How the Speed of Light was First Measured
Prior to a few hundred years ago, it was generally agreed or at least assumed that the speed of light was infinite, when in actuality it's just really, really, really fast- for reference, the speed of light is just slightly slower than the fastest thing in the known universe- a teenage girl's response time if
The first known person to question the whole "speed of light is infinite" thing was the 5th century BC philosopher Empedocles. Less than a century later, Aristotle would disagree with Empedocles and the argument continued for more than 2,000 years after.
One of the first prominent individuals to actually come up with a tangible experiment to test whether light had a speed was Dutch Scientist, Isaac Beeckman in 1629. Despite living in a time before lasers- which gives me the chills just thinking about- Beeckman understood that, lacking lasers, the basis of any good scientific experiment should always involve explosions of some kind; thus, his experiment involved detonating gunpowder.
Beeckman placed mirrors at various distances from the explosion and asked observers whether they could see any difference in when the flash of light reflected from each mirror reached their eyes. As you can probably
A similar more famous experiment that didn't involve explosions was possibly conducted or at the very least proposed by Galileo Galilei just under a decade later in 1638. Galileo, like Beeckman also suspected that the speed of light wasn't infinite and made passing references to an experiment involving lanterns in some of his work. His experiment (if he ever conducted it at all), involved placing two lanterns a mile apart and trying to see if there was any noticeable lag between the two; the results were inconclusive. The only thing Galileo could surmise was that if light wasn't infinite, it was fast and that experiments on such a small scale were destined to fail.
It wasn't until Danish Astronomer, Ole Romer entered
Specifically, while studying one of Jupiter's moons, Romer noticed that the time between eclipses would vary throughout the year (based on whether the Earth was moving towards Jupiter or away from it). Curious about this, Romer began taking
Unfortunately, the exact calculations he used were lost in the Copenhagen Fire of 1728, but we have a pretty good account of things from news stories covering his discovery and from other scientists around that time who used Romer's numbers in their own work. The gist of it was that using a bunch of clever calculations involving the diameter of the Earth's and Jupiter's orbits, Romer was able to conclude that it took around 22 minutes for light to cross the diameter of Earth's orbit around the Sun. Christiaan Huygens later converted this to more commonplace numbers, showing that by Romer's estimation, light traveled at about 220,000 kilometres per second. This figure is a little off (about 27% off) from the figure noted in the first paragraph, but we'll get to that in a moment.
When Romer's colleagues almost universally expressed doubt in his
Romer's colleagues were right to be astounded in his estimation, as even today, his estimation of the speed of light is considered to be amazingly accurate, considering it was made 300 years before the existence of both lasers, the internet, and Conan O'Brien's hair. Okay so it was 80,000 kilometres per second too slow, but given the state of science and technology at the time, that is remarkably impressive, particularly given he was primarily just working off a hunch to begin with.
What's even more amazing is that the reason for Romer's estimation being a little too slow is thought to have less to do with any mistake on his part and more to do with the fact that the commonly accepted diameter of the Earth's and Jupiter's orbits were off when Romer did his calculations. Meaning
So even though he was technically wrong and even though
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- The energy required to stop the Earth orbiting the sun is about 2.6478 x 1033 joules or 7.3551 x 1029 watt hours or 6.3285*1017 megatons of TNT. For reference, the largest nuclear explosion ever detonated (the Tsar Bomba by the Soviet Union) "only" produced 50 megatons of
TNTworth of energy. So it would take about 12,657,000,000,000,000 of those nuclear bombs detonated at the correct location to stop the Earth from orbiting the sun.
- Aside from the debate over whether the speed of light was infinite or not, a common side debate throughout history was whether or not light originated in the eye itself or from something else. Among the famous scientists to believe in the "light emitted from the eye" theory were Ptolemy and Euclid. Most who thought this theory correct also thought the speed of light must be infinite, because the instant we open our eyes, we can see a vast number of stars in the night sky and that number does not increase the longer we look, unless of course we were previously looking at a bright light and our eyes are adjusting to darkness.
This post has been republished with permission from TodayIFoundOut.com .