Do Photons Have a Gravitational Effect?

[Dale]

Point granted. However, we can agree that 'rest mass being zero (while energy and momentum nonzero) is a false reason to argue that something doesn't produce gravity (as threadmark has argued). Thus, if a quantum gravity theory eventually says individual photons don't produce gravity, it will not be simply because their rest mass is zero.

Correct, it will be because of other more subtle issues, of which there are plenty!

 

[Passionflower]

Thus, if a quantum gravity theory eventually says individual photons don't produce gravity, it will not be simply because their rest mass is zero.

Perhaps, but I am definitely not absolutely sure of that. We really can't tell as such a theory does not even exist.

 

[atyy]

I would say we don't rule out Nordstrom based on EP at all. It is the only theory other than GR that is indistinguishable from it in this way. For other theories of gravity, we may use EP to rule them out. For Nordstrom we simply use major conflict with experiment.

Yes, that's what I meant. My second sentence was about trying to figure out if the EP data shows light bends spacetime, ie. use EP to get down to GR and Nordstrom, then use global light deflection to rule out Nordstrom in which light does not bend spacetime. (And yes, this seems like a very delicate chain of reasoning.)

 

[atyy]

We do have a quantum theory of gravity and it says photons cause spacetime curvature.

http://arxiv.org/abs/gr-qc/9512024

 

[PAllen]

Correct, it will be because of other more subtle issues, of which there are plenty!

I will throw out another intuitive argument to believe that photons probably produce gravity. That is, if a quantum gravity theory ends up being similar in key ways to QFT, and if gravity is mediated by gravitons, and if gravitons interact with all particles (a lot of ifs, but all fairly commonly assumed in many guesses about general features of quantum gravity), then it would seem to follow that photons must both produce and respond to gravity.

 

[threadmark]

Point granted. However, we can agree that 'rest mass being zero (while energy and momentum nonzero) is a false reason to argue that something doesn't produce gravity (as threadmark has argued). Thus, if a quantum gravity theory eventually says individual photons don't produce gravity, it will not be simply because their rest mass is zero.

No, it would be propagation and momentum that world say it wouldn’t affect space time because
(A ) a light wave …sigh is not a constant state and its bodies to create this light wave…sigh constantly shift positions, so they would not occupy the same point in space. Although a solar system is constantly moving, it to would never pass the same point in space twice. But because its state is coherent its affect on space time is constant. Where you are all saying that the theoretical occurrence of photons somehow have a moment of vector symmetry would create gravity. I would humor this by saying fluctuation in space time but that’s it

(B) the photon has no (mass)

 

[Passionflower]

We do have a quantum theory of gravity and it says photons cause spacetime curvature.

http://arxiv.org/abs/gr-qc/9512024

That looks like a darn interesting article!

 

[Dale]

No, it would be propagation and momentum that world say it wouldn’t affect space time because
(A ) a light wave …sigh is not a constant state and its bodies to create this light wave…sigh constantly shift positions, so they would not occupy the same point in space. Although a solar system is constantly moving, it to would never pass the same point in space twice. But because its state is coherent its affect on space time is constant. Where you are all saying that the theoretical occurrence of photons somehow have a moment of vector symmetry would create gravity. I would humor this by saying fluctuation in space time but that’s it

(B) the photon has no (mass)

threadmark, I wish you would learn to write coherent sentences. I can't parse this post either. I get the feeling that there is a severe language barrier.

Can you answer my previous question, are you claiming that GR is wrong?

 

[threadmark]

No, I am saying you are all wrong. Every person adding to this discussion in affirmative is wrong. I agree that a state of momentary coherence/vector symmetry in photons would create a fluctuation at best but I don’t think you understand the difference between a curvature and a fluctuation. A gravitational field in my opinion and I have done math to prove this is... Gravitational fields exerts equal amount of pressure on the propagating body due to momentum shifts. This can not be the case due to Alberts notation that if the sun was to instantly vanish you would feel the affects instantly, you should note that he was suggesting that gravity is a state produced from mass density and is dependent on it. Though I think he is wrong in this notation, Its no ground to throw the theory out all together. My opinion\formulas prove that gravity is a state of space time not the density and complete dependence of a body of mass and the creation of this field is time dependent on the coherence of matter. So if a body of mass instantly vanished, the gravity would remain continuing the velocity decreasing its magnitude or field strength by the same amount as it was created so the field would take the same time disperse as it did to create. That is my theory and would not say Albert’s theory is wrong he just hasn’t had evidence to create formulas that would predict this occurrence. Yes I have dyslexia it means numbers and words get jumbled. But I assure you my white boards provent me from making to manymistakes in formulation and math so if its on the board i can correct the numbers just not in my head. I am sorry you can't understand me.

 

[Passionflower]

My opinion\formulas prove...

Ok, let's cut this short shows us your formulas.

 

[pervect]

No, I am saying you are all wrong. Every person adding to this discussion in affirmative is wrong. I agree that a state of momentary coherence/vector symmetry in photons would create a fluctuation at best but I don’t think you understand the difference between a curvature and a fluctuation.

Do you have a reference to support your viewpoint? Or is this some personal theory? Have you looked at the references I supplied?

 

[threadmark]

the page is not formated like i need it to. I am tired I am going to bed

 

[PAllen]

This can not be the case due to Alberts notation that if the sun was to instantly vanish you would feel the affects instantly, .

This is false, according to Einstein and every reputable expert on general relativity. If you believe that this is what Einstein's theory says, you have essentially no understanding of it.

1) This scenario cannot actually be set up in GR; there are no solutions where matter simply disappears;

2) If you set up a solution where matter distribution rapidly changes, the change in curvature/gravity propagates with speed c.

3) There is a significant, limited sense in which gravity appears to propagate instantaneously. The direction of attraction is to the quadratically extrapolated position of a gravitating source. This means that a gravitating body must have changing acceleration before you could (in principle) detect the finite propagation speed of gravity. Here is a famous paper explaining this:

http://arxiv.org/abs/gr-qc/9909087

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[Vanadium 50]

I think it is a bad idea to claim to know how a quantum theory of gravity would function.

But we don't need a quantum theory of gravity to answer this question. All we need is QED in curved spacetime, and that is no problem at all.

1. Observationally, we know single photons fall.
2. GR says that momentum is conserved (in this case).
3. Therefore, single photons must gravitate.

That conclusion can only be escaped by asserting GR is incorrect. Alternatively, one can put in a single photon in T and again GR shows the effect on G. Again, the conclusion can only be escaped by asserting GR is incorrect.

 

[Passionflower]

But we don't need a quantum theory of gravity to answer this question. All we need is QED in curved spacetime, and that is no problem at all.

1. Observationally, we know single photons fall.
2. GR says that momentum is conserved (in this case).
3. Therefore, single photons must gravitate.

That conclusion can only be escaped by asserting GR is incorrect. Alternatively, one can put in a single photon in T and again GR shows the effect on G. Again, the conclusion can only be escaped by asserting GR is incorrect.

I do not believe the topic is whether photons gravitate, the topic is whether a single photon can create a gravitational field, these are in my mind two different things.

 

[cragar]

When we have pair production , a photon turns into an electron and positron , I would like to think that the gravitational field of the electron and positron came from the photon,
And vice versa if we collide an electron and positron and we get a photon out, It seems like the G field of the electron and positron would get transferred to the photon.

 

[D H]

I do not believe the topic is whether photons gravitate, the topic is whether a single photon can create a gravitational field, these are in my mind two different things.

Caveat: I am not an expert in GR.

My understanding is that a single photon does not create a gravitational field. A collection of photons can, however. The intrinsic mass of a collection of particles is

$$m = \frac{\sqrt{E^2 - p^2c^2}}{c^2}$$

where E is the total energy of the collection of particles and p² is the square of the net momentum of the collection. While energy and momentum are both frame-dependent quantities, the difference E² - p²c² is frame independent.

For a single photon, E=pc, so the intrinsic mass of a single photon is zero. Now consider photons created by an electron-positron annihilation. In the rest frame of the (former) electron-positron pair, the created photons have zero net momentum. The total energy of these photons is equal to the 2m_ec² plus any kinetic energy of the electron-positron pair. The intrinsic mass of the photons created by this annihilation event is identically equal to the intrinsic mass of the electron + positron system prior to the annihilation event.

 

[Dale]

No, I am saying you are all wrong.

If you believe that GR is correct and that we are wrong then you do not understand GR. I recommend further study. In particular, you should learn about pp-wave spacetimes.

 

[Dale]

But we don't need a quantum theory of gravity to answer this question. All we need is QED in curved spacetime, and that is no problem at all.

1. Observationally, we know single photons fall.
2. GR says that momentum is conserved (in this case).
3. Therefore, single photons must gravitate.

That conclusion can only be escaped by asserting GR is incorrect.

I like this. That is a good point.

Alternatively, one can put in a single photon in T and again GR shows the effect on G.

This one is the dangerous approach. How can you define T when the photon does not have a definite energy, momentum, and location at any given time? Actually, I am not even sure that spacetime can be represented by a manifold at sufficiently small scales due to quantum effects.

 

[Vanadium 50]

A single photon does create a gravitational field, because T is non-zero. If T is non-zero, so is G.

 

[Dale]

If T is non-zero then what is T?

 

[Driftwood1]

"everything" distorts/curves/interrupts etc space-time

thats what gravity is

 

[pervect]

While it is true that photons do not have mass, it is incorrect to conclude that because they don't have a mass, they can't cause gravity. Photons don't need mass to cause gravity, all they need is energy and momentum, which they do have, because it's the stress energy tensor that causes gravity and not "mass".

While GR is a classical theory, and doesn't have anything to do directly with photons per se, you can model a photon in GR as a packet of light. Which is essentially what Tolman et al did in the 1931 paper I mentioned earlier, with the results I mentioned - parallel light packets don't attract each other, there is no "self focusing" effect of light due to gravity, but beams in opposite directions do interact gravitationally.

 

[Troponin]

Please! In this thread there has been nothing but manipulation of Albert’s general relativity to produce a theoretical scenario where imaginary particle states can produce gravitation. Its not the photon with gravitation that is bugging me, it’s the use of Albert’s notions in producing general relativity to prove your hypothesis of bosons produce gravity is false because the theory in its entirety didn’t explain theoretical zero mass particles producing gravity and your existence to interpret the information in such a way to try and change theoretical understandings of a particle. What are you suggesting number 1? Where in Einstein’s formulas does it produce an explanation of zero mass particles producing gravity 2. And please note that a wave’s propagation can be seen as action at a distance but not gravity. How can you compress a field for density not field compression or amplification which will create distortion not density . Propagation is not gravity. Waves like light (sigh), do not produce gravity

This thread is in the relativity section, and according to GR, "light" does produce gravity.

If you looked at a completely "empty" Universe that was void of any form of energy, matter, radiation, etc., in a 4 dimensional spacetime where

$$\mathbf{R(X,Y)Z}=R^{a}_{\ bcd}X^{c}Y^{d}Z^{b}=0=R_{bd}$$

and then let a wave of radiation pass through then you get the interesting scenario where calculating the Ricci tensor will still give you zero
$$R_{bd}=0$$
but the Riemann tensor isn't required to vanish and you can find calculations where $$R^{a}_{\ bcd}X^{c}Y^{d}Z^{b}\neq 0$$, ie., the radiation causes curvature of the spacetime (in 4 or greater dimensions).The fact that GR predicts that light alters the spacetime geometry is much more general, but that is a situation where nothing exists to cause curvature, so "gravitational" curvature is entirely from the radiation.

 

[Vanadium 50]

If T is non-zero then what is T?

It's been a while, but I believe the upper left 2x2 is 1 and the other components are 0.

 

[bcrowell]

Please! In this thread there has been nothing but manipulation of Albert’s general relativity to produce a theoretical scenario where imaginary particle states can produce gravitation.

I posted information about experimental tests in #4, but your #8 showed no signs of having looked at that information. I posted more about experimental tests in #23, #26, and #31, but your #34 showed no signs of having looked at that, either. In #35, I asked whether you had read any of the four references to experimental peer-reviewed scientific papers I gave in #31. You replied in #37 without giving any signs that you had looked at any of those references. Therefore it is simply not true that this thread has consisted of nothing but theoretical arguments. You have been provided with evidence about experiments, but you've simply chosen not to read it.

 

[Dale]

It's been a while, but I believe the upper left 2x2 is 1 and the other components are 0.

I believe that is correct for a classical pulse of light at a definite location and of known (unit) energy density propagating in the +x direction. But that is not the same as an EM quantum with uncertain location and non-definite energy. What you are describing is simply GR for classical pulses of light, not for photons. Do you see the difference and why I am reluctant to make conclusions for a photon based on classical pulses of light?

 

[atyy]

There's a little bit about coupling quantum gravity to photons in section 3.2.1 of http://www.emis.de/journals/LRG/Articles/lrr-2004-5/ .

 

[Tantalos]

I like this. That is a good point.

This one is the dangerous approach. How can you define T when the photon does not have a definite energy, momentum, and location at any given time? Actually, I am not even sure that spacetime can be represented by a manifold at sufficiently small scales due to quantum effects.

The QM theory gives only probability distributions of photon location, its momentum and energy, but photon must have a definite energy, momentum and location in time that we cannot know by QM.

 

[pervect]

Energy, momentum, etc would only be expectations for a photon. But we expect that any quantum theory of light is going to have to include gravity in the classical limit, because we know that collections of photons do gravitate under certain circumstances, and we know which ones.

Furthermore, I already posted a link to a book by Zee which discusses how you get quantum gravity for the photon perturbatively - though it's outside the scope of GR.

So, I'd suggest continuing the QM side of the debate in the "beyond the standard model" forum.

I'd also encourage people interested to look at the reference by Zee, perhaps it got lost in the shufle.