Things that travel faster than lightIt is a common belief among the people who are somewhat familiar with the work of Einstein and even those who have studied his relativity principle in detail that nothing can travel faster than light. But there are certain physical phenomena that can travel faster than the speed of light. This will come as a shock to most people, especially those who are proud of proclaiming that the ultimate speed of everything is that of light and nothing can travel faster than it, Einstein proved it. But if there are phenomena which travel faster than the speed of light in vaccum it seems necessary to discuss what Einstein actually meant by his statement.

Einstein’s statement actually tells us that the speed of light is the ultimate speed for the transmission of messages, or of mass and energy. So, we can say anything which isn't carrying mass, energy and information may travel faster than light. This statement may sound confusing, how can something which is travelling not carry any of mass, energy or information. I will explain this by using some examples.

Let’s start from scissors, if you notice the point of intersection of two blades you will realize that this specific point, the locus of intersection of two blades can travel faster than c. As the scissors are closed the blades get more and more nearly parallel and the speed at which the intersection point move keeps on increasing and increasing. now if the blades are long enough it may cross the ultimate speed. Just see we have taken an object as simple as a scissors and have broken the record. But this is just a trick, the point of intersection is nothing but a geometrical point. We can do this trick from all kind of geometrical points.

Just take a laser, point it at moon and the spot which it makes on the moon can travel all across the moon in just one second. No law is broken here. The photons travel at there usual speed its just the point that the laser beam will be making that will cross the ultimate speed. Now, we can all argue that whether we will be able to see this point or not but the gist is this if we make the screen far enough than the slight angular displacement in the position of source will make the point projected on screen travel thousands of kilometers. In this way we can even make a shadow travel faster than light. So, in a way Darkness can travel faster than light. Darth lords would be really happy to know this.

In all three cases mentioned above no mass or energy is traveling but one may argue that we can still transfer messages using these methods.Unfortunately, that’s not true, If we take the scenario of laser point and shadow we can easily see that no information can be transferred from point A to B by just moving shadows and points across them. Moreover information travels from source to these points rather than getting transferred from one point to another. But, scissors seems to offer a possibility. Not just scissor but any object will serve our purpose. All we

need is an object(let's take a stick) of large enough length, we can use this stick to turn on a bulb situated at one of its end and with the help of morse code we can use it to transfer messages from one end to the other instantaneously. But there is a flaw in this grand plan, in formulating this trick we have falsely assumed the stick to be infinitely rigid so that any motion occuring at its one end gets transferred to the other end instantaneously. In reality, the stick is not rigid but elastic. The wave carrying our message is transmitted through the stick with a velocity that depends on its elastic properties. In other words, the wave carrying the message will travel with the speed of the sound in that medium.

Another example would be that of matter waves (waves associated with particles). Infact, not just matter waves but certain electromagnetic waves can also travel faster than light. Now, we need to be very careful here. when we talk about velocitiy in case of waves, we must keep in mind that they have two types of velocity. Phase velocity, it is the velocity with which the phase of one frequency component travels. Group velocity with which the wave packet travels. It is significant to not that information and messages are carried through wave packets i.e with group velocity. while the phase velocity is related to phenomenas like refraction, as it carries no information or energy it may under some circumstances get past c.

There are many more examples of things which travel faster than light. but what we really need to understand is about the whole concept and what relativity truly states.