The propagation of light through a vacuum.

[thomasxc]

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

 

[maverick_starstrider]

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.

 

[Bob S]

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

 

[thomasxc]

i am familiar w/ the michaelson-morley experiment. the exchange of photons makes more sense for me.are your questions rhetorical, bob s?

 

[maverick_starstrider]

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.

 

[negitron]

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/(c^{2[/μ₀) so, naturally, 1/sqrt((μ₀ ε₀) = the speed of light.}

 

[Bob S]

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.

 

[negitron]

Once again, μ₀ and ε₀ are not real, physical properties of vacuum free space--neither is actually measured. They are both simply defined values:

http://en.wikipedia.org/wiki/Permittivity_of_free_space
http://en.wikipedia.org/wiki/Permeability_of_free_space

 

[cragar]

how do we know space is empty could it be the higgs field .

 

[Vanadium 50]

A field is a set of numbers for all points in space. It has little to do with whether something is "empty" or not.