# How did Scientists Determine the Speed of Light?

There once with a guy named **Albert Einstein** who you’ve probably heard of and he developed the equation e equals MC squared which you have probably heard of also.

using this equation the relationship between mass and energy can be calculated using the speed of light which is a universal constant the value for the speed of light is exactly 299,792,458 meters per second

now this is the maximum speed at which matter and information can travel in the universe

but how did scientists determine the speed of light?

philosophers in ancient Greece were the first to think about and debate the speed of light

way back in the fifth century BCE Empedocles made the first claim that light had a finite speed

Aristotle however disagreed and said that light was instantaneous

you couldn’t tell me thought that light came from the eyes which are what enabled site

this would seem to imply that lightness have an infinite speed which allows us to see really distant objects like stars immediately upon opening our eyes

over a thousand years later the Islamic philosopher out hazing proposed that line actually travels from an object into our eyes and therefore light has a finite speed

like 600 years later really smart people like Johan Kepler and Rene Descartes were saying that the speed of light must be infinite

because there is nothing in any space to slow it down and during a lunar eclipse the Sun Earth and Moon should be out of alignment which had never been observed

so far more than 2,000 years the debate as the whether the speed of light was finite or infinite raged on

the problem thus far was that no one had developed an experiment that showed that lie either around instantaneously or whether it took some time reaching its destination

but that was about to change in 1620, not Isaac Beckman proposed an experiment in which observers watch the flash of a cannon being reflected off of mirrors at different distances from the blast

the observers with in detail whether the flashes around at different times

the problem was the mirrors were not far enough apart so the experiment was inconclusive

Galileo came up with another experiment in order to determine the speed of light in which two people with lanterns withstand a mile apart and take turns flashing each other with the left take turns flashing each other with the Leonard’s and then determine if there was a lag in the amount of time it took that light to reach them

they’re actually would have been a delay in this experiment of about eleven microseconds which is way too fast for our feeble human senses to detect

so again the results were inconclusive it wasn’t until 1676 that someone would finally prove the speed of light was an infinite

that someone was the danish astronomer the only roamer was studying I owe the moon of Jupiter and its orbit around the planet which took place every 1.76 days knowing this Romo believe he could precisely predict the motion of Io but he couldn’t he noticed sometimes I Oh seem to be behind schedule while other times it seemed to be ahead of schedule

but what was causing this apparent change and iOS orbit wasn’t thinking about it for a while Romo notice that the moon of Jupiter seem to be behind schedule when Earth and Jupiter were farther apart in their orbit and ahead of schedule when they were closer together

it wasn’t that I was changing its orbit at all it was added to light less time to reach Earth and Jupiter was closer and more time when it was farther away

this must mean that light has a finite speed but at the time they were still a lot of doubters who believed that light was instantaneous

but like any great Theory roamer could use it to make predictions and predict he did he let his colleagues know that our November nine 1676 iOS eclipse what happened ten minutes later than they expected when the time finally came they were astonished to see the Eclipse happen just as aroma foretold and using what Romo figured out the dutch scientist Christiaan Huygens was able to calculate the speed of light to be 220 million meters per second

well but wait we learned earlier the speed of light was 299,792,458 meters per second I mean that’s a good first attempt to know but we still haven’t answered our question how did scientists determine the speed of light well the centuries that followed so many sciences is performing many different experiments

from James Bradley and 1729 using the effect of stellar aberration to calculate the speed of 301 million meters per second to our Mickelson and 1879 using rotating mirrors to calculate the speed of 299 million nine hundred thousand meters per second but it wasn’t until the seventies the nineteen seventies that lasers finally made it possible to start nailing down the speed of light we all know lasers make everything better duh and using lasers the speed of light was determined to be 299,792,458 6.2 m/s a decimal

Are you kidding me well believe it or not in 1983 the definition of the meter was actually redefined so that the speed of light could be a whole number that whole number is 299,792,458 meters per second the speed of light as we know it today so that’s how scientists determined speed of light you see that’s the cool thing about science even if it takes years or decades or even centuries to answer the questions we have about the natural world no matter how impossible they seem there’s no better way to go about finding those answers than with science so stay curious keep asking questions and continue exploring the world around you because there’s no telling what discovery still await us just around the corner.