Is light bound to travel at C?

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    Bound Light Travel
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Discussion Overview

The discussion revolves around the nature of light and its speed, particularly whether light is bound to travel at the speed of light (c) and how gravity affects its propagation. Participants explore concepts related to the speed of light in different contexts, including local versus distant observations and the implications of gravity on light's trajectory.

Discussion Character

  • Exploratory
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants propose that if objects cannot reach the speed of light, then light must always travel at that speed, suggesting a form of symmetry in the laws of physics.
  • Others clarify that while a local observer measures the speed of light as c, a distant observer may perceive light as traveling slower near massive objects due to gravitational effects.
  • It is noted that gravity can change the direction of light but does not affect its speed in a local frame of reference.
  • One participant challenges the logic of equating the behavior of light with that of massive objects, arguing that the conclusion drawn about light's speed does not logically follow from the premises about objects with mass.
  • There is a discussion about the distinction between speed and velocity, emphasizing that velocity includes direction and that gravity influences the path of light rather than its speed.

Areas of Agreement / Disagreement

Participants express differing views on the implications of light's speed and the effects of gravity, indicating that multiple competing perspectives remain without a clear consensus.

Contextual Notes

Some statements rely on specific interpretations of relativistic physics and may depend on the definitions of speed and velocity. The discussion includes assumptions about local versus distant measurements that are not fully resolved.

CAllFlow
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So I'm kind of new to the whole physics thing so be nice please :P


If i guess "nature" keeps objects from being able to go the speed of light then does "nature" keep light from going slower/faster than that speed? I first thought of this when i read a thread asking if gravity actually pulls on light. I didn't want to hijack his thread with my questions so I decided to start a new one.

Basically he was wondering if light was to say bend around Earth due to gravity, wouldn't the area of this beam of light , the side closest to Earth, move quicker than the area on the outside?
-1MileCrash

But I was thinking... if objects are bound to never go 100% of light speed then wouldn't light be bound to always go 100% of light speed? Just as an object say a car gets close to light speed and seems to slow down wouldn't light particles adjust to going faster than they're "supposed to" and govern themselves?

I don't know as I said I'm kinda new to this stuff and would really appreciate some enlightenment.
 
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Welcome to PF!

Hi CAllFlow! Welcome to PF! :wink:
CAllFlow said:
If i guess "nature" keeps objects from being able to go the speed of light then does "nature" keep light from going slower/faster than that speed?
…
... if objects are bound to never go 100% of light speed then wouldn't light be bound to always go 100% of light speed? Just as an object say a car gets close to light speed and seems to slow down wouldn't light particles adjust to going faster than they're "supposed to" and govern themselves?

Yes, that's right, the speed of light in vacuum (as measured by a local inertial observer) has to stay the same. :smile:

(though a distant observer may for example measure the light as slowing down near a massive object)
 
CAllFlow said:
But I was thinking... if objects are bound to never go 100% of light speed then wouldn't light be bound to always go 100% of light speed? Just as an object say a car gets close to light speed and seems to slow down wouldn't light particles adjust to going faster than they're "supposed to" and govern themselves?

I don't know as I said I'm kinda new to this stuff and would really appreciate some enlightenment.

Hi, welcome to PF :smile:

As tiny-tim said the speed of light near a massive body can appear slow to a distant observer, but the important things are:

1) A local observer always measures the the speed of light to be c.

2) If a distant observer measures the speed of a photon to be less than c, then he will also measure all distant material objects local to that photon to be traveling at less than the speed of the photon.

3) No observer ever sees a material object overtaking a local photon, whatever they think the speed of light is, it is always the local maximum speed for everything.

Or put another way:

All particles with rest mass are constrained to travel at less than the local speed of light.
All particles with zero rest mass are constrained to travel at c measured locally.
 
hi yuiop! :wink:

i like 2) and 3) ! :smile:

would you like to try writing a PF Library article on "speed of light" ?​
 
CAllFlow said:
So I'm kind of new to the whole physics thing so be nice please :P


If i guess "nature" keeps objects from being able to go the speed of light then does "nature" keep light from going slower/faster than that speed? I first thought of this when i read a thread asking if gravity actually pulls on light. I didn't want to hijack his thread with my questions so I decided to start a new one.
Force causes acceleration but acceleration means a change in velocity, not necessarily a change in speed. The difference is that velocity is a vector quantity (with both magnitude and direction) while speed is a number (the magnitude of the acceleration). Gravity causes light to change direction, not speed.

Basically he was wondering if light was to say bend around Earth due to gravity, wouldn't the area of this beam of light , the side closest to Earth, move quicker than the area on the outside?
-1MileCrash
That would be true assuming that the light on the "side closer to the earth" had to arrive at some destination at the same time as the light on the "outside" which is not true.

But I was thinking... if objects are bound to never go 100% of light speed then wouldn't light be bound to always go 100% of light speed? Just as an object say a car gets close to light speed and seems to slow down wouldn't light particles adjust to going faster than they're "supposed to" and govern themselves?
That's not even logically valid! You are essentially asserting that "all things of type A" (objects) "must satisfy law L" (travel at less than the speed of light) and concluding that something that is not of type A (light) then must NOT satisfy law L. Saying "if A then B" does NOT imply "if not A then not B".

As for ' light particles adjust to going faster than they're "supposed to" and govern themselves', I have no idea what that means!

I don't know as I said I'm kinda new to this stuff and would really appreciate some enlightenment.
 

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