If you got a chance that you visit the Paris Observatory on the left bank of the Seine, you’ll see a plaque on its divider declaring that the velocity of light was initially measured there in 1676. The odd thing is, this outcome came to fruition accidentally.
Light goes at around 300,000 km for each second. Why not quicker? Why not slower?
we have several incomplete answers to this because some of its properties are still a mystery to scientists
Light isn’t the only thing that moves so quickly — any particle without mass moves through the vacuum at the “speed of light”. This includes gluons, which carry the strong force (the same way that particles of light, called “photons” carry the electromagnetic force) and hold together the nuclei of atoms.
For a long long time, it was thought that neutrinos had no mass, in which case they would also move at “lightspeed”. In 1998, it was shown that neutrinos do has mass, it is just very very tiny (the smallest we know that isn’t actually zero!). So although the neutrinos move at close to the speed of light, they are ever so slightly slower.
The speed of light (or gluons) is a built-in constant of the universe. It falls naturally out of the electromagnetic wave equations and was known before Einstein came along and invented special relativity (in which the finite speed of light plays a crucial role in causing time dilation and messing up our concepts of simultaneity). Any massless particle MUST move through the vacuum at this speed; for them, it isn’t just a speed limit, it’s also a minimum speed. For any massive particle, the speed of light is forever out of reach. Even for those with tiny masses, like neutrinos. They can come very very close… but it would require infinite energy to bring them up to lightspeed.
Why is this particular speed (exactly 299,792,458 meters per second, by definition) so special? No one knows. There is no a priori reason that this should have been the universal speed limit, and we can easily imagine a universe forming where the top speed is twice this value. That said, in our universe, it is what it is and makes up one of the fundamental constants of the universe.
The speed of light in a vacuum is 186,282 miles per second, and in theory, nothing can travel faster than it.
Early scientists were unable to think of light as ‘moving’ – they originally thought it shot out instantaneously from our eyes – a bit like laser beams. But, over time, and with more understanding the measurements of the motion of these wave-like particles of light became more and more precise. Thanks to the work of Einstein on relativity, we now understand light speed to be a theoretical limit which can’t be beaten by anything with mass.
According to relativity, as an object moves faster, its mass increases, while its length contracts. At the speed of light, such an object has an infinite mass, while its length is 0 — which is theoretically impossible. Light can travel at light speed because it has no mass and no definable size.
Light travels so fast because everything else travels much slower. The theory of relativity learns us that the universe has set a maximum velocity in the fabric of space a time. There isn’t a way to squeeze a higher velocity for moving particles out of this space-time then this maximum. In this universe some particles can have this maximum velocity, they need to be massless. By experiment, this maximum velocity was found to be 299792458 meter/second.
Is there anything which can travel faster than light ?
Most textbooks say that nothing can go faster than light, but that statement actually should be qualified: The answer is yes, you can break the light barrier, but not in the way we see in the movies. There are, in fact, several ways to travel faster than light:
1. The Big Bang itself expanded much faster than the speed of light. But this only means that “nothing can go faster than light.” Since nothing is just empty space or vacuum, it can expand faster than light speed since no material object is breaking the light barrier. Therefore, empty space can certainly expand faster than light.
2. If you wave a flashlight across the night sky, then, in principle, its image can travel faster than light speed (since the beam of light is going from one part of the Universe to another part on the opposite side, which is, in principle, many light years away). The problem here is that no material object is actually moving faster than light. (Imagine that you are surrounded by a giant sphere one light year across. The image from the light beam will eventually hit the sphere one year later. This image that hits the sphere then races across the entire sphere within a matter of seconds, although the sphere is one light year across.) Just the image of the beam as it races across the night sky is moving faster than light, but there is no message, no net information, no material object that actually moves along this image.
3. Quantum entanglement moves faster than light. If I have two electrons close together, they can vibrate in unison, according to the quantum theory. If I then separate them, an invisible umbilical cord emerges which connects the two electrons, even though they may be separated by many light years. If I jiggle one electron, the other electron “senses” this vibration instantly, faster than the speed of light. Einstein thought that this, therefore, disproved the quantum theory since nothing can go faster than light.
But actually this experiment (the EPR experiment) has been done many times, and each time Einstein was wrong. Information does go faster than light, but Einstein has the last laugh. This is because the information that breaks the light barrier is random, and hence useless. (For example, let’s say a friend always wears one red sock and one green sock. You don’t know which leg wears which sock. If you suddenly see that one foot has a red sock, then you know instantly, faster than the speed of light, that the other sock is green. But this information is useless. You cannot send Morse code or usable information via red and green socks.)
4. Negative matter. The most credible way of sending signals faster than light is via negative matter. You can do this either by:
a) compressing the space in front of your and expanding the space behind you so that you surf on a tidal wave of warped space. You can calculate that this tidal wave travels faster than light if driven by negative matter (an exotic form of matter which has never been seen.)
b) using a wormhole, which is a portal or shortcut through space-time, like the Looking Glass of Alice.
In summary, the only viable way of breaking the light barrier may be through General Relativity and the warping of space-time. However, it is not known if negative matter exists, and whether the wormhole will be stable. To solve the question of stability, you need a fully quantum theory of gravity, and the only such theory which can unite gravity with the quantum theory is string theory (which is what I do for a living). Sadly, the theory is so complex that no has been able to fully solve it and give a definitive answer to all these questions. Maybe someone reading this blog will be inspired to solve string theory and answer the question whether we can truly break the light barrier.