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  • [♩INTRO]

  • It's usually not a great idea to break laws.

  • But breaking the laws of science is an exception

  • in fact, it's often how we make progress.

  • See, scientific laws are just formulas that do a good job

  • of describing how the stuff in the world interacts.

  • Like, there are laws to describe how objects with mass attract,

  • or how objects with the same charge repel.

  • And we call them laws because everything we observe seems to obey them.

  • But even after laws are in place,

  • scientists keep looking for conditions that break them.

  • Because when laws break down,

  • they almost always tell us something completely new about reality.

  • In fact, there's one law scientists have been testing for over 200 years,

  • even though it has never failed a test:

  • Coulomb's law for the force between two charged particles.

  • Because if it ever breaks, it could have an enormous impact on what we believe

  • to be true about our universe

  • including concepts as fundamental as the speed of light.

  • Coulomb's law was invented by the French physicist

  • Charles-Augustin de Coulomb in 1785.

  • And it describes the way force is related to

  • the distance between two electrically-charged particles.

  • It says that, as you increase the distance between two charged particles,

  • the force between them drops off in a way that's proportional to that distance,

  • or radius, squared.

  • Which basically means that as the particles move farther apart,

  • the force between them gets smaller fast.

  • Generations of physicists have used and tested this formula,

  • and it's never failed them.

  • But history gives us a pretty good reason to keep testing the laws of physics,

  • even the ones that have held up as long as this one.

  • See, Coulomb's law looks a lot like another familiar law

  • one you've probably seen if you've taken high school physics:

  • Newton's law of gravity.

  • Like a lot of formulas in physics, they both have that radius-squared in the bottom

  • of their fractions, and they both describe how forces drop off with distance.

  • And they do a really good job. Most of the time.

  • But back in the mid-1800s, astronomers discovered that the planet Mercury's

  • orbit didn't quite follow Newton's law.

  • Over time, the point where the planet passed closest to the Sun was happening

  • at slightly different points in the orbit.

  • For a while, no one knew what to make of that.

  • Some astronomers even suggested that there was a hidden planet

  • tugging Mercury around.

  • Another astronomer, named Simon Newcomb, attempted to fix Newton's law

  • by tweaking that r-squared exponent.

  • Instead of two, he suggested that it could be 2.0000001612.

  • But even he knew that was just a Band-Aid.

  • Because, sure, it helped solve the problem with Mercury,

  • but it didn't address why Newton's law broke down.

  • Then, in 1915, Albert Einstein came up with his theory of general relativity,

  • which fundamentally changed how we look at our universe.

  • With general relativity, Einstein introduced the idea that mass warps spacetime.

  • And Newton's law doesn't quite cut it when you're near a very massive object

  • that's warping the spacetime around it.

  • For example: the Sun.

  • Newton's law broke down because he didn't have the full picture

  • of how mass affects spacetime.

  • And that's a good reminder that things we call laws work

  • only under the right conditions.

  • So when we find the conditions that break the law,

  • we can learn some really radical things.

  • So, scientists have a decent reason to question Coulomb's law,

  • which is almost a mirror image of Newton's.

  • And they've put a ton of effort, across centuries, into testing it.

  • One way physicists do that is by measuring the precision

  • of that two in the exponent.

  • Like what happened with Mercury, one sign of a problem in Coulomb's law

  • would be if certain conditions required an exponent other than exactly two.

  • That could be a sign that the whole formula needs an overhaul.

  • For now, it seems to be exactly two, as close as we can tell,

  • but scientists have been testing it ever since Coulomb published his law in 1785.

  • In fact, Coulomb himself was already thinking about it.

  • He knew his measurements couldn't prove that the exponent was exactly two...

  • there was some uncertainty.

  • The exponent could be two plus or minus a smidge,

  • and he put that smidge at 0.04.

  • Over time, scientists designed better experiments with better equipment,

  • and our confidence in the value of that two improved.

  • In the 20th century, researchers shrank the smidge down to about one billionth.

  • Today, it's less than a quadrillionth.

  • That means we know that the exponent in Coulomb's law is two to nearly 20 digits.

  • So Coulomb's law has stood the test of time, so far.

  • But if it ever does break down,

  • it would mean our universe is wilder than even we realize.

  • For example, physicists have shown that if Coulomb's law breaks,

  • it would tell us that photons, or particles of light, have mass.

  • Photons are what carry the electromagnetic force,

  • which Coulomb's law describes.

  • And theorists have shown that the exponent can only be two

  • when the mass of a photon is exactly zero.

  • The inverse is also true: In a universe where that exponent is off by just a little,

  • photons have mass.

  • A really tiny mass, but mass nonetheless.

  • If that were the case, it would mean photons can't travel at the speed of light.

  • Because nothing with mass can reach the speed of light.

  • Meaninglight would not travel at the speed of light.

  • That would change what we understand about how

  • electricity, magnetism, and quantum mechanics are related

  • and it would likely take radically new ideas about reality to reconcile them.

  • Seriously, the universe becomes a bizarre place if Coulomb's law breaks down

  • if that little number 2 has anything other than a bunch of zeros after it.

  • And scientists have found a lot of zeros, but their job is to be skeptical,

  • and to test even the things they think are true.

  • Because when laws break down, they show us the seams in our understanding

  • of reality and force us to rethink the entire nature of our world.

  • Thanks for watching this episode of SciShow! If you enjoyed this video,

  • you might also like our episode about another law of physics

  • one that was made to be broken.

  • You can check it out right after this.

  • [♩OUTRO]

[♩INTRO]

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科學家為何一直試圖打破這個18世紀的定律? (Why Scientists Keep Trying to Break This 18th Century Law)

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    林宜悉 發佈於 2021 年 01 月 14 日
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