The speed of light is one of the many universally-known facts that virtually everyone encounters at school and when taking physics tuition. But in the spirit of scientific inquiry, it’s appropriate to delve deeper into this cornerstone of physics and raise some rarely asked questions. For instance, why does it have the specific value of 299, 792, 458 m/s and not some other number? How did it become one of the most important pillars of physics? And why should we care about this arbitrary speed of electromagnetic waves?
Overall, the speed and nature of light is simply bizarre, and that’s what makes it worth looking into.
The Initial Discovery of the Speed of Light
To better understand the speed of light, it is best to explore the very beginnings of its discovery, which was during the late 1600s courtesy of an astronomer called Ole Romer. He was the first ever to realise that light had a speed at all while he was observing the strange motions of Io, one of the many moons of Jupiter. From time to time, the planet would block our view of this particular moon and cause an eclipse. However, the timing between these celestial events seemed to change throughout the year. As such, Romer thought either there was an unusual phenomenon affecting Io’s orbit or something else was causing such changes.
Only after several years of observation did Romer make the connection. Essentially, it is Earth’s position in its orbit that is causing these changes. Whenever we see Io get eclipsed, we’re always in a different position that is either closer or farther away from Jupiter. If it’s the latter case during our last observation of the eclipse, that means we’ll need to wait longer to see the next one since it takes longer for the light to reach us. Naturally, the reverse is true if it’s the former case.
In essence, light having a finite speed is the only way to explain why the timing of Io’s eclipses is never constant.
Laying the Foundation for Future Discoveries
Over the next few centuries, continued measurements helped solidify the speed of light, with everything finally starting to come together during the mid-1800s. This time, it was James Clerk Maxwell and his accidental invention of light that truly kicked things off.
At this point in time, the phenomena of magnetism and electricity were still poorly understood. Maxwell had been playing around with them when he stumbled upon a singular unified picture that he believed might explain the many disparate observations around the two concepts.
Simply put, he came up with equations which led to him discovering that changing magnetic fields can create electric fields and vice versa. This meant electric waves can create magnetic waves, which would also make more electric waves and so on, resulting in a back and forth process of leapfrogging over one another that had the ability to travel through space.
Maxwell then calculated the speed of these electromagnetic waves and arrived at the same number that countless scientists throughout the centuries had been measuring as the speed of light. This discovery led him to believe that light is composed of electromagnetic waves and moves at that speed since it’s exactly how electricity and magnetism traverse space.
How Einstein Tied Everything Together
Several decades later, Einstein made his own discovery which is that the speed of light was completely unrelated to light itself. His special theory of relativity led him to realise the true connection between space and time, which is what we now refer to as the unified fabric of space-time. But as we know, space and time are not the same, i.e. a foot or a metre are not on the same footing as a second or an hour.
There was a need for a connection or way to translate movement between the two ideas or an exchange rate between space and time. Einstein then came across the single constant which had a certain speed that made everything fall into place. His theories did not state the exact number, but upon applying his special relativity to Maxwell’s old equations, he discovered that the conversion rate was an exact match with the speed of light.
Apparently, Maxwell had already discovered this number without even knowing it since all massless particles–including light–can travel at such impossible speeds. From there, the speed of light attained its status in modern physics.
Wrapping Up
With all that said, the question remains as to why nature settled for that specific or value. The truth is that it’s not as important as the units attached to it. In the world of physics, any number with set units can have any value it wants since one must establish what the units are in the first place. For instance, expressing the speed of light in metres per second requires deciding on what a metre and a second represents. Therefore, the speed of light and its definition is tied to the meanings of length and time.
As you may already know, physics is more concerned with constants that lack dimensions or units as they are more fundamental and don’t rely on any definitions. An example of this is the fine structure constant whose value is 0.0007 and is essentially a combination of Planck’s constant, permittivity of free space, and the speed of light.
Conclusion
In essence, the speed of light can and cannot be whatever it wants to be. This is because it has units and it falls on us to define what they are, but at the same time it cannot be anything else lest the fine structure constant changes. The universe we live in has decided that this constant is approximately 0.007, nothing more, nothing else, and we have no choice in the matter. It is because of this fixed and universal nature that the speed of light can only be exactly what it is.
If you’re keen to learn more about the many established concepts in physics, Tuition Physics can guide you to the answers you seek. As one of the leading physics tuition centres in Singapore, we provide you with not just quality instruction and guidance but also a genuine love for the subject.
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