Is There a Speed of Darkness? And Other Questions About Light and Perception

[time traveller d]

there is the speed of light. just wondering, is there a speed of darkness. if so, what is it.

 

[brewnog]

Well, darkness is simply the absence of light. Therefore 'darkness' will take the same time to reach something (following extinguishing of a light source) as light would (following illuminating of the source).

 

[dimensionless]

I suppose that if you were in an enclosure then there might be some optical equivalent of reverberation.

 

[Danger]

Yeah... it's called reflection; but it still is simply light moving at light speed.

 

[krab]

, is there a speed of darkness.

That's a funny one. Reminds me of something I used to tell the kids to get them to close the door at night: "Don't let the dark in."

 

[Ki Man]

absence of light is darkness

darkness is like the wagon tied to the back of the bike going light speed. when the bike goes by the wagon takes its place just as quickly. it has no definite speed because it is nothing. even though it technically goes at the speed of light, there's no way of telling because we can't measure how quickly nothing moves

we'll solve this problem right after we figure out the speed of silence

 

[Tide]

The speed of darkness has been measured as negative 300,000 km/s. :)

 

[deepak9191]

darkness doesn't existbcoz light is present everywhere . remember that light is a wave and has no definite size and shape so it can be present everywhere . even the black hole is not devoid of it. its just a matter that in a black hole we are una ble to see light

 

[deepak9191]

wud u say that speed of silence in air is - 330m/s ?

 

[Tide]

Deepak,

That was an attempt at humor! :)

 

[ahrkron]

Since darkness is not a result of a physical process, but rather a name we give to a condition, I think there is no limit on its speed.

For instance, imagine a screen onto which you shining ten lamps. If you switch them off one by one, you can see "darkness" traveling from one side of the screen to the other.

Varying the timing for switching off the lamps, you can vary the speed of darkness from very slow to infinite (turning them all off at the same time), and all values in between.

 

[benzun_1999]

can anyone define darkness? darkenesss is different for different conditions. we are just talking about visible region wat about infra red and others. i know all travel at same speed but their imactas on the surrounding differ.

 

[siddharth]

I agree with ahrkron.
For example, If I shine a torch and wave my hand in front of it, the shadow which falls on a very very far away wall, can move extremely fast. The further away the wall is, the faster the shadow travels across the wall.
Isn't that right?

 

[-Job-]

Not exactly. Initially, the farther away the wall is, the faster the shadow will appear to move, but, eventually, the speed of "darkness" should stop increasing with the distance. If you had a really big hand and covered a star in a nearby galaxy with your hand, then as you waved your hand around you'd still have to wait for the light to travel to the "wall". So you can't make "darkness" have infinite velocity or be faster than light.
The relation between the "speed of darkness" and distance from the hand to the wall is somewhat bellshaped. Meaning that, initially, as the distance increases, the faster darkness will seem to move, until this distance reaches a point after which the darkness not only can't move any faster, but will start to move more slowly.

Also, on ahrkron's example, it wouldn't be possible to turn off all the lights at the same time if you have a lot of lights (for instance a light year's distance of lights), there will always be a delay so i think you're making use of an invalid assumption.

 

[GOD__AM]

darkness doesn't existbcoz light is present everywhere . remember that light is a wave and has no definite size and shape so it can be present everywhere . even the black hole is not devoid of it. its just a matter that in a black hole we are una ble to see light

I would like to take issue with this comment. Being a certified cave diver I have experienced complete and total darkness many times. When your light goes out a few thousand feet from the cave entrance is gets pitch black. There is certainly no visible light being emitted by the cave walls or the water.
As far as your black hole comment goes, I believe that is total speculation.
Darkness is a human concept to explain the absence of visible light. It doesn't mean an absence of EM waves, just absence of detectable visible spectrum light. Since it takes a certain number of photons to stimulate sight in humans, anything less than that number can be considerd total darkness, even if there is some light present.
As for the "speed" of darkness I think some people are reaching here. For something to have a speed it has to move relative to something else. Darkness surely doesn't move or propigate in any way. Seems that we are just debating semantics.

 

[siddharth]

Not exactly. Initially, the farther away the wall is, the faster the shadow will appear to move, but, eventually, the speed of "darkness" should stop increasing with the distance. If you had a really big hand and covered a star in a nearby galaxy with your hand, then as you waved your hand around you'd still have to wait for the light to travel to the "wall". So you can't make "darkness" have infinite velocity or be faster than light.

Even if I wait for the light to travel to the "wall", I still don't see why the shadow which is moving across the wall can't travel faster than the speed of light.

The relation between the "speed of darkness" and distance from the hand to the wall is somewhat bellshaped. Meaning that, initially, as the distance increases, the faster darkness will seem to move, until this distance reaches a point after which the darkness not only can't move any faster, but will start to move more slowly.

Why is it going to be bell shaped? And why should it slow down suddenly?

 

[Integral]

Darkness is a physiological state rather then a physical one. Darkness is determined by the sensitivity of the eye and varies with the species (the observer). To speak of it physically we would have to define intensity levels of the wavelengths in the visible spectrum. How can something so defined have a speed?

 

[-Job-]

I think it can be seen as a physical one. If i have a laser beam shooting against a wall and i temporarily obstruct it with my hand there will be a gap in the laser beam traveling at the speed of light (assuming no radiation gets through my hand).
Ok, to make this more scientific i did a drawing depicting the situation. While doing this i realized that it may be the case that the shadow can seem to move faster than light (even if I'm sticking to my original opinion). It does show the bell curve i was talking about.

 

[Rade]

I would view "darkness" (e.g., lack of photons) the same as I view "death" (e.g., lack of life). For me, dead folks move at the speed set by the "arrow of time" (here I think of my dead parents, whose memory fades for me at a speed set by the arrow of time). Perhaps darkness moves at the same rate as death ? Thus, the example given by God_Am of "pure" darkness experienced in a cave, does not this experience move at the speed set by the arrow of time ?

 

[Night Owl]

absence of light is darkness
...
it is nothing
...
we'll solve this problem right after we figure out the speed of silence

I believe Ki Man has made the best contribution to this thread so far.

"Darkness" is the absence of light. I suppose you could think of the "speed of darkness" as being the speed with which light leaves a particular region of space, but it's not like darkness is a physical entity independent of light. When you speak of the "speed of darkness," that's really what you're doing...and honestly, it sounds pretty silly.

Also, if you view the "speed of darkness" in this regard (simply as the speed with which light leaves a region of space), then it's not really proper to say that you can make it any speed simply because you can wave your hand in front of a lamp and observe a shadow moving on some surface very far away at a speed faster than light. You can do this with light, too. Just wave a laser in the same arc at the same object, and you will observe the point of light to move faster than the speed of light could across the surface of the object. This doesn't mean that the light broke its own speed limit; it's a bunch of different photons (or different parts of the same wave, if you prefer that) hitting different parts of the object at very close instants in time. It would be similar to concluding light traveled faster than the speed of light as we know it simply because you saw two lightbulbs which were 1 lightyear apart flash within 1 second of each other.

EDIT: I wanted to mention this, as well. Although whenever we see light, it HAS a speed by its nature, whenever we observe darkness, it only has "speed" when we observe that light is also present (and therefore moving in some direction). So you can't speak of the "speed of darkness" when you have no light at all (which happens), which is another reason why this is a silly question.

 

[tribdog]

is there a speed of duh? threads like this are crazy. there is no such thing as a speed of darkness. darkness is no light.
If you get hit by a car you might ask how fast that car was going. You won't say "how fast was that car not hitting me going.

 

[z-component]

This reminds me of the http://64.233.187.104/search?q=cache:Y5PtgJL1KfEJ:www.netcom.com/~rogermw/darksucker.html&hl=en" . Although the original author's site is gone, I managed to retrieve a cached version of this infamous crackpot theory.

 

[tribdog]

I posted something about the dark sucker as well I didn't even look for the original author's site though and probably took credit for the idea.

 

[Johnson]

The speed of darkness has been measured as negative 300,000 km/s. :)

Wouldn't it still be positive 300 000km/s? Its moving in the same direction as the light is moving away from it, therefore both signs would be positive? If it was moving at -300 000km/s, wouldn't it be moving backwards? and then nothing would take the spot of the light or the darkness, which would infact be darkness itself! Omg, now i am confused, way to go.

 

[pallidin]

It's really very simple: Darkeness is a concept/attribute related to light(or photons)
Now, since the actual propagation of darkness can not exist without the presence of photons defining that "darkness" the propagation of darkness is identical to the propagation of light, as it is immutably bounded.

 

[burbadam]

since darkness is already present just covered by the light the speed of darkness would be 0 it is statonary

 

[ThomasT]

there is the speed of light. just wondering, is there a speed of darkness. if so, what is it.

There have been a lot of good replies to your question so far. Here's my two cents.

First, for the speed of dark, you might try this link:

http://home.netcom.com/~rogermw/darksucker.html#energy

But seriously, darkness is often called the absence of light. It might be more precise to call darkness the inability to detect light. I guess that amounts to the same thing for all practical purposes, but there is a difference.

Arthur Zajonc, in his book Catching the Light, described an experiment where you make a box and line the inside with some sort of light absorbing material, then project a light through a hole in one end. There is a fairly large viewing hole in one side from which you cannot see the light source, and a larger viewing hole in the top from where you can see the light source. When you look through the hole in the side it looks completely dark inside -- even though the box is filled with light. If you put a pencil or something through the top, then the light (reflected from the pencil) becomes visible.

 

[explorer2909]

Well, brewnog observes that darkness is simply absence of light. Recently, I downloaded an article in the SCRIBD titled, 'Everything we knew about light is wrong' that proves that light and darkness are relative phenomenon through the observation that multiple light sources form multiple shadows.

I am not an expert but the observations appear logical. can more learned members clarify the issue?

 

[explorer2909]

I think I am supposed to give the link of the document I quote, here is the link, Crackpot link deletedI have two more questions after reading the article, 'How do we perceive light?' 'Why we cannot see the sun or any other light source even when our eyes can absorb the photons emitted by the sun?'

and, as shown in one of the experiment in the article, 'how can image in the mirror be formed even when path of the light between the mirror and the object is blocked?'

 

[kipper]

Here might be an interesting interpretation, depending on defining through speed or velocity, if we take example from the flow of current in electronics then we find we have the flow of positive charge and negative charge, we postulate that the electrons are flowing in a circuit however in conventional current we use the flow of positive charge, supposing the same happens here,
1 = photon
0 = no photon
then
0 0 0 0 0 1 0 0
0 0 0 0 1 0 0 0 timestep
. ...^^
. ...a,b
does a move to the left or does b move to the right?
in which case, does darkness have velocity as -c' where c' is the velocity of the photons moving.

i think in order to answer this kind of question then the assumption that darkness = lack of photons and lightness = presence of photons
from there then we apply this to visible spectrum/gamma rays/ infra red/ whatever really.

as for the moving shadow, well i guess it depends on how long it takes for the detector te register a lack of photons after the object has blocked photons along that particular path,
however this will have errors anyway because you then have to view photons as waves, in which case there will be a whole wavefunction thing and defraction, and then just probability stuff which means can you ever really have an absendce of photons because surely they will "curve" if you will to some degree around the object blocking their paths.
I am thinking specifically of the youngs double slit experiment and taking very close limits. is it ever truly posibly to actually get a fully clear defined shadow
or does it just get a bit fuzzy for example if you were to try and draw it?
however looking at purely the speed of darkness then using the above assumptions i would say that it was the same as the speed of light!