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Stever
2009-Nov-11, 12:41 PM
The title pretty much sums up the question.
To add I guess I could ask, is this the currently accepted idea?

bebe7
2009-Nov-11, 03:44 PM
Hypothetical elementary particle which mediates the forces of gravity in QFT.

Happy Day

Stever
2009-Nov-12, 04:31 AM
Thanks for the responce
To clarify, my real question was more to do with weather or not gravitons are currently accepted by the main stream as factual, or at least likely, or is an alternate concept more accepted by the main stream?

Thanks
Steve

WayneFrancis
2009-Nov-12, 04:58 AM
No they are hypothetical. We expect given the standard model that they should exists and if they do exists that they have certain properties but until they are discovered mainstream won't accept them as "factual".

The big problem is that directly observing an individual graviton is near impossible if the model is correct. So they are looking for emergent properties of gravitons like gravity waves that would support the concept of gravitons.

DrRocket
2009-Nov-12, 05:20 AM
No they are hypothetical. We expect given the standard model that they should exists and if they do exists that they have certain properties but until they are discovered mainstream won't accept them as "factual".

The big problem is that directly observing an individual graviton is near impossible if the model is correct. So they are looking for emergent properties of gravitons like gravity waves that would support the concept of gravitons.

I don't understand this one.

Gravity waves are a prediction of general relativity, which is not compatible with quantum theory as it stands.

So how would observations of gravity waves provide support for gravitons ?

NorthernBoy
2009-Nov-12, 11:29 AM
I don't understand this one.

Gravity waves are a prediction of general relativity, which is not compatible with quantum theory as it stands.

So how would observations of gravity waves provide support for gravitons ?

Particle wave duality?

Waves imply fields, and we believe that all fields ought to be quantised, and so it follows that we'd expect a particle as the root of this, as the quantised field carrier.

It need not definitely be so, but it would seem a logical progression, so the waves would definitely provide support, but would be far from providing proof.

bebe7
2009-Nov-12, 02:47 PM
Particle wave duality?

Waves imply fields, and we believe that all fields ought to be quantised, and so it follows that we'd expect a particle as the root of this, as the quantised field carrier.

It need not definitely be so, but it would seem a logical progression, so the waves would definitely provide support, but would be far from providing proof.

I think wave-particle duality is more googleable.

ShinAce
2009-Nov-12, 05:07 PM
I think wave-particle duality is more googleable.

"Particle wave duality" = 630,000 hits
"wave-particle duality" = 139,000 hits

The hyphen got the best of you, but the idea is good.

DrRocket
2009-Nov-12, 08:13 PM
Particle wave duality?

Waves imply fields, and we believe that all fields ought to be quantised, and so it follows that we'd expect a particle as the root of this, as the quantised field carrier.

It need not definitely be so, but it would seem a logical progression, so the waves would definitely provide support, but would be far from providing proof.

Waves do not imply fields.

The necessity for quantized fields arose because it was found necessary in order to develop a quantum mechanics that is compatible with special relativity.

Acoustic waves are generally treated without fields and without quantization.

Gravity waves are predicted by general relativity and have no link to any version of quantum gravity.

In short, I disagree completely.

cosmocrazy
2009-Nov-12, 09:20 PM
I was under the impression that they are looking for the Higgs Boson, the predicted mass giving particle. I don't know the details but IIRC finding this particle will be the first step towards quantising gravity. Since a graviton would be like a photon, massless with a velocity of C, observing it directly would surely be impossible.

DrRocket
2009-Nov-12, 10:52 PM
I was under the impression that they are looking for the Higgs Boson, the predicted mass giving particle. I don't know the details but IIRC finding this particle will be the first step towards quantising gravity. Since a graviton would be like a photon, massless with a velocity of C, observing it directly would surely be impossible.

I'm not sure who "they" are. If you are referring to those who will be conducting experiments at the LHC or perhaps Batavia, then the Higgs boson is one thing that they are looking for, but not the only thing.

The Higgs boson is already predicted by the Standard Model. The Standard Model tells us nothing whatever about gravity. Finding the Higgs Boson will be a feather in the cap of the Standard Model, but it doesn't do much for quantum gravity.

A graviton is expected to be massless and hence travel at c. But that is not why they would be difficult to detect. We detect photons with regularity (it is called vision).

It is the weakness of the gravitational interaction that one would expect to make it difficult to detect a single graviton. That and the fact that there is no theory of quantum gravity to tell us much about the expected properties, beyond spin and mass.

What is really needed for the "existence" of the graviton is a viable theory of quantum gravity. The name for the carrier of the force is already in place (that is what a graviton is). What is missing is the fundamental quantum theory of the force that it is supposed to carry. Since the graviton would interact with itself, construction of the theory has been plagued with mathematical inconsistencies (infinities that just won't go away). It is a really hard problem.

bebe7
2009-Nov-13, 08:39 PM
The title pretty much sums up the question.
To add I guess I could ask, is this the currently accepted idea?

You should try to google "List of hypothetical particles."

Moonhead
2009-Nov-14, 01:39 PM
(NB I don't want to hijack this thread, but I think my questions are close enough to the OP to make a separate thread more an annoyance than a benefit to the forum. If the mods think otherwise, feel free to split it off.)

I (think I) can understand the need for the graviton from a theoretic point of view, but I have a hard time to imagine what it would do. How it would "work", so to speak.

Of course, me having a hard time imagining something shouldn't bother particle physicists, but what I mean is, that with all of the other particles, i think I've got at least a basic (admittedly possibly oversimplified) idea of what they "do".

I assume gravitons would be emitted by all objects with mass. Is that correct? So, then the gravitons will bump into other gravitons, and this makes the two objects, say a star and a planet, or a planet and a frog, attract each other?

trinitree88
2009-Nov-14, 04:06 PM
Waves do not imply fields.

The necessity for quantized fields arose because it was found necessary in order to develop a quantum mechanics that is compatible with special relativity.

Acoustic waves are generally treated without fields and without quantization.

Gravity waves are predicted by general relativity and have no link to any version of quantum gravity.

In short, I disagree completely.

DrRocket. Not quite. In his text "Gravity", Nobel Laureate George Gamow describes the neutrino / antineutrino pair as a graviton....circa 1964. Since the neutrino/antineutrino pair is one of only two variants of the Z0 boson at energies below 1.022 Mev, they can be formed as part of the neutral current interaction of the weak force. The other is photon/antiphoton, which is it's own antiparticle. As such, the Z0 couples to all the particles in Howard Georgi's Standard Model matrix, making it universal, as a graviton should.
Feel free to use the search function when you open this forum, then the advanced search, to posts by me with this topic over the years. Put my money where my mouth is and predicted the coincidences seen at the IMB, Baksan, Kamiokande, and Mont Blanc neutrino detectors, and the Rome and Maryland gravitational wave detectors seen during supernova 1987a, and peer reviwed and published about 25 times since, ( including Ap. J. and Il Nuovo Cimento C) in April 1982, ~5+ years before they occurred using a simplified quantum theory of gravitation. This is the only quantum gravitational theory with a prediction of a physical effect that has been seen independently by six different international collaborations, peer-reviewed and published. It violates none of the hierachy of conservation laws, uses a known and corroborated force carrier and fits into the Standard Model. It uses no dark energy, no dark matter, no inflationary spacertime, no mirror matter, no SUSY particles, no sparticles, no axions, no time reversal.
It does predict that a change in the ambient neutrino flux from an isotropic one to an anisotropic one will always be accompanied by a change in the local gradient of the ambient gravitational field, and that was seen.
It should be seen again the next time a nearby supernova goes off, within the range of the Large Magellanic Cloud, perhaps further considering recent improvements in the sensitivity of the detectors. pete