Insights Blog
-- Browse All Articles --
Physics Articles
Physics Tutorials
Physics Guides
Physics FAQ
Math Articles
Math Tutorials
Math Guides
Math FAQ
Education Articles
Education Guides
Bio/Chem Articles
Technology Guides
Computer Science Tutorials
Forums
Classical Physics
Quantum Physics
Quantum Interpretations
Special and General Relativity
Atomic and Condensed Matter
Nuclear and Particle Physics
Beyond the Standard Model
Cosmology
Astronomy and Astrophysics
Other Physics Topics
Trending
Featured Threads
Log in
Register
What's new
Search
Search
Search titles only
By:
Classical Physics
Quantum Physics
Quantum Interpretations
Special and General Relativity
Atomic and Condensed Matter
Nuclear and Particle Physics
Beyond the Standard Model
Cosmology
Astronomy and Astrophysics
Other Physics Topics
Menu
Log in
Register
Navigation
More options
Contact us
Close Menu
JavaScript is disabled. For a better experience, please enable JavaScript in your browser before proceeding.
You are using an out of date browser. It may not display this or other websites correctly.
You should upgrade or use an
alternative browser
.
Forums
Physics
Special and General Relativity
How to rule out that the speed of light was different in the past?
Reply to thread
Message
[QUOTE="vanhees71, post: 6848162, member: 260864"] It's a matter of definition, and within the SI ##c## is defined, and both ##\epsilon_0## and ##\mu_0## must be measured somehow. It's of course enough to measure one of them and then use the relation to ##c## to calculate the other. Historically it was the other way around: the analogue of ##\epsilon_0## and ##\mu_0## was known in the 19th century from measuring the relation of the charge in electrostatic and magnetostatic units (Kohlrausch and Weber 1855, measuring the charge on a Leiden bottle by measuring forces on test charges (electrostatic measurement) and comparing it to the magnetic flux due to the current when discharging it (magnetostatic measurement)). Then famously Maxwell discovered his equations of the electromagnetic field, i.e., he added the "displacement current" to the Ampere Law, as it was known from action-at-a-distance models (e.g., a la Neumann) at the time, and predicted the existence of electromagnetic waves with a phase velocity given by the said relation between electrostatic and magnetostatic units of charge, which is analogous to ##c=1/\sqrt{\epsilon_0 \mu_0}## when using SI units. The resulting value was pretty close to the then known speed of light, so that Maxwell could conjecture that light might be just electromagnetic waves. [/QUOTE]
Insert quotes…
Post reply
Forums
Physics
Special and General Relativity
How to rule out that the speed of light was different in the past?
Back
Top