299,792,458.
At first glance, it looks like a random number from a calculator. But it is actually one of the most important numbers in physics.
It is the speed of light in a vacuum, measured in metres per second. That is almost 300,000 kilometres every second. In just one second, light could travel around Earth about 7.5 times. This seems fast, but also slower than I expected to be honest.
And that is only the beginning.
This number tells us something fascinating about the universe, how we measure distances, and even how we look into the past.
Does it not have Decimal Places?
Is the speed of light really exactly 299,792,458 metres per second? What about the decimal places?
Surprisingly, the answer is yes. It is exact.
In 1983, scientists officially defined the metre using the speed of light. Instead of constantly measuring how fast light travels, we now use its speed to define distance.
One metre is the distance light travels in a vacuum in 1/299,792,458 of a second.
That means the speed of light is exactly 299,792,458 metres per second by definition. There are no missing decimal places but it also does not mean that the speed of light is not naturally a whole number. We simply designed our measurement system around it.
Unlike pi, which has infinitely many non-repeating decimal places, the number representing the speed of light depends on the units we choose.
For example in the egyptian Royal Cubit the speed of light would be around: 5.743.150,53639847
We live in the Past
Sunlight takes about 8 minutes and 20 seconds to reach Earth. This means that when you look at the Sun , you are seeing it as it was more than eight minutes ago.
Moonlight takes about 1.3 seconds to reach us.
Some galaxies are so far away that their light has been travelling for BILLIONS of years.
Imagine looking through a telescope tonight and seeing light that started its journey before Earth even existed.
Fun Fact: Water slows light down
You might think light always travels at the same speed -> But that is not true. 299,792,458 metres per second only applies to light travelling through a vacuum.
In materials like water or glass, light travels more slowly.
For example, light travels through water at roughly 225,000 kilometres per second. That is still incredibly fast, but noticeably slower than in empty space.
Also this helps to explain something beautiful: rainbows.
When sunlight enters a raindrop, it changes direction. This is called refraction.
Different colors of light bend by slightly different amounts, which separates white sunlight into the colours of a rainbow.
Can Anything Travel Faster Than Light?
You have probably heard that nothing can travel faster than light.
That is true when we are talking about the speed of light in a vacuum.
However, there is a surprising exception when light travels through materials.
Some electrically charged particles can move through water faster than light itself moves through that water.
They are still slower than light in a vacuum, so Einstein's speed limit remains safe.
But when these particles travel through water fast enough, they produce a beautiful blue glow called Cherenkov radiation.
This effect can be seen in certain nuclear reactors, where the water surrounding the reactor core glows blue.
It is almost like a sonic boom, except instead of sound, it involves light.
Also it sets the speed limit for our universe.
According to Einstein's theory of relativity, no object with mass can be accelerated to the speed of light in a vacuum. Information and physical influences cannot travel faster than this universal limit.
The last facinating Point is that Visible light is only a tiny part of the electromagnetic spectrum.
Radio waves, microwaves, infrared radiation, ultraviolet radiation, X-rays, and gamma rays are all forms of electromagnetic radiation.
Although they seem completely different, they all travel at exactly the same speed in a vacuum.