Curious about the Graviton

[Thefourth]

I am by no means an expert or even close to a novice when it comes to quantum physics matters but I am extremely curious about the subject and try my best to read about it. One thing that surprises me is that scientists never found the Graviton, the particle that could be responsible for Gravity. How is it that we haven't found it? If large objects, such as the Earth, have a gravitational field around them (around us at all times too) shouldn't this be one of the easiest particles to find? What if the Graviton doesn't exist after all, would we have to rethink our ideas on Gravity?

[Janus]

Of the four forces, gravity is the weakest. As a result, the graviton would be a very low energy particle. Also, it is important to note that gravity would be mediated by virtual gravitons and virtual particles cannot be directly detected. IOW the Earth can maintain a gravitational field without ever emitting a "real" graviton.

[Thefourth]

Of the four forces, gravity is the weakest. As a result, the graviton would be a very low energy particle. Also, it is important to note that gravity would be mediated by virtual gravitons and virtual particles cannot be directly detected. IOW the Earth can maintain a gravitational field without ever emitting a "real" graviton.

 

Makes sense, thanks for the reply.

[lemur]

Generally, I don't get how it's possible to have an attractive particle. When a particle hits another particle, it pushes it. How can a particle hit another particle and pull it?

[Thefourth]

Generally, I don't get how it's possible to have an attractive particle. When a particle hits another particle, it pushes it. How can a particle hit another particle and pull it?

 

The charges of the particles could be attracting one another.

[ajb]

What if the Graviton doesn't exist after all, would we have to rethink our ideas on Gravity?

 

This is a real possibility. Quantum gravity might not be a theory of gravitons.

 

A graviton is to general relativity what a photon is to electromagnetism.

 

Electromagnetism via Maxwell's equations one can apply perturbative quantisation. That is one can expand about a known classical solution and do some "mathematical magic" and end up with a consistent quantum theory. The quanta of the electromagnetic field are called photons.

 

Trying the same standard methods with to general relativity fail. The theory seems not to have a consistent perturbative quantisation. Now, particles, like the photon are by their very nature a perturbative notion. It is not very clear how to discuss quanta of fields outside perturbation theory. Thus, we may have to face the fact that quantum gravity is not a theory of particles.

 

This is not the same as saying that a quantum version of general relativity does not exist. What this means is methods other that a perturbative expansion are required in quantising gravity. There is some evidence, via renormalisation group flow that quantum general relativity or some variant of is consistent outside of perturbation theory.

 

Their is a classical version of gravitons called gravitational waves. (These are what we want to quantise.) These also have been quite elusive.

[lemur]

The charges of the particles could be attracting one another.

If that were the case, I would expect to see some charge-type phenomena, like lightning, occurring with due to gravity. I assume that by having charges, particles of matter would have to be distinguished into positive and negative gravitation. If all particles had both charges, they would attract each other and cancel each other out the way proton and electron charge do in a molecule, no? Also, it seems as though all particles can exist independently of other particles in a vacuum. Does this mean gravitons could exist independently of protons, electrons, neutrons, photons, and whatever all the sub-atomic constituents of these may be? Also, it seems like other particles have multiple behaviors, i.e. a proton has charge but also nuclear force and mass/inertia/gravitation. Photons have electrical and magnetic fields (and possibly gravitation?). Does that mean gravitons could also have other qualities than attracting each other?

[michel123456]

I am by no means an expert or even close to a novice when it comes to quantum physics matters but I am extremely curious about the subject and try my best to read about it. One thing that surprises me is that scientists never found the Graviton, the particle that could be responsible for Gravity. How is it that we haven't found it? If large objects, such as the Earth, have a gravitational field around them (around us at all times too) shouldn't this be one of the easiest particles to find? What if the Graviton doesn't exist after all, would we have to rethink our ideas on Gravity?

 

Yes.

[timo]

It's kind of funny that my spontaneous thought is that if the non-existence of a graviton was proven (however that might happen), we'd have to rethink our ideas about (the application of) perturbative quantum field theory, not our ideas of gravity. Can't quite put the finger on what I mean by that, though.

[michel123456]

It is quite difficult to prove the non-existence of something. It means if graviton does not exist, we can wait for centuries and still looking for it. The right way to deal with the problem should be (IMHO) to send a large part of scientists to find another path on a theoretical point of vue. Searching for a Theory where no graviton is needed.

[Farsight]

I'm afraid the graviton as generally presented is a myth. It's one of those hypothetical things which have been advocated in certain quarters for decades, for which there is no evidence whatsover. Ahhhh, some will say, but you can't prove it doesn't exist. To which you should shrug and say you can't prove that fairies don't exist either.

 

The graviton is put up as the equivalent of the photon, as something that makes gravity "work", and that's a myth too. Because photons don't make electromagnetism work. Some people will claim that virtual photons make electromagnetism work, but look closely and you appreciate that there are no actual particles flying back and forth making that balloon cling to your curtains. Magnets don't shine, and cavorite doesn't exist. Because those virtual particles are virtual. That means they aren't real, not that they have a short lifetime. Take a look at the wiki article on near and far field. Pay close attention to the quantum field theory view. What it says is near field effects are due to a mixture of real and virtual photons. Says who? It's the other way round. The near field is also called the evanescent wave. It's something real, you can use it to charge up your mobile phone. But that coupling is a field effect, or a standing wave effect if you prefer, not particles rattling back and forth. A better way to say it is the evescent wave is the reality that underlies virtual photons. See Evanescent modes are virtual photons for more.

 

Think about what a photon is. It's an electromagnetic field variation, maybe 1500m long, zipping through space at c. If you've got a +1022keV photon, you can use it to make an electron and a positron, via pair production. The electron has an electromagnetic field, which you've just made from a photon, and you can can trap that electron in an orbital around a proton. People tend to say it remains trapped because of messenger particles, virtual photons being exchanged between the electron and the proton. But there aren't any photons of any kind rattling back and forth. It's just field, made from field variation. There aren't any other field variations rattling back and forth. In the same vein the gravitational field is just field, and there are no gravitons or virtual gravitons rattling back and forth either.

 

You can of course think of the earth's gravitational field as one big graviton. That would be like the evanescent wave, which is rather like half a photon that isn't going anywhere, a bit like the bow wave of a bridge pier. Or you can think of a gravitational wave as one big graviton. There's not so much of a problem with that, because close-orbiting neutron stars will lose energy, and it's got to go somewhere. The gravitational wave is then like a photon. It's going somewhere, and doing it fast. But in itself, it isn't made of tiny little particles, just as an electromagnetic wave isn't. Just a a photon isn't, and just like the earth's gravitational field isn't.

[lemur]

Supposedly it takes gravity just as long to get from the sun to the Earth as it does light. So where do we get the idea that light and gravity are not instantaneous? I mean, if the sun would somehow vanish without a trace, it would affect Earth gravitationally at the same moment we would see it happen, so in effect the speed of light and gravity are just a principle whereby events happening in two distant places cannot be simultaneous. It's not really that light/gravity reaching the Earth from the sun left the sun 8 minutes earlier. It's that the sun's present is Earth's past and Earth's present is the sun's past.

 

So, is it not possible to simply think of the sun and Earth, or any two distant objects really, as being directly in contact as a function of the amount of gravity they exert on each other? In other words, could gravitation simply be the same thing as direct contact between objects? We tend to think of space as an empty container for matter, I think, because of the distinction between radiation/light and matter. If we would think of light emissions as the "photosphere" of electrons or other light-emitting particles (if other particles emit light as well that is), then could light and gravity simply be seen as very large elementary particles with very small cores?

 

In that sense, it wouldn't be light and gravity taking 8 minutes to get from the sun to Earth. Instead, the sun and Earth would simply be in contact via their gravitational and photon spheres, and the lag would just be due to the fact that smaller particles are more dense and therefore more agile. If two cruise ships were pushing against each other's bows, for example, a passenger could run from the stern of one to that of the other in 8 minutes even though the two sterns came in contact at the same moment as the two bows, if you take the two ships as contiguous units. I.e. the two ships would be simultaneous but the position of the person running across them could still take time.

 

So in the same way as the two cruise ships, the Earth's gravitational and photon spheres could be in direct contact with Earth's, only particles of matter are like passengers on the ships that take a long time to get from one side of the ship to the other; and tend toward the centers and perimeters of the ships, respectively. Traversable space, then, could be a function of matter but not of gravity and light. Why isn't light simultaneous then? Because it is measured in terms of speed and space that are derived from interactions among particles of matter. Sorry if this post is too speculative - it just seemed like something to bring up in light of the issue of gravity as something (particles) that must be in transit to connect distant atoms.

Edited October 29, 2010 by lemur

[ajb]

Or you can think of a gravitational wave as one big graviton. There's not so much of a problem with that, because close-orbiting neutron stars will lose energy, and it's got to go somewhere. The gravitational wave is then like a photon. It's going somewhere, and doing it fast. But in itself, it isn't made of tiny little particles, just as an electromagnetic wave isn't. Just a a photon isn't, and just like the earth's gravitational field isn't.

 

A graviton in the context of general relativity would be the quanta associated with quantising a gravitational wave. You certainly should think of a gravitational wave as the "classical graviton" in the same way you think of an electromagnetic wave as the "classical photon".

 

Of course this is more of a philosophy than theory. Quantum decoherence effects should allow a classical description, maybe in some limit. Without a well founded theory of quantum gravity is not obvious how this would all work.

Edited October 29, 2010 by ajb

[Carlos Guevara]

matter and energy are made from the same substance. the only difference is their structure.

 

in this case the structure of the quantum elementary particle of matter is bubble shaped. inside it is pure nothingness. which gives matter partiles the potentiality to colaspe and form a smaller and solid shape. but of corse, under nomal conditions it does not collaspe. but it is the potentiality that it can; is what gives off gravitation.

 

gravity depends, on the shape of a particle. however a when a bubble shaped particles colaspes, and forms a solid one: it becomes a charge. it becomes energy. in this case they do the exact oposite of gravity. they repel eachother.

 

 

[timo]

matter and energy are made from the same substance. the only difference is their structure.

 

in this case the structure of the quantum elementary particle of matter is bubble shaped. inside it is pure nothingness. which gives matter partiles the potentiality to colaspe and form a smaller and solid shape. but of corse, under nomal conditions it does not collaspe. but it is the potentiality that it can; is what gives off gravitation.

 

gravity depends, on the shape of a particle. however a when a bubble shaped particles colaspes, and forms a solid one: it becomes a charge. it becomes energy. in this case they do the exact oposite of gravity. they repel eachother.

It's somewhat refreshing to read such a nonsense without a reference to string theory (which no one here really knows what it really is about, while at the same time it certainly says what was just claimed).

Edited November 6, 2010 by timo

[Carlos Guevara]

well i was not refering to string theory. i was refering to a theory called disequlibrium. it was never published, nor does many people know about it. its a theory that explanes exactly what happened at the moment of creation and all the consequenses of this events. such as matter, space, mass, gravity, dark energy, black holes etc. its been the core secret of a secret society of philosophers. lol i shouldent be telling you this, but what the hell. they are about to make public these concepts anyways. very very soon

[ajb]

... its been the core secret of a secret society of philosophers.

 

As if Dan Brown needs any more encouragement

[michel123456]

Generally, I don't get how it's possible to have an attractive particle. When a particle hits another particle, it pushes it. How can a particle hit another particle and pull it?

 

In some other thread, I assumed it could happen if you turn Time backward. If you take a movie of a particle hitting another one, and then look at the movie backward, what would you see?

But the idea was debunked. Gravity is attractive under time reversal everybody say. So I agree with you I cannot see how it is possible to have an attractive particle.

[timo]

That is presumably because you guys don't know what a particle is within the context of particle physics. It's just not that little metal sphere that bounces around that one might imagine it to be. Could you see how say an electric field could cause attraction? I assume so. Consider particles being pieces of the fields.

[michel123456]

That is presumably because you guys don't know what a particle is within the context of particle physics. It's just not that little metal sphere that bounces around that one might imagine it to be. Could you see how say an electric field could cause attraction? I assume so. Consider particles being pieces of the fields.

 

You are right. I am a Neanderthal and I can only understand reality in terms of bones and sand. I don't even understand what positive and negative means (negative bone???) and "negative charge" has no meaning to me. A "positive bone" being attracted by a "negative bone" ??? In my world, all bones are positives (or simply they "are") and attract each other. Don't bother, I' am returning in my cave.

Edited November 8, 2010 by michel123456

[timo]

I did not mean to offend you. But I don't think you're helped if I am pseudo-encouraging rather than realistic. See it this way: physicists take about 4-5 years of university training to get a basic degree. Believe me: after those 4-5 years they still know preciously little about how particle physics works - even those that specialize in that field (I know what I speak of ). In that view, I simply don't consider it an offense to tell someone who obviously doesn't have this basic training that they don't have a proper understanding of a quantized field. And that non-understanding is definitely not going to change if you're being pissed by that statement rather an acknowledging that I gave you a hint how to think of it.

[michel123456]

I did not mean to offend you. But I don't think you're helped if I am pseudo-encouraging rather than realistic. See it this way: physicists take about 4-5 years of university training to get a basic degree. Believe me: after those 4-5 years they still know preciously little about how particle physics works - even those that specialize in that field (I know what I speak of ). In that view, I simply don't consider it an offense to tell someone who obviously doesn't have this basic training that they don't have a proper understanding of a quantized field. And that non-understanding is definitely not going to change if you're being pissed by that statement rather an acknowledging that I gave you a hint how to think of it.

 

Thank you for the hint.

You're right again, I was pissed.

But there is something else if my post. Correct me but gravity don't seem to work on the basis of positive/negative concept. Everything is positive.

Edited November 8, 2010 by michel123456

[ajb]

Correct me but gravity don't seem to work on the basis of positive/negative concept. Everything is positive.

 

Classically, this seems to be the case, under some sensible conditions we have the various energy conditions, which more or less say no negative masses or energies. Note that these conditions are added to the geometric formulation of general relativity to place sensible constraints on what we mean by a physical matter content.

 

Quantum mechanically the situation is far less clear and negative energies arise. See the Casimir effect, for example. Such effects could create "antigravity" at the subatomic scale and support exotic configurations like wormholes.

 

It is also possible that classically the energy conditions do not hold and we have exotic matter.

[pioneer]

If you look at a photon, it moves at the speed of light. Paradoxically, something at C should be totally distance contracted and time dilated, yet photons show finite expressions in space and time we call wavelength and frequency. This suggests photons have one foot in C reference and one foot in inertial reference.

 

Say a graviton was more by the book with respect to C and therefore did not have a finite aspect like photons. In this scenario, since they move at C, they will give every indication of something moving at C without any outward expression such as we see with photons, since they lack the finite leg. Their finite leg is dissociated and remains as mass.

Edited November 8, 2010 by pioneer

[IM Egdall]

If you look at a photon, it moves at the speed of light. Paradoxically, something at C should be totally distance contracted and time dilated, yet photons show finite expressions in space and time we call wavelength and frequency. This suggests photons have one foot in C reference and one foot in inertial reference.

 

Say a graviton was more by the book with respect to C and therefore did not have a finite aspect like photons. In this scenario, since they move at C, they will give every indication of something moving at C without any outward expression such as we see with photons, since they lack the finite leg. Their finite leg is dissociated and remains as mass.

 

Regarding the photon, I think Einstein's light postulate is important to consider here. No matter what reference frame you choose, the photon is still traveling at the speed of light. In other words, no matter how fast you are going, the photon always goes at speed c (in a vacuum) with respect to you.

 

Consider a reference frame traveling at c. Now look at a photon from this reference frame. It still sees that photon traveling at c! No matter what reference frame you chose, the photon is not stationary. So that it possesses a frequency/wavelength is not a contradiction.

 

I believe a graviton also fits within Einstein's light postulate. I think anything traveling at speed c does. Thus no matter what refererence frame you chose, the graviton is always traveling at speed c with respect to you.

Edited November 8, 2010 by I ME