# Simplifying complex topics | How to reach the speed of light and what is faster than it

We will explain this to you now.

## 1. What is the speed of light in a vacuum?

The speed of light is the highest speed that anything can have in our Universe. It is the speed at which not only electromagnetic waves of the visible spectrum move in a vacuum, but also any radiation.

This value is exactly 299,792,458 m/s. In 1975, it was determined with an accuracy up to meter, and since 1983, the meter itself in the International System of Units is the distance that light travels in 1/299,792,458 seconds. Therefore, this is perhaps the only constant whose value will not be specified in the future.

## 2. Are there cases when the speed of light is lower?

All of the above applies only to the speed of propagation of electromagnetic waves in a vacuum. In an environment that is at least partially capable of scattering them, it will be much lower. The exact value will depend on the wavelength and the refractive index of the medium itself.

For example, in absolutely pure water, the speed of light in the visible range is about 225,341 km/s, in glass it is 200,000 km/s, and in sugar it is only 192,300 km/s. In air, it is just slightly less than in a vacuum.

## 3. What is a “light cone”?

The concept of a “light cone” is related to the speed of light. Any interaction between two objects in the Universe, including the transfer of information, is possible only with the help of particles or waves. And they cannot move faster than light.

Therefore, no event in the Universe can affect other objects in less time than it takes light to travel the distance between them. For example, an event that happened on the Moon cannot affect the Earth earlier than a second and a quarter.

For the Sun, this value is as much as almost 8.5 minutes, for Pluto — about 4.5 hours, for α Centauri — more than 4 years, and for the black hole Sagittarius A* — 27 thousand years. This is called the “light cone”.

## 4. What happens if you try to reach the speed of light?

Newtonian mechanics tells us that if a force is constantly applied to a body — for example, the impulse of jet engines — it will accelerate, i.e. its speed will increase. So what prevents us from reaching the speed of light?

The answer to this is given by the Theory of Relativity. According to it, the closer the speed of a body is to the speed of light, the more energy is required to increase it by the same amount for each unit of mass of that body.

In order to accelerate any mass to the speed of light, an infinite amount of energy must be applied to it. That is why in nature, in most cases, only particles with no mass, such as photons, have this speed.

## 5. Can anything move faster than light?

Although physics emphasizes that the speed of light is the limit for any body, there are theories that predict the existence of particles that move faster than light. These particles are called tachyons, from the Greek word for “fast”.

Tachyons have a number of strange properties: for example, their mass is imaginary. That is, it is expressed by a number that is the square root of a negative value.

Scientists have no evidence of the real existence of tachyons. In addition, there are doubts about tachyon particles and fields, whether they are capable of carrying information and whether they really move faster than light. However, no one can completely rule out the possibility of such a particle.