Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Second Postulate of Special Relativity

  1. Mar 8, 2005 #1
    This would make perfect sense if light was instataneous; i.e., if c equals (that's right, equals, not approaching) infinity distance unit / time unit. But it isn't. How does one make sense of it?
  2. jcsd
  3. Mar 8, 2005 #2


    User Avatar

    Staff: Mentor

    Its simple once you abbandon the concepts of absolute time and distance. Abbandoning those concepts is, admittedly, pretty difficult.
  4. Mar 8, 2005 #3


    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    How come, when one tries to force a square (cube) object through a round hole, and have trouble doing it, one always put the blame on the round hole and very seldom on the fact that one has a square object?

    The WHOLE point of special relativity is that your "sense" is built on a set of biases based on the perception that light is instantaneous. It isn't nature that is causing the problem, it's our built-in prejudices that we acquired from the classical world. In this very case, there is no need for light to be instantaneous, because the fault lies in our "common sense".


    "Common sense is the collection of prejudices acquired by age eighteen."
    -- A. Einstein
  5. Mar 8, 2005 #4


    User Avatar

    Staff: Mentor

    You make sense of it by accepting experimental results on the speed of light emitted by moving objects, and giving up the preconceived notion, based on extrapolation from everyday experience, that light must behave like slowly-moving material objects such as baseballs.

    it does take some time to become comfortable with the idea that the speed of a particular light beam or pulse is the same for all inertially-moving observers. You have to carry out (or at least follow) some of the calculations that are based on this idea, and see that they agree with actual experimental results, and do not introduce any contradictions in actual direct physical observations.
  6. Mar 10, 2005 #5
    Einstein's second postulate is best understood from the Lorentz transformation. Fortunately, there are derivations of the Lorentz transformation that do not require presupposing Einstein's second postulate. :smile:

  7. Mar 10, 2005 #6


    User Avatar
    Science Advisor
    Homework Helper

    From a theorist's perspective,deriving consequences (LT) from the axioms (Einstein's postulates) is the only logical way.

  8. Mar 10, 2005 #7
    There are axiom sets for special relativity possessing greater elegance and richness than the postulates advocated by Einstein one hundred years ago.

    I believe it would be smart to retire Einstein's two postulates as the academic standard for deriving special relativity and to adopt an approach to teaching special relativity that is conceptually simpler, more insightful and less confusing to students. I propose that beginning math and physics students should learn how to derive the Lorentz transformation from Newton's first law of motion and the homogeneity of time alone.

    See section 4 of http://www.everythingimportant.org/relativity/special.pdf

    The ineffectiveness of standard university instruction in the concept of time in special relativity has been carefully researched and documented. http://arxiv.org/ftp/physics/papers/0207/0207109.pdf
    Isn't it time to try something new?
  9. Mar 10, 2005 #8


    User Avatar
    Science Advisor
    Homework Helper

    I think the axiomatization of SR and QM (especially QM) is absolutely remarkable...They need no change.Experiment can overthrow them (the axioms),but for at least 100 yrs exactly,it just couldn't...

Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: Second Postulate of Special Relativity