Light thinks it travels faster than anything but it is wrong. No matter how fast light travels, it finds the darkness has always got there first, and is waiting for it.

― Terry Pratchett

Accepting the limitations of the speed of light ensures beyond doubt, that mankind will never live further away than a desolated planet in our own solar system.

## What Exactly, is Light?

Light belongs to the spectrum of electromagnetic waves just like microwaves and radio waves.

These waves are fluctuations of magnetic and electric fields, which are able to carry energy.

An electromagnetic wave is transverse, meaning that it travels in a manner perpendicular to the direction of its propagation.

Light only differs from other waves in this spectrum in that it can be detected by the human eye.

Even though the medium in which a light wave travels affects its speed (reducing it by the material’s index of refraction), light is also able to pass through a vacuum, hence providing a unique background for calculating its speed.

Over the centuries, accurately measuring this speed has proven to be very difficult. It is only with advancement in laboratory techniques, especially laser technology, that precise measurement became possible.

1n 1972, an experiment using a helium-neon laser with a fixed frequency and a methane molecule produced a measurement that was a hundred times more accurate than previous measurements.

## Speed of Light Vs Speed of Sound

In 1983, at the General Conference on Weights and Measures, the speed at which light travels was defined as 299,792,458 meters per second.

To get a perspective of how high this speed is, we can compare it with the speed of sound in air, which has been calculated at 331.5 meters per second at zero degrees Celsius or 32 degrees Fahrenheit (although unlike light, sound requires a medium to pass through and is affected by properties of the medium such as stiffness, temperature and density).

## Relativity,time dilation and time travel

The speed at which light travels in a vacuum, normally denoted in physics as c, forms a key building block of Einstein’s theory of relativity, since it sets the maximum limit for speeds in the whole universe.

Consequently, it appears in many physical formulas, perhaps the best known of which is E=mc2 where E means ‘Energy’, ‘m’ means ‘mass’ and ‘c2’ denotes ‘speed of light squared’.

Einstein stated that when we multiply mass with the speed at which light travels squared, we get the total energy that is stored in that piece of mass.

Simply put, this equation means that energy and matter are the same stuff. In the formula,the speed at which light travels is the constant, meaning that if an object was transformed into pure energy, it would move at that speed.

For moving objects the formula becomes E2 = (mc2 )2 + (pc)2 where ‘p’ denotes momentum.

Einstein’s special theory of relativity states that the speed at which light travels is the same for any person measuring it, whether they are standing or in motion.

Therefore, time is an illusion, and it is relative to anyone observing it at a particular speed.

The theory also introduces the element of time as a fourth dimension, in addition to width, length and height-which comprise ‘space’ in the theory.

Consequently, as a person travels with increasing speed, space and time would have to contract or expand which means nothing can ever exceed the speed at which light travels. This space-time continuum means that time, for any object in motion,always changes.

One of the most remarkable consequences of Einstein’s theory is that it means a moving clock will always slow down in relation to an observer who is stationary.

This slowing of a clock due to motion is referred to as time dilation.

Another aspect of relativity is the redefinition of gravity.

In the theory of general relativity, gravity has the ability to bend time. The theory observed that when an object with mass rests on the space-time fabric, it causes a dimple or a bend.

This bending makes object to travel on a curved path and this curvature is what we refer as gravity.

The relativity theories have been proved by satellite and GPS technology which use highly accurate time systems on board.

Gravitational effects combined with their increased speed over the earth relative to ground observers causes unadjusted clocks to gain about 38 microseconds each day.

Satellite engineers are forced to make calibrations to compensate for this difference.

Time dilation means that astronauts are time travelers.

For example an astronaut with a twin will return to earth just a little bit younger than the twin who had been left on earth.

The concept of time dilation is important when discussing time travel, which is a popular theme in modern culture.

Einstein’s theory suggests that it is possible to have scenarios for going back in time. The required equations and calculations are however difficult to achieve physically.

If for example we were to travel faster than light (which means over speeds of 299,792 km/s in a vacuum) any object at that speed requires to have infinite mass and zero length.

Therefore, is it possible to travel faster than the speed of light? The simple answer is no.

Other suggested ways of traveling back in time include using ‘wormholes’ created at certain points between time and space. However such wormholes would collapse very rapidly and would only permit very tiny particles to pass through.

Therefore, time travel as seen on popular science fiction movies and books is currently not possible.

**Do you think we will ever be able to travel faster than light?**