# Thread: Photon at both origin and finish at the same?

1. ## Photon at both origin and finish at the same?

Hello all,
I spent some time pondering something I heard Neil Degrasse Tyson say on a video.
Can't remember the video though, I have watched several by him recently.
Anyways, he said that to a photon travel time is instantaneous.
So I made a diagram to help understand what he was saying, using from what I knew about Einstein's mirror setup.
Basically in one second a photon travels 150,000 kilometers in half a second bounces off a mirror and returns traveling 150,000 kilometers more to arrive at the point of origin.
For sake of this argument I am using the value of 300,000 km per second. ( seems close enough for me )

In Fig. 1 The red line is the photon traveling from the origin and the blue line is the return. Line AB and then Line BC
The magenta line is the distance the photon would experience, and that value changes when the origin is moved. Line BD

In the first triangle in my diagram ( fig 2. ) the origin travels left to right 100,000 km in one second ( 1/3 the speed of light ), and the magenta line is the distance the photon experiences.
The distance the photon experiences is less than when the origin is static, since light travels at a constant the time that the photon was moving is less ( total travel time about ~.94 seconds ).

In Fig. 3 the distance the origin travels is 2/3 the speed of light and the reduction in time for the photon is greater and the overall time the photon experiences traveling is ~.74 seconds.

In Fig 4, the origin of the photon moves at the speed of light, and the magenta line has no length so that means the time the photon traveled for zero seconds yet was able to traverse the distance from origin beginning and end ( a cycle of 300,000 km).

I don't know how to say it but for distances less than 300,000 km ( roughly the speed of light ) photons travel instantaneously, maybe for greater distances ( but I have not modeled it so I don't know ).
Strange maybe I got it wrong but that is how I understand it.
Hopefully it isn't too confusing.

2. It is very simple: since the photon travels at speed of light its time is infinitely slower.

3. Time is not absolute; it depends on the motion of the observer. An observer that accelerates rapidly experiences time passing more slowly than one that does not accelerate. A photon accelerates instantly to c when it is emitted, and accelerates (or if you prefer, decelerates) instantly from c to zero when it is absorbed; as a result it experiences no elapsed time between the emission event and the absorption event, even if these events are separated by billions of light-years.

All objects with zero rest mass behave in this way.

4. Originally Posted by Juma
It is very simple: since the photon travels at speed of light its time is infinitely slower.
Or you could look at it as because of Lorentz contraction the distance light travels is zero from the perspective of the light even though another observer may see it as many light years travel. Each end of light's travel is at the same point from the light's point of view. Most people have problems understanding relativity because of the natural tendency to select some preferred reference frame which the OP seems to be doing - assuming that what the observer sees is what the light sees.

5. This video explains time dilation quite nicely, https://www.youtube.com/watch?v=HHRK6ojWdtU . Start it from 3:33.

6. Originally Posted by ryan
This video explains time dilation quite nicely, https://www.youtube.com/watch?v=HHRK6ojWdtU . Start it from 3:33.
yeah, I basically model the same event but take it to the logical end.
Fig 4 shows that from the perspective of the electron the electron experiences no time yet is at a distance of 300,000 km from the starting point.
I dare say the it might be at both places.. but I don't think so.

7. Originally Posted by none
Originally Posted by ryan
This video explains time dilation quite nicely, https://www.youtube.com/watch?v=HHRK6ojWdtU . Start it from 3:33.
yeah, I basically model the same event but take it to the logical end.
Fig 4 shows that from the perspective of the electron the electron experiences no time yet is at a distance of 300,000 km from the starting point.
I dare say the it might be at both places.. but I don't think so.
For the photon there is no distance either.

8. Originally Posted by none
Originally Posted by ryan
This video explains time dilation quite nicely, https://www.youtube.com/watch?v=HHRK6ojWdtU . Start it from 3:33.
yeah, I basically model the same event but take it to the logical end.
Fig 4 shows that from the perspective of the electron the electron experiences no time yet is at a distance of 300,000 km from the starting point.
I dare say the it might be at both places.. but I don't think so.
As Juma says, there is no distance for the photon. Both the lines BD and AC in your diagrams are zero in length in the photon's referemce frame because of time dilation and Lorentz contraction. They only have the length's you observe from your reference frame.

Which reference frame is "correct" depends on which reference frame the observer is in. There is no universally "correct" reference frame... that is what special relativity is all about. General relativity expands on this into quite a bit more.

The GPS system wouldn't work to give us position information on Earth if corrections were not constantly made to compensate for the differences seen between the the reference frames of the satellites and the reference frame of the Earth.

9. Originally Posted by skepticalbip
Originally Posted by none
Originally Posted by ryan
This video explains time dilation quite nicely, https://www.youtube.com/watch?v=HHRK6ojWdtU . Start it from 3:33.
yeah, I basically model the same event but take it to the logical end.
Fig 4 shows that from the perspective of the electron the electron experiences no time yet is at a distance of 300,000 km from the starting point.
I dare say the it might be at both places.. but I don't think so.
As Juma says, there is no distance for the photon. Both the lines BD and AC in your diagrams are zero in length in the photon's referemce frame because of time dilation and Lorentz contraction. They only have the length's you observe from your reference frame.

Which reference frame is "correct" depends on which reference frame the observer is in. There is no universally "correct" reference frame... that is what special relativity is all about. General relativity expands on this into quite a bit more.

The GPS system wouldn't work to give us position information on Earth if corrections were not constantly made to compensate for the differences seen between the the reference frames of the satellites and the reference frame of the Earth.
thanks for this clarification, to me it is simply amazing.

10. Originally Posted by none
Originally Posted by ryan
This video explains time dilation quite nicely, https://www.youtube.com/watch?v=HHRK6ojWdtU . Start it from 3:33.
yeah, I basically model the same event but take it to the logical end.
Fig 4 shows that from the perspective of the electron the electron experiences no time yet is at a distance of 300,000 km from the starting point.
I dare say the it might be at both places.. but I don't think so.
Interesting point (I will assume that you meant "photon" instead of "electron"). It is no wonder why there is entanglement since distance is irrelevant, at least for the photon.

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