# Refractive index

The light travel by it's in a straight line in vacuum, but when we see through the glass the glass has a refractive index which slows down the speed of light so when I see through the glass I don't see the actual distance. Moreover, the gases particles has refractive index and slows down the speed of light. Does this mean that I don't see the actual distance?

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By it's actual speed

Nugatory
Mentor
A post and a correction one minute apart? Dude.... learn to use that edit button... or check your post a few times before you submit it.

I am really sorry, but can you answer my question?

Nugatory
Mentor
The light travel by it's in a straight line in vacuum, but when we see through the glass the glass has a refractive index which slows down the speed of light so when I see through the glass I don't see the actual distance. Moreover, the gases particles has refractive index and slows down the speed of light. Does this mean that I don't see the actual distance?
You don't ever "see" a distance, you measure it, and you have to understand the operation of your measuring instruments to know what your measurements are telling you and whether they might be introducing errors that must be corrected for. If you're measuring the distance to an object using a light signal (the the radar method) that passes through a pane of glass, you have to allow for the signal needing a bit more time to pass through the glass.

I mean when I there is a car front of me I don't see it's real position because of the refractive index of the gas particles that slows down the speed of light?

Nugatory
Mentor
I mean when I there is a car front of me I don't see it's real position because of the refractive index of the gas particles that slows down the speed of light?
If the refractive medium is set up to change the course of the light, then yes of course you have to allow for this effect when deciding where the car was when the light left it on the way to your eyes.

Does the gas particles change the course of light?

That is why the sky is blue, same with a prism, all matter that light travels through even gas will distort the direction of the light until it exits. Away from the normal.

So everything I seeks not in its actual position?

I don't see anything in its actual position?

I don't see anything in its actual position?
Unless you are standing perpendicular to the plane of entry and the light enters the plane at a 90 degree angle no. For example, If your on earth and the sun cast no shadow (90 degrees with you) then it is where it appears to be. If you stand directly over a fish in a pond it is where it seems to be, If you look at the fish from an angle the light has refracted and it is not where it appears to be. If you are looking through any medium at an angle there will be a slight refraction of the light. Minuscule but still there.

The light travel by it's in a straight line in vacuum, but when we see through the glass the glass has a refractive index which slows down the speed of light so when I see through the glass I don't see the actual distance. Moreover, the gases particles has refractive index and slows down the speed of light. Does this mean that I don't see the actual distance?
I think what you are looking for is "optical path length" vs real path length.
The difference between the two for a car windshield would not be resolvable
And distance would be relative to what you have always seen (no delta)
Lets use the car example.
A car is 30 meters in front of you,
Now lets add in the delay of 4 mm of glass at an index of 1.5.
4 mm of glass has an optical path length of 6 mm, or +2mm
and the delay of the air at 1.000023
30 m X 1.000023= 30.00069 m.
So the true distance vs the optical distance is a Delta of 2.69 mm.
Add to this the delays look normal, as it is what we have always seen.