# How can light be slowed?

## Main Question or Discussion Point

Has there been a previous thread that discusses how light can be slowed?

Thanks,
Tim13

Drakkith
Staff Emeritus
Light can be slowed by making it pass through a physical medium such as glass, air, water, etc.

Chronos
Gold Member
Light can be slowed when emitted from a gravitational well. This is not effective for light passing by a gravitational well since it is blue shifted on the way in.

Light can be slowed when emitted from a gravitational well. This is not effective for light passing by a gravitational well since it is blue shifted on the way in.
You mean it gets red shifted? [en.wikipedia.org]. Speed is the same I believe, unless you run it through anything other than vacuum/air.

Shooting a lazer through super-cooled sodium atoms will slow the light to 34mph.

Shooting a lazer through super-cooled sodium atoms will slow the light to 34mph.
If something can be slowed, then perhaps it may also be stopped? Perhaps the properties of light (its duality of wave and particle) are reactive based on environmental conditions? Is the particle nature more dominant in super cooled states and hence the light slows? Is the word "dominant" not the right choice?

If something can be slowed, then perhaps it may also be stopped? Perhaps the properties of light (its duality of wave and particle) are reactive based on environmental conditions? Is the particle nature more dominant in super cooled states and hence the light slows? Is the word "dominant" not the right choice?
You can think of light in the particle sense as an important man walking in a room. If he is just walking through an empty room, he is not really affected, as in, he is not bouncing around. If he just made an important speech, he will be shaking peoples hands a lot, just bouncing around, always going the speed of light, just in a zig-zag path. I don't think light will ever look like it is going completely at 0 speed relative to anyone else.

mfb
Mentor
It is possible to "stop" light - but what really happens is that those photons are converted to other excitations, and back to photons afterwards.

If something can be slowed, then perhaps it may also be stopped? Perhaps the properties of light (its duality of wave and particle) are reactive based on environmental conditions? Is the particle nature more dominant in super cooled states and hence the light slows? Is the word "dominant" not the right choice?

When the lazer is suddenly turned off the light freezes for a fraction of a second within the gas only to resume after the lazer is turned back on .