: How do you create the flat region in between a warp bubble for a warp drive?

[can't_think_of_a_name]

Lets ignore the warp bubble for the second question. How could I have 2 regions of space that bend space and in between the two warped space regions be flat? If you are having trouble understanding the second question let me make a diagram. "u=u" The diagram isn't perfect. The u represents the bending of space and the = represents the flat space. I don't have an understanding of general relativity so this might make it harder to get a comprehensive answer

[swansont]

Flat would be a matter of degree. Curvature small enough it can be ignored.

 

Warp drive is science fiction.

[can't_think_of_a_name]

I want to delete this comment.

Edited May 24, 2020 by can't_think_of_a_name

[Strange]

8 hours ago, can't_think_of_a_name said:

How could I have 2 regions of space that bend space and in between the two warped space regions be flat?

Have two masses separated by empty space

[Markus Hanke]

9 hours ago, can't_think_of_a_name said:

How could I have 2 regions of space that bend space and in between the two warped space regions be flat?

There will be different ways to do this, but the simplest one I can think of is a hollow sphere (i.e. a massive shell) in an otherwise empty region of space. Once you go far enough away from the sphere, spacetime will be approximately flat; spacetime in the hollow interior of the shell is also flat (shell theorem); but the region in between is not flat - it has exterior Schwarzschild geometry.

Note though that, even though both of these distant regions are flat, if you were to place a clock into the interior hollow of the shell, you would find that it is gravitationally time-dilated with respect to a reference clock in the flat region for away.

[can't_think_of_a_name]

So I had to do a little googling shell theory is the theory that gravity is the same on a shell. An example could be earth. So if I was on a planet curvature is flat assuming there is nothing else. Can I be on the surface of the earth or do I have to be inside the earth? What happens if space isn't empty besides the sphere? Any other ways to create the flat region besides what you have mentioned? This question is open to anyone?

17 hours ago, Markus Hanke said:

There will be different ways to do this, but the simplest one I can think of is a hollow sphere (i.e. a massive shell) in an otherwise empty region of space. Once you go far enough away from the sphere, spacetime will be approximately flat; spacetime in the hollow interior of the shell is also flat (shell theorem); but the region in between is not flat - it has exterior Schwarzschild geometry.

Note though that, even though both of these distant regions are flat, if you were to place a clock into the interior hollow of the shell, you would find that it is gravitationally time-dilated with respect to a reference clock in the flat region for away.

 

Edited May 25, 2020 by can't_think_of_a_name

[Markus Hanke]

13 hours ago, can't_think_of_a_name said:

So if I was on a planet curvature is flat assuming there is nothing else. Can I be on the surface of the earth or do I have to be inside the earth?

Spacetime is flat in the interior region enclosed by the shell, not on its surface. The Earth is not a hollow shell, so this case does not apply here.

13 hours ago, can't_think_of_a_name said:

What happens if space isn't empty besides the sphere?

You will then get what is called a relativistic 2-body problem, which is vastly more complicated. If you are a beginner just starting to learn General Relativity (I assume that is what you are), then I would not worry about this particular case, it is better to stick to the basics first.

13 hours ago, can't_think_of_a_name said:

Any other ways to create the flat region besides what you have mentioned?

If you have two massive bodies, such as the Earth and the moon, then there will be what is called Lagrange points. To put it very simply, these are locations where the gravitational attraction from the two bodies cancel each other out. If you place a test particle there, it will remain at rest and not be moved by either gravitating body. Spacetime in a small local region around these Lagrange points will also be approximately flat.

[can't_think_of_a_name]

I still learning special relativity I have not got to general relativity yet.

Are there any other ways besides mentioned to create conditions of a flat region of space? Can you list every possible way?

Also I heard from an earlier post that space curvature can be relativity flat. I quoted it. Can you take that into consideration? 

Also I mention gravity curvature needs to be on both sides and flat region between. What about instead of sandwiched in between two curvatures of gravity I Just have one curvature one either right or left side. Can you take that into consideration?

Do you need a flat or low curvature region from gravity for the warp drive?

Is there anyway for an object to not feel the effect of gravity in a curvature of gravity or be a low region of curvature? An example would be a way to block gravity to feel  flat. I know you mentioned shell theory. Are there any other ways?

Does the positive mass need to = the negative mass for the warp drive to work?

What happens to negative mass in a positive mass curvature?  

Thanks.  

[Markus Hanke]

14 hours ago, can't_think_of_a_name said:

Are there any other ways besides mentioned to create conditions of a flat region of space? Can you list every possible way?

Also I heard from an earlier post that space curvature can be relativity flat. I quoted it. Can you take that into consideration? 

Every small enough region of spacetime will be locally flat, just as every small enough area of the Earth‘s surface appears locally flat, even though the planet overall is spherical. What “small enough” means depends on the exact circumstances.
Over and above that, it is not possible to list “every possible way”, since there are infinity many solutions to the Einstein equations, each of which may or may not contain regions of locally flat spacetime, depending on boundary conditions. 

14 hours ago, can't_think_of_a_name said:

Also I mention gravity curvature needs to be on both sides and flat region between.

Not necessarily. You can have a single mass in otherwise empty space; if you go far enough away from that mass, spacetime will become approximately flat (“asymptotic flatness”).

14 hours ago, can't_think_of_a_name said:

Do you need a flat or low curvature region from gravity for the warp drive?

I don’t know what you mean by “warp drive” - we do not have any such device.

14 hours ago, can't_think_of_a_name said:

Is there anyway for an object to not feel the effect of gravity in a curvature of gravity or be a low region of curvature?

Sure, just put the object into free fall. The local frame of a freely falling object is an inertial frame, it won’t feel any gravity (“weightless”).

14 hours ago, can't_think_of_a_name said:

An example would be a way to block gravity to feel  flat.

Unlike electromagnetic fields, gravity cannot be blocked by any known means.

14 hours ago, can't_think_of_a_name said:

What happens to negative mass in a positive mass curvature?

To the best of current knowledge, such a thing as “negative mass” does not exist. If it did, it would free-fall normally towards the gravitational source, just like ordinary matter. However, if the gravitational source is itself composed of ordinary matter, then it will fall away from negative mass; thus, if both masses are of comparable magnitude, you would end up with a run-away effect. 

[can't_think_of_a_name]

Do you need a flat or low curvature region from gravity for the warp drive?  I meant warp bubble.

Does the positive mass need to = the negative mass for the warp bubble to be created?

19 hours ago, Markus Hanke said:

Every small enough region of spacetime will be locally flat, just as every small enough area of the Earth‘s surface appears locally flat, even though the planet overall is spherical. What “small enough” means depends on the exact circumstances.

I am having trouble understanding the above it is vague answer. Are you trying to say that every region is flat enough for a warp bubble? Can you explain? What I mean by small enough is small enough for a warp bubble.

I realize the warp drive doesn't exist but am curious.Thanks for the answers.

[Markus Hanke]

8 hours ago, can't_think_of_a_name said:

Do you need a flat or low curvature region from gravity for the warp drive?  I meant warp bubble.

What do you mean by “warp bubble”? Are you referring to some specific spacetime geometry here? Is it the Alcubierre warp drive you are alluding to?

[can't_think_of_a_name]

Yes.

[can't_think_of_a_name]

Also what is horizon problem for the warp drive in simple language?

What do they mean by a ring of negative energy?

Also does the bubble move like this? If not how does it move?

Edited May 27, 2020 by can't_think_of_a_name