Photon motion

[amrit]

Does photon move in space-time or it moves only in space ?

 

We say that at photon speed time stops. What does that mean?

[IDMclean]

Something to understand about photons, they define space-time. Particularly, they define the rate of change, velocity, in space-time. In my view, photons don't move through space and time. They are space and time; thus, space and time moves relative to inertial bodies. Not a popular interpretation, I know.

[Qfwfq]

Does photon move in space-time or it moves only in space ?

It doesn't really make sense to say which because the very meaning of motion is a dependence of position on time.

 

We say that at photon speed time stops. What does that mean?

It means nothing really, because it is just a very loose way of saying that a coordinate transformation is singular. To understand it properly, you need to learn the appropriate formalism for special relativity: Lorentz covariant mechanics.

 

They are space and time; thus, space and time moves relative to inertial bodies. Not a popular interpretation, I know.

Definitely not a popular interpretation.

[Natural]

Here's my 2 cents... (and ramblings)

Everything moves in space-time but you can't really call a photon a "thing". And to say that something "moves" means, for example: An atom moves from point A to point B. Meaning that a measurement was taken when it was at point A and another measurement was taken when it arrived at point B. But when that atom arrives at point B it is still the same atom that left point A. But photons are not matter they are energy. Which means that since they are like the reciprocal of mass that they really have no substance to measure position. And it would be hard to say that the photon that arrived at point B was still the same packet of energy. Especially since energy is more like what makes things move more than it is the something that is moving.

I know that's kind of a funny definition but photons are funny things.

[Ben]

It means nothing really, because it is just a very loose way of saying that a coordinate transformation is singular. To understand it properly, you need to learn the appropriate formalism for special relativity: Lorentz covariant mechanics.

Just to add to this admirably succinct response, if I may.

 

Consider a body in uniform motion relative to some arbitrary spacetime coordinate system. This coordinate system is called an "inertial reference frame" if and only if there exists a coordinate transformation that will bring this body to rest on its new coordinates, and the motion of our body is then called "inertial motion".

 

Now, one of the (two) postulates of the Special Theory is that light is measured to be the same in ALL inertial reference frames. So simple logic says that there can be no coordinate transformation that will bring light to rest on new coordinates - a case of damned if you can and damned if you can't! So there is no inertial reference frame associated to the photon.

 

Moreover, one of the consequences of the theory is that coordinate transformations of inertial reference frames induce the phenomenon of "time dilation", i.e. slower relative clock rates, of which stopped clocks is an extreme case. But since there is no inertial reference frame associated to the photon, time dilation of ANY degree is a meaningless concept for a photon.

 

In relativity, the notions of time dilation and length contraction are, in a sense, "built in" to the concepts of time and length, and since time dilation is meaningless for a photon it is usual shorthand to say the "the photon experiences no time".

 

Which is not say that photons leave one place and arrive at another instantly - experiment shows that they don't

[Natural]

Just to add to this admirably succinct response, if I may.

 

Consider a body in uniform motion relative to some arbitrary spacetime coordinate system. This coordinate system is called an "inertial reference frame" if and only if there exists a coordinate transformation that will bring this body to rest on its new coordinates, and the motion of our body is then called "inertial motion".

 

Now, one of the (two) postulates of the Special Theory is that light is measured to be the same in ALL inertial reference frames. So simple logic says that there can be no coordinate transformation that will bring light to rest on new coordinates - a case of damned if you can and damned if you can't! So there is no inertial reference frame associated to the photon.

 

This all sounds connected to my previous post (which nobody seems to be able to answer) here: http://hypography.com/forums/physics-and-mathematics/23595-accelerated-protons-and-time-dilation.html

 

 

Moreover, one of the consequences of the theory is that coordinate transformations of inertial reference frames induce the phenomenon of "time dilation", i.e. slower relative clock rates, of which stopped clocks is an extreme case. But since there is no inertial reference frame associated to the photon, time dilation of ANY degree is a meaningless concept for a photon.

 

In relativity, the notions of time dilation and length contraction are, in a sense, "built in" to the concepts of time and length, and since time dilation is meaningless for a photon it is usual shorthand to say the "the photon experiences no time".

 

Which is not say that photons leave one place and arrive at another instantly - experiment shows that they don't

 

That's a great explanation. Thanks. :D

However that last sentence makes me wonder if there exists a contradiction with the statement of "the photon experiences no time". (which would seem to be correct) And the idea that time and space are connected. Because if they have no time, which works in a time dilation sense, then they should have no space (or length) either. Which would mean that they don't really have motion. And if they do have motion, (which they obviously do) then why isn't it instantaneous? Since time at c should be 0. :D

 

This all sounds connected to my previous post (which nobody seems to be able to answer) here: http://hypography.com/forums/physics-and-mathematics/23595-accelerated-protons-and-time-dilation.html