5

Marc Lange writes (page 29)

It was known by about the 19th century that any action at a distance involving electric or magnetic forces would be retarded and so undermine not only spatial locality, but also temporal locality.

How was it discovered in the 19th century that electric or magnetic forces were not instantaneous?

I would be interested in survey articles, but I am mainly interested in reading how those who discovered the result described what they found.

Lange, M. (2002). An Introduction to the Philosophy of Physics Locality, Fields, Energy, and Mass. Blackwell Publishing.

Frank Hubeny
  • 239
  • 1
  • 3
  • 8
  • Does Mr. Lange provide a reference or bibliography entry for his claim? (one would hope so!) – Carl Witthoft May 07 '19 at 13:13
  • @CarlWitthoft He does not provide a reference, but I don't think it is relevant to his philosophical, rather than historical, approach to fields. He explains why he focuses on electromagnetic fields rather than gravitational fields. The belief in instantaneous propagation is not strong. – Frank Hubeny May 07 '19 at 15:04

1 Answers1

4

This was noticed when observations of eclipses of Jupiter satellites deviated from prediction. Before that there could be only speculations (and these speculations existed from antiquity). Jupiter satellites gave the first hard evidence.

From the very beginning, Jupiter satellites were proposed by Galileo as a natural clock for determination of longitude. For that reason, very careful observations were made, and finally the disagreement with Kepler laws was found. This happened in 17th century.

Romer and Huygens conjectured that the reason is the finite speed of light and measured it (assuming that Jupiter satellites do obey Kepler laws). They obtained a number which was not very precise but of the right order of magnitude.

Since then observations were made more and more precise.

By the way, Jupiter satellites gave the most precise way of synchronizing clocks at different locations (=measuring of longitude) until the invention of telegraph. But the method could only be applied on land, not on a ship.

https://gizmodo.com/how-the-speed-of-light-was-first-measured-1138348467

That other electromagnetic oscillations are spread with the same speed as light was discovered by Maxwell.

Alexandre Eremenko
  • 48,930
  • 3
  • 80
  • 177
  • This turns the question into "when was it realized that light was an electric and/or magnetic force"? – Mark May 06 '19 at 20:27
  • @Mark: But this is well known: Maxwell made this discovery. – Alexandre Eremenko May 06 '19 at 21:14
  • You should probably add that to your answer, then. – Mark May 06 '19 at 21:15
  • Are there experiments that show electric attraction or magnetism travel at finite speed? (Without using light and drawing the conclusion from Maxwell by computation.) Can it be observed directly? – Gerald Edgar May 07 '19 at 12:16
  • @Gerald Edgar: Nowadays, yes. Every time you measure a distance to an object with a radar, you use this finite speed. Also when you communicate with an object in the space, sufficiently remote. But of course radio waves were discovered after Maxwell, and due to Maxwell. – Alexandre Eremenko May 07 '19 at 16:37
  • OK ... Can we observe finite speed for electricity or for magnetism. Not using finite speed of electromagnetic radiation and then theoretical computations. I assume this is what Marc Lange means in the quote. – Gerald Edgar May 07 '19 at 17:25
  • @GeraldEdgar First you need to define what you mean by "electricity" and by "magnetism" if you don't allow for a propagating E-M field. – Carl Witthoft May 07 '19 at 17:35
  • I am just trying to interpret the original quote. "...any action at a distance involving electric or magnetic forces". Was it, indeed (as seemingly implied by Lange) known that these speeds were finite, before it was known that they were connected to any sort of radiation? Similarly, much more recently, physicists have tried to observe that the speed of gravitation is finite ... but can that be observed separately from observing "gravitational waves"? – Gerald Edgar May 07 '19 at 17:41
  • He is taking about the speed of electric fields and magnetic fields. That's a good question. Does the changed position of charge isntantaneouly affects the force on other charge. When did people realise it and how? – Arsenal Creation Jan 13 '23 at 13:50