Placeholder Image

字幕表 動画を再生する

  • {♫Intro♫}

  • In 1956, a team of scientists was working

  • on an experiment that, at first glance, seemed

  • kind of trivial.

  • They had lined up a bunch of cobalt atoms

  • and were patiently waiting to see which direction

  • they would spit out some electrons.

  • According to the knowledge of the time,

  • theelectrons should have come out

  • in random directions

  • but that's not what happened.

  • Instead, the electrons tended to favor

  • a specific direction.

  • And to me, and probably you,

  • this doesn't seem like that big of a deal.

  • But the implications

  • of this tiny, quiet experiment were groundbreaking.

  • Because these results weren't just about

  • some specific atoms:

  • They challenged one of our fundamental beliefs

  • about the entire universe

  • and ultimately opened the door to some of

  • the biggest mysteries in physics.

  • Here's why this little experiment turned out

  • to be such a big deal.

  • The reason these results threw physicists for a loop

  • is because they violate something called

  • parity symmetry.

  • At its heart, parity symmetry says

  • that the laws of physics shouldn't differentiate

  • between left and right, or up and down,

  • or backward and forward.

  • Because, really, those directions just depend on your perspective.

  • Take gravity, for example.

  • Normally, you might say gravity pulls things down. But of course, we only call it down

  • because that's where gravity is pulling things.

  • But if you change your perspective and stand on your head, that doesn't mean gravity

  • is going to start pulling everythingdowntoward your feet and toward the sky.

  • It's going to keep pulling stuff toward the Earth, no matter what direction you say

  • that is.

  • And if that sounds obviouswell, yeah.

  • For decades, parity symmetry was this reasonable, inarguable thing, one that physicists had

  • used countless times to predictcorrectly! — the results of experiments.

  • It felt like common sense, and was a major assumption we relied on when figuring out

  • how stuff should work.

  • But by the 1950s, some researchers had begun to realize that maybe we shouldn't always

  • be making this assumption.

  • In particular,

  • two researchers pointed out that parity symmetry had been tested, but not in all circumstances.

  • Like, it had never been tested in certain particles decays.

  • So three teams of researchers decided to tackle this questionand one of them was responsible

  • for that now-famous cobalt experiment.

  • This group was headed by a researcher named Chien-Shiung Wu, and they studied a type of

  • radioactive cobalt called cobalt-60.

  • When the cobalt decayed, it spat out electrons. And if parity symmetry were true, those electrons

  • should have come out about equally in all directions.

  • It should have happened like this mainly because these atoms are basically sitting still, and

  • you can more or less ignore gravity when it comes to particle physics.

  • So it's not like there's some force on this cobalt that would cause it to decay in

  • a specific direction.

  • Instead, if you did happen to see more electrons coming out a certain way, it would mean you

  • had a problem on your hands.

  • If, say, more electrons came out the tops of the cobalt atoms rather than the bottoms,

  • it would mean that electronsfor some reasonhad an easier time moving up than

  • down.

  • And according to parity symmetry, there shouldn't be any difference between those directions.

  • After all, what's up from one perspective is down from another.

  • To test if all of this were true, Wu's team used a magnetic field to line up all their

  • cobalt in the same way. Then, they set up equipment to figure out how many electrons

  • came out, and in which directions.

  • And their results were a bit of a shock.

  • Instead of seeing the particles come out in random directions, they found that the electrons

  • tended to come flying out in the opposite direction of the atom's spin.

  • So if you swapped left and right in this experimentin other words, if you gave the atoms

  • clockwise spin instead of counter-clockwise, you would get a different result: You would

  • see the electrons fly out in a different direction.

  • And that's not supposed to happen!

  • These results suggested that there is some kind of fundamental difference between left

  • and right. The universe somehow has a sense of direction.

  • So, yeah, something was very wrong with parity symmetry: It didn't exist!

  • Wu's team published their findings in January 1957, as did two other teams that had done

  • similar research on other particles.

  • But just because we had made this discovery didn't mean we were out of the woods.

  • We might have figured one thing out, but a gigantic can of physics-worms had also been

  • opened.

  • For one thing, researchers had to grapple with the fact that directions might not be

  • as arbitrary as they once thought. Because apparently, there's an innate left and right

  • to the universe

  • which is absolutely bizarre.

  • But they also had to figure out why this happened. What was so special about cobalt that made

  • it act this way?

  • Well, as research went on, it turned out that the cobalt wasn't necessarily the problem.

  • It was something called the weak nuclear force, which is the force that governs how atoms

  • including cobaltdecay.

  • For some reason,

  • the weak force tends to act differently than the other fundamental forces of physics.

  • And figuring out why is one of the most ambitious projects in the field right now.

  • Because the weak force doesn't just treat left and right differently. It also treats

  • matter differently than antimatter, which we believe shouldn't happen.

  • And it even treats time differently than all the other forceswhich is exactly as bizarre

  • as it sounds.

  • Scientists believe that if we figure one one more weird thing about the weak force, it

  • could potentially break our understanding of physics.

  • But then againit could also help us understand why the universe looks like it does.

  • So a tiny experiment from 1956 didn't just affect how we saw a handful of atoms.

  • It taught us that one of the four fundamental forces of physics is more strange then we

  • could have ever imagined. And it set us on a path to understanding the laws of the universe

  • — a path we're still walking down today.

  • But that's a much bigger story.

  • And if you want to learn more,

  • we have whole other video

  • on it!

  • But as always, thanks for watching

  • this episode of SciShow.

  • {♫Outro♫}

{♫Intro♫}

字幕と単語

動画の操作 ここで「動画」の調整と「字幕」の表示を設定することができます

B1 中級

物理学を変えた小さな実験 (The Tiny Experiment That Transformed Physics)

  • 1 0
    林宜悉 に公開 2021 年 01 月 14 日
動画の中の単語