how do we say that light travels at constant velocity?

Answer 1

I think you meant to ask "how do we know that light travels at a constant velocity?" Well, there are two ways:

1. make direct measurements of light's velocity while on the ground, and while in a moving object

2. based on Einstein's theory of Special Reltivity, we know if we assume that the speed of light is constant in all moving reference frames, then there are consequences we can also measure. For example, Einstein predicted that there would be a time dilation effect for fast moving objects, meaning time would slow down for them. So we can measure 2 atomic clocks, one on the ground and one moving on an airpane that travels around the world. And indeed, we do see that the moving atomic clock is slower by some fractions of a second.

Answer 2

Correction. Light travels at a constant velocity, c, IN A VACUUM. When light travels through materials its speed is reduced, that is the principle behind the prism. That is why the sky is blue. The property of materials that affects light speed is the index of refraction.

In a sense, any light travelling through a medium other than a vacuum travels below c, as a result of refraction. However, certain materials have an exceptionally high refractive index; in particular, the optical density of a Bose-Einstein condensate can be very high. In 1999, a team of scientists led by Lene Hau were able to slow the speed of a light beam to about 17 metres per second, and in 2001, they were able to momentarily stop a beam.

In 2003, Mikhail Lukin, with scientists at Harvard University and the Lebedev Institute in Moscow, succeeded in completely halting light by directing it into a mass of hot rubidium gas, the atoms of which, in Lukin's words, behaved "like tiny mirrors", due to an interference pattern in two "control" beams.

Answer 3

Because the speed of light is the maximum speed anything can travel.

Since the speed of light is the fastest anything can go, fudemental physics concepts don't apply.

If you are running and turn on a flashlight, the beam of light is travelling at the speed of light, not the speed of light plus your velocity.

As light particles do not have mass, their vector or velocity is not altered by atmospheric conditions that would alter the speed of particles with mass.

Hence, light travels at a constant velocity.

Edit:

Wow, I really need to use spell check

Answer 4

Light travels at a constant velocity. That's how we say it!

Answer 5

Electromagnetic radiation is generally described as a self-propagating wave in space with electric and magnetic components. These components oscillate at right angles to each other and to the direction of propagation, and are in phase with each other. EM radiation with a wavelength between approximately 400 nm and 700 nm is detected by the human eye and perceived as visible light.

Maxwell discovered that self-propagating electromagnetic waves would travel through space at a constant speed, which happened to be equal to the previously measured speed of light. From this, Maxwell concluded that light was a form of electromagnetic radiation:

so u see EM waves like light are self propagating waves.and hence travel at constant speed.

Answer 6

Light quantum has different velocity.
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Llight quantum has the absolute speed c=1 in Vacuum.
No other particle can travel with the speed c = 1.
Other particle can travel only with the speed v=s/t.
But if quantum of light flies always rectilinearly c=1,
it is a mad one.
Is he really mad?
I don,t think so.
Light quantum travels slower in a gravitational field ( c<1).
And in nuclear light quantum has other speed (c>1)
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Answer 7

It has been proven that despite the speed of the source light travels at the same speed, although the wavelength can vary (ex, - red shift). This leads to some very interesting effects such as variable simultaneity. Events can be simultaneous for one person, but and different times for another.

If you are really interested read Physics for the Rest of Us by Roger S. Jones

Answer 8

Velocity of light at vacuum is measured and verified to be a constant with in the accuracy of measurement. There are lots of other things we are not sure about but not this one.

Answer 9

Late in the 19th century two American scientists accurately measured the speed of light (in a vacuum). They found it was always the same speed, regardless of the motion of the observer.
It's not anything that you "say"; it's just the way the universe seems to operate.

Answer 10

All inertial (non accelerating) observers get the identical effects. Strictly the faculty room isn't inertial via fact it has acceleration via gravity and to the curve of the Earth. usually those ought to be surpassed over yet get away speed on the earth is barely approximately 11km/s so going at C could have a super result. the two you may fly into area or if the practice is saved on the rails you may all be squashed to the ceiling.