What If Light Could Travel Slower?

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Discussion Overview

The discussion revolves around the hypothetical scenario of light traveling at a slower speed than its established speed in a vacuum. Participants explore the implications of this idea, questioning the nature of light and its properties in different mediums, as well as the concept of "stopping" light.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • One participant questions what would happen if light could travel at a speed of 299,742,450 m/s instead of its standard speed, asking if it would still be considered light.
  • Another participant notes that light travels slower than 3E8 m/s in all mediums except a vacuum, suggesting that the speed of light is context-dependent.
  • A participant mentions that in water, light travels at about 225,500,000 meters per second, questioning whether light is still visible in that medium.
  • Some participants discuss the interaction of photons with electrons in materials, which leads to the perception that light travels slower in those contexts.
  • There is a claim that light can be "stopped," with a participant expressing confusion about how light can still be considered light if it is stopped.
  • One participant argues that if light were to travel at any speed other than its defined speed, it would not be light, suggesting a strict definition of light's existence tied to its speed.
  • A participant attempts to work through equations related to the energy and momentum of photons, concluding that if a photon has zero momentum and energy, it may not exist in a meaningful way.

Areas of Agreement / Disagreement

Participants express differing views on the implications of light traveling at slower speeds, with some suggesting that it would not be light, while others explore the conditions under which light behaves differently in various mediums. The discussion remains unresolved regarding the nature of light and the consequences of altering its speed.

Contextual Notes

Participants reference various equations and concepts from physics, but there are indications of uncertainty and lack of formal training among some contributors, which may affect the rigor of the arguments presented.

burt reynolds
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so i just graduated high school taking only one physics class in 4 years. it was an academic level class and i only took it to fulfill a requirment, but I am glad i took it because it got me thinking. i don't plan to do anything with phusics in the fuutre, but i do have some questions that will probably seem elementary to most of you. here's the question: i know light travels 299,792,458 meters per second, but what if it could somehow travel slower to say 299,742,450 m/s? what would happen? would it still be light? has this ever been done? physics is hard.
 
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burt reynolds said:
so i just graduated high school taking only one physics class in 4 years. it was an academic level class and i only took it to fulfill a requirment, but I am glad i took it because it got me thinking. i don't plan to do anything with phusics in the fuutre, but i do have some questions that will probably seem elementary to most of you. here's the question: i know light travels 299,792,458 meters per second, but what if it could somehow travel slower to say 299,742,450 m/s? what would happen? would it still be light? has this ever been done? physics is hard.

Light travels slower that 3E8 m/s in all mediums except vaccuum.
 
ok, i got that number off some website, but does that answer my question then?
 
In water, for example, light travels at about 225,500,000 metres per second.

Can you still see light in water?
 
Photons still travel at c, it's just that they interact with electrons in material which averages out so that it seems as if light travels slower.

Forgive my ignorance, but how old does one have to be to "just graduate from High School?"
 
i see, so is that slowest speed light travels?
 
burt reynolds said:
i see, so is that slowest speed light travels?

People claim to have stopped light.

The misconception is that people say "Light travels at 300,000 km/second" and leave off "in a vacuum"
 
disregard that last post, i didnt see masudr's post. I'm 18.
 
how the f do you stop light, and how is it still light at that point?
 
  • #10
burt reynolds said:
so i just graduated high school taking only one physics class in 4 years. it was an academic level class and i only took it to fulfill a requirment, but I am glad i took it because it got me thinking. i don't plan to do anything with phusics in the fuutre, but i do have some questions that will probably seem elementary to most of you. here's the question: i know light travels 299,792,458 meters per second, but what if it could somehow travel slower to say 299,742,450 m/s? what would happen? would it still be light? has this ever been done? physics is hard.

To answer your question, no it wouldn't be light. Light can only travel at one speed, so if it travels at another speed it's not light. If light did, somehow, slow down (I think -- and if I'm wrong someone will correct me) then it wouldn't be capable of existing.

I'm going to take a stab at working through some equations to try to prove this, because if I make a mistake, maybe I can learn something from this too. :redface: But I haven't had any formal training, so don't take this on blind faith.

The equation for the energy of a relativistic particle is [tex]E^2=m^2c^4+p^2c^2[/tex]. A photon doesn't have a rest mass (m = 0), so this reduces to [tex]E^2=p^2c^2[/tex] (Eq. 1).

The equation for relativistic momentum (p) is [tex]p=\frac{mv}{\sqrt{1-\frac{v^2}{c^2}}}[/tex]. Since m is 0, the numerator (mv) will be 0, which at first may make it look like p will be 0, but if v = c, then the denominator will also be 0, and 0/0 is indeterminate, so as long as v=c, momentum doesn't have to be 0. If, however, v < c, then the denominator will become greater than 0, thus the momentum of a particle with zero rest mass moving at a speed less than the speed of light is zero. If a particle has both zero rest mass and zero momentum, then based on Eq. 1 it also has no energy. Something with no energy, no mass, and no momentum doesn't really seem to exist to me...
 
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