If light can travel with certain speed, then there should be speed for dark too. Can anyone tell me what is the speed of dark

crazy lol, like if I punch a person, can I defend myself saying that person's face hit on my fist?

@ Ved555, when i say c and -c, i am trying to say the same thing you said, thanks for putting it into words.

Ved, wasn't that what NightElf meant?

300000000 m/s

It's like train passing through the tunnel, where speed of train represents speed of light and leaving the tunnel behind for another train to come. Therefore, I would say darkness is a stationary trail on which light can travel. Also, I guess 100percent devoid of light  means less traffic (something like: the more darkish the trail, gives the best chance for visibility or flow of light(Particular beam).
Since I am not Physics major I was just curious if there is something like frictional force  between energy and stationary body. Like collision of electron slows down the reaction ultimately by transforming into different form of energy is there similar phenomenon in light energy?

Light and darkness works on counter direction. Like upthrust principle, when you put some object on water - water tries to push the object upward direction and the object tries to push the water in downward direction. Who so ever's force is higher will appear.

Like air pressure on atmosphere and blood pressure of human which balances the body. Our blood pressure inside ourself tries to oubrust but the air pressure outside keeps it normal.

In the case of light and darkness. Its like air pressure of atmosphere which is found every where and blood pressure inside us (single instance for each one of us and every living being)

. Darkness covers most of the part in universe but when the light comes out of any single instance lets say sun , stars etc it tries to covers a portion of it on the universe and replaces the darkness according to its power. Just trying to find its existance.

Its just my thought.........

Are you guys shi**ing me??

To understand why darkness doesn’t have a speed, we have to understand why Light has the speed.

Speed = D/T, where D is distance traveled and T is time taken. This implies there has to be an “object” that is doing the traveling.

In case of Light, it is the electromagnetic radiation that is doing the traveling. Light wave or light energy travels with a constant speed of “c” in a vacuum.

 

As somebody (NightElf) pointed out, darkness is the LACK of light. It is not an energy or an entity. Like coldness is absence of heat (which is another energy), dark is absence of light. If there is no energy or entity, who is doing the traveling?

 

Hence, darkness has NO speed.

 

Stiffler :- How do you say darkness doesn't have energy? if you say light has energy darkness do have energy. (yet more research needs to be done in order to claim darkness as an energy).

Suppose, if you switch on the light it should have light all the time if the darkness doesn't have energy. It is the energy that comes out of darkness that fades away the energy of light when you switch of the light.  Also it is the energy of the light which fades away the energy of the darkness when the light is switched on.

We see light because the energy comes out of the light (may be photon (i don't know what its called)) sparkle the airparticles in our environment and is visible. We see darkness because the energy that comes out of darkness sets-off the sparkled particles and is invisible.

In simple term its like , Setting off the fire with water where both fire and water are energy.

 

Does light have mass?

The short answer is "no", but it is a qualified
"no" because there are odd ways of interpreting the question which
could justify the answer "yes".

Light is composed of photons so we could ask if the
photon has mass. The answer is then definitely "no":
The photon is a massless particle. According to theory it has
energy and momentum but no mass and this is confirmed by experiment
to within strict limits. Even before it was known that light is
composed of photons it was known that light carries momentum and
will exert a pressure on a surface. This is not evidence that it
has mass since momentum can exist without mass.
[ For details see the Physics FAQ article
What is the mass of the photon? ].

Sometimes people like to say that the photon does have mass
because a photon has energy E = hf where h is
Planck's constant and f is the frequency of the photon.
Energy, they say, is equivalent to mass
according to Einstein's famous formula E = mc².
They also say that a photon has momentum and momentum is related
to mass p = mv. What they are talking about is
"relativistic mass", an outdated concept which is best
avoided [ See Relativity FAQ article
Does mass change with velocity? ]
Relativistic mass is a measure of the energy E of a
particle which changes with velocity. By convention relativistic
mass is not usually called the mass of a particle in contemporary
physics so it is wrong to say the photon has mass in this way.
but you can say that the photon has relativistic mass if you
really want to. In modern terminology the mass of an object is
its invariant mass which is zero for a photon.

If we now return to the question "Does light have mass?"
this can be taken to mean different things if the light is moving freely
or trapped in a container. The definition of the invariant mass
of an object is m = sqrt{E²/c⁴ -
p²/c²}. By this definition a beam of light,
is massless like the photons it is composed of. However, if light is
trapped in a box with perfect mirrors so the photons are continually
reflected back and forth in the box, then the total momentum is zero
in the boxes frame of reference but the energy is not. Therefore the
light adds a small contribution to the mass of the box. This could be
measured - in principle at least - either by an increase in inertia
when the box is slowly accelerated or by an increase in its
gravitational pull. You might say that the light in the box
has mass but it would be more correct to say that the light
contributes to the total mass of the box of light. You should not
use this to justify the statement that light has mass in general.

It might be thought that it would be better to regard the
relativistic mass as the actual mass of photons and light, instead
of invariant mass. We could
then consistently talk about the light having mass independently
of whether or not it is contained. If relativistic mass is used
for all objects then mass is conserved and the mass of an object
is the sum of the masses of its part. However, modern usage defines
mass as the invariant mass of an object mainly because the invariant
mass is more useful when doing any kind of calculation. In
this case mass is not conserved and the mass of an object is
not the sum of the masses of its parts. For example the mass of
a box of light is more than the mass of the box and the sum
of the masses of the photons (the latter being zero). Relativistic
mass is equivalent to energy so it is a redundant concept.
In the modern view mass is not equivalent to energy. It is
just that part of the energy of a body which is not kinetic energy.
Mass is independent of velocity whereas energy is not.

Let's try to phrase this another way. What is the meaning
of the equation E=mc²? You can interpret
it to mean that energy is the same thing as mass except for
a conversion factor equal to the square of the speed of light.
Then wherever there is mass there is energy and wherever there
is energy there is mass. In that case photons have mass but
we call it relativistic mass. Another way to use
Einstein's equation would be to keep mass and energy as separate
and use it as an equation which applies when mass is converted
in energy or energy is converted to mass as in nuclear
reactions. The mass is then independent of velocity and is closer
to the old Newtonian concept. In that case only total of
energy and mass would be conserved but it seems better to try
to keep conservation of energy. The interpretation most widely used
is a compromise in which mass is invariant and always has energy
so that total energy is conserved but kinetic energy and radiation
does not have mass. The distinction is purely a matter of
semantic convention.

Sometimes people ask "If light has no mass how can it
be deflected by the gravity of a star?" One answer
is that any particles such as photons of light, move along
geodesics in general relativity and the path they follow is
independent of their mass. The deflection of star-light
by the sun was first measured by Arthur Eddington in 1919. The
result was consistent with the predictions of general relativity
and inconsistent with the Newtonian theory. Another answer is that
the light has energy and momentum which
couples to gravity. The energy-momentum 4-vector of a particle,
rather than its mass, is the gravitational analogue of electric
charge. The corresponding analogue of electric current is the
energy-momentum stress tensor which appears in the gravitational
field equations of general relativity. A
massless particle can have energy E and momentum
p because mass is related to these by the equation
m² = E²/c⁴ -
p²/c² which is zero for a photon
because E = pc for massless radiation. The energy
and momentum of light also generates curvature of space-time
so according to theory it can attract objects gravitationally.
This effect is far too weak to have been measured. The
gravitational effect of photons does not have any cosmological
effects either (except perhaps in the first instant after the
big bang). There are far too few with too little energy
to make up any noticeable proportion of dark matter.

http://www2.corepower.com:8080/~relfaq/light_mass.html

Hemu you are not asking the right questions.

There is always a source of light energy.

There is never any source of dark.

I will tell you that once you tell me what is the speed of silence...

@ved55, a lot of people would be happy if you summed that article up into a paragraph.

@ Hemu, we see light because when it hits our cells in retina they generate a small electric impulse that is transferred to our brain, this impulse is interpreted differently in different brains to give us a sense of what our eyes saw.  When those retina cells don't generate electric impulse, when there is too little or no light, our brain processes the absence of such impulses, giving us an idea that its dark.
I am not saying that absence of matter or energy is insignificant, such absence is not quantifiable in standard physics.


One more random thought:
would there still be darkness if there were no people or any other intelligent minds that observe the absence of light?? I am asking this because no matter how dark we think it is, there is always some light, maybe a single ray from a distant star that is passing by the area under observation.


PS: check out the wikipedia article on Darkness,
http://en.wikipedia.org/wiki/Darkness
and look at the pic of a chess board and a cylinder to the right, its kinda cool.

Obamania - Do we human beings ever been able to identify the source of air, vacuum, all elements like h, he, li, be, br, etc? Are we able to identify the source of stars, sun, etc. Does it mean that it doesn’t exist?

If it is beyond the imagination and beyond our research we cannot say that it doesn't have any source, yet more research needs to be done. If we say darkness doesn't have source in terms of scientific findings then let me remind you we have till now succeed only 0.0001% or even less(just my observation) on defining any substance or its existence proportion to the whole universe/beyond galaxies. And darkness is a big topic. Go for it you will contribute something for human kind.

You can always think darkness as a universal set where light present. Without darkness there is not even a single penny value of light and I believe light doesn't exist without darkness. So getting into conclusion with 0.0001% of findings makes us insane right?

Fortunefaded - Where do you find sound in the midst of the silence right? If anybody have known the speed of silence then you would have told me before you had asked me. Nobody has defined the speed of silence so i can't tell you right now but i do believe there exists the speed of silence too. Just we need to do more research in order to relate silence with (as the speed is calculated in terms of relation like speed of anything is calculated in terms of still object where speed=distance/time don't get confused with this formula go beyond this formula you will find still object which is constantly providing you distance of an object)

Fortunefaded - do you consider sound as energy and does it have mass? Please try to do research on it. You won't be getting an answer like what is the speed of silence but i assure you that you will realize something should be there to relate silence with. Darkness is similar to it.

NightElf - Actually we were talking about the speed but you were more relating it to its presence and absence. I am totally agreed upon you regarding processing the impulse of light by our retina and giving the vision of brightness through our mind. But I am little bit disagree on absence of light means absence of everything. Darkness is what presents on the absence of light.  So physics should quantify it. What do you think?

Without mass there is no speed.
Edit: Without energy.

y we see objects, because of the light rays being reflected in our eyes or i would say light being striking in rods and cones of our eyes. For example

No matter how you explains.. still you are never be correct.... all these science humans came up... it cannot explain the real TRUTH. All these things as explained are only illusions....

YOu ask why the leaf is green... who can answer that simple question? No matter how you try to answer that still you never answered that questions.. because anything you propose/explain, there will still be question "why" to that.... so don't go after these things.. JUST GO AFTER SEXY GIRL>> AND BANG HER.. then you will get the most realistic answer.

alright....speed of dark is pretty much done about,
can anyone suggest "SPEED OF IMAGINATION"

Infinity m/s is the speed of imagination, didn;t you hear that from your grandma...

 no sir i didn't in the mean time i was dating your grand mama...she was hot though. i still miss your grand mama son

aamnepali,

My statement was not intended as an insult to you or your grandma but i forgive you for your ignorance and inability to comprehend English language.

My Grandma had told me, nothing could travel faster than the imagination.