# Light speed question **URL:** \ **Category:** Factual Questions\ **Created:** [June 11, 2001, 1:02am UTC](https://boards.straightdope.com/t/light-speed-question/68353 "2001-06-11T01:02:42Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![insider](https://avatars.discourse-cdn.com/v4/letter/i/bbe5ce/32.png) [@insider](https://boards.straightdope.com/u/insider)\ **Post date:** [June 11, 2001, 1:02am UTC](https://boards.straightdope.com/t/light-speed-question/68353/1 "2001-06-11T01:02:42Z")
Does all light travel at the same speed in a vacuum and through other medium? ---
**Author:** ![John\_Kentzel-Griffin](https://avatars.discourse-cdn.com/v4/letter/j/ccd318/32.png) [@John\_Kentzel-Griffin](https://boards.straightdope.com/u/John_Kentzel-Griffin)\ **Post date:** [June 11, 2001, 1:28am UTC](https://boards.straightdope.com/t/light-speed-question/68353/2 "2001-06-11T01:28:22Z")
All light travels at the same speed in a vacuum as measured by an inertial reference frame. Light slows down when it travels thru a medium. ---
**Author:** ![Ring](https://avatars.discourse-cdn.com/v4/letter/r/6a8cbe/32.png) [@Ring](https://boards.straightdope.com/u/Ring)\ **Post date:** [June 11, 2001, 3:27am UTC](https://boards.straightdope.com/t/light-speed-question/68353/3 "2001-06-11T03:27:39Z")
> [@](#): > > All light travels at the same speed in a vacuum as measured by an inertial reference frame. Light slows down when it travels thru a medium. All true. However just to finish it up; photons still travel at c between absorption and emission by the medium. Which is, of course, just another way of saying that light and its quanta always travel at c in a vacuum. ---
**Author:** ![Phobos](https://avatars.discourse-cdn.com/v4/letter/p/3d9bf3/32.png) [@Phobos](https://boards.straightdope.com/u/Phobos)\ **Post date:** [June 11, 2001, 1:24pm UTC](https://boards.straightdope.com/t/light-speed-question/68353/4 "2001-06-11T13:24:30Z")
[Is the speed of light constant?](http://math.ucr.edu/home/baez/physics/speed_of_light.html)