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Speed of light boundary ?

  1. Feb 4, 2013 #1
    Speed of light "boundary" ?

    I have a simple question :

    When everyone is talking about the "speed of light boundary" what is it relative to ?

    Speed is ALWAYS relative to "something" else, otherwise it doesnt even make any sense.

    Which brings a second point : if there is indeed a speed of light boundary (at least a boundary for "something else" to happen : infinite mass / dematerialize / instant travel you name it) it must be relative to a supposedly fixed point in the Universe, which must make authority FOR THE WHOLE UNIVERSE. Otherwise I don't see how the so called speed of light boundary can make any sense. It could be the "place" where the big bang happened (if you cope with that theory) meaning everything is expanding away from this point (center of the Universe).

    To me space "emptiness" can be compared to air. Just like soundwaves are vibrating through air (which is its basic construct) at a fixed speed limit, I would make the analogy that light is vibrating thru the basic construct of space/emptiness (which isnt "nothing" at all) at another fixed speed limit.

    Then space could be compared as a fluid just like wind would change the speed of sound relative to you (not the air). I would call this space wind, which is affected by gravity. Gravity would speed up that construct just like a blackhole swallows everything around it and opens a wormhole some say.

    Now back to the speed of light, in my mind the speed of light can only be relative to the construct it vibrates through (space/"emptiness") just like the speed of sound is relative to air.

    Now if you go faster than the speed of light relative to that construct (now this sets a reference...) then "something" might happen.

    Russians have already experienced fields reacting at far more than the speed of light, supposedly at infinite speed and they call them torsion fields, but it doesn't say more about matter ;)

    What are you thoughts about this ?
     
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  3. Feb 4, 2013 #2

    HallsofIvy

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    Re: Speed of light "boundary" ?

    The speed of "light boundary" is relative to everything except light. One of the crucial points of relativity, that makes it different from Newtonian physics, is that the speed of light, in any frame of reference is the same. I see light coming to me from a specific star at c, the "speed of light". If you were were moving directly toward that star at, relative to me, half the speed of light, you would also see light coming to you, from that star, at c.
     
  4. Feb 4, 2013 #3
    Re: Speed of light "boundary" ?

    I'm sorry but this doesnt make any sense.

    If light is a vibration then it needs a construct to vibrate into, just like sound is a vibration into air.

    Furthermore, can you please explain to me how you would measure the speed at which light comes at you ?

    Another thing, consider the sun : it shoots in every direction. So you are going to tell me the light coming from the sun in our direction goes away at the speed of light from the light that shoots from the sun in the opposite direction, and yet it comes to us at the speed of light ? So basically it goes to us at the speed of light and at half the speed of light at the same time ? This sounds ridiculous and stupid to me, excuse me.

    I must correct something. I was going to say this :

    - Im pretty sure if you go to some star say half the speed it's light comes at you, you will see it 2x times brigther or so, just like a police car or ambulance syren rushing at you in the streets will tone higher than when it goes away from you. And this is because light must vibrate in a construct.

    Just realized it is wrong for this reason : the higher tone is not due that the sound comes faster at you. It is due that the soudwaves are compressed, given the movement of the car. So the sound still goes and the speed of sound but to your hear at a higher frequency. So now speaking of light : im pretty sure you will see the star a different color !!! I dont know if you will see it brighter but you should, giving you get a higher quantity of light per units of time as you approach the star.

    It seems everyone overlooked that for anything to vibrate into, it needs a construct, which for light is etheral and that we can't mesure yet, but in "nothing", nothing can go through, because where there is "nothing", then nothing exists to hold what exists.
     
  5. Feb 4, 2013 #4

    ZapperZ

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    Re: Speed of light "boundary" ?

    This is based on a faulty starting premise.

    I have an electron sitting in space, stationary (in my frame). Due to it, there's an electrostatic E-field everywhere. Presumably, you have no issue with the E-field not needing a "construct" since nothing is vibrating here, ya?

    Now, I take the electron and shake it real fast. Now the E-field due to it is "vibrating" due to the motion of that electron. Voila! I've created light! Based on your "logic", you feel no need to have a medium when it is static, but now you switch gears and require a medium since you now detect oscillating E-field.

    Does this make "sense" to you that you are switching the rules that quickly?

    You need to examine what you are requiring.

    Zz.
     
  6. Feb 4, 2013 #5

    Dale

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    Re: Speed of light "boundary" ?

    It is relative to any frame of reference.

    More than a century ago this was the mainstream scientific thought. Unfortunately, despite decades of the most careful testing they were unable to detect this space wind. It was a concept that was eventually dropped as simpler explanations became available.
     
    Last edited: Feb 4, 2013
  7. Feb 4, 2013 #6
    Re: Speed of light "boundary" ?

    I don't say particle electrons don't need a construct, at all. As far as I know photons/electrons flip from from space-time to time-space, as wave and particle states, so yes it is vibrating imo and you can't hold an electron stationary can you ? Even if it's frozen 0K.

    I could say exactly the same thing based on what I just said. I don't think anyone proved light is more than a vibration as far as I know, or a flip-flop between wave state and particle-like state. Now there isnt "sound particules" as well.

    No I don't feel the need of a medium when it is static cuz it is never static. Your example is way too simplified.

    I have another simple physics (noob) question : does light lose frequency over time and distance ? That is, in "empty" space ?

    Thank you
     
  8. Feb 4, 2013 #7
    Re: Speed of light "boundary" ?

    Light, an electromagnetic wave, does not require any transmission medium. That's how sunlight gets to earth, for example, even though there is hardly anything in the 93,000,000 miles of space between us. So it's fundamentally different than, say, a water wave.

    If the distance is a stationary one, not like in our cosmological models where distances increase, a photon does not change it's color during transit...not anymore than an electron loses some charge in transit.
    But in expanding space, the behavior of photons and particles becomes more interesting. In one view, the above description applies. A photon is a photon and nothing changes as it moves through expanding space. What changes are the frames [references] of the observer relative to the emitter...a Doppler effect. [Like police radar]

    The other valid viewpoint is "of course the frequency changes in expanding space":A technical way to say this is "the wavelength is proportional to the scale factor".
    A less technical way to explain this is to note the early cosmic background microwave radiation was emitted at almost 3000 degrees K [when it was too hot for complex atoms to have formed] ; today we see it as about 2.73 degrees...it has 'cooled'....its wavelength is about 1090 times as long, and it about 1090 times cooler, than 13.4 B years ago when it was emitted. If it hadn't cooled, we could not exist because atoms could not.

    There are a number of discussions about this issue in these forums. It's an interesting issue in cosmology.
     
  9. Feb 4, 2013 #8

    ZapperZ

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    Re: Speed of light "boundary" ?

    This is goobly-gook.

    How do you think your radio antenna works?

    Way too simplified? An electrostatic situation that can be easily done in an undergraduate lab? Yet, it works to nullified your idea.

    Let's get this straight: you are USING the very concept that you don't believe in.

    And if you cannot provide proper physics or references to back your claim, this falls under personal, speculative ideas, which is in violation of the PF Rules that you had agreed to. Rather than trying to learn, you appear to be proud of your aggressive ignorance.

    Zz.
     
  10. Feb 4, 2013 #9

    Dale

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    Re: Speed of light "boundary" ?

    Where is the evidence of the medium even when it isn't static?
     
  11. Feb 4, 2013 #10

    robphy

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    Re: Speed of light "boundary" ?

    The following reply may not be satisfactory...
    but its answer is based on the geometry of Special Relativity
    ...and hopefully gets to the heart of the matter (without possible distractions).


    The speed of light is a boundary (i.e. unattainable) speed for all massive particles,
    from whatever frame of reference you view this. A massive particle may asymptotically approach that speed, but never attain it.

    I suspect part of the problem in appreciating this
    is that the speed of light is finite and
    that one is likely thinking with everyday Galilean intuition (specifically, with the addition of velocities).


    Consider this for a minute...
    in Galilean physics, the maximum signal speed is infinite.
    With respect to what frame of reference?
    It doesn't matter... that signal speed is infinitely far away.
    infinity - 5 = infinity.

    In special relativity, there is a similar notion for its maximum signal speed (the speed of light). There is a parameter called the rapidity or (spacetime-angle) that ranges (non-inclusively) from minus-infinity to plus-infinity, which is related to the velocity of massive particles by v=c tanh(rapidity), where tanh is the hyperbolic tangent. (This is a consequence of the geometric interpretation.) tanh ranges from (non-inclusively) -1 to 1.

    When the rapidity is zero, the velocity is zero.
    For small rapidities, v ~ c*(rapidity)... that is, the velocity is approximately-proportional to the rapidity. So, one often doesn't notice the distinction in everyday life... and, in fact, one may boldly extrapolate the apparent-proportionalities to larger velocities (and maybe even forget about the rapidity altogether). However, for larger rapidities and velocities, the proportionality-approximation fails... and it is a common mistake to ignore that.

    While one may make the rapidity as large as one likes, a rapidity of infinity (which corresponds to the speed of light) is not attainable:
    very large + anything finite < infinity.
    With respect to what frame of reference?
    It doesn't matter... that rapidity is infinitely far away.
    infinity - 5 = infinity.


    Here's a geometric argument that doesn't explicitly use the rapidity idea.
    On a position vs time graph, starting from the origin of the x-axis at a given starting event, have a bunch of runners with different velocities mark the start with a firecracker and mark when their wristwatches read 1 hour with another firecracker. On a position vs time graph, those "my watch reads 1 hour" events lie on a hyperbola centered at the start event. No matter what your speed, your "my watch reads 1 hour" event must lie on that hyperbola. On that graph, that hyperbola has an asymptote (actually two) which is NOT part of that hyperbola, and which corresponds to an unattainable slope, an unattainable velocity (the velocity of light).
    With respect to what frame of reference?
    It doesn't matter...
    if the diagram were redrawn from one of the other runner's frame of reference,
    although different runners would have different slopes than before,
    one would still see the same hyperbola... and one would still see the same asymptote.

    So, according to special relativity, the speed of light is unattainable by massive particles [regardless of the frame of reference].
     
    Last edited: Feb 4, 2013
  12. Feb 4, 2013 #11

    Nugatory

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    Re: Speed of light "boundary" ?

    You work with single flash of light. You know when and where it was emitted relative to you (establishing this is trickier than it sounds, and the words "relative to you" are more important than they seem at first, but it can be done). You know when and where the flash of light hits your eye relative to you (this is a lot easier as you know where you are and a glance at your wristwatch will tell you when). Now you can calculate the speed of light using speed=distance/time.

    Sounds ridiculous, but....
    (There are real problems with talking about the speed of light relative to ligh, like for example you can;t use the measurement process I described above, so let's consider two spaceships, each flying away from the star in opposite directions at .5c relative to the star, one heading straight towards you and one away). You might expect that someone on one of the ships would see the other one moving away at .5c+.5c=c, thereby traveling at the speed of light relative to the other ship. Not so, it turns out that speeds don't add that way. Google around for "relativistic addition of velocity" to see the right answer.

    Red-shifted if you and the star are moving apart, blue-shifted if moving closer, and yes, more light energy per unit of your time if moving closer.
     
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