Special relativity and photon dimensionality

Click For Summary

Discussion Overview

The discussion revolves around the implications of special relativity on the dimensionality of photons. Participants explore the concept of length contraction and whether photons possess any dimensionality when considered from different reference frames, including the notion of a photon's proper length.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • Some participants discuss the formula for length contraction and its application to photons, questioning if a photon has no dimensionality in our reference frame.
  • There is a contention regarding the existence of a reference frame for photons, with some asserting that a photon does not have a reference frame, while others explore the implications of measuring a photon's length if it were stationary.
  • One participant suggests that while light moves at the speed of light in all frames, this does not necessarily imply that a photon's proper length is zero.
  • Another participant emphasizes that length can only be measured in a reference frame, reiterating that since photons lack a reference frame, questions about their dimensionality may be meaningless.
  • A later reply introduces the idea that while photons exhibit particle-like behavior in certain experiments, they fundamentally behave as waves, leading to the conclusion that they do not possess dimensionality in the traditional sense.

Areas of Agreement / Disagreement

Participants generally agree that photons do not have a reference frame, which complicates the application of special relativity to them. However, there is disagreement about the implications of this lack of a reference frame on the dimensionality of photons, with some suggesting they may have a proper length while others argue against this notion.

Contextual Notes

The discussion highlights limitations in applying special relativity to light, particularly regarding the measurement of length and dimensionality, which remains unresolved and dependent on the definitions used.

Aziza
Messages
189
Reaction score
1
according to length contraction, L=Lp√(1-v^2/c^2), where Lp is proper length as measured by observer at rest with respect to the two ends of the object. So the length of objects moving relative to us we measure as less than the length the observer at rest measures.
Applying this to light itself, if you plug in c for v, you get zero, so does this mean that a photon necessarily has no dimensionality to it as viewed in our reference frame? And does this mean that in its own reference frame, the photon does possibly actually have some length/width/etc?
 
Physics news on Phys.org
Aziza said:
according to length contraction, L=Lp√(1-v^2/c^2), where Lp is proper length as measured by observer at rest with respect to the two ends of the object. So the length of objects moving relative to us we measure as less than the length the observer at rest measures.
Applying this to light itself, if you plug in c for v, you get zero, so does this mean that a photon necessarily has no dimensionality to it as viewed in our reference frame? And does this mean that in its own reference frame, the photon does possibly actually have some length/width/etc?

A photon doesn't HAVE a reference frame.
 
phinds said:
A photon doesn't HAVE a reference frame.

sorry i didnt mean reference frame, bad wording. I guess I just mean that if you travel along with a photon such that the photon is stationary to you, will the photon have a length/width/etc? I am basically confused about how we can say light is also particle if that particle has no dimensions
 
Aziza said:
sorry i didnt mean reference frame, bad wording. I guess I just mean that if you travel along with a photon such that the photon is stationary to you, will the photon have a length/width/etc? I am basically confused about how we can say light is also particle if that particle has no dimensions

That's what phinds was saying: you can't travel along with a photon so that it appears stationary. Light travels at c in every frame, which means you can't possibly find a frame in which it is stationary.
 
elfmotat said:
That's what phinds was saying: you can't travel along with a photon so that it appears stationary. Light travels at c in every frame, which means you can't possibly find a frame in which it is stationary.

ohh i see right right. ok but still, let's say light itself measures its own proper length. Since in all frames, light moves at same speed of light, then in all frames we would say light has no length. But this does not mean proper length of photon is zero. right or no?
 
Aziza said:
ohh i see right right. ok but still, let's say light itself measures its own proper length. Since in all frames, light moves at same speed of light, then in all frames we would say light has no length. But this does not mean proper length of photon is zero. right or no?

You (or a photon) can only measure length in a reference frame. A photon doesn't HAVE a reference frame, so your question is meaningless.
 
phinds said:
You (or a photon) can only measure length in a reference frame. A photon doesn't HAVE a reference frame, so your question is meaningless.

oh...so basically there is no way to apply special relativity to light itself to get any meaningful results?
also however I am still curious, does photon have any known dimensionality to it?
 
Aziza said:
does photon have any known dimensionality to it?

Now that's a reasonable question. I THINK, and I'm not an expert here, is that you have to say no because although it acts like a particle in some experiments, it's basically a wave and you can't hit a photon with a photon. Obviously a photon DOES hit other things, but that's because THEY have size.
 

Similar threads

Undergrad Basic Special Relativity question but the math isn’t working
  • · Replies 17 ·
Replies
17
Views
2K
Undergrad I think the special theory of relativity self-contradicts
  • · Replies 32 ·
2
Replies
32
Views
3K
Undergrad How Does Special Relativity Affect Perceptions of Simultaneity?
  • · Replies 32 ·
2
Replies
32
Views
3K
Undergrad Question about special relativity and magnetism
  • · Replies 5 ·
Replies
5
Views
2K
High School A thought experiment regarding special relativity
  • · Replies 15 ·
Replies
15
Views
2K
Undergrad Why is the Lorentz Force always perpendicular to velocity?
  • · Replies 55 ·
2
Replies
55
Views
4K
Undergrad Understanding Einstein's second postulate of special relativity
  • · Replies 57 ·
2
Replies
57
Views
8K
High School Do photons travel instantaneously?
  • · Replies 41 ·
2
Replies
41
Views
6K
Graduate Special Relativity in Rotating Reference frame
  • · Replies 20 ·
Replies
20
Views
2K
Undergrad Relativity of Simultaneity and Length Contraction
  • · Replies 54 ·
2
Replies
54
Views
5K