Photon's gravity

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Re: Photon's gravity

by dougettinger » Tue Nov 23, 2010 5:32 pm

Please excuse the previous submission. I hit the wrong button at the wrong time.

Virtual particles are an invention to explain force fields. Neither photons or gravitons are virtual particles because they can be detected. So how is a graviton detected ?

I have some questions about virtual lives as shown. When you receive undeserved wealth why does your life path go for a loop? Is a conservation law violated ? What generally happens after the third post-doctorate ? Does the 2.1 children depict a possible quantum entanglement of one birth of a child ?

Doug Ettinger
Pittsburgh, PA

Re: Photon's gravity

by dougettinger » Tue Nov 23, 2010 5:21 pm

neufer wrote:
v13 wrote:
So, if photons cause gravity, how can the gravity propagate along the path of photon's propagation?
Photons, like other particles, cause gravity by exchanging virtual gravitons
mostly perpendicular to the path of the photon's propagation.

Even gravitons cause gravity by exchanging virtual gravitons
mostly perpendicular to the path of the graviton's propagation.

In any event, such virtual particles simply do not obey the laws of real particles:

Re: Photon's gravity

by neufer » Wed Nov 17, 2010 1:24 pm

v13 wrote:
So, if photons cause gravity, how can the gravity propagate along the path of photon's propagation?
Photons, like other particles, cause gravity by exchanging virtual gravitons
mostly perpendicular to the path of the photon's propagation.

Even gravitons cause gravity by exchanging virtual gravitons
mostly perpendicular to the path of the graviton's propagation.

In any event, such virtual particles simply do not obey the laws of real particles:

Re: Photon's gravity

by v13 » Wed Nov 17, 2010 9:52 am

So, if photons cause gravity, how can the gravity propagate along the path of photon's propagation?

Re: Photon's gravity

by neufer » Wed Nov 17, 2010 4:48 am

rstevenson wrote:
Oh yeah, that tensor. :shock:
Just be thankful I didn't mention then most "offal" tensor of them all:

Riemann–Christoffel tensor as written using Christoffel symbols:

Image

The Ricci(-Ticci) tensor is related to the Riemann–Christoffel tensor: Image

Re: Photon's gravity

by rstevenson » Wed Nov 17, 2010 2:41 am

Oh yeah, that tensor. :shock:

Rob

Re: Photon's gravity

by neufer » Wed Nov 17, 2010 2:31 am

Chris Peterson wrote:
rstevenson wrote:
One quick thing I can say, and then I'll duck while others more knowledgeable answer. ...

1. Gravity is a consequence of mass, and photons have no rest mass - so, no gravity as a result of photons.
That's absolutely true, but the concept of rest mass is a matter of theory, not practice. Photons are never at rest, so they do have an effective mass. That mass is determined by E=mc^2, or by calculating the photon momentum p = h / lambda, and then using the classical p = mv with v=c. It is because photons have momentum, and therefore an equivalent mass, that things like solar sails work, or that radiation can affect the orbits of astronomical bodies.
Image
One of Eddington's photographs
of the total solar eclipse of 29 May 1919,
confirming Einstein's theory that light "bends"
Note that since Eddington observed that the sun attracts photons
then it naturally follows that those same photons must also attract the sun.
-----------------------------------------------------------------------------------------------
Technically, gravity is a consequence of the momentum energy tensor
(i.e., the symmetric stress-energy tensor):

Image

Image

Image

Image
Got it?

Re: Photon's gravity

by Chris Peterson » Wed Nov 17, 2010 12:24 am

rstevenson wrote:One quick thing I can say, and then I'll duck while others more knowledgeable answer. ...
1. Gravity is a consequence of mass, and photons have no rest mass - so, no gravity as a result of photons.
That's absolutely true, but the concept of rest mass is a matter of theory, not practice. Photons are never at rest, so they do have an effective mass. That mass is determined by E=mc^2, or by calculating the photon momentum p = h / lambda, and then using the classical p = mv with v=c. It is because photons have momentum, and therefore an equivalent mass, that things like solar sails work, or that radiation can affect the orbits of astronomical bodies.

Re: Photon's gravity

by rstevenson » Tue Nov 16, 2010 11:45 pm

One quick thing I can say, and then I'll duck while others more knowledgeable answer. ...
1. Gravity is a consequence of mass, and photons have no rest mass - so, no gravity as a result of photons.

Rob

Photon's gravity

by v13 » Tue Nov 16, 2010 10:22 pm

Hello dear APODers,

I came with a thought experiment which I'm not sure how to answer, so I'm asking your help:

Do photons cause gravity? I mean: If you create some very-very energetic photons (a beam of very energetic photons), will they attract matter?

I bet that possible answers are "yes" and "no". So:
  • If Yes: What's the deal of the propagation? Since gravity propagates with the speed of light, the propagation of photons' gravity along their movement is a mind mess. Photons will always catch-up with their "gravitational wave", causing a constant "sonic boom". If so, shouldn't this result in an ever increasing gravitational force?
  • If No: Isn't it statistically possible for a black hole to convert part of its mass to photons, leaving it with less than the critical mass and explode in the most energetic "supernova" ever seen?

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