I've been looking around, and can't find a solid answer. Many websites say darkness is the speed of light due to the fact it is the absence of light, but other sources say otherwise, that in some cases darkness is actually faster in some cases. Could someone clarify this for me?

  • $\begingroup$ astro.uni-bonn.de/~dfischer/dark_sucker_2.html is a humorous take on the subject $\endgroup$
    – user21
    Commented Dec 20, 2015 at 14:56
  • $\begingroup$ Darkness is not "a thing". It's just a linguistic shorthand for a type of absence. How fast does the absence of a thing occur? $\endgroup$
    – Jeff Y
    Commented Dec 20, 2015 at 17:36
  • $\begingroup$ Take a laser, put a slotted disk in front of it, and point the thing at a planet of alpha centauri, where the beam will have spread out to say 100,000km. Aim a telescope at your laser from that distant planet, and measure how long the light flashes and dark periods last. You'll get some astoundingly rapid numbers for the rate of shadow propagation. However, nothing is actually traveling faster than light, you've just enlarged a small thing to a huge degree. $\endgroup$ Commented Jan 13, 2017 at 14:37

2 Answers 2


The darkness does not have a speed, as it's just the space the light travels through. It's always there until the brief instant a photon whizzes through.

It would be analogous to asking what speed the road is travelling at, rather than the car.

  • $\begingroup$ But the speed at which darkness fills that space back up, that's something to take in to factor- right? $\endgroup$ Commented Dec 20, 2015 at 5:14
  • 2
    $\begingroup$ The space is not being "filled" by darkness, but emptied of light. So the darkness, again, does not move. And the space is not empty anyway. The darkness is a myth. The photon is, in a sense, always passing through and always leaving and always elsewhere - it's spread out, a wave. $\endgroup$ Commented Dec 20, 2015 at 5:39

Darkness is not a thing. It is just the absence of light. It doesn't have speed. Try observe the image: enter image description here

In this image this is shown that suppose there is darkness on any many light year far object if someone switch the torch in the direction of object and after some instant raise his hand and cover the light then before the light the darkness will reach on object which is completely wrong. Since the darkness which is assumed to be reach before light is the darkness there before the light reach on the object.


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