Thermos aquaticus
Well-Known Member
You are jumping between frames again. The photon does not exist in a valid reference frame. The observer does. What we are describing is what you would observe travelling at those speeds.
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Seeing things in their past? You are full of beans!
- Thread starter james blunt
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You are jumping between frames again. The photon does not exist in a valid reference frame. The observer does. What we are describing is what you would observe travelling at those speeds.
TrueBeliever37
Well-Known Member
The problem is you can't use what you call the relativistic time to really determine anything, so what good is it? It just seems like some kind of imaginary concept.
It takes way more blind faith to believe this, than to believe there is a God.
For things going slower than light, the proper time is what the observer would actually experience in the journey. In the case of the photon, that proper time is always 0 (even in general relativity, by the way).
In fact, it is the proper time between events that is the same in all reference frames. If you compute it in one frame you will always get the same answer in every other frame. In many ways, that makes it more 'real' than measured time or distances.
TrueBeliever37
Well-Known Member
Right, but the observer always notices the photon taking twice as long to go twice the distance.
Thermos aquaticus
Well-Known Member
We can use relativistic time to program the clocks on GPS satellites so that they run close to the appropriate speed. Even then, they have to be adjusted on a daily basis. This is because time runs at a different pace in orbit than it does on the surface of the Earth due to relativity, and it has real consequences for the accuracy of GPS.
Why would it take faith when we can measure relativistic effects in multiple experiments?
Thermos aquaticus
Well-Known Member
The observer does, yes.
Yes. So? You asked what the *photon* experiences. The only reasonable answer to that question is the proper time for the path the photon takes. And that proper time is 0.
TrueBeliever37
Well-Known Member
For me the so, is that, if that is what an observer sees at all times, then that is what the truth of the matter must be. The photon always takes twice as long to go twice the distance.
Even though it might appear to be different in some reference frame that doesn't really exist.
First of all, the reference frames from all the ships *do* exist.
And, if you compute the proper time (which *is* a valid thing to compute), the proper time for all photons is always 0. And, guess what? twice zero is zero!
We don't even need the fictional frame to compute the proper time. We just need the two events (position and time) at either end of the path.
As I said, in many ways, this proper time is more 'real' than any time measured in any frame. Furthermore, the proper time is zero even in general relativity and that fact makes it easier to determine the path of light in many cases than the paths of things like planets and stars.
TrueBeliever37
Well-Known Member
I am not jumping between frames. I asked you using several different valid frames as examples, if it took the photon twice as long to go twice the distance, and you replied yes to all the frames I had asked about.
Yes, then you asked what the photon 'experienced'. That is a different frame.
Fortunately, there is a frame-independent answer: the proper time. And the proper time for the photon in all cases is 0.
Thermos aquaticus
Well-Known Member
GPS satellites are real things, and they experience a difference in passage of time compared to time on the surface of the Earth that has real consequences for the accuracy of GPS measurements. There is even an Air Force squadron whose entire job is to update the time on GPS satellites so that they stay accurate.
The combination of these two relativitic effects means that the clocks on-board each satellite should tick faster than identical clocks on the ground by about 38 microseconds per day (45-7=38)! This sounds small, but the high-precision required of the GPS system requires nanosecond accuracy, and 38 microseconds is 38,000 nanoseconds. If these effects were not properly taken into account, a navigational fix based on the GPS constellation would be false after only 2 minutes, and errors in global positions would continue to accumulate at a rate of about 10 kilometers each day! The whole system would be utterly worthless for navigation in a very short time.
The engineers who designed the GPS system included these relativistic effects when they designed and deployed the system. For example, to counteract the General Relativistic effect once on orbit, the onboard clocks were designed to "tick" at a slower frequency than ground reference clocks, so that once they were in their proper orbit stations their clocks would appear to tick at about the correct rate as compared to the reference atomic clocks at the GPS ground stations. Further, each GPS receiver has built into it a microcomputer that, in addition to performing the calculation of position using 3D trilateration, will also compute any additional special relativistic timing calculations required [3], using data provided by the satellites.
Relativity is not just some abstract mathematical theory: understanding it is absolutely essential for our global navigation system to work properly!
GPS and Relativity
TrueBeliever37
Well-Known Member
I appreciate the time and effort you and Thermos have put into discussing this with me. I can't say that I agree with you, but still appreciate your civility.
Thermos aquaticus
Well-Known Member
"But my point is the photon would always experience/take twice the time for twice the distance, no matter what valid reference frame you are using."--TruBeliever37
You shifted to what the photon experiences, not what the observers in those reference frames observe.
TrueBeliever37
Well-Known Member
I was trying to say that no matter what valid reference frame was used, that to the observer it appears that the photon always takes twice the time to go twice the distance. Which I equate to being the same thing as the photon experiencing twice the time (in that reference frame).
Given that our replies have been based on physics that has been verified in many different ways, from GPS to particle accelerators, why do you disagree? Because it goes against your intuition on how things *should* be? Then maybe the intuition is what needs to change.
But different frames measure different amounts of time. So NONE of them is what the photon 'experiences'.
But, like I said, the 'proper time' is something that all frames agree on, and that gives the clock time for all slower-then-light observers. It is the proper time that is 'experienced'. So, the best answer to your question of what the photon experiences is the proper time. And that proper time is 0 for all photons in all situations.
And, once again 2*0=0. if the photon goes twice as far and the distance covered is twice as much, the proper time *is* doubled. But it doubles from 0 to 2*0 = 0.
TrueBeliever37
Well-Known Member
It just seems to defy logic.
Thinking an alien could travel into the past and possibly see dinosaurs roaming the earth.
Thinking that actual physical distances become 0, so that 8 light minutes = 30 million light years.
Using a frame of reference to try to prove something, but then saying that frame doesn't really exist.
Noticing that it takes light 8m and 20s to get here from the sun, but yet believing it doesn't experience any time.
Seeing that in every valid reference frame, to an observer it took the photon twice as long to go twice the distance. Surely it shows the photon experienced a time difference using that reference frame.
TrueBeliever37
Well-Known Member
I am talking about what the photon experiences in the other valid reference frames. Two different distances and two different times.
Why do you keep using a reference frame that doesn't even exist?
Subduction Zone
Veteran Member
Your quest is rather pointless The photon doesn't "experience" anything in its journey. It simply is. When it comes to frames of reference what one is describing is what the observer in that frame sees.