The speed of Gravity

Discussions on classical and modern physics, quantum mechanics, particle physics, thermodynamics, general and special relativity, etc.

Re: The speed of Gravity

Postby bangstrom on July 8th, 2018, 4:29 am 

DJ_Juggernaut » July 4th, 2018, 4:59 am wrote:
Gravitational waves and the 'speed of gravity' are the not same.
I also find a distinction between the speed of gravity and the speed of gravitational waves. Gravity is a universal spacetime curvature or gradient that is responsible for the effects we call “gravity” while gravity waves are waves within this medium much like sound waves in the air. Gravity is the medium that surrounds us and it has movements involving changes in densities but gravity isn't a force radiating away from a source so I find it difficult to say that gravity has a speed but gravity does appear to contain waves move through space at speed c.

“Spooky action at a distance” may be a completely different phenomenon from gravity or gravity could be a non-local attraction among objects with mass, in which case, the “speed” of gravity is instant, or more likely, far too fast to measure. If the latter is the case, then the time delay we see with gravity is the same c related delay we see where any two objects separated by space are also separated by time.
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Re: The speed of Gravity

Postby bangstrom on July 8th, 2018, 4:54 am 

Dave_Oblad » July 7th, 2018, 10:37 pm wrote:Hi Event Horizon,

Imagine the collision two equal Black Holes where one is composed of Anti-Matter. Sure, they would annihilate each other and supposedly produce a tremendous amount of energy.. inside of a Black Hole.

The results would be the conversion of both Matter types to Energy.. But would the Energy trapped within still maintain the Gravitational Field Space-Time distortion? Can that Energy escape the Gravity Well? Is Time itself actually distorted within the Black-Hole.. or is Matter (ie: clocks) the only real (temporal) distortion affected by a Gravity Well?

One way to think of gravity is to consider gravity as an energy deficit. Pascual Jordan speculated that the energy of a star consists of equal amounts of both positive and negative energy so the total energy of a star is zero and, consequently, the net total energy of the universe is also zero.

By this “Zero Energy” theory, the universe may have begun as a quantum fluctuation with one half of the fluctuation being positive energy and the other half being negative energy. The positive half became what we call mater and ordinary energy while the negative half remained as negative energy that we recognize as gravity. Gravity is considered negative energy because it takes energy to remove matter from a gravitational field. We can think of gravity as a “hole” left behind in the false vacuum resulting from the half of the quantum fluctuation that went into positive energy so gravity is the energy deficit left behind.

If positive energy/mater can form black holes, I would imagine that negative energy (gravity) could do the same and form negative-energy/anti-matter and anti-mater black holes. And, since gravity is negative energy, an anti-mater black hole would be composed of gravity so a collision between an ordinary black hole and an anti-matter black hole would be the annihilation of positive energy by negative energy or the annihilation of matter by gravity depending on what you choose to call it.

Anyhow, it would likely be a local catastrophe and messy collision but it would eventually be the annihilation of both black holes, both energies (positive and negative) and the gravity well and a return to the false vacuum from whence it all came. Every-thing would all go back to being nothing.
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Re: The speed of Gravity

Postby bangstrom on July 8th, 2018, 5:16 am 

Dave_Oblad » July 6th, 2018, 12:18 pm wrote:
Anyway, the results of that discussion ended without a solid resolution. For the time being, Science holds that the speed of Gravitational Collapse is the same as Gravity Wave propagation (unless something has changed since that time). My objection was that they are two completely different things from a mechanical point of view (Stress Release in a Medium <vs> Wave Propagation in a Medium).

Your analysis makes sense. If the sun or a black hole were to suddenly disappear, it would result in the propagation of gravity waves into space at speed c but gravity waves are not what hold the planets in orbit. The waves might make them wobble but, only after the waves began to dampen, would they uniformly begin to drift away from the center.
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Re: The speed of Gravity

Postby Dave_Oblad on July 9th, 2018, 1:06 pm 

Hi Bangstrom,

What I can say about Gravity is that it is not a pulling force, but rather a difference in the Space-Time Medium. That difference (I Believe) is a gradient in the Scale of the Planck Length.

1. The Space-Time Medium is absolutely pixelated (made of discrete cells).

Without Scale.. Any distance between two objects is infinite.. if the distance can be infinitely sub-divided. Without Scale nothing can be a constant (size of particles and distance between such etc). Time also must be Scaled or any temporal distance between events becomes meaningless (The Planck Interval). Without a controlling background Scale we would have Big Atoms and Small Atoms mixed and then, of course, there would be no compatibility for bonding in various Atomic configurations (water for example). Speed becomes meaningless without units of measure that are constant. Scale is extremely important for the Universe to operate.

2. The Universe is expanding by the addition (growth) of new Space-Time Medium structure.

If the Universe is pixelated, then new pixels (cells) are grown on previous cells and of course must match the Scale of the previous cells. Matter has the effect of forcing new cell growth to be compatible with previous cells, thus stunting the growth of Scale.. local to Matter (inside and around said Matter). Connecting new cells are therefore also restricted in Scale Growth. This means that large objects (Galaxies) do not Grow/Inflate/Expand at the same rate as cells between Galaxies. This would lead one to the conclusion that Scale is variable, meaning that the Planck Length is not the same out in Deep Flat Space as one would find around a Black-Hole. So, even though the Planck Length is indivisible, there is no reason to presume the Planck Length is the same everywhere. The Planck Length Scale is conditional to the previous layer of cells that new cells are grown upon.

3. When Matter is Accelerated, it must take on a new Geometry to uphold the exchange of information carriers (photons etc) within the Geometry of said Matter.

Matter will shorten along the axis of travel and because it is accelerating.. the atomic geometry at the front and back of an object must not be linear. When acceleration is removed, said Matter stabilizes with uniform Geometry but is not the exact same Geometry as Matter not moving as fast. This is the result of a simple fact that information exchange has a fixed speed limit (light speed) and thus information flow in the direction of motion must have different timing than information flow opposite of the direction of motion. To accommodate this difference requires a change in the Geometry of Matter. The compensation for said timing irregularity results in an increase in the Complexity of the Geometry of Matter. This is called Momentum. If a change in speed is gradual enough, then the morphing of Matter Geometry is suitable enough to hold stability. If Matter changes velocity fast enough, then Matter can not change Geometry fast enough to maintain stability and it will fall apart into an array of atomic components and energy.

4. Matter under acceleration can not be fully symmetrical along its axis of motion.

Matter at the front of an object is the first to be subjected to a required change in Geometry while Matter at the rear of an object always lags (last to know). This makes Matter Geometry under acceleration non-linear down its length in the direction of motion. Basically, Matter must become slightly more dense on the leading edge as opposed to the trailing edge during acceleration. This is the same regardless of whether said Matter is being pushed or pulled. The front is always the first to know about changes required, while the rear is always lagging a tiny bit.

5. Matter is not independent of Space-Time Structure. Matter Geometry is supported by the structure of Space-Time.

If the Planck Length Scale is smaller (restricted growth) near an object of Mass then the structure of Space-Time is non-linear. Matter must conform to this non-linear Gradient and must become non-linear in itself. This forces the Geometry of Acceleration on said Matter.

Thus Matter is always Accelerated towards a denser Space-Time Gradient, held as such by the presence of Matter which is restricting the Scale of the natural growth of new cells, because Matter has now taken on the non-linear Geometry of Acceleration to conform with the supporting structure of local Space-Time.

That is Gravity.

This is greatly over simplified but has implications that are consistent with observations and avoid issues with the mathematical singularity breakdown of Black-Holes. The breakdown in Math is because Science tends to reject the concept that the Planck Length (while indivisible) is a constant size everywhere.

Once one accepts Variable Planck Scale, held in check by local history, then a lot of other issues fade away.

This is a Universe Model based on a Growing 4D Cellular Automaton where we exist on the expanding 3D surface of said architecture. This defines Time as Expansion of growth via new cells added on the 3D surface.

I'll stop here.. as to go further may put this theory outside mainstream Physics. While several notable Physicists are currently exploring this line of reasoning, it may take awhile for Science to switch tracks. If the above is proven correct then the Science of Black-Holes may soon take a serious blow to the proverbial head. I hope to live long enough to see it..lol.

Regards,
Dave :^)

Ps. If anyone wants to dig deeper, open a new thread in personal theories and I'll respond there. Note: I only drop by every few days to check on things. Meanwhile I'm keeping busy on other fronts at home.
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Re: The speed of Gravity

Postby mitchellmckain on July 9th, 2018, 3:46 pm 

Dave_Oblad » July 9th, 2018, 12:06 pm wrote:Hi Bangstrom,

What I can say about Gravity is that it is not a pulling force, but rather a difference in the Space-Time Medium. That difference (I Believe) is a gradient in the Scale of the Planck Length.

Gravity is a pulling force by the definition of the terms. Say rather that gravity does not depend on visualizing it as something apart from the geometry of space-time. BUT there is nothing wrong with visualizing it in such a way and for that we have the QFT picture of graviton exchange particles. I like the geometry explanation too, but it goes too far from science to say that gravity is one thing and not the other.

Dave_Oblad » July 9th, 2018, 12:06 pm wrote:1. The Space-Time Medium is absolutely pixelated (made of discrete cells).

Without Scale.. Any distance between two objects is infinite.. if the distance can be infinitely sub-divided. Without Scale nothing can be a constant (size of particles and distance between such etc). Time also must be Scaled or any temporal distance between events becomes meaningless (The Planck Interval). Without a controlling background Scale we would have Big Atoms and Small Atoms mixed and then, of course, there would be no compatibility for bonding in various Atomic configurations (water for example). Speed becomes meaningless without units of measure that are constant. Scale is extremely important for the Universe to operate.

Sounds like a resurrection of Xeno's rhetoric, which was buried with the mathematics of Calculus.

Dave_Oblad » July 9th, 2018, 12:06 pm wrote:2. The Universe is expanding by the addition (growth) of new Space-Time Medium structure.

If the Universe is pixelated, then new pixels (cells) are grown on previous cells and of course must match the Scale of the previous cells. Matter has the effect of forcing new cell growth to be compatible with previous cells, thus stunting the growth of Scale.. local to Matter (inside and around said Matter). Connecting new cells are therefore also restricted in Scale Growth. This means that large objects (Galaxies) do not Grow/Inflate/Expand at the same rate as cells between Galaxies. This would lead one to the conclusion that Scale is variable, meaning that the Planck Length is not the same out in Deep Flat Space as one would find around a Black-Hole. So, even though the Planck Length is indivisible, there is no reason to presume the Planck Length is the same everywhere. The Planck Length Scale is conditional to the previous layer of cells that new cells are grown upon.

This is where the whole pixelated discrete space picture becomes absurd. I can buy into the idea of quantizing space such as in loop quantum gravity, but I don't think this supports what you are claiming.

It frankly sound like a picture of the universe attractive to computer people the way that a 4000 or 6000 year time scale is attractive to Biblical enthusiasts.

Dave_Oblad » July 9th, 2018, 12:06 pm wrote:3. When Matter is Accelerated, it must take on a new Geometry to uphold the exchange of information carriers (photons etc) within the Geometry of said Matter.

Matter will shorten along the axis of travel and because it is accelerating.. the atomic geometry at the front and back of an object must not be linear. When acceleration is removed, said Matter stabilizes with uniform Geometry but is not the exact same Geometry as Matter not moving as fast. This is the result of a simple fact that information exchange has a fixed speed limit (light speed) and thus information flow in the direction of motion must have different timing than information flow opposite of the direction of motion. To accommodate this difference requires a change in the Geometry of Matter. The compensation for said timing irregularity results in an increase in the Complexity of the Geometry of Matter. This is called Momentum. If a change in speed is gradual enough, then the morphing of Matter Geometry is suitable enough to hold stability. If Matter changes velocity fast enough, then Matter can not change Geometry fast enough to maintain stability and it will fall apart into an array of atomic components and energy.

Are you talking about acceleration due to an external force or a gravitational gradient? Acceleration alone does not imply what you are talking about.

Dave_Oblad » July 9th, 2018, 12:06 pm wrote:4. Matter under acceleration can not be fully symmetrical along its axis of motion.

Matter at the front of an object is the first to be subjected to a required change in Geometry while Matter at the rear of an object always lags (last to know). This makes Matter Geometry under acceleration non-linear down its length in the direction of motion. Basically, Matter must become slightly more dense on the leading edge as opposed to the trailing edge during acceleration. This is the same regardless of whether said Matter is being pushed or pulled. The front is always the first to know about changes required, while the rear is always lagging a tiny bit.

Are you taking about encountering a gravitational wave or entering the gravitational field of a spherical mass?

[quote="[url=http://www.sciencechatforum.com/viewtopic.php?p=337971#p337971]Dave_Oblad » July 9th,
2018, 12:06 pm[/url]"]
This is a Universe Model based on a Growing 4D Cellular Automaton where we exist on the expanding 3D surface of said architecture. This defines Time as Expansion of growth via new cells added on the 3D surface.

I'll stop here.. as to go further may put this theory outside mainstream Physics. While several notable Physicists are currently exploring this line of reasoning, it may take awhile for Science to switch tracks. If the above is proven correct then the Science of Black-Holes may soon take a serious blow to the proverbial head. I hope to live long enough to see it..lol.
[/quote]
personal theory ah... not science then. I see.
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Re: The speed of Gravity

Postby Event Horizon on July 30th, 2018, 8:45 pm 

I seem to recall that gravity waves were detected momentarily before photons were from a cosmic collision or major event. I should have said gravitational anomalies in spacetime. How? A wave travelling through the Higgs field? This is fundamental stuff, and I am trying to understand it.
I get string theory, but don't adhere to multiverse theory, which is pointless anyway as they can never be observed or contacted if they haven't imploded anyway. Wouldn't these universes have detectable gravitational signatures anyway? There is only one gravity, it should be ubiquitous surely?
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Re: The speed of Gravity

Postby mitchellmckain on July 31st, 2018, 1:11 am 

bangstrom » July 8th, 2018, 3:29 am wrote:
DJ_Juggernaut » July 4th, 2018, 4:59 am wrote:
Gravitational waves and the 'speed of gravity' are the not same.
I also find a distinction between the speed of gravity and the speed of gravitational waves. Gravity is a universal spacetime curvature or gradient that is responsible for the effects we call “gravity” while gravity waves are waves within this medium much like sound waves in the air.

To clarify, when we talk about the speed of things like gravity and electromagnetic fields, what we are talking about is the propagation of changes in the field. Gravity is no different -- we just have this way of representing the gravitational field as the curvature of space-time. And by the way, by doing General Relativity in 5 dimensions (Kaluza-Klein theory) we can do the same for electromagnetic fields. The field acts instaneously because it is NOT acting at a distance. The field is already right there. What take time is any change in the field which can only propagate at the speed of light or less via gravity waves and photons.

For example, suppose the source of an electric field (i.e. the charge) or a gravity field were to simply disappear. What would happen? Well at a distance things would behave as if the source were still there, because the field at that location hasn't changed -- the change has to propagate at the speed of light or less.
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Re: The speed of Gravity

Postby Event Horizon on July 31st, 2018, 1:42 pm 

It's fascinating stuff. Suppose Dave that two black holes collided. One matter, the other antimatter. They would annihilate each other in a ferocious conflagration for sure.
The mass would be lost as energy and a huge distortion in spacetime might well be as a huge loss of colossal amounts of gravity from a region of spacetime would occur in short order. This might be expected to propagate through spacetime, but how? It's not going to be shed particles, they do not have the mass. I'm thinking as the Higgs field seems stretchable and compressible its density may be determinable allowing us to predict gravitational events, how they travel, and exactly how fast, definitely.

It's most interesting, I agree.
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Re: The speed of Gravity

Postby mitchellmckain on July 31st, 2018, 9:19 pm 

Event Horizon » July 31st, 2018, 12:42 pm wrote:It's fascinating stuff. Suppose Dave that two black holes collided. One matter, the other antimatter. They would annihilate each other in a ferocious conflagration for sure.
The mass would be lost as energy and a huge distortion in spacetime might well be as a huge loss of colossal amounts of gravity from a region of spacetime would occur in short order. This might be expected to propagate through spacetime, but how? It's not going to be shed particles, they do not have the mass. I'm thinking as the Higgs field seems stretchable and compressible its density may be determinable allowing us to predict gravitational events, how they travel, and exactly how fast, definitely.

It's most interesting, I agree.


Incorrect. A black hole is simply a black hole. There is not one for matter and one for antimatter. The collision of two black holes simply produces a larger black hole (and a gravity wave of course).

If you want an annihilation then you should stick to neutron stars. Since there is both a neutron and an anti-neutron then you can have both neutronium and anti-neutronium and thus a neutron star and an anti-neutron star. Even in this case there is a possibility they could end up collapsing into a black hole, but it is more likely that the annihilation on contact would blow the two of them apart before that could happen. In that case, you would probably have the triple explosion of annihilation in the center with the two neutron stars destabilizing also.

You are also incorrect in supposing that annihilation means no matter comes out of the explosion. This is incorrect. Whenever you have high concentrations of energy there will be particle anti-particle pairs produced. They do this at particle-colliders to create antimatter. But as I explained above, the complete annihilation of two large bodies one of matter and one of antimatter will never happen, because the energy from annihilation at contact will blow much of the matter and anti-matter away from each other.

In any case, none of this is likely to happen in real life. There are no anti-matter stars or galaxies. If there were, they would stand out because of interactions with all the matter around them.
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Re: The speed of Gravity

Postby mitchellmckain on August 1st, 2018, 2:35 am 

On the collision of neutron star and anti-neutron star here is another opinion...

https://www.quora.com/What-could-happen-when-an-anti-neutron-star-and-a-normal-neutron-star-collide

I only find it hard to believe the neutron stars could absorb much energy from the annihilation that it wouldn't destabilize them. Since he didn't even mention this, I wondered if he even considered it. I find his picture of the two neutron stars bouncing away from each other due to this explosion to be a far fetched. But it is possible that both ideas are correct and it only depends on the velocity of the collision.
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Re: The speed of Gravity

Postby Watson on August 2nd, 2018, 1:11 am 

Incorrect. A black hole is simply a black hole. There is not one for matter and one for antimatter. The collision of two black holes simply produces a larger black hole (and a gravity wave of course).


I realize this can not happen, but If a BH/anti-BH did collide the matter anti-matter collision would annihilate in equal parts removing a portion of the gravitational mass? This would weaken gravitation forces. I would expect the BH to be of a lesser size or strength, not larger?

Or is it, there is no anti-matter black holes, anti-matter does not exist except in the text book and collider labs, and there is not enough anti-matter existing to be affected by gravity?
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Re: The speed of Gravity

Postby mitchellmckain on August 2nd, 2018, 1:50 am 

Watson » August 2nd, 2018, 12:11 am wrote:
Incorrect. A black hole is simply a black hole. There is not one for matter and one for antimatter. The collision of two black holes simply produces a larger black hole (and a gravity wave of course).


I realize this can not happen, but If a BH/anti-BH did collide the matter anti-matter collision would annihilate in equal parts removing a portion of the gravitational mass? This would weaken gravitation forces. I would expect the BH to be of a lesser size or strength, not larger?

Or is it, there is no anti-matter black holes, anti-matter does not exist except in the text book and collider labs, and there is not enough anti-matter existing to be affected by gravity?


There is no such thing as an anti-BH. Black holes are a purely gravitational phenomenon. There is no anti-gravity. Even if you suppose that one black hole was made by a collapse of antimatter. In the singularity there is no matter or antimatter -- only mass/energy. Nothing escapes from Schwarschild radius of the black hole and so any supposed annihilation of matter and antimatter (such as outside the singularity) would make no difference anyway. If you have been thinking that matter meeting anti-matter just results in a cancellation of each other with nothing left over then you had it all wrong. The annihilation produces all the energy equal to the two masses put together according to E=mc2. The mass of the black hole remains the same because the energy remains the same -- annihilation does not make that energy disappear and the energy equals the same mass. Thus it would NOT weaken the gravitational forces. Antimatter does not have negative mass or negative energy so the mass and energy would ADD together!!!

don't like my explanation?

How about this one. https://www.universetoday.com/121487/wh ... lack-hole/
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Re: The speed of Gravity

Postby Braininvat on August 2nd, 2018, 9:48 am 

There is no anti gravity.


Lambda!

:-)
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Re: The speed of Gravity

Postby Event Horizon on August 7th, 2018, 7:27 pm 

Time is only relevant if there is some means of measuring it. As all information is lost once it gets beyond the event horizon (and hence my screen-name) rather aptly. What you could get is the two black holes annihilating each other with a sudden and massive loss of gravity in that region.
I'm not sure if gravity loss would cause a spacetime to kinda rebound and cause ripples to propagate.
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Re: The speed of Gravity

Postby Watson on August 7th, 2018, 9:56 pm 

don't like my explanation?


No, generally I appreciate your explanation, of this questions and other comments you provide. I think it is more the attitude I don't care for.

But thanks for the link.
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Re: The speed of Gravity

Postby Watson on August 7th, 2018, 9:59 pm 

Braininvat » Thu Aug 02, 2018 8:48 am wrote:
There is no anti gravity.


Lambda!

:-)


You probably need to explain that cause google doesn't seem to have a clue?
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Re: The speed of Gravity

Postby mitchellmckain on August 8th, 2018, 3:27 am 

Watson » August 7th, 2018, 8:56 pm wrote:
don't like my explanation?


No, generally I appreciate your explanation, of this questions and other comments you provide. I think it is more the attitude I don't care for.

But thanks for the link.

Attitude? Your imagination... unless... you don't like the attitude of a teacher. It's what I am. Do you have a hard time accepting that some people know things you do not? If so, I feel sorry for any medical doctors you might have. To be sure they can go a little too far, I have had one of those. But when I suggest a solution to a doctor and he says flat out that I am wrong, then I don' think he has an attitude, I just accept the fact he has training which I do not.

I have made it abundantly clear that some things are a matter of opinion and some things are a matter of scientific fact. I will never do any tap-dance pretending that an example of the latter is one of the former. Call it "attitude" if you want, but I will call it simple honesty. It is the pussy-footing around which would sound condescending to me. Do you know what a meeting of academics is like? It is taken for granted that other know things they do not and they certainly don't get ruffled feathers when told something they say is wrong. Instead, they say thank you -- because they know the limits of their own expertise.

Watson » August 7th, 2018, 8:59 pm wrote:
Braininvat » Thu Aug 02, 2018 8:48 am wrote:
There is no anti gravity.


Lambda!

:-)


You probably need to explain that cause google doesn't seem to have a clue?


It is the symbol used for the cosmological constant and this is often used to explain inflation which can be said to be a sort of anti-gravity. But is only sort of like that and plays a very different role in physics so nobody would imagine it producing a black hole. BV suggested this more in jest rather than actual criticism -- at least, I took it so.
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Re: The speed of Gravity

Postby mitchellmckain on August 8th, 2018, 3:58 am 

Event Horizon » August 7th, 2018, 6:27 pm wrote:Time is only relevant if there is some means of measuring it. As all information is lost once it gets beyond the event horizon (and hence my screen-name) rather aptly. What you could get is the two black holes annihilating each other with a sudden and massive loss of gravity in that region.
I'm not sure if gravity loss would cause a space-time to kinda rebound and cause ripples to propagate.


Incorrect. There is no loss of gravity. Antimatter has a positive mass - same as matter. And when matter is converted into pure energy that energy has the same gravitational force as the matter did, even if it is composed entirely of mass-less particles. Likewise since light is made of mass-less particles we do not say that it has mass but we do say it contributes to the mass of any system which it is a part of and that would include a black hole. Shooting a laser at a black hole does add to its mass even though the laser is made of mass-less particles.
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Re: Gravity Rabbit Out of An Electromagnetic Hat

Postby Faradave on August 9th, 2018, 11:52 am 

No one disputes the enormous utility of Maxwell's equations: He assembled from others (Gauss, Faraday & Ampere) and completed them by surmising a "displacement current". In as manty years, this set of 20 equations were condensed into the familiar four, in integral or differential forms, by Oliver Heaviside & Heinrich Hertz.

Beyond that Maxwell brilliantly used the equations and some vector identities to derive wave equations for electric and magnetic fields, each of which has for the propagation term c, such that:

c² = 1/ε0μ0,

where ε0 is the electric constant and μ0 is the magnetic constant.

The apparent independence of c from inertial frames was likely the most important inspiration to Einstein in developing Special Relativity. So what?

So how is it that the electric constant and magnetic constant give the propagation speed of neutral gravity? As Spock might say (if he didn't already know the answer):

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Re: The speed of Gravity

Postby Event Horizon on August 10th, 2018, 7:29 pm 

I don't know what to make of this. I don't see why sound would do this, or its ramifications if it is a real thing. I will post the link and you can decide what if anything it means...

https://www.livescience.com/63305-sound ... tification
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Re: The speed of Gravity

Postby mitchellmckain on August 10th, 2018, 9:41 pm 

Event Horizon » August 10th, 2018, 6:29 pm wrote:I don't know what to make of this. I don't see why sound would do this, or its ramifications if it is a real thing. I will post the link and you can decide what if anything it means...

https://www.livescience.com/63305-sound ... tification


Phonons are an example of quasi-particles -- things that are not particles but behave just like they are. Another example is an electron hole. In certain materials the absences of an electron can behave like a particle much like the electron but with a positive charge. Because they are not really particles, the usual limitations do not apply. An electron hole would also behave like a particle with a negative mass. And unlike an electron and anti-electron (or positron) whose annihilation leaves behind a double portion of mass energy, a free electron and a hole can annihilate with nothing left over except whatever total momentum and kinetic energy they had (and these will probably have to be quite small in order for the annihilation to occur). After all, this is really just a matter of the free electron filling the hole in the material's array of bound electrons, so it is not like the electron really disappeared.
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Re: The speed of Headlines

Postby Faradave on August 11th, 2018, 12:13 am 

Event Horizon wrote:I don't know what to make of this.

There's more than a little sensationalism in the article's term "negative gravity" as there is in the choice of a supersonic jet graphic. Neither is appropriate.

You're aware that a convex lens will focus incoming parallel light rays by slowing them. The longer the light path through the lens, the more it slows, i.e. most at the center and least at the thin edges. This causes the parallel rays to converge.
Image

Using just the bottom half of such a lens, incoming parallel rays would be bent upward. A prism (thick on the bottom) will do the same sort of thing. Should the effect on the upward beams be called negative gravity?

That's essentially what the article describes for sound. Earth's gravity causes a density gradient in its atmosphere, more dense lower down. Because sound travels faster in denser air, the gradient acts as half a converging lens, guiding sound waves and the phonons associated with them slightly upward. That's hardly negative gravity.

"...gravity acts downward. Fluid particles will compress the particles below it, so that it's slightly denser lower down ...sound typically moves faster through denser media than through less-dense media — so the speed of sound above a phonon will be slower than the speed of sound through the slightly denser particles below it. That causes the phonon to "deflect" upward..."
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Re: The speed of Headlines

Postby mitchellmckain on August 11th, 2018, 12:40 am 

Faradave » August 10th, 2018, 11:13 pm wrote:Fluid particles will compress the particles below it, so that it's slightly denser lower down ...sound typically moves faster through denser media than through less-dense media — so the speed of sound above a phonon will be slower than the speed of sound through the slightly denser particles below it. That causes the phonon to "deflect" upward...[/i][/color]"


Yeah! Its like saying that bubbles rise in water and helium balloons rise in air because of negative gravity -- totally bogus! The proper term for this is buoyancy force not negative gravity. Though I think describing the quasi-particles as having negative mass would be legit -- but that also implies that the use of the term "negative gravity" is logically/mathematical all wrong! So called negative gravity acting on negative mass would be in the same direction as positive gravity acting on positive mass.
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Re: Thickheaded

Postby Faradave on August 11th, 2018, 11:00 am 

Agreed.

Correction to my post: I should have said a prism, thick on top, would do the same sort of thing (as a half lens bending light upward).
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Re: The speed of Gravity

Postby hyksos on August 11th, 2018, 10:43 pm 

DJ_Juggernaut » July 4th, 2018, 10:09 pm wrote:
Lincoln wrote:DJ_Juggernaut, your statement is simply incorrect. In GR, gravity is assumed to travel at the speed of light.

At the risk of agreeing to disagree with you, I will retort that the distance between most celestial objects (sun and earth for eg) is too large for it not to be instantaneous. If the earth suddenly changed its distance relative to the sun, then the new resultant gravity force would have to travel or take effect instantaneously in order for it to maintain a stable orbit. If speed of gravity travels at the speed of light, it would take 8 mins for the new resultant gravity force to take effect. By then the earth's orbit would travel in a tangent for 8 mins. And the earth is constantly changing its distance relative to the sun. So...

Note, that I agree with you that a 'gravitational wave' can travel at a finite velocity. But not the "speed of gravity". They are not the same entities. Apples and oranges. The evidence you speak of is highly questionable if you say that it addresses the "speed of gravity". They are not the same beasts, so to speak.

It is true that Jupiter is pulled towards where the sun is, not to a location in space where the sun "was" 43 minutes ago.

Regular magnetic fields have a property called Lorentz Covariance. THis means that if an object, O, generates a magnetic field, then the field is in some sense "dragged along" with O , if O is coasting in an inertial reference frame. Changes to the field locally will propagate to distant observers at the speed of light, even while the field itself is being "dragged". The gravitational field likely does the same thing. Coasting along at constant velocity does not legally constitute a "change" to the field, hence the Jupiter issue.

The Einstein Field Equations say nothing about any particular physical system. Rather, EFEs have to be converted into a form in which they can make quantitative predictions. This conversion requires that you first commit to some configuration of massive objects ahead of time. The predictions that pop out of the mathematical machinery only apply to a particular observer -- and have no meaning to other observers in another frame. In short, you must set the initial conditions, and then tell me which reference frame you intend to predict for. A couple chalkboards later, it pops out some predictions that your selected observer will measure.

I will agree that thinking about physics in this way is repugnant and psychologically uncomfortable. We (being human) prefer that physics should tell us something objective about the world from a God's eye Point-of-View. In situations of very strong gravity, and if General Relativity is correct, such a beast has no physical meaning.

Regarding the issue of the speed of gravity, we likely cannot refer to a speed that it "actually moved" unless we are accidentally in a happy scenario where that fudging and approximating is possible. (e.g. the earth is in the same free-fall as Lincoln's distant neutron star binary. )

Like other situations in special relativity , we note that speed is defined as distance divided by time. A person might take what I have said so far, and try to doctor a scenario in which it would be broken. One example would be placing an observer near the event horizon of a black hole. In that situation, the observer near the black hole (call him Bob) will still see changes to gravity propagating at the speed of light. While Alice , who is situated safely at a huge distant from the BH, also sees gravity propagating at c. We might wave our hands and cry "contradiction!". However, the reason why both Bob and Alice see gravity propagating at c, is because the universe conspires to make him see that from his reference frame. It does this by perfectly slowing down his local clock. (..and because speed = distance/time etc etc). Bob and Alice will disagree on many physical facts about events (Bob will see stars blueshifted) but they will not disagree on the speed of gravity.
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Re: The speed of Gravity

Postby Event Horizon on August 12th, 2018, 8:03 pm 

Amazing depth of thought here, thanks so much.

If a black-hole were to self-annihilate, we might hope to pick p the gravitational shockwave of event. Not carried by particles or gravitions, but by a distortion from a wave pulse or shockwave.
Obviously not enough particles lost are gravitationally dense enough to create a wave, and it's not an EM wave, it is other.
Could it be radiative propagation of gravity causes particles in the area traversed to interact strongly with the Higgs field, moving through spacetime like electrons through a wire?
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Re: The speed of Gravity

Postby hyksos on August 13th, 2018, 12:29 am 

Event Horizon » August 13th, 2018, 4:03 am wrote:Amazing depth of thought here, thanks so much.

If a black-hole were to self-annihilate, we might hope to pick p the gravitational shockwave of event. Not carried by particles or gravitions, but by a distortion from a wave pulse or shockwave.
Obviously not enough particles lost are gravitationally dense enough to create a wave, and it's not an EM wave, it is other.

As far as I can make out, you only get a gravity wave if the source undergoes extreme acceleration. To get the most out of your gravity wave, you would want an accelerated black hole, rather than a self-annihilating one. Large solid objects are normally 'pushed' out of their inertial reference frame by energy being transferred. Because mechanics works in a lazy way, we would expect that solid objects would "bend less" in the presence of a gravitational wave, whereas gases and liquids would bend more.

https://www.ligo.caltech.edu/LA/page/ligo-technology

Could it be radiative propagation of gravity causes particles in the area traversed to interact strongly with the Higgs field, moving through spacetime like electrons through a wire?

Unlikely. The strength of interaction with the Higgs is determined by a particle's native properties. If particles changed their interaction strength with Higgs on-the-fly, it would cause fundamental forces to temporarily act differently than they usually do.
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Re: The speed of Gravity

Postby Event Horizon on August 28th, 2018, 6:52 pm 

Is there a standard theory of how the gravitational waves detected in (2014?) propagated through spacetime caused by two black holes interacting? I understand about how we think the Higgs field works on a basic level but know almost nothing of its nature as an energy or force per se.
This is a fundamental thing, and it makes me curious.
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Re: The speed of Gravity

Postby Event Horizon on September 3rd, 2018, 7:47 pm 

If gravity is mass, and gravity waves arrived here marginally faster than photons etc did, it would seem to suggest gravity/mass must travel at relativistic speeds. But nothing with mass can do that according to Einstein. Could there be a case for gravitation having a duality to it, and this could get complicated. It would mean a particle that travels at speed C that can be part of a wave or be a particle still conferring gravity either way.

How best can we rationalise this? I'm not a Physicist so pls excuse my ignorance.

Edit: This is why in this incarnation here my moniker is Event Horizon. Once beyond my skull, all information is lost!
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Re: Take your pick

Postby Faradave on September 3rd, 2018, 9:02 pm 

You can push a floating ball up and down with different frequency, yet the waves all travel across the pool surface with the same characteristic velocity. What changes with frequency is the wavelength.

Take a laser pointer (or flashlight) and trace circles on the wall. The light travels at lightspeed but your hand moves much, much slower.

If you accelerate electrons up and down an antenna, you create radio waves (EM) that travel as fast a light. Yet the electrons all travel below speed limit c. The higher the frequency of oscillation the shorter the wavelength that you create.

Same with gravity waves which are believed to propagate at c in a vacuum. Mass is gravitational charge with a gravitational field, the way an electron has an electric charge with an electric field.

Event Horizon wrote:pls excuse my ignorance

Six bucks (includes shipping) will get you a nice, easy book (you can tell by the title) written by a very well-recognized genius. He speaks plain English (w Brooklyn accent) & no homework problems. I've read my "used" copy at least 4 times and will no doubt double that. Very insightful.

Or you can try some of his lectures free (Project Tuva gives the best treatment). They're also very understandable.

I like both but there's nothing like hard copy for highlighting and making notes in the margins.
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