Hello friends, often we have to rethink what we know, and this is why I bring this question up.

Of course, if we ask any physicist, he will answer that it is impossible. He will reason that special relativity specifically prohibits any material particle reaches the speed of light. The reason is that as the particle is accelerated, its mass increases; therefore, the required energy to accelerate it also increases.

However, in the equations of the dynamics of a perfect fluid without pressure appears a new variable that is the density. The density of a fluid can vary due to forces of compression or decompression.

This subtle difference allows, in certain cases, that a fluid can reach the speed of light. For example, in the case of a perfect fluid without pressure, relativistic equations of the dynamics allow a class of solutions in which fluid density decreases as speed increases until becomes zero when it reaches the speed of light . Thanks to this effect, the amount of energy transferred to the fluid to reach the speed of light becomes finite, contrary to what happens in the case of the point particle.

This opens the possibility of travelling to the past as it can be seen in more detail in the section “THE PHYSICS OF TIME TRAVEL”.