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gravity and light

miklamar

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POSTS: 2154

Report this Jan. 26 2011, 11:16 pm

Some people have theorized that gravitons form gravitational waves and that there are also antigravitons, which may resemble photons.  Perhaps some of you physicists could answer a few questions for me.


Since strong gravitational forces can bend light and even absorb or capture it (black hole), could gravity be considered anti-light?  And, then, would light possibly be considered to be anti-gravity?  Is gravity just negative light (dark energy), while light is positive gravity (actually negative negative light)?


Just as gravity can modify light, could a powerful-enough light source modify gravity?


I am a Zakdorn engineer, not a physicist or science officer, so please forgive my ignorance.


Var Miklama--Zakdorn, engineer. "A sound mind in a FULL body!" "Time, like latinum, is a limited quantity in the galaxy."

lanceromega

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POSTS: 3859

Report this Jan. 27 2011, 10:46 am

First Graviton are theoretical, there has been no detection of a Graviton particle. What we presently know of Gravity is that it arise from the warpage of space by mass and energy. This is how Einstein Explain gravity and so far his explaintation is the best.


Only when we attempt to link gravity to quantum mechanics do we attempt to use the exchange of gravitons as an explaintation. All attempts to date to explain gravity as exchange of partical have failed.


Gravity effect light thru the Warping of space. So the path that photons take are changes, they are traveling in straight line thru a curve space. While Gravity waves are actually the oscillation of the fabric of space time..


If Graviton exist, they would in essence be their own antiparticle ( just like Photons).. AntiGravity would arise from the properties of what emitted the Graviton particle, causing them to repel instead of attracting as we normally see. The kind of material or mass energy need to create a Graviton would need to have either negative pressure or energy in order for a emitted graviton to be repulsive.

miklamar

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Report this Jan. 29 2011, 2:47 am

I have some understanding of physics, but I am not as knowledgeable about the most-comprehensive or latest theoretical developments in physics, since we engineers are more concerned about keeping the ship running (a lot of diagnostics and maintenance) than theories.

Var Miklama--Zakdorn, engineer. "A sound mind in a FULL body!" "Time, like latinum, is a limited quantity in the galaxy."

The Master

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POSTS: 404

Report this Feb. 05 2011, 1:16 pm

Indeed as lanceromega mentioned above gravitons are theoretical in a sense that noone has detected them. Well, we can all weight things and we definetely experience gravity. Then we want to theoretically describe it. First of all non-relativistically. For this aim we use Newtonian law of universal gravitation. Then we want to take into account relativistic physics. For this aim we need to describe gravity in a context of general theory of relativity. The later describes gravity in a completely different from Newtonian way. It says that gravity is actually not a force but rather a warp or curvature of space-time. So if space-time is warped then you will experience corresponding force - and by this force you can effectively describe gravity in non-relativistic limit (when velocities are small and gravity is weak). But if gravity is strong then you are bound to use GR. So you decide to use GR. Then you can calculate in the context of general relativity that when gravitational source (that is mass) is moving in a complicated enough way (when it has quadrupole moment) then gravitational wave forms. This wave is described by a function. The function has parameter - spin. This parameter indicates how function changes when space-time is rotated. The spin of gravitational wave is equal to 2 (for photon - electromagnetic wave mode in classical sense - spin is equal to 1 - see that photon is not antigraviton, I'll return later to it again). Then when you quantize gravitational field you get particles with spin 2. They are gravitons. They are a natural objects in quantum theory of gravity. However gravitational force is too weak compared to nuclear, EM and weak () forces and is not taken into account in Standard Model of particles. The later describes (almost) all observed high-energy particle physics phenomena in a perfect way without gravity. Again, there're no antigravitons. More precisely gravitons coincide with their anti-particles. And gravity and electromagentism can't cancel each other. They are differnt forces with different field strength and different causes of production (charge for photons and all energy - including photons - for gravity production).


 


By the way in quatum field theory virtual particles mediate force. So in quantum gravity virtual gravitons mediate gravitational force anyway.


You can hide a lot in a large-N matrix

The Master

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Report this Feb. 05 2011, 1:27 pm

By the way, string theory predicts gravity. That is it predicts that gravitons exist. And that they are necessary exactly the same particles which mediate Einsteinian (general relativistic) gravitational force that is warping of space-time. That force in non-relativistic limit goes to Newtonian law which we can check easily as people have done before. Gravity is one of the most amazing predictions of string theory.

You can hide a lot in a large-N matrix

The Master

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Report this Feb. 06 2011, 3:21 am

Hello, 4_o_20. Thanks, yeah, maybe there's something that I know. Indeed, I have studied it in university.

You can hide a lot in a large-N matrix

The Master

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Report this Feb. 07 2011, 12:19 am

Theoretical physics

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lanceromega

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Report this Feb. 07 2011, 1:53 pm

Quote: The Master @ Feb. 05 2011, 1:27 pm

By the way, string theory predicts gravity. That is it predicts that gravitons exist. And that they are necessary exactly the same particles which mediate Einsteinian (general relativistic) gravitational force that is warping of space-time. That force in non-relativistic limit goes to Newtonian law which we can check easily as people have done before. Gravity is one of the most amazing predictions of string theory.


Actually string theory predict a 2 spin boson, for the lowest energy level of string oscillation, it a perfect candidate for a graviton, what it fails to predict or show how, these spin 2 bosons would interact with vacuum ( space time itself) to form the warpage that predict by general relativity. String theory like quantum mechanics basically occurs in an unchange vacuum background ( unchanging as compare to general Relativity where matter warp space and space tell matter how to move)

That is why when string theory was expanded out to M theory ( as the various subset of string theory are in part of the larger M theory) Penrose's Spin networks was incorporated into M Theory to create a working model of how this could occur. At this point an actual graviton particle is not really needed. Gravitons would and could be show to be pseudo particles just like phonons,polarons , etc...

The Master

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Report this Feb. 08 2011, 12:44 am

Yes, string theory predicts massless spin-2 bosons. To obtain Lagrangian for this bosons you must impose condition of vanishing of beta-function which is condition of keeping of conformal invariance on quantum level. The thing is that conformal invariance is indeed preserved when you go to quantum theory if space-time dimension is 26. So consitency requires vanishing of beta function. And the later gives exactly Einstein equations. Then purely stringy effects give corrections to Einstein, but for conceivable energies Einstein is reproduced. You may read about this in e.g. Green, Shwarz, Witten Superstring Theory vol. I. The same thing about supergravity in superstring theory. Actually in the case of supergravity - when you have 32-parametric supersymmetric gravitational multiplet the Lagrangian for it is kinda unique. So you can draw Lagrangian for your particle content even withou using renormalization condition and effective action technique.

As for M-theory - string theory actually wasn't expanded to it. M-theory doesn't have any strings whatsoever. It even can't have them consistently because it has one dimension more to be conformally invariant on quantum level. What string theory is is actually high-coupling limit of type-IIA superstring theory - which contains on massless level 11D supergravity. Then you can actually build string from 2D membrane in M-theory when one dimension is compact.

I've never heard of spin networks being part of M-theory.

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lanceromega

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Report this Feb. 08 2011, 10:00 am

Quote: The Master @ Feb. 08 2011, 12:44 am

Yes, string theory predicts massless spin-2 bosons. To obtain Lagrangian for this bosons you must impose condition of vanishing of beta-function which is condition of keeping of conformal invariance on quantum level. The thing is that conformal invariance is indeed preserved when you go to quantum theory if space-time dimension is 26. So consitency requires vanishing of beta function. And the later gives exactly Einstein equations. Then purely stringy effects give corrections to Einstein, but for conceivable energies Einstein is reproduced. You may read about this in e.g. Green, Shwarz, Witten Superstring Theory vol. I. The same thing about supergravity in superstring theory. Actually in the case of supergravity - when you have 32-parametric supersymmetric gravitational multiplet the Lagrangian for it is kinda unique. So you can draw Lagrangian for your particle content even withou using renormalization condition and effective action technique. As for M-theory - string theory actually wasn't expanded to it. M-theory doesn't have any strings whatsoever. It even can't have them consistently because it has one dimension more to be conformally invariant on quantum level. What string theory is is actually high-coupling limit of type-IIA superstring theory - which contains on massless level 11D supergravity. Then you can actually build string from 2D membrane in M-theory when one dimension is compact. I've never heard of spin networks being part of M-theory.


wow, i just a simple nuclear engineer, can we have that all in plain english ...
let keep it simple, M theory is an extension of string theory in which 11 dimensions are identified. Because the dimensionality exceeds the dimensionality of superstring theories in 10 dimensions, it is believed that the 11-dimensional theory unites all five string theories (and supersedes them). Though a full description of the theory is not known, the low-entropy dynamics are known to be supergravity interacting with 2- and 5-dimensional membranes.

So m theory cover and includes the 4 stable version of string theories ( yes there is multiples string theories) and super gravity...

Edward Witten (well also Lee Smolin) then adapted Penrose spin networks to formulation how how perturbative strings may arise as small fluctuations around histories in a formulation of non-perturbative dynamics of spin networks. The warping of space time is caused by the changes in spin networks and gravity is in essence not a particle but an alteration in the distribution of spin network due to vibrations of string.

if you wish i can list several paper on the all this such as:

Strings as perturbations of evolving spin networks
Lee Smolina, , a, 1

Supersymmetric spin networks and quantum supergravity

Yi Ling*
Department of Physics, Pennsylvania State University, University Park, Pennsylvania 16802

Lee Smolin†

It is correc that the formulation of string theory does yield Einstein's General Relativitic Equation, but it doesnot on it own show how vibration of strings create the warpage of space time and by linking string and m theory to spin network we come up with mechanism



The Master

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Report this Feb. 08 2011, 10:34 am

Hello lanceromega. There're 5 superstring theories and all of them are related by dualities. It means that you can say what in one theory matches in the other theory. For example type-IIA and type-IIB theories are related by T-duality. Note that dualities are held in all orders of perturbation theory - that is it's not just some low-energy correspondence. In some cases it's actually high energy-low energy correspondence (S-duality). Because of these dualities one can say that superstring theory is rather unambiguous theory. There's also 11D supergravity. The relation of this theory to superstring theory was unknown untill discovery of M-theory. After M-theory was discovered by Ed. Witten to be high coupling limit of type-IIA superstring theory it also became evident that while total formulation of M-theory is unknown (it still is) we know that low-energy limit of it is 11D sugra. So supersymmetric specter of this sugra contains field A3 which interacts with two-dimensional membrane in exactly the same way as charge interacts with electromagnetic field. I just wanted to formulate it again but most of these points you've already made yourself. I want to correct you on different point however. In your last sentence you make an error - the conditional after "if" and before "but" actually does imply that string theory explains warpage of space-time. Because Einstein relativity is exactly about it. And string theory reproduces GR. You don't need spin networks for it. Actually you don't need spin networks for string theory at all (at the present level of formulation string theory works just fine without it). As I know spin network is rather a tool for LQG which is kinda different type of theory. Many people tried to reconcil it with string theory but unsuccessfull. It's actually a different topic completely unrelated to the present one - because you said that one needs SN to explain warping of space-time in string theory and I said that it's not really true.


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The Master

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Report this Feb. 08 2011, 10:45 am

By the way, I've checked out the "Supersymmetric spin networks and quantum supergravity". And I've observed that it's not really developed by people who do string theoy - try scholar.google. At the same time mathematical fact about string theory predicting gravity is 25-yeras old established one.

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The Master

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Report this Feb. 08 2011, 10:48 am

For others who are interested - you can read first 150 pages of Superstring Theory by Green, Shwarz and Witten vol 1. It will give you rather simple (yes) and detailed explanation of what string theory is on example of 26d bosonic string. You will also read how 2d string action goes to 26d gravity action. But it actually assumes that you know math on the level of quantum field theory and general relativity.

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The Master

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Report this Feb. 08 2011, 10:49 am

It's really a better way to understand stuff and check out mathematical details yourself than go to philosophical discussions.


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dryson

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Report this Feb. 08 2011, 1:49 pm

Microbiology, a baker? What are you baking up crystal meth?


Just as gravity can modify light, could a powerful-enough light source modify gravity?


No light cannot effect gravity as a light photon does not have enough gravitational factors to effect gravity.


Everyone thinks that gravity is an outside influence of an actual particle or matter.


Gravity is basically the same as magnetism. The colder an object becomes the more tightly compact the particles are together until a point is reached where even metal crumble and breaks like it was glass.


The hotter an object becomes the less compact the particles are until a point is reached when the metal becomes a liquid.


The question is would it be possible to create a photon where at a given point the interactions within the photon are changed so that less heat is generated which would cause the photon to collapse in on itself?



 



A bullfrog with a light in its belly is nothing more than a glutton looking to shine otherwise.

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