The propagation of light through a vacuum.

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Discussion Overview

The discussion revolves around the nature of electromagnetic (EM) waves and their propagation through a vacuum. Participants explore the concepts of electric and magnetic fields, the significance of the Michaelson-Morley Experiment, and the properties of vacuum such as permittivity and permeability. The conversation includes both classical and quantum perspectives on light and fields.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants question what electric and magnetic fields represent if EM waves do not require a medium, suggesting they might be disturbances of spacetime.
  • Others explain that the classical visualization of EM waves involves oscillating electric and magnetic fields, while quantum mechanically, EM is treated as the exchange of photons.
  • There are inquiries about the existence of permeability (μ0) and permittivity (ε0) in a vacuum, with some participants asking why these properties exist if space is considered "empty."
  • Some participants assert that μ0 and ε0 are defined values rather than measurable physical properties, leading to further questions about the implications of these definitions.
  • One participant raises the possibility that the Higgs field could be related to the nature of "emptiness" in space.
  • A participant emphasizes that a field is a mathematical construct that assigns values to points in space, which may not correlate with the physical emptiness of space.

Areas of Agreement / Disagreement

Participants express varying viewpoints on the nature of EM waves, the significance of the Michaelson-Morley Experiment, and the interpretation of vacuum properties. There is no consensus on the underlying reasons for the existence of permittivity and permeability in a vacuum, nor on the implications of these properties.

Contextual Notes

Some discussions involve unresolved questions about the definitions and implications of μ0 and ε0, as well as the nature of fields in relation to the concept of emptiness in space.

thomasxc
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all i have under my belt is a high school physics class, so please bear with me. i have a pretty good understanding of light and waves, but this question still gets me. and nowhere can i find a decent answer, or rather, and answer i can comprehend. if EM waves don't require a medium, then what exactly are the electric and magnetic fields if they arent a disturbance of something besides the initial medium. are they a disturbance of spacetime? any help is Immensely appreciated.



-Tom
 
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thomasxc said:
all i have under my belt is a high school physics class, so please bear with me. i have a pretty good understanding of light and waves, but this question still gets me. and nowhere can i find a decent answer, or rather, and answer i can comprehend. if EM waves don't require a medium, then what exactly are the electric and magnetic fields if they arent a disturbance of something besides the initial medium. are they a disturbance of spacetime? any help is Immensely appreciated.



-Tom


Oh :( I thought the underlined "immensely" was a link and was curious what it was. Anywho, the visualization of EM as oscillating magentic and electric field is actually a classical one. Quantum mechanically we often treat EM as the exchange of photons (i.e. particles of light) which might give you a visualization of what it is. The fact that there is no medium through which EM waves travel was established over a hundred years ago through what is called the "Michaelson-Morley Experiment" which is of great importance (wiki it). It was this understanding that light didn't propagate through any medium that made Einstein's theory of (special) relativity possible.
 
maverick_starstrider said:
The fact that there is no medium through which EM waves travel was established over a hundred years ago through what is called the "Michaelson-Morley Experiment" which is of great importance (wiki it). It was this understanding that light didn't propagate through any medium that made Einstein's theory of (special) relativity possible.
Why does a vacuum ("empty" space) have a permeability μ0 and a permittivity ε0? Why does sqrt(μ0/ε0) = 377 ohms (the sqrt of E/H in a plane wave)? why does 1/sqrt((μ0 ε0) = the speed of light?


α β γ δ ε ζ η θ ι κ λ μ ν ξ ο π ρ ς σ τ υ φ χ ψ ω
 
i am familiar w/ the michaelson-morley experiment. the exchange of photons makes more sense for me.are your questions rhetorical, bob s?
 
Bob S said:
Why does a vacuum ("empty" space) have a permeability μ0 and a permittivity ε0? Why does sqrt(μ0/ε0) = 377 ohms (the sqrt of E/H in a plane wave)? why does 1/sqrt((μ0 ε0) = the speed of light?


α β γ δ ε ζ η θ ι κ λ μ ν ξ ο π ρ ς σ τ υ φ χ ψ ω

Because when we defined our unit of force (the Newton) we made no attempt to make it map onto our unit of charge via coloumbs law. Thus you need conversion factors. Look up GAUSSIAN UNITS for a more natural set of units for EM.
 
Bob S said:
Why does a vacuum ("empty" space) have a permeability μ0 and a permittivity ε0? Why does sqrt(μ0/ε0) = 377 ohms (the sqrt of E/H in a plane wave)? why does 1/sqrt((μ0 ε0) = the speed of light?

Definitions. μ0 has a defined value and is not a measured (or measurable) quantity. And ε0 is defined to be 1/(c2[/μ0) so, naturally, 1/sqrt((μ0 ε0) = the speed of light.
 
thomasxc said:
i am familiar w/ the michaelson-morley experiment. the exchange of photons makes more sense for me.are your questions rhetorical, bob s?
Yes, I am familiar with all that, and the usefulness of permittivity and permeability in both physics and electrical engineering. The question I am asking what causes free space to have these properties? What is there in free space that leads to permittivity and permeability, in any system of units. Why isn't there a solution where free space is completely empty.
 
how do we know space is empty could it be the higgs field .
 
  • #10
A field is a set of numbers for all points in space. It has little to do with whether something is "empty" or not.
 

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