After deciding to long ago, I have finally gotten around to starting my “5 things you didn’t know about…” series, in which I intend to explain 5 interesting, impressive, weird, unusual or widely unknown facts on broad topics.
I’m going to start off the series with something we are all very familiar with; Light:
- I’m sure most people know that light gets to us from the sun travelling as a wave. Actually, light is composed of small packet-like particles of energy (quanta) called photons, and light will sometimes act as a wave and sometimes as a particle, and will sometimes behave as if it has mass, sometimes as if it has no mass.
- You probably know that light is exceptionally fast, clocking in at about 299,792,458 metres a second in a vacuum, which is believed to be the universal speed limit. However, did you know that some particles (most notably neutrinos) have been noted to have travelled faster than the speed of light (with as of yet no explanation), and areas of space aren’t confined by this limit, meaning due to the expansion of our universe, some galaxies are effectively moving away from us faster than the speed of light; meaning we may never be able to see them.
- In the universe there are peculiar things called “Black Holes”. And technically, although we know they are there, no one has ever or will ever see a black hole. This is because, if one looks at a black hole, one simply sees an empty black region in space; the light that heads toward the centre of a black hole cannot bounce off of its surface and travel to our eyes, as once the light that travels past a point of no return called the “Event Horizon” the force of gravity is too strong to allow anything to escape (as to escape, something would need to travel faster than light).
- Take a look at panel A of the picture below; we see things when light comes from a source (the bulb), bounces off of a surface (the right side of the blue box) and travels into our eye, imprinting on the retina, sending a signal along the optic nerve to the brain. The green arrows symbolise a path of light that successfully gets to the eye. The red arrows symbolise light that does not make it to the eye; the eye cannot see the bottom side of the blue box as the light that bounces off of this side cannot reach the eye.
However, did you know that light itself is actually invisible? Have a look at panel B; the eye sees the right side of the blue box as before. The red arrows represent a beam of light that crosses our field of vision; not only do we not see these beams of light, but they in no way obscure our view of the blue box. Even when you see a laser beam fired, you see air particles that the light hits, and not the light beam itself.
- Did you know that the idea of making something or someone “invisible” is not only theoretically possible, but may be a possibility of the not so distant future ? So far, scientists have only been able to make things invisible to radio and microwaves, but the light we see is just like these forms of radiation (Electromagnetic Radiation), except light has a much smaller wavelength. The concept of how to make something invisible (using the same method that has been implemented to make objects invisible to microwave radiation) is briefly shown in panel C;
As before, light travels from the bulb and bounces off of a blue box. The light heads towards the eye. However now, there is a gold box blocking the view of the blue box. In a normal situation, the eye would observe the gold box, and maybe see the edges of the blue box behind it. But, using a cloak (the gold circles around the gold box) made of metamaterial (material that is enhanced beyond its natural abilities), the light from the blue box can be bent around the gold box, and returned to its original course toward the eye. If this is done flawlessly, and from each direction, everything inside the golden rings will appear fully invisible, and the eye will just observe the blue box.
It is also theoretically possible to achieve a similar effect by manipulating gravity, which bends light, or by altering an object to have a refractive index (factor by which it bends light) equal to that of air. However the implementation of these theories for visible light is still many years off.