# Photon Questions: Elasticity, Gravity & Diffraction

• vin300
In summary, the conversation discussed the elasticity of photons and the possibility of proving the gravity of photons along their line of motion. It was concluded that photons cannot be elastic because it would allow for manipulation of their energy, and there is evidence of gravitational redshift. The concept of gravitons and their exchange between photons was also brought up, along with a thesis on detecting elastic photon-photon scattering. The idea of photons having a gravitational field was also discussed, with one explanation being the collision of matter and anti-matter releasing photons while still maintaining a gravitational field.
vin300
1) Is a photon elastic?
2)Is it possible to prove gravity of photon along its line of motion?
IMO no, because this would causse the photon to travel at either more or less than c, or change its frequency.
Perhaps diffraction can be taken as a cause of gravity of photon perpendicular to its motion, it is observed "when" the photon passes through the slit, not before or after.
We have also learned the force required to circulate a photon in a grav.field.

on your second question if you are asking if a photon has a graviational field i can tell you yes it does . that's about all i can add

Since a photon does not have "size" or "shape" in the usual sense, it makes no sense to talk about "elasticity" of a photon.

The photon cannot be elastic because it would then be possible to manipulate its energy by means of forces(gravity, collision etc.) causing a change of frequency, which is not observed.
A similar argument would not be in favour of gravitational effects of the photon along or opposite to its motion and so the force "mustn't work".Any instance of this kindhttp://www.adamauton.com/warp/emc2.html"only mentions recoil of the surface when the photon approaches and hits a reflective surface

Last edited by a moderator:
There is a not overly popular idea called the tired light mechanisms, one of the versions of which states that over long periods of time, photons loose energy slowly and their frequency decreases. No mechanism however has been proposed for this effect, but it does offer an alternative explanaiton for certain redshifts we observe.

Personally, I'm a little skeptical, but with science one must always keep an open mind.

Galap said:
but with science one must always keep an open mind.

Nonsense. An open mind does not mean "believing in things that have been excluded by data".

Tired light can't be correct - among other problems, it requires a degree of blurring of distant objects that is unobserved, and it makes the wrong prediction about distant supernova light curves.

Last edited:
Nonsense. An open mind does not mean "believing in things that have been excluded by data".

Tired late can't be correct - among other problems, it requires a degree of blurring of distant objects that is unobserved, and it makes the wrong prediction about distant supernova light curves.

Hmmm. I didn't happen to know that information about it. Now I'm a lot more skeptical.

Can anyone cite me a derivation of the formula of grav. force on pg.14? The force acts on the photon, but if it doesn't accelerate, then what happens?
Could it be that the gravitons emitted by the photon keep traveling with the photon at its own speed so information transfer is not possible and all the energy is absorbed at once during collision?

Last edited by a moderator:
vin300 said:
The photon cannot be elastic because it would then be possible to manipulate its energy by means of forces(gravity, collision etc.) causing a change of frequency, which is not observed.

The Compton effect is a case where an electron and a proton collide and then move away from each other with conservation of energy as well as conservation of momentum. The term "perfectly elastic collision" is usually applied to the event. The photon's frequency is indeed changed.

The experiment in post#4 is also an example of perfectly elastic collision, but the trick is that during collision the velocity of the photon is not c, and something which does not move at c is not a photon.So the "photon" does not change frequency on collision.
The compton effect is a case of absorption and reemission, not of interest here.
the term "point particle" has the clue.

Are you here to ask questions or to lecture us about how photons behave? Your first post suggests the former, but your later posts suggest the latter. They also include some iconoclastic views - I would recommend you take a look at the PF Rules on overly speculative posts.

vin300 said:
2)Is it possible to prove gravity of photon along its line of motion?
IMO no, because this would causse the photon to travel at either more or less than c, or change its frequency.
The change in frequency (gravitational redshift) for a vertically-travelling photon was clearly measured in the Pound-Rebka experiment.

mikelepore said:
The Compton effect ... electron and a proton collide

I made a serious typo. I meant to write that an electron and a photon collide.

DaleSpam said:
The change in frequency (gravitational redshift) for a vertically-travelling photon was clearly measured in the Pound-Rebka experiment.

Thanks

They also include some iconoclastic views -
Which part are you talking about?The gravitons part, most probably.How do gravitons emitted by the photon reach the heavier mass when both travel at the same speed?

Are you here to ask questions or to lecture us about how photons behave? Your first post suggests the former, but your later posts suggest the latter.
That's because first these questions came to my mind and posted them, then I kept thinking about them and posted my thoughts

I found this thesis from arXiv.
arXiv:hep-ph/0512033
Detection of elastic photon-photon scattering through four-wave coupling

vin300 said:
Which part are you talking about?The gravitons part, most probably.How do gravitons emitted by the photon reach the heavier mass when both travel at the same speed?

ya I'm also confused here... photons have a gravitational field? that means they exchange gravitons? so the photon loses energy as it travels? (since gravitons can't catch up to the photon)
can someone point me to an article to explain how photons have a gravitational field?

Last edited:
milford30 said:
can someone point me to an article to explain how photons have a gravitational field?
I don’t know if this is the explanation you are looking for but we can show that photons have a gravitational field by imagining a bar of matter and a bar of anti-matter and they both have a gravitational field associated with them and when they collide they will annihilate and photons will be released and the gravitational field will still be there it won't go away. And another way if light can be bent in a gravitational field then based on action -reaction it must also have a force .

cragar said:
I don’t know if this is the explanation you are looking for but we can show that photons have a gravitational field by imagining a bar of matter and a bar of anti-matter and they both have a gravitational field associated with them and when they collide they will annihilate and photons will be released and the gravitational field will still be there it won't go away. And another way if light can be bent in a gravitational field then based on action -reaction it must also have a force .

with the matter and anti matter example, your saying that gravity IS different from EM? if they can become 1 force at high enough energy (as the 4 forces unite) they they should be the same thing right? then your example wouldn't work right?

about bending light, then that implies the picture about gravitational field bending space-time itself is wrong and the gravitons are actually interacting with the photon(s)?
or they can co-exist and we can abandon the bending space-time itself picture?
and in the action reaction picture the photons can pull on say a marble in space if there are enough of them? since photons are bosons the number of photons in the same spot can be limitless? so if we sum their gravitational effects it should be able to pull on a marble?
or am i missing something again?

milford30 said:
ya I'm also confused here... photons have a gravitational field? that means they exchange gravitons? so the photon loses energy as it travels? (since gravitons can't catch up to the photon)
can someone point me to an article to explain how photons have a gravitational field?
Yes, photons have a gravitational field. If they didn't their paths wouldn't be curved by the sun. But having a gravitational field or "exchanging gravitons" does not mean anything loses energy.

HallsofIvy said:
Yes, photons have a gravitational field. If they didn't their paths wouldn't be curved by the sun. But having a gravitational field or "exchanging gravitons" does not mean anything loses energy.

if photons have a gravitational field, then gravitons must be emitted spontaneous right?
if the above is wrong then the photon must absorb a graviton to emit one?

which 1 is correct?
i was thinking the exchange of gravitons in the 'traditional' way (bouncing quickly between the bodies) is impossible since gravitons travels at the speed of light...

the photon must absorb the gravitons right? so the energy of photon changes as it travels through space?

completely confused... can this effect not be explained in the semi-classical way? and can only be explain with field theories?

vin300 said:
How do gravitons emitted by the photon reach the heavier mass when both travel at the same speed?
Or how does a graviton emitted by the Earth "catch up" with a photon that is moving away?

vin300 said:
Or how does a graviton emitted by the Earth "catch up" with a photon that is moving away?

the graviton could be traveling (from the planet) head on / perpendicular to the photon and hitting the photon and still giving the bending effect, does not have to catch up with it...

Unless someone can cite specific references to a gravitational quantum field theory papers that can validate this line of discussion, this thread is in danger of being locked.

Zz.

I agree with ZapperZ. Since we don't have a working theory of quantum gravity it is inherently speculative to guess what the interactions between photons and gravitons would be. Such speculation may be valuable, but does not belong here.

## 1. What is the relationship between photons and elasticity?

Photons are particles of light that do not have mass, but they do have energy and momentum. When they interact with matter, they can cause the atoms or molecules to vibrate, which is a form of elasticity. This means that photons can transfer energy to matter and cause it to stretch or compress.

## 2. How does gravity affect photons?

Gravity affects all objects with mass, including photons. However, since photons do not have mass, they are not affected by gravity in the same way as other objects. They do experience a slight gravitational pull, but it is so small that it is usually negligible. This is why light from distant stars can still reach us, despite the immense gravitational pull of the universe.

## 3. What is diffraction and how do photons exhibit it?

Diffraction is the bending of waves around obstacles or through small openings. Since photons behave as both particles and waves, they can exhibit diffraction. This means that when light passes through a narrow slit or around an obstacle, it can spread out and create a diffraction pattern. This phenomenon is commonly observed in experiments such as the double-slit experiment.

## 4. Can photons have different wavelengths?

Yes, photons can have different wavelengths, which determines the color of the light they emit. The wavelength of a photon is related to its energy, with shorter wavelengths corresponding to higher energies. This is why different types of light, such as visible light, ultraviolet light, and infrared light, have different colors and properties.

## 5. How do photons interact with matter?

Photons interact with matter through various processes such as absorption, emission, and scattering. When a photon is absorbed by an atom or molecule, it transfers its energy to the matter, causing it to vibrate or produce heat. Emission occurs when an excited atom or molecule releases a photon as it returns to a lower energy state. Scattering is when a photon changes direction after colliding with an atom or molecule, which is how light is reflected and refracted.

Replies
25
Views
962
Replies
26
Views
960
Replies
5
Views
3K
Replies
15
Views
3K
Replies
16
Views
2K
Replies
5
Views
2K
Replies
7
Views
455
Replies
2
Views
1K
Replies
19
Views
2K
Replies
38
Views
4K