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Thread: Have we got speed/time backwards?

  1. #1 Have we got speed/time backwards? 
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    So, they say that the speed of light is the universal speed limit. And, the nearer you get to it, the slower time passes by. As in, the slower things happen in the sub atomic level...

    It sounds awfully like the speed of light is actually Zero.


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  3. #2  
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    Quote Originally Posted by nandoanalog View Post
    It sounds awfully like the speed on light is actually Zero.
    If that were true then light wouldn't propagate and everywhere would be dark.


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  4. #3  
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    Quote Originally Posted by Dywyddyr View Post
    Quote Originally Posted by nandoanalog View Post
    It sounds awfully like the speed on light is actually Zero.
    If that were true then light wouldn't propagate and everywhere would be dark.
    I'm not quite sure that light actually propagates.
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    Quote Originally Posted by nandoanalog View Post
    I'm not quite sure that light actually propagates.
    Wave propagation - Wikipedia, the free encyclopedia
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    What's getting me, is that time doesn't happen if you're going at the speed of light (right?). Which is something that light does. So, does time happen to a photon?
    (and somehow, space expansion is clouding the whole thing in my mind too)
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  7. #6  
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    Quote Originally Posted by nandoanalog View Post
    I'm not quite sure that light actually propagates.
    So, when you turn on a light bulb you're left in the dark?
    If light didn't propagate then, essentially, there'd be no light.
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  8. #7  
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    Quote Originally Posted by nandoanalog View Post
    What's getting me, is that time doesn't happen if you're going at the speed of light (right?).
    Not really. If you extrapolate time dilation to the speed of light then the photon's time as seen by us would slow to nothing. However, that is not really a valid frame of reference, as you end up dividing by zero.

    and somehow, space expansion is clouding the whole thing in my mind too
    As that seems to be irrelevant, this probably just indicates that you haven't fully understood things.
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    Quote Originally Posted by Dywyddyr View Post
    Quote Originally Posted by nandoanalog View Post
    I'm not quite sure that light actually propagates.
    So, when you turn on a light bulb you're left in the dark?
    If light didn't propagate then, essentially, there'd be no light.
    Sure, it obviously looks like light propagates. As it also looks like the sun goes round the earth. As it also looks like things touch each other.

    It's just that, the faster we appear to go, the slower time goes by. So, time and movement, seem have a linear connection. It makes me think that time, is just the rate at which events occur. And by events, I mean things moving. No movement, no time. Which really makes me think that the speed limit (be it light speed or not) has actually a value of zero.

    Plus, what defines velocity? We need a reference point to know that something has a velocity, right? And that reference point can not be a point in space, because otherwise time wouldn't go by to anything, because things move FTL from each other in a cosmic scale.

    So, shouldn't the reference point of velocity be Zero? Specially if said velocity limit seems to be unbreakable? It surely makes more sense to be impossible to go bellow zero velocity, than to go above a positive valued velocity...
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    Quote Originally Posted by Strange View Post

    and somehow, space expansion is clouding the whole thing in my mind too
    As that seems to be irrelevant, this probably just indicates that you haven't fully understood things.

    Of that, you can be sure.
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  11. #10  
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    Quote Originally Posted by nandoanalog View Post
    [ Plus, what defines velocity? We need a reference point to know that something has a velocity, right? And that reference point can not be a point in space, because otherwise time wouldn't go by to anything, because things move FTL from each other in a cosmic scale.
    Speed is only relative. You can measure speed relative to whatever is convenient. We measure the speed of cars relative to the road. We measure the speed of satellites relative to a stationary Earth. We measure the movement of galaxies relative to the cosmic microwave background. They are all arbitrary choices for convenience and simplicity.

    So, shouldn't the reference point of velocity be Zero? Specially if said velocity limit seems to be unbreakable? It surely makes more sense to be impossible to go bellow zero velocity, than to go above a positive valued velocity...
    Well, I suppose one reference point is zero. It might be better to think of the speed of light as infinity; a value you can get as close as you want to but never reach. But it is more conventional to think of it as 1 (in natural units).
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    Quote Originally Posted by nandoanalog View Post
    Sure, it obviously looks like light propagates. As it also looks like the sun goes round the earth.
    Apples and oranges.
    If light didn't propagate then there wouldn't be light available for vision.

    It's just that, the faster we appear to go, the slower time goes by.
    Depends on where your reference point is.

    Which really makes me think that the speed limit (be it light speed or not) has actually a value of zero.
    But it doesn't.

    So, shouldn't the reference point of velocity be Zero?
    Relative to what?

    Specially if said velocity limit seems to be unbreakable? It surely makes more sense to be impossible to go bellow zero velocity, than to go above a positive valued velocity...
    Er, if the speed of light is zero and that's the maximum limit then, by your reasoning, any positive speed is impossible.
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    You're not getting it.
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    Quote Originally Posted by nandoanalog View Post
    You're not getting it.
    Perhaps you are not explaining it properly.
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    Quote Originally Posted by Strange View Post
    Quote Originally Posted by nandoanalog View Post
    You're not getting it.
    Perhaps you are not explaining it properly.
    True. My linguistic skills are not up to par.

    One step at a time then... As we approximate the speed of light, events happen at a slower rate, right? So, what do you recon that might happen if one were to actually reach the speed of light?
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  16. #15  
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    Quote Originally Posted by nandoanalog View Post
    One step at a time then... As we approximate the speed of light, events happen at a slower rate, right?
    Events are perceived to happen slower (by the person "at rest"). For the person travelling at speeds approaching the speed of light there is no apprent change.

    So, what do you recon that might happen if one were to actually reach the speed of light?
    It is impossible, so the question is meaningless. Maybe demons will fly out of your nose. Maybe you will turn into chocolate.
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    If it were impossible to reach light speed, then, light itself wouldn't reach it. So, to put the question in another way, does a photon experience time?
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    Quote Originally Posted by nandoanalog View Post
    If it were impossible to reach light speed, then, light itself wouldn't reach it.
    An object with mass can never accelerate to the speed of light. Photons have no mass and always travel at the speed of light.

    So, to put the question in another way, does a photon experience time?
    Photons don't "experience" anything. They don't age or decay. So it is a pretty meaningless question.
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    Quote Originally Posted by Strange View Post

    So, to put the question in another way, does a photon experience time?
    Photons don't "experience" anything. They don't age or decay. So it is a pretty meaningless question.
    If they don't decay/age, maybe one could say they're not affected by time?
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  20. #19  
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    Quote Originally Posted by nandoanalog View Post
    If they don't decay/age, maybe one could say they're not affected by time?
    One could indeed say that. So what?
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    So, it goes hand in hand with this silly idea of mine, that time is a byproduct of movement. And that light doesn't actually move. Hence, light speed = Zero

    I know, I know, it's silly....
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  22. #21  
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    Quote Originally Posted by nandoanalog View Post
    So, it goes hand in hand with this silly idea of mine, that time is a byproduct of movement.
    Except it isn't.

    And that light doesn't actually move.
    Except it does.

    Hence, light speed = Zero
    Except it isn't. And the earlier question is a good one: if the speed of light is zero, then how fast does anything else travel?

    I know, I know, it's silly....
    Very.
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    Quote Originally Posted by Strange View Post
    Quote Originally Posted by nandoanalog View Post
    So, it goes hand in hand with this silly idea of mine, that time is a byproduct of movement.
    Except it isn't.
    Why?
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  24. #23  
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    Quote Originally Posted by nandoanalog View Post
    Quote Originally Posted by Strange View Post
    Quote Originally Posted by nandoanalog View Post
    So, it goes hand in hand with this silly idea of mine, that time is a byproduct of movement.
    Except it isn't.
    Why?
    Well, strictly speaking, as you are the one making a claim it is up to you to provide evidence to support it.

    But just a few simple examples:

    1. we can cool things to nearly absolute zero where there is almost no motion and we see no evidence of time slowing down.

    2. the second is defined in terms of radiation produced by a caesium atom "at rest at a temperature of 0 K" so no motion there (especially as, according to you, the radiation has a speed of zero ).
    Source: BIPM - second

    3. a muon is an elementary particle like an electron; a stationary muon will decay after about 2us therefore time must have passed.

    4. there are solutions to Einstein's field equations which describe space and time that have no matter or energy and therefore no movement.

    5. I could go on but ...

    Your turn: the evidence for time being dependent on movement is ...
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    I am very thankful for your time and dedication to answer me. And I do understand all of your reasoning, as it obviously seems to be the most intuitive.
    But, you're not getting my view. I'm looking at the whole thing backwards. I'm saying that whatever seems to move at the maximum speed possible, be it light or not, is actually standing still in time.

    This all came to me when I was thinking about some hypothetical rocket accelerating towards light speed. To be more specific, the reaction that propels the rocket. Be it burning fuel, or some other means that involves interaction between particles.

    I'll stick with burning fuel for the sake of simplicity. So, as a rocket approximates light speed, time slows down relative to the "space" it is moving through. Which means that interactions between particles, within the rocket, slow down. Which means that the fuel it burns, also burns at a slower rate.

    Which makes it look like the more the rocket accelerates towards light speed, the more it slows down. Until eventually it reaches zero velocity.

    How can something propel itself towards the speed of light, if all interactions/reactions slow down as it does so?
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  26. #25  
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    Quote Originally Posted by nandoanalog View Post
    I'm saying that whatever seems to move at the maximum speed possible, be it light or not, is actually standing still in time.
    I know that is what you are saying. I am askling you to support that with, you know, evidence. (This is a science forum, after all.)

    Which makes it look like the more the rocket accelerates towards light speed, the more it slows down. Until eventually it reaches zero velocity.
    You may be confusing the decreasing rate at which speed increases with the speed itself.

    As something accelerates towards the speed of light, using a constant thrust as you suggest, then we can look at it from two points of view:

    1. The people in the rocket will feel a constant acceleration (say 1g) and will therefore assume that there velocity is increasing continuously at the same rate.

    2. An external "stationary" observer will see their rate of acceleration gradually decrease. Their speed will continue to increase; it will asymptotically approach c but never get there.

    This might help: Relativistic Velocities
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    In the rockets own frame of reference time does not slow down, but moves at it's normal rate. It's only when measured from a differing reference frame that time is seen as moving slower for the rocket, and that only applies within the rockets frame, the rocket keeps moving through the universe at near the speed of light. As measured by another frame. All motion is relative.
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  28. #27  
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    In summary...

    In special relativity, the equation for velocity due to constant acceleration is given by:
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    There is no actual "movement" in space-time; particles ( including photons ) are just static world-lines in 4-dimensional space-time. Velocity is defined simply as the unit tangent vector at each point along that world line with respect to its arc length. It's all just simple geometry, really.
    The only difference between photons and massive particles is that the world-line of a photon has zero arc length, which is why it is not a valid frame of reference, and "experiences" no proper time. That does not mean, however, than one cannot define a velocity vector for it - that is perfectly possible, and its magnitude is exactly c, i.e. for every 300,000km it spans, one second passes for an outside observer performing the measurement. Mind you, this is true for any observer, regardless of his own state of relative motion, because arc length and unit tangent 4-vectors are invariants in 4-dimensional space-time.
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    Quote Originally Posted by Markus Hanke View Post
    There is no actual "movement" in space-time; particles ( including photons ) are just static world-lines in 4-dimensional space-time. Velocity is defined simply as the unit tangent vector at each point along that world line with respect to its arc length. It's all just simple geometry, really.
    The only difference between photons and massive particles is that the world-line of a photon has zero arc length, which is why it is not a valid frame of reference, and "experiences" no proper time. That does not mean, however, than one cannot define a velocity vector for it - that is perfectly possible, and its magnitude is exactly c, i.e. for every 300,000km it spans, one second passes for an outside observer performing the measurement. Mind you, this is true for any observer, regardless of his own state of relative motion, because arc length and unit tangent 4-vectors are invariants in 4-dimensional space-time.
    Whatever you just said, is way above anything I can even remotely start to pretend to understand.
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    Quote Originally Posted by nandoanalog View Post
    Whatever you just said, is way above anything I can even remotely start to pretend to understand.
    If that is the case then I can only suggest you first study the subject matter in greater detail, before once again examining your idea in light of what you have studied. The key here is some elementary differential geometry, followed by the basic concepts of General Relativity. You will see then that it all falls into place quite naturally, not only from a physical point of view, but more importantly as a consequence of mathematical principles. Like I said, it is all really just geometry in 4-dimensional space-time.
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    I blinked, and it was yesterday......
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    Quote Originally Posted by nandoanalog View Post
    Whatever you just said, is way above anything I can even remotely start to pretend to understand.
    You are not alone...I think I understood about 30%.
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    Quote Originally Posted by nandoanalog View Post
    Quote Originally Posted by Markus Hanke View Post
    There is no actual "movement" in space-time; particles ( including photons ) are just static world-lines in 4-dimensional space-time. Velocity is defined simply as the unit tangent vector at each point along that world line with respect to its arc length. It's all just simple geometry, really.
    The only difference between photons and massive particles is that the world-line of a photon has zero arc length, which is why it is not a valid frame of reference, and "experiences" no proper time. That does not mean, however, than one cannot define a velocity vector for it - that is perfectly possible, and its magnitude is exactly c, i.e. for every 300,000km it spans, one second passes for an outside observer performing the measurement. Mind you, this is true for any observer, regardless of his own state of relative motion, because arc length and unit tangent 4-vectors are invariants in 4-dimensional space-time.


    Whatever you just said, is way above anything I can even remotely start to pretend to understand.
    Have a seat next to me. We can sit in the "dummy" section! *L*
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  36. #35  
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    So what?
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    Another basically meaningless piece of youtube.

    Youtube, technology's modern equivalent of a soapbox to stand on and preach any nonsense.
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    Its the way nature is!
    If you dont like it, go somewhere else....
    To another universe, where the rules are simpler
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    Quote Originally Posted by Dywyddyr View Post
    So what?
    I win?

    Just kidding...
    It's nice to find out that someone else had the same idea... Specially if it's someone who seems to actually know a thing or two. Unlike..........
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    It's rather interesting, the "closed mind" feeling I'm getting in this philosophy forum.
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    An open mind in philosophy just let's your brains dribble out your ears.
    Its the way nature is!
    If you dont like it, go somewhere else....
    To another universe, where the rules are simpler
    Philosophically more pleasing, more psychologically easy
    Prof Richard Feynman (1979) .....

    Das ist nicht nur nicht richtig, es ist nicht einmal falsch!"
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    Quote Originally Posted by nandoanalog View Post
    It's rather interesting, the "closed mind" feeling I'm getting in this philosophy forum.
    Yeah.
    The funny thing about philosophy is that it relies on supported argument.
    So far you haven't managed that.
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    Quote Originally Posted by Dywyddyr View Post
    Quote Originally Posted by nandoanalog View Post
    It's rather interesting, the "closed mind" feeling I'm getting in this philosophy forum.
    Yeah.
    The funny thing about philosophy is that it relies on supported argument.
    So far you haven't managed that.
    Mr. Duck, that was a very cranky statement!! *L* ok...and fair....but CRANKY!
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    Quote Originally Posted by PhDemon View Post
    known facts
    There's no such thing.
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    Quote Originally Posted by nandoanalog View Post
    There's no such thing.
    The sun set yesterday evening. That's a known fact.
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    Quote Originally Posted by Markus Hanke View Post
    Quote Originally Posted by nandoanalog View Post
    There's no such thing.
    The sun set yesterday evening. That's a known fact.
    It's a belief at best.
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    Quote Originally Posted by nandoanalog View Post
    Quote Originally Posted by Markus Hanke View Post
    Quote Originally Posted by nandoanalog View Post
    There's no such thing.
    The sun set yesterday evening. That's a known fact.
    It's a belief at best.
    At best, eh? Earlier- you complained about the claimed "closed mindedness" on the forum.
    On BAUT, they used to say (Maybe they still do) "An open mind needs a screen door to keep the bugs out."


    You are a bug.
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    Quote Originally Posted by nandoanalog View Post
    It's a belief at best.
    I also believe that there may be an invisible pink unicorn in Strange's garden. So where does that leave us ?
    You live in a pretty strange world of your own, mate
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    Quote Originally Posted by Markus Hanke View Post
    Quote Originally Posted by nandoanalog View Post
    It's a belief at best.
    I also believe that there may be an invisible pink unicorn in Strange's garden. So where does that leave us ?
    You live in a pretty strange world of your own, mate
    I'm not the one believing in pink unicorns here
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    Quote Originally Posted by nandoanalog View Post
    It's a belief at best.
    You don't know that.
    SayBigWords.com/say/3FC

    "And, behold, I come quickly;" Revelation 22:12

    "Religions are like sausages. When you know how they are made, you no longer want them."
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    Quote Originally Posted by nandoanalog View Post
    I'm not the one believing in pink unicorns here
    No, instead you're the one believing that the sun might not have set last night, since you assert it isn't a fact.

    The pink unicorn cannot be disproved.
    The sun not having set can be disproved, because when I look out the window it isn't there; on other other hand my solar batteries are 79% charged from yesterday, and all plants in my garden are still alive. That leaves only two possibilities : either the sun was indeed there and has set, or there are no valid causal relationships in space-time. The first one is a reasonable assumption, the latter one isn't.

    You pick yourself which one you prefer.
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    Quote Originally Posted by RedPanda View Post
    Quote Originally Posted by nandoanalog View Post
    It's a belief at best.
    You don't know that.
    I have come to believe that "knowing" is impossible.
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    Quote Originally Posted by nandoanalog View Post
    I have come to believe that "knowing" is impossible.
    Yeah, but you're wrong.
    "[Dywyddyr] makes a grumpy bastard like me seem like a happy go lucky scamp" - PhDemon
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    Quote Originally Posted by nandoanalog View Post
    I have come to believe that "knowing" is impossible.
    So then how do you know that you believe that ?
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    Quote Originally Posted by nandoanalog View Post
    Quote Originally Posted by RedPanda View Post
    Quote Originally Posted by nandoanalog View Post
    It's a belief at best.
    You don't know that.
    I have come to believe that "knowing" is impossible.
    You don't know that.
    Strange likes this.
    SayBigWords.com/say/3FC

    "And, behold, I come quickly;" Revelation 22:12

    "Religions are like sausages. When you know how they are made, you no longer want them."
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    Quote Originally Posted by nandoanalog View Post
    Quote Originally Posted by RedPanda View Post
    Quote Originally Posted by nandoanalog View Post
    It's a belief at best.
    You don't know that.
    I have come to believe that "knowing" is impossible.
    I've come to believe that your brains are dribbling out your ears.
    Its the way nature is!
    If you dont like it, go somewhere else....
    To another universe, where the rules are simpler
    Philosophically more pleasing, more psychologically easy
    Prof Richard Feynman (1979) .....

    Das ist nicht nur nicht richtig, es ist nicht einmal falsch!"
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    Quote Originally Posted by nandoanalog View Post
    What's getting me, is that time doesn't happen if you're going at the speed of light (right?). Which is something that light does. So, does time happen to a photon?
    (and somehow, space expansion is clouding the whole thing in my mind too)
    I'm not 100% certain as to your inquiry. But, a way to view it is that light is perceived of as moving in an instant/immediately (from a time perspective), for lack of a better word, but when we look at it in terms of longer distances light can be seen as having notable effects. What do u mean by does time "happen" to a photon?
    Last edited by wegs; August 21st, 2013 at 10:19 AM.
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    I'm not a great ''explainer'' of these things sometimes, but this site might help answer your questions. It's very easy to understand. On another note, why is this thread in the philosophy section? Time and the Speed of Light
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    I may not wake up in the morning!

    *chuckle*

    sometimes the arguments in here are pretty amusing....
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    Quote Originally Posted by nandoanalog View Post
    So, they say that the speed of light is the universal speed limit. And, the nearer you get to it, the slower time passes by. As in, the slower things happen in the sub atomic level...

    It sounds awfully like the speed of light is actually Zero.
    I think it just means that something traveling at light speed just doesn't age. So no half-life decay, entropy, or any other measure of time's effects. Time still passes for everything around it, just not for the thing traveling at light speed.
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    Quote Originally Posted by Daecon View Post
    I think it just means that something traveling at light speed just doesn't age. So no half-life decay, entropy, or any other measure of time's effects. Time still passes for everything around it, just not for the thing traveling at light speed.
    It is not as straightforward as it may seem at first; the problem is that the arc length of the world line between any two events for a massless particle is zero, i.e. the notion of proper time is not defined. In other words - a massless particle is not a valid frame of reference so far as this discussion is concerned. In a way one could say that such particles do not "age", but actually defining what that means in a rigorous way isn't easy. I think one can best understand it as a limiting case of the time dilation formula for v -> c.
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    Quote Originally Posted by Daecon View Post
    Quote Originally Posted by nandoanalog View Post
    So, they say that the speed of light is the universal speed limit. And, the nearer you get to it, the slower time passes by. As in, the slower things happen in the sub atomic level...

    It sounds awfully like the speed of light is actually Zero.
    I think it just means that something traveling at light speed just doesn't age. So no half-life decay, entropy, or any other measure of time's effects. Time still passes for everything around it, just not for the thing traveling at light speed.
    Remember that this is just as seen from another frame of reference.After all, we are travelling at near light speed relative to something and we don't feel we are slowing down.
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    Quote Originally Posted by Strange View Post
    .After all, we are travelling at near light speed relative to something and we don't feel we are slowing down.
    That's what doesn't make any sense to me. Why have a point in space as a frame of reference to determine speed? Wouldn't it be better if the reference point was constant anywhere, at any time? Such as light speed?
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    Quote Originally Posted by nandoanalog View Post
    Wouldn't it be better if the reference point was constant anywhere, at any time? Such as light speed?
    You cannot determine your speed with respect to light, because a photon isn't a valid frame of reference. In fact, such a "relative speed" isn't even defined, because all observers measure the exact same value of c, regardless of their own state of motion.
    There are no reference points in the universe which are constant everywhere at all times; such a point would amount to an absolute frame of reference, which does not exist.
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    Quote Originally Posted by nandoanalog View Post
    That's what doesn't make any sense to me. Why have a point in space as a frame of reference to determine speed? Wouldn't it be better if the reference point was constant anywhere, at any time? Such as light speed?
    Markus has said it. But this seems to be a stumbling block for you so ...

    Velocity is a change in spatial location over time. Therefore it needs to be measured with respect to some point in space. Remember that velocity is direction as well as speed, so we also need to be able to say what direction (relative to that fixed point) we are going. Even when you compare your speed relative to something else (e.g. "he is travelling at 20 mph and I am travelling at 50 mph") you are just referring both speeds to some arbitrary stationary reference point.

    The speed of light is not a "reference point". It is not a position and, as Markus notes, it is the same for everyone everywhere. So how can you define your speed relative to the speed of light?

    Imagine I am heading away from the Sun at 0.2c. I measure the speed of light as c. Now you are heading away from the Sun at 0.9c. You measure the speed of light as c. So how can either of us define our speed relative to that. If we speed up, slow down or change direction then we will still measure the same speed of light in all directions. I suppose, contrary to your original point, it could be argued that all speeds except the speed of light are zero (relative to light). But that would be silly and not at all useful.
    ei incumbit probatio qui dicit, non qui negat
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    Quote Originally Posted by Strange View Post
    Quote Originally Posted by nandoanalog View Post
    That's what doesn't make any sense to me. Why have a point in space as a frame of reference to determine speed? Wouldn't it be better if the reference point was constant anywhere, at any time? Such as light speed?
    Markus has said it. But this seems to be a stumbling block for you so ...

    Velocity is a change in spatial location over time. Therefore it needs to be measured with respect to some point in space. Remember that velocity is direction as well as speed, so we also need to be able to say what direction (relative to that fixed point) we are going. Even when you compare your speed relative to something else (e.g. "he is travelling at 20 mph and I am travelling at 50 mph") you are just referring both speeds to some arbitrary stationary reference point.

    The speed of light is not a "reference point". It is not a position and, as Markus notes, it is the same for everyone everywhere. So how can you define your speed relative to the speed of light?

    Imagine I am heading away from the Sun at 0.2c. I measure the speed of light as c. Now you are heading away from the Sun at 0.9c. You measure the speed of light as c. So how can either of us define our speed relative to that. If we speed up, slow down or change direction then we will still measure the same speed of light in all directions. I suppose, contrary to your original point, it could be argued that all speeds except the speed of light are zero (relative to light). But that would be silly and not at all useful.
    I read this three times......and I kind of even understood what you were saying!!

    I said KIND OF!! .......
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    Strange, does the speed of light appear to be the same to everyone due to time dilation?
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    Quote Originally Posted by nandoanalog View Post
    Strange, does the speed of light appear to be the same to everyone due to time dilation?
    I think so, yeah. That's why no matter how fast you yourself are going, the speed of light will always look like 300 million meters per second from your frame of reference.
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    Quote Originally Posted by nandoanalog View Post
    Strange, does the speed of light appear to be the same to everyone due to time dilation?
    Time dilation is a consequence of the constancy of light speed.
    "[Dywyddyr] makes a grumpy bastard like me seem like a happy go lucky scamp" - PhDemon
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    Quote Originally Posted by Dywyddyr View Post
    Quote Originally Posted by nandoanalog View Post
    Strange, does the speed of light appear to be the same to everyone due to time dilation?
    Time dilation is a consequence of the constancy of light speed.
    ok....I know Sir Duckness probably a dumb question but what is the "consequence of the constancy of light speed" in duckling terms. Please...
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    Quote Originally Posted by nandoanalog View Post
    Strange, does the speed of light appear to be the same to everyone due to time dilation?
    Time dilation and length contraction.

    But ... which is cause and which is effect? That is not obvious (to me).

    Certainly, in terms of the derivation of the theory of relativity and the corresponding understanding of how space and time work, the starting point is the constancy of the speed of light (as described by Maxwell's equations). But it is not unreasonable to say that the constant speed of light is the result of time and space being relative (observer dependent).

    But, why does the universe require time and space to be observer dependent? To make sure that the laws of physics are the same for everyone, regardless of their state of motion. So, for example, everyone will measure the same fundamental constants. These include permittivity and permeability. Which define the speed of light.

    It is all interrelated.
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    ~ Well, firstly we have a fellow that thinks time is dead from the point of view of the photon and that That seems to be what we agree on.. The rest of it is utter nonsense ;ie The Sun does not set. ? What .. Oh all right the planet you are observing from seems to have rotated about it's axis so as to place you into the unlit part. You are in Earths shadow.. Relax, this happens a lot...

    Just to confound you 'nandoanlog' explain this.. Light velocity = 0 then it must be a very dark hole you are standing in...
    The fact that some light photons reach our eyes from distant stars and that it has taken some time for this to have happened ?
    I will just wait over here in the margin watching... >>>
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    Quote Originally Posted by astromark View Post
    ~ Well, firstly we have a fellow that thinks time is dead from the point of view of the photon and that That seems to be what we agree on.. The rest of it is utter nonsense ;ie The Sun does not set. ? What .. Oh all right the planet you are observing from seems to have rotated about it's axis so as to place you into the unlit part. You are in Earths shadow.. Relax, this happens a lot...

    Just to confound you 'nandoanlog' explain this.. Light velocity = 0 then it must be a very dark hole you are standing in...
    The fact that some light photons reach our eyes from distant stars and that it has taken some time for this to have happened ?
    I will just wait over here in the margin watching... >>>
    Well, hate to tell ya this, but right now, my right eye is almost legally blind..so I never saw the light photons reaching my eyes from a distant star and so I have no ********* idea how long the time span has been.

    So you can stop watching me!

    Oh and if I respond incorrectly....for hopefully a short time..I can blame it on my eyes and not my brain.

    Mahalo!
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    Quote Originally Posted by nandoanalog View Post
    Strange, does the speed of light appear to be the same to everyone due to time dilation?
    No, it is the same for everyone due to the geometry of space-time itself. Time dilation and length contraction between inertial frames are a consequence of the same geometric considerations; these are all intrinsically linked.
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    Quote Originally Posted by babe View Post
    Quote Originally Posted by Dywyddyr View Post
    Quote Originally Posted by nandoanalog View Post
    Strange, does the speed of light appear to be the same to everyone due to time dilation?
    Time dilation is a consequence of the constancy of light speed.
    ok....I know Sir Duckness probably a dumb question but what is the "consequence of the constancy of light speed" in duckling terms. Please...
    Time dilation. And length contraction.

    Although, as Markus pointed out, we can't definitively say that things are that way round.
    But the way we found out is due to Einstein working from the premise that light speed is constant. Thus, given that that is true, time dilation (and length contraction) are the "result" (consequence) of that constancy.
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    Quote Originally Posted by Strange View Post
    Quote Originally Posted by Daecon View Post
    Quote Originally Posted by nandoanalog View Post
    So, they say that the speed of light is the universal speed limit. And, the nearer you get to it, the slower time passes by. As in, the slower things happen in the sub atomic level...

    It sounds awfully like the speed of light is actually Zero.
    I think it just means that something traveling at light speed just doesn't age. So no half-life decay, entropy, or any other measure of time's effects. Time still passes for everything around it, just not for the thing traveling at light speed.
    Remember that this is just as seen from another frame of reference.After all, we are travelling at near light speed relative to something and we don't feel we are slowing down.
    So does that mean that from a photon's perspective, we're traveling at light speed?
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    Quote Originally Posted by Daecon View Post
    So does that mean that from a photon's perspective, we're traveling at light speed?
    Let me answer a different question: from the point of view of a cosmic ray travelling at 99.999% of the speed of light, yes we are travelling at 99.999% of the speed of light.

    And the reason I say that is because the photon's perspective isn't a valid frame of reference. If you try and work out what a photon would "see" then you end up dividing by zero. There is no frame of reference in which we, or any object with mass, will travel at the speed of light.
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    Quote Originally Posted by nandoanalog View Post
    Quote Originally Posted by Strange View Post
    Quote Originally Posted by nandoanalog View Post
    You're not getting it.
    Perhaps you are not explaining it properly.
    True. My linguistic skills are not up to par.

    One step at a time then... As we approximate the speed of light, events happen at a slower rate, right? So, what do you recon that might happen if one were to actually reach the speed of light?
    If you're moving at .9C from my perspective. (By which I mean I observe that I am stationary and you are moving at 0.9C), then... I am moving at 0.9C from your perspective also. (You observe that you are the one who is stationary and I am moving at 0.9C.)

    In relativity, we both perceive the other to be the one for whom time is nearly stopped.


    Quote Originally Posted by nandoanalog View Post
    Quote Originally Posted by Strange View Post
    .After all, we are travelling at near light speed relative to something and we don't feel we are slowing down.
    That's what doesn't make any sense to me. Why have a point in space as a frame of reference to determine speed? Wouldn't it be better if the reference point was constant anywhere, at any time? Such as light speed?
    You can't use points in space as frames of reference, only other objects.


    Quote Originally Posted by Strange View Post
    Quote Originally Posted by nandoanalog View Post
    That's what doesn't make any sense to me. Why have a point in space as a frame of reference to determine speed? Wouldn't it be better if the reference point was constant anywhere, at any time? Such as light speed?
    Markus has said it. But this seems to be a stumbling block for you so ...

    Velocity is a change in spatial location over time. Therefore it needs to be measured with respect to some point in space. Remember that velocity is direction as well as speed, so we also need to be able to say what direction (relative to that fixed point) we are going. Even when you compare your speed relative to something else (e.g. "he is travelling at 20 mph and I am travelling at 50 mph") you are just referring both speeds to some arbitrary stationary reference point.

    This is nitpicking of me, but we don't measure relative to points in space. Only other objects. Space itself is not a valid frame of reference.
    Some clocks are only right twice a day, but they are still right when they are right.
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    So we can't use a specific region of cosmic microwave background radiation as a viable reference point then, because it would be like measuring your position relative to a distant point on the horizon, right?
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    Quote Originally Posted by Daecon View Post
    So we can't use a specific region of cosmic microwave background radiation as a viable reference point then
    The issue is that such a frame would be no different than any other frame; it would be neither absolute nor preferred.
    So no, we can't use it as an absolute reference point.
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    Quote Originally Posted by Daecon View Post
    So we can't use a specific region of cosmic microwave background radiation as a viable reference point then, because it would be like measuring your position relative to a distant point on the horizon, right?
    Cosmologists do use the CMBR as a convenient reference frame. For example, we can measure our motion relative to the CMBR (it is very slightly red shifted in one direction and blue shifted in the other which show we are moving relative to it). This is a useful reference because it would (as far as we know) the same for all observers in the universe.
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    Quote Originally Posted by Daecon View Post
    So we can't use a specific region of cosmic microwave background radiation as a viable reference point then, because it would be like measuring your position relative to a distant point on the horizon, right?
    The CMBR was emitted by physical objects/particles. So really when we use it, we're using those objects.

    In reality whenever we use any object as a reference point, we're using its "last known location", which is where it was distance/C seconds ago. We can't use the location where it is right now because we don't know that location until the light gets to us.

    The CMBR is kind of a special case where, according to BBT, the "last known location" we are using was true a very long time ago.
    Some clocks are only right twice a day, but they are still right when they are right.
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    The CMBR was emitted by physical objects/particles. So really when we use it, we're using those objects.
    The CMBR was emitted evenly throughout the universe all at the same time. So it can't be said to have been emitted by an object or particle.
    Its the way nature is!
    If you dont like it, go somewhere else....
    To another universe, where the rules are simpler
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    Quote Originally Posted by AlexG View Post
    The CMBR was emitted by physical objects/particles. So really when we use it, we're using those objects.
    The CMBR was emitted evenly throughout the universe all at the same time. So it can't be said to have been emitted by an object or particle.
    Right, but each individual photon was emitted by something. It just so happens that all of the universe was full of those objects.


    This brings up an interesting side issue, though. Most of the observable universe shares one frame of reference. Not exactly, but approximately. I mean to say that most of the objects we observe in space are moving at a small fraction of the speed of light relative to us (ignoring Hubble Redshift, since the BBT suggests that that's not due to actual motion).

    In a sense, any view substantially different from the one we have about speed and time and distance, is kind of a minority view.
    Some clocks are only right twice a day, but they are still right when they are right.
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    Right, but each individual photon was emitted by something
    Each individual photon was emitted by a free electron, evenly distributed throughout the universe. So the photons, when they were finally free to travel, were everywhere, evenly distributed, traveling in all directions, and that situation continues today. Every cubic meter of space contains approximately 400 million photons of the CMBR.
    Its the way nature is!
    If you dont like it, go somewhere else....
    To another universe, where the rules are simpler
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    Quote Originally Posted by Dywyddyr View Post
    Quote Originally Posted by babe View Post
    Quote Originally Posted by Dywyddyr View Post
    Quote Originally Posted by nandoanalog View Post
    Strange, does the speed of light appear to be the same to everyone due to time dilation?
    Time dilation is a consequence of the constancy of light speed.
    ok....I know Sir Duckness probably a dumb question but what is the "consequence of the constancy of light speed" in duckling terms. Please...
    Time dilation. And length contraction.

    Although, as Markus pointed out, we can't definitively say that things are that way round.
    But the way we found out is due to Einstein working from the premise that light speed is constant. Thus, given that that is true, time dilation (and length contraction) are the "result" (consequence) of that constancy.
    MAHALO SIR DUCKNESS, and don't you go sticking your tongue out at me, SIR, ya might get more than ya wished for! *chuckle*

    good explanation...thank you
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