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dapifo
2012-Oct-28, 08:06 PM
What is the oppinion of Mainstream Science, about the new theories of Gravity that supose that iGravity is generated by an interchance of gravitons between atoms (bodies)?

Shaula
2012-Oct-28, 09:31 PM
Gravitons are part of the standard model.

dapifo
2012-Oct-28, 11:34 PM
OK...but I donīt know if it is standard model that the Gravitons are interchanged between bodies....that the Grvitons move from the bodies between them...not doing atraction function without moving.

Shaula
2012-Oct-28, 11:49 PM
Gravitons are the quanta of the gravitational field. The picture of beams of them just flying around is not an accurate one. They are virtual particles, exchanged between two bodies undergoing a gravitational interaction. Just like photons mediate the EM force.

Grey
2012-Oct-29, 04:11 AM
Gravitons are part of the standard model.This is not the case. The Standard Model (http://en.wikipedia.org/wiki/Standard_Model) covers the strong, weak, and electromagnetic interactions, but does not incorporate gravity. Gravity is currently best described by general relativity, which does not use gravitons to describe gravitational interactions.

If someone ever develops a successful quantum theory of gravity, we do expect it to model gravitation as an exchange of virtual gravitons, and we know some of the features such a particle would have to have (for example, it would need to be a massless boson with a spin of 2). However, at this point, there is no complete quantum theory of gravity, and the graviton remains a hypothetical particle, not considered part of the Standard Model.

madus
2012-Oct-29, 07:27 AM
This is not the case. The Standard Model (http://en.wikipedia.org/wiki/Standard_Model) covers the strong, weak, and electromagnetic interactions, but does not incorporate gravity. Gravity is currently best described by general relativity, which does not use gravitons to describe gravitational interactions.

If someone ever develops a successful quantum theory of gravity, we do expect it to model gravitation as an exchange of virtual gravitons, and we know some of the features such a particle would have to have (for example, it would need to be a massless boson with a spin of 2). However, at this point, there is no complete quantum theory of gravity, and the graviton remains a hypothetical particle, not considered part of the Standard Model.

If the particle is 'virtual' instead of 'actual', then its features would also be imaginary. What is the point?

Shaula
2012-Oct-29, 07:43 AM
This is not the case.
You are right in the sense that they are not fully worked out. What I should have said are that they are postulated to exist in mainstream extensions to the standard model. My major point was that gravitons per se are not new ideas or anything. Dapiro needs to give more details about these new theories for a proper assessment to be made of them against what is already known or speculated.


If the particle is 'virtual' instead of 'actual', then its features would also be imaginary. What is the point?
That is not what virtual means at all. The point is that they are part of theories which make useful, testable and validated predictions.

madus
2012-Oct-29, 08:28 AM
That is not what virtual means at all. The point is that they are part of theories which make useful, testable and validated predictions.

http://en.wikipedia.org/wiki/Virtual_particle
- "In physics, a virtual particle is a mathematical conception..."

http://en.wikipedia.org/wiki/Graviton
- "In physics, the graviton is a hypothetical..."

With fields we get vectors that we can measure as force. How do you measure gravitons?

http://upload.wikimedia.org/wikipedia/commons/thumb/0/0e/NewtonsLawOfUniversalGravitation.svg/200px-NewtonsLawOfUniversalGravitation.svg.png

What is equivalent 'graviton equation' for the above interaction?

Shaula
2012-Oct-29, 10:45 AM
What is equivalent 'graviton equation' for the above interaction?
That the mechanism that generates the force is an exchange of virtual particles.

I can turn it around - what is a force? What precise mechanism do you propose for it?

In QFT forces are modelled as an exchange of virtual particles which carry things like energy between two objects. As you probably know because it says so in the article you are quoting at me from Wikipedia.


The point is that they are part of theories which make useful, testable and validated predictions.
This still stands.

Cougar
2012-Oct-29, 12:04 PM
http://upload.wikimedia.org/wikipedia/commons/thumb/0/0e/NewtonsLawOfUniversalGravitation.svg/200px-NewtonsLawOfUniversalGravitation.svg.png

By the way, the above equation is wrong. F1 does not equal F2.

Jim
2012-Oct-29, 12:09 PM
http://en.wikipedia.org/wiki/Virtual_particle
- "In physics, a virtual particle is a mathematical conception..."

http://en.wikipedia.org/wiki/Graviton
- "In physics, the graviton is a hypothetical..."

(snip)

Madus, I would remind you that this is not your thread and you are not addressing the thread question, which asks about Mainstream science.

If you have another question, you can open your own thread. If you wish to argue against the Mainstream, there is a forum just for that.

Don't hijack someone else's thread.

Xibalba
2012-Oct-29, 12:28 PM
Particles do not mediate forces between each others, except if they are bosons, so I guess that if gravitons become part of the Standard Model, they would be massless and have a spin 2 and mediate the gravitation between two massive particles, and even between bosons, like photons, that have non-rest mass.

Of course, this is a simple way of visualizing it and I would not be able to go much deeper than this :)

Shaula
2012-Oct-29, 12:42 PM
Particles do not mediate forces between each others, except if they are bosons
Actually they do. The residual strong force is mediated by pions. Underlying this is a virtual gluon exchange, but at a higher level it is mediated by pions and other mesons.

Xibalba
2012-Oct-29, 12:55 PM
Actually they do. The residual strong force is mediated by pions. Underlying this is a virtual gluon exchange, but at a higher level it is mediated by pions and other mesons.

Yes, but pions are mesons, and mesons are bosons. Composite bosons, though, so they aren't elementary. So no force is mediated without bosons, elementary or composite.

Shaula
2012-Oct-29, 12:59 PM
Sorry, my bad. You are right. I was thinking gauge bosons when I read your post.

caveman1917
2012-Oct-29, 11:46 PM
By the way, the above equation is wrong. F1 does not equal F2.

I think it does. What's probably leading you to believe it isn't is because the accelerations will be different, F = ma so the larger mass only accelerates slightly whereas the smaller mass accelerates more, but the forces are equal.

ETA: unless you mean that there is a negative sign missing if we interpret them as vectors rather than magnitudes?

Cougar
2012-Oct-30, 01:09 AM
I think it does. What's probably leading you to believe it isn't is because the accelerations will be different, F = ma so the larger mass only accelerates slightly whereas the smaller mass accelerates more, but the forces are equal.

ETA: unless you mean that there is a negative sign missing if we interpret them as vectors rather than magnitudes?

What I mean is that the force caused by a body with larger mass is larger than the force caused by a body with a smaller mass.

Grey
2012-Oct-30, 01:45 AM
What I mean is that the force caused by a body with larger mass is larger than the force caused by a body with a smaller mass.No, caveman is right here. The force is the product of the two masses, so it's the same in both cases, regardless of which mass is "pulling". The forces are equal and opposite, as they must be by Newton's third law.

AGN Fuel
2012-Oct-30, 01:51 AM
What I mean is that the force caused by a body with larger mass is larger than the force caused by a body with a smaller mass.

Not sure if I agree with this. The force is created by the existence of both massive bodies and is equal on both bodies. Increase the mass of one of them and the force between them will increase proportionally to be sure, but will still be equal on both bodies.

caveman1917
2012-Oct-30, 02:28 AM
What I mean is that the force caused by a body with larger mass is larger than the force caused by a body with a smaller mass.

As another way of seeing it, the force equation is symmetric in the indices of the masses, so how can it be different for both masses?

Delvo
2012-Oct-30, 04:18 AM
You might be thinking of the fact that a large planet creates more force on things passing by or sitting on the surface than a small planet does. But in the equation you're looking at, two planets' effects on a given third object such as a NASA probe are not being compared. What's being compared is the effects of the NASA probe and one planet on each other.

1. When the probe is on Earth, it pulls Earth up with the same force as Earth pulls it down with.
2. When the probe is on Mars, it pulls Mars up with the same force as Mars pulls it down with.
3. The force in sentence 1 is different from the force in sentence 2.

(This might help with the conceptualization of sentences 1 and 2: if either were false, then having the probe on the surface of whichever planet it's on would mean the total forces acting on the planet-probe system would not be balanced/cancelling, which means they would begin accelerating together, in one direction or the other along the line connecting their centers of gravity. If having the probe sitting on the planet's surface doesn't cause such an acceleration, then the forces must be balanced/cancelling, which means the forces each exerts on the other must have equal magnitude.)

dapifo
2012-Nov-01, 11:48 PM
Then we can accept as mainstream the possibility that gravity works by transfering gravitons between mass objects?

caveman1917
2012-Nov-01, 11:49 PM
Then we can accept as mainstream the possibility that gravity works by transfering gravitons between mass objects?

(my bold)

With that important qualifier added, i think the answer is yes. Well, it would actually be virtual gravitons, but i think i've already done my share of pedantry for the day :)

dapifo
2012-Nov-02, 12:49 AM
Then..in this case, we could also supose that we could deflect these gravitons in the same way we can deflect photons with the mass?

Cougar
2012-Nov-02, 01:18 AM
I think it does. What's probably leading you to believe it isn't is because the accelerations will be different....

Oh, you're right - it's the accelerations. When simulating orbiting bodies, the body with one-tenth the mass of another will only move the other body one-tenth as much as it gets moved. And in the calculation, doesn't the mass of the body being moved essentially get canceled out?

Xibalba
2012-Nov-02, 01:49 AM
Then..in this case, we could also supose that we could deflect these gravitons in the same way we can deflect photons with the mass?

Gravitons are massless, but as with photons, they can be influenced by gravity if they are not at rest (which they aren't, since they're massless).

caveman1917
2012-Nov-02, 02:01 AM
Oh, you're right - it's the accelerations. When simulating orbiting bodies, the body with one-tenth the mass of another will only move the other body one-tenth as much as it gets moved. And in the calculation, doesn't the mass of the body being moved essentially get canceled out?

Yes, F_1 = m_1 a_1 = G\frac{m_1m_2}{r^2} \Rightarrow a_1 = G\frac{m_2}{r^2}, so everything falls the same way irrespective of its mass.

Tensor
2012-Nov-02, 03:06 AM
Then..in this case, we could also supose that we could deflect these gravitons in the same way we can deflect photons with the mass?Gravitons are massless, but as with photons, they can be influenced by gravity if they are not at rest (which they aren't, since they're massless).

Ok, you have to be careful here. As caveman points out, there is a possibility of gravity being the transfer of virtual gravitons between massive objects (although it would also have to explain why gravity, in GR, couples to total energy and pressure, not just mass).

However, you have to remember this is a quantum mechanical model and it is virtual gravitons that are exchanged to produce gravity and those virtual particles are not deflected by masses. The virtual photons that are exchanged for the EM force are also not deflected. While there is a description of the deflection of massless particles in GR (and Newtonian gravity for that matter), I'm not aware of any valid quantum mechanical descriptions of the deflection of real massless particles by gravity. The problem here is that you are trying to combine quantum gravity descriptive aspects (the graviton), with GR descriptive aspects (deflection). And, while we assume that any quantum gravitational theory would have to explain the deflection seen in GR, we don't have a Quantum Mechanical explanation for deflection. So your supposition that masses could deflect gravitons, while logical, is premature.

cjameshuff
2012-Nov-02, 03:49 AM
Yes, F_1 = m_1 a_1 = G\frac{m_1m_2}{r^2} \Rightarrow a_1 = G\frac{m_2}{r^2}, so everything falls the same way irrespective of its mass.

Except for massless particles like photons. The deflection calculated this way is only half of what actually occurs. And as Tensor said, you shouldn't just assume this follows for gravitons as well...we just don't have a working quantum description of gravity yet.

Xibalba
2012-Nov-02, 02:45 PM
Ok, you have to be careful here. As caveman points out, there is a possibility of gravity being the transfer of virtual gravitons between massive objects (although it would also have to explain why gravity, in GR, couples to total energy and pressure, not just mass).

However, you have to remember this is a quantum mechanical model and it is virtual gravitons that are exchanged to produce gravity and those virtual particles are not deflected by masses. The virtual photons that are exchanged for the EM force are also not deflected. While there is a description of the deflection of massless particles in GR (and Newtonian gravity for that matter), I'm not aware of any valid quantum mechanical descriptions of the deflection of real massless particles by gravity. The problem here is that you are trying to combine quantum gravity descriptive aspects (the graviton), with GR descriptive aspects (deflection). And, while we assume that any quantum gravitational theory would have to explain the deflection seen in GR, we don't have a Quantum Mechanical explanation for deflection. So your supposition that masses could deflect gravitons, while logical, is premature.

And I also thought that the fact gravitons escape black holes where photons can't might be a valid argument against the deflection of gravitons by massive particles.

Strange
2012-Nov-02, 03:00 PM
And I also thought that the fact gravitons escape black holes where photons can't might be a valid argument against the deflection of gravitons by massive particles.

I believe there is a difference between gravity being mediated by virtual gravitons and (real) gravitons "escaping" a black hole. If a black hole had charge then the electrostatic force would be mediated by virtual photons (so they don't need to "escape" from the black hole, either).

caveman1917
2012-Nov-02, 10:47 PM
Except for massless particles like photons. The deflection calculated this way is only half of what actually occurs. And as Tensor said, you shouldn't just assume this follows for gravitons as well...we just don't have a working quantum description of gravity yet.

I did not assume that, I'm not calculating the deflection or anything about gravitons, this is just about the difference between acceleration and force in newtonian gravity. The post you quote is in the little sidetrack started by post 10 through posts 16 and 25, which you can see if you follow the quotes backwards. I fully agree with you that we cannot assume anything about the specific behaviour of gravitons until we have a working quantum theory of gravity.

Xibalba
2012-Nov-03, 10:02 AM
I believe there is a difference between gravity being mediated by virtual gravitons and (real) gravitons "escaping" a black hole. If a black hole had charge then the electrostatic force would be mediated by virtual photons (so they don't need to "escape" from the black hole, either).

The quantum world is full of trickery.

Tensor
2012-Nov-03, 04:35 PM
The quantum world is full of trickery.

Just some thoughts on the last few posts.

It's not that it's full of trickery, it's that we currently have two different descriptions (Newtonian (NT) and General Relativity (GR) that are valid, within their realm of applicability. Now we are trying to add a third (Quantum Gravity (QG)). The problem comes from trying to describe one in terms of the other, where it it may not apply. caveman very validly points out that the mass of an object doesn't matter, as far as the acceleration goes and he uses a equation with force in it. Which immediately puts that explanation in the NT camp. There is no sense in trying to apply GR reasoning for this. If you want to explain deflection, you have to state up front, what you mean by deflection and what model you are using. We model deflection as a force in NT gravity, but we don't know how that force is transferred between objects. In GR, deflection isn't a force, it's all geometry as objects follow paths in spacetime. If we ever get a valid description for QG, deflection will be back to being caused by a force, the exchange of virtual gravitons), but we, as yet don't know how to describe that.

Their can't be a claim that one person answered a question incorrectly, because the answer to a question was specific to one model. While another person gave a correct answer to another question specific to a different model. While we think, based on the behavior of gravity, that we have a handle on the properties of the gauge boson for QG, that doesn't mean we have a full blown description of QG, nor does it mean that the properties we think the gauge boson has can't change.

I want to point out that, from what I've seen, caveman is one of the top 5 people here in their knowledge of GR and is quite aware of the differences between NT and GR and the speculations of QR. He is also well versed in the math of NT and GR. I know enough GR to be somewhat dangerous, but one thing my knowledge does allow me to know is when someone does have a good handle on it. caveman does.

caveman1917
2012-Nov-03, 11:49 PM
Their can't be a claim that one person answered a question incorrectly, because the answer to a question was specific to one model. While another person gave a correct answer to another question specific to a different model. While we think, based on the behavior of gravity, that we have a handle on the properties of the gauge boson for QG, that doesn't mean we have a full blown description of QG, nor does it mean that the properties we think the gauge boson has can't change.

I want to point out that, from what I've seen, caveman is one of the top 5 people here in their knowledge of GR and is quite aware of the differences between NT and GR and the speculations of QR. He is also well versed in the math of NT and GR. I know enough GR to be somewhat dangerous, but one thing my knowledge does allow me to know is when someone does have a good handle on it. caveman does.

Thanks for the vote of confidence, although i certainly wouldn't place myself in the top 5 here. However i think the last few posts here are based on a misunderstanding. My post was not meant to answer a question about the deflection of gravitons. I did not reply to that because for that i am out of my league. My post was simply on a tangent started by someone posting a picture of newtonian gravity to which Cougar replied that the forces couldn't be equal, a mistake which seemed to come from confusing force for acceleration which was what i answered. Cougar then replied that was indeed the mistake he made and asked about mass dropping out of the equation for acceleration, so i replied by showing how it indeed drops out.

I did not intend to calculate a deflection for gravitons (since that would be wrong from the start as much as it is for photons, as cjameshuff pointed out), nor did i intend to answer the deflection question in a newtonian framework as you seem to think. It simply had nothing whatsoever to do with any of that, it was just on its own little tangent island, completely oblivious to the rest of the discussion :)

dapifo
2012-Nov-04, 10:45 PM
And I also thought that the fact gravitons escape black holes where photons can't might be a valid argument against the deflection of gravitons by massive particles.

Really this is a very good remark....that gives us a great difference between photons and gravitons...some can not escape from the gravity, while the others continue to exchange between other bodies.

Them Gravitons cannot be deflected by gravity...but possible yes by other fiedls...EM?

dapifo
2012-Nov-04, 10:48 PM
I believe there is a difference between gravity being mediated by virtual gravitons and (real) gravitons "escaping" a black hole. If a black hole had charge then the electrostatic force would be mediated by virtual photons (so they don't need to "escape" from the black hole, either).

I donīt understand what do you mean (??)

Strange
2012-Nov-04, 11:19 PM
I donīt understand what do you mean (??)

Neither gravitons nor photons can escape from the inside of the event horizon.

Black holes can have electrical charge; if they do then the electrostatic force due to that charge is mediated by virtual photons. There is no need for these to escape the event horizon.

Black holes have mass; the gravitational force due to that mass is mediated by virtual gravitons (if they exist). There is no need for these to escape the event horizon.

dapifo
2012-Nov-06, 01:44 AM
Neither gravitons nor photons can escape from the inside of the event horizon.

Black holes can have electrical charge; if they do then the electrostatic force due to that charge is mediated by virtual photons. There is no need for these to escape the event horizon.

Black holes have mass; the gravitational force due to that mass is mediated by virtual gravitons (if they exist). There is no need for these to escape the event horizon.

What do you mean by "mediated"?...See bold.

dapifo
2012-Nov-06, 02:08 AM
If gravitons exist ... where they would be located (neutrons, protons,...) and what dimensions would they have (length 10 ^ -20 meters)?

Tensor
2012-Nov-06, 04:13 AM
Neither gravitons nor photons can escape from the inside of the event horizon.

Black holes can have electrical charge; if they do then the electrostatic force due to that charge is mediated by virtual photons. There is no need for these to escape the event horizon.

Black holes have mass; the gravitational force due to that mass is mediated by virtual gravitons (if they exist). There is no need for these to escape the event horizon.

What do you mean by "mediated"?...See bold.

Here's a couple of definitions of mediate that pertain to this explanation. 1). To effect or convey as an intermediate agent or mechanism. 2) Acting through, involving, or dependent on an intervening agency. Basically, by saying the EM force is mediated by photons or Gravity is mediated by Gravitons, if they exist, it simply means that(photons, gravitons) convey or the force acts through those virtual particles.




If gravitons exist ... where they would be located (neutrons, protons,...) and what dimensions would they have (length 10 ^ -20 meters)?

You're asking specific questions about something we don't have a model for (or a model that we know doesn't work, take your pick). However, if it eventually works as the rest of the Standard Model, they aren't located anywhere. They are simply created, exchanged, and then destroyed by the objects that are interacting. As far size goes, the particles are modeled as points. I can point out some further reading on virtual particles (http://en.wikipedia.org/wiki/Virtual_particle) and interactions (http://en.wikipedia.org/wiki/Fundamental_interaction) and particle exchange (http://en.wikipedia.org/wiki/Static_forces_and_virtual-particle_exchange). Remember though, those description, as far as currently known don't apply, as yet, to gravitons.