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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.

Quote from: jeffreyH on 28/09/2013 23:59:55In 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: ...sorry, you cannot view external links. To see them, please REGISTER or LOGINFor 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).

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?

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.

Quote from: jeffreyHDoes the mass-energy density affect gravity at higher densities?Yes. Quote from: jeffreyHDoes any amplification of field strength occur?I don’t understand what this means so I’ll just say no. Quote from: jeffreyHHow 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.

Quote from: jeffreyH on 29/09/2013 07:49:45It 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.

Quote from: jeffreyH on 30/09/2013 05:30:34The 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.

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.

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.

Quote from: jeffreyH on 30/09/2013 05:49:56You 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: ...sorry, you cannot view external links. To see them, please REGISTER or LOGINQuoteIf 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.

The gravitational force experienced between two bodies is related to the mass and distance between them. In some sense, density doesn't matter.

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?

Quote from: jeffreyH on 28/09/2013 07:17:03Does 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 ...sorry, you cannot view external links. To see them, please REGISTER or LOGIN

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.

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?

Quote from: Pmb on 04/10/2013 01:36:24That 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).Quote from: jeffreyH on 04/10/2013 06:40:18Just 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.

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).

It is so good to have someone tell you WHY you are wrong.

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?

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?

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?

Quote from: jeffreyHTo 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: jeffreyHMass 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: jeffreyHHas 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?

Quote from: jeffreyH on 05/10/2013 08:22:28Is 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?

The effects on gravitational field strength. Does it increase or decrease overall? This is assuming a Kerr black hole.

Quote from: Supercryptid on 05/10/2013 06:29:13Interesting...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.

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?

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.