The Unachievable Dream: Light Speed Travel

The speed of light is a universal constant, often referred to as a cosmic speed limit. According to Einstein's theory of special relativity, on which much of modern physics is based, nothing in the universe can travel faster than light.

The speed of light is so immutable that it is used to define international standard measurements like the metre (and by extension, the mile, foot and inch).

The theory states that as matter approaches the speed of light, its mass becomes infinite. That means that, theoretically, to reach the speed of light, an infinite amount of energy would be required.

However, one source offers a different explanation, suggesting that everything travels at the speed of light, but in a four-dimensional spacetime, rather than three-dimensional space. In this theory, a stationary object is moving at the speed of light through time, but not through space.

As objects approach the speed of light, their mass becomes infinite

According to Einstein's theory of special relativity, as an object approaches the speed of light, its mass becomes infinite. This is because the speed of light is a constant across the cosmos, and escaping its pull would require an infinite amount of energy.

The speed of light is incredibly fast—approximately 300,000 kilometres per second (186,000 miles per second). In Einstein's famous equation, E=mc^2, energy (E) and mass (m) are interchangeable. However, because the speed of light is squared in this equation, tiny amounts of mass contain vast amounts of energy.

As an object moves faster, its observed mass increases. While this increase is negligible at everyday speeds, as an object nears the speed of light, its mass becomes infinite. This is because, as an object speeds up, its mass increases compared to its mass at rest. This increase in relativistic mass means that every extra unit of energy put into speeding up the object is less effective at making it move faster.

As the speed of the object increases and starts to reach a significant fraction of the speed of light, the portion of energy going into making the object more massive becomes bigger and bigger. Thus, at or near the speed of light, any extra energy put into an object does not make it move faster but instead increases its mass.

This explains why nothing can travel faster than light—at light speed, an infinite amount of energy would be needed to make an object move.

It would take an infinite amount of energy to accelerate an object to the speed of light

According to Einstein's theory of special relativity, it is impossible to accelerate an object with mass to the speed of light because it would take an infinite amount of energy to do so. As an object approaches the speed of light, its mass increases, and thus more and more force is required to accelerate it further. This is because, as something speeds up, its mass increases relative to its mass at rest, with the mass of the moving object determined by multiplying its rest mass by the Lorentz factor. This increase in relativistic mass makes every extra unit of energy put into speeding up the object less effective at making it move faster. As the speed of the object increases and starts to reach appreciable fractions of the speed of light, the portion of energy going into making the object more massive gets bigger and bigger.

This can be explained by the fact that space and time are unified into a single entity known as spacetime. Even a stationary object is moving at the speed of light through spacetime, but only through time and not space. Every object travels through spacetime at the speed of light, and an object moving through space at the speed of light has no speed left over to move through time. Thus, the absolute maximum speed an object could move through space or time individually is also the speed of light.

The speed of light is an invariant speed

According to Einstein's theory of special relativity, the speed of light is an upper limit, and nothing in the universe can travel faster than this. As an object with mass approaches the speed of light, its relativistic mass increases without bound, and it would take infinite energy to accelerate it to the speed of light. Thus, the speed of light serves as an immutable speed limit in our universe.

This speed limit can be understood by considering spacetime, a unification of space and time proposed by Einstein. In spacetime, objects are travelling at the speed of light, either through time (for stationary objects) or through space (for objects with a spatial velocity). Since the total speed in spacetime is constant, increasing the speed of an object through space means decreasing its speed through time, leading to time dilation. Thus, the speed of light is an invariant speed that cannot be exceeded.

Time slows down for an object as its speed gets faster

According to special relativity, time is not absolute. A moving clock ticks more slowly than a stationary one. Travel at the speed of light, and, theoretically, time would stop altogether.

This phenomenon is known as time dilation, and it can be calculated using the Lorentz factor, which takes into account the velocity of an object relative to a stationary reference point.

As an object approaches the speed of light, time dilation increases exponentially. This means that, from the perspective of an observer, the object's acceleration will appear to drop off, tending towards zero as it gets closer to the speed of light, even though, in its own frame of reference, it is maintaining a constant acceleration.

The faster an object travels, the more massive it becomes. As an object gains mass, more force is required to accelerate it further. As the speed of light is approached, the force needed to accelerate the object approaches infinity, meaning that only massless particles like photons can travel at the speed of light.

The speed of light, denoted as "c", serves as a universal speed limit. It is an immutable constant, always remaining the same regardless of the speed of the observer.

Therefore, objects with mass cannot reach the speed of light. If an object with mass were to reach the speed of light, its mass would become infinite, and the energy required to move it would also become infinite, an impossibility.

Only massless particles can travel at the speed of light

The speed of light is a constant defined by the properties of the material through which the waves move. Nothing with mass can travel at the speed of light because, as an object's velocity approaches the speed of light, its energy and, thus, its apparent mass increases significantly. This requires a tremendous amount of energy to continue accelerating. As an object's mass approaches infinity, it would need an infinite amount of energy to reach the speed of light.

Massless particles, such as photons, can travel at the speed of light because they have no mass. This is a result of special relativity. Any particle with zero mass must move at the speed of light, and no other speed.

In the case of massless particles travelling at a speed less than light, their momentum and energy would be zero in all frames of reference. This is because the momentum of a particle travelling at a speed less than light is given by p = m0*v*sqrt(1/(1-(v/c)2)), where m0 is the rest mass of the particle. For a massless particle, m0 = 0, so the momentum is always zero.

In the case of massless particles travelling at a speed greater than light, this would violate the principle of causality. If a particle were emitted that travelled faster than the speed of light, and then absorbed elsewhere, and then another particle was emitted that travelled faster than the speed of light back towards the original source, the returning particle would arrive before the first one was sent. This would mean that the events had no cause, which goes against the idea that natural phenomena can be explained in terms of the laws of physics.

Therefore, since massless particles may travel neither faster nor slower than the speed of light, they must travel at the speed of light.

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