K^2

Yeah, not for manned missions, because Earth gravity-assist alone takes an extra year. Rosetta used a similar maneuver, though. So it's certainly doable. If you don't care when you get there, you can get to anywhere in the Solar System with the fuel it takes you to get to a Trans-Lunar orbit, which is about the same as getting into GEO.

ISP is expressed in seconds, not inverse seconds. The rest is right in adnrewas post. It's worth pointing out that it's measurement units all the way down. US engineers use pounds of weight/mass interchangeably. The exact definition is impulse (lb*s) per weith of the fuel (lb). Pounds cancel, leaving you with seconds. Soviet rocket engineers used a definition of impulse (N*s) per mass of the fuel (kg), leaving ISP in m/s, and different from US definition by exactly the Earth's gravity factor g. Many reference sources still give ISP in m/s, so it's something to keep in mind.

It's an artifact of the geometry. FTL = Time Travel is a frigin theorem. And dV cost can be as low as you want, so long as your FTL is sufficiently "fast". But for anything remotely sane, you need to get close to speed of light. So yeah, nobody says it's practical time travel. Just the fact that feasibility of one implies feasibility of the other, and physics has to deal with it. If time travel is flat-out impossible, than so is FTL. And that's that. If you can go FTL, however, it means that there is at least a theoretical possibility of going backwards in time, even if you'll never be able to actually manage it.

If you are moving FTL in one frame of reference, you are moving backwards in time in another, and change of local frame of reference is merely a matter of accelerating. More precisely, if you accelerate to high enough speed, then perform an FTL jump, then accelerate in the opposite direction, and jump back, the net effect is moving backwards in time. You arrive at your starting point before you depart. Such is the geometry of Minkowski space.

So, absolutely every part of that is wrong, including observing things. (We have observations from expansion of the Universe.) This is actually very, very simple. We only discuss means of traversing space-time that leave it asymptotically flat. Which means that we can entirely ignore the warp bubble, wormhole, subspace, or any other implement of getting from A to B faster than light would. And the only thing we care about is world lines (or their projections) in associated flat Minkowski Space. Easy, right? Any world line that puts you outside of the light cone from starting point is FTL travel. Regardless of whether it was FTL locally. If we want to get to a point 10ly away in less than 10 years, we have to take such a trajectory. And any such trajectory would also permit time travel. More importantly, whether you think FTL is possible or not is absolutely irrelevant. We have established constraints on hypothetical modes of travel that are consistent with all known laws of physics. If you know some laws of nature not known to scientific community, I would appreciate you publishing them in a peer-reviewed journal before insisting we take them into consideration.

No, you can actually leave after photon left and come back before it left. That's the problem. It's a genuine CTC, and it's possible with ANY method of FTL travel. Several people have explained this in detail several times.

It can pull. In fact, it can, in theory, do anything you'd do with much smaller particles using laser tweezers.

There are plenty of interpretations that do not require non-local interactions but allow for entanglement. Many Worlds comes to mind immediately.

Why? There would be thousands of more interesting stars closer to them. Even if they were looking for life, and managed to image Earth with a giant interferometer, at best, they'd know we have oxygen. And maybe they've sent a probe to take a look. Odds are, it would have passed through our system many thousands of years ago. And even if they kept watching, given speed-of-light delay, we're still going through late Roman Empire days for them. So no signs of civilization that they'd be able to detect. Maybe, if they are still watching, 1,400 years from now, they'll detect radio signals from Earth and send another probe. Maybe it will get here in 10,000 years or so.

Typical reentry trajectories are difficult to predict because they are so much at the mercy of upper reaches of atmosphere. This thing is coming back from highly elliptical orbit. That means, in all likelihood, very steep re-entry at very nearly the escape velocity. Atmosphere will have little effect on the impact location. The rest is up to having enough tracking data to predict the trajectory up to reentry.

Importance that it won't make a difference if it's machines we build or machines built by some other civilization on some other star. It's not a continuation of our civilization in any sense.

Nah, both FTL and hyper relativistic sublight warp ships will have the same kind of shielding. Warp bubble is going to atomize and likely ionize anything going in. From perspective of the ship, any obstacle just becomes a burst of particle radiation. If you can disperse it with a mag field, from there on you just need thick led lining to protect the crew. It's all quite manageable at high sublight or low FTL speeds. Unless you hit a sizable rock, of course, in which case, the radiation will just burn through whatever shielding you have. The sublight we're talking about for in-System travel, circa 0.01c - 0.1c is a different matter. Yes, you can have stray microasteroid impacts, and grain of sand at .1c is not something you can just ignore. Fortunately, even here, warp can be of help. You can design the warp bubble geometry in such a way that by far most of the debris to miss the ship.

If we "replace ourselves" with machines that can spend millenia in interstellar void and then reintegrate into society that's been busy all that time, it will not be us. Anything that makes us human will be foreign to these creatures. They will travel the stars. Not us. For us, it's FTL or bust.

Magnemoe is talking about warp. Warp doesn't have the same limits on acceleration. It's not quite instant, but the limiting factor is how fast you can put necessary energy into bubble. In any case, ship's crew doesn't experience any acceleration during warp. So 1g has no significance at all. Oh, and warp scheme can incorporate partial shielding. It will certainly atomize anything it encounters, making it much easier to deflect resulting radiation with mag fields or w/e.

Surviving 3g is trivial. Enduring 3g for 5 days is not. If you give people an option between a 5 day trip at 3g or 9 day at 1g, everyone will chose the later. It will be cheaper too. But yeah, the point was that the limiting factor here is propulsion. If you can build an engine that can pump out 1g worth of thrust for a passenger ship for over a week, Solar System isn't such a big place. Incidentally, this is right around the theoretical limits for nuclear-powered propulsion. So even without warp, we can expand throughout the Solar System. Beyond Sol, though... If we can't do FTL warp, we're not in a good place as far as building interstellar civilization goes.

Run the numbers for a trip to Saturn at constant acceleration of 1G for half way, then deceleration at 1G. I'm sure you'll be surprised.

Yes, I am sure you understand these things better than people who studied the subject for decades. The only mystery to us all is why you have not published your revolutionary findings yet. Of course, if you spend a little time researching the subject, you will learn that fairly large chunks of rock end up on earth intact in routine meteorite impacts. That rock and ice are both excellent thermal insulators. That interior of the meteorite never heats up significantly during its brief decent through atmosphere unless meteorite breaks up, and finally, that we have found organic compounds in meteorites that landed on Earth. Including compounds that denature at modest temperature. Oh, and organics, the kind necessary for life, most certainly denature at molten-rock-everywhere temperatures. Some take a while, but these were conditions for millions of years. Not the few seconds of a comet strike.

L2 cache is shared, IIRC. So that is something to keep in mind if you have threads.

Absolutely nothing. Like I said above, Alcubierre has same requirements for FTL ans sublight. If you can build Alcubierre drive, you should go FTL. Alcubierre is a special case of warp drive, however. There are warp metrics that are inherently sublight. As such, they are not subject to CTC conjecture constraints. They can also have thicker bubbles, making them far more feasible. In short, we might one day build a sublight warp drive for solar system exploration. Probably sooner than skeptics think, but still not soon. That drive will not be an Alcubierre drive. For starters, it will have Lorentz boosted interior metric. As for uses, the obvious one is cycler ships. You still have to produce exhaust to change energy and angular momentum of your ship. Warp is not magic. That means you need to be in transfer orbit with correct semi-major axis, eccentricity, inclination, and argument of the ascending node. This leaves argument of periapsis and mean anomaly as free parameters. These the warp drive will have access to. Which means you can throw a ship into cycler orbit, ignoring phase sync, and warp yourself between the two planets in a tiny fraction of the time. Best part, if you can recover part of energy needed to create the bubble when you drop out, you can make the trips pretty cheap. And an Earth-Mars cycler can be making trips in days or weeks, depending on relative phases, with very reasonable energy investments.

Most of these molecules decompose under extreme heat of planetary formation. You have to wait for planet's surface to cool down before complex organic molecules can be formed or deposited.

It did not. That statement is completely wrong. FTL and sublight Alcubierre drive requirements are identical.

Sugar and alcohol? Is it fermenting?

Higgs. It's all Higgs. That's why they have mass and why they propagate at sub-luminal speeds. Not that it has any impact on the thread as a whole. Just thought I'd point it out for these curious.

Nah. Tidal forces would make it unusable. The only reason Stargate's portals are somewhat feasible is because they explicitly state that the wormhole is used to transfer disassembled matter and information needed to reassemble it. The gates themselves are universal constructors with a buffer. You step through, get disassembled on atomic level at the interface, while a virtual simulation is maintained in the buffer, providing continuity (and ability to still have blood circulating while you're just half-way through). Once you're fully in the buffer, simulation gets suspended, and the buffer contents, matter and data, are sent over to the other gate where the process is reversed. If you want a wormhole that you're just going to fly through, it's going to have to be huge. We are talking about having hard time finding a good place to park it in the Solar system.

I was going to jump in after reading previous comments, but this right here is exactly right. I'm tempted to fill in a lot of details, but it gets technical fast. For detail breakdown of theory of shock waves, best thing I can recommend is Fluid Mechanics by Landau and Lifshitz, chapter IX Shock Waves specifically. Heavy reading for people with suitable background. I'm sure wizzlebippi can recommend something that's more practical from an engineering perspective, and more directly applicable to aircraft design.