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I Can the speed of light be constant and absolute?

  1. May 29, 2018 #1
    Hi all
    I have struggled with the assumptions that the speed of light is absolute and constant. I have some logic to this which is based on the common assumptions that light behaves both as a wave and a particle. It is also based on light having mass, the effects of heat and vacuum environments. Without going into details, does anyone have views on this or study it?

    Cheers
    Matt
     
  2. jcsd
  3. May 29, 2018 #2

    russ_watters

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    Welcome to PF!

    Constant and the same for all observers is a subset of absolute, isn't it?

    In any case, I'm sorry but basically everything else you said about light is wrong. Please start by reading this and let us know if there are things you still need cleared up:

    https://en.m.wikipedia.org/wiki/Special_relativity
     
  4. May 29, 2018 #3
    Thanks Russ. Will do.
     
  5. May 29, 2018 #4

    Drakkith

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    It's not clear what you're looking for. Are you asking for papers or articles giving the theoretical foundation supporting the invariant nature of the speed of light? If so, I recommend Einstein's original paper on special relativity:
    https://einsteinpapers.press.princeton.edu/vol2-trans/154
     
  6. May 31, 2018 #5
    Hi Russ
    Thanks for the link and direct feedback. I should have posted the comment as a question, not statement so I understand why you said it was wrong.

    I have read through the link you sent and it does make me ask more questions. One in particular is that if space-time cannot tolerate or prohibits motion faster than the speed of light (c) then c squared cannot be achieved, making e=mc2 a false formula?
     
  7. May 31, 2018 #6

    russ_watters

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    C2 has units of m2/s2. It isn't a speed. It really isn't anything except most of the units for energy. Completed, it is kg-m2/s2, or just J (Joules); the unit for energy. This should look similar to you to the equation for Newtonian kinetic energy, which also contains speed squared.

    This is a common misunderstanding, caused by not recognizing how integral the units are to the equations. They aren't just doing math to numbers. Indeed, it is often useful to use the units without numbers!
     
  8. May 31, 2018 #7
    Got it thanks.

    To ask a question in my most logical way and why I joined this forum....if it is pure supposition and wrong, let me know. Likewise if it is an interesting question for a layperson.

    I was speculating in my layperson mind that: if it is true that light behaves / has properties of both waves and particles (is this wrong?)
    Then
    Particles behave differently under both extreme pressure and heat.
    If
    We look at a macro level, pressure and heat exist to extremes is black holes and supernovas respectively.
    So
    Particle light behaviour should be different and it's speed should be faster.
    Then
    Our assumptions about celestial bodies being x million light years away is false and they are in fact closer.

    To tell me these factors have been considered could be naive because "postulates" that support current thinking have not been proven in these conditions.
     
  9. May 31, 2018 #8
    Thanks. So it's an acceleration formula not velocity.
     
  10. May 31, 2018 #9

    russ_watters

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    I would usually answer this question "yes", which could get me in trouble with the physicists here (I'm an engineer) and in this case would lead you down this wrong path you are on. Simply put, just because light has some behaviors in common with particles (or waves), doesn't mean it has all the behaviors in common with particles (or waves). At this point, to avoid the confusion over what it does and doesn't have in common with particles and waves, physicists would say light is neither [classical] particles or waves, but a separate type of entity that has its own specific set of properties/behaviors.

    Fluid pressure is not one of those properties/behaviors.
    While it's true that there are some limitations to our knowledge/understanding, I'd caution you to not speculate on where those limitations are. You're basically suggesting that thousands of PhD physicists who individually have spent tens of thousands of hours studying the behavior of light haven't thought this through as far as you have. You may get some gruff responsese to that suggestion...
     
  11. May 31, 2018 #10

    russ_watters

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    No, acceleration is m/s2. As I said, C2 is most of a forumula for energy.
     
  12. May 31, 2018 #11
    Thanks Russ
    I am a middle aged person who enjoyede matriculation physics only. These types of questions have stuck with me for a long time and, based on your reply, is a somewhat valid and inquisitive question? By no means do I want to be disrespectful to anyone regarding the postulates comment. Sorry.
     
  13. May 31, 2018 #12
    OK but e is the output here (being joules or energy). The two inputs are mass and C...I never memorised formula but rembered them by the story...if you take a mass and accelerate it to the speed of light squared it will give off a huge amount of joules. The key here for me was accelerate it to c2. It will give off joules over the acceleration curve but you will/cannot reach the end velocity of c2...you will respond huge joules even before you get to c1....
     
  14. May 31, 2018 #13

    russ_watters

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    Somewhat. But mostly at the starting question. You took the logic pretty far based on the incorrect premise though. You're doing fine, I just don't want you to waste your own time or get in trouble going so far down a closed road, when reading the sign at the intersection could have avoided it.
     
  15. May 31, 2018 #14

    berkeman

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    Wowie, that makes no sense... :wink:
     
  16. May 31, 2018 #15
    Really? And your feedback is constructive how?
    Thanks. Appreciate the constructive advice. I will keep reading before posting.
     
  17. May 31, 2018 #16

    russ_watters

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    Well, that's actually not what that equation is for. What it tells you is the energy equivalent of mass; it's what you get when an amount of mass is converted to energy.
    https://en.wikipedia.org/wiki/Mass–energy_equivalence

    What you are describing is [kind of] the Relativistic Kinetic Energy equation (which the mass/energy equivalence is simplified from). It actually goes to infinity as you approach C.
    https://en.wikipedia.org/wiki/Kinetic_energy#Relativistic_kinetic_energy_of_rigid_bodies

    And again: the speed is just C. Not C2.
     
  18. May 31, 2018 #17

    berkeman

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    Well, I couldn't find one thing correct in it to try to build on, sorry.

    For example, this makes no sense no matter how hard I try to figure out what you are trying to say:
    It seems it would be best for you to spend some time at Wikipedia or Hyperphysics learning some basic stuff. I'll see if I can find some links to recommend...
     
  19. May 31, 2018 #18
    It is fine. Russ actually understood it and has already clarified it for me.
     
  20. May 31, 2018 #19

    berkeman

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    Yeah, Russ is pretty good at that! :smile:
     
  21. May 31, 2018 #20

    PeroK

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    If you choose units where ##c = 1## then ##c## and ##c^2## disappear from the formulas. You then have, for example:

    ##E = m##

    In any case, this is the formula for the energy of a massive particle at rest. Speed doesn't come into it. And it doesn't apply to light, which has no mass and no rest energy.
     
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