The answer to the question “How fast does light travel?” is quite simple. The speed of light is 299 792 458 m / s (186000 mi/s for our non-metric friends) – in a vacuum.
But we’re not able to comprehend what this number means.
The following video is perfect to visually demonstrate just how fast light travels. It also shows you how unbelievable big our universe is and how far different planets are.
Before I show you the video, let’s start with a brief lesson in the history of the theory behind the speed of light.
The ancient Greek philosopher Aristotle believed that light traveled instantaneously, another Greek scientist Empedocles disagreed. He believed that light moved and therefore needed time to travel.
In 1667, the Italian astronomer Galileo Galilei stood two people on hills less than a mile apart, each holding a shielded lantern. One uncovered his lantern; when the second saw the flash, he uncovered his, as well. By observing how long it took for the light to be seen by the first lantern-holder (and factoring out reaction times), he thought he could calculate the speed of light. Unfortunately, Galileo’s experimental distance of less than a mile was too small to see a difference, so he could only determine that light traveled at least 10 times faster than sound.
A lot of scientists tried to calculate the speed of light throughout history. In 1728, English physicist James Bradley based his calculations on the change in the apparent position of the stars due to Earth’s travels around the sun. He put the speed of light at 185,000 miles per second (301,000 km/s), accurate to within about 1 percent.
Light travels fast – we’ve come to understand that. But our universe is so big not even the speed of light is enough to travel around. To put the speed into perspective. If we took out the fastest rocket to the nearest star which is 4,3 light-years away it would take ~80,000 years to get there. Even at the speed of light, it would take years and we can’t ever reach that speed.
Another phrase you might have heard in this context is “light year”. One could think it’s a time frame, but it’s not. It’s a distance.
Sunlight takes about 8 minutes to reach our eyes, so the sun is about 8 light-minutes away. Light from the nearest star system, Alpha Centauri (it creates gravity wells), requires roughly 4.3 years to get here, so that star system is said to be 4.3 light-years away.
Can we travel faster than light? According to Albert Einstein an object gains mass the faster it travels, while its length contracts. At the speed of light, the object has an infinite mass, while its length is 0 – an impossibility.
According to Einstein’s general theory of 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 — an impossibility. Thus, no object can reach the speed of light, the theory goes.