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OK, let’s suppose I have a structurally sound ship—it could take a shaking—and that space debris isn’t a problem. I have access to a high level fusion reactor, which can, for all intents and purposes, output a near-unlimited amount of electrical energy.

The humans of my world have developed artificial gravity. Could they use this type of technology, combined with their massive energy source, to theoretically warp the space in front of their ship in an imitation of a large body of mass, basically creating a gravity well that consistently remains in front of the spaceship, “sucking” it forward?

About how far outside the realm of plausible physics do you think this lies?

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    $\begingroup$ You're basically describing this: en.wikipedia.org/wiki/Alcubierre_drive. Also, a high level fusion generator won't produce an amount of energy that's near-unlimited when compared with the scale of energy required for interstellar travel. $\endgroup$ – ckersch Jul 6 '17 at 22:57
  • $\begingroup$ @ckersch Well, kind of. I don’t envision it as quite that Trekky, but thanks for the information! And you’re right, my fusion reactors probably aren’t quite strong enough for the job but hey :P it’s called science fiction for a reason. $\endgroup$ – Kai Christensen Jul 6 '17 at 23:31
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    $\begingroup$ Actually, the description sounds more like a "carrot on a stick" drive, which actually falls in the category of impossible devices like perpetual motion machines (the force on the "stick" holding the gravity well in front of the ship would be equal and opposite to the force exerted by the gravity well itself). $\endgroup$ – Thucydides Jul 7 '17 at 2:06
  • $\begingroup$ Used in Alan Dean Foster's Humanx Commonwealth universe alandeanfoster.com/version2.0/spacecraftouterframe.htm as the Kurita-Kinoshita warp drive: "power is channeled to the Caplis generator at the bottom of the generating fan. This in turn creates a small spherical gravity field just in front of the fan. The strength of the field is allowed to increase until it exceeds the ship's natural gravity. The ship is allowed to move towards the drive field..." $\endgroup$ – jeffronicus Jul 7 '17 at 3:49
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If you could create a perpetual acceleration due to gravity using energy (matter-antimatter reactors would be better for this), it would be like falling towards a planet that is always moving away from you. This is different from the Alcubierre Warp Drive because the sip is being dragged through space. Your gravity drive might make a ship move, but it would always be at sub-light speed because the ship has mass and is moving through space. It could be done by using energy to curve spacetime, but it would take a lot of energy, and the gravity generator would have to be at the very front of the ship. If you want faster than light travel using gravity, you'll have to use an Alcubierre Warp Drive.

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Manipulation of gravity is currently impossible so the plausibility of your question will largely depend on how far outside the realm of plausible physic you think it is.

Due to general relativity, it is impossible differentiate gravitation and acceleration on an object from the object's point of view so in theory if you could generate gravitation, you are generating acceleration.

Other than that, this is what you are describing if you take out all the physic mumble jumble:

instead of magnetic pull, you are talking about gravitational pull

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  • $\begingroup$ Only if there's a mechanical link between the gravity well and the ship. $\endgroup$ – ckersch Jul 6 '17 at 23:11
  • $\begingroup$ @ckersch precisely. I was considering detaching the gravity wells from the ship. $\endgroup$ – Kai Christensen Jul 6 '17 at 23:25
  • $\begingroup$ @A. C. A. C. I agree, you wouldn’t be able to find the difference between acceleration and gravitation, but at the same time, we know that energy warps spacetime, right (feel free to correct me like crazy if that’s wrong)? So couldn’t I hypothetically bend spacetime in the same way a planet does if I have enough energy and know how to use it, thus creating gravity wells? $\endgroup$ – Kai Christensen Jul 6 '17 at 23:29
  • $\begingroup$ I guess that I really want to know is whether or not I could create the gravity wells in the first place $\endgroup$ – Kai Christensen Jul 6 '17 at 23:30
  • $\begingroup$ @chersch It really doesn't matter if you are connected to the object physically or not, just the fact that it must remain there means that an force has to keep you both away from it while it somehow pulls you forward. It's comes down to newton's third law which means every action must have an equal and opposite reaction. The thing keeping it there can be anything and it would still be physically impossible to gain any acceleration. $\endgroup$ – A. C. A. C. Jul 7 '17 at 15:45
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It's definitely outside of the realm of known physics, but it's not that far beyond how resonant cavity thrusters supposedly might work. RCTs appear to violate conservation of momentum, but might work by pushing against virtual particles to generate thrust.

Now, based on our current understanding of physics, that shouldn't work, and it shouldn't be possible to generate usable force from a vacuum, or to break the symmetry of particle formation from a vacuum.

If, however, you had a means of causing the vacuum in front of you to generate a temporary imbalance in virtual particles, those particles would have mass, in a similar way that the particles providing the thrust in and RCT gain mass. Those particles would have gravity, and as such would exert a small pull on your ship. Again, that violates the laws of physics as we currently understand them, and probably couldn't happen.

Even if that did work, though, the forces involved would be incredibly small. Gravity is a VERY weak force, and generally huge amounts of matter are required to actually create noticeable effects. Either large amounts of matter, or incredibly dense matter, would be required for any significant acceleration. Your best bet would be to cause microscopic black holes to coalesce just in front of your ship, where they'd exert a reasonably strong force for a brief moment before popping back into nothingness. Even so, this type of drive would likely be best for long voyages, where a ship could spend days or months steadily accelerating, rather than for anything requiring quick, precise acceleration.

All of that, again, is probably impossible, but it's about as close as you can get to reality for a drive that's generating gravity wells to accelerate your ship in violation of half the laws of physics.

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  • $\begingroup$ Pushing against virtual particles is not really outside our current understanding of physics. It's just on the very edge of it. $\endgroup$ – Mołot Jul 7 '17 at 19:12
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No external fields or components are required

The combination of gravitics and ping-pong balls are all you need. Use gravitics to accelerate your ping-pong balls to the desired speed, then have them bounce off the wall. Each impact will transfer a little momentum to the ship. All you need to add is a ball return to automate reloading of the space drive.

It is awfully convenient to have magical physics.

I should also point out that physicists evaluating similar drives actually come to the conclusion that such a drive is impossible even with gravitics mostly because of violation of other laws such as conservation of energy, momentum, etc. E.g., as the ball exits the region of alter gravity, it must push against the flow to reenter normal space Sorry about the anthropomorphism.

As Barbie says, Gravitics class is tough.

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  • $\begingroup$ "Physicists evaluating similar drives" Can you provide a source? $\endgroup$ – BobTheAverage Jul 7 '17 at 4:07
  • $\begingroup$ @BobTheAverage A recent link I read was The Physics of Portal Guns, sure it is a portal gun, not gravitics, but the idea is about the same -- things that bother physicists include violation of conservation laws, etc. so magic tech must be explainable in a manner compatible with such laws. $\endgroup$ – Gary Walker Jul 7 '17 at 11:34
  • $\begingroup$ That's the main complaint leveled at EM drives. Of course the fact that various tests have shown that EM drives may actually possibly work is a bit of a crimp on that theory $\endgroup$ – Tim B Jul 7 '17 at 17:24
  • $\begingroup$ @TimB Not scientist myself, Mechanical engineer though. I have some hope myself for the EM Drive, but not because it will be proven to violate conservation of momentum, energy, etc. but that it could be found to transfer momentum via a novel mechanism such as coupling to vacuum state, some other field field, dark matter, or something else. New science often starts when the experimental result are: that's odd, I don't understand this result. But, I would not be surprised if the hole thing turns out to be experiment error either at this point - disappointed though. $\endgroup$ – Gary Walker Jul 7 '17 at 18:58

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