AJ©Hodgson Posted October 22, 2015 Share Posted October 22, 2015 (edited) Time-dilation due to relative velocity states that: From the frame of reference of a moving observer traveling at the speed v (diagram at lower right), the light pulse traces out a longer, angled path. The second postulate of special relativity states that the speed of light is constant in all frames, which implies a lengthening of the period of this clock from the moving observer's perspective. That is to say, in a frame moving relative to the clock, the clock appears to be running more slowly. Source - http://en.wikipedia.org/wiki/Time_dilation I disagree that the light pulse traces out a longer, angled path. Rather I propose that the length of the path is exactly the same, and the discrepancy lies instead at the point on the mirror where the light pulse hits. Imagine two mirrors A and B, a light pulse is emitted from the far right of mirror A toward B, however as B is moving at near light speed, by the time the light pulse reaches B it hits the mirror in the middle, and reflects back toward A. Again by the time the pulse reaches A, it has continued to move and so the pulse hits at the far left of the mirror. Another example is as follows: Imagine having a photon gun that could shoot individual photons, a friend located a distance away also had a gun that could fire single particles close to the speed of light, now, I called 'pull' and he let his particle fly, that particle/clay pigeon is travelling at near the speed of light, meanwhile I am at a right angle from it, and so I would have to fire my photon in front of my friends shot in order to intercept it, as light takes time to traverse space/reach the pigeon. I do not view the light as travelling sideways and hence tracing out a longer, angled path rather I view the mirrors as travelling sideways, and lets face it at a speed very close to the speed of light, resulting in the pulse hitting at a different place on the mirror, and hence mainting its speed, and distance travelled, nullifying any need to introduce time-dilation. Edited October 22, 2015 by AJ©Hodgson Link to comment Share on other sites More sharing options...
pzkpfw Posted October 22, 2015 Share Posted October 22, 2015 First up, do you deny the first postulate of special relativity? Link to comment Share on other sites More sharing options...
swansont Posted October 23, 2015 Share Posted October 23, 2015 I do not view the light as travelling sideways and hence tracing out a longer, angled path rather I view the mirrors as travelling sideways, and lets face it at a speed very close to the speed of light, resulting in the pulse hitting at a different place on the mirror, and hence mainting its speed, and distance travelled, nullifying any need to introduce time-dilation. How much of a deflection do you expect if the source is a distance d away from the target, and the system is moving at v? Link to comment Share on other sites More sharing options...
John Cuthber Posted October 23, 2015 Share Posted October 23, 2015 How do you explain the fact that a moving clock runs at a different rate? Link to comment Share on other sites More sharing options...
studiot Posted October 23, 2015 Share Posted October 23, 2015 (edited) Games with mirrors are not the only way to come at special relativity, they are really just an attempt to offer a simple example. The mathematical theory contains no mirrors at all. Secondly you miss the key point of the second postulate. For all waves, not just light, the speed of the wave is independent of the speed of the source, relative to the medium. The speed is determined by the characteristics of the medium of propagation alone. The key point of the second postulate that makes light different from other waves is that for all other waves the observed speed depends upon the speed of the observer relative to the medium. The second postulate states that the speed of light is independent of the speed of the observer as well as the speed of the source and hence is the same for all observers. Another corollary is that the speed of light is independent of the relative speed between source and observer. It is this last version that is used to deduce the effect on time and space. Edited October 23, 2015 by studiot Link to comment Share on other sites More sharing options...
Janus Posted October 23, 2015 Share Posted October 23, 2015 Time-dilation due to relative velocity states that: From the frame of reference of a moving observer traveling at the speed v (diagram at lower right), the light pulse traces out a longer, angled path. The second postulate of special relativity states that the speed of light is constant in all frames, which implies a lengthening of the period of this clock from the moving observer's perspective. That is to say, in a frame moving relative to the clock, the clock appears to be running more slowly. Source - http://en.wikipedia.org/wiki/Time_dilation I disagree that the light pulse traces out a longer, angled path. Rather I propose that the length of the path is exactly the same, and the discrepancy lies instead at the point on the mirror where the light pulse hits. Imagine two mirrors A and B, a light pulse is emitted from the far right of mirror A toward B, however as B is moving at near light speed, by the time the light pulse reaches B it hits the mirror in the middle, and reflects back toward A. Again by the time the pulse reaches A, it has continued to move and so the pulse hits at the far left of the mirror. Then. the path the light follows would be longer as measured by someone moving with the mirrors. The distance from one edge of A to the middle of B and then back to the other edge of A is longer than the path from the middle of A to the middle of B and back to the middle of A. But light doesn't behave like that, It will bounce back and forth between the middle of the mirrors. We know this because experiments going back as far as 1887 have shown this to be the case. Another example is as follows: Imagine having a photon gun that could shoot individual photons, a friend located a distance away also had a gun that could fire single particles close to the speed of light, now, I called 'pull' and he let his particle fly, that particle/clay pigeon is travelling at near the speed of light, meanwhile I am at a right angle from it, and so I would have to fire my photon in front of my friends shot in order to intercept it, as light takes time to traverse space/reach the pigeon. But in this case, there is a relative velocity between you and the target. If both you and the target particle had the same velocity with respect to your friend, you would just aim directly at the particle and hit it with your photons.I do not view the light as travelling sideways and hence tracing out a longer, angled path rather I view the mirrors as travelling sideways, and lets face it at a speed very close to the speed of light, resulting in the pulse hitting at a different place on the mirror, and hence mainting its speed, and distance travelled, nullifying any need to introduce time-dilation. It doesn't matter how you view how light acts, it only matters how light has demonstratively been shown to behave. If light behaved as you view it as behaving, then you could use light to determine your absolute motion. If you standing at the edge of mirror A and aimed your photon at the opposite edge, but the photon you fired hits the middle of B and bounces back to the other edge of A, this would tell you that you are moving. But as I already have mentioned, numerous experiments, that would have been able to detect such behavior have shown that this is not the case. The other aspect of light is that its speed is invariant. This means that if two people are measuring the speed of light relative to themselves, they both get the same answer, no matter how fast they are moving relative to each other. Thus the light travels at c back and forth between the middle of the mirrors at c in a straight line as measured by someone at rest with respect to the mirrors, and follows a zig-zag path, at c as measured by person 2 with a relative motion with respect to the mirrors, and since the zig-zag path is the longer of the two, it takes longer by the second persons clock for the light to bounce between the mirrors than it does for someone at rest with respect to the mirrors. In addition, it doesn't whether we consider the mirrors as moving and person 2 is at rest, or the mirrors are at rest and person 2 is moving. Beside this, the whole argument over the light clock example is a moot point. It is a thought experiment meant to show what occurs if the postulates of Relativity are adhered to. Today, we have real life experiments and observations that show that time dilation actually does occur. The entire GPS system had to be design around that fact in order to work properly. So it's a little late at this point of the game to "shove the genie back in the bottle" as far as time dilation goes. Link to comment Share on other sites More sharing options...
studiot Posted October 23, 2015 Share Posted October 23, 2015 (edited) The other aspect of light is that its speed is invariant. This means that if two people are measuring the speed of light relative to themselves, they both get the same answer, no matter how fast they are moving relative to each other. Easy there, that statement needs backup. Speed invariance is a (very reasonable) assumption underlying Einstinian relativity, it is not, however a postulate. The point is that we accept the einstinian explanation over other conceivable ones as it best fits observational data. But note that we have only done this after exhaustive experimentation. For instance many structures for the aether (as a transmission mediim for light) have been proposed and much effort has been put into finding it. No experiment has ever demonstrated its existence. So we conclude that light generates its own medium as it goes along, there is no aether. So we cannot attribute the observed effects to the medium, they must be part of time and space. However that does not make lightspeed invariant. It is possible to produce a model whereby lightspeed varies just enough dring its journey from source to observer to make it the same for all observers. Again we reject this model after experimentation. Constant lightspeed is equivalent to asserting the homogeny and isotropy of space(time) which we consider a desirable property. So there are deep and fundamantal reasons for choosing the conventional explanatory path, it is not just a whim or response to a single observation or experience. Edited October 23, 2015 by studiot Link to comment Share on other sites More sharing options...
swansont Posted October 23, 2015 Share Posted October 23, 2015 Easy there, that statement needs backup. Speed invariance is a (very reasonable) assumption underlying Einstinian relativity, it is not, however a postulate. Yes, it is. It's the second postulate. http://www.nobelprize.org/educational/physics/relativity/postulates-1.html Link to comment Share on other sites More sharing options...
studiot Posted October 23, 2015 Share Posted October 23, 2015 From Swanson't's link The speed of light in vacuum is actually the only speed that is absolute and the same for all observers as was stated in the second postulate. Isn't that exactly what I said? Link to comment Share on other sites More sharing options...
swansont Posted October 23, 2015 Share Posted October 23, 2015 Isn't that exactly what I said? No. You said it wasn't a postulate of relativity 1 Link to comment Share on other sites More sharing options...
studiot Posted October 24, 2015 Share Posted October 24, 2015 No. You said it wasn't a postulate of relativity I can see that I didn't explain my thoughts at all well so I will put some effort into producing a better post. 2 Link to comment Share on other sites More sharing options...
metacogitans Posted November 29, 2015 Share Posted November 29, 2015 (edited) I hope I can maybe shed some light on Special Relativity; there are two seemingly-contradicting principles that are both true: 1. No matter how fast you are travelling in one direction, if you turn on a flashlight, light will still seem to be travelling away from you at the speed of light c 2. Light travels at the same speed locally. Or, the speed of light is constant in a vacuum. Since both of those principles have to be true, somethings gotta give in the example in #1: time dilates to compensate for you still observing light travelling at the same speed as usual when you're travelling at a relativistic speed - everything else in the universe would be happening faster than usual. If you had a clock with you, it would be behind everyone else's clock when you got back. Because you'll always observe light travelling away from you at the speed of light, you can never travel as fast as the speed of light; and if you try to accelerate up to 300,000km/s, time dilation prevents you from ever reaching it. The Lorentz Factor describes this mathematically: https://en.wikipedia.org/wiki/Lorentz_factor v is the relative velocity between inertial reference frames, β is the ratio of v to the speed of light c. τ is the proper time for an observer (measuring time intervals in the observer's own frame), t is coordinate time c is the speed of light in a vacuum. Edited November 29, 2015 by metacogitans Link to comment Share on other sites More sharing options...
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