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Astrodude
15th December 2010, 12:14 PM
The Alcubierre Drive is a theoretical means of propulsion that is faster-than-light from an observer's frame of reference. If someone were to build a spaceship with Alcubierre Drive to leave Earth, if they could get to Neptune before the light from the Sun. Alcubierre's method is consistent with General Relativity because the propulsion essentially manipulates space-time.

Aside from numerous practical obstacles, the major problem with the theory of Alcubierre Drive is that it supposedly requires exotic matter, which is anything with a hypothetically negative mass. My question is how so?

I've carefully looked at the math. There is no reason mathematically that a traveler would need to obtain negative energy for this propulsion. The only mathematical need for negative energy is for the observer to witness the faster than light travel, or to be precise, the travel at the essentially superluminal speed. As far as I can tell, Alcubierre drive could be done without exotic matter with many bizarre consequences.

If a ship were to really travel at a speed of 1000c from the stationary observer's frame of reference with strict Alcubierre propulsion, the observer would simply see the ship to be one thousand times closer to him than it actually is. The ship reached its long destination traveling at 1000c and then returned to the observer using the Alcubierre drive, the observer would see the ship near him and far away at the same time. In fact, the observer could witness the spaceship's journey and the spaceship at the same time after the spaceship has been out of the bubble and near Earth for some time. Theoretically by altering speeds of the distortion in spacetime, the ship could appear to be in an infinite number of places at once for the observer.

The calculations used to claim that negative energy is required for the Alcubierre drive rely on the metric of the observer, but it's not the metric of the observer at the time of observation that's relevant because the ship is in the spacetime distortion. It's the metric of the of the observer at the time of flight, when he is ironically not observing, that matters concerning the flightpath.

Please point out any mistakes.

Bishadi
15th December 2010, 12:29 PM
Space dont bend

ElMondoHummus
15th December 2010, 12:37 PM
Huh... Alcubierre drive...

"In 1994, the Mexican (http://forums.randi.org/wiki/Mexican_people) physicist (http://forums.randi.org/wiki/Physicist) Miguel Alcubierre (http://forums.randi.org/wiki/Miguel_Alcubierre) proposed a method of stretching space in a wave which would in theory cause the fabric of space ahead of a spacecraft to contract and the space behind it to expand.[1] (http://forums.randi.org/#cite_note-Christopher_Pike-0) The ship would ride this wave inside a region known as a warp bubble of flat space."
http://en.wikipedia.org/wiki/Alcubierre_drive

All I know is that it sounds like this:

Cubert J. Farnsworth: I understand how the engines work now. It came to me in a dream. The engines don't move the ship at all. The ship stays where it is, and the engines move the universe around it.

;)

Astrodude
15th December 2010, 01:12 PM
Huh... Alcubierre drive...
...



All I know is that it sounds like this:

Originally Posted by Futurama
Cubert J. Farnsworth: I understand how the engines work now. It came to me in a dream. The engines don't move the ship at all. The ship stays where it is, and the engines move the universe around it.
;)

Alcubierre drive is a legitimate deduction from general relativity. From the traveler's perspective, it would look like Cubert Farnsworth is right.

RecoveringYuppy
15th December 2010, 01:20 PM
But it's the best example of "Can't get there from here".

Metullus
15th December 2010, 01:45 PM
Is it faster than a von Däniken Drive?

ElMondoHummus
15th December 2010, 02:14 PM
Alcubierre drive is a legitimate deduction from general relativity. From the traveler's perspective, it would look like Cubert Farnsworth is right.

Look, I don't know enough about physics to comment on this. My education was in chem and biology and it was nothing more than a bachelors. My physics knowledge is miniscule relative to folks like Sol Invictus, MattusMaximus, etc. So unfortunately, I'm not going to be able to get deep into the argument; I simply don't know enough.

But that said, from what little I do know, I can say this: Alcubierre's theory may indeed be a legitimate deduction from GR, but like anything with an FTL component, there's an inherent problem with causality (http://www.theculture.org/rich/sharpblue/archives/000089.html) that needs to be addressed. And until it is, that's reason enough to suspect its actual validity, legitimate deduction from proven theory nonwithstanding. If you can address such issues, please feel free. I wouldn't mind the education, and in fact would love to know how that aspect of the consequences get handled.

But as far as actual participation from me, I again simply don't have the knowledge. I'll turn back into an audience member and student and let you and others teach me what I need to know. So I'll bow out now and leave the details of that to be hashed out by the folks in here who're far smarter than I on the topic. But anyway, in the end, my point is that to elevate such a thing as the Alcubierre "drive" from interesting to possible, the consequences of FTL phenomenon must be addressed. Causality is the one I'm thinking of, and I'm sure others will chime in with more.

Thanks for your time.

RecoveringYuppy
15th December 2010, 02:18 PM
Actually I don't the drive does raise causality issues because the same theory that the "drive" is deduced from also implies there can't be any causal relationship between objects in our space and objects in the space containing the drive.

Soapy Sam
15th December 2010, 02:29 PM
The reason the universe looks like a rubber sheet is that sometimes, god wets the bed.

Astrodude
15th December 2010, 02:53 PM
Actually I don't the drive does raise causality issues because the same theory that the "drive" is deduced from also implies there can't be any causal relationship between objects in our space and objects in the space containing the drive.

Causality is not clearly defined in either general or special relativity. I contend that causality is an abstraction that depends on one's frame of reference.

Madalch
15th December 2010, 03:16 PM
The reason the universe looks like a rubber sheet is that sometimes, god wets the bed.
Yes, but he usually warns us before it happens.

At least one of us, anyway- that lucky person gets to build an ark.

Uncayimmy
15th December 2010, 03:18 PM
In other words, this drive will make a cart go down space faster than the space???

KingMerv00
15th December 2010, 04:29 PM
Space dont bend

*Can't resist*

Why do you think Einstein was wrong?

Astrodude
15th December 2010, 05:24 PM
In other words, this drive will make a cart go down space faster than the space???

Yes.

Vorpal
15th December 2010, 06:43 PM
The calculations used to claim that negative energy is required for the Alcubierre drive rely on the metric of the observer, but it's not the metric of the observer at the time of observation that's relevant because the ship is in the spacetime distortion. It's the metric of the of the observer at the time of flight, when he is ironically not observing, that matters concerning the flightpath.
That doesn't make any sense. There is no such thing as a "metric of the observer", because all observers have the same metric. The metric is a tensor--a geometrical object that's observer-independent. Its particular coordinate representation depends on the coordinate chart used, but that's not relevant to any observable quantity. Nor is any particular observer obliged to use a particular coordinate chart; all observers can use the same chart if they wish to, or different ones if it strikes their fancy.

If you have an observer with four-velocity u (also a geometrical object independent of coordinate representation!) at some event in spacetime then T(u,u) is the energy density measured by that observer. The weak energy condition is equivalent to saying that all possible observers measure a non-negative energy density, and the Alcubierre spacetime violates this. There is nothing coordinate-dependent in this statement: if it's violated in one system of coordinates, then it's violated in all.

Vorpal
15th December 2010, 06:55 PM
Causality is not clearly defined in either general or special relativity. I contend that causality is an abstraction that depends on one's frame of reference.
That is simply not true. While "causality" in general may be considered a philosophically slippery concept, it does have a very clear, geometrical and observer-independent definition in relativity. In fact, several of them, of various 'strength'. One can discuss the merits of each and how well they match any pre-formed intuitive notion, but that doesn't seem to be a physical or mathematical issue.

Yes.
No.

Astrodude
15th December 2010, 07:42 PM
That doesn't make any sense. There is no such thing as a "metric of the observer", because all observers have the same metric. The metric is a tensor--a geometrical object that's observer-independent. Its particular coordinate representation depends on the coordinate chart used, but that's not relevant to any observable quantity. Nor is any particular observer obliged to use a particular coordinate chart; all observers can use the same chart if they wish to, or different ones if it strikes their fancy.



I mean to say the space measured accurately. I could have used the wrong term, but I was taught that there is a difference between metric and metric tensor and that the metric changes according to relativity while the metric tensor does not. I was referring to measurement of the three dimensions of space in Minkowski space, independent of the time when I said 'metric'. Minkowski space considers time also so as a metric tensor it would not change. All stationary observers would have approximately the same metric but travelers would not. However, all travelers and stationary observers would have the same metric tensor because the yielded scalar doesn't change but the individual vectors do. If the coordinate system changes, as it does if only considering 3 of the four dimensions, the metric changes.

The different respective metrics for the traveler and the observer form the cornerstone of the Alcubierre drive.

Astrodude
15th December 2010, 07:45 PM
In other words, this drive will make a cart go down space faster than the space???

Did you mean the space making the cart move? I took that to mean gravity and said yes.

Did you mean actually racing the space bubble? If then, no.

sol invictus
15th December 2010, 07:52 PM
Vorpal is correct. The stress-energy tensor of the Alcubierre metric either violates the weak energy condition or it doesn't (I haven't checked, but my understanding is that it does). There is no "observer dependence" - energy conditions in GR are formulated in coordinate invariant form.

Of course one can question whether the energy conditions must be obeyed, but one reason to think they must be is the fact that violating them allows faster-than-light travel, and all the very serious problems with causality that go along with it.

Astrodude
15th December 2010, 08:35 PM
That is simply not true. While "causality" in general may be considered a philosophically slippery concept, it does have a very clear, geometrical and observer-independent definition in relativity. In fact, several of them, of various 'strength'. One can discuss the merits of each and how well they match any pre-formed intuitive notion, but that doesn't seem to be a physical or mathematical issue.

This rebuttal is correct. There are definitions of causality in relativity but they aren't consistent with traditional definitions where a cause must have some type of instantaneous effect. Causality wouldn't be violated anyways because the observer couldn't signal the ship it watches travel.

The Kilted Yaksman
15th December 2010, 08:49 PM
This rebuttal is correct. There are definitions of causality in relativity but they aren't consistent with traditional definitions where a cause must have some type of instantaneous effect. Causality wouldn't be violated anyways because the observer couldn't signal the ship it watches travel.
Y'mean there'd be no transwarp beaming or subspace communications from Starfleet Command?

Astrodude
15th December 2010, 08:51 PM
If you have an observer with four-velocity u (also a geometrical object independent of coordinate representation!) at some event in spacetime then T(u,u) is the energy density measured by that observer. The weak energy condition is equivalent to saying that all possible observers measure a non-negative energy density, and the Alcubierre spacetime violates this. There is nothing coordinate-dependent in this statement: if it's violated in one system of coordinates, then it's violated in all.

All this shows is that the observer cannot measure the ship traveling at superluminal velocity!!!

Once the claim becomes that because it is impossible for something to be measured at one position, the claim then is coordinate dependent because a metric by definition is how you measure something.

Astrodude
15th December 2010, 08:53 PM
Y'mean there'd be no transwarp beaming or subspace communications from Starfleet Command?

Oh there could be in a few thousand years.


Of course one can question whether the energy conditions must be obeyed, but one reason to think they must be is the fact that violating them allows faster-than-light travel, and all the very serious problems with causality that go along with it.

Then I see no reason why they must be obeyed and the problems with causality are with causality.

sol invictus
15th December 2010, 09:40 PM
All this shows is that the observer cannot measure the ship traveling at superluminal velocity!!!

Once the claim becomes that because it is impossible for something to be measured at one position, the claim then is coordinate dependent because a metric by definition is how you measure something.

I can't make any sense of that.


Then I see no reason why they must be obeyed and the problems with causality are with causality.

The problems with causality induced by FTL travel are extremely severe; most likely they render physics logically inconsistent. Since physics works extraordinarily well, that's a very strong argument against the possibility of FTL (and therefore for certain energy conditions).

Vorpal
15th December 2010, 09:50 PM
I could have used the wrong term, but I was taught that there is a difference between metric and metric tensor and that the metric changes according to relativity while the metric tensor does not.
The metric is by definition a certain rank-2 tensor. It exists over all of spacetime as part of the definition of being a Lorentzian manifold, and is the same thing for everyone up to a diffeomorphism. I'm not sure what you're referring to. What relativity does is tell how matter (and other stuff) determines the Ricci curvature of spacetime, and through div T = 0 how the Ricci curvature moves that matter.

I was referring to measurement of the three dimensions of space in Minkowski space, independent of the time when I said 'metric'.
It still sounds like you're referring to different coordinates, since the Alcubierre metric is asymptotically flat. This is not a physically relevant difference. If not, then if you could do a simple example and point to the thing you mean, I could try to help clear up this issue. As a guess, it could be that you're confused about the global vs. local distinction. The weak energy condition is a local statement... is that where you're trying to go?

There are definitions of causality in relativity but they aren't consistent with traditional definitions where a cause must have some type of instantaneous effect.
??? By what tradition?

All this shows is that the observer cannot measure the ship traveling at superluminal velocity!!!
Locally, what you just said is that Tαβuβ is not spacelike. That is not equivalent to non-negativity of Tαβuαuβ, and neither one implies the other.

Once the claim becomes that because it is impossible for something to be measured at one position, the claim then is coordinate dependent because a metric by definition is how you measure something.
And the metric is coordinate-independent!

Astrodude
15th December 2010, 10:43 PM
The metric is by definition a certain rank-2 tensor. It exists over all of spacetime as part of the definition of being a Lorentzian manifold, and is the same thing for everyone up to a diffeomorphism. I'm not sure what you're referring to. What relativity does is tell how matter (and other stuff) determines the Ricci curvature of spacetime, and through div T = 0 how the Ricci curvature moves that matter.
I always thought that was the metric tensor.


It still sounds like you're referring to different coordinates, since the Alcubierre metric is asymptotically flat. This is not a physically relevant difference. If not, then if you could do a simple example and point to the thing you mean, I could try to help clear up this issue. As a guess, it could be that you're confused about the global vs. local distinction. The weak energy condition is a local statement... is that where you're trying to go?

No, the global vs. local distinction I get. Let me try explaining what should happen according to the math in regular words:

1) When the ship travels under Alcubierre drive, space in front should contract while space in back should lengthen.
2) This contraction should effect the metric
3) The calculations show that a negative energy density is only necessary to observe the superluminal speed.
4) The real local energy density required just for the actual travel is positive.





Locally, what you just said is that Tαβuβ is not spacelike. That is not equivalent to non-negativity of Tαβuαuβ, and neither one implies the other.

When did I say otherwise? I'm just suggesting that negative energy isn't needed to use an Alcubierre drive.

Drachasor
15th December 2010, 11:06 PM
Here's a simple way of pointing out how it doesn't make sense.

What direction does this ship without negative mass go?

Think about it.

Vorpal
15th December 2010, 11:59 PM
When did I say otherwise? I'm just suggesting that negative energy isn't needed to use an Alcubierre drive.
You did just previously:
If you have an observer with four-velocity u (also a geometrical object independent of coordinate representation!) at some event in spacetime then T(u,u) is the energy density measured by that observer. The weak energy condition is equivalent to saying that all possible observers measure a non-negative energy density, and the Alcubierre spacetime violates this. ...
All this shows is that the observer cannot measure the ship traveling at superluminal velocity!!!
If you quote a discussion on the weak energy condition and its violation and make such a reply, any normal person would interpret the "this" as referring to the weak energy condition and its violation.

I always thought that was the metric tensor.
Nope.

Let me try explaining what should happen according to the math in regular words:
I would rather you give the math, actually.

1) When the ship travels under Alcubierre drive, space in front should contract while space in back should lengthen.
2) This contraction should effect the metric
3) The calculations show that a negative energy density is only necessary to observe the superluminal speed.
If your claim is that the weak energy condition is not violated for subluminal Alcubierre drive, then you're in disagreement with Alcubierre's paper. If it's something else, then I've no idea what you mean. Either way, you should at least outline the math--what exactly are you calculating and how?

4) The real local energy density required just for the actual travel is positive.
'Real'?

rwguinn
16th December 2010, 08:51 AM
The Alcubierre Drive is a theoretical means of propulsion that is faster-than-light from an observer's frame of reference. If someone were to build a spaceship with Alcubierre Drive to leave Earth, if they could get to Neptune before the light from the Sun. Alcubierre's method is consistent with General Relativity because the propulsion essentially manipulates space-time.

Aside from numerous practical obstacles, the major problem with the theory of Alcubierre Drive is that it supposedly requires exotic matter, which is anything with a hypothetically negative mass. My question is how so?

I've carefully looked at the math. There is no reason mathematically that a traveler would need to obtain negative energy for this propulsion. The only mathematical need for negative energy is for the observer to witness the faster than light travel, or to be precise, the travel at the essentially superluminal speed. As far as I can tell, Alcubierre drive could be done without exotic matter with many bizarre consequences.

If a ship were to really travel at a speed of 1000c from the stationary observer's frame of reference with strict Alcubierre propulsion, the observer would simply see the ship to be one thousand times closer to him than it actually is. The ship reached its long destination traveling at 1000c and then returned to the observer using the Alcubierre drive, the observer would see the ship near him and far away at the same time. In fact, the observer could witness the spaceship's journey and the spaceship at the same time after the spaceship has been out of the bubble and near Earth for some time. Theoretically by altering speeds of the distortion in spacetime, the ship could appear to be in an infinite number of places at once for the observer.

The calculations used to claim that negative energy is required for the Alcubierre drive rely on the metric of the observer, but it's not the metric of the observer at the time of observation that's relevant because the ship is in the spacetime distortion. It's the metric of the of the observer at the time of flight, when he is ironically not observing, that matters concerning the flightpath.

Please point out any mistakes.
Negative energy?
Would that not mean that energy is a vector?

Astrodude
16th December 2010, 08:52 AM
My claim is that the weak energy condition would only be violated if the superluminal travel were to be observable. I see no reason why it would be violated if the travel merely took place. I'm looking at the steps where[edited for spelling] Alcubierre differentiated and he differentiated with respect to variables that aren't relevant to the actual flightpath.


If your claim is that the weak energy condition is not violated for subluminal Alcubierre drive, then you're in disagreement with Alcubierre's paper. If it's something else, then I've no idea what you mean. Either way, you should at least outline the math--what exactly are you calculating and how?

'Real'?

By 'real', I mean the energy density actually required for the travel to occur.

Astrodude
16th December 2010, 08:55 AM
Negative energy?
Would that not mean that energy is a vector?

Yep, it would mean energy is a vector. Negative energy has been observed sometimes by Gravity Probe B and E.S. Miksch had a widely respected theory that posited negative energy of gravitational radiation, but I can't find what it is because he died. But, I don't see why negative energy is even needed for the Alcubierre drive.

edd
16th December 2010, 09:12 AM
Negative energy?
Would that not mean that energy is a vector?

Despite what astrodude just said, no it wouldn't. Scalars can have negative values.

edit to add: and don't forget what gravitational potential energy looks like, if you need further convincing.

sol invictus
16th December 2010, 09:44 AM
My claim is that the weak energy condition would only be violated if the superluminal travel were to be observable. I see no reason why it would be violated if the travel merely took place.

That makes no sense at all. How is "ship 1 departed point A and arrived at point B, 1 light year distant from A, 6 months later" not an observation of superluminal travel?

And regardless, as I said - either the metric violates the weak energy condition or it doesn't. Evidently this one does. That statement has nothing to do with any "observer"; it's a coordinate- and observer-independent fact.

I'm looking at the steps were Alcubierre differentiated and he differentiated with respect to variables that aren't relevant to the actual flightpath.


So you're saying he made a mistake in his paper? If so, please show us what it is.

Astrodude
16th December 2010, 10:45 AM
Despite what astrodude just said, no it wouldn't. Scalars can have negative values.

edit to add: and don't forget what gravitational potential energy looks like, if you need further convincing.

He's right, energy is usually considered a scalar and I goofed there, but it might be useful to represent it as a vector's magnitude. Particularly, I think it could be represented by the modulus of a complex number. It's a semantic issue and somewhat subjective because if energy is positional, you can consider it to have a direction. -5 does not equal 5, but they must have the same magnitude since magnitude cannot be negative. Only the directions can differ. This is where I think it gets a little subjective.

A scalar can have a negative value, but it only matters if it can be related to a vector. Energy can always be defined as a dot product classically so it is therefore dependent on a angle, a direction. To get a one-to-one function, limit the domain of theta from 0 to 90 degrees so only one possible angle can yield one possible work value for a given distance and force. A magnitude of a vector cannot be negative. Therefore, in order to distinguish between work in one direction from work in another direction, you would need to treat it like a vector. If you pushed a box at a 45 degree angle, and there a two possible angles defined as 45 degrees to get a one-to-one function, how else would you distinguish forward work from backwards work?

rwguinn
16th December 2010, 10:52 AM
He's right, energy is usually considered a scalar and I goofed there, but it might be useful to represent it as a vector's magnitude. Particularly, I think it could be represented by the modulus of a complex number. It's a semantic issue and somewhat subjective because if energy is positional, you can consider it to have a direction. -5 does not equal 5, but they must have the same magnitude since magnitude cannot be negative. Only the directions can differ. This is where I think it gets a little subjective.

A scalar can have a negative value, but it only matters if it can be related to a vector. Energy can always be defined as a dot product classically so it is therefore dependent on a angle, a direction. To get a one-to-one function, limit the domain of theta from 0 to 90 degrees so only one possible angle can yield one possible work value for a given distance and force. A magnitude of a vector cannot be negative. Therefore, in order to distinguish between work in one direction from work in another direction, you would need to treat it like a vector. If you pushed a box at a 45 degree angle, and there a two possible angles defined as 45 degrees to get a one-to-one function, how else would you distinguish forward work from backwards work?
By it's resultant on matter and the direction of motion induced [/engineering mode]
I get the point, but it is interesting to see how you folks in the "why is there air" fields define things.
In my case, as an engineer, I think of it as absorbing or releasing energy, so depending on your reference frame, I guess you could describe it as "Negative energy" and "positive energy"
Carry on--this is interesting stuff.

Fnord
16th December 2010, 11:08 AM
Is anyone going to actually build one of these things and demonstrate whether or not it actually works? Or is everyone satisfied with arguing about the meanings of words?

This thread reminds me of a story about a controversy in the Vatican over the number of teeth in a horse’s mouth (http://answers.google.com/answers/threadview?id=713157), involving great debates and learned philosophical discourses. Finally, someone suggested that they find a horse, open its mouth and count the teeth.

That person was immediately excommunicated. ;)

Astrodude
16th December 2010, 11:14 AM
That makes no sense at all. How is "ship 1 departed point A and arrived at point B, 1 light year distant from A, 6 months later" not an observation of superluminal travel?

If ship 1 departed from point A, arrived at point B which is one light year away from A, and returned to point A in two months, the observer at point A would see the ship once it exited the bubble and was close to the point A. It would look like it came out of nowhere or literally skipped space if you could actually see it with all of the would-be radiation and from this alone the observer would not be able to calculate velocity because he would've observed a discontinuous flight.

However, a few months after the ship's arrival, the observer would be able to view the ship traveling from point B to point A but simply at a much slower apparent speed because the speed of light is the same in all frames of reference because the space has gotten longer than it was when the ship was actually traveling. If the ship could be piloted(another tough matter altogether) by a human pilot, the human pilot could theoretically watch himself fly the ship after he flew it with a telescope. However, it would look like he was traveling much more slowly. Also, with a hypothetically super powerful telescope, you could watch historical events on Earth by traveling superluminally to far away places.

I'll be glad to show the math when I can figure out how to write equations on the webforum; I need to remember LaTeX symbols.

So you're saying he made a mistake in his paper? If so, please show us what it is.

As far as I can tell, on page 8 of his "The warp drive: hyper-fast travel within general relativity" at the bottom. Just because the velocity calculated by the observer would be sub-luminal, doesn't mean that the real velocity was sub-luminal.

Astrodude
16th December 2010, 11:27 AM
Is anyone going to actually build one of these things and demonstrate whether or not it actually works? Or is everyone satisfied with arguing about the meanings of words?

This thread reminds me of a story about a controversy in the Vatican over the number of teeth in a horse’s mouth (http://answers.google.com/answers/threadview?id=713157), involving great debates and learned philosophical discourses. Finally, someone suggested that they find a horse, open its mouth and count the teeth.

That person was immediately excommunicated. ;)

Hell yeah! First, we need to build really tiny models and test the Alcubierre drive a subluminal velocities because we don't have enough energy to build a big one currently.

Plus, until it could be piloted, according to my apparently contentious observation, it is really difficult to determine whether it worked or not because we couldn't actually see it travel faster than light. If it traveled with the Alcubierre method at an overall speed slower than light to test it, I think we should see the ship traveling without length contraction and time would pass the same for the traveler and the observer. A good way to test it would be to measure if would be to see if time dilation was mitigated. Also, it's important to point out that we'd still observe the traveler moving at just a fraction of his actual velocity.

Drachasor
16th December 2010, 01:22 PM
It won't work without negative mass.

Again, without negative mass, what direction does the ship travel in?

Astrodude
16th December 2010, 01:36 PM
It won't work without negative mass.

Again, without negative mass, what direction does the ship travel in?

I think it would travel with the bubble without negative rest mass.

I'm logging off for now, but I'll be back Saturday.

AvalonXQ
16th December 2010, 01:52 PM
But that said, from what little I do know, I can say this: Alcubierre's theory may indeed be a legitimate deduction from GR, but like anything with an FTL component, there's an inherent problem with causality (http://www.theculture.org/rich/sharpblue/archives/000089.html) that needs to be addressed.

FTL implies atemporal causality; that's all.
Just because we can't predict all of the resolutions to such a phenomenon doesn't mean that it's impossible; it just means that we don't understand it yet.

Drachasor
16th December 2010, 02:39 PM
I think it would travel with the bubble without negative rest mass.

You aren't thinking this through.

What direction is that? Think about the physical object. How does the physics define a direction there? Consider how very massive objects work in real life.

Astrodude
25th December 2010, 09:55 AM
You aren't thinking this through.

What direction is that? Think about the physical object. How does the physics define a direction there? Consider how very massive objects work in real life.

Sorry I'm back a week later than I expected.
You might be getting at something else, but you imply an interesting point, that the expansion of spacetime engendered by the motion of large objects necessitates negative mass to contract it. As far as I can tell, the so called negative mass needed for this already exists in the gravitational field! The gravitational radiation should act as negative mass naturally. I wouldn't call that 'negative mass' for practical purposes, but you certainly could.

Since gravitational radiation only moves at the speed of light, it still would be impossible for an observer to witness the flight path in real time, if that isn't an oxymoron here, but it could still fly.

sol invictus
25th December 2010, 10:21 AM
If ship 1 departed from point A, arrived at point B which is one light year away from A, and returned to point A in two months, the observer at point A would see the ship once it exited the bubble and was close to the point A. It would look like it came out of nowhere or literally skipped space if you could actually see it with all of the would-be radiation and from this alone the observer would not be able to calculate velocity because he would've observed a discontinuous flight.

However, a few months after the ship's arrival, the observer would be able to view the ship traveling from point B to point A but simply at a much slower apparent speed because the speed of light is the same in all frames of reference because the space has gotten longer than it was when the ship was actually traveling. If the ship could be piloted(another tough matter altogether) by a human pilot, the human pilot could theoretically watch himself fly the ship after he flew it with a telescope. However, it would look like he was traveling much more slowly. Also, with a hypothetically super powerful telescope, you could watch historical events on Earth by traveling superluminally to far away places.

What difference do you think it makes what you could see with a telescope? If an object travels superluminally - that is, if it arrives before a pulse of light fired in the same direction - there are major problems with causality. It doesn't make the slightest bit of difference whether a particular observer could watch it travel.


As far as I can tell, on page 8 of his "The warp drive: hyper-fast travel within general relativity" at the bottom. Just because the velocity calculated by the observer would be sub-luminal, doesn't mean that the real velocity was sub-luminal.

I'm not sure what you're referring to. On the bottom of page 8 is eq. (19), which shows that the weak energy condition is violated. Are you claiming that equation is incorrect?

Chucky
25th December 2010, 12:25 PM
The problems with causality induced by FTL travel are extremely severe; most likely they render physics logically inconsistent. Since physics works extraordinarily well, that's a very strong argument against the possibility of FTL (and therefore for certain energy conditions).

I'm sorry, but as a science fiction buff I can't help asking that if some mad race of aliens did find a way to a way to exceed the speed of light one time, how localized would a rendering of logical inconsistency of physics be? Would one event violate all of time and space?

INRM
26th December 2010, 05:06 PM
Recovering Yuppy,

Actually I don't the drive does raise causality issues because the same theory that the "drive" is deduced from also implies there can't be any causal relationship between objects in our space and objects in the space containing the drive.

How could you not have a causal relationship?

RecoveringYuppy
26th December 2010, 05:22 PM
By not being able to cause anything. Basically the opening part of the opening post

The Alcubierre Drive is a theoretical means of propulsion that is faster-than-light ...

is wrong. The theoretical, by that I mean the supposed phenomena consistent with theory, also comes with the theoretical limitation that it can never interact with anything that has never been in the phenomena in the first place. Therefore it's not a "drive" or proplusion system. Regions within the phenomena can't interact with anything outside the region.

CaveDave
27th December 2010, 01:46 AM
In other words, this drive will make a cart go down space faster than the space???

Did you mean the space making the cart move? I took that to mean gravity and said yes.

Did you mean actually racing the space bubble? If then, no.

UY was making a joke, somewhat inside type.

Some time ago there was an endless thread about a wind-powered cart that would supposedly travel "directly downwind faster than the wind."

Before your time.

HTH

Dave

sol invictus
27th December 2010, 07:24 PM
I'm sorry, but as a science fiction buff I can't help asking that if some mad race of aliens did find a way to a way to exceed the speed of light one time, how localized would a rendering of logical inconsistency of physics be? Would one event violate all of time and space?

All of it, unless the region is hidden behind an event horizon.

Astrodude
1st January 2011, 02:08 PM
I'm not sure what you're referring to. On the bottom of page 8 is eq. (19), which shows that the weak energy condition is violated. Are you claiming that equation is incorrect?

His equation is mathematically correct, as he differentiated correctly. However, I don't see how his inference is correct, although everyone else apparently makes the same inference, that an event must be observable to occur. Why do the observers need to observe the negative energy density for it to be there?

The Gravity Probe B results among other things suggest that negative energy densities exist at the macroscopic scale without direct observation.

Vorpal
1st January 2011, 03:27 PM
His equation is mathematically correct, as he differentiated correctly. However, I don't see how his inference is correct, although everyone else apparently makes the same inference, that an event must be observable to occur. Why do the observers need to observe the negative energy density for it to be there?
I'm a bit confused about what you're asking; what you just said are two different things. Everything physically really must make some observable effect at least in principle. "There is a negative energy density" means that a hypothetical test measuring device would give such a result. But there is no suggestion that it actually was observed, since (unlike QM), GTR does not care to give observers or measuring devices any extra-special role. Talking about different observers is just another way of talking about different reference frames that the hypothetical measurement occurs in.

That's what the stress-energy tensor means: the density of four-momentum along some direction measured by a hypothetical observer with a given four-velocity u, i.e., dPμ/dV = Tμνuν. If you don't like it, then you're simply not doing GTR, because that's exactly what makes GTR have physical content. Without such an interpretation, the Einstien field equation would be reduced to a definition.

The Gravity Probe B results among other things suggest that negative energy densities exist at the macroscopic scale without direct observation.
Really? Could you give some reference and elaborate on what "without direct observation" means.?

Astrodude
14th January 2011, 10:19 AM
I'm a bit confused about what you're asking; what you just said are two different things. Everything physically really must make some observable effect at least in principle. "There is a negative energy density" means that a hypothetical test measuring device would give such a result. But there is no suggestion that it actually was observed, since (unlike QM), GTR does not care to give observers or measuring devices any extra-special role. Talking about different observers is just another way of talking about different reference frames that the hypothetical measurement occurs in.

That's what the stress-energy tensor means: the density of four-momentum along some direction measured by a hypothetical observer with a given four-velocity u, i.e., dPμ/dV = Tμνuν. If you don't like it, then you're simply not doing GTR, because that's exactly what makes GTR have physical content. Without such an interpretation, the Einstien field equation would be reduced to a definition.


Really? Could you give some reference and elaborate on what "without direct observation" means.?

Without direct observation means that they aren't seeing negative matter, but they are seeing what might be the effects of negative matter. Hyoyoung Choi has a paper suggesting that Dark Energy has negative mass:
http://vixra.org/abs/0907.0015

E.S. Miksch allegedly made similar observations, but he died recently and his website is down. I would feel awkward contacting his kin for his papers by looking them up from an obituary. I might do it eventually though.

Both of these men are well respected in the Physics community.


It also looks like someone beat me to the punch by over a decade and did a better job of explaining it than I did. His name is Eric Baird. http://arxiv.org/abs/gr-qc/9903068v1

Vorpal
14th January 2011, 07:24 PM
I don't even know what you're arguing anymore. You're seemingly treating three completely different claims as if they were completely interchangeable:
-- Whether the Alcubierre drive has a negative energy density somewhere.
-- Whether negative energy should be considered physically possible.
-- Whether there exists some method of superluminal travel within GTR that does not require negative energy.
Your OP began with the first, some time later the second creeped in, and now you're apparently saying that you've argued for the third all along.

How about some clarification about what your position is and your reasons for it?

Astrodude
13th September 2011, 06:25 PM
I don't even know what you're arguing anymore. You're seemingly treating three completely different claims as if they were completely interchangeable:
-- Whether the Alcubierre drive has a negative energy density somewhere.
-- Whether negative energy should be considered physically possible.
-- Whether there exists some method of superluminal travel within GTR that does not require negative energy.
Your OP began with the first, some time later the second creeped in, and now you're apparently saying that you've argued for the third all along.

How about some clarification about what your position is and your reasons for it?

I said some inconsistent things and a couple of downright stupid things here. Those were mistakes. However, I did realize some of what I meant to say and now have better terms to articulate it. In short, there is no reason to assume that gravity is positive definite!

Why should positive mass always have attractive(positive) gravity under all conditions while the universe expands? If gravity is not positive definite, a "bubble" could be generated and stabilized using only positive energy.

At page 8 of the paper on equation 19, Alcubierre assumes the real numbers to comprise the entire metric space of the given metric from page 1! These assumptions do not necessarily hold, particularly the latter. If the metric space is described with hypercomplex numbers or plain quaternions, the energy density could be positive in the given equation.

Also, if his metric doesn't always apply, gravity could be non-positive definite for particles with positive mass.
If gravity is non-positive definite, then the Einstein field equations used by Alcubierre to calculate the energy density was the wrong equation to use for all situations.

I was drawn to the concept by a man named Douglas Sweetser, but the only thorough theory that describes repulsive gravity that I've encountered is one by a professor at University of Buffalo named Mendel Sachs. I read his book "Physics of the Universe" and it gives a good explanation of his theory that I was able to follow. It helps to thoroughly practice math with quaternions though or else you can't follow his work.

Also, neither Sachs nor Sweetser have ever claimed that indirect faster than light travel without negative mass is a consequence of their theory, as far as I know. I don't even know if either of them has read Alcubierre's paper, so if I made mistakes about their theories, please correct me.

Almo
14th September 2011, 09:00 AM
Funny. The Alcubierre Drive was mentioned in a sci-fi book I read recently called Ark (by Stephen Baxter). Was a great book, BTW.

CNY_Dave
14th September 2011, 10:04 AM
snippage...
If... The ship reached its long destination traveling at 1000c and then returned to the observer using the Alcubierre drive, the observer would see the ship near him and far away at the same time. In fact, the observer could witness the spaceship's journey and the spaceship at the same time after the spaceship has been out of the bubble and near Earth for some time.

The Picard maneuver.


Dave

Vorpal
14th September 2011, 03:39 PM
Why should positive mass always have attractive(positive) gravity under all conditions while the universe expands?
If you realize that the universe expands, then the simple answer is: it doesn't. Gravity couples to more than energy density. The assumptions of your question are inconsistent.

Locally, gravity being attractive can be characterized as Rμνuμuν≥0 for timelike future-pointing u (i.e., the volume of a small ball of comoving test particles does not expand under gravity). But the Einstein field equation says that the Ricci curvature is the trace-reversed stress-energy tensor... so positive energy density is neither required for nor required by attractive gravity. It just constrains it. This is known as the strong energy condition; for a perfect fluid of energy density ρ>0, it simplifies to just a restriction on the pressure: p≥-ρ/3. The dark energy that causes cosmological expansion violates it (for cosmological constant in particular, p = -ρ).

If gravity is not positive definite, a "bubble" could be generated and stabilized using only positive energy.
Can it? I don't know, but I don't find it obvious that violating the SEC while having everywhere positive energy density can still get you a warp drive.

At page 8 of the paper on equation 19, Alcubierre assumes the real numbers to comprise the entire metric space of the given metric from page 1! These assumptions do not necessarily hold, particularly the latter. If the metric space is described with hypercomplex numbers or plain quaternions, the energy density could be positive in the given equation.
Alcubierre's metric is within standard GTR using standard differential geometry. If you want some other theory, feel free, but then there's no reason to fixate on Alcubierre at all. (Exploring what happens with quaternions sounds pretty interesting, but even if it works out sensibly, it's definitely an alternative theory~I don't think even the number of degrees of freedom of would match GTR.)

Also, if his metric doesn't always apply, gravity could be non-positive definite for particles with positive mass.
If the metric doesn't always apply, then it's a different warp bubble, and we're not talking about Alcubierre any longer.

If gravity is non-positive definite, then the Einstein field equations used by Alcubierre to calculate the energy density was the wrong equation to use for all situations.
Whoa, slow down. Are you saying that Alcubierre did not do GTR right or that GTR itself is wrong? It sounds like you're saying the latter, in which case you might consider making a new thread about the consequences of this alternative theory you're advocating.

JCM
14th September 2011, 04:20 PM
Is there a relation to the theorical Alcubierre and theorical B.E.C. generated magnetic torsion field engines?

theorical B.E.C. generated magnetic torsion field engines

If you stick a ferrious B.E.C. within a suitable hollow taurus doughnut container and use electromagnetic fields to rotate it at 60,000 RPMs, torsional magnetic fields are generated. Would a 'warp field' generate if you electronically pulse this super-ferrio-fluid at the quantum transtition speed, 1.094 MHz-m? (That is, the velocity of mechanical waves inside the nucleus. If you reformulate the Coulomb attraction of a Hydrogen atom into the form of a spring constant you get a harmonic oscillator with a specific velocity. This velocity is that of the transitional Quantum State.)

JCM
14th September 2011, 04:24 PM
Funny. The Alcubierre Drive was mentioned in a sci-fi book I read recently called Ark (by Stephen Baxter). Was a great book, BTW.
I enjoy Baxter's use of plausible science in his science fiction, he is a wonderful writer. Do you or anyone know of any science fiction that mentions B.E.C.s by chance?

sol invictus
14th September 2011, 04:28 PM
Is there a relation to the theorical Alcubierre and theorical B.E.C. generated magnetic torsion field engines?



If you stick a ferrious B.E.C. within a suitable hollow taurus doughnut container and use electromagnetic fields to rotate it at 60,000 RPMs, torsional magnetic fields are generated. Would a 'warp field' generate if you electronically pulse this super-ferrio-fluid at the quantum transtition speed, 1.094 MHz-m? (That is, the velocity of mechanical waves inside the nucleus. If you reformulate the Coulomb attraction of a Hydrogen atom into the form of a spring constant you get a harmonic oscillator with a specific velocity. This velocity is that of the transitional Quantum State.)


The answer to the question asked in the spoiler (to the extent it makes sense at all) is "no".

JCM
14th September 2011, 04:43 PM
The answer to the question asked in the spoiler (to the extent it makes sense at all) is "no".

Can you break down the scientific flaws with the "theorical B.E.C. generated magnetic torsion field engine"? I am trying to reformulate the idea of such a thing. The concept comes from the two short videos below. It appearently relates to Dr. Ning Li's AC Gravity Ltd.

Older Video on B.E.C. engine
9xnh5Nd4DzM
Updated discussing a B.E.C. engine in relation to the quantum transtition speed, 1.094 MHz-m
F4I5mgBKPZY

sol invictus
14th September 2011, 04:52 PM
Can you break down the scientific flaws with the "theorical B.E.C. generated magnetic torsion field engine"? I am trying to reformulate the idea of such a thing. The concept comes from the two short videos below. It appearently relates to Dr. Ning Li's AC Gravity Ltd.

Older Video on B.E.C. engine
9xnh5Nd4DzM
Updated discussing a B.E.C. engine in relation to the quantum transtition speed, 1.094 MHz-m
F4I5mgBKPZY

I'm not going to watch any videos, sorry. The answer to the question is "no" because the configuration described does not produce the type of (extremely exotic and almost certainly unphysical and impossible) energy needed to generate a "warp" field.

Spinning up a BEC or generating magnetic fields adds to the energy, which simply makes the whole thing a little heavier. Pulsing it with some EM radiation doesn't change that in the slightest.

JCM
14th September 2011, 05:12 PM
I'm not going to watch any videos, sorry.
Thanks anyway. Since they are embedded if anyone will and breakdown what's wrong with them I'd thank you.

Spinning up a BEC or generating magnetic fields adds to the energy, which simply makes the whole thing a little heavier.
The spinning up the B.E.C. is done with magnetic fields which generate magnetic torsion fields and supposedly it makes the whole thing a little lighter.
The answer to the question is "no" because the configuration described does not produce the type of (extremely exotic and almost certainly unphysical and impossible) energy needed to generate a "warp" field.
Pulsing it with some EM radiation doesn't change that in the slightest.
Understandable. The effects of the EM radiation pulsation at the quantum transition speed is not understood by me fully so I can't comment further. Thanks for your input.

Beerina
14th September 2011, 05:24 PM
Space dont bend

It does, as does the larger, encompassing 4D spacetime continuum. IIRC, that was one of the experiments that proved Einstein's theories -- the sun bent the rays of light from stars that passed close to it. This bending was different from what might be expected if the light "fell" towards the sun as it passed.

sol invictus
14th September 2011, 06:08 PM
The spinning up the B.E.C. is done with magnetic fields which generate magnetic torsion fields and supposedly it makes the whole thing a little lighter.


I don't know what a "magnetic torsion field" is - that's a made-up term that seems like someone wanted to sound technical and impressive. Regular old magnetic fields have positive energy, so they make things heavier (gravity acts on all forms of energy).

According to the known laws of physics, you cannot make things lighter no matter how many pseudo-scientific terms you add to the mix.

JCM
14th September 2011, 06:32 PM
I don't know what a "magnetic torsion field" is - that's a made-up term that seems like someone wanted to sound technical and impressive. Regular old magnetic fields have positive energy, so they make things heavier (gravity acts on all forms of energy).

According to the known laws of physics, you cannot make things lighter no matter how many pseudo-scientific terms you add to the mix.
Cute quips. So you do not know what a torsion field is? Do you know what a scalar wave is? Torsion field just google it. A torsion field that is magnetically induced/charged is a "magnetic torsion field". Perhaps "magnetically charged torsion field" is better ontology. It involves tensor physics. Regular old magnetic fields are not torsion fields AFIAK.
According to the known laws of physics, you can make things lighter. Sorry. Pseudo-scientific sounds like your grasp of what I am speaking of. I know it is asking the world for you to spare the time but maybe you should watch the short clips and then can comment being more informed? I doubt in fact you wish to be so but just in case
9xnh5Nd4DzM
F4I5mgBKPZY

sol invictus
14th September 2011, 06:40 PM
Cute quips. So you do not know what a torsion field is?

Sure: it's two technical terms separated by a space.

Do you know what a scalar wave is?

Yes. Why do you ask?

Torsion field just google it.

"Torsion" has a meaning in differential geometry, but it cannot be "induced" by a magnetic field, because it doesn't exist in the physical world (at least not according to the known laws of physics).

I googled anyway. Guess what I found: Torsion field (pseudoscience), a field alleged to make faster-than-light communication and paranormal phenomena possible (http://en.wikipedia.org/wiki/Torsion_field_(pseudoscience)).

JCM
14th September 2011, 06:45 PM
Sure: it's two technical terms separated by a space.
Correct. I am not being clear. I mean EM fields obeying torsional geometries.
Yes. Why do you ask?
Because they are related to torsion geometery EM fields. Calling them "scalar waves" when they are scalar geometery obeying EM waves is akin to what I have done in calling torsion geometery EM fields "torsion fields"
"Torsion" has a meaning in differential geometry, but it cannot be "induced" by a magnetic field, because it doesn't exist in the physical world (at least not according to the known laws of physics).
EM fields obeying torsional geometries are as real as B.E.C.s which the known laws of physics knew nothing of not all that long ago
I googled anyway. Guess what I found: Torsion field (pseudoscience), a field alleged to make faster-than-light communication and paranormal phenomena possible (http://en.wikipedia.org/wiki/Torsion_field_(pseudoscience)).
Yes they have been wooified. Being more clear I meant to state torsional geometry obeying EM fields. Since you have the time to google you have the time to watch the clips. Watch them

Astrodude
14th September 2011, 07:09 PM
Alcubierre's metric is within standard GTR using standard differential geometry. If you want some other theory, feel free, but then there's no reason to fixate on Alcubierre at all. (Exploring what happens with quaternions sounds pretty interesting, but even if it works out sensibly, it's definitely an alternative theory~I don't think even the number of degrees of freedom of would match GTR.)

I think you're right about fixating on Alcubierre; it's not a good idea because his paper is specific for a certain metric and I'm speaking generally.


If the metric doesn't always apply, then it's a different warp bubble, and we're not talking about Alcubierre any longer.



It would be a different warp bubble, but it's still Alcubierre's initial idea. It's the general idea that I'm defending.


Whoa, slow down. Are you saying that Alcubierre did not do GTR right or that GTR itself is wrong? It sounds like you're saying the latter, in which case you might consider making a new thread about the consequences of this alternative theory you're advocating.

The general postulates of GTR hold, but it's the number of equations that's problematic. Noether's first theorem demands a Lie group to describe relativity as long as energy and momentum are conserved, but a Lie group for 4-dimensional spacetime of relativity needs 16 equations! Each of the four elements in [x,y,z,t] need to be differentiated with respect to each of the four elements in [x',y',z',t']. That's 4^2=16 unknowns. With 16 unknowns, you'll need 16 equations. Otherwise, I don't see how you can show the functions to be smooth, which is a requirement for the functions to be analytic.

I'll get around to starting a new thread.

sol invictus
14th September 2011, 07:27 PM
Correct. I am not being clear. I mean EM fields obeying torsional geometries.

That doesn't make sense. I assume you have in mind an exotic theory in which there is torsion as well as something like E&M? If so, what's the theory, and why didn't you say so?

Because they are related to torsion geometery EM fields. Calling them "scalar waves" when they are scalar geometery obeying EM waves is akin to what I have done in calling torsion geometery EM fields "torsion fields"

"Scalar geometry obeying EM waves" is technical word salad. I have no idea what you're trying to say. Neither torsion nor EM fields nor geometry are scalars.

EM fields obeying torsional geometries are as real as B.E.C.s which the known laws of physics knew nothing of not all that long ago

Nonsense. "BEC" stands for "Bose-Einstein condensate". Those two names should give you a hint regarding how long physics has known of them.

Torsion simply doesn't exist in the real world - or at least that's what mathematics and experiment tell us. If you want to make up new laws of physics, be my guest - but be honest about what you are doing, tell us what your theory is, and then we'll see.

Yes they have been wooified. Being more clear I meant to state torsional geometry obeying EM fields. Since you have the time to google you have the time to watch the clips. Watch them

Sorry, no.

JCM
14th September 2011, 07:40 PM
That doesn't make sense. I assume you have in mind an exotic theory in which there is torsion as well as something like E&M? If so, what's the theory, and why didn't you say so?
"Scalar geometry obeying EM waves" is technical word salad. I have no idea what you're trying to say. Neither torsion nor EM fields nor geometry are scalars.
Nonsense. "BEC" stands for "Bose-Einstein condensate". Those two names should give you a hint regarding how long physics has known of them.
Torsion simply doesn't exist in the real world - or at least that's what mathematics and experiment tell us. If you want to make up new laws of physics, be my guest - but be honest about what you are doing, tell us what your theory is, and then we'll see.
Sorry, no.
You are right it would probably have to be nested in some sort of Einstein–Cartan–Sciama–Kibble or other exotic type theory. And the two short video clips explain what I am refering better than I ever could. Regardless this whole discussion about what I am speaking seems like a derail until it can be clearly stated and related to warp/Alcubierre neither of which I can obviously do. If anyone wants to watch the videos then relate them to a warp/Alcubierre type tech be my guest I can't elaborate without slidding further down the whole I've dug.

sol invictus
14th September 2011, 08:01 PM
Fine - I wasted 10 minutes of my life watching one of the videos. Apart from being randomly sprinkled with a few vaguely psychotic conspiracy theories, the physics is significantly stupider than I had guessed. It's not based on some exotic new theory, but simply a basic misunderstanding of general relativity - and it has nothing to do with "torsion fields".

Yes, moving objects and currents create gravitational fields that are somewhat analogous to magnetic fields. No, those fields do not allow anti-gravity - their effects are perfectly well understood, have been for 50 years or more, and that simply isn't one of them.

Vorpal
14th September 2011, 08:28 PM
The general postulates of GTR hold, but it's the number of equations that's problematic. Noether's first theorem demands a Lie group to describe relativity as long as energy and momentum are conserved, but a Lie group for 4-dimensional spacetime of relativity needs 16 equations!
In GTR, Noether's first theorem shows up whenever spacetime has a Killing field. Local conservation of stress-energy follows from Noether's second theorem.

Or, more geometrically, on any torsion-free spacetime, the (contracted) Bianchi identities guarantee that the trace-reversed Ricci curvature has zero divergence. By the EFEs, that's the local conservation of stress-energy in the sense that there are no sinks or sources of it anywhere in spacetime.

I'm not sure what kind of sense one can make of a general spacetime and Noether's first theorem. If your spacetime is stationary, you'll get energy, sure, and similarly for some other special cases. But in general?

Vorpal
14th September 2011, 08:31 PM
Fine - I wasted 10 minutes of my life watching one of the videos.
I did too. I want a refund.

Fine - I wasted 10 minutes of my life watching one of the videos. Apart from being randomly sprinkled with a few vaguely psychotic conspiracy theories, the physics is significantly stupider than I had guessed. It's not based on some exotic new theory, but simply a basic misunderstanding of general relativity - and it has nothing to do with "torsion fields".
To summarize for everyone else: the video starts off talking about an approximation to another approximation of GTR, which is torsion-free. So no new physics. It gets substantially worse from there.

JCM
14th September 2011, 09:20 PM
Fine - I wasted 10 minutes of my life watching one of the videos. Apart from being randomly sprinkled with a few vaguely psychotic conspiracy theories, the physics is significantly stupider than I had guessed. It's not based on some exotic new theory, but simply a basic misunderstanding of general relativity - and it has nothing to do with "torsion fields".

Yes, moving objects and currents create gravitational fields that are somewhat analogous to magnetic fields. No, those fields do not allow anti-gravity - their effects are perfectly well understood, have been for 50 years or more, and that simply isn't one of them.
I did too. I want a refund.


To summarize for everyone else: the video starts off talking about an approximation to another approximation of GTR, which is torsion-free. So no new physics. It gets substantially worse from there.
Sorry I'm out of temporal refunds. :( Did you both watch the first or second? The second brings in the speed of quantum transition stuff.
and it has nothing to do with "torsion fields".
It mentions them as an effect of the B.E.C.s rotation at 60,000 RPM?

Vorpal
14th September 2011, 11:10 PM
Sorry I'm out of temporal refunds. :( Did you both watch the first or second? The second brings in the speed of quantum transition stuff.
The first and parts of the second. But I'm hoping that with more alcohol, it'll go away.

It mentions them as an effect of the B.E.C.s rotation at 60,000 RPM?
What do you think happens? Sol is completely right: the whole construction is more massive, because you put in rotational energy into it.
You've got a perfect fluid (you're not heating it)--nearly the simplest possible case for GTR. GTR is completely torsion-free. It's built into the theory, no exceptions, and you're working in an approximation to it. Unless the fluid magically develops an exotic pressure and density just by spinning it, you're not going to get any kind of antigravity, and even in that case, there would be no torsion.

Ironically, the only way you might get gravitational torsion here is if instead of centrifugally rotating the fluid, every small bit of it was rotating on its own axis, in the limit of zero size... which is exactly what the author of the video says he doesn't want.

JCM
18th September 2011, 07:47 PM
Unless the fluid magically develops an exotic pressure and density just by spinning it, you're not going to get any kind of antigravity, and even in that case, there would be no torsion.
Would the 1.094Mhz/m EM stimulus cause exotic pressures/densities to arise?

Vorpal
18th September 2011, 08:57 PM
No. Why would it?

Besides, even with an exotic fluid, the most it would mean is that the tiny field it produces is repulsive, not that it suddenly trumps that of the Earth of the Sun. The contraption is still going to fall the same way in the Earth's gravitational field, because that's the spacetime around it. Unless you're spinning up quantities of exotic fluid comparable to the Earth's mass, you'd still be stuck here. The whole idea about this UFO propulsion is broken on just about every level.