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Ether? Space/Time?


jajrussel

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I am reading a book that mentioned that in the early 1900's it was believed that an ether was thought necessary. After thinking about why they thought it was necessary, and the fact that no one can seem to find any. I wondered if the reason they couldn't find any was because they expected a medium or field of mass particles, so in essence they were looking for they were wrong clues. Action at a distance was thought to be improbable. Then I thought of all they needed was a medium, that space itself wasn't sufficient then what about time? What if they already had what they were looking for but couldn't see it because they were expecting more.

 

So now the question. Is spacetime a sufficient medium? It bends, it stretches, it shrinks. It seems to have that which is necessary to create the illusion of action at a distance. No ether necessary.

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No, they didn't. They looked for the effect it had to have — the measurement of our speed through it — and that effect was absent. The idea that we might be at rest with respect to it had already been ruled out.

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No, they didn't. They looked for the effect it had to have the measurement of our speed through it and that effect was absent. The idea that we might be at rest with respect to it had already been ruled out.

let me try to clarify my thought and question. At the time action at a distance was thought improbable because a medium was necessary. Sounds waves need air, water waves need water, etc. So they were looking for a substance they called ether that would present similar qualities.

 

Einstein looking for answers to other questions came up with the thought that space and time were interrelated and needed to be thought of just that way.

 

It seems to me that space/time presents a substance that allows propagation. That in effect Einstein redefined ether and didn't realize it because it was not what he set out to do. The result being he still felt some need for ether.

 

Okay, after this much thought what started out as a simple question has moved into speculation, and maybe I allowed my question to be influenced by speculation, so I'll change the question. Does anyone else see the similarities that I seem to see between spacetime effects, and this ether that they used to believe needed to exist?

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No Einstein's GR doesn't reinvent ether, that's not how spacetime curvature works. Many people like to think space time as some form of ether or fabric. However that's not what GR tells us.

 

The easiest way to correlate space time curvature is to realize it is a mathematical descriptive of coordinate change due to how gravity influences particles. ( I often like to describe this as a distribution function of the strength of an influence, described in geometric coordinates)

 

GR is a coordinate metric system. It doesn't mean space requires a substance.

 

All interactions of any form of energy is via particle to particle interactions. Energy being a property of particles. No medium is required, QFT, also doesn't require a medium to work.

Edited by Mordred
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You should think in terms of fields, which are loosely assignments of mathematical objects to every point in space-time. The 'aether' as such are these fields.

 

For example, electromagnetic radiation are ripples in the electromagnetic field.

 

You can also have small ripples in the local geometry of space-time, the so called gravitational waves. These are predicted by general relativity and these is some evidence that these are realised in nature. This is really the closest to 'space-time aether' as you mean it.

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Key word of importance in Ajb's answer is "assign". For example a vector field you assign every point in space a baseline vector value. Then describe the regions of influence upon that vector field.

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...

 

Okay, I should have done a little research before stumbling through my question.

 

I just read Ether and the Theory of Relativity by Albert Einstein, so apparently he did realize that relativity redefined to some extent ether. Not saying that it did exist, but that under conditions relativity does not disallow ether.

 

It just seems to me that the effects of relativity delete any need for ether as a means of propagation. Spacetime seems to interact with matter. It seems to have substance. To me it appears to have density when given that c has a speed limit. Oh well, I was just thinking...

 

Also the seems to have been some kind of delay between responses. The only reply that I had seen before this post was the first.

Edited by jajrussel
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In point of interest the QFT specific study of gravity is Quantum geometrodynamics,

 

No problem thinking is good, the Einstein field equations do include the ideal gas laws. So your thinking isn't particularly far fetched.

 

It's just not the same as ether.

Also the seems to have been some kind of delay between responses. The only reply that I had seen before this post was the first.

Lol were just online at the same time on this thread

(As you are asking a legit question in true interest in learning +1)

Edited by Mordred
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You should think in terms of fields, which are loosely assignments of mathematical objects to every point in space-time. The 'aether' as such are these fields.

 

For example, electromagnetic radiation are ripples in the electromagnetic field.

 

You can also have small ripples in the local geometry of space-time, the so called gravitational waves. These are predicted by general relativity and these is some evidence that these are realised in nature. This is really the closest to 'space-time aether' as you mean it.

Doesn't space and time react to mass? Don't these fields follow a geodesic? Wouldn't the density of these fields increase as the space they occupy becomes smaller as the result of the geodesic? I am not trying to be argumentative. I am just trying to think this through.

 

Let's say you have a black hole surrounded by sources of electromagnetic radiation. My understanding is that a black hole is a central dense point of mass surrounded by space which in this case would be filled with electromagnetic radiation. As the field of radiation nears the central point following the geodesic I am assuming that the density of the field would increase. Is the gravitational field, in a sense, acting as the carrier for the electromagnetic field, or is the electromagnetic field following the geodesic of warped space?

 

Is warped space a property of space under a specific condition, or is warped space simply the shape of the gravitational field.

 

I need to read a little more because I thought that a ripple was the result of particle, or particle wave interaction.

Edited by jajrussel
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Doesn't space and time react to mass?

Yes, space and time 'react' to the presence of energy and momentum via the Einstein Field Equations. They say, very loosely that 'local geometry = matter content'.

 

Don't these fields follow a geodesic?

The particles associated to these fields will classically flow geodesics. For example, photons indeed follow null geodesics.

 

Wouldn't the density of these fields increase as the space they occupy becomes smaller as the result of the geodesic?

The energy density you mean?

 

I am not sure I quite follow you. You can have converging and diverging geodesics. Infinitesimally this is measured by the Jacobi vector field.

 

I am not trying to be argumentative. I am just trying to think this through.

No problem, it is always worth asking questions.

 

Let's say you have a black hole surrounded by sources of electromagnetic radiation. My understanding is that a black hole is a central dense point of mass surrounded by space which in this case would be filled with electromagnetic radiation.

I would expect any black hole to have lots of high energy particles sat behind the horizon. The problem is we will not see this as external observers.

 

As the field of radiation nears the central point following the geodesic I am assuming that the density of the field would increase.

One has to remember that near the classical singularity general relativity breaks down. I am not sure how much we can really say about what happens very near the singularity.

 

Is the gravitational field, in a sense, acting as the carrier for the electromagnetic field, or is the electromagnetic field following the geodesic of warped space?

Even without black holes the electromagnetic field need space-time to 'support it', in the sense that the electromagnetic field is an assignment of a particular mathematical object to every point in that space-time. This is true whatever the geometry of the space-time.

 

Is warped space a property of space under a specific condition, or is warped space simply the shape of the gravitational field.

Depending on exactly what you want to view as the gravitational field, in general relativity gravity is essentially equated with the local shape of space-time. You may wish to describe this with just the metric or a connection or something else equivalent. It is all in the local geometry.

 

I need to read a little more because I thought that a ripple was the result of particle, or particle wave interaction.

In quantum field theory particles are little ripples in the field associated with that particle. For example the photon is associated with the electromagnetic field. The election is associated with the electron field and so on.

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Lets try this approach,

Special relativity

 

has the following relation.

 

[latex]ds^2=c^2dt^2-dx^2-dy^2-dz^2[/latex] (coordinate in Cartesian form)

lets define the conservation laws of a perfect fluid in the rest frame of CoM that homogeneous and isotropic.

 

[latex]\rho=0[/latex] =energy density=0

 

[latex]\bigtriangledown p=0[/latex]

 

Energy density defined by

 

[latex]\rho=nmc^2[/latex]

n is number of particles of mass m.

 

Pressure is in direction i

 

[latex]p_i=nmv_i^2[/latex]

 

Pressure is

[latex]p=\frac{f}{A}[/latex]

 

Where the force acting on a surface area (radius) is[latex] f=\frac{mv}{dt}(nvdt)A[/latex]

 

This equates to the stress energy tensor relations to energy density and pressure relations.

 

[latex]T{\mu\nu}=(\rho+p)v^{\mu}v^{\nu}-pg^{\mu\nu}[/latex]

 

The above is in the Minkowskii special relativity limits.

 

However it shows the relationship between gravity and how it correlates to energy density and pressure

 

How a particle moves is defined by the curvature tensor (which incorporates the stress energy tensor)

 

[latex]G_{\mu\nu}=R_{\mu\nu}-\frac{1}{2}g_{\mu\nu}R[/latex]

 

The Reimann manifold is defined by the ricci tensor.

 

[latex]R_{\mu\nu}-\frac{1}{2}g_{\mu\nu}R[/latex]

 

Don't worry if you can't follow the math itself. This is just to show how energy density and pressure due to gravity distribution relations correlates to the curvature of what is oft termed space time.

 

Space is simply volume. That volume has the standard model particles. Gravity influences those particles. The geometric relation of that influence via the strength of gravity at various distances is what is referred to as space time curvature.

 

(None of the above requires a medium. Just standard model particles and subsequently gravity via mass.)

 

Hope this helps

By the way the electromagnetic force is carried via particle to particle interactions by the electromagnetic force boson which is photons.

 

Edit minor correction of curvature tensor formula

Edited by Mordred
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let me try to clarify my thought and question. At the time action at a distance was thought improbable because a medium was necessary. Sounds waves need air, water waves need water, etc. So they were looking for a substance they called ether that would present similar qualities.

 

Einstein looking for answers to other questions came up with the thought that space and time were interrelated and needed to be thought of just that way.

 

It seems to me that space/time presents a substance that allows propagation. That in effect Einstein redefined ether and didn't realize it because it was not what he set out to do. The result being he still felt some need for ether.

The aether, as the medium through which light travels, was discarded following the Michelson-Morley experiment; they were looking to measure the speed with which we travel through the aether. The got essentially zero. It had already been determined that we must be moving, via stellar aberration, observed back in ~1725 by Bradley. What Einstein did was come up with a framework for mechanics that relied on the invariant speed of light, already a part of electrodynamics, confirming that there was no rest frame needed. i.e., no aether.

 

Even if you substitute spacetime for this, you still have the question of whether we are moving or at rest with respect to it, and how would you measure that. In that regard, there is no aether.

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