Is the Speed of Light Constant?

[sreekant]

guys, i got a simple question i'll make it in parts after stating what i think is well known...

a) speed of light decreases in a medium...that is it decreases when it movers through matter

b) there is dark matter present throughout the entire galaxy and so is present on Earth as well

c) we measure the speed of light experimentally and find its value as 299 792 458 m / s

does this not mean that due to presence of dark matter..the speed of light as we measure it here is not the absolute constant?..that there is a slight error in what we consider as a universal constant? ...please answer me..its eating my head out

 

[JaredJames]

Firstly, please use proper English. Text speak is unacceptable.

a) Ok.

b) I'm not sure if that is actually the case. Someone else can ok that one.

c) Ok.

So I read your question as "does dark matter affect the speed of light and therefore is our measured maximum speed actually slightly off because it's actually traveling through the medium of dark matter?".

I'm under the impression that dark matter doesn't interact with light any different to 'regular matter'. As per another thread here, gravity doesn't affect the speed of light but can change it's direction. Someone else can probably explain it far better than I ever could.

 

[Janus]

guys, i got a simple question ill make it in pts after stating wat i think is well known...

a) speed of light decreases in a medium...that is it decreases when it movers through matter

The apparent speed of light changes, but not the actual speed of light

b) there is dark matter present throughout the entire galaxy nd so is present on Earth as well

Yes, but only in extremely small amounts. The total estimated amount of DM in the entire volume of the Solar system is about that of a Dwarf planet, so the percentage of that which would coincide with the Earth would be miniscule.

c) we measure the speed of light experimentally nd find its value as 299 792 458 m / s

does this not mean that due to presence of dark matter..the speed of light as we measure it here is not the absolute constant?..that there is a slight error in wat we consider as a universal constant? ...please answer me..its eating my head out

One of the properties of (non-baryonic)dark matter is that it would not interact with light at all( other than gravitationally), so even if there was a significant amount, it would not slow light.

 

[Chalnoth]

The reason why normal matter slows light waves is because of the electromagnetic interaction. Dark matter cannot interact electromagnetically, because otherwise it wouldn't be dark.

 

[sardar]

I can tell you that the speed of light is indeed considered to be a constant in the scientific community. It is a fundamental physical constant that is used in many equations and theories, and it is defined as the speed at which electromagnetic radiation (light) travels in a vacuum. This means that in a vacuum, the speed of light will always be the same, regardless of any external factors.

While it is true that the speed of light can change when it passes through a medium, such as air or water, this is due to the interaction of the light with the particles in the medium. In a vacuum, where there are no particles to interact with, the speed of light remains constant.

As for the presence of dark matter, it is important to note that dark matter does not interact with light in the same way that normal matter does. This means that it does not affect the speed of light in a vacuum. Therefore, the presence of dark matter does not change the constant value of the speed of light.

In regards to your concern about a slight error in the universal constant, it is important to understand that scientific measurements are never 100% accurate. There will always be a margin of error, but this does not mean that the fundamental constants, such as the speed of light, are not constant. Scientists take great care to minimize errors in their measurements and constantly strive to improve their accuracy.

In conclusion, the speed of light is considered a constant in the scientific community and is not affected by the presence of dark matter. Any slight errors in measurements do not change its fundamental value.