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What is the mechanism that allows gravity to latch onto a photon?

Photons could be considered to have mass based on the principle of mass-energy equivalence.

They have no rest mass, but since they are never at rest...

This is a tricky one, because I've read in more than one place that objects with finite energy density should generate gravitional fields. I've seen suggestions that concentrating enough high-energy light inside of its own Schwarzchild radius should allow for the creation of a black hole.

Light can also transfer momentum to other objects (solar sail technology).

Perhaps what I should have said is that light behaves as if it has mass.

Photons are massless. If you think they have mass, explain how an object with non zero mass m can have finite energy moving at c, since its momentum p is:p = m/sqrt[1 - (v/c)^{2}]Put v = c and tell me how much is p.

One feature of this new law is quite easy to understand is this: In Einstein relativity theory, anything which has energy has mass -- mass in the sense that it is attracted gravitationaly. Even light, which has energy, has a "mass". When a light beam, which has energy in it, comes past the sun there is attraction on it by the sun.

We have already discussed that and we didn't agree. About what Feynman writes, I have explained the concept in my previous post. You are one of the few left who still talk of relativistic mass.

MikeS - Light can generate a gravitational field.

Quote from: Pmb on 05/09/2011 19:04:46MikeS - Light can generate a gravitational field.We are discussing about photons. Can a photon generate a gravitational field?

Quote from: lightarrow on 05/09/2011 22:51:29Quote from: Pmb on 05/09/2011 19:04:46MikeS - Light can generate a gravitational field.We are discussing about photons. Can a photon generate a gravitational field?yes.

Quote from: Pmb on 06/09/2011 01:31:15Quote from: lightarrow on 05/09/2011 22:51:29Quote from: Pmb on 05/09/2011 19:04:46MikeS - Light can generate a gravitational field.We are discussing about photons. Can a photon generate a gravitational field?yes.Anything with energy/momentum should be able to do so, and a photon has both. By the way, a lot of the mass in matter is caused by the binding energy in the nucleus, and to a far lesser extent by electromagnetic binding energies between atoms. All this binding energy can be described in terms of gluons/photons, which are massless.

Quote from: JP on 06/09/2011 02:12:59Quote from: Pmb on 06/09/2011 01:31:15Quote from: lightarrow on 05/09/2011 22:51:29Quote from: Pmb on 05/09/2011 19:04:46MikeS - Light can generate a gravitational field.We are discussing about photons. Can a photon generate a gravitational field?yes.Anything with energy/momentum should be able to do so, and a photon has both. By the way, a lot of the mass in matter is caused by the binding energy in the nucleus, and to a far lesser extent by electromagnetic binding energies between atoms. All this binding energy can be described in terms of gluons/photons, which are massless.I think it is debatable whether a photon has momentum.Is this a mainstream answer, as I understand the situation, where mass comes from is still open to question.Why would anything with energy be able to generate a gravitational field?

Quote from: MikeS on 06/09/2011 08:15:10Quote from: JP on 06/09/2011 02:12:59Quote from: Pmb on 06/09/2011 01:31:15Quote from: lightarrow on 05/09/2011 22:51:29Quote from: Pmb on 05/09/2011 19:04:46MikeS - Light can generate a gravitational field.We are discussing about photons. Can a photon generate a gravitational field?yes. energy is equivalent to mass - we calculate the spacetime curvature with the stress energy tensor within einsteins field equations. you might just as well ask why mass is able ... physics models and explains at lower and more basic levels - but the eternal verities are left to philosophers and drunksThe fact that energy is equivalent to mass is irelevant. It does not mean they can be thought of as being the same. In most ways they are the complete opposites of each other. Mass is heavy, photons are light.

Quote from: JP on 06/09/2011 02:12:59Quote from: Pmb on 06/09/2011 01:31:15Quote from: lightarrow on 05/09/2011 22:51:29Quote from: Pmb on 05/09/2011 19:04:46MikeS - Light can generate a gravitational field.We are discussing about photons. Can a photon generate a gravitational field?yes. energy is equivalent to mass - we calculate the spacetime curvature with the stress energy tensor within einsteins field equations. you might just as well ask why mass is able ... physics models and explains at lower and more basic levels - but the eternal verities are left to philosophers and drunksThe fact that energy is equivalent to mass is irelevant. It does not mean they can be thought of as being the same. In most ways they are the complete opposites of each other. Mass is heavy, photons are light.

Quote from: Pmb on 06/09/2011 01:31:15Quote from: lightarrow on 05/09/2011 22:51:29Quote from: Pmb on 05/09/2011 19:04:46MikeS - Light can generate a gravitational field.We are discussing about photons. Can a photon generate a gravitational field?yes. energy is equivalent to mass - we calculate the spacetime curvature with the stress energy tensor within einsteins field equations. you might just as well ask why mass is able ... physics models and explains at lower and more basic levels - but the eternal verities are left to philosophers and drunks

Someone above thought that the photon doesn't interact with a gravitational field because "light has no mass" meaning that the proper mass of a photon is zero. Light is affected by a g-field because light has passive gravitational mass.

A photon can interact with a gravitational field because it has 'passive' mass. Can you please explain the term 'passive' as it implies it has no effect?

A photon can not interact with the gravitational field.

It only appears to because it follows the geodesics of curved space time as caused by gravity.

Quote from: lightarrow on 05/09/2011 22:51:29We are discussing about photons. Can a photon generate a gravitational field?yes.

We are discussing about photons. Can a photon generate a gravitational field?

I think it is debatable whether a photon has momentum.

And which is the quantum theory of gravity which says this?Hint: there still isn't any accepted quantum theory of gravity...

Phillip Morrison made several suggestions and convinced us not to invoke that weird quantum particle, the photon, in a treatment of classical theory of relativity (except in some exercises).

Consider a uniform gravitational field. The field will deflect matter, including light. However a uniform gravitational field has zero spacetime curvature, yet there can be a non-gravitational field present with a suitable change in spacetime coordinates from an inertial frame.

Hmm... In Newtonian gravity, a uniform field won't deflect matter, since it has zero gradient.

Quote from: MikeS on 06/09/2011 11:09:37A photon can interact with a gravitational field because it has 'passive' mass. Can you please explain the term 'passive' as it implies it has no effect?Active gravitational mass refers to the mass that generates a gravitational field. Passive gravitational mass is the mass that gravity acts on. QuoteA photon can not interact with the gravitational field.Sure it does. What would make you believe otherwise? There is an example of a pulse of light generating a gravitational field. Why would you think that light can generate a grvitational field but photons wouldn't?Quote It only appears to because it follows the geodesics of curved space time as caused by gravity.That is incorrect. Consider a uniform gravitational field. The field will deflect matter, including light. However a uniform gravitational field has zero spacetime curvature, yet there can be a non-gravitational field present with a suitable change in spacetime coordinates from an inertial frame.

First off all quantum theories of gravity must reduce to GR in any acceptable theory. What I've done above is to use the approximation that a photon is a point particle with zero proper mass.

You're asking me about a quantum notion in a classial theory. I do know that people I've talked to about this, and friends/acquantances who are experts in their field, think of photons just like I do.

It can be show, with classical GR, that a g-field which has been created by a source consisting of beam of EM radiation (a "pencil of light" as they call it) deflects particles.

A pulse of light can be thought of as a collection of photons and the result is an interaction of the photon and g-field. How could you accept that a beam of light is deflected but a single photon can't?

There is no such thing as a uniform gravitational field from any reference frame other than the free falling reference frame.

If it were uniform there would be no gravity.

So you also have found a model for the photon! Fantastic!You didn't say that all this is your New Theory, however...

Yes, and there isn't even need of talking of photons, since in that case you have a region of space with non zero energy density and so Einstein's equation tells us that there must be curvature, but unfortunately this has nothing to do with a single photon creating curvature.

From the viewpoint of an observer free falling in curved space-time an object falling with them will appear to be stationary, likewise a beam of light will have a constant frequency.[/color]

QuoteThere is no such thing as a uniform gravitational field from any reference frame other than the free falling reference frame.Sure there is. Here's a Newtonian example whose size is finite in extent - ...sorry, you cannot view external links. To see them, please REGISTER or LOGIN

QuoteFrom the viewpoint of an observer free falling in curved space-time an object falling with them will appear to be stationary,[/color] likewise a beam of light will have a constant frequency.[/color]Relativity states that that cannot happen. Also, measurements from different frames will yield measure different values

From the viewpoint of an observer free falling in curved space-time an object falling with them will appear to be stationary,[/color] likewise a beam of light will have a constant frequency.[/color]

I don't know what you mean. I havent' found anything "new". Here's an interesting article - "The mass of a gas of massless photons," H. Kolbenstvedt, Am. J. Phys. 63 (1), January 1995

QuoteYes, and there isn't even need of talking of photons, since in that case you have a region of space with non zero energy density and so Einstein's equation tells us that there must be curvature, but unfortunately this has nothing to do with a single photon creating curvature.What makes you believe that?

This is why Einstein said, in his 1916 review paper on GR, that if you change frames of reference you can go from a frame with no g-field to one that does have a g-field.

Do you have a link (not in german, possibly [])?

By Tilman Sauer; ...sorry, you cannot view external links. To see them, please REGISTER or LOGIN

Quote from: lightarrow on 10/09/2011 20:02:28Do you have a link (not in german, possibly [])?I found on on the internet. See ...sorry, you cannot view external links. To see them, please REGISTER or LOGIN. It has all the relevant statements made by Einstein on this topic, at least all I could find.