Gravitation of the light

[marcofuics]

Hi
Can the light be a source for the gravitation; a region filled by
radiative energy can attract gravitationally?
And photons enclosed in a cavity? Do they feel gravity of partners?

[S Rathnakumar]

Yes, anything which has energy can be source of gravitation.

[marcofuics]

On 9 Set, 19:42, S Rathnakumar <s.rathnakuma...@gmail.com> wrote:
> Yes, anything which has energy can be source of gravitation.

And the light, does the light has energy? Or maybe the energy blows
out only when we measure that light? Then in a situation of radiative
energy in a cavity where photons don't interact with charged-matter?
Imagine a cavity at a T temperature, filled with photons. Do they feel
the effective gravitational potential made by others and so exhibiting
a condensation of the <<radiative>> cloud?

[avijeet prasad]

Each photon has got an energy which is proportional to its frequency.

When radiation is trapped in a cavity, the photons interact with each other
predominantly through collisions (they interact gravitationally also, but the gravitational
potential due to the photons themselves i.e. the gravitational self energy will
be too small to have any appreciable effect on their motion). It is the weak
interaction between the photons through collisions which is responsible for
relaxation of the system into a uniform temperature.

  
One can create a <<radiative>> cloud, if you can trap the radiation in a small
region, in effect creating a region of high number density which will result in
large number of collisions and small mean free path and the photons will take
a long time to come out of the cloud. A similar situation occurs near the center
of sun where the density of photons is so large that it takes a photon  millions
of years to come upto the surface of the star from its center. I comparison after
it escapes the star it covers about 100 times the same distance in few minutes !
 

[marcofuics]

On 10 Set, 10:01, avijeet prasad <avijeet.ka...@gmail.com> wrote:

> Each photon has got an energy which is proportional to its frequency.

OK
yes... but do you think that this energy <<lives>> in the free space
during the <<photon's>> fly?

or maybe this energy is simply a flow between 2 different charged
particles that appears to us as a <<time>> dependency?

> When radiation is trapped in a cavity, the photons interact with each other
> predominantly through collisions (they interact gravitationally also, but
> the gravitational
> potential due to the photons themselves i.e. the gravitational self energy
> will
> be too small to have any appreciable effect on their motion).

Ok
So, standing at your words, the photons... as particles/or waves have
energy, and so they demonstrates <<a gravity>> (little little as you
want, but a non-zero gravity).

Einstein teaches us that the energy (Tmn energy tensor) acts as source
for gravitation, deflects spacetime in accordance with equation of GR.
Question: (if you know)
[Does it exists a calculation about the spacetime of the unique
Electromagnetic energy Tmn tensor? Maxwell-Einstein solutions?]

[avijeet prasad]

yes... but do you think that this energy <<lives>> in the free space
during the <<photon's>> fly?

 

As far as i am aware the position of a photon in not a well defined physical
quantity in quantum field theory. So, maybe it is not meaningful to attribute
energy with the spacial location of photon.

or maybe this energy is simply a flow between 2 different charged
particles  that appears to us as a <<time>> dependency?

 

I did not understand what you meant by "flow between two charge particles".
Could you please explain what is flowing? In any case, we can think of an
universe where all charges which were initially sources of radiation neutralised each other.
i.e. a universe filled with radiation only and no matter. The concept of energy is still valid.

Einstein teaches us that the energy (Tmn energy tensor) acts as source
for gravitation, deflects spacetime in accordance with equation of GR.
Question: (if you know)
[Does it exists a calculation about the spacetime of the unique
Electromagnetic energy Tmn tensor? Maxwell-Einstein solutions?]

There are known solutions of Einstein equation with only electromagnetic
energy as part of the energy momentum tensor. These fields are called Geon
(Gravitational electromagnetic entity). I can look up the details if you are interested.

[marcofuics]

On 10 Set, 14:54, avijeet prasad <avijeet.ka...@gmail.com> wrote:
> As far as i am aware the position of a photon in not a well defined physical
>
> quantity in quantum field theory. So, maybe it is not meaningful to
> attribute
> energy with the spacial location of photon.

And this is my doubt: where does the gravity act if we cant say where
is its source?
Using for example the Double-slit experiment, we know that the
particle/wave photon passes through both the slits if we dont ask
nothing else to the experiment.... so in this perspective we must
conclude that se <<gravity>> is made by a cloud of radiative dust
uniformly distributed throughout all the available space?

> I did not understand what you meant by "flow between two charge particles".

hmmm i dont know exactly, but my question arises from another one...
Can be a charged particle be massless?

> energy as part of the energy momentum tensor. These fields are called Geon
> (Gravitational electromagnetic entity). I can look up the details if you are
> interested.

Geon... thx, I will see on web