# How do fields retain their uniformity with interposing objects?

• B
• Clueless123
In summary, the presence of interposing objects like Mercury or Venus between the Sun and the Earth does not significantly reduce the amount of gravity that the Earth experiences. This is because fields in physics are described by mathematical models rather than physical mechanisms, and these models exhibit linearity where the total field at a point is simply the sum of the fields from each source. However, this linearity is an approximation and in more advanced theories like quantum electrodynamics and general relativity, non-linear effects can occur. Additionally, while static fields are not described by waves or particles, changing fields can be described in this way and may be affected by objects they encounter.
Clueless123
Why don't interposing objects interfere with the integrity of a field's energy between the source and its absorber?

For example, the Sun's gravitational field spreads uniformly through space. If there are interposing objects like Mercury or Venus between the Sun and the Earth, why don't they reduce the amount of gravity that the Earth experiences? The gravitational field may act as a particle or wave (that wraps around the interposing object), but there would be less energy past that point by doing so in either case.

So, if there are a number of interposing objects between the source and target, how does a field retain its integrity and uniformity wrt its inverse square aspect?

In general, there are no mechanisms in physics. Only the appropriate mathematical model. I used the example recently of the electric field being uninterrupted by intervening charged particles.

GR is more sophisticated mathematically than classical EM, but there is still no mechanism to "explain" the Einstein Field equations. Newtonian gravity is physically inexplicable, as Newton himself famously declared.

A static field is not described by a wave or a particle. Changing fields can be described by waves or particles (if one has a quantum theory for that field), and may well be affected by objects they encounter. As far as I know we expect gravitational waves to experience gravitational lensing in much the same way EM radiation does. Our gravitational wave detectors are not yet sensitive enough to confirm that, however.

Clueless123 said:
the Sun's gravitational field spreads uniformly through space. If there are interposing objects like Mercury or Venus between the Sun and the Earth, why don't they reduce the amount of gravity that the Earth experiences?
Ok, so just a small bit of terminology. The word you are looking for is “linearity”, not “uniformity”.

A uniform field would be a field that is the same everywhere. An inverse-square field is not uniform, it gets weaker the further away you go from the source.

A linear field is one where the total field at a point is simply the sum of the fields from each of the sources. This is the concept you are looking for.

Newtonian gravity is linear. The gravity from 2 sources, say the Sun and Venus, is simply the sum of the gravity from each source alone. Venus does exert its own gravity, but it doesn’t change the influence of the sun.

Maxwell’s equations are also linear, so they exhibit this same feature you are interested in. However, both Maxwell’s equations and Newtonian gravity are approximations to other theories (quantum electrodynamics and general relativity) that are non-linear. So there are scenarios where you cannot treat the fields as linear and the presence of two sources does result in a loss of “integrity” as you described.

nasu
Ibix said:
A static field is not described by a wave or a particle. Changing fields can be described by waves or particles (if one has a quantum theory for that field), and may well be affected by objects they encounter. As far as I know we expect gravitational waves to experience gravitational lensing in much the same way EM radiation does. Our gravitational wave detectors are not yet sensitive enough to confirm that, however.
A field is a field. When quantized there are specific states of the quantum fields, which can be interpreted in some sense as "particles". I'd rather talk about "quanta" though, because particularly for the electromagnetic field, a spin-1 massless field, the particle interpretation is pretty far from being a good intuitive picture. There's no way to localize a photon. There's not even a position observable in the usual sense!

• Classical Physics
Replies
16
Views
1K
• Quantum Physics
Replies
29
Views
2K
• Classical Physics
Replies
12
Views
807
• Classical Physics
Replies
8
Views
928
• Classical Physics
Replies
2
Views
626
• Classical Physics
Replies
86
Views
4K
• Classical Physics
Replies
1
Views
792
• Introductory Physics Homework Help
Replies
5
Views
1K
• Introductory Physics Homework Help
Replies
4
Views
909
• Cosmology
Replies
6
Views
1K