These particles are moving at very near the speed of light.

For example, these particles must always move at the speed of light.

There is only one type of particles moving with such speed.

When these particles move close to the speed of light, they can live long enough to get here from other stars.

So what happens when the two particles have moved apart?

Suppose that the two particles were moving away very fast and a long time had gone by.

The particles moved as if they were in a complete vacuum.

In a liquid the particles move around, pass each other, like people walking on a street.

It also is used to determine how the particles will move in the fluid.

Therefore, even though the plasma is cold, the particles must be moving very fast on average.