I Lorentz derivation of length contraction in electrodynamics

Babbeus
Messages
2
Reaction score
0
Here is a quote from this website:

What Lorentz was able to show was that Maxwell's theory of electromagnetism predicted precisely this much longitudinal contraction.To get this result, Lorentz modeled matter composing a body as a large collection of electric charges, all held together in equilibrium by electric and magnetic forces.
lattice_at_rest.png

The equilibrium was disturbed if the entire object was set in motion. Moving electric charges create magnetic fields that in turn act back of electric charges. All these changes settle out into a new equilibrium configuration. What Lorentz could show was that new configuration consists in a contraction of the body in the direction of motion in just the amount needed to eradicate a possible result from the Michelson Morley experiment.

lattice_moving.png

My question is: is this derivation of length contraction considered to be sound and correct today? Are they treated in modern textbooks?
 
Physics news on Phys.org
Length contraction was postulated by George FitzGerald and H.A Lorentz (1892) to explain the negative outcome of the Michelson–Morley experiment and to rescue the hypothesis of the stationary aether .

It was considered an ad hoc hypothesis, because at this time there was no sufficient reason to assume that intermolecular forces behave the same way as electromagnetic ones.

Eventually, Albert Einstein (1905) was the first to completely remove the ad hoc character from the contraction hypothesis, by demonstrating that this contraction did not require motion through a supposed aether, but could be explained using special relativity, which changed our notions of space, time, and simultaneity.

Now a days the special theory of relativity and Lorentz Transformations are used to derive contraction as a consequence of STR.
one can see details of historical development in <https://en.wikipedia.org/wiki/Length_contraction>
 
Last edited by a moderator:
drvrm said:
Length contraction was postulated by George FitzGerald and H.A Lorentz (1892) to explain the negative outcome of the Michelson–Morley experiment and to rescue the hypothesis of the stationary aether .

It was considered an ad hoc hypothesis, because at this time there was no sufficient reason to assume that intermolecular forces behave the same way as electromagnetic ones.

Eventually, Albert Einstein (1905) was the first to completely remove the ad hoc character from the contraction hypothesis, by demonstrating that this contraction did not require motion through a supposed aether, but could be explained using special relativity, which changed our notions of space, time, and simultaneity.

Now a days the special theory of relativity and Lorentz Transformations are used to derive contraction as a consequence of STR.
one can see details of historical development in <https://en.wikipedia.org/wiki/Length_contraction>

Thank you very much for your reply.
If I understand well what happened I would say the objections of "ad hoc" hypothesis addressed to Lorentz actually vanished not just because of Einstein's revolution but also because Loretnz's hypothesis that intermolecular forces are electromagnetic turned out to be true. Is this right? So it makes sense to consider the possibility that Lorentz derivation was indeed sound/correct and if it is so maybe it would be remarkable enough to deserve to be treated in textbook today. Is this the case?
 
Last edited by a moderator:
The question that Lorentz left open but Einstein answered is what happens to matter that is not held together by electromagnetic forces. Michelson and Morley's interferometer was built on a solid base. But what would happen to an interferometer with mirrors floating freely in vacuum? Einstein says that it will behave the same way as the one with the solid base. But the argument you laid out above gives no reason to expect the distance between free-floating unconnected mirrors to change. That makes it a detailed application of Einstein's more general argument to the case of solid matter, I think.
 
Thread 'Can this experiment break Lorentz symmetry?'
1. The Big Idea: According to Einstein’s relativity, all motion is relative. You can’t tell if you’re moving at a constant velocity without looking outside. But what if there is a universal “rest frame” (like the old idea of the “ether”)? This experiment tries to find out by looking for tiny, directional differences in how objects move inside a sealed box. 2. How It Works: The Two-Stage Process Imagine a perfectly isolated spacecraft (our lab) moving through space at some unknown speed V...
Insights auto threads is broken atm, so I'm manually creating these for new Insight articles. The Relativator was sold by (as printed) Atomic Laboratories, Inc. 3086 Claremont Ave, Berkeley 5, California , which seems to be a division of Cenco Instruments (Central Scientific Company)... Source: https://www.physicsforums.com/insights/relativator-circular-slide-rule-simulated-with-desmos/ by @robphy
Does the speed of light change in a gravitational field depending on whether the direction of travel is parallel to the field, or perpendicular to the field? And is it the same in both directions at each orientation? This question could be answered experimentally to some degree of accuracy. Experiment design: Place two identical clocks A and B on the circumference of a wheel at opposite ends of the diameter of length L. The wheel is positioned upright, i.e., perpendicular to the ground...
Back
Top