Light speed; time dialation theory and its age

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Discussion Overview

The discussion centers around the concept of time dilation in the context of light traveling at the speed of light (c). Participants explore the implications of this theory on the notion of age for light and the challenges of defining a rest frame for light, as well as the limitations of applying physical laws at light speed.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions whether light experiences age, suggesting that if time becomes zero at light speed, then light has no age.
  • Another participant argues that discussing a frame moving at the speed of light is unphysical and suggests consulting the Relativity FAQ for clarification on the rest frame of a photon.
  • A different participant explains that while an observer sees someone moving near light speed aging more slowly, this does not imply that the person is younger in their own frame, emphasizing the distinction between worldtime and proper time.
  • One participant acknowledges the impossibility of measuring light's age from its rest frame, suggesting that it may have some age in that frame.
  • Another participant asserts that the inertial frame of light is constant and that physics laws apply only below light speed, referencing singularities in general relativity as analogous situations.
  • A later reply clarifies that light propagates at c in any inertial frame and that it is meaningless to discuss a rest frame for light, as no object can reach c in any inertial frame.

Areas of Agreement / Disagreement

Participants express disagreement regarding the feasibility of defining a rest frame for light and the implications of time dilation on the concept of age for light. Multiple competing views remain on these topics.

Contextual Notes

The discussion highlights limitations in understanding the behavior of light at c, particularly regarding the application of physical laws and the definitions of rest frames. There are unresolved assumptions about the nature of time and age as they relate to light.

rgprasannakum
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Hi All..
I have a basic doubt in time dilation theory. As per time dilation theory, when an object moves with the velocity of light, then relatively its time becomes zero. In that case, light is traveling at 'velocity of light'. So for light, there is no age? Or I misconcepted time dilation theory?
 
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You are asking for an unphysical situation. We don't have the ability to transform and know what laws work in the frame moving with velocity c.

I suggest you read the Relativity FAQ

https://www.physicsforums.com/forumdisplay.php?f=210

...especially the entry on the rest frame of a photon.

Zz.
 
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When you look at an someone moving with the velocity near to that of light, in your rest frame, you see that he gets older more slowly than if he was in your inertial frame, and obviously it doesn't mean that he is younger in his inertial frame too. The fact is that you are talking about the worldtime while his age, which is defined by himself, is according to the propertime (time in his rest frame). It is clear that matter never reach to c and your question is about light, but it seems the approach to it the same, for measuring the light's age you should go to its rest frame that is impossible while we can never reach to c.
 
@ Saeide: As you said, we're not potential enough to reach velocity of light to measure its age. Maybe in light's frame; it might have some ages. But What I'm talking about is the intertial frame where the light does exist.
 
The inertial frame where the light exists and the light's frame are the same, while the light velocity is constant and as a result we can say that the frame is inertial. Of course our physics laws are applicable only for velocities less than c, just like singularities in GR that we are not aware of what is going on in them.
 
In Special Relativity, light is defined to propagate at c in any inertial frame you choose. When we talk about an object's inertial frame, we mean one in which the object is at rest. Therefore, it is meaningless to talk about light's frame. This isn't just a semantic issue, the mathematics won't support one inertial frame moving at c relative to another inertial frame so we can safely conclude that no object can move at c in any inertial frame.
 

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