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Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: jeffreyH on 28/09/2013 07:17:03

Title: What effect does mass-energy density have on gravitational field strength?
Post by: jeffreyH on 28/09/2013 07:17:03
Does the mass-energy density affect gravity at higher densities? Does any amplification of field strength occur? How could we test if this were true?
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: Kryptid on 28/09/2013 07:44:40
The gravitational force experienced between two bodies is related to the mass and distance between them. In some sense, density doesn't matter. If you replaced the Sun with a high-density object like a black hole of equal mass, the planets would retain their normal orbits because the mass/distance factor has remained unchanged. The difference with a black hole is that, since all of the mass is concentrated in the center, you can get very close to it (thus experiencing a much higher attractive force). If you got the same distance from the center of the Sun, the gravitational attraction would not be nearly so strong because much of the Sun's mass would be above you as well as below you (effectively cancelling out some of the attractive force).
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: jeffreyH on 28/09/2013 22:10:51
Can this ever be confirmed experimentally? The mathematics may point in this direction but does the experimental situation agree.
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: jeffreyH on 28/09/2013 23:59:55
In this situation if we have a mass M1 with radius R1 and a smaller mass M2 with radius R2 then the gravitational field strengths at the respective surfaces would be G1 and G2.
If we compress M1 to the same radius as R2 then length contraction and time dilation should increase. However by the reasoning above the change in the dimension of R1 should alter G1 at the surface (if we wish to preserve orbits around the mass) even though the mass has not increased and is simply compressed. Therefore G1 must increase with compression if the above statements are true. Meaning that the same mass exhibits higher field strength at its surface under compression. I.E. Gravitational amplification.
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: jeffreyH on 29/09/2013 07:03:39
I am working on an equation for mass-energy density for gravity. I will post a graph of the results when done.
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: Kryptid on 29/09/2013 07:21:33
In this situation if we have a mass M1 with radius R1 and a smaller mass M2 with radius R2 then the gravitational field strengths at the respective surfaces would be G1 and G2.
If we compress M1 to the same radius as R2 then length contraction and time dilation should increase. However by the reasoning above the change in the dimension of R1 should alter G1 at the surface (if we wish to preserve orbits around the mass) even though the mass has not increased and is simply compressed. Therefore G1 must increase with compression if the above statements are true. Meaning that the same mass exhibits higher field strength at its surface under compression. I.E. Gravitational amplification.
The field strength at the surface has increased because you have decreased the distance to the center. Shell theorem predicts that the strength of gravity at the surface of a sphere is dependent only upon the mass of the sphere and its radius, not its density: http://en.wikipedia.org/wiki/Shell_theorem (http://en.wikipedia.org/wiki/Shell_theorem)

For example, imagine if the Earth was a giant, hollow shell only one foot thick, but that this shell was super-dense such that it had the same mass as the real Earth. Shell theorem predicts that the gravitational force at the surface of this "shell Earth" is the same as that of "real Earth". You could do the same by positing that the Earth is hollow and 99% of its mass is tied up inside of a black hole at its center. This "black hole Earth" still exhibits the 1G force at its surface. The density and arrangement of mass within a sphere does not affect its surface gravity (assuming that the mass is distributed in a spherically-symmetrical manner).
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: jeffreyH on 29/09/2013 07:49:45
In this situation if we have a mass M1 with radius R1 and a smaller mass M2 with radius R2 then the gravitational field strengths at the respective surfaces would be G1 and G2.
If we compress M1 to the same radius as R2 then length contraction and time dilation should increase. However by the reasoning above the change in the dimension of R1 should alter G1 at the surface (if we wish to preserve orbits around the mass) even though the mass has not increased and is simply compressed. Therefore G1 must increase with compression if the above statements are true. Meaning that the same mass exhibits higher field strength at its surface under compression. I.E. Gravitational amplification.
The field strength at the surface has increased because you have decreased the distance to the center. Shell theorem predicts that the strength of gravity at the surface of a sphere is dependent only upon the mass of the sphere and its radius, not its density: http://en.wikipedia.org/wiki/Shell_theorem (http://en.wikipedia.org/wiki/Shell_theorem)

For example, imagine if the Earth was a giant, hollow shell only one foot thick, but that this shell was super-dense such that it had the same mass as the real Earth. Shell theorem predicts that the gravitational force at the surface of this "shell Earth" is the same as that of "real Earth". You could do the same by positing that the Earth is hollow and 99% of its mass is tied up inside of a black hole at its center. This "black hole Earth" still exhibits the 1G force at its surface. The density and arrangement of mass within a sphere does not affect its surface gravity (assuming that the mass is distributed in a spherically-symmetrical manner).

It is not simply having decreased the distance to the centre. I can decrease the distance to the centre be digging down into the earth to the same point. However the gravitational effect would decrease and not increase. The radius makes no sense inside the mass itself as it becomes a fraction. In the inverse square nature of gravitation this will not explain compression without a functional adjustment of mass to radius.
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: jeffreyH on 29/09/2013 23:48:06
Here is a plot I have done as density increases/radius decreases. Does anyone know at what percentage of the radius of a mass that we get the Schwarzschild radius? I would like to see if it falls correctly on this graph. The y-axis is gravity strength and the x-axis percentage of the uncompressed radius.

Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: jeffreyH on 30/09/2013 00:20:11
Oops. That wasn't the density plot.

Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: Pmb on 30/09/2013 03:52:26
Quote from: jeffreyH
Does the mass-energy density affect gravity at higher densities?
Yes.

Quote from: jeffreyH
Does any amplification of field strength occur?
I don’t understand what this means so I’ll just say no.

Quote from: jeffreyH
How could we test if this were true?
When you tell me what amplification of field strength occur[/I] means I’ll let you know.
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: Kryptid on 30/09/2013 05:24:29
It is not simply having decreased the distance to the centre. I can decrease the distance to the centre be digging down into the earth to the same point. However the gravitational effect would decrease and not increase.
I explained this before with the Sun example. The reason that the gravity decreases when you dig into the Earth is because some of the mass of the planet is now above your head and therefore pulling on you in a direction away from the center. At the center of the Earth, gravity is at its weakest because all of the mass is around you, not below you. It pulls on you in all directions roughly equally, cancelling out the attractive force. In a black hole, the center is where gravity is the strongest because that's where all of its mass is concentrated.
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: jeffreyH on 30/09/2013 05:30:34
Quote from: jeffreyH
Does the mass-energy density affect gravity at higher densities?
Yes.

Quote from: jeffreyH
Does any amplification of field strength occur?
I don’t understand what this means so I’ll just say no.

Quote from: jeffreyH
How could we test if this were true?
When you tell me what amplification of field strength occur[/I] means I’ll let you know.

The way I am looking at it the compression of mass produces tighter gravitational flux lines. The reason why photons get trapped is that they are outnumbered by a denser graviton field. It is like a laser beam for photons except this is an intensification of gravitons much like a laser beam. That is the 'amplification' I am exploring.
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: Kryptid on 30/09/2013 05:36:15
The way I am looking at it the compression of mass produces tighter gravitational flux lines. The reason why photons get trapped is that they are outnumbered by a denser graviton field. It is like a laser beam for photons except this is an intensification of gravitons much like a laser beam. That is the 'amplification' I am exploring.
The more proper analogy would be to compare a gravitational field with an electromagnetic field, not a laser. Although both laser beams and EM fields are made up of photons, they have rather different properties (virtual vs. real photons). The best equivalent to a laser would be a uniform beam of gravitational waves.
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: jeffreyH on 30/09/2013 05:49:56
It is not simply having decreased the distance to the centre. I can decrease the distance to the centre be digging down into the earth to the same point. However the gravitational effect would decrease and not increase.
I explained this before with the Sun example. The reason that the gravity decreases when you dig into the Earth is because some of the mass of the planet is now above your head and therefore pulling on you in a direction away from the center. At the center of the Earth, gravity is at its weakest because all of the mass is around you, not below you. It pulls on you in all directions roughly equally, cancelling out the attractive force. In a black hole, the center is where gravity is the strongest because that's where all of its mass is concentrated.

You appear to be talking about a mass at normal density. I am dealing with collapsing masses. The radius here is related to an isolated mass and not a two mass interaction.
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: jeffreyH on 30/09/2013 05:54:21
The way I am looking at it the compression of mass produces tighter gravitational flux lines. The reason why photons get trapped is that they are outnumbered by a denser graviton field. It is like a laser beam for photons except this is an intensification of gravitons much like a laser beam. That is the 'amplification' I am exploring.
The more proper analogy would be to compare a gravitational field with an electromagnetic field, not a laser. Although both laser beams and EM fields are made up of photons, they have rather different properties (virtual vs. real photons). The best equivalent to a laser would be a uniform beam of gravitational waves.

A uniform beam works for me. Bearing in mind that like light the waves are not parallel and disperse with distance. If we could ever produce a directed graviton field we may be able to create a graviton uniform beam that would act laser like..
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: jeffreyH on 30/09/2013 05:55:59
Interestingly with this sort of technology it would be possible to tow quite large object in space.
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: jeffreyH on 30/09/2013 06:00:24
A clarification on the two graphs above. They are both in natural units. Graph 1 is the increase in gravitational strength as the radius contracts. Graph 2 is the mass density increase as the radius contracts. There is a proportionality as would be expected but what ties then together? That is my next mission.
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: Kryptid on 30/09/2013 07:39:18
You appear to be talking about a mass at normal density. I am dealing with collapsing masses. The radius here is related to an isolated mass and not a two mass interaction.

What's the fundamental difference between "normal" densities and collapsing masses? It's just a matter of degree, really. Besides, if a higher density object has even slightly more gravity than an object of similar mass with a lower density, then that would mean that the Sun (hypothetically) collapsing into a black hole would affect the orbits in the Solar System. This is in contradiction to current physics knowledge. Look what NASA has to say on the subject: http://spaceplace.nasa.gov/review/dr-marc-sun/black-hole-sun.html (http://spaceplace.nasa.gov/review/dr-marc-sun/black-hole-sun.html)

Quote
If the Sun were somehow compressed enough to become a black hole, it would be less than 6 kilometers (well under 4 miles) across. It would exert no more gravitational force on Earth or the other planets in the solar system than it does now. Why? Because it would contain no more matter than it does now and it would be no closer to the planets than it is now.
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: jeffreyH on 30/09/2013 07:56:00
You appear to be talking about a mass at normal density. I am dealing with collapsing masses. The radius here is related to an isolated mass and not a two mass interaction.

What's the fundamental difference between "normal" densities and collapsing masses? It's just a matter of degree, really. Besides, if a higher density object has even slightly more gravity than an object of similar mass with a lower density, then that would mean that the Sun (hypothetically) collapsing into a black hole would affect the orbits in the Solar System. This is in contradiction to current physics knowledge. Look what NASA has to say on the subject: http://spaceplace.nasa.gov/review/dr-marc-sun/black-hole-sun.html (http://spaceplace.nasa.gov/review/dr-marc-sun/black-hole-sun.html)

Quote
If the Sun were somehow compressed enough to become a black hole, it would be less than 6 kilometers (well under 4 miles) across. It would exert no more gravitational force on Earth or the other planets in the solar system than it does now. Why? Because it would contain no more matter than it does now and it would be no closer to the planets than it is now.

You misunderstand. I agree with you. Yes the orbits would be consistent outside of the collapse. Within the collapsing region density prevails. Working out towards the original radius you arrive at the same values as you had before collapse.
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: jeffreyH on 01/10/2013 09:57:57
I have attached a plot of standard gravity plot against density. Where these cross at a value of 1 represents normal solid matter at an ideal density. To the right series 1 represents densities above melting point, first liquid and then gas. To the left is solid matter compression which will ultimately lead to a singularity. Series 2 is the inverse square plot for gravity without reference to density. I am thinking through some conclusions at the moment.

Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: jeffreyH on 02/10/2013 14:41:53
The graph above needs some correctional factor to converge the plot of high densities with normal mass density. This will reflect the distortion in gravitation experienced by collapsing objects. This distortion would result in the theoretical frame dragging experienced around the event horizon of a black hole. This effect will lesson and become 'normal' at the point where the original uncompressed mass surface would have been. I currently have no idea what this factor would be but I am looking at Hooke's law, the theory of elasticity and the linear mapping of tensors. I need to relate this to the stress energy tensor. As this relates to densities it could get very interesting.
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: jeffreyH on 02/10/2013 15:31:37
I have just been looking into the  Lense–Thirring effect and the equations are just a little beyond me. Is there any background on how this is put together?
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: jeffreyH on 02/10/2013 15:37:09
If I am correct and there is a loss of field strength at the equator around a massive collapsed object, could this gravitational field explain the relativistic jets as gravitational waves spiral up and away from the mass. Thus pulling matter away with them? This factor could explain a weakening gravitational field in the plane of the equator.
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: jeffreyH on 03/10/2013 03:53:56
The wikipedia article for the Lense-Thirring effect notes that it need further explanation.

http://en.wikipedia.org/wiki/Lense%E2%80%93Thirring_precession

Some of the symbols have no explanation. I don't believe this will lead to a gravitational explanation for the jets anyway but would like some help with clarification of the symbols.
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: jeffreyH on 04/10/2013 00:11:18
The gravitational mass-density convergence may well explain relativistic jets and the speed of matter expulsion. Internal to the event horizon this convergence may cause a bow shaped gravity at the poles perpendicular to the equator. This bow may converge at the poles to a point-like gravitational beam and outwardly produce the conical shape of the jets. This is where the gravitational field strength would be lost from the equatorial plane and elsewhere. The origin of the bow would be the singularity and induced by the angular momentum of rotation. The intensification of the gravitational field, rather than drawing matter in, pulls matter outward in its wake. The field strength may make it more mass-like than normal. As the field reduces in strength it leaves a bulge of matter at the extremities of the jet. This gas cloud is then held together by its own gravitation.
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: jeffreyH on 04/10/2013 00:25:22
Here is a quick sketch of the concept. Comments on this would be appreciated. How wrong am I?

Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: Pmb on 04/10/2013 01:36:24
The gravitational force experienced between two bodies is related to the mass and distance between them. In some sense, density doesn't matter.
That is incorrect. The greater the mass density is then the greater the mass that occupies the volume the

It's accurate in some sense to think of mass density in gravity as you would charge density in electrodynamics.
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: Pmb on 04/10/2013 02:18:23
Does the mass-energy density affect gravity at higher densities? Does any amplification of field strength occur? How could we test if this were true?
Mass-energy is only one source of gravity. Momentum and stress also contribute. You need to take all of these into account to determine what happens. I'm not sure what you mean by amplification effects though. The geometric object which acts as the source of gravity is called the stress-energy-momentum tensor. It's definition is given here http://home.comcast.net/~peter.m.brown/sr/energy_momentum_tensor.htm

I've been playing with different distributions of mass to show how mass-energy comes into play as do momentum and stress. They're at http://home.comcast.net/~peter.m.brown/gr/gr.htm
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: jeffreyH on 04/10/2013 05:16:46
Does the mass-energy density affect gravity at higher densities? Does any amplification of field strength occur? How could we test if this were true?
Mass-energy is only one source of gravity. Momentum and stress also contribute. You need to take all of these into account to determine what happens. I'm not sure what you mean by amplification effects though. The geometric object which acts as the source of gravity is called the stress-energy-momentum tensor. It's definition is given here http://home.comcast.net/~peter.m.brown/sr/energy_momentum_tensor.htm

I've been playing with different distributions of mass to show how mass-energy comes into play as do momentum and stress. They're at http://home.comcast.net/~peter.m.brown/gr/gr.htm

It is so good to have someone tell you WHY you are wrong. I will look at both your links and work through any equations. I have just ordered "The Absolute Differential Calculus (Calculus of Tensors) Levi-Civita, Tullio". That should be a fun read!
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: jeffreyH on 04/10/2013 06:40:18
Just a thought. Could the zero point energy be an effect of gravity propagating through matter? Could the definition of phonon be equivalent to graviton?
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: Kryptid on 04/10/2013 21:26:07
That is incorrect. The greater the mass density is then the greater the mass that occupies the volume the

It's accurate in some sense to think of mass density in gravity as you would charge density in electrodynamics.

The gravity is only greater because the higher density causes there to be more mass (assuming a constant volume). If distance from the mass and the mass itself are kept constant, then gravity stays the same (regardless of what changes in radius and density may occur).

Just a thought. Could the zero point energy be an effect of gravity propagating through matter? Could the definition of phonon be equivalent to graviton?

Zero-point Energy has to do with Heisenberg's Uncertainty Principle and quantum vacuum fluctuations. Gravity isn't required to explain it.
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: jeffreyH on 04/10/2013 22:59:16
That is incorrect. The greater the mass density is then the greater the mass that occupies the volume the

It's accurate in some sense to think of mass density in gravity as you would charge density in electrodynamics.

The gravity is only greater because the higher density causes there to be more mass (assuming a constant volume). If distance from the mass and the mass itself are kept constant, then gravity stays the same (regardless of what changes in radius and density may occur).

Just a thought. Could the zero point energy be an effect of gravity propagating through matter? Could the definition of phonon be equivalent to graviton?

Zero-point Energy has to do with Heisenberg's Uncertainty Principle and quantum vacuum fluctuations. Gravity isn't required to explain it.

Firstly gravity over square surface area must increase if gravity is a particle based field and we take mass-density into account. This causes problems with the inverse square law for reasons I won't go into now.

Secondly I agree the zero point energy is not gravity related after having read up on it a bit more. Also it is not a multi-directional effect.
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: Pmb on 05/10/2013 02:14:16
Quote from: Supercryptid
The gravity is only greater because the higher density causes there to be more mass (assuming a constant volume). If distance from the mass and the mass itself are kept constant, then gravity stays the same (regardless of what changes in radius and density may occur).
Not in general relativity. If you have more mass packed into a smaller space and there is more pressure due to this compactness then the pressure also contributes to the gravitational field. GR is much different than Newtonian gravity. It's much more complicated.
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: Pmb on 05/10/2013 02:16:07
Just a thought. Could the zero point energy be an effect of gravity propagating through matter? Could the definition of phonon be equivalent to graviton?
Zero-point energy contributes to the gravitational field just like all other sources of energy. But no. The rest is wrong. There is no reason to make such assumptions either. BTW a phonon is a classical entity and the graviton a quantum mechanical one.
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: Pmb on 05/10/2013 02:20:59
Quote from: jeffreyH
It is so good to have someone tell you WHY you are wrong.
And its so good to know I can still be useful even though I'm disabled.

There are many good books on geometry such as that of Bernhard F. Schutz. Also Differential Forms and Connections by R.W.R Daring comes highly recommended by a GR expert friend of mine. I myself will be studying it when I'm better (still ill due to lengthy recovery from surgery). Introduction to Vectors and Tensors by Bowen and Wang looks good. I bought a copy a couple of months ago and haven't been well enough to study that either. :(
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: Pmb on 05/10/2013 04:07:26
Quote from: Supercryptid
The gravity is only greater because the higher density causes there to be more mass (assuming a constant volume). If distance from the mass and the mass itself are kept constant, then gravity stays the same (regardless of what changes in radius and density may occur).
As I said, that is wrong. At least in general.

I'd like to point out that what was said above only applies to the special situation of a point particle or something of that nature. When its something like a long line of mass then its different. Suppose we wish to determine the gravitational field a distance d from the z axis where along the z-axis is a long line of of constant mass density. The gravitational field at a distance r from the z-axis is proportional to the mass density, not the mass, and inversely proportional to r. So there really are situations where the field is proportional to mass density and not to the entire mass. This will hold for a very long line of matter when we want to look at the field close to the line.

The GR calculation is found here
http://home.comcast.net/~peter.m.brown/gr/grav_field_rod.htm
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: Kryptid on 05/10/2013 06:29:13
Interesting...can the effect of added pressure increase gravity significantly? Does that make the "replace the Sun with a black hole" analogy I mentioned earlier wrong then?
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: jeffreyH on 05/10/2013 06:40:15
Interesting...can the effect of added pressure increase gravity significantly? Does that make the "replace the Sun with a black hole" analogy I mentioned earlier wrong then?

I don't think it would but this is only a hunch at the moment.
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: Pmb on 05/10/2013 07:45:11
Interesting...can the effect of added pressure increase gravity significantly? Does that make the "replace the Sun with a black hole" analogy I mentioned earlier wrong then?
No. That remains correct.

Each case must really be analzed individually. It's dangerous to form general conclusions. Let me give you an example; you've heard of cosmic strings, right? A straight cosmic string has an enormous linear mass density. It's extremely thin, less than the width of an atom but never ends in an open universe. It has an equally large tension too. Tesion is like pressure but is negative. They contribute equally in the case of the cosmic string. The end effect is that you could be standing right next to a cosmic string and not know it from its gravitational field. The only gravitational effect a cosmic string has is to change tghe topology of the surrounding space from planar to conical. Amazing stuff, isn't it? :)

A vacuum domain wall is another example. In this case the wall is a two dimensional object rather than a one dimensional object like the string. The tension contributes twice as much so the wall has a replusive gravitational field. Interesting thing about the vacuum domain wall is that the gravitaitonal field it generates has zero spacetime curvature.

In three dimensions there is even more repulsion and this is how the accelerating expansion of the universe works.

On the other hand the effective active gravitational mass density of radiation is that the (positive) contribution of the raditation pressure contributes a significant amount to the active-grav-mass.
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: jeffreyH on 05/10/2013 08:22:28
Is then gravitation expressed at the event horizon of the black hole as a result of the in falling matter. If so then what part would the original mass play? Or is this looking at it wrong?
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: jeffreyH on 05/10/2013 08:26:38
To collapse below the Schwarzchild radius some of the mass is already contained within this volume. Mass outside this region, when collapsing inwards, will approach the radius with escape velocity increasing proportionally. Has anyone tried working this through during the collapse event to calculate the effects on gravity as the process evolves?
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: Pmb on 05/10/2013 08:37:10
Is then gravitation expressed at the event horizon of the black hole as a result of the in falling matter. If so then what part would the original mass play? Or is this looking at it wrong?
I'm sorry but I don't understand this question. Can you rephrase it for me please?
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: Pmb on 05/10/2013 08:40:12
Quote from: jeffreyH
To collapse below the Schwarzchild radius some of the mass is already contained within this volume.
As observed from outside the event horizon, nothing can pass through the event horizon and go inside.

Quote from: jeffreyH
Mass outside this region, when collapsing inwards, will approach the radius with escape velocity increasing proportionally.
Actually, as matter approaches the event horizon it slows down and comes to a stop at the event horison and never crosses it.

Quote from: jeffreyH
Has anyone tried working this through during the collapse event to calculate the effects on gravity as the process evolves?
I don't understand what you mean by "the effects on gravity." Can you clarify this for me please?
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: jeffreyH on 05/10/2013 08:47:26
Quote from: jeffreyH
To collapse below the Schwarzchild radius some of the mass is already contained within this volume.
As observed from outside the event horizon, nothing can pass through the event horizon and go inside.

Quote from: jeffreyH
Mass outside this region, when collapsing inwards, will approach the radius with escape velocity increasing proportionally.
Actually, as matter approaches the event horizon it slows down and comes to a stop at the event horison and never crosses it.

Quote from: jeffreyH
Has anyone tried working this through during the collapse event to calculate the effects on gravity as the process evolves?
I don't understand what you mean by "the effects on gravity." Can you clarify this for me please?

The effects on gravitational field strength. Does it increase or decrease overall? This is assuming a Kerr black hole.
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: jeffreyH on 05/10/2013 08:49:04
Is then gravitation expressed at the event horizon of the black hole as a result of the in falling matter. If so then what part would the original mass play? Or is this looking at it wrong?
I'm sorry but I don't understand this question. Can you rephrase it for me please?

I would forget this one. I need to know what I mean myself first. :-)
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: Pmb on 05/10/2013 14:15:24
Quote from: jeffreyH
The effects on gravitational field strength. Does it increase or decrease overall? This is assuming a Kerr black hole.
Not sure. I'm not an expert on black holes so I'd rather remain silent on questions requiring great detail like this.
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: Kryptid on 05/10/2013 20:48:22
Interesting...can the effect of added pressure increase gravity significantly? Does that make the "replace the Sun with a black hole" analogy I mentioned earlier wrong then?
No. That remains correct.

Each case must really be analzed individually. It's dangerous to form general conclusions. Let me give you an example; you've heard of cosmic strings, right? A straight cosmic string has an enormous linear mass density. It's extremely thin, less than the width of an atom but never ends in an open universe. It has an equally large tension too. Tesion is like pressure but is negative. They contribute equally in the case of the cosmic string. The end effect is that you could be standing right next to a cosmic string and not know it from its gravitational field. The only gravitational effect a cosmic string has is to change tghe topology of the surrounding space from planar to conical. Amazing stuff, isn't it? :)

A vacuum domain wall is another example. In this case the wall is a two dimensional object rather than a one dimensional object like the string. The tension contributes twice as much so the wall has a replusive gravitational field. Interesting thing about the vacuum domain wall is that the gravitaitonal field it generates has zero spacetime curvature.

In three dimensions there is even more repulsion and this is how the accelerating expansion of the universe works.

On the other hand the effective active gravitational mass density of radiation is that the (positive) contribution of the raditation pressure contributes a significant amount to the active-grav-mass.

Forgive me for taking this a bit off topic, but I find these conclusions rather fascinating. I've heard of domain walls before, but never that they were gravitationally-repulsive. If only we could prove their existence and duplicate them on a tiny, controlled scale. Then antigravity machines may prove plausible. Not that I expect this to happen any time soon.

You sound fairly confident about the gravitational repulsion that causes the Universe's expansion. Yet I've never heard of that explanation before. It does sound like a nice model, as it doesn't invoke a mysterious "dark energy" to explain it. Is this a mainstream theory?
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: Pmb on 06/10/2013 01:02:52
Quote from: Supercryptid
Forgive me for taking this a bit off topic, but I find these conclusions rather fascinating. I've heard of domain walls before, but never that they were gravitationally-repulsive.
 If only we could prove their existence and duplicate them on a tiny, controlled scale.
If we could create that kind of matter and control it then we could try it. That's way off in the future if you ask me though.

Quote from: Supercryptid
You sound fairly confident about the gravitational repulsion that causes the Universe's expansion.
That is what the entire cosmology community believes. Who am I to differ?

Quote from: Supercryptid
Yet I've never heard of that explanation before. It does sound like a nice model, as it doesn't invoke a mysterious "dark energy" to explain it. Is this a mainstream theory?
Yes. Please understand that the term "dark energy" is simply the name given to the cause of gravitational repulsion. See
http://news.nationalgeographic.com/news/2012/02/120215-dark-energy-antimatter-physics-alternate-space-science/# - Is Dark Energy Really "Repulsive Gravity"?

See also http://en.wikipedia.org/wiki/Dark_energy
Quote
This accelerating expansion effect is sometimes labeled "gravitational repulsion", which is a colorful but possibly confusing expression. In fact a negative pressure does not influence the gravitational interaction between masses—which remains attractive—but rather alters the overall evolution of the universe at the cosmological scale, typically resulting in the accelerating expansion of the universe despite the attraction among the masses present in the universe.
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: jeffreyH on 06/10/2013 09:33:42
I have often thought that collapsing systems such as black holes and neutron stars can only exist in an expanding system. If the system were collapsing we should see white holes. This is why white holes are unstable but in the collapsing system it would be black holes that were unstable.
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: yor_on on 06/10/2013 15:29:40
That would make traveling the astronomical 'void' a very dangerous experience me thinks :) when matter and antimatter meet you get radiation, does you not? Shouldn't that be measurable, or is the assumption that this only took place in some beginning never more happening? also it makes me think of a  twisted 'mirror universe' in where half of its existence finds the other half non-existing, as non measurable. A very weird concept which reminds me of Bakers SF (think it was him?) depicting a ultimate 'war of resources',  between beings of matter and anti matter, arranging the universe to a anti matter state, ultimately making it inhabitable for us of matter.
==

It is a nice idea though in the sense of explaining why we then could have a equal amount of anti matter matter, possibly? From a big Bang without those annihilating each other at the moment they emerge. But if they exist in equal proportions, and they should if they do not 'naturally meet', due to gravity/anti gravity, what exactly would make the universe expand, and accelerate? Reminds me of my old idea (my joke actually) about 'virtual particles', although I doubt that one too, it's just too simplistic. You can as easily argue that it then need a equal amount of virtual 'photons' of mass to come into existence, and then you should have no expansion I think, neither a acceleration.

I think geometry holds the answer myself, with probably more degrees of freedom, or less? :) Depending on how you look at it. It all depends on if we got that one right I guess? I can alternatively imagine another sort of topology, solely defined from local measurements, in where the real question becomes what allows a 'local point' to in any way being able to measure another point (connect to). That universe does have a topology (dimensions) defined by our measurements, but its consistency is ultimately a local experience. And ultimately a question of pure logic.

As if what define a universes geometry is a question of some principle allowing local points to measure on other points, a 'point like' universe if one like :) Such a universe, should allow for entanglements easily as our definitions of distance, and motion, would need to be retranslated to fit such a concept.
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: Pmb on 06/10/2013 23:43:38
Quote from: jeffreyH
I have often thought that collapsing systems such as black holes and neutron stars can only exist in an expanding system.
I can't see why? What leads you to believe this?

Quote from: jeffreyH
If the system were collapsing we should see white holes.
What system are you referring to and why would you expect to see white holes. There's no evidence that such objects even exist.

Quote from: jeffreyH
I This is why white holes are unstable ...
Do you have a source for this assertion? I can't imagine why it would be so.

Jeff - You seem to enjoy black holes. You should consider reading Exploring Black Holes - 2nd Ed by Taylor, Wheeler and Bertschinger at http://exploringblackholes.com/

I think you'd also get a great deal of satisfaction reading Black Holes and Time Warps - Einstein's Outrageous Legacy by Kip Thorne. Thorne is the worlds leading theorist on black holes.
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: jeffreyH on 07/10/2013 00:00:13
Quote from: jeffreyH
I have often thought that collapsing systems such as black holes and neutron stars can only exist in an expanding system.
I can't see why? What leads you to believe this?

Quote from: jeffreyH
If the system were collapsing we should see white holes.
What system are you referring to and why would you expect to see white holes. There's no evidence that such objects even exist.

Quote from: jeffreyH
I This is why white holes are unstable ...
Do you have a source for this assertion? I can't imagine why it would be so.

Jeff - You seem to enjoy black holes. You should consider reading Exploring Black Holes - 2nd Ed by Taylor, Wheeler and Bertschinger at http://exploringblackholes.com/

I think you'd also get a great deal of satisfaction reading Black Holes and Time Warps - Einstein's Outrageous Legacy by Kip Thorne. Thorne is the worlds leading theorist on black holes.

Sorry this is getting to be a personal theory and this topic isn't really the place for that. I will get the references you suggest and may pursue this further.
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: Pmb on 07/10/2013 02:56:25
No apology necessary. Let me know when you get the reference in a PM please. I’m curious as to what that’s all about. Thanks.
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: jeffreyH on 08/10/2013 03:35:20
I was wondering if the Pauli exclusion principle could be one of the principle mechanisms of gravitational interaction. Note I didn't say gravitational generation, because I still doubt that gravitation comes out of matter. The spin combinations may be a clue.
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: Pmb on 08/10/2013 03:52:17
I was wondering if the Pauli exclusion principle could be one of the principle mechanisms of gravitational interaction.
Yes. In some cases it plays a role. Neutron stars is a perfect example. See http://en.wikipedia.org/wiki/Pauli_exclusion_principle
Quote
Astronomy provides a spectacular demonstration of the effect of the Pauli principle, in the form of white dwarf and neutron stars. In both types of body, atomic structure is disrupted by large gravitational forces, leaving the constituents supported by "degeneracy pressure" alone. This exotic form of matter is known as degenerate matter. In white dwarfs atoms are held apart by electron degeneracy pressure. In neutron stars, subject to even stronger gravitational forces, electrons have merged with protons to form neutrons. Neutrons are capable of producing an even higher degeneracy pressure, albeit over a shorter range. This can stabilize neutron stars from further collapse, but at a smaller size and higher density than a white dwarf. Neutrons are the most "rigid" objects known; their Young modulus (or more accurately, bulk modulus) is 20 orders of magnitude larger than that of diamond. However, even this enormous rigidity can be overcome by the gravitational field of a massive star or by the pressure of a supernova, leading to the formation of a black hole.

Thanks for asking this question. I learned asomething today, i.e. a new term "degenerate matter" - an exotic form of matter!
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: jeffreyH on 09/10/2013 10:13:39
In my mental musings over the past few days it appears to me that the most crucial component of e=mc^2 is actually the distance c. This distance bears a direct relationship to Planck scales which is critical to the understanding of forces in the universe.

We can rewrite this as e=m(Planck length)^2.
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: Kryptid on 09/10/2013 16:48:23
In my mental musings over the past few days it appears to me that the most crucial component of e=mc^2 is actually the distance c. This distance bears a direct relationship to Planck scales which is critical to the understanding of forces in the universe.

We can rewrite this as e=m(Planck length)^2.

That "c" is the speed of light, which is not a distance.
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: jeffreyH on 09/10/2013 16:59:47
In my mental musings over the past few days it appears to me that the most crucial component of e=mc^2 is actually the distance c. This distance bears a direct relationship to Planck scales which is critical to the understanding of forces in the universe.

We can rewrite this as e=m(Planck length)^2.

That "c" is the speed of light, which is not a distance.

If you do not believe this is a distance then e=mc^2 must be telling us how fast energy is travelling rather than how much of it relates to the mass. To expand on this c is important in the relationship between energy and inertia. When viewed that way yes c is a speed.
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: webplodder on 09/10/2013 17:23:45
If I throw a ball, presumably the mass of the ball will increase since I have imparted some kinetic energy to it but would I lose energy? My arm would be travelling at the same speed as the ball before I let it go so the ball and arm would experience the same kinetic energy. However, I must have used up some energy in the process of throwing the ball so what is the net result of all this?
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: yor_on on 09/10/2013 23:54:16
Mostly transformed into heat, as I understands it, the 'thing' missing from your muscles etc, costing 'energy' for you. But if you mean that there seems to be something weird about the concept that everything just transforms, and nothing ever is lost, the universe being in a equilibrium I agree :) Just turn it around and ask yourself why accelerations and life exist, if there just is a equilibrium? Doesn't mean it has to be wrong though, but there is some aspect missing to it. The one explaining why accelerations and life exist.
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: jeffreyH on 10/10/2013 00:59:07
Mostly transformed into heat, as I understands it, the 'thing' missing from your muscles etc, costing 'energy' for you. But if you mean that there seems to be something weird about the concept that everything just transforms, and nothing ever is lost, the universe being in a equilibrium I agree :) Just turn it around and ask yourself why accelerations and life exist, if there just is a equilibrium? Doesn't mean it has to be wrong though, but there is some aspect missing to it. The one explaining why accelerations and life exist.

Acceleration is one of the things Einstein should have concentrated on a bit more. Dimension and momentum have a relationship that brings into play a weird effect regarding density. I have only just started putting this together. If I start discussing too much of it now it will only cause a lively debate without the mathematics in place to back it up.
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: webplodder on 10/10/2013 10:17:35
If I throw a ball, presumably the mass of the ball will increase since I have imparted some kinetic energy to it but would I lose energy? My arm would be travelling at the same speed as the ball before I let it go so the ball and arm would experience the same kinetic energy. However, I must have used up some energy in the process of throwing the ball so what is the net result of all this?

Mostly transformed into heat, as I understands it, the 'thing' missing from your muscles etc, costing 'energy' for you. But if you mean that there seems to be something weird about the concept that everything just transforms, and nothing ever is lost, the universe being in a equilibrium I agree :) Just turn it around and ask yourself why accelerations and life exist, if there just is a equilibrium? Doesn't mean it has to be wrong though, but there is some aspect missing to it. The one explaining why accelerations and life exist.

Ok, I see. So, most of the energy used in throwing the ball would be expended as heat although a tiny amount of mass in my arm would be increased due to acceleration.
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: Pmb on 10/10/2013 11:06:51
Quote from: jeffreyH
If you do not believe this is a distance ...
It's a given that nobody believes that's distance, not just Supercryptid. c is, by definition the speed of light and thus a speed which is distance/time it's given that tis is not distance. But you know that already, right. Since you surely know that this is different than distance what exactly are you trying to imply here?
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: jeffreyH on 10/10/2013 12:23:58
Quote from: jeffreyH
If you do not believe this is a distance ...
It's a given that nobody believes that's distance, not just Supercryptid. c is, by definition the speed of light and thus a speed which is distance/time it's given that tis is not distance. But you know that already, right. Since you surely know that this is different than distance what exactly are you trying to imply here?

There is a time element to energy, kilowatt hours being an example, because that is the most sensible way to view it as energy and momentum are linked. This is not the actual momentum but the amount in that time. The speed component of c translates into amount of energy per second squared with no implicit momentum. I know what I mean but sometimes explain it in a bad way.
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: Pmb on 10/10/2013 16:40:43
Quote from: jeffreyH
There is a time element to energy, kilowatt hours being an example, because that is the most sensible way to view it as energy and momentum are linked.
That's incorrect. It's wrong to say that there is a time element to energy because time is related to power by P = E/t. This is like saying that a spatial location has a time element because v = S/t 

You need to rethink your response.
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: jeffreyH on 10/10/2013 17:39:38
Quote from: jeffreyH
There is a time element to energy, kilowatt hours being an example, because that is the most sensible way to view it as energy and momentum are linked.
That's incorrect. It's wrong to say that there is a time element to energy because time is related to power by P = E/t. This is like saying that a spatial location has a time element because v = S/t 

You need to rethink your response.

But also E=Pt where multiplying by a time element gives energy. So power is energy over time. The time is implicit.
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: Kryptid on 10/10/2013 22:18:19
Time may be implicit in power, but it isn't in energy. Power and energy are two different concepts. E=mc2 deals with energy, not power.
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: Pmb on 11/10/2013 00:48:28
Quote from: jeffreyH
There is a time element to energy, kilowatt hours being an example, because that is the most sensible way to view it as energy and momentum are linked.
That's incorrect. It's wrong to say that there is a time element to energy because time is related to power by P = E/t. This is like saying that a spatial location has a time element because v = S/t 

You need to rethink your response.

But also E=Pt where multiplying by a time element gives energy. So power is energy over time. The time is implicit.
You're twisting things to meet what you'd like to see written. That's bad science.
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: jeffreyH on 11/10/2013 01:36:46
Quote from: jeffreyH
There is a time element to energy, kilowatt hours being an example, because that is the most sensible way to view it as energy and momentum are linked.
That's incorrect. It's wrong to say that there is a time element to energy because time is related to power by P = E/t. This is like saying that a spatial location has a time element because v = S/t 

You need to rethink your response.

But also E=Pt where multiplying by a time element gives energy. So power is energy over time. The time is implicit.
You're twisting things to meet what you'd like to see written. That's bad science.

OK. Bear with me a while. Humour me in other words.
Firstly c is distance travelled over time taken. So yes in respect to light that is a speed. Can we agree on that first? Then I will proceed to the next step in my thinking.
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: Pmb on 11/10/2013 04:19:19
Quote from: jeffreyH
OK. Bear with me a while. Humour me in other words.
Firstly c is distance travelled over time taken.
Yes. That is correct.

Quote from: jeffreyH
So yes in respect to light that is a speed. Can we agree on that first? Then I will proceed to the next step in my thinking.
And I will do the same in my thinking as well. Space and time are primative quantities. That means that they are not defined in terms of other quantities. Defined terms such as speed v = distance/time are defined in terms of other quantities.

Words such as "element" as in "There is a time element to energy, .." are not defined in physics. However without such a definition we use the one found in a dictionary

See http://www.merriam-webster.com/dictionary/element

However your use is far from clear as it can be found in a dictionary. Otherwise when you start solving for variables in equations and saying "There is an x element to this physics because x is in the equation" isn't a very useful notion.

It'd be far better if you clearly stated what you mean by ""element".
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: jeffreyH on 11/10/2013 12:23:26
Quote from: jeffreyH
OK. Bear with me a while. Humour me in other words.
Firstly c is distance travelled over time taken.
Yes. That is correct.

Quote from: jeffreyH
So yes in respect to light that is a speed. Can we agree on that first? Then I will proceed to the next step in my thinking.
And I will do the same in my thinking as well. Space and time are primative quantities. That means that they are not defined in terms of other quantities. Defined terms such as speed v = distance/time are defined in terms of other quantities.

Words such as "element" as in "There is a time element to energy, .." are not defined in physics. However without such a definition we use the one found in a dictionary

See http://www.merriam-webster.com/dictionary/element

However your use is far from clear as it can be found in a dictionary. Otherwise when you start solving for variables in equations and saying "There is an x element to this physics because x is in the equation" isn't a very useful notion.

It'd be far better if you clearly stated what you mean by ""element".

Let's ditch the element issue for now. Einstein came to the conclusion that there was a link between inertia and energy. Inertia is applicable in two situations. when a mass it at rest or moving at a constant velocity as long as no external forces are applied. Acceleration, deceleration and change of direction are the external forces. This is the next issue to agree upon.
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: Pmb on 11/10/2013 12:59:23
Quote from: jeffreyH
Einstein came to the conclusion that there was a link between inertia and energy. Inertia is applicable in two situations. when a mass it at rest or moving at a constant velocity as long as no external forces are applied. Acceleration, deceleration and change of direction are the external forces. This is the next issue to agree upon.
The essence of his derivation is found in my website here
http://home.comcast.net/~peter.m.brown/sr/mass_energy_equiv.htm
Take a look at it and let me know what you think.
[/quote]
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: jeffreyH on 13/10/2013 01:19:01
Quote from: jeffreyH
Einstein came to the conclusion that there was a link between inertia and energy. Inertia is applicable in two situations. when a mass it at rest or moving at a constant velocity as long as no external forces are applied. Acceleration, deceleration and change of direction are the external forces. This is the next issue to agree upon.
The essence of his derivation is found in my website here
http://home.comcast.net/~peter.m.brown/sr/mass_energy_equiv.htm
Take a look at it and let me know what you think.

Very interesting. The energy-momentum relation is not what I am investigating. It is the simplified e=mc^2. I will post some more points when I get some time to put a document together. One thing to ponder. Is the Planck scale invariant with regard to the distortion of spacetime? The answer to this has a great bearing on how the search for a workable theory of quantum gravity.
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: Pmb on 13/10/2013 08:25:36
Quote from: jeffreyH
The energy-momentum relation is not what I am investigating.
Sorry, but I don't see your point. I never mentioned that.

Quote from: jeffreyH
It is the simplified e=mc^2.
Huh? What does that mean? I.e. what is the simplified e=mc^2? Do you believe that there is there a non-simplified e=mc^2?

Quote from: jeffreyH
One thing to ponder. Is the Planck scale invariant with regard to the distortion of spacetime?
Yes. I believe so.
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: jeffreyH on 13/10/2013 10:52:41
Quote from: jeffreyH
The energy-momentum relation is not what I am investigating.
Sorry, but I don't see your point. I never mentioned that.

Quote from: jeffreyH
It is the simplified e=mc^2.
Huh? What does that mean? I.e. what is the simplified e=mc^2? Do you believe that there is there a non-simplified e=mc^2?

Quote from: jeffreyH
One thing to ponder. Is the Planck scale invariant with regard to the distortion of spacetime?
Yes. I believe so.

Not E^2=(pc)^2+(m0c^2)^2.
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: yor_on on 14/10/2013 17:25:47
at webplodder: Your relative mass should increase I guess, as you accelerate your arm, as well as the balls mass should, but as soon as you both are uniformly moving, it must be gone:) Interesting idea, better check it with Pete though.
=

That's wrong, your relative mass will still be there, in a uniform motion as well as in a acceleration. What I was thinking of was inertia there, not relative mass. That is what will be gone in after you finished accelerating. That relative mass you have will be expressed as kinetic energy in a collision. And there your speed will matter, acceleration or no acceleration. The inertia is still existent in a uniform motion though, although unmeasurable for you. and the inertia accelerating, can in a uniformly constant acceleration (at one gravity), translate into the same gravity we meet on Earth. Maybe it's more correct to call it your arm feeling gravity :) accelerating? This is definitely Pete:s field of interest.

Hmm rereading it again: I must have meant that as soon as your arm stops moving it also has decelerated to the same speed it had before starting to throw a ball for example. And in so motto it is correct.
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: jeffreyH on 16/10/2013 21:42:48
Quote from: jeffreyH
The energy-momentum relation is not what I am investigating.
Sorry, but I don't see your point. I never mentioned that.

Quote from: jeffreyH
It is the simplified e=mc^2.
Huh? What does that mean? I.e. what is the simplified e=mc^2? Do you believe that there is there a non-simplified e=mc^2?

Quote from: jeffreyH
One thing to ponder. Is the Planck scale invariant with regard to the distortion of spacetime?
Yes. I believe so.

On the Planck scale issue, if the universe were measured out into Planck cubes and the cubes that were being traveled through by mass undergoing acceleration, would a length contraction be observed at that scale? On a macroscopic scale an observer external to the accelerating system would see length contraction. How can this be separated from the finer grained resolution?

What if contraction itself and the inherent momentum of the scaling factor produced the gravitational effect WITHOUT any elementary particle. Maybe we are looking for a graviton that doesn't exists. That might be the reason for all the failure. If momentum and mass-energy density are interlinked some strange effects may become apparent.
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: Pmb on 17/10/2013 15:26:43
Quote from: jeffreyH
On the Planck scale issue, ...
The Planck scale comes from quantum gravity. Since I don't know quantum gravity you're going to find me very silent on questions about the "Planck scale issue" including your questions here. Sorry. I just don't think it's wise to talk about physics I'm not familiar with. I wish more people felt that way.
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: jeffreyH on 20/10/2013 17:18:37
One thing that never gets mentioned with respect to gravitational issues is parallax. We take it for granted but there are issues to do with this effect on a local scale.
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: Pmb on 21/10/2013 07:42:52
Quote from: jeffreyH
One thing that never gets mentioned with respect to gravitational issues is parallax.
That's because there's no reason why it should. It has absolutely nothing to do with gravity. It only pertains to optical observation of celestial bodies. Why do you think it should have anything to do with gravity at all?

Quote from: jeffreyH
We take it for granted but there are issues to do with this effect on a local scale.
When making assertions like this its helpful to back it up with facts. E.g. what are these issues that you're referring to?
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: jeffreyH on 21/10/2013 21:33:49
Quote from: jeffreyH
One thing that never gets mentioned with respect to gravitational issues is parallax.
That's because there's no reason why it should. It has absolutely nothing to do with gravity. It only pertains to optical observation of celestial bodies. Why do you think it should have anything to do with gravity at all?

Quote from: jeffreyH
We take it for granted but there are issues to do with this effect on a local scale.
When making assertions like this its helpful to back it up with facts. E.g. what are these issues that you're referring to?

If you had a disc whose circumference was 300000000 meters you could never achieve one revolution per second as the angular momentum would reach light speed at the edges. Length contraction would be greater at the edges of the disc as it approached light speed which would mean that the spacetime distortion would produce strange parallax effects. Gravitation and momentum cannot be separated so these effects are important in understanding these forces.
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: Pmb on 22/10/2013 01:27:42
Quote from: jeffreyH
If you had a disc whose circumference was 300000000 meters you could never achieve one revolution per second as the angular momentum would reach light speed at the edges. Length contraction would be greater at the edges of the disc as it approached light speed which would mean that the spacetime distortion would produce strange parallax effects.
First let's be clear on something. The contraction of the circumference of a disk does not mean that there is any spacetime distortion whatsoever. The only way that spacetime can be distorted here is due to the energy of the rotating disk rotating such that parts of it have near superluminal speeds.

All you're really saying is that light is bent by gravity. Bringing in parallax only serves to confuse things. There's no need for it to be quite honest.

Let's be clear here. Parallax is defined as follows
http://en.wikipedia.org/wiki/Parallax
Quote
Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight, and is measured by the angle or semi-angle of inclination between those two lines.
Bringing in parallax confuses things and as such I recommend not using it in this sense.

Quote from: jeffreyH
Gravitation and momentum cannot be separated so these effects are important in understanding these forces.
Why are you now bringing momentum into this? And why would you make such a statement as this? What does it have to do with the present subject? And momentum is not a force either.

Some of the stuff you say is really confusing Jeff.
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: jeffreyH on 22/10/2013 10:01:35
Think of the parallax effects of frame dragging. This is a similar situation. This is the reason c^2 is related to mass-energy and not any other value. The effects at light speed and under gravitation have intimate links.
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: Pmb on 22/10/2013 10:23:23
Quote from: jeffreyH
Think of the parallax effects of frame dragging.
Since parallax has nothing to do with frame dragging I have no idea what you're talking about. Sorry.

Quote from: jeffreyH
This is a similar situation. This is the reason c^2 is related to mass-energy and not any other value.
The reason c2 relates mass to energy is due to its presence in the Lorentz trasformation. How you connect it otherwise is beyond. How did you come to such a conclusion?

Quote from: jeffreyH
The effects at light speed and under gravitation have intimate links.
"Under" gravitation? Is that an error? In any case you once more lost me.
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: jeffreyH on 27/10/2013 16:20:21
Quote from: jeffreyH
Think of the parallax effects of frame dragging.
Since parallax has nothing to do with frame dragging I have no idea what you're talking about. Sorry.

Quote from: jeffreyH
This is a similar situation. This is the reason c^2 is related to mass-energy and not any other value.
The reason c2 relates mass to energy is due to its presence in the Lorentz trasformation. How you connect it otherwise is beyond. How did you come to such a conclusion?

Quote from: jeffreyH
The effects at light speed and under gravitation have intimate links.
"Under" gravitation? Is that an error? In any case you once more lost me.

Under the influence of gravitation.

Think of mass for a moment. What property of mass produces gravitation? If we take a number of spheres 1 meter in diameter made of iron. If these spheres were contained within a mesh to produce a spherical shape we could produce something that looks like a planet. If the mass of the spheres plus the mesh was the same of the mass of the earth then what would the combined gravity be when placed in the same orbit as the earth? Each sphere has its own gravitation which drops in an inverse square relationship and individually are much weaker than that of the earth. A very pertinent point is whether the gravitation would accumulate under these conditions. Would we reproduce the field strength of the earth? Before I can elaborate on other ideas this point needs to a answered conclusively.
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: Pmb on 01/11/2013 15:05:39
Quote from: jeffreyH
Think of mass for a moment. What property of mass produces gravitation?
Mass doesn't have any properties. Mass is a property. Therefore your question is meaningless.
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: jeffreyH on 11/11/2013 23:06:57
Quote from: jeffreyH
Think of mass for a moment. What property of mass produces gravitation?
Mass doesn't have any properties. Mass is a property. Therefore your question is meaningless.

The properties of mass are surely gas, liquid, solid, plasma etc. Or if you prefer, states.
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: Pmb on 12/11/2013 00:01:50
Quote from: jeffreyH
The properties of mass are surely gas, liquid, solid, plasma etc. Or if you prefer, states.
Sorry but that's not going to work either my friend. :) Those are the properties of things that have mass, not the properties of mass.
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: jeffreyH on 13/11/2013 18:58:43
Quote from: jeffreyH
The properties of mass are surely gas, liquid, solid, plasma etc. Or if you prefer, states.
Sorry but that's not going to work either my friend. :) Those are the properties of things that have mass, not the properties of mass.

Yes mass is a property of matter but properties can themselves have properties. Colour, for instance, has the properties of luminescence and brightness. I specifically did not relate the properties to matter as I believe it is the mass that is the defining factor with relation to gravitation. An atom will have less gravitation than a molecule, which in turn has less gravitation than a solid made up from molecules.
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: Pmb on 14/11/2013 01:13:31
Jeff - This is getting way off subject and I'm not interested in this side track. What exactly is it you wish to discuss or ask me about? Thanks! - Pete
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: jeffreyH on 14/11/2013 18:35:50
Jeff - This is getting way off subject and I'm not interested in this side track. What exactly is it you wish to discuss or ask me about? Thanks! - Pete

Well I suppose what I want to discuss is this.

http://burro.cwru.edu/Academics/Astr221/LifeCycle/jeans.html

The Jeans criteria for gas collapse under gravitation. What does this process tell us about gravity?
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: Pmb on 15/11/2013 00:20:07
Jeff - This is getting way off subject and I'm not interested in this side track. What exactly is it you wish to discuss or ask me about? Thanks! - Pete

Well I suppose what I want to discuss is this.

http://burro.cwru.edu/Academics/Astr221/LifeCycle/jeans.html

The Jeans criteria for gas collapse under gravitation. What does this process tell us about gravity?
I don't know. That's astrophysics and in astrophysics I'm a layman, just like you. :)
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: JP on 15/11/2013 02:23:48
The Jeans criterion seems to be fairly straightforward from that link.  Basically,  a bunch of particles of gas in space will tend to attract each other and coalesce to form a star.  However, in actuality, gas particles move about due to the temperature of a gas and this motion can keep them from clumping together (if they get too close, they'll bump into each other and fly apart again).  Basically, if there's enough mass in a cloud of gas compared to the temperature of that gas, it will coalesce into a star.  If the temperature is too high compared to the mass, it will stay a cloud of gas and not form into a star.
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: jeffreyH on 17/11/2013 23:03:02
The Jeans criterion seems to be fairly straightforward from that link.  Basically,  a bunch of particles of gas in space will tend to attract each other and coalesce to form a star.  However, in actuality, gas particles move about due to the temperature of a gas and this motion can keep them from clumping together (if they get too close, they'll bump into each other and fly apart again).  Basically, if there's enough mass in a cloud of gas compared to the temperature of that gas, it will coalesce into a star.  If the temperature is too high compared to the mass, it will stay a cloud of gas and not form into a star.

Interesting. So then a fall in kinetic energy should initiate gravitational collapse for a mass of sufficient density. This appears to show that gravitation tends to aid in the solidification of matter somehow. Does this also suggest that spin 2 particles operate to initially reduce kinetic energy for matter moving away from the source of gravitation? What better way to add matter to a mass than hurling it inwards.
Title: Re: What effect does mass-energy density have on gravitational field strength?
Post by: jeffreyH on 18/11/2013 18:44:15
This train of thought got me thinking about singularities with regard to the mass-energy density topic. If increase in gravitation reduces kinetic energy and the reduction in kinetic energy leads to time dilation (rate of atomic change slows down) then the singularity is an inevitable consequence of gravity and the ideal equalibrium for such a force. A question of interest would be this. What would an observer outside the earth determine would be the speed of an object falling to earth under gravitation? How many metres per second of acceleration would they record as compared to an earth bound observer?

P.S. Does this imply zero kinetic energy at the singularity? Could frame dragging occur because it is moving around a time-free zone and is forced to do so because of the consequences of the lack of kinetic energy at the singularity?