How can nothing be faster than light when speed is only relative?

Question

You always hear this phrase if you watch something about astrophysics ‘Nothing can move faster than light’. But speed is only relative. How can this be true if speed can only be experienced/measured relative to something else?

In: Physics

Answer 1

Speed of objects is relative when measured from different viewpoints, but not in the case of light.
Light is measured at the same speed regardless of the viewpoint of the observer. That’s part of the principle of relativity.

I’m not a physicist, but I think it works thus:

2 spaceships, one stationary and one travelling at 10000kph, both turn on their spotlights at exactly the same moment, pointing to a stationary observer placed mid way between them.
In theory, the light from the moving ship should arrive at the observer sightly earlier, because it has a 10000kph running start.
However, the observer will measure the speed of the arriving light as exactly the same from both ships.
As the distance between the objects is objectively known, then the only way that physics can accommodate the consistent speed of light is to allow time to distort.
Time moves slower for the speeding spaceship to allow the light to arrive at the same time as that from the stationary ship.

Edit to answer the actual question!

Light has no mass. Everything else has a mass which requires energy to accelerate it.
As an objects speed increases, so does it’s mass. Increased mass requires increased energy to accelerate it. This becomes exponential as the object approaches light speed, meaning that the object requires an ever increasing amount of energy to accelerate it. This becomes an impossible achievement just short of the speed of light.
E=mc2 is the equation that states this principle.