Does darkness have a speed?

Is it possible (or proven) that there is anything faster than light? If light is the fastest speed and dark is the opposite of light, does dark have a speed? Does ‘dark’ even exist, If so what is darkness?

If you can’t answer in fact, could you please answer in theory?

Darkness isn’t the opposite of light. Darkness is the absence of light. So its speed is effectively the same as the speed of light (though for any given vector of light you would have to reverse it, of course).

Insofar as darkness propagates (e.g. following the end of transmission of light) it does so at the same speed as light.

Last night I looked at the constellation Orion. I stared at the red giant at the Hunter’s right hand; then my gaze quickly passed to his left foot.

The target of my gaze moved 130 light-years in a fraction of a second.

There is no limit to how fast shadows can move. This doesn’t violate the cosmic speed limit © because shadows don’t contain information.

Not as fast as Cool Papa Bell.


Yes, this. If I have a hallway 3*10^8 m long, lit by a lightbulb at one end, if I turn off the light, the other end will be dark one second later.

If you can detect a shadow, then it contains information.

The movement of the shadow from one place to another place does not carry information from the first place to the second place. The only information carried by the shadow is the source of the shadow itself, and that information travels at the speed of light.

Light is a photon. It is only detectable when it hits something.
Dark is absence of a photon interacting with something. Dark does not exist as a thing. It is the absence of things being hit by light or reflecting light. You can’t see a photon that does not hit your retina. You can’t see photons going by you. Darkness is not a thing. It has no speed, no mass, no existence.

Constant illumination doesn’t carry any more information than “there’s light.” Add a shadow, and you can encode any information that you want. You can attribute the information the the light or the shadow, but it’s the transitions that are important.

What you are seeing are the photons that are about to hit your eye. It’s not like you are seeing what’s at 130 light years distant as it appears now.

Yes, but you can’t transmit any information by moving the shadow.

If I cast a shadow over location A then I am transmitting information to location A, i.e., the shape of my shadow. I can also move my shadow from A to B by moving the light source. The shape information in the shadow is now being transmitted to location B. Now, I can “move” my shadow from A to B faster than the speed of light, BUT, I can’t use that to transmit information from A to B. I can only transmit information from me to where-ever my shadow is cast, and that will only happen at the speed of light.

It is no different from shining a torch at one spot and then “moving” the torchlight to another spot.

J.R.R. Tolkien and George Lucas both disagree with you.

Well there are all sorts of semantic issues here.

If it is totally dark in my room, I can’t make it more dark. If it is light in my room, I can make it more light.

But if it is light, and I turn off the light source, the boundary between light and dark travels at c. Indeed, if I turn the light intensity up or down, the boundary of the change travels at c.

The question does bring to mind the phenomenon of psuedo-particles. Probably the best known being the electron hole. In a structure filled with electrons, does the space where one could have been behave like a thing? The answer is that it does. With remarkable accuracy too. Right down to important quantum theory properties.

Then one could you ask. Does the Casmir effect count as a kind of special darkness? Here we have done the seemingly illogical. For a certain set of wavelengths, the space is actually darker than dark. It would still be limited to c.

Evil is not merely the absence of good. Success is not merely the absence of failure. But darkness is merely the absence of light.

What you saw happened 130 light-years ago.

The point is, when a shadow moves from point A to point B, there is no information being transmitted from point A to point B. The only information flow is from the object casting the shadow (call it point C) to point A, and from point C to point B.

Similarly, you can point a laser pointer at a distant screen, and move it quickly. The spot can move faster than light. But the spot doesn’t carry information from one point of the screen to the other. The information is being transmitted from your laser pointer to the screen, at the speed of light.

Some level of talking past one another I think.

If there is a source of illumination, it is the thing that casts the shadow that encodes the information. Not the point where the shadow falls, or ceases to fall.

If a shadow is cast on A, and then the object X casting the shadow moves, so that the shadow is now cast on B, both A and B receive information from the object casting the shadow. Neither A or B are in control of the shadow, and neither receive information from one another. The speed that the shadow moves in 3D space is c. That is the speed that the light from the source travels at, and the speed that the shadow cast by X moves toward either A or B (or both). Any arbitrary projection of the light/dark boundary onto a 2D surface may be superluminal, but it isn’t a physical thing. The speed of the dark edge isn’t the speed of darkness any more than the speed of the light edge is the speed of light.

You mean 130 years ago. Light-years are a measure of distance not time. Unless you’re making the Kessel run in less than 12 parsecs… :smiley: