How can light travel at the speed of light?

There are two kinds of particles in our Universe: Those with (rest) mass and those without it.

Electrons, protons, neutrons, quarks, and the Higgs (if it exists), W and Z bosons have mass and can not be accelerated to the speed of light.

Photons, gluons, and gravitons (if they exist) are massless.

The massless particles travel at c *in a vacuum*. In air or any other medium, the speed of photons is reduced and is generally wavelength dependent.

It is believed that the neutrino has a small mass, but this has not yet been proven. The experiment that showed neutrinos traveling faster than c could have profound implications for all of particle physics if it is confirmed. Not only (according to the currently most accepted model) can neutrinos NOT travel at c (because they have mass), **nothing** can travel faster than c.

Light is both a wave and a particle, so it doesn't really make sense. It moves as fast as it does because it has the properties of both substances; if it wasn't a wave it would have mass, and if it wasn't a particle it would be invisible to our eyes. It stills conforms to some physics, though, as we can change things about it, such as sending light through a prism or other substances. Because of this particle-wave duality, it has the ability to travel at this incomprehensable speed.

However, the speed of light is only relative to the medium in which it travels- light speed is a reference to how fast light particles travel through empty space, but through air or water or liquid nitrogen it travels much slower, sometimes even slow enough to watch.

One doesn't need an infinite amount of energy to reach lightspeed, rather a different kind of energy or a different mode of transport. For example, a tachyon (a theoretical particle) can travel like the TARDIS does in Doctor Who; through space AND time at the same time. Arguably, this is travelling faster than light. Another way to travel faster than light is through a wormhole. These do in fact exist, but are so tiny that we probably won't have the technology for 100 years to enlarge them, let alone travel through them. These will allow us to make shortcuts through space-time, the fabric of everything, a bit like folding a piece of paper in half then sticking a pencil through it (the pencil being your spaceship).

Light has zero rest mass. It takes infinite energy per unit rest mass to get something to the speed of light.

What is infinity multiplied by zero? Well, that can be any finite number you want it to be.

Or better said as: any finite number that other means might indicate. And in fact, other means do indicate a finite energy per photon of light. The E=h*f equation indicates it in terms of Planck's constant and frequency.

It would take an infinite amount of energy to accelerate anything with mass to the speed of light. Light doesn't have mass.

Another point to add to previous answers.

Since light does travel at the speed of light, it's sense of time is essentially stopped. Since the photon's time is stopped, then it does not realize that it actually took time for it to travel from point A to point B. Thus a photons lifetime is instantaneous. It is born and dies out at exactly the same time (from the photons point of view, of course).

Any kind of lights travel at the same speed. No matter if it is gamma rays, ultraviolet or radio waves. U would never experience light to travel faster or slower than 186000 miles in vacuum. So, that is how light avoided these problems for itself :)

Light has no "at rest mass" ... it does not need to accelerate to the speed it travels, it starts at that speed.

Photons which propogate light have zero mass therefore don't violate Einstein's relativity.

NOTE:

Photons do have a tiny >rest< mass, but are never at rest.

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Hind

It lacks mass...