Photon - Frozen in Time-Space..?!

[everneo]

" Light is not affected by time dilation at all. A photon effectively experiences no time in its own frame of reference*. "

All the conventional physicists, especially JR (*quotes from him), are requested to clarify and discuss in detail for the sake of rest of us- learners..!

[chroot]

This is actually an easy one. :)

Let's say you're the captain of your very own spacecraft capable of relativistic velocities. You're standing on the helm, and you're timing your trip between distant locations to measure your velocity relative to them (just as a car's speedometer measures its speed relative to the road).

Let's say you set course for Proxima Centauri, which is ~4 light-years away. You might think it would take you a minimum of 4 years to arrive at Proxima, but that is not true.

If you continue to fire your thrusters, you will continue to gain velocity relative to Proxima, and it will take less and less time to get there. It might take you 3 years... or 1 year... or 4 seconds to get there. In your own frame of reference, everything is hunky-dorky -- you don't notice anything weird going on. Your clock ticks, your speedometer works, and your accelerometers measure constant thrust, no matter what velocity you measure yourself as moving. Flashlight beams flashed across the cabin still take the "right" amount of time, as if the spacecraft were just standing still. This is the notion that there is [with only one exception] no such thing as absolute velocity. Inside your spaceship, you'll always experience physics the same old way. You'll never be able to tell how fast you're moving with respect to Proxima unless you open the blinds and look outside the spacecraft.

Now, to an external observer, your spacecraft does not appear to be accelerating uniformly. Instead, an outside observer sees your spacecraft as becoming more massive; he sees your experiments run slowly; he sees your acceleration constantly decreasing.

Back on the helm, if you continue to accelerate your craft practically forever, you'll arrive at what you'd measure as a "practically infinite" velocity. It will take you 0.00001 nanoseconds to fly from here to Proxima, for example. In the limit as you accelerate forever, it will take zero time to get anywhere, and you'll measure your own velocity (relative to Proxima) as infinite. However, something peculiar happens to your experiments when you get to what you measure as infinite speed -- they stop working! (Of course, you can't accelerate forever, so it's a moot point).

An outside observer watching you would measure that you're approaching the speed of light. In the [physically impossible] limit of reaching "infinite velocity" at the helm, the outside observer will measure you going the speed of light.

One way to think about your experiments no longer working is that your "clock" has "stopped." Even though you didn't notice anything at all happening as you approached infinite velocity, when you obtain infinite velocity, all your experiments stop working -- and rightly they should! If you had an experiment onboard to measure the speed of light, you'd discover that there's no longer any light to measure! There's no way for an experiment to occur in less than zero time, and you can be anywhere in the universe in what you'd measure as zero time -- time has been frozen on the helm of your spacecraft.

You, on the helm, measure yourself as going infinite speed because it takes zero time to go anywhere. An outside observer will measure you as going the speed of light. If you, inside the spacecraft, measure the speed of light, it'll be zero, since it won't ever cross the cabin. So there's a "paradox" here: are you going c, or infinite speed? The answer to the paradox, of course, is that this situation isn't physically possible. You can view the paradox as a reason why it's not physically possible, if you'd like.

- Warren

[everneo]

Warren, thanks for the detailed explanation thro thought experiment. Please correct me if i miss some points :

However hard i increase my acceleration, once i reach velocity of light c, my time freezes and acceleration does not happen any more. Outside observer observes i decelerate when approaching the speed of light and remain in c once a reached that velocity. So infinite velocity ruled out and maximum velocity remains at c in my reference frame as well as the outsider's.

still hard to visualize something :-

1. At constant velocity c, if i pass thro 4 stars, on my path, with distance between them be anything - as my time remains frozen do i cross these stars at the same time (my proper-time).. in short, am i present everywhere along the straight path ahead of me..

2. if so, does that mean that i've lost a dimension (direction of probagation, that contracted to, well, say zero) in my frame of reference.. since i have no path to proceed..

[chroot]

Originally posted by everneo
However hard i increase my acceleration, once i reach velocity of light c, my time freezes and acceleration does not happen any more.
You'd have to accelerate for an infinite time to reach c. When you reach c, it'll take zero time to go anywhere -- so it doesn't even make any sense to accelerate anymore. How can you go between two places in less than zero time?
1. At constant velocity c, if i pass thro 4 stars, on my path, with distance between them be anything - as my time remains frozen do i cross these stars at the same time (my proper-time).. in short, am i present everywhere along the straight path ahead of me..
Yes, the distances are foreshortened to zero. If you have four stars along your path, you'll appear to be at all four stars simultaneously.
2. if so, does that mean that i've lost a dimension (direction of probagation, that contracted to, well, say zero) in my frame of reference.. since i have no path to proceed..
You've effectively lost the notion of time!

- Warren

[everneo]

I got your point. At velocity c, time is frozen and time is not effective in any way and one looses the notion of time.

Now let us turn to photon. So far it was observed by us to pass thro time and space though photon has no notion of time and unaffected by time on its own.


1. Is the transverse oscillation of photon (i know i mix wave function with particle, just ignore the mistake..! it would be learning experience for me and others) just an observed phenomenon or photon/wave really goes thro that.

a) If the oscillation is intrinisic to light then it still needs/percieves time to oscillate...

b) If it is just an observed phenomenon what makes it to appear so...

(am i sounding like a CP..?:D )

[Natural]

Sorry chroot, but I don't get your point. I can't understand the utility in discussing in such detail all the aspects of a situation that cannot exist-- even in principle. It would appear to me that to reach light speed a body would have to become massless. End of (the body's) story. I think other discussions I've seen you post that do remain within the limits of what is relativistically possible make the point better-- but that's just me!
But don't get me wrong, I do enjoy your input. :D

[WhiteKnight]

This has always bugged me with every sci-fi movie, tv show, novel, whatever I've ever read.

Once you achieve "infinite" speed, is there any way to stop? :bugeye:

[everneo]

Originally posted by Natural
I can't understand the utility in discussing in such detail all the aspects of a situation that cannot exist-- even in principle. It would appear to me that to reach light speed a body would have to become massless. End of (the body's) story.

Thats why this is just a thought experiment to visualize what happens at speed c. No matter with a mass can ever reach the velocity of light. Actually this discussion is not about whether a matter with mass can reach/exceed the velocity c or not.

[Crisp]

Hi all,

For those that wonder what use it is to talk about "what happens when you reach lightspeed" even though in practice you can't...

What happens at c is extrapolated from what happens very, very, very close to c (infinitely close as a matter of fact). Mathematically this comes down to taking a limit (v -> c). You can see what happens with your formulas when you do this limit/extrapolation procedure, and it turns out that special relativity predicts that the more your speed v approaches c, the shorter all distances become and the shorter times you require to travel them. As a matter of fact, extrapolating what happens reveals that at v = c, all distances become zero (you are "everywhere" from your point of view) and you can go anywhere in zero seconds.

Bye!

Crisp

[synergy]

Agree with all of you. It might be noticed that, as I've speculated elsewhere and now find chroot agreeing with me, that IN THE FRAME OF REFERENCE OF THE TRAVELLER, since his clock slows, he can actually perceive himself to be surpassing light-speed at the same time that a stationary observer perceives him to be approaching that speed. My question is, is the traveller's frame of reference right? Could it be that he is going faster than light, and it only looks to us that he isn't because of our inability to measure in his frame of reference? If so, it probably wouldn't change current equations, we would need a new approach to find out which is the truth.

[chroot]

Originally posted by synergy
Agree with all of you. It might be noticed that, as I've speculated elsewhere and now find chroot agreeing with me, that IN THE FRAME OF REFERENCE OF THE TRAVELLER, since his clock slows, he can actually perceive himself to be surpassing light-speed at the same time that a stationary observer perceives him to be approaching that speed. My question is, is the traveller's frame of reference right? Could it be that he is going faster than light, and it only looks to us that he isn't because of our inability to measure in his frame of reference? If so, it probably wouldn't change current equations, we would need a new approach to find out which is the truth.
Neither view is "right." Both views are valid.

- Warren

[Crisp]

Hi synergy,

It might be good to note that even the observer going at a very high speed will not think he is going faster than light. For him, he is just travelling a short distance at a fast speed (i.e. it requires a short amount of time). To us, it seems that he is travelling a longer distance at a longer amount of time. There is no FTL in this scenario...

That's why they are both right as Warren pointed out.

Bye!

Crisp.

[Natural]

The thought experiment by Warren above sounds good so long as he stays at 99.9999% c. It's when he goes to c he erres:

Back on the helm, if you continue to accelerate your craft practically forever, you'll arrive at what you'd measure as a "practically infinite" velocity. It will take you 0.00001 nanoseconds to fly from here to Proxima, for example. In the limit as you accelerate forever, it will take zero time to get anywhere, and you'll measure your own velocity (relative to Proxima) as infinite. However, something peculiar happens to your experiments when you get to what you measure as infinite speed -- they stop working! (Of course, you can't accelerate forever, so it's a moot point).

He's clearly talking about the traveler measuring his speed as approaching infinte. Relative to what? Proxima Centauri. But SR absolutely forbids anyone from measuring any relative velocity faster than c. So tell me, when we extrapolate from 99.999% c to c, how do we jump from measuring all speeds less than c to measuring the reference frame of Proxima Centuari as infinite?

Nearly all he said thereafter was likewise flawed.

[zanket]

Natural - You’d measure your own velocity (relative to Proxima) as infinite if you used the craft’s proper time but distances as measured when you were at rest relative to the stars. Using both proper time and proper distance your velocity would be c. I think chroot was describing how, if you traveled at c, practically speaking your velocity would be infinite. In this respect, the speed c is the maximum comprehendible proper speed. And he did say his point is moot because you’d need to accelerate forever.