Do high and low energy photons follow the same trajectory around a planet?

[nuby]

Do higher energy photons have the same trajectory around planet/gravity as low energy photons? I.e: If you were shooting photons from the same position wrt a planet would their path be the same?

 

[Fredrik]

As long as the spacetime curvature caused by the photon is negligible compared to the curvature caused by the planet, then yes.

 

[lightarrow]

Do higher energy photons have the same trajectory around planet/gravity as low energy photons? I.e: If you were shooting photons from the same position wrt a planet would their path be the same?

Doeis it depend on photon's energy or on energy density? How big is a photon? And if you are talking of a laser beam, instead of single photons, does it really depend on wavelenght or on intensity? The latter, I presume; a photon's energy doesn't seem relevant to me.

 

[N721YG]

"The energy and momentum of a photon depend only on its frequency ν or equivalently, its wavelength." The entire spectrum travels at the speed of light and should follow the curvature of space/time. One possible exception being examined is a "gamma ray anomaly" but there is nothing conclusive. I am a layman so any other input or corrections are welcome.

 

[N721YG]

As long as the spacetime curvature caused by the photon is negligible compared to the curvature caused by the planet, then yes.

Can a photon cause a spacetime curvature? Please explain and include a link.

 

[yenchin]

Can a photon cause a spacetime curvature? Please explain and include a link.

Negligible but yes. Look at the Einstein Field Equation, right hand side is the energy-momentum tensor. So energy, as well as mass, cause spacetime curvature. There's a discussion at https://www.physicsforums.com/showthread.php?t=232899

 

[N721YG]

Negligible but yes...

Interesting but "negligible" may be an understatement. It may be worthy of it's own thread for the rubber room folks but if it can't be measured, it probably should not be introduced as fact in this type of thread. That's my take on what I read. But again, I am very much a layman.

 

[lightarrow]

"The energy and momentum of a photon depend only on its frequency ν or equivalently, its wavelength." The entire spectrum travels at the speed of light and should follow the curvature of space/time. One possible exception being examined is a "gamma ray anomaly" but there is nothing conclusive. I am a layman so any other input or corrections are welcome.

Assuming (but not still proven, as far as I know) that a photon creates a spacetime curvature, according to the fact that it has energy, what counts is not *energy* but *energy density*.
Let's talk about a simpler case: a continuous laser beam between a source and an absorber, which has specific cross section and lenght. If it's red but with high intensity, it will bend spacetime more than if it's blue but with low intensity.

 

[N721YG]

Assuming (but not still proven, as far as I know) that a photon creates a spacetime curvature,...
...a continuous laser beam between a source and an absorber, which has specific cross section and lenght. If it's red but with high intensity, it will bend spacetime more than if it's blue but with low intensity.

You say "but not still poven" and then say "If it's red but with high intensity, it will bend spacetime more than if it's blue but with low intensity". Is that a yes and a no? Can we say some think the math shows that Photons can bend spacetime but it has never been observed? There are many theories that deserve attention but until observations support the math, shouldn't we be careful not to present it as fact? I am new here and what to learn and would just like to have the facts straight.

 

[DrGreg]

You say "but not still poven" and then say "If it's red but with high intensity, it will bend spacetime more than if it's blue but with low intensity". Is that a yes and a no? Can we say some think the math shows that Photons can bend spacetime but it has never been observed? There are many theories that deserve attention but until observations support the math, shouldn't we be careful not to present it as fact? I am new here and what to learn and would just like to have the facts straight.

It is undoubtedly true that general relativity theory says that photons cause spacetime curvature. I'm no expert but I doubt anyone has been able to experimentally confirm this, because the amount of curvature would be unfeasibly small to measure. You'd need an amount of energy that was a significant fraction of a planet's mass multiplied by c² to get a big enough effect.

However, just because we haven't measured it doesn't mean there's any doubt about it. If there were no curvature, it would mean the whole of general relativity were wrong, but we have no evidence to doubt its accuracy yet.

Curvature-by-photon isn't some take-it-or-leave-it optional add-on to relativity, it's an intrinsic part of it.

Similarly, no one has ever measured the gravitational attraction between two grains of salt, but there is no doubt that such attraction exists (either from the Newtonian or relativistic viewpoint). But when considering grains of salt orbiting a planet, we can dismiss such attraction as "negligible". (And the energy in a grain of salt is huge compared with one photon!)

 

[N721YG]

It is undoubtedly true that general relativity theory says that photons cause spacetime curvature... because the amount of curvature would be unfeasibly small to measure. You'd need an amount of energy that was a significant fraction of a planet's mass multiplied by c² to get a big enough effect.

...If there were no curvature, it would mean the whole of general relativity were wrong, but we have no evidence to doubt its accuracy yet.

I thought GR had to do with mass and a photon has no mass. There is no doubt there is energy in a photon, is that what is being considered in GR? If so, it would seem the photon energy of the sun would be huge but is not even considered when calculating time on the GPS satellite clocks. When you say unfeasibly small, would it be like considering Earth's gravity 12 billion light years away? Thanks for your reply, I am trying to learn.

 

[lightarrow]

You say "but not still poven" and then say "If it's red but with high intensity, it will bend spacetime more than if it's blue but with low intensity". Is that a yes and a no? Can we say some think the math shows that Photons can bend spacetime but it has never been observed? There are many theories that deserve attention but until observations support the math, shouldn't we be careful not to present it as fact? I am new here and what to learn and would just like to have the facts straight.

"If it's red but with high intensity, it will bend spacetime more than if it's blue but with low intensity" is "the light beam", not "the photon" as I wrote. They are not the same thing. You don't need to talk about photons, to find (from GR) what I said.
About if photons bend spacetime or not, I don't know because I don't even know what is a photon...
If others are so sure that photons do that, I would like to know how much a photon bends spacetime in a reference frame where the photon has a much lower energy. The spacetime curvature *as far as I know* should *not* depend on the frame of reference.

 

[N721YG]

"If it's red but with high intensity, it will bend spacetime more than if it's blue but with low intensity" is "the light beam", not "the photon" as I wrote. They are not the same thing. You don't need to talk about photons, to find (from GR) what I said.
About if photons bend spacetime or not, I don't know because I don't even know what is a photon...

But...

http://en.wikipedia.org/wiki/Photon
In physics, the photon is an elementary particle, the quantum of the electromagnetic field and the basic unit of light and all other forms of electromagnetic radiation.

 

[Fredrik]

Only a quantum theory of gravity can tell us how photons affect the geometry of spacetime, but it's clear that they must have some effect on the geometry since they carry energy and momentum.

 

[Dale]

I thought GR had to do with mass

Mass is not the source of gravity in GR, the stress-energy tensor is. There have been half a dozen posts on this in the last week.

 

[N721YG]

Mass is not the source of gravity in GR, the stress-energy tensor is. There have been half a dozen posts on this in the last week.

You see how I write, that is also how I read.

After going through a few threads, it is like a F-16 over my head. Is there a layman definition in English anywhere? Just so I know what is being considered.

 

[Fredrik]

Try this one. Note that the stress-energy tensor has 16 components, but only 10 of them are independent. One of them is the energy density.

 

[N721YG]

Try this one. Note that the stress-energy tensor has 16 components, but only 10 of them are independent. One of them is the energy density.

First glance says I can get through it. Thanks.

 

[lightarrow]

But...

http://en.wikipedia.org/wiki/Photon
In physics, the photon is an elementary particle, the quantum of the electromagnetic field and the basic unit of light and all other forms of electromagnetic radiation.

Ok, then, please, telle me:
1. where is the photon between source and detector
2. how big is it, width, lenght, thickness
3. which shape it has
4. what is made of.

 

[N721YG]

Ok, then, please, telle me:
1. where is the photon between source and detector
2. how big is it, width, lenght, thickness
3. which shape it has
4. what is made of.

I understand that a photon could be the length of the known universe with a frequency from 1 through gamma rays. It has 0 mass and exhibits both wave and particle properties. In flat space (vacuum) it travels at the speed of light and that speed is relative to it's current location (frame). The link I provided has a lot of information.

 

[The Dagda]

Mass is not the source of gravity in GR, the stress-energy tensor is. There have been half a dozen posts on this in the last week.

To further explain this point, in general relativity mass and energy are the same thing essentially. E=mc^2, it therefore makes sense in objects with mass to talk about energy rather than mass which tends to confuse the issue, it also makes the idea that mass bends space, or rather gravity does more easy to comprehend in real time, at least mathematically if you ask me. Objects without mass have their own specific rules like e=hf.

 

[Naty1]

It occurred to me discussions on gravitational lensing might offer insights.
Wikipedia says:

In general relativity, a point mass deflects a light ray with impact parameter b by an angle alpha = 4GM/c²b. ...

As usual wiki offers no constraints nor assumptions so it's again difficult to interpret the scope of applicability of this quantification. Taken at face value looks like light color plays no part.

If different light frequencies did curve differently would not gravitational deflection of light produce a rainbow spectrum like a prism?? Does it produce such a spectrum??

 

[N721YG]

To further explain this point, in general relativity mass and energy are the same thing essentially. E=mc^2, ...

I tried this formula in google and it did not work, E=(mass of Earth)c^2. What is the energy of Earth? And show me an equivalent equation to
(G * mass of Earth) / (radius of Earth * (c^2)) = 6.95453588 × 10^-10
that uses energy rather then mass.
Thank you

 

[The Dagda]

I tried this formula in google and it did not work, E=(mass of Earth)c^2. What is the energy of Earth? And show me an equivalent equation to
(G * mass of Earth) / (radius of Earth * (c^2)) = 6.95453588 × 10^-10
that uses energy rather then mass.
Thank you

I don't understand what you are asking me, are you questioning the validity of e=mc^2 or just that the Earth doesn't have a uniform mass?

Either way both special and general relativity owe their derivation to this equation, so that is all that matters. If you're suggesting that energy isn't equal to mass times the speed of light squared, that the two terms either side are not equivalent or that they cannot go from one form to the other and back in a relation suggested by that equation, and that the laws of special and general relativity are wrong, I think you're in the wrong part of the forum.

 

[Fredrik]

I don't even know what is a photon...

http://en.wikipedia.org/wiki/Photon
In physics, the photon is an elementary particle, the quantum of the electromagnetic field and the basic unit of light and all other forms of electromagnetic radiation.

Ok, then, please, telle me:
1. where is the photon between source and detector
2. how big is it, width, lenght, thickness
3. which shape it has
4. what is made of.

The answer you got was really lame. He just told you what everyone knows. I would find that annoying too. But if you meant to suggest that only a person who can tell you the location, size and shape of a photon can claim to know what a photon is, I have to disagree. The answers to 1-3 are all "not well defined" (which was probably your point), and I'm not sure that question 4 even makes sense.

In case you're wondering, I would say that what you need to know to understand what a photon "is", is a) the theory of unitary representations of the Poincaré group's universal covering group, and b) how to construct the appropriate representation using the appropriate quantum fields. So it definitely takes more than a single university course in quantum mechanics (or a quick look at a Wikipedia article ) to really know what a photon is.

 

[N721YG]

I don't understand what you are asking me, are you questioning the validity of e=mc^2 or just that the Earth doesn't have a uniform mass?

You said "in general relativity mass and energy are the same thing essentially."
I am not trying to say anything but am trying to understand.
Are you saying:
Earth mass = 5.9742 × 1024 kilograms
and
Earth energy = 5.9742 × 1024 kilograms
if not,
Earth energy = ?

 

[The Dagda]

You said "in general relativity mass and energy are the same thing essentially."
I am not trying to say anything but am trying to understand.
Are you saying:
Earth mass = 5.9742 × 1024 kilograms
and
Earth energy = 5.9742 × 1024 kilograms
if not,
Earth energy = ?

If you could take all the matter on Earth and convert it over to energy entirely efficiently then yes. But let's just say that a proton and an anti proton if they collided and taking account of their energy in total in theory have equivalent energy to mass according to e=mc^2.

Put it this way if you restricted the energy in a box and didn't let it escape and you could convert energy to mass then it would be equivalent to e=mc^2.

 

[N721YG]

The answer you got was really lame. He just told you what everyone knows. I would find that annoying too...
... So it definitely takes more than a single university course in quantum mechanics (or a quick look at a Wikipedia article ) to really know what a photon is.

I am new to these forums and came here to learn. Twice in my post I indicated I am a layman when it comes to physics. I usually do not try to answer questions unless they are basic and within my understanding.

Lightarrow indicated he didn't know that light is a photon and I gave him very basic reply and pointed him to a link he could get a better understanding. You on the other hand told him

"So it definitely takes more than a single university course in quantum mechanics (or a quick look at a Wikipedia article ) to really know what a photon is."

While you claim my post was lame, yours post was a lot of words that said NOTHING to answer the question.

I didn't come here to be insulted and if a degree in physics is needed to fit in I will leave.

 

[The Dagda]

I am new to these forums and came here to learn. Twice in my post I indicated I am a layman when it comes to physics. I usually do not try to answer questions unless they are basic and within my understanding.

Lightarrow indicated he didn't know that light is a photon and I gave him very basic reply and pointed him to a link he could get a better understanding. You on the other hand told him

"So it definitely takes more than a single university course in quantum mechanics (or a quick look at a Wikipedia article ) to really know what a photon is."

While you claim my post was lame, yours post was a lot of words that said NOTHING to answer the question.

I didn't come here to be insulted and if a degree in physics is needed to fit in I will leave.

It takes an interest in physics, I don't have a degree in physics either. Perhaps he was having a bad day?

 

[N721YG]

If you could take all the matter on Earth and convert it over to energy entirely efficiently then yes. But let's just say that a proton and an anti proton if they collided and taking account of their energy in total in theory have equivalent energy to mass according to e=mc^2.

Put it this way if you restricted the energy in a box and didn't let it escape and you could convert energy to mass then it would be equivalent to e=mc^2.

Thank you, I have been trying to use google calculator to calculate E=MC^2 with different arbitrary #'s without luck. Could you give me an example?

 

[lightarrow]

I understand that a photon could be the length of the known universe with a frequency from 1 through gamma rays. It has 0 mass and exhibits both wave and particle properties. In flat space (vacuum) it travels at the speed of light and that speed is relative to it's current location (frame). The link I provided has a lot of information.

The frequency cannot be less than 1? Why?
The speed is c even in a curved spacetime.

However, we were discussing if a photon bends spacetime, and I wrote that I don't even know what a photon is. Let's say that you find that a photon is "a quantum of excitation of the electromagnetic field". Does it help you to understand if it bends spacetime? To me, it doesn't.

 

[The Dagda]

Ok take the mass of proton and anti-proton:

both = 2x1.6726 x 10^-27, so you have a combined mass of 2 protons.

Plug them into e=mc^2.

Sorry I don't know the level of people here, so I mistakenly thought you were trying to make a subtle point I wasn't getting.

Interestingly masses of particles this small are often given in units known as e/c^2, because m=e/c^2.

 

[lightarrow]

The answer you got was really lame. He just told you what everyone knows. I would find that annoying too. But if you meant to suggest that only a person who can tell you the location, size and shape of a photon can claim to know what a photon is, I have to disagree. The answers to 1-3 are all "not well defined" (which was probably your point), and I'm not sure that question 4 even makes sense.

I agree with you. However, if we could know where a photon is and how much is its volume (and I'm NOT saying that such answers can be found) we could try to compute if, how and how much a photon bends space. The volume would be required to have the energy density (the parameter in the stress-energy tensor).

 

[The Dagda]

I agree with you. However, if we could know where a photon is and how much is its volume (and I'm NOT saying that such answers can be found) we could try to compute if, how and how much a photon bends space. The volume would be required to have the energy density (the parameter in the stress-energy tensor).

Since the curvature experienced by the lensing by the moons gravitation can be precisely modeled in an eclipse, if light did curve space to any measurable degree we would be able to pick it up as a discrepancy in what we measured, or we could just do it in the lab. If it does bend space it logically is so small that we could not measure it with the technology we have now.

 

[N721YG]

The frequency cannot be less than 1? Why?
The speed is c even in a curved spacetime.

However, we were discussing if a photon bends spacetime, and I wrote that I don't even know what a photon is. Let's say that you find that a photon is "a quantum of excitation of the electromagnetic field". Does it help you to understand if it bends spacetime? To me, it doesn't.

Frequency is often measured in cycles per second. You can drop down to a straight line, 1 cycle per second frequency.


"a quantum of excitation of the electromagnetic field" means nothing to me as far as proving light bends spacetime.