The common experience of turning on a light switch certainly shows that light travels very quickly. But careful experiments reveal that it travels at a finite speed. This speed, which we call "c," is measured to be 300,000,000 meters per second.
Because the speed of light is finite, we never see things as they are, but only as they were. In a sense, we are always looking at the past; information from the past comes swiftly to us in the form of light.
Light just keeps going and going until it bumps into something. Then it can either be reflected or absorbed. Astronomers have detected some light that has been traveling for more that 12 billion years, close to the age of the universe. Light has some interesting properties.
Constant Speed
No matter how you measure it, the speed of light is always the same. Einstein's crucial breakthrough about the nature of light, made in 1905, can be summed up in a deceptively simple statement: The speed of light is constant.
Energy transport is limited to the speed of light, according to Einstein's laws, but there are no physical limitations on the phase velocity. When it reaches zero, meaning there is no movement of the peaks and valleys of the wave, the phase velocity becomes infinite, making the wavelength of light nearly infinite.
But Einstein showed that the universe does, in fact, have a speed limit: the speed of light in a vacuum (that is, empty space). Nothing can travel faster than 300,000 kilometers per second (186,000 miles per second).
From the perspective of a photon, there is no such thing as time. It's emitted, and might exist for hundreds of trillions of years, but for the photon, there's zero time elapsed between when it's emitted and when it's absorbed again. It doesn't experience distance either.
That something, the universal conversion factor, is the speed of light. The reason that it is limited is simply the fact that a finite amount of space is equivalent to a finite amount of time.
In the relativity theory, Einstein told us the curved space and inflation of time [3] . If the space is really curved and time is inflated, the ratio of space over time must keep constant. Only under this condition, there exists the possibility for the speed of light to keep as a constant.
A light-year is a measurement of distance and not time (as the name might imply). A light-year is the distance a beam of light travels in a single Earth year, which equates to approximately 6 trillion miles (9.7 trillion kilometers).
In all the Universe, only a few particles are eternally stable. The photon, the quantum of light, has an infinite lifetime.
Light exists in tiny packets called photons. Photons have no rest mass and they do not occupy any volume. So light is not matter. It is the radiation of energy.
In special relativity, the speed of light is the ultimate speed limit to the universe. Nothing can travel faster than it.
By the time an object reached the speed of light, Einstein calculated, its mass would be infinite, and so would the amount of energy required to increase its speed. To go beyond the infinite is impossible.
The Universe has only a finite number of stars. The distribution of stars is not uniform. So, for example, there could be an infinity of stars, but they hide behind one another so that only a finite angular area is subtended by them.
Light has an enormous influence on life, being the basic source of energy that maintains the ecosystems.
Paradox of light Being a Constant
Maxwell's equation claims that the speed of light is a universal constant, 186,000 miles per second so long as that speed of light is measured in a vacuum. But this statement leads to a paradox, as velocities are additive in our everyday experience.
Darkness travels at the speed of light. More accurately, darkness does not exist by itself as a unique physical entity, but is simply the absence of light. Any time you block out most of the light – for instance, by cupping your hands together – you get darkness.
So light is the fastest thing. Nothing can go faster than that. It's kind of like the speed limit of the universe.
Now quantum physicist Pasi Lähteenmäki at Aalto University in Finland and his colleagues reveal that by varying the speed at which light can travel, they can make light appear from nothing.
Then again, if the speed of light were infinite, massless particles and the information they carry would move from A to B instantaneously, cause would sit on top of effect and everything would happen at once. The universe would have no history and no future, and time as we understand it would disappear.
Likewise, the sounds you hear travel at the speed of sound (professional science writer right here) through the air as pressure waves that eventually reach your ears to vibrate your eardrums. If you stopped time, all light and sound would stop, too.
In zero seconds, light travels zero meters. If time were stopped zero seconds would be passing, and thus the speed of light would be zero. In order for you to stop time, you would have to be traveling infinitely fast.
Light travels at a constant, finite speed of 186,000 mi/sec. A traveler, moving at the speed of light, would circum-navigate the equator approximately 7.5 times in one second. By comparison, a traveler in a jet aircraft, moving at a ground speed of 500 mph, would cross the continental U.S. once in 4 hours.
As particles travel through the Universe, there's a speed limit to how fast they're allowed to go. No, not the speed of light: below it. Cosmic rays, which are ultra-high energy particles originating from all over the Universe, including particles emanating from the Sun, strike atomic nuclei everywhere they exist.