It appears to be a fundamental property of our Universe that nothing can travel faster
than the speed of light.
This is the Universal speed limit.
The Higgs field is a quantum field that permeates all of space.
Particle interactions with the Higgs field impart particles with their mass which in
turn slows them down.
As particles of light - photons - don’t interact at all with the Higgs field they
travel at their maximum possible speed - the speed of light.
When we attempt to accelerate particles to the speed of light, the closer and closer
the particle gets to light speed, the more and more massive they become until an infinite
amount of energy would be required to accelerate the particle to light speed.
And of course, we cannot provide infinite energy.
It has been experimentally shown that the speed of light is the same for all observers.
And taking this constant into account Einstein revealed an amazing thing about the nature of time.
It is not the same for everyone.
Imagine a beam of light being reflected between two mirrors.
Let’s replicate this set up so we have another beam of light being reflected between another
set of mirrors but this time the mirrors are moving close to the speed of light.
In the moving set of mirrors the beam of light is moving a greater distance.
Now, place a couple of observers in this scenario.
Meet Alex, who sits inside the moving set of mirrors and Bill who sits inside the stationary
set of mirrors.
The speed of light must be the same for both Alex and Bill and their light beams must hit
the bottom mirror after the same amount of time
has passed. But as Alex’s light beam is covering a
longer distance how is that possible?
Well, the only way for that to work is if time for Alex slows down which gives his light
beam more time to travel a greater distance.
Look at it this way, speed equals distance divided by time. As the distance Alex’s
light beam travels is more the value of his time must be more to keep the speed constant
for all observers or rather Alex’s one minute actually turns out to be longer than Bill’s
one minute when you compare the two.
And this is called time dilation.
Time slows down for objects travelling close to the speed of light; and time stops all
together for objects travelling at the speed of light
We established before that particles cannot be accelerated to light speed but that doesn’t
prevent hypothetical particles from already traveling at or faster than light speed.
A tachyon is such a hypothetical particle that travels faster than light and it would
take an infinite amount of energy to slow a tachyon down.
As time slows down for objects travelling close to the speed of light, time stops all
together for objects travelling at the speed of light; it then follows that time must go backward
if objects travel faster than the speed of light.
Tachyons therefore are also traveling back in time.
However most physicists do not believe in the existence of tachyons or the possibility
of traveling back in time as it would violate the causality principle, which states that
an effect cannot come before it’s cause.
Rather like how a bullet cannot hit a target before the trigger of the gun has even been pulled.
Einstein preferred to think of space and time as one entity - spacetime.
One hypothetical proposition as to how we could travel between distant regions of spacetime
without faster than the speed of light technology is to use wormholes.
Wormholes are theoretical tears in spacetime that could act as shortcuts between distant
regions in space.
Stretching of the Universe.
Although it seems nothing can move faster than the speed of light in space that does
not preclude space itself from stretching faster than the speed of light.
There are galaxies in the Universe moving away from one another at a velocity greater
than the speed of light.
Quantum entanglement.
Quantum entanglement describes how two particles can become connected in such a way that when
the property of one particle is changed, an instantaneous change in the property of the
other particle occurs.
Entangled particles have the opposite properties to each other.
So in theory, if a pair of entangled particles are separated by an entire universe, when
the property of one particle is measured the other particle on the other side of the universe
will take on the opposite property.
This seems to indicate faster than light communication between the pair of particles.
Despite these exceptions the assertion remains true that no particle can travel faster
than the speed of light in space and the reason is because this speed limit is a fundamental
property of our Universe.
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