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    (Original post by Duke Flipside)
    Pineapolis, I can't say that I've heard anything like what you're suggesting, and I think the generally-accepted theory is that they travel at c...still, just because I haven't seen it doesn't mean you haven't. D'you have any links? *is an astrophysics geek, as you may've guessed...*

    Also, light does move through time...hence the reason we see the sun as it was eight minutes ago; if it didn't move through time it would have an infinite velocity, rather than a high-but-finite velocity.
    I'll see if I can dig out one of the links I had from a while back. One moment.
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    http://www.ldolphin.org/vanFlandern/gravityspeed.html

    There we go. It's a fairly long paper but the jist of it is that the speed of gravity must be greater than 2*10^10 m/s.
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    (Original post by Duke Flipside)
    Also, light does move through time...hence the reason we see the sun as it was eight minutes ago; if it didn't move through time it would have an infinite velocity, rather than a high-but-finite velocity.
    Light from the sun doesn't travel through time, it travels through space, but from our perspective it takes time for it to get to us. Light travels though space at light speed:
    (Original post by Brian Greene: The Elegant Universe)
    Something travelling at light speed through space has no speed left for motion through time. Thus light does not get old; a photon that emerged from the big bang is the same age today as it was then. There is no passage of time at light speed
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    Wouldn't attempting that kind of speed completely screw up the universe, or create a black hole or a singularity or something?

    (Physics, especially theoretical physics, leaves me a trembling heap of ignorance)
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    I have basically no grounding in any sort of advanced sciences at all. So apologies if these questions overlook very basic concepts, but...

    Why is it assumed that you'd suddenly acquire infinite mass at reaching the speed of light? It is, after all, simply another speed... I'd perhaps believe infinite mass would be required to reach infinite velocity, but the speed of light is not infinite - far from it.

    (Original post by F1 fanatic)
    Also as was kind of said causality would screw up if you could travel faster than light. So effect would come before cause. Which would be rather weird. Plus although you would see only an image, surely seeing yourself would be weird enough. The point is we are separated from the stars by distance. The fact they are in the "past" is because they are far away. However, seeing into the past stood next to you wouldn't be allowed.
    Why not? If you travel faster than sound, you can hear yourself in the past. Surely sight is just another sense that you deceive yourself into relying upon as an ultimate source of experience? Imagine a blind man - for him, experiencing this wouldn't be weird at all...
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    (Original post by LibertineNorth)
    I have basically no grounding in any sort of advanced sciences at all. So apologies if these questions overlook very basic concepts, but...

    Why is it assumed that you'd suddenly acquire infinite mass at reaching the speed of light? It is, after all, simply another speed... I'd perhaps believe infinite mass would be required to reach infinite velocity, but the speed of light is not infinite - far from it.



    Why not? If you travel faster than sound, you can hear yourself in the past. Surely sight is just another sense that you deceive yourself into relying upon as an ultimate source of experience? Imagine a blind man - for him, experiencing this wouldn't be weird at all...
    If you travel faster than sound you never hear yourself. Because it can never catch up. Hence in a jet you never hear the sonic boom.

    Also whether or not you see it isnt the point. The point is you can affect things if they are close to you. If you met yourself then you could interact with yourself and you can start creating all sorts of stupid paradoxes. The killing yourgrandfather 1 being the classic 1.

    Edit: In answer to your other question the maths says it is. Energy and mass are equivalent from E=(gamma-1)*mc^2. So if you gain KE to speed up you equivalently gain mass. The more mass you have the more energy you need to put in to speed up further. And the gamma constant means that there comes a limit when you can pick up no further speed and any further energy just adds to the mass. So you need infinite energy and therefore infinite mass to reach c.

    That is why paticles that do travel at c - ie photons, are massless
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    (Original post by F1 fanatic)

    Edit: In answer to your other question the maths says it is. Energy and mass are equivalent from E=(gamma-1)*mc^2. So if you gain KE to speed up you equivalently gain mass. The more mass you have the more energy you need to put in to speed up further. And the gamma constant means that there comes a limit when you can pick up no further speed and any further energy just adds to the mass. So you need infinite energy and therefore infinite mass to reach c.

    That is why paticles that do travel at c - ie photons, are massless
    For the last time, you do not "gain mass".
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    (Original post by LibertineNorth)

    Why is it assumed that you'd suddenly acquire infinite mass at reaching the speed of light? It is, after all, simply another speed... I'd perhaps believe infinite mass would be required to reach infinite velocity, but the speed of light is not infinite - far from it.
    Einstein postulated that time is not absolute - that is that if I measure something on my watch, your watch (despite being the same make and model) may not agree - unlike Newtonian physics where all clocks everywhere read the same time.

    From here, Einstein said that the speed of light is constant in all inertial frames of reference. This means a frame where no force is felt, i.e. no acceleration. By taking C to be constant, you can then use the speed of light to measure times and distances etc. What follows (from the Lorentz transformations) is time dilation and length contraction, as well as the introduction of the gamma. It also follows that the simultaneity of events is not so clear in relativity.
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    (Original post by F1 fanatic)
    Edit: In answer to your other question the maths says it is. Energy and mass are equivalent from E=(gamma-1)*mc^2. So if you gain KE to speed up you equivalently gain mass. The more mass you have the more energy you need to put in to speed up further. And the gamma constant means that there comes a limit when you can pick up no further speed and any further energy just adds to the mass. So you need infinite energy and therefore infinite mass to reach c.
    1. (gamma-1)*mc^2 is not total energy, it is just kinetic energy.
    2. you don't gain mass (as said above)
    3. there is no such limit for the velocity tending toward c where acceleration becomes zero, it just becomes very small. The "limit" would be at v=c, but as we've all agreed, this is impossible.
    4. infinite energy is not equivalent to infinite mass, and infinite mass is not a requirement of travelling at v=c. My guess is that with an infinite mass, you couldn't accelerate the particle at all, let alone get it anywhere near c.
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    (Original post by F1 fanatic)
    If you travel faster than sound you never hear yourself. Because it can never catch up. Hence in a jet you never hear the sonic boom.

    Also whether or not you see it isnt the point. The point is you can affect things if they are close to you. If you met yourself then you could interact with yourself and you can start creating all sorts of stupid paradoxes. The killing yourgrandfather 1 being the classic 1.

    Edit: In answer to your other question the maths says it is. Energy and mass are equivalent from E=(gamma-1)*mc^2. So if you gain KE to speed up you equivalently gain mass. The more mass you have the more energy you need to put in to speed up further. And the gamma constant means that there comes a limit when you can pick up no further speed and any further energy just adds to the mass. So you need infinite energy and therefore infinite mass to reach c.

    That is why paticles that do travel at c - ie photons, are massless

    As for massless particles, p=mv is not entirely accurate.

    (Lorentz factor)
    a = [root(1 - v^2 / c^2)]

    (m-relativistic mass M-invariant mass)
    m = aM

    p = mv = aMv

    E = mc^2 = aMc^2 (the famous equation)

    E^2 - (pc)^2 = (mc^2)^2 (relativistic energy-momentum equation) --> so for where m=0

    E^2 - (pc)^2 = 0

    E = pc

    p = E / c --> therefore massless particles can have momentum (energy-momentum)

    The so called gamma constant (a) does not signify a limit where any energy adds to mass but a gradual asymptote where m = M/x where x tends to zero.
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    (Original post by dazmanultra)
    Einstein postulated that time is not absolute - that is that if I measure something on my watch, your watch (despite being the same make and model) may not agree - unlike Newtonian physics where all clocks everywhere read the same time.

    From here, Einstein said that the speed of light is constant in all inertial frames of reference. This means a frame where no force is felt, i.e. no acceleration. By taking C to be constant, you can then use the speed of light to measure times and distances etc. What follows (from the Lorentz transformations) is time dilation and length contraction, as well as the introduction of the gamma. It also follows that the simultaneity of events is not so clear in relativity.
    1. einstein postulated two things.. neither is that time isn't absolute. he showed that from his two postulates. (that there is no absolute velocity frame, and that the speed of light is constant in all frames)

    2. I don't think time dilation and length contraction follow from the lorentz transformations.

    not really anything wrong with what you said, Im just being fussy
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    (Original post by ghost101)
    Photons are not massless. This is evident in photoelectric emission.
    how exactly?
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    (Original post by john!!)
    how exactly?
    sorry ive made a correction - meant momentumless
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    (Original post by john!!)
    1. einstein postulated two things.. neither is that time isn't absolute. he showed that from his two postulates. (that there is no absolute velocity frame, and that the speed of light is constant in all frames)

    2. I don't think time dilation and length contraction follow from the lorentz transformations.

    not really anything wrong with what you said, Im just being fussy
    The notion of personal time may not have been one of his postulates, but it's an important point from SR.

    Interestingly enough:
    One of the most astounding predictions of special relativity was the idea that time is relative. More precisely, each observer carries their own personal clock and time flows different for different observers. This was a direct prediction from the Lorentz transformations and is called time dilation. Other effects can also be derived from the transformations, such as length contraction. The transformation of electric and magnetic fields was also found to be necessary in accordance with the relativity principle.
    http://en.wikipedia.org/wiki/Lorentz...tion_equations

    (Bold emphasis added myself)
    I don't remember much of SR to be far, we did it last year. Electromagnetism is harder.
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    (Original post by ghost101)
    As for massless particles, p=mv is not entirely accurate.

    (Lorentz factor)
    a = [root(1 - v^2 / c^2)]

    (m-relativistic mass M-invariant mass)
    m = aM

    p = mv = aMv

    E = mc^2 = aMc^2 (the famous equation)

    E^2 - (pc)^2 = (mc^2)^2 (relativistic energy-momentum equation) --> so for where m=0

    E^2 - (pc)^2 = 0

    E = pc

    p = E / c --> therefore massless particles can have momentum (energy-momentum)

    The so called gamma constant (a) does not signify a limit where any energy adds to mass but a gradual asymptote where m = M/x where x tends to zero.
    May all that criticism be a lesson to me not to dabble in things I havent done or looked at in over a year . Fair points though.
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    I can go faster that the speed of time! On a plane you can catch up with and overtake dawn! Thats going faster than the speed of light and time!
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    (Original post by Stikatoo)
    nothing's impossible because there is an infinite amount of time for it to happen in. I went back and added the word 'near' because we don't know what can be achieved in the future.
    Something exists. Is that impossible?
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    AH okay, yes the Lorentz were proposed before Einstein made his postulates about SR so yeah that's right. I don't think they were derived, just kind of a "stab in the dark" to explain Maxwells equations.
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    Lorentz Attractors are cool.
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    They definitely float my boat.
 
 
 
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