Light as a Relativistic invariant

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Discussion Overview

The discussion revolves around the concept of the speed of light as a relativistic invariant, exploring the historical and logical steps taken by physicists to arrive at the conclusion that the speed of light (c) is constant in all reference frames. Participants delve into the contributions of various physicists, particularly Einstein, and the implications of Maxwell's equations and the Michelson-Morley experiment.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant expresses curiosity about the logical steps taken by physicists to conclude that c is constant across reference frames, suggesting a reverse engineering approach to understanding this concept.
  • Another participant asserts that the realization of c's constancy was primarily due to Einstein's work, referencing specific books for further reading.
  • A participant questions the ability of another to summarize complex ideas succinctly, indicating a perceived lack of understanding based on a misspelling of Einstein's name.
  • In response to the previous point, a participant argues that the misspelling may not necessarily indicate ignorance and highlights the commonality of such errors online.
  • One participant proposes that Maxwell's equations imply the speed of light is invariant in all inertial frames, noting that these equations are not Galilean invariant, which was a previously held assumption.
  • Another participant provides a historical context, referencing Galileo's principles of relativity and the implications of electromagnetic experiments, particularly the Michelson-Morley experiment, which suggested that light's speed is the same in all frames of reference.

Areas of Agreement / Disagreement

Participants express differing views on the historical contributions to the understanding of light's speed, with some attributing it primarily to Einstein while others emphasize the role of Maxwell's equations and experimental evidence. The discussion remains unresolved regarding the definitive factors leading to the conclusion of c's invariance.

Contextual Notes

Participants reference various historical figures and experiments, but there is no consensus on which specific contributions are most significant or how they interrelate. The discussion includes assumptions about the audience's prior knowledge and understanding of the topic.

FunkyDwarf
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Hey guys,

I know this subject is a bit of an old chesnut but i thought id ask it anyway.

What logical steps did the various physicists take to realize that c was constant in all reference frames? I've sort of found some weird ways to justify that fact in my head, but its more reverse engineering than actually arriving at it from nothing.

Id like to know how these guys game up with this, was it just lortenz's work or something more.

Thanks
-G
 
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Einstein, in a word

FunkyDwarf said:
What logical steps did the various physicists take to realize that c was constant in all reference frames?

Actually, that was all Einstein. Two good books:

Abraham Pais, Subtle is the Lord, Oxford University Press, 1982.

Peter Galison, Einstein's clocks, Poincare's maps, Norton, 2003.
 
At the risk of sounding impatient could you not put it in a nutshell for me? I already have einstines original book on SR and GR so I've got most of the basics down.
 
FunkyDwarf said:
At the risk of sounding impatient could you not put it in a nutshell for me? I already have einstines original book on SR and GR so I've got most of the basics down.


No you don't. The types that misspell his name the way you did and who use lower case don't know (and don't deserve to be taught).
 
nakurusil said:
No you don't. The types that misspell his name the way you did and who use lower case don't know (and don't deserve to be taught).
That's a bit harsh, isn't it? It's common on the internet to not capitalise proper nouns (this is partially due to URLs not being case sensitive, and partially laziness). As for the misspelling, we are not yet sure if it's a typo or a case of ignorance.

FunkyDwarf said:
could you not put it in a nutshell for me?
Once convincing argument is that according to Maxwell's equations, the speed of light is c in all inertial frames. Another way of saying the same thing is that Maxwell's equations aren't Galilean invariant (which was assumed to be the invariance of the universe until the Lorentz group was discovered).
 
Last edited:
Thanks, masudr!

And FunkyDwarf, don't worry about nakurusil; speaking for myself, I know I can get a bit cranky at times.

To some extent this might be a function of not knowing whether one is addressing a graduate student (whom one would expect to follow up citations by reading the books mentioned), or a younger person who might not yet appreciate the "scholarly ethos" (according to which it could be considered a bit rude to demand that I summarize a book for you). But don't worry, I am not holding you to that because I am assuming you didn't know this.
 
"In a nutshell": Gallileo asserted that if you were riding in a closed carriage (no windows) at a constant speed on a perfectly level, smooth surface, there is no way for you to determine your speed or even if you are moving: that's referred to as "Gallilean relativty". Essentially, that is due to "F= ma". In order to have a force to feel or to move a pointer or other indicator of speed.

But Galilleo didn't know about electricty: magnetic force on an electron depends upon the speed of the electron relative to the magnetic field. A result of that is that Maxwells equations for eletro-magnetic fields have a "speed" term. Doing an "electro-magnetic" experiment (i.e. light) should tell you your speed relative to light itself. The Michaelson-Morley experiment was designed to do that but gave a null result- leading to the conclusion that every frame of reference has the same speed relative to light (or, conversely, light has the same speed relative to every frame of reference).
 
Ah ok, so would it be fair to say that the michaelson-morley experiment (no capitals?! oh the horror!) would be the defining factor in c being the same in all reference frames?
 

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