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Thread: Maxwell's Paradox

  1. #1 Maxwell's Paradox 
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    Ok, so I've started The Elegant Universe and I'm a little confused by Maxwell's paradox associated with light always traveling at light speed. Supposedly, Einstein pondered the state of affairs if we chased a beam of light at light speed, thereby causing the light beam to "appear" stationary.

    The question I have is, how is that a paradox? Just seems like common sense to me. We don't even need light to recreate the paradox.

    How about a car? If a car is traveling at 5 miles per hour, and I run 5 miles per hour along side it, then it will appear stationary relative to me.

    In both scenarios the car and the light are still traveling at their respective speeds, but I'm just running along with them.

    I just don't see how that's a "paradox". Am I missing something?


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    Everything must travel in lightspeed, since mass and momentum is preserved when energy becomes mass. Then how come mass stands "still", since photons can travel from one place to another and still stay in the same universe? Light and mass have different vektors, and still they can catch up with eachother. That is a "paradox" if you do not accept that the universe is a brane.


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    ParanoiA, dont listen to LeavingQuietly he is hippie like, i suspect his best friend is opium

    i dont know what the paradox is but light has allways the same speed and the paradox propebly come from the belife of aether they had before.
    I am zelos. Destroyer of planets, exterminator of life, conquerer of worlds. I have come to rule this uiniverse. And there is nothing u pathetic biengs can do to stop me

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    I have never used any reall drugs. Have you zelos?
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  6. #5  
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    How about a car? If a car is traveling at 5 miles per hour, and I run 5 miles per hour along side it, then it will appear stationary relative to me.

    In both scenarios the car and the light are still traveling at their respective speeds, but I'm just running along with them.

    You didn't quite get it right. If you are standing at the side of the road and you measure the cars speed in your reference frame it will be 5 mph. If you run along with the car at the same speed, you will measure 0 mph relative speed (the car will appear to stand next to you). So you have two different speeds, depending on the reference frame (moving or stationary).

    So far so good. But if it's a light wave it would be different. If you're standing and you see it pass by you, you will measure the speed of light. However, if you move along at any speed and you take your measurement, the speed of the light wave will still be the original speed of light, relative to you! Unlike the speed of the car, the speed of light is invariant of the reference frame. Makes sense? No? Well, that's why it's a paradox. :wink:
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    Quote Originally Posted by M
    How about a car? If a car is traveling at 5 miles per hour, and I run 5 miles per hour along side it, then it will appear stationary relative to me.

    In both scenarios the car and the light are still traveling at their respective speeds, but I'm just running along with them.

    You didn't quite get it right. If you are standing at the side of the road and you measure the cars speed in your reference frame it will be 5 mph. If you run along with the car at the same speed, you will measure 0 mph relative speed (the car will appear to stand next to you). So you have two different speeds, depending on the reference frame (moving or stationary).

    So far so good. But if it's a light wave it would be different. If you're standing and you see it pass by you, you will measure the speed of light. However, if you move along at any speed and you take your measurement, the speed of the light wave will still be the original speed of light, relative to you! Unlike the speed of the car, the speed of light is invariant of the reference frame. Makes sense? No? Well, that's why it's a paradox. :wink:
    I didn't make clear that at this point in the book, we were still working with Newtonian laws, and Einstein was only 16, but caught up in Maxwell's "paradox" about the speed of light being constant.

    Apparently, Eistein asked what would happen if he chased light, at light speed? Intuitively ( albeit wrong ), light would then appear stationary.

    So, it wasn't realized yet, that the speed of light would be constant to any observer, in motion or stationary. Einstein hadn't worked that out yet.

    That's what I mean about it not really sounding like a paradox to me. But it is presented as a paradox, before Einstein did his work. What is so paradoxical about matching the speed of a moving object so that it looks stationary?
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    If you travel at the speed of light and look in a mirror you will still see your reflection. That seems counterintuitve right? That's why it is a paradox.

    It's like the old theory that when you are moving towards a light source, light will appear to be travelling faster than if you are moving away from it. It seems like that should happen, but it doesn't - which is why it's a paradox!!
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    Quote Originally Posted by billiards
    If you travel at the speed of light and look in a mirror you will still see your reflection. That seems counterintuitve right? That's why it is a paradox.

    It's like the old theory that when you are moving towards a light source, light will appear to be travelling faster than if you are moving away from it. It seems like that should happen, but it doesn't - which is why it's a paradox!!
    I appreciate the replies, but it doesn't appear anyone is reading what I'm typing.

    I know that light travels away from you at 186,000 miles per second, whether you're stationary or moving. I got that. And yes that's a really cool paradox and yadda yadda yadda....

    BUT THAT'S NOT THE PARADOX I'M TALKING ABOUT. The particular paradox I'm talking about was called a "paradox" BEFORE EINSTEIN WORKED THAT OUT. A 16 year old Einstein didn't know that yet, and everyone was using Newtonian physics.

    It was stated that Maxwell said that light always traveled at light speed, never resting. The 16 yr old Einstein was drawn to the "paradox" that if you were to chase a light beam at light speed, that light would appear stationary.

    That's it. I don't understand how that is a paradox. And I was just wondering if anyone could tell me why that is considered paradoxical. The true properties of light were not known yet, so please DO NOT REPLY WITH YET ANOTHER POST RELATIVITY OBSERVATION. THIS IS BEFORE RELATIVITY.
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  10. #9  
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    Can you point to a description of this paradox on the net?
    I tried looking but could not find it.
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  11. #10  
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    Quote Originally Posted by Megabrain
    Can you point to a description of this paradox on the net?
    I tried looking but could not find it.
    No, it's not available online, I don't think anyway. Here it is, straight out of the book:

    "....Maxwell realized that visible light itself is nothing but a particular kind of electromagnetic wave. Maxwell's theory also showed that all electromagnetic waves - visible light among them - are the epitome of the peripatetic traveler. They never stop. They never slow down. Light always travels at light speed.
    All is well and good until we ask, as the sixteen year old Einstein did, What happens if we chase after a beam of light, at light speed? Intuitive reasoning, rooted in Newton's laws of motion, tells us that we will catch up with the light waves and so they will appear stationary;light will stand still. But according to Maxwell's theory, and all reliable observations, there is simply no such thing as stationary light: no one has ever held a stationary clump of light in the palm of his or her hand. Einstein pondered the paradox of Maxwell and Newton largley in the pristine of his own thoughts."




    Now, forget about relativity for a minute. This still sounds rather...well, dumb. What would make anyone think that it IS stationary, when it's obvious that you're chasing it??

    I don't understand how that's a paradox, even pre-relativity. Just because I match the speed of something and look over at it, suddenly I'm supposed to be dumbfounded?

    Of course, I'm glad he did think of it as a paradox and then shake the world with the truth...
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  12. #11  
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    Now, forget about relativity for a minute. This still sounds rather...well, dumb. What would make anyone think that it IS stationary, when it's obvious that you're chasing it??
    Please, take a minute and reread my previous post. It's exactly what Einstein was pondering about and directly relates to the quote from your book. Einstein may have been only 16, but he wasn't the one who first contended that the speed of light is invariant of the reference frame. That came out of Maxwell's work. Einstein realized how this seemed to contradict Newton, and hence his assessment as a 'paradox'.

    What would make anyone think it should be stationary? Newton certainly would think so. I think you still have trouble keeping your reference frames straight. You are right, that this has nothing to do with Einstein's 'relativity'. However, it does have something to do with 'relative motion'. Back to your car example: If the car moves at 5mph and you walk along at 5mph, the car appears to be stationary from your point of view (i.e. in your reference frame). That's because you stay with the car, and the car never moves away from you. In your reference frame, it looks like the car and you are stationary, and the road is moving away under your feet. You follow? This is what's meant by "we will catch up with the light waves and so they will appear stationary;light will stand still". Read on, only if you understand this.

    Einstein and Newton may now think, why should light waves be any different from cars. If we could move along with the speed of light, the wave should be always at our side, never moving away from us, appearing stationary with respect to us. Do you follow? Only read on if you understand this.

    The point is, that light is not like car! What holds for the car completely breaks down for the light wave, according to Maxwell. We can move along with the wave at the speed of light, assuming to catch up with it, but we never will. The light wave will always be faster than us, by exactly the speed of light! Does this seem weird and paradoxical now? It sure did to Einstein.

    Now read your quote again. It's exactly what I am trying to describe.
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    Quote Originally Posted by LeavingQuietly
    I have never used any reall drugs. Have you zelos?
    and yet you talk like youre on them all the time

    and no i havent. i dont want to use drugs. dont want to go mad. In your case drugs wont make any differens if you havent taken any
    I am zelos. Destroyer of planets, exterminator of life, conquerer of worlds. I have come to rule this uiniverse. And there is nothing u pathetic biengs can do to stop me

    On the eighth day Zelos said: 'Let there be darkness,' and the light was never again seen.

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  14. #13  
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    and no i havent. i dont want to use drugs. dont want to go mad. In your case drugs wont make any differens if you havent taken any
    Alcohol is a drug, and so are nicotine and even caffeine. All of them are addictive and mess with your brain. The commercial food industry will strongly disagree with me, but they are just playing with labels. You never had any of those? That's hard to believe. Almost everyone is a drug addict of some sort. Some are just more hardcore. :-D

    Not trying to hijack this thread. I don't think you need any drugs to understand Maxwell's paradox.
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    I think that when you consider that photons do not experience time, if you travelled at that speed you too would not experience time. The point being missed here (in my humble opinion) is that you are assuming time stops for the photon and not for the observer - if you take time into consideration there does not seem to me to be any paradox at all.
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  16. #15  
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    Quote Originally Posted by M
    Now, forget about relativity for a minute. This still sounds rather...well, dumb. What would make anyone think that it IS stationary, when it's obvious that you're chasing it??
    Please, take a minute and reread my previous post. It's exactly what Einstein was pondering about and directly relates to the quote from your book. Einstein may have been only 16, but he wasn't the one who first contended that the speed of light is invariant of the reference frame. That came out of Maxwell's work. Einstein realized how this seemed to contradict Newton, and hence his assessment as a 'paradox'.

    What would make anyone think it should be stationary? Newton certainly would think so. I think you still have trouble keeping your reference frames straight. You are right, that this has nothing to do with Einstein's 'relativity'. However, it does have something to do with 'relative motion'. Back to your car example: If the car moves at 5mph and you walk along at 5mph, the car appears to be stationary from your point of view (i.e. in your reference frame). That's because you stay with the car, and the car never moves away from you. In your reference frame, it looks like the car and you are stationary, and the road is moving away under your feet. You follow? This is what's meant by "we will catch up with the light waves and so they will appear stationary;light will stand still". Read on, only if you understand this.

    Einstein and Newton may now think, why should light waves be any different from cars. If we could move along with the speed of light, the wave should be always at our side, never moving away from us, appearing stationary with respect to us. Do you follow? Only read on if you understand this.

    The point is, that light is not like car! What holds for the car completely breaks down for the light wave, according to Maxwell. We can move along with the wave at the speed of light, assuming to catch up with it, but we never will. The light wave will always be faster than us, by exactly the speed of light! Does this seem weird and paradoxical now? It sure did to Einstein.

    Now read your quote again. It's exactly what I am trying to describe.
    Thanks M. I guess I just was not getting that Maxwell's theory suggested constancy of light regardless of reference frame, contradicting Newton. I thought Maxwell and Newton were in agreement, and Einstein just simply did not agree. I could see no paradox in that.

    And the book did point out that Galileo, I believe, suggested also that light was constant.

    I'll tell you though...I'm reading this thing slowly. It's hard to get a grip on the speed of light and reference frames. I understand it, but just barely - clinging by my fingers dangling off of a cliff.

    I wish I had an instructor that I could bounce a ton of questions off of...

    By the way, I heard as a child, that astronauts experience time dilation. Is this true? I can see how traveling in a faster motion over a period of time, would make this apparent, but aren't they orbiting the same speed as we're revolving? I guess there's no real reason to assume so, but I did anyway.
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  17. #16  
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    I understand the confusion. I would think everyone goes through that when trying to undestand.

    One thing to keep in mind (that my own physics teacher failed to point out): The invariance of the speed of light is the basis (and not the result) of Einstein's relativity theory. Once you assume that this postulate is true, then strange consequences follow, such as time dilatation. Proof of the postulate that the light speed be constant has been obtained indirectly, through validation of some of its consequences in experiments on quantum mechanics. Sorry to be so vague, as I do not remember the details. My point is: To "understand" relativity you simply have to believe that the assumption of constant light speed is true, and then get a grasp of all its consequences. Einstein is credited with his bravery to defy convention (Newton). Once that was done, the mathematical and physical analysis that followed was elementary!
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  18. #17  
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    Hmm..good points. I'll keep that in mind. I did actually assume the invariance of the speed of light to be a result rather than a basis, so thanks for pointing that out.
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