantages, but it's far from paradox-free.

Beam power is not a very useful parameter for particle physics. The JLab accelerator produces a beam that's just 12W. But each electron in that beam carries 6GeV of energy. In contrast, an arc current when they open switches on power sub-stations can be carrying hundreds of kW of power. Yet, each electron is just a few keV, so it's not terribly useful for any experiments. So the question shouldn't be just how much beam power you need, but what energy each particle carries, and how much current you need. Of course, knowing both, figuring out beam power is trivial.

This is sound, so long as there are no collisions/docking. And it's essentially how any good MP server works. Because of network lag, everyone playing in a shooter is at a slightly different delay from the server. So when you shoot someone, how does the server know if you hit? Well, info on when and where you shot is sent to the server, and server keeps some logged data on movement of every entity. So it sees if you'd hit the enemy based on where that enemy was when you fired. And if so, it subtracts health. Of course, in a shooter, we are talking less than a second of data being buffered this way. And if you got shot, typically, all it means is that you found out that you've been killed a fraction of a second later than it actually happened. Not a problem. even with explosions, if your position shifts slightly due to prediction miss, it's not a huge deal. But in KSP, if you even nudge someone most gently during docking, it will shift their future location by hundreds of kilometers. If server suddenly decides to take that into account, it can mean all sorts of trouble for the player that leads the warp ceiling. You really need to figure out how to deal with these sorts of situations if you want warp to be de-synchronized. P.S. Memory isn't an issue, by the way. So long as you only store changes of ship configuration and trajectories of individual ships, it's peanuts. You can have years worth of data stored in RAM. Which is what you want here, of course.

Hm... If you can get/build a small electron gun and manage to draw decent vacuum, the e/m of electron experiment is fairly straight forward. What you do is set up as uniform a magnetic field as you can manage, typically with Helmholtz Coils and measure the radius of the loop the electron beam makes. It helps if you can get a bit of neon into your near-vacuum chamber, because it will make the beam that much easier to see. But even with rarified air, you can usually see the track if you pump enough electrons through it. You will need a fairly high DC voltage source and a vacuum pump, which constitute the "dangerous" parts of the experiment. If you know how to handle that sort of equipment, it's pretty safe. There is no need for anything fancy for electron gun. You can actually build it yourself. You will probably want to salvage a hot cathode from a radio lamp or similar, but other parts you can literally make out of aluminum can. You will need to set up accelerator potential and a focusing one. You want to be able to tune both independently, so that you get a nice, tight beam with whatever energy you want to give it. The accelerator potential will tell you kinetic energy of the electrons, as a multiple of elementary charge e. You can then work out the radius of the beam loop given magnetic field strength, and you can either tune the field strength or accelerator potential (or both!) to get a number of data points. The results will let you estimate electron's e/m ratio. Naturally, you can also pick up an electron gun from a CRT screen. But these, typically, have a ton of different inputs you'd have to figure out. Either option has advantages and disadvantages, so go with what you are more comfortable with. We have set up for this experiment at the department, and it's pretty straight forward. But the gun/vacuum chamber setup is pre-built, which makes this experiment just a number-crunching exercise. Your task would be a lot harder if you are trying to build it yourself.

It's more like, if you can make a warp drive, you can make black holes as well. The thinner you can make the warp bubble, the less energy you need, and you only get reasonable energy amounts when you get really close to Plank scales.