it is not mass that causes gravity, it is "extreme energy densities" ???

[scruffy]

Hm... no further comment at this point...

Experimental Spacetime Distortion: Generating Gravitational Waves in the Laboratory | European Journal of Engineering and Technology Research

www.ej-eng.org

 

[toobfreak]

Hm... no further comment at this point...

Two thoughts:

1. One implication is the creation anti-gravity spacetime disruptions which repel rather than attract. This could lead to a theoretical explanation to "dark energy" or, the expansion of space.
2. Nice to see them quantify the velocity of light in a vacuum, driving home a fact many are not aware of, that the speed of light varies according to the medium it travels in, the basic cause of refraction of light. Blue light bends more than other colors passing through glass causing the light to take a slower, longer pathway, which we see as it "bending" more than green or red light, the prismal dispersion effect.

 

[The Sage of Main Street]

Hm... no further comment at this point...

Experimental Spacetime Distortion: Generating Gravitational Waves in the Laboratory | European Journal of Engineering and Technology Research

www.ej-eng.org

Physics Hasn't Risen from Flatland

Since I believe that gravity takes place in an outside spatial dimension, I can't follow any distortions of three-dimensional space. The energy part I can believe, because it is swallowed up into the outside dimension and forces either a graviton or a current in that dimension to enter 3D and affect distant objects.

 

[zaangalewa]

Two thoughts:

1. One implication is the creation anti-gravity spacetime disruptions ...

Why? How? Spacetime is flat = no gravity. A spacetime-distortion is the same like gravity. So what means "anti-gravity" in this context? A spacetime which is flater than flat?

I love science fiction - but whatever is written in in science fiction stories are more or less plausible fantasy and ideas and nothing has to be true. Perhaps anti-gravity in spaceships is able to be an impossible thing. How to know? ...

 

[scruffy]

Physics Hasn't Risen from Flatland

Since I believe that gravity takes place in an outside spatial dimension, I can't follow any distortions of three-dimensional space. The energy part I can believe, because it is swallowed up into the outside dimension and forces either a graviton or a current in that dimension to enter 3D and affect distant objects.

I would start with entanglement, which is directly measurable using information. The long distance correlation does suggest another (not necessarily spatial) dimension, in fact the equivalence of action at widely varying distances suggests it's not spatial.

The other clue is the hyperbolic geometry, which is related to a particular kind of Clifford algebra and can possibly be understood and manipulated with Lie groups.

String theory is the only thing we know of so far, that can explain both situations.

 

[toobfreak]

String theory is the only thing we know of so far, that can explain both situations.

And yet Sheldon abandoned it as a dead end in physics.

 

[zaangalewa]

I would start with entanglement, which is directly measurable using information. The long distance correlation does suggest another (not necessarily spatial) dimension, in fact the equivalence of action at widely varying distances suggests it's not spatial.

The other clue is the hyperbolic geometry, which is related to a particular kind of Clifford algebra and can possibly be understood and manipulated with Lie groups.

String theory is the only thing we know of so far, that can explain both situations.

The problem is in this context that no one seems really to know whether the string theory is "only" a theory of mathematics or is really a theory of physics. On the other side: Physics without mathematics is an impossible thing.

Example:

 

[scruffy]

And yet Sheldon abandoned it as a dead end in physics.

Here is an interesting video that shows us something fundamental about dimensionality.

It uses geometry to show us, therefore it's very intuitive.



They're talking about "curved surfaces", so like spacetime.

The first thing you'll notice is that they're using a method called "extrinsic" geometry, because it's very difficult to intuit curvature without embedding your surface into a higher dimension.

They show you how this method works. Let's say you start with a flat sheet, like a two dimensional plane. You can draw a squiggle "in" the plane, which has curvature "within" the plane. But we want to describe curvature "of" the plane, and they show you how you can use a function to bend the plane into a 3-dimensional shape.

This procedure is not possible without the higher embedding dimension. And once you've morphed the surface in this manner, you discover that the tangent planes also live in the higher dimension, and so do the normals.

If your surface is curved, you need a "mapping" between the tangent planes at any two points, because they may be at different angles relative to each other and relative to the surface. Such a mapping is called a "connection", and you can use the metric tensor combined with the Christoffel symbols to construct the mapping. The most famous connection is called the Levi-Civita connection, which lets us calculate parallel transport around a loop within the surface.

So intuitively, if spacetime is curved, there "must" be a higher embedding dimension. The concept of curvature would make no sense otherwise. Topologists have a way of describing and constructing such higher dimensions, using the concept of "bundles". For example the tangent planes at any point on the surface is called TpM (the "tangent manifold at point p"), and the collection of all such planes is called the "tangent bundle" for the surface.

But having a tangent bundle does not necessarily mean that you can describe all the normals this way. The normals may or may not be included in the tangent bundle. So a "bundle" is only a subset of a dimension, it's not necessarily "complete". But you can still do math with the bundle, "as if" it were complete, by mapping down to the base space (the original surface), using the concept of a "fiber". A fiber is a mapping from points in the base space to points in the higher dimension. The "fiber bundle" consisting of all such mappings doesn't have to be complete either. You can think of this situation like bristles on a hairbrush, where the handle and body of the brush are the base space (the original surface which started from a plane and was then bent into the shape of a handle), and the bristles are the fibers, that are sticking up into the higher dimension.

If you have a bunch of hair stuck between the bristles, you can "map down" from the intersections of the hair with the bristles, to the point where the bristles join the handle, and in this way obtain a "connection" that maps one point of hair to another. However this does not tell you what happens between the bristles, it only allows you to describe the tangents of the hair at the points of intersection. So the math you can then do along the hairs is "limited". It's still useful though, you can measure distances and angles and thereby obtain some equivalence relations that let you calculate geodesics, even if you can't say for sure that the hairs follow them.

In a sense then, this construction "implies" the higher dimension. You end up with what is essentially a "point cloud" and if you have enough points you can sometimes ascertain shape.

 

[scruffy]

So the idea of calculating a "shortest path" turns out to be very simple, even on (or in) a curved manifold.

You only have to do two things:

1. calculate the Christoffel symbols
2. plug them into the geodesic equation

Easy peasy. This video shows you how to do it, for flat and curved manifolds in any number of dimensions.

 

[toobfreak]

So the idea of calculating a "shortest path" turns out to be very simple, even on (or in) a curved manifold.

Just #1 is a video of painfully glaring flaws in treating 3D surfaces as 2D ones where one can only travel along the 2D surface of the 3D object instead of taking the /actual/ shortest path THROUGH it like one would in a true 3D space.

The mind reels.

 

[scruffy]

Just #1 is a video of painfully glaring flaws in treating 3D surfaces as 2D ones where one can only travel along the 2D surface of the 3D object instead of taking the /actual/ shortest path THROUGH it like one would in a true 3D space.

The mind reels.

There is a way to reconcile these concepts. It's pretty out there though. It has to do with "synthesizing dimensions". I alluded to it in a couple of my brain threads. The easy way to think about it is in terms of "space filling curves", which require recursive processes. Basically they translate a recursion into a degree of freedom. Whether that's actually physical is debatable, it works on paper though.