I was reading that article on non-propellant travel methods and I had a thought... how well would something like a gravity well drive work... What I mean by GWD (gravity well drive, easier to type) is that a ship would produce some sort of gravitational anomaly just in front of itself at a distance that remains constant so that the gravity of this thing would pull the ship forward and as it does since the ship is creating the anomaly it too would move forward. couldn't something like this work?

also could the gravitational anomaly power itself once it's on by using the same gravity force to generate energy to generate the anomaly?

And how fast could something like this travel...I would doubt anything too fast, but if it could be something that could be use for super long flights considering if it did work the way i think it would it would need very little energy beyond the initial coming on phase...

It would work incredibly well. Ha, get it? And don't underestimate the speed, I'm pretty sure you'd get up to a small fraction of the speed of light in a jiffy. Only possible reason that it might not work, is that it defies most of the known laws of physics. Other than that ...

How well would something like a gravity well drive work?

Beats me, and physics, if you ever find an answer I'm sure we would all be very interested.

Why to bother with GWD? Tie a rope to your ship and pull it with whatever speed you like it to travel at. The method was used successfully by Baron Munchausen long time ago when he escaped from a swamp by pulling himself up by his own hair.

If it had the gravity of a super massive black hole it'd go fast. How fast I don't know, maybe the speed of light?

About 10% the speed of light, before it would run into some serious issues colliding with intersteller gas and dust.

JimJast, let's call it the Munchausen Drive, in honor of the good Baron.

This sounds very much like a popular description of the celebrated Alcubierre warp drive spacetime and related constructions, which naively would yield effectively superluminal transport of a warp bubble, with the inhabitants of the "bubble" feeling no accelerations and thus perfectly comfortable, in the manner of Star Trek (hence the name). See
http://arxiv.org/abs/gr-qc/0009013
Note that the eprint version dates from 2000 but is substantially identical to the printed paper, which was published in 1994. This paper lead to a large literature on warp drives. Unfortunately, very bad popularizations at cranky organs like New Scientist has lead many amateur fans of Star Trek to believe that these are "solutions of the EFE". The short story is that are not, although the reasons why require tedious explanations. They are however Lorentzian manifolds and their physically implausible properties (when they are interpreted as spacetime models) have pedagogical value for getting some intuition about what kinds of "weird" Lorentzian manifolds are (mostly likely) ruled out by gtr and other viable theories.

If you want to pursue this, you might consider doing some reading and then starting a thread on warp-drive spacetimes. One thing to look for as you read: it is known that if warp-drives were physically possible, they would require "stuff" which behaves quite unlike anything known to physics. Even worse, they would entail various causal anomalies and huge amounts of ( negative!) energy (just how much is a bit controversial). There are other objections (although the issue of how interstellar dust might affect a hypothetical warp bubble is a bit controversial), but these are apparently already fatal. (It is true that "negative energy density" can occur in effective field theory models in gtr, but the quantum inequalities, which you can think of as elaborations of the Heisenberg uncertainty principle, place strong constraints on how much you can have for how long, in how small a region.)

It turns out that this whole topic is closely related to some other highly speculative topics which have generated large literatures, time machines and Lorentzian wormholes. If you search the arXiv, you'll probably find eprints by Krasnikov; I'd caution you to read those with a critical eye. This topic is quite complex and technical, and I am oversimplifying shamelessly, but the key point is that exotic matter, warp drives, time machines, and Lorentzian wormholes are all highly speculative and even dubious concepts. That situation might change in the future, but I think that at present this is a fair characterization of the State of the Art.

This version of a Wikipedia article I (mostly) wrote may help you better understand the nature of claims that some Lorenzian spacetime "is a solution of the EFE":
Exact solutions in general relativity
And if you're really serious, see the papers and books cited in that article.

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Unless you put an anti-gravity thing behind you to repel you forward. Then instead of pulling insterstellar dust and lost stray asteroids and such in toward you, it's pushing them away from you.

[QUOTE=Durakken;1262832]a ship would produce some sort of gravitational anomaly just in front of itself at a distance that remains constant so that the gravity of this thing would pull the ship forward and as it does since the ship is creating the anomaly it too would move forward. couldn't something like this work?
QUOTE]

As far as we know, gravity works in all directions, so why would the anomaly move? It would equally attract the whole universe around it, so would stay stationary, while the nearest object the space ship, being attracted mostest, would be engulfed by the black hole. I presume you refer to a BH?

And if the BH was not 'turned on' until the spaceship was travelling at some speed, the same would apply.

I think, as a carrot on a stick is rarely used as a inducement to speed on horse-drawn carts, this is about as useful. A 'deus ex machina', or in this case a 'machina sine deus' is an attractive literary device, but bl**dy useless in the real world and ultimately disappointing in a novel.

John

chris, I don't mean to sound rude but I know very much that this will. Please stop with the overly physics geek speak when explaining things. I appreciate your answer, but I understand very little of it... and it does very little to give at least an understandable answer to the common person. I have to imagine...as with a lot of the questions that have come up... not everyone knows all this stuff nor most of what your talking about and it defeats the point of you answering... I don't mean to sound rude I just don't like reading lines of stuff that mean very little to most people without a physics degree.

Also, you lack the understanding of what a star trek warp bubble is...And I'm too out of it to actually explain it... but the ST warp bubble warps space..what i am talking about would not.

Now... as far as other things i have read...

the gravity well wouldn't have to be a black hole. It just has to be enough to pull the ship towards it... Now I know it seems impossible but i remember a special about micro wormholes that could be expanded... Now if you put one at say a black hole or a sun and attach the other on a ship all you have to do is let the gravity of the object pass through the wormhole... now the ship doesn't get closer to the blackhole/sun because the gravity is going through an item that is being pushed by the ship with the force of large mass, but weighs nothing in comparison to the ship and further is attached to the ship. The real problem that i see is how to stop and control and such and the only thing i can think of is that it would be on a bevel of some sort which could spin at whatever degree it wanted and to maintain position it would just spin around the ship...the same could be used for a horizontal drive as well allowing for complete 3D control.

The only other problem is speed as it would prolly be hard to control speed but i assume it could be done...

You are pushing on the earth, but you are also gravitationally attracted to it. The forces balance, so it doesn't make for a useful space drive. Sorry, but you're trying to get something without paying for it.

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The Leif Ericson Cruiser

Yes, but you're at 10% of c, while they're stationary. They will begin accelerating, but only about 1/1000th of a second before you smash through them at a relative velocity of 9.999999999% of c.

You take him to task for being a Geek because the answer was too complicated and then complain because he isn't the right kind of Geek to understand Fiction.

Why not ask for clairifications, simplifications or links to something easier if you don't understand.

What about the people reading the thread who do understand or want to read the 'Geekyness'?
Are they Geeks as well?

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The whole idea behind this thread violates basic physical principles. It's like the proverbial "lifting oneself by his bootstraps". It dimply doesn't work because it violates the physical law of conservation of energy. I hope this discussion is motivated by sense of humor rather than serious pursuit of knowledge.

uhh.. first off, my $.02

not such an impossible idea given that gravity is (in theory) caused by the geometry of spacetime itself. and we all know that mass warps or changes the shape of space time by well.. being heavy. the more massive something is, the more influence it will have on spacetime and will cause a stronger gravitational attraction.

I would assume that the relationship between energy and mass could mean that if you had enough energy in one spot, you could make a gravity well. but using the energy mass conversion equation, in order to obtain enough mass to warp spacetime to the point where it would attract a starship, you would need an absolutely ridiculous amount of energy, and if you have that amount of energy to spare, then it would be my contention that you could use it for better purposes.

but that is neither here nor there, the real reason this concept will not really work is because while you can "fall" into a gravity "well", your journey will be short lived because unless the gravity "well" is also moving in the direction and speed you need to go, your ship will just fall into the "well" and become crushed in the center.

you would need to somehow make your gravity well move forward which would be like placing your ship in tow.

it seems to me that while a gravity well could be used for many cool things, a drive would not really be one of them i would liken the concept of trying to drive a sail boat with a fan on the deck of boat pointed at the sails. No matter how powerful your fan is you wont go anywhere because the fan is pushing backward and the sails are pushing forward.

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-work in progress--

Yes, these explanations are accurate and help the understanding of why this brilliant idea can not actually work. The concept of being dragged along by a controlled gravity mass... this sounds great but for the fact that it does not work.
Back to the drawing board....

The 'exotic drive' which I have always found the most amusing is the Diametric drive, described by Robert Forward and Jamie Woodward
http://en.wikipedia.org/wiki/Diametr...iametric_drive
At one time we used this type of drive extensively in OA, but the extreme unphysicality of negative-mass-matter means we are discontinuing its use. We are now using a modified form of the Alcubierre/Van den Broeck drive, but with the proviso that they can't exceed light speed because of some (as yet undiscovered) Cosmic Censorship principle.

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Yeah, the geek physicists are right. Remember, in the real world and real universe you can't win, and you can't even break even.

Sigh.

Well, let's sublimate the dreams, folks, and get to work on a one-way 1/10 c probe to Alpha Centauri. It'll get there while most of the project members are still alive.

Indeed. The most promising line of research is probably finding ways of obtaining or generating large amounts of power, and somehow using that power to accelerate payloads to reasonable fractions of light speed (without vapourising them in the process).

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Captain Swoop, I'm not saying it's bad or wrong...I'm saying it's pretty obvious if someone does get the question then they aren't going to get the answer if it's more advanced in most cases especially when the terms aren't familiar.

As far as the Star Trek thing... the warp bubble encircles the ship, and warps the space around the ship... which is completely different than what I am asking about...

Hi Durakken,
It seems to me that your post has raised a red flag namely describing an anti-gravity drive. That might explain some of the replies you have received.

IMHO a gravity drive like you mention does not necessarily violate any laws other than the law of preservation of momentum, which would be pretty bad except that I know of at least one serious research in the field, conducted by ESA.

See about it here.

That should be reason enough to keep an open mind about it.
Consider that the center of gravity of a ship & it's-chemical-fuel does not move regardless of how far it travels (i.e. not considering external influences). There just has to be a more efficient way to space travel.

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"They reasoned that an object situated at the center and related equally to the extremes in every direction can have no impulse to move in any specific direction. In fact, they compared the situation of such an object with that of a man violently but equally hungry and thirsty, standing at the same distance from food and drink and unable to decide in which direction to move." - Aristotle

This is a link to info on the ESA gravitomagnetism experiment. How would that break conservation of momentum? And, I don't see much similarity between that experiment and Durraken's question.

By the way, here's a post by 01101001 with some information and links to other threads on gravitomagnetism:

The ESA have developed artificial Gravity!?

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The Leif Ericson Cruiser

Theoretically speaking, if a closed system could alter it's center of gravity it would violate the law of preservation of momentum or so I figure. This seems feasible if you could alter the gravitational field of a closed system without directly altering it's mass or energy. Needless to say if you could move the center of gravity of a closed system you have means of propulsion. That is how the subject is similar to OP.

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"They reasoned that an object situated at the center and related equally to the extremes in every direction can have no impulse to move in any specific direction. In fact, they compared the situation of such an object with that of a man violently but equally hungry and thirsty, standing at the same distance from food and drink and unable to decide in which direction to move." - Aristotle

Durakken's proposal might be imaginable when the gravity is not actually there all the time, but 'logged into' (by opening a wormhole to it) when the drive must accelerate, then turned off again. That implies each engine comes with it's own little seperated bubble of spacetime containing a few jupiter masses of, well, anything...

I'd buy that in a movie or a book. Plus we would get many cool items for Seconds from disaster.

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Neptune, Titan, Stars can Frighten...

I'm surprised I haven't seen two plausible "gravity well drive" scenarios. One is so plausible that we've been using it for several decades! The other is not very plausible at this time, but may become so in the future with advancements in materials technology.

The first is best demonstrated by two scenarios:

1. A rocket ship in free space fires it's 1 M-newton rocket engine for 1 minute. Let's say the delta-V is 1,000 fps.

2. A rocket ship closes in on a planet in free space (not orbiting anything) coming close to the planet, but remaining outside it's atmosphere (any appreciable density thereof...), and does the same where at the 30 sec mark the rocket is at it's point of closest approach, always keeping the rocket firing along it's instantaneous velocity vector.

Will the 2nd rocket ship come out of that gravity well with a delta-V greater or less than 1,000 fps?

It turns out, it's delta-V will be significantly greater than 1,000 fps, and that's without using the slingshot effect. Why? That answer gets into some pretty hairy orbital dynamics. Let's suffice to say that it works.

The second scenario may help you intuitively understand the first.

A rocket ship approaches a planet as in #2, above. Instead of firing it's engine, however, it simply extends a heavy mass on a tether in front of it. As the mass nears the planet, it's in a position to fall to a much lower orbit than the rocket. In doing so, it accelerates, pulling the rocket only partially in the direction it's going, until the rocket is nearly directly overhead, like the end ice-skater on a whip (those who've done any ice-skating know what I'm talking about). At the point where the ship is directly overhead, it cuts loose (any longer and it would begin raising the mass, slowing the ship in the process).

From what I understand, if the ship/mass initially approached the planet at the planet's escape velocity, and the mass of the ship and the mass were identical, assuming no atmospheric friction and that the mass barely kissed the planet as the ship passed overhead and released the tether, the ship's final velocity would be twice the planet's escape velocity.

Either way, both approaches utilize the same effect of gravity wells, which is, in essence, a gravity well drive, and neither violate currently known laws of physics!

HA!
I just thought of that, if you could construct a gravity well, then fall into it, and right before you hit the center, you shut it down, you could be shot like a rock out of a slingshot.
NASA does it all of the time using natural gravity wells, but instead of evaporating the gravitational mass (planet or moon) they hit it at a glancing blow and the craft gets slung at a higher velocity toward its destination.

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It would be terrible; see for example the reaction (no pun intended!) from physicists to Roger Shawyer's psychoceramic claim to have invented what he called the EmDrive, which also violated conservation of momentum.
See for example this thread in the N-category Cafe.

You're talking about claims by Martin Tajmar and Clovis de Matos to have measured in a laboratory an gravitomagnetic field generated in a superconducting coil.

Gravitomagnetism is a topic of mainstream research in gravitation physics, and it is a genuine prediction of gtr. Roughly speaking: in Newtonian physics, the gravitational field is entirely determined by mass density, but in gtr, by mass-energy density together with momentum density. That is, the source of the gravitational field is more elaborate in gtr, and so is the gravitational field itself. Roughly speaking: the nearest equivalent in gtr to the field treated in Newtonian gravitation is the tidal tensor or electrogravitic tensor (evaluated wrt some timelike congruence), which is comparable to the tidal tensor studied in Newtonian gravitation. But there is also a non-Newtonian part of the field, the magnetogravitic tensor (evaluated wrt our congruence), and in non-vacuum solutions, the topogravitic tensor. This splitting of the Riemann curvature tensor is formally analogous to splitting the EM field tensor (a spacetime tensor field) into electric and magnetic fields (which are spatial vector fields defined on spatial hyperplane elements).

Well, their claim is so-far unconfirmed and IMO appears dubious on various grounds. IIRC, one other team has tried to confirm it without success.

I'd also caution that both ESA and NASA have some "in-house" fringe groups, without neccessarily implying anything about Tajmar (whom, to his credit, has been careful to stress that his claims are unrelated to the long-since debunked "antigravity" claims of Podkletnov). In addition, these organizations plus aerospace firms like Boeing and BAE do from time to time ask some of their engineers to listen to one-hour presentations from kooks. These meetings are invariably portrayed in the crankweb as "Boeing is seriously investigating", but the engineeers have, shall we say, a very different take ;-/ (Let's say that spending a little time with kooks is not their favorite job responsibility.)

No doubt, but trying to violate fundamental principles like conservation of momentum and the laws of thermodynamics seems absurdly futile. As someone else said, devising practical methods to get a spacecraft up to 0.1 wrt Earth (and avoiding destruction by collision with interstellar dust) is quite challenging enough!

One of the last things Donald Crowhurst wrote in his "philosophy notebook" was this:
Decades later, his wife told interviewers for the documentary film Deep Water
Perhaps so, but scientists do need to debunk claims which do not withstand scientific scrutinity. This may hurt individual dreamers but it is in the best interests of society--- this is particularly true when it comes to "new energy production schemes", since for example, it would be disastrous if the NSF were pressured into spending (wasted money) on "water fuel cars" rather than lines of research and development which have a positive probability of resulting in useful devices.

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Read these PF posts. Avoid Wikipedia--- except for these versions. Read this and this suggested sticky. When asked for advice, I always say: never take advice!

When referring to the ideas of a person you consider to be a "crank", and in need of an adjective for such ideas, please use "crankish" or maybe "cranked". "Cranky" is already in use to indicate an emotional state. (Yes, I know they're all "invented" words rather than real ones, but this is not a technical correction; it's a request for the sake of linguistic cleanness.)

Done! (Psychoceramic is a humorous euphemism for crackpot.)

Although crackpots do tend to be cranky in the sense you mean...

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Chris Hillman

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