Photon's Point Sized Universe or plane sized?

[WannabeNewton]

There's no need to be overtly rude to Bruce. $d\tau^2 = -ds^2$ is a standard definition for timelike worldlines (see Schutz p.17). For null worldlines $ds^2 =0$ which is just the simple statement that null worldlines cannot be parametrized by proper time.

The fact that he can still remain polite after all the belittling is quite endearing. Even I as a bystander find it frustrating.

 

[PeterDonis]

Using a non-standard definition doesn't mean I don't understand the concept.

But it does mean that, as a Homework Helper, you are putting the people you are trying to help at a disadvantage by not using the standard terminology that is in their textbooks.

 

[PeterDonis]

There's no need to be overtly rude to Bruce.

We're not being rude (at least, I'm not, and I don't think ghwellsjr is either when his statements are taken in context). Remember that BruceW has a Homework Helper badge.

$d\tau^2 = -ds^2$ is a standard definition for timelike worldlines (see Schutz p.17).

As I understand his definition, he would apply the term "proper time" to *any* interval, including null and spacelike intervals.

For null worldlines $ds^2 =0$ which is just the simple statement that null worldlines cannot be parametrized by proper time.

Which means that using the term "proper time" to refer to such an interval is, to say the least, confusing. And using that term to refer to a spacelike interval, IMO, goes beyond confusing to misleading.

 

[WannabeNewton]

I don't disagree with any of the objections raised against Bruce's statements, I just think it can be stated in a way that won't potentially hurt his feelings.

 

[Naty1]

BruceW posts:

And I find the standard definition of 'proper time' to be not very useful (personally). Therefore I define 'proper time' to be synonymous to 'spacetime interval'.

seems like a good subject for you to ask about in a separate thread...and the implications in GR particularly.

 

[yuiop]

Hi aayushgsa,

Assuming that is meaningful for a photon to have an inertial reference frame, (i.e that there is an inertial reference frame in which the photon can be said to be at rest) causes a contradiction with the fundamental assumption of relativity, that the speed of light is c in any irf.

 

[PhotonCurve]

Hello,
I recently read about a photon's point of view according to relativity(which is a fascinating thing for a high school boy), It said to photon's perspective the universe is point sized. But recently I learned that lorentz contraction occurs in the dimension in which the object is travelling. If this is so, Imagine a photon traveling in the z direction according to lorentz transformation formulas, Contraction would only be in the Z direction and the photon will see the universe as an Infinite plane with an infinitesimal thickness. isn't it?. But the thing that photon sees universe as point sized seems contrary. Where I am Wrong? Please use some maths(but simple because i am still a high schooler).
Thank-You

The photon does not have a perspective as such, because it doesn't have a frame of reference. The reason why, is because if it did, it would actually never traverse a space in any amount of time.

 

[Bill_K]

We don't seem to be talking about the OP any more. Wouldn't it be appropriate to start a new thread?

EDIT: Per Bill_K's suggestion the off topic posts have been moved to a new thread: https://www.physicsforums.com/showthread.php?t=705544

 

[BruceW]

ah, thanks. yes, sorry I pulled the thread off-topic quite a bit.