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

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Discussion Overview

The discussion revolves around whether high and low energy photons follow the same trajectory around a planet under the influence of gravity. Participants explore the implications of spacetime curvature caused by photons and the conditions under which their paths may differ, considering both theoretical and conceptual aspects.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • Some participants propose that as long as the spacetime curvature caused by a photon is negligible compared to that caused by a planet, both high and low energy photons would follow the same trajectory.
  • Others question whether the trajectory depends on the energy of the photon or the energy density, suggesting that intensity may play a role, particularly in the context of laser beams.
  • A participant mentions that the energy and momentum of a photon depend on its frequency or wavelength, asserting that all photons travel at the speed of light and should follow the curvature of spacetime.
  • There is a discussion about whether photons can cause spacetime curvature, with some participants acknowledging that while it is theoretically possible, the effect is likely too small to measure.
  • Some participants express uncertainty about the implications of photons bending spacetime, noting that while general relativity suggests this is true, experimental confirmation is lacking.
  • Concerns are raised about presenting unverified claims as facts, especially regarding the effects of photons on spacetime curvature.
  • Participants discuss the distinction between photons and light beams, emphasizing that the behavior of light beams may not directly correlate with individual photons.
  • One participant highlights the need for a quantum theory of gravity to fully understand how photons affect spacetime geometry.

Areas of Agreement / Disagreement

There is no consensus on whether high and low energy photons follow the same trajectory, as participants present competing views on the influence of energy, intensity, and spacetime curvature. The discussion remains unresolved regarding the extent to which photons can bend spacetime and the implications of this bending.

Contextual Notes

Participants note limitations in measuring the curvature caused by photons, suggesting that the effects may be negligible compared to those caused by larger masses. There is also an acknowledgment of the complexity surrounding the definitions and implications of energy density versus energy in the context of photon behavior.

  • #31
N721YG said:
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.
 
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  • #32
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.
 
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  • #33
Fredrik said:
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).
 
  • #34
lightarrow said:
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.
 
  • #35
lightarrow said:
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.
 
  • #36
N721YG said:
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.

Since the whole thing is more or less arm waving, nothing we can define light as can be held to account in a theory of light bending space. If it did though then there should in theory be a discrepancy in the http://en.wikipedia.org/wiki/Michelson-Morley_experiment" experiment also, but just how you'd go about setting up something to measure a "particle" like a photons effect on space-time is beyond anyone, even dare I say it the finest minds in physics, so it's a moot point.

Generally we just assume light speed is constant in a vacuum and leave it at that. For the same reason we assume the photon has no mass, because to say otherwise is a matter for philosophy not science.
 
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  • #37
The Dagda said:
nothing we can define light as can be held to account in a theory of light bending space.

As far as I know, classical electrodynamics adapts OK to curved spacetime, and that's what people use when calculating the gravitational effects of light. I've seen references to such calculations here.

It's photons that we have problems with, because we don't have a generally accepted quantum theory of gravity yet.
 
  • #38
The Dagda said:
Since the whole thing is more or less arm waving, nothing we can define light as can be held to account in a theory of light bending space. If it did though then there should in theory be a discrepancy in the http://en.wikipedia.org/wiki/Michelson-Morley_experiment" experiment also, but just how you'd go about setting up something to measure a "particle" like a photons effect on space-time is beyond anyone, even dare I say it the finest minds in physics, so it's a moot point.

Generally we just assume light speed is constant in a vacuum and leave it at that. For the same reason we assume the photon has no mass, because to say otherwise is a matter for philosophy not science.

Well said and I second the motion.

What I was looking for earlier, and I get a real DUH for not catching my own mistake. I need to work on making myself clear. :smile:
E=MC^2
mass of Earth * (the speed of light^2) = 5.36934319 × 10^41 joules
 
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  • #39
N721YG said:
Frequency is often measured in cycles per second. You can drop down to a straight line, 1 cycle per second frequency.
It's better if you study again the concept of frequency.
"a quantum of excitation of the electromagnetic field" means nothing to me as far as proving light bends spacetime.
Exactly. So, if you post here what wikipedia or anything else says about photons, doesn't mean anything for what concern that question...
 
  • #40
N721YG said:
Well said and I second the motion.

What I was looking for earlier, and I get a real DUH for not catching my own mistake. I need to work on making myself clear. :smile:
E=MC^2
mass of Earth * (the speed of light^2) = 5.36934319 × 10^41 joules

To be accurate you'd probably need to account for all the different masses, and since it's a massive object it will no doubt be extremely complicated, with various energy interactions not to mention the system is not closed. But in theory I suppose that is correct. Of course this is all hypothetical until I finish constructing my dooms day device, but your calculations are appreciated. :smile:
 
  • #41
lightarrow said:
It's better if you study again the concept of frequency...

I said "Frequency is often measured in cycles per second. You can drop down to a straight line, 1 cycle per second frequency." You may be right though, an oscilloscope measures "0" frequency so 1 may be wrong. This of course is not in the visible light spectrum. Maybe think DC current. :smile: If you have a link that can teach me something please post it.
 
  • #42
The Dagda said:
To be accurate you'd probably need to account for all the different masses, and since it's a massive object it will no doubt be extremely complicated, with various energy interactions not to mention the system is not closed. But in theory I suppose that is correct. Of course this is all hypothetical until I finish constructing my dooms day device, but your calculations are appreciated. :smile:

Actually I let google do all my math since it knows all about the mass of Earth and the speed of light. You probably already know this but anyone who doesn't, just copy and paste (mass of earth)c^2 into google search and hit enter. There are more meaningful and more complicated equations it can work with.

I am glad that I am not the only one building a dooms day device. Most of my friends think I am nuts. :biggrin:
 
  • #43
N721YG said:
Actually I let google do all my math since it knows all about the mass of Earth and the speed of light. You probably already know this but anyone who doesn't, just copy and paste (mass of earth)c^2 into google search and hit enter. There are more meaningful and more complicated equations it can work with.

I am glad that I am not the only one building a dooms day device. Most of my friends think I am nuts. :biggrin:

Well that's not a problem for me as I have gotten rid of my friends, if you know what I mean, they knew too much!
 
  • #44
N721YG said:
I said "Frequency is often measured in cycles per second. You can drop down to a straight line, 1 cycle per second frequency." You may be right though, an oscilloscope measures "0" frequency so 1 may be wrong. This of course is not in the visible light spectrum. Maybe think DC current. :smile: If you have a link that can teach me something please post it.
There is no need of links, just think that frequency is 1/T (T = period of oscillation) so if something, included EM fields, takes more than 1 second to complete the oscillation, the frequency is lower than 1 Hz. Take a point charge and put it on the border of a disk and rotate the disk at constant speed so that it takes 2 seconds to make one rev. Then the EM field generated has a frequency of 0.5Hz.
 
  • #45
lightarrow said:
There is no need of links, just think that frequency is 1/T (T = period of oscillation) so if something, included EM fields, takes more than 1 second to complete the oscillation, the frequency is lower than 1 Hz. Take a point charge and put it on the border of a disk and rotate the disk at constant speed so that it takes 2 seconds to make one rev. Then the EM field generated has a frequency of 0.5Hz.

Didn't I correct myself in my last post when I said "You may be right though, an oscilloscope measures "0" frequency so 1 may be wrong."? So I believe a straight line would be 0 hz.
 
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  • #46
N721YG said:
Didn't I correct myself in my last post when I said "You may be right though, an oscilloscope measures "0" frequency so 1 may be wrong."? So I believe a straight line would be 0 hz.
Ok, I didn't write that to show you again that you are incorrect :smile: I just meant to show you how I reasoned about it (then you can use the information as you prefer...)
 

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