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Why don't photons experience time? 
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#127
Jan3013, 03:51 PM

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#128
Jan3013, 05:19 PM

C. Spirit
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#129
Jan3013, 07:23 PM

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You may see that I'm asking it again and again, but each expert has different way to express their understanding about relation of time and photon. Yes now I realized, when an expert say "photon don't experience time" the context of that saying only the explanation photon using SR and GR. That is why I'm asking what else branch of Physic that need to be used to analyzing massless particle. More over, relation between massless particle and time. Perhaps like you said, added by Quantum Physics explanation. It just in my opinion, after explaining that the two event of emitted and reabsorb of photon are said to be separated by a lightlike, or null interval, it should be explain also that this two event can not be call as single event. As ordinary people, this kind of explanation is lot more make sense. 


#130
Jan3013, 08:26 PM

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Events
"An event is a given place at a given time. Einstein, and others, suggested that we should think of space and time as a single entity called spacetime. An event is a point p in spacetime. To keep track of events we label each by four numbers: p = (t,x,y,z), where t represents the time coordinate and x, y and z represent the space coordinates (assuming a Cartesian coordinate system)." In coordinate (x,y,z) if we got 2 point with null interval, then it the same point. In coordinate (t,x,y,z) if we got point with null interval, will it be the same point also? 


#131
Jan3013, 08:40 PM

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Or it just has meaning, we should avoid the word "experience" all together? 


#132
Jan3013, 08:49 PM

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Consider two points in spacetime: a spot on the the surface of the sun at a particular time; and a spot on the retina of my left eye about nine minutes later as measured by my watch. That's the path of a photon from the surface of the sun to my left eye, and the spacetime interval between those two events is zero. But they are most certainly NOT the same point: they are nine minutes and 100,000,000 miles apart from each other as far as I'm concerned... and a good thing too. 


#133
Jan3013, 09:26 PM

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That is, to answer the original question The different with the twin paradox, the twin still can see through telescope the other clock. In the photon case, we can not look at photon clock. Out clock ticking normally and tell us, about around 9 minute, the photon arrive from the sun. When we check the clock of the photon, it will be not ticking at all. The same thing with the twin paradox, when we check the clock from the twin that travel at nearly the speed of the light (after he is arrive), his clock nearly not ticking at all, which is agree with the his experience. He will said, "I've been gone for 0.00000000001 second, but why you get older nine minute"? 


#134
Jan3013, 10:38 PM

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#135
Jan3013, 11:04 PM

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"If E1 is the emission of photon at one point in spacetime, event E2 is the absorption of that photon at the same other point in space time, then the interval between them is always zero"
So how to write down E1 and E2? is that still in E1=p1=(t1, x1, y1, z1) and E2=p2=(t2, x2, y2, z2) ? Than how to calculate the null interval of it? ds^2 = (cdt)^2  dl^2 since ds=0 is because dt=0 and dl=0 or because c.dt=dl ? 


#136
Jan3013, 11:24 PM

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#137
Jan3013, 11:54 PM

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The same way [tex] \lim_{x\to a^} f(x)\ = 0 [/tex] when right left limit in not same, we still draw empty circle at the end of the line, that is at y=0 But then off course the saying is different when v=c. I get it now. Btw, saying "Time stand still" is better than saying "There is no time" or "Time do not apply", imho. Can you answer my previous question, how to write down the event of emitted and absorb of photon and why it's null interval is zero, is because dt=0 and dl=0, or because c.dt=dl 


#138
Jan3113, 12:07 AM

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My point is that, by focusing on the speed the particle is traveling, instead of the fact that it goes out, then turns around and comes back, you're focusing on the wrong thing. (0, 0, 0, 0) and (1000, 1000, 0, 0) I used units where c = 1, so we have dt = 1000 and dl = 1000; the interval is null because the two are equal. 


#139
Jan3113, 12:17 AM

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Thank you for your answer. :) 


#140
Jan3113, 01:23 AM

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just to play Lucifer's Lawyer in the photon cause:
I submit that there is ample reason to consider the passage of photon time. Consider: Our concept and measure of time is based on change, Periodic fluctuation. In this regard photons are intrinsically endowed. SO the photon proper time interval between two points is simply the number of cycles of EM phase transition. [itex]\Delta[/itex]t=(D/c)f The time difference between two photons of varying frequency is obviously relative Time Dilation Lite. I rest my case 


#141
Jan3113, 10:18 AM

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PeterDonis
very helpful insight....I had forgotten the distinction between a null interval in space versus a null interval in spacetime....... a nice brief discussion here for others who may be learning: http://en.wikipedia.org/wiki/Spaceti...time_intervals and also 'null events of a photon' trace out a lightcone....illustration here, in flat spacetime http://en.wikipedia.org/wiki/Lightcone This kind of lightcone has some characteristics of null surfaces in cosmological, also accelerated, horizons, right?? 


#142
Jan3113, 10:54 AM

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