Our resident science guru contemplates the true speed of light
For some reason, we humans are obsessed with speed. The faster a thing goes, the more impressive it is to us. This fascination probably has some sort of basis in how we evolved. The faster a person was, the more likely they were to escape predators and pass on their genes.
What is “Speed?”
The most basic definition of speed is the distance something covers in a given unit of time. Today, in the rest of the world, that means “meters per second.” (A meter is about 3.3 feet long. Here in the USA, we generally think of speed in terms of “miles per hour,” but, I’ll stick with meters per second or kilometers per hour for the examples here.)
So, the further something moves in some unit of time, the “faster” it’s going. So, with that out of the way, let’s look at the fastest and slowest things in the universe.
The Fastest Thing
The fastest known thing in the universe is light, which travels at 299,792,458 meters per second in a vacuum. The reason light is the fastest thing is that it has no mass and is effectively pure energy. Only mass-less particles such as light can travel this fast.
Why? Well, common sense tells us that, to make something go faster, you have to put more energy into it. However, to make something with even a tiny amount of mass (like a proton) travel at the speed of light, Einstein’s Theory of Relativity tells us we would have to apply an infinite amount of energy, which is impossible.
So, while particles can be accelerated to nearly the speed of light in, say, a particle accelerator, they will never actually get there.
Note that while the speed of light seems really fast at first, space is so big that, it turns out that the speed of light is really kind of slow if you want to go anywhere interesting in the universe. For example, it takes light eight entire minutes to travel from the Sun to the Earth, and it would take light four years to get from here to the nearest star.
The Slowest Thing
This…is a tricky one. The reason is that Einstein also showed us that speed is calculated relative to some frame of reference. For example, to us, a photon of light moves at the speed of light.
But, from the photon’s point of view (i.e. it’s frame of reference), it’s not moving at all. So, to find the slowest thing, you would need a truly universal frame of reference.And, even when something appears to be absolutely still, it’s still “full” of motion at the atomic level.
But, in physics, there is the concept of “absolute zero.” This is a temperature where all motion stops. That includes atomic motion…everything is perfectly still with no movement at all. It’s literally colder than the vacuum of space.
As you might expect, this is a theoretical construct, as it’s impossible to remove all energy from a system. (At least with today’s technology.) However, scientists regularly perform experiments that cool systems to near absolute zero. (Which is -459.67º F.)
These are useful for studying superconductivity (where electrical resistance disappears) and strange states of matter, like Bose-Einstein Condensates, can be studied.
Still, even when scientists cool something to near absolute zero, those molecules only stop moving within the frame of reference of the experiment. They are still pulled along with the Earth as it speeds around the Sun, and the Sun around the Galaxy.
Another fun fact Einstein taught us about speed is that, the faster you go, the slower time moves for you. And, if you move at the speed of light, time actually stops for you.
So, for a photon of light that was born in the one of the first stars and finished its journey in, say, a detector in the Hubble Space Telescope 13 billion years later, no time has passed at all. It’s born and dies in the same instant.
So, in a strange way, light is both the fastest and the slowest thing in the universe. It just depends on your frame of reference.
Steven W. Disbrow is the proprietor of “Improv Chattanooga” on the South Side of town. He also creates e-commerce systems and reads comic books when he’s not on stage acting like a fool.