Gravitons

[Tormod]

I think the quantum-mechanical wave/partical duality should not be taken too literally. It is a duality because light can be described BOTH as moving particles AND as waves. So if you measure light as a set of streaming particles, then that is what you get. If you look for waves, you will see waves. This insight formed the basis of quantum mechanics! Einstein explained that matter can be described in terms of energy. Photons have energy - but not charge, nor mass.

 

So it is a semantic question. What is matter?

 

Here is a set of definitions which more or less contradict each other. Take a pick:

 

http://www.webster-dictionary.org/definition/matter

[BlameTheEx]

Linda

 

Semantics aside, a photon may not be matter but it does have mass (just not rest mass), and momentum.

 

It has mass because it has energy, and with that mass naturally follows momentum.

 

The proof of momentum is that you can make a light sail move by bouncing photons off it.

 

Given that we can test the momentum we can prove the mass. A beam of light passing close by the sun is bent a little. That was tested to confirm one of Einstein's theories. Now as light has momentum, and this beam's direction has been changed, momentum has to be conserved. Basically as the beam has been dragged towards the sun, the sun must also have been dragged towards the beam, although not by any measurable amount. Still, the mass of light is matched by an equal gravitational force. It can be attracted by a gravitational field, and it also creates a gravitational field, small though it might be.

 

If you could bottle a sunbeam, say inside a hollow sphere with a perfect mirror coating, it would add mass to the sphere, as if its energy was stored in matter.

[lindagarrette]

I'm still confused. Matter is not mass and mass is not matter., but a phoiton has mass because it is matter in motion -- energy.

 

Here is a web page I found that probably explains some of the things we are trying to figure out. Don't fuss at me for copying the entire abstract. The author says it explains the particle wave duality mystery. Not to me. Would anyone like to take a stab at it?

 

The Photon - Electron Interactions in the Electron Positron Lattice (EPOLA) Space Vs. Feyman's QED with his "Nobody Understands" and "Nature is Absurd"

 

by Menahem Simhony, Hebrew University Retired Associate Professor

 

 

--------------------------------------------------------------------------------

In the epola model [1] electromagnetic (EM) radiation represents elastic epola waves, in which each vibrating epola particle transfers the wave energy quantum - the photon, to the next epola particle. A free particle on the path of this energy transfer may be "knocked" by an epola particle carrying the wave energy quantum. As a result, the photon energy may be tranferred to the free particle. Hence the particle properties of the EM wave are those of the epola particles carrying the waves. The wave properties of a free nuclear particle are those of EM epola waves of de Broglie wavelengths that accompany each motion of these particles in the epola. This explains the "particle - wave duality" mystery. Another mystery is the assumed but physically impossible direct transfer of kinetic energy from a several eV photon to a free electron of a 511,000 eV mass-energy equivalent, as, e.g., in Einstein's 1905 interpertation of the photoelectric effect. The solution is that photons do not exist in nature, and the acting particle is the epola electron or positron that momentarily carries the photon energy and is thus able to transfer it to any nuclear particle of comparable mass (not much above an alpha particle). [1] M. Simhony, Invitation to the Natural Physics of Matter, Space, and Radiation, World Scientific, 1994, ISBN 981-02-1649-1. Website: http://www.word1.co.il/physics .

[BlameTheEx]

linda

 

Its very simple. Everything that has energy has mass. A photon "at rest", if such a thing has any meaning, has no energy so it is massless. From this point of view, matter has mass BECAUSE it has energy. It only becomes complicated if you think of gravity as a property of matter, rather than energy.

 

Sadly, I am as confused by Simhony's explanation as you.

 

There is a somewhat simpler way to explain the particle/wave duality. A photon actually exists as a particle only at two events. The event where it is transmitted, and the event where it interacts at it's destination. Between those two points it doesn't exist except as a wave covering the entire field of it's possible directions of travel. It doesn't travel as a particle. The proof is that a single photon can suffer from interference effects.

[lindagarrette]

It seems the only time something could be at rest would be if abruptly changing direction say, by colliding with something else. What happens when atoms collide? Energy fields run into each other not particles, right? The interference effect still has to be a wave event. (Am I doing any better?)

[Aki]

How much energy does a photon or graviton have anyways?

[lindagarrette]

If light is not a wave, it would then consist of little particles, or quanta, called photons, each with an energy of Planck's constant times its frequency.

[BlameTheEx]

Linda

 

"It seems the only time something could be at rest would be if abruptly changing direction say, by colliding with something else. What happens when atoms collide? Energy fields run into each other not particles, right? The interference effect still has to be a wave event. (Am I doing any better?)"

 

Much better. NOTHING, and that includes atoms exist as particles EXCEPT when they interact, At all other times they exist only as a field of posible positions. Interactions can't happen unless there is motion, and moving objects are waves, so interference effects are inevitable.

 

One use of particles is the election microscope. Beamed electrons can be focused very well indeed, but there are still limits. The limits are due to the wavelength of the elections. The faster they move, the shorter their wavelength. A practical proof that moving objects exist as waves. If larger particles were used, say protons, the waves would be shorter, and the microscopes definition better. Of course one could wonder if the sample being examined would survive such a battering. Probably not.

 

Admittedly something as large as, say, a thrown brick will have a wavelength that is too short for measurement. The uncertainty in it's position is not measurable ether. In theory the probability of its interactions are dependent on the whole universe, and it could be anywhere. In practice, it is better to assume that it will go just where it is thrown, and duck.

 

Aki

 

Regarding Gravitons.

 

They are as yet purely theoretical particles. They should follow Planck's constant too, but who knows for sure? I think neutrinos may yet prove to be gravitons. Does anybody know of evidence that they are not?

[Tormod]

Originally posted by: BlameTheEx

Regarding Gravitons.

 

They are as yet purely theoretical particles. They should follow Planck's constant too, but who knows for sure? I think neutrinos may yet prove to be gravitons. Does anybody know of evidence that they are not?

 

I know of no evidence that they *are* photons.

 

Here is the wikipedia antry on gravitons:

http://en.wikipedia.org/wiki/Graviton

 

Note the comment that some theories do not need gravitons at all, for example the loop quantum gravity theory.

 

Neutrinos have been found to have mass, thus they could not be photons if this is correct.

 

Here is one source (altough it is almost 5 years old now):

Neutrinos Have Mass: Experimental Evidence for Neutrino Oscillations

(University of Wisconsin)

http://www.pheno.info/hottopics/neutrinoshavemass/

[BlameTheEx]

Tormod

 

Yet again my thanks.

 

The evidence for neutrino mass seems rather indirect, with experimental evidence only setting an upper value of 3ev. Still, is very much a blow against them being gravitons.

[maddog]

To answer Aki first.

 

Gravitons are the Bosons thought to carry the force of gravity. The conventional wisdom as

part of the Standard Model is that all massless Boson (force carriers) travel at the same

speed as light. However, no experiment has yet verified the existence of such Graviton

particles (or Gravitational Waves for that matter). Like the Dual theory nature of Light,

analogously it is thought Gravity should also have this same nature and can be described

both as particles (Bosons) interacting with Fermions (that have mass) or as waves. Yes, it

is true that this expression according to Einsteins General Theory of Relativity has that space

is bent in the process. As an aside, it was the first success in String Theory that predicted

that spin of a Graviton would be 2 and not 1 like the photon. It was this that have people

thinking Gravitons have no mass.

 

Lindagarette comment that gravity can extend into the other branes is what some Physicists

are thinking. This may be another approach to look for dark matter.

 

In string theory (Supersymmetric or otherwise) all particles can be composed of strings

(open or closed).

 

Another way of thinking about photons as they do have a "sense of time". Photons can be

viewed interacting with matter in a time independant fashion. This eliminates the concern or rest mass. Instead is the notion of the vacuum potential or the Potential Energy of nothing. Now as for the Higgs Boson, this is a particle I desire to understand more fully

myself. It is covered more thoroughly in Quantum Field Theory (a course I have yet to take).

From what little I do understand on the Higgs Field (the expression of the particle) is that

particles in a Higgs Field "feel" there mass. Brian Greene talks about it a bit in the Elegant

Universe. He also has a new book out (I haven't read yet) called "Fabric of the Universe".

 

From Special Relativity a Photon travels at the speed of Light in all reference frames. As I said earlier were a Graviton to be massless then this would be true for it as well. String

Theory even implies this.

 

Mass is a measure of how much something is with respect to its resistance to inertia. That

is the resistence to being put in motion by a force. A photon does Not have mass. It does

have energy and momentum (mass times velocity). The article cited is very interesting. I

think I would have to read it in its entirety.

 

Aki: The energy of a photon (assumed the same with gravitons) is inversely proportional to

its wavelength.

 

Linda: Light is both a wave and a particle (that dual theory again), just not at the same time.

Still confused ? It turns (from Quantum Mechanics) the matter can be expressed as waves

as well (De Broglie wave mentioned in the article).

 

I think I have said too much now. So I will rest. Have a good weekend. Later.

 

Maddog

[Aki]

And Greene says that gravitons probably are made up of closed strings (loop), and thus, they are able to escape to other universes, unlike fermions or other bosons, where they are open-ended strings that can attach to the brane.

Greene's new book is actually called the Fabric of the Cosmos. I recently got a copy, but haven't had time to read it yet.

[maddog]

Yeah I have seen that book by Greene. I have yet buy it, I have waiting for a paperback.

I made an erroneous statement earlier by mistakenly implying that photons have a "sense of

time". There is a "not" missing in that statement. Basically the notion of time does not exist

for a photon. This is what forces a photon to behave differently wrt Heisenbergs eqaution for

energy. Oops!

 

Also about photons, they don't have rest mass as they never rest. Period. Created/destroyed

and move at the speed of c throughout their whole life.

 

Neutrinos (of any flavor) could not be gravitons as they are leptons (a kind of fermion) having

half integral spin. A graviton (Boson) has integral spin of 2. Very different critters. It is now

thought that if Neutrinos were very light yet a mass more than 0 might account for their being

non-interacting as they are.

 

Just a few of the flawed comments made in this thread. Cheers.

 

Maddog

[Xenosis]

not to get off topic..but I just wanted to answer this question is all...

OK, now I am confused. I sure don't want to argue with an astrophysicist. But c is only c in a vacuum. The "speed of light"/ thus the speed of a photon (I would assume) is not a constant except in a vacuum. It slows thru mass.

 

In fact you have a Hypog News link which discusses slowing the speed of light dramatically

 

Researchers use semiconductors to set speed limit on light

http://www.hypography.com/article.cfm?id=34291

 

It says "31,000 times slower than the 186,000 miles (or 300 million meters) per second that light normally clocks while traveling through a vacuum."

 

We aren't going to let oyu off that easy! :-)

 

That is not entirely true, if I understand it correctly, It all has to do with the density of the matter that the light is going throuugh, since photons cannot pass through atoms, they are bounced around, thus travelling a further distance then the straight path that would be possible in a vacuum. so microscopicly, the speed is still the same (distance/time), but macroscopicly(is that a word?) the speed is slower, since we cannot see the light bouncing around, we only see it enter the matter at t=0 and exit at some other time.

 

I drew a diagram that shows what I am talking about...just don't make fun of my paint ing skills :)

 

 

[Tormod]

since photons cannot pass through atoms

Since when can photons not pass through atoms? :)

[Xenosis]

...I didn't think they could...thats the only reason I would think that my explination would be true, and if they could pass through them...whats from stopping them from going through everything? walls, and what not

 

I will have to read up on that later, I have class in a few...but I would think that photons would have to interact with matter, for example, from the process behind lasers.

 

maybe I just used bad terminology, but I think that the photons would have to interact with the atoms in the matter

[Tormod]

Every time particles interact, other particles are created as byproducts, and the old particles change into new ones. Photons can pass straight through atoms because atoms are mostly nothing at all.

 

Photons are in fact created inside atoms every time an electron changes energy level from a higher level to a lower level. The opposite is also true - an electron can absorb a photon to climb upwards on the energy ladder.

 

Here's a link:

http://curious.astro.cornell.edu/question.php?number=85