# Falloff behaviour of light vs gravitation

• shalayka
In summary, the shape of an emitter has a significant impact on the intensity falloff rate in raytracing. The falloff rate for a spherical emitter is 1/r^2, for a cylindrical emitter it is 1/r^1, and for a plane emitter it is 1/r^0. The gravitational field of a macroscopic spherical mass is not generated by the acceleration of its constituent particles. The field is not affected by the presence of other masses, similar to light. Gravitational waves are self-interacting, but it is unclear how a more compact form of energy, such as mass, would interact with them. The idea of particles oscillating to emit gravitational waves is extrapolated from the concept of a planet emitting waves
shalayka
After doing some playing around with area lights in raytracing, I realized that the shape of the emitter has a lot to do with the intensity falloff rate (when the "photons" are always emitted in a direction normal to the surface).

ex: A spherical emitter's field falls off with 1/r^2, a cylindrical emitter's field with 1/r^1, and a plane emitter's field with 1/r^0 (no falloff). I'm assuming there is a law or postulate associated with this falloff-curvature relation, but I don't know what it's called.

What I'm wondering about is whether or not the gravitational field of a macroscopic scale spherical mass is considered to be generated purely by the acceleration of its constituent microscopic / atomic / sub-atomic scale particles (similar to braking radiation)?

ex: Is the field considered to consist of many tiny gravitational waves?

The reason I ask is that if this is the case, and the constituent particles could be formed into a disc and made to oscillate only along the plane (no "up/down" oscillation), would the gravitational field fall off at a rate of 1/r? (The "field" would also be 2D at this point).

To take this further would be to make the constituent particles oscillate along only one direction, forming a 1D field (beam) of gravitational waves with no falloff. From what I understand, this would be similar to the macroscopic gravitational wave, except that there would be many small waves instead of just a single big one?

Is the falloff for a spherical emitter in 4D based on 1/r^3? A spherical emitter in 5D based on 1/r^4?

From what I can gather from various books, there is no such thing as a gravitational "shadow". That is, gravitation isn't blocked by mass like light is. Is this interpretation correct? The reason I wonder is because I also gathered that gravitational waves are self-interacting, so I can't see how a more compact form of energy (mass) wouldn't interact as well, also causing a deflection of the waves. I've also considered that the frequency of the gravitational wave might be a factor, similar to the photoelectric effect, where the absorption and conversion of the photon's energy into an electron's kinetic energy depends on whether or not the energy of the photon meets the requirement of the material's work function.

Thank you for any info you have on the subject. I know it's a lot of questions.

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shalayka said:
After doing some playing around with area lights in raytracing, I realized that the shape of the emitter has a lot to do with the intensity falloff rate (when the "photons" are always emitted in a direction normal to the surface).

ex: A spherical emitter's field falls off with 1/r^2, a cylindrical emitter's field with 1/r^1, and a plane emitter's field with 1/r^0 (no falloff). I'm assuming there is a law or postulate associated with this falloff-curvature relation, but I don't know what it's called.

What I'm wondering about is whether or not the gravitational field of a macroscopic scale spherical mass is considered to be generated purely by the acceleration of its constituent microscopic / atomic / sub-atomic scale particles (similar to braking radiation)?
I don't know where you go this idea. The gravitational field has nothing to do with acceleration.

ex: Is the field considered to consist of many tiny gravitational waves?

The reason I ask is that if this is the case, and the constituent particles could be formed into a disc and made to oscillate only along the plane (no "up/down" oscillation), would the gravitational field fall off at a rate of 1/r? (The "field" would also be 2D at this point).
You could imagine a "test point" at a point at distance r from an infinite plate of mass and, by integrating the gravitational force due to each point mass over the plate, determine that the gravitational field is proportional to 1/r. That's straightforward Newtonian gravity.

To take this further would be to make the constituent particles oscillate along only one direction, forming a 1D field (beam) of gravitational waves with no falloff. From what I understand, this would be similar to the macroscopic gravitational wave, except that there would be many small waves instead of just a single big one?
I don't know of any theory of gravitation that involves particles oscillating.

[/quote]Is the falloff for a spherical emitter in 4D based on 1/r^3? A spherical emitter in 5D based on 1/r^4?

From what I can gather from various books, there is no such thing as a gravitational "shadow". That is, gravitation isn't blocked by mass like light is. Is this interpretation correct?[/quote]
Yes, that is correct.

The reason I wonder is because I also gathered that gravitational waves are self-interacting, so I can't see how a more compact form of energy (mass) wouldn't interact as well, also causing a deflection of the waves. I've also considered that the frequency of the gravitational wave might be a factor, similar to the photoelectric effect, where the absorption and conversion of the photon's energy into an electron's kinetic energy depends on whether or not the energy of the photon meets the requirement of the material's work function.

Thank you for any info you have on the subject. I know it's a lot of questions.

The example you give of a plane of mass -- when you say the gravitational field is proportional to 1/r, are you talking about potential (as in, it's the same potential generated by a spherical mass), or are you talking about acceleration (as in, it's not the same acceleration generated by a spherical mass)?

re: Oscillations. I was extrapolating from the notion that if you made a planet oscillate, it would emit gravitational energy in the form of a wave each time acceleration occurs. The extrapolation comes from the notion that this should be scale independent, ex: An oscillating atom, pig or planet should all emit gravitational waves. Whether or not atomic-scale gravitational waves are what makes up the gravitational field was my inquiry.

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Well, you would be right to believe any accelerating mass emits gravitational waves. This includes any rotating or orbiting masses. But stationary mass is sufficient to generate a gravitational field. For example, an electron.

But you might be interested in a thread about another thought experiment that occurred to me, where inertia and a gravitational field arise from confined photons [it appears to be perfectly correct to say that the instantaneous acceleration of the photons causes the gravitational field as well as inertia!]

It seems plausible that everything moves at the speed of light, and it is only oscillations in motion that cause what we see as particle mass. This hypothesis is an enthusiastic generalisation of the ideas that Dirac arrived at after he found a relativistic equation for the electron.

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## What is the difference between the falloff behaviour of light and gravitation?

The falloff behaviour of light and gravitation refers to how the intensity or strength of these forces changes with distance. Light follows an inverse square law, meaning that its intensity decreases by the square of the distance from the source. On the other hand, the force of gravity follows an inverse square law only for point masses, but for larger masses or at large distances, it follows an inverse cube law.

## Why does the falloff behaviour of light and gravitation differ?

The difference in falloff behaviour is due to the nature of these forces. Light is an electromagnetic wave, meaning it is transmitted through a field, and it spreads out equally in all directions. Gravitation, on the other hand, is a fundamental force of nature described by Einstein's theory of general relativity, which is based on the concept of spacetime curvature. This results in a different falloff behaviour for gravity compared to light.

## How does the falloff behaviour of light and gravitation affect our understanding of the universe?

The falloff behaviour of light and gravitation plays a crucial role in our understanding of the universe. The inverse square law for light allows us to measure the distances to stars and galaxies based on their brightness. The inverse square/cube law for gravity helps us understand the motion of planets and other celestial bodies. It also explains the structure of galaxies and the overall expansion of the universe.

## Can the falloff behaviour of light and gravitation be tested or observed in real-life situations?

Yes, the falloff behaviour of light and gravitation can be tested and observed in various real-life situations. For example, the intensity of light from a light source can be measured at different distances to verify the inverse square law. Similarly, the strength of gravitational fields can be measured at different distances from a massive object to verify the inverse square/cube law.

## Is there any theoretical explanation for the falloff behaviour of light and gravitation?

Yes, both the falloff behaviours of light and gravitation can be explained theoretically. As mentioned earlier, the inverse square law for light is a consequence of the nature of electromagnetic waves. The inverse square/cube law for gravity can be derived from Einstein's theory of general relativity, which describes how the curvature of spacetime is affected by the presence of matter and energy.

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