In the early 20th century, it was thought that the constant had a value of precisely 1/137. So why does it have the value it does? Remember, that value itself is important and might even have meaning, because it exists outside any unit system we have. Life as we know it would be outright impossible if the fine-structure constant had even a slightly different value. If the fine-structure constant had a different value, then atoms would have different sizes, chemistry would completely change and nuclear reactions would be altered. In time, we came to recognize it as the fundamental measure for the strength of how charged particles interact with electromagnetic radiation.Ĭhange that number, change the universe. It seemed to crop up anytime charged particles interacted with light. Sommerfeld originally didn't put much thought into the constant, but as our understanding of the quantum world grew, the fine-structure constant started appearing in more and more places. Once you nailed down how we express our numbers, you would then have to define things like meters and seconds.īut the fine structure constant? You could just spit it out, and they would understand it (as long as they count numbers the same way as we do). If you were to meet an alien from a distant star system, you'd have a pretty hard time communicating the value of the speed of light. You can have whatever unit system you want and whatever method of organizing the universe as you wish, and that number will be precisely the same. Your choice of units (meters per second, miles per hour or leagues per fortnight?) and the definitions of those units (exactly how long is a "meter" going to be?) matter if you change any of those, the value of the constant changes along with it.īut that's not true for the fine-structure constant. The actual value of the speed of light, for example, doesn't really matter, because that number depends on other numbers. ![]() The other constants in physics aren't like this. There are no dimensions or unit system that the value of the number depends on. And so on.īut there was something different in Sommerfeld's little constant: It didn't have units. ![]() The spring constant, k, tells us how stiff a particular spring is. The speed of light, c, tells us about the relationship between electric and magnetic fields. Isaac Newton's formula for universal gravitation had a constant, called G, that represents the fundamental strength of the gravitational interaction. ![]() After all, physics equations throughout history have involved random constants that express the strengths of various relationships. The introduction of a constant wasn't all that new or exciting at the time. Related: 10 mind-boggling things you should know about quantum physics ![]() He found that to develop the physics to explain the splitting of spectral lines, he had to introduce a new constant into his equations - a fine-structure constant. And one of the first people to take a crack at understanding this was physicist Arnold Sommerfeld. The full explanation for the "fine structure" of the spectral line rests in quantum field theory, a marriage of quantum mechanics and special relativity. Instead of just a single line, there were sometimes two very narrowly separated lines. When electrons change levels, they can emit or absorb radiation, but that radiation will have exactly the energy difference between those two levels, and nothing else - hence the specific wavelengths and the spectral lines.īut in the early 20th century, physicists began to notice that some spectral lines were split, or had a "fine structure" (and now you can see where I'm going with this). An electron orbiting around a nucleus in an atom can't have just any energy it's restricted to specific energy levels. Those wavelengths are so specific because of quantum mechanics. Atoms have a curious property: They can emit or absorb radiation of very specific wavelengths, called spectral lines.
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