Speed of Light: Questions Answered

[king123]

TL;DR Summary

About the manifestation speed of light?

Yess! speed of light it's driving me crazy. I know it might sound too noob and silly but please enlighten me, First of all how does we concluded that speed of light is constant for every observer in all possible inertial frames of reference. Next thing how come a photon doesn't experience time,if I assumed and considered it as an event of emission and absorption of a single photon(I heard about the relativistic effects on different observers ,does that means that photon can't possibly know that it's been emitted and absorbed),as far as I know events are generally based on time. Please correct me if I'm wrong.

Thanks in advance.

 

[berkeman]

Here is an Insights article to get you started...

https://www.physicsforums.com/insights/speed-light-frames-reference/

 

[king123]

Here is an Insights article to get you started...

https://www.physicsforums.com/insights/speed-light-frames-reference/

Thank you

 

[Dale]

Summary:: About the manifestation speed of light?

First of all how does we concluded that speed of light is constant for every observer in all possible inertial frames of reference

Basically we built experiments of many different designs that were designed to measure the change in the speed of light in different reference frames. They all came back with the same constant with no change in different frames. It isn't something that we just invented, it was a fact in the data that we had to adapt our theories to include.

 

[Nugatory]

First of all how does we concluded that speed of light is constant for every observer in all possible inertial frames of reference.

There is a ton of experimental evidence, starting with the Michelson-Morley experiment in the late 19th century. Some of this evidence is described in the sticky thread at the top of this forum on experimental evidence for relativity.

Even before this experiment, nature had already given us a big hint that the speed of light might well behave that way. James Maxwell was able to calculate the speed of light from the laws of electricity and magnetism in 1865. Those laws are the same in all inertial frames (you don’t observe any differences in how electricity works between noon and midnight even though the rotation of the Earth is changing your speed in every inertial frame) so the the speed of light ought to be as well. Indeed, the disconnect between this prediction of E&M and the commonsense expectation that the speed of light would be not be the same in all inertial frames (all other speeds behave that way) was the great unsolved problem of 19th century physics, until Einstein discovered special relativity. There’s much discussion in many older threads here.

Next thing how come a photon doesn't experience time,

That’s just plain incorrect, although the misunderstanding is so common that we have a FAQ about it.

 

[king123]

That’s just plain incorrect, although the misunderstanding is so common that we have a FAQ about it.

Can you please provide me an insight about why it's incorrect, because if it's incorrect I want to know why? To make myself clear

 

[Nugatory]

Can you please provide me an insight about why it's incorrect, because if it's incorrect I want to know why? To make myself clear

Someone will post up a link to the FAQ in a moment and we have many older threads on the subject (like I said, it’s a common misunderstanding).

My quick answer is that you got that “time doesn’t pass for a photon” result by plugging $v=c$ into the time dilation equation and seeing infinite time dilation come out. However, the time dilation formula only works between things that are at rest in different inertial frames - and there is no inertial frame in which light is at rest. The infinite time dilation result is just another division by zero error, the way the math tells you that you’ve made a mistake.

 

[DrGreg]

There is a Relativity FAQ List at the top of the relativity forum and within it you will find:

• Why is the speed of light the same in all frames of reference?
• Rest frame of a photon

 

[king123]

There is a Relativity FAQ List at the top of the relativity forum and within it you will find:

• Why is the speed of light the same in all frames of reference?
• Rest frame of a photon

Thank you