Interesting facts - light

Light is a form of energy that travels freely through space. It is electromagnetic radiation, just like radiowaves, infrared radiation and x-rays. We can only see part of the range of elecromagnetic radiation (the spectrum). The part we can see is light.

Most of the light we see originally comes from very hot objects. The hotter the object, the further towards the blue end of the spectrum is the light that it gives out. The surface of the sun is at a temperature of about 6000 degrees C and gives out the sunlight which we see.

Travelling at the speed of light

Even though light travels at 299,792,458 meters per second (in a vacuum), it takes it years to travel across the vast distances in space. Just think of how many unexplored galaxies we could visit if we could travel at, or faster than, the speed of light!

Physicists think that it is impossible for us to travel at these speeds - but why?

What is the smallest thing you can think of? An electron?

N.B. An electron is a tiny and very, very light particle that forms part of an atom (everything around us is made out of atoms but they are far too small to see without a scanning electron microscope).

Ok, say we want to accelerate an electron to the speed of light. Since it's so small and light, we can make it travel at the speed of light, can't we?

This has been tried, but so far physicists have only actually managed to send electrons flying round at 99.999999995% of the speed of light, which is very close to, but not quite the speed of light.

So, why is it so difficult to make an electron go at the speed of light?

In order for an electron to accelerate it needs energy. The energy given to an electron is converted into kinetic energy which is associated with the forward motion of the electron. At low speeds the more energy given to the electron, the faster the electron goes; but as the speed gets closer to the speed of light, the electron does not go much faster as energy is put in but seems to just store kinetic energy (this was first noticed by a scientist called W. Bertozzi in 1964).

What happens to all of the kinetic energy?

The famous scientist, Albert Einstein, created the equation (link opens in a new window):

E = mc²

(E is for energy, m for mass and c is the speed of light)

According to Einstein's theory, represented by the above equation, as the electron approaches the speed of light, the kinetic energy is turned into mass, making the electron heavier and heavier. This means that the electron would need an infinite amount of energy to reach the speed of light, but by this time it will have an infinite amount of mass.

Why is this a problem? Could we simply give the electron an infinite amount of energy!

We would if we could but this Universe does not have infinite amounts of energy so we cannot make an electron (or anything else) travel as fast or faster than the speed to light.

Trips to distant galaxies at the speed of light will have to wait for now...

but who knows what will happen in the future!

Why the sky is blue

John Tyndall, a clever scientist who succeeded Michael Faraday as director of the Royal Institution in 1867, first discovered why the sky is blue.

Tyndall noticed that when you shone a torch through clean filtered air you can not see the beam but if it is shone though normal air you could often see the beam.

He realised you can only see light beams because the air is full of particles that scatter the light. Tiny dust particles floating in the air scatter blue light more than red and yellow so the sky looks blue.