生活不能没有阳光的滋润，否则，一切美好的事物都将黯然失色。白天，阳光透过淡薄的云层，照耀着苍茫大地，给生命带来希望，给人们带来温暖。沐浴着阳光，我们在成长。 可是，每当夜幕降临，阳光似乎和我们玩起了捉迷藏，独留寒冷夜色静静的陪伴着我们。因此，光是让万物生长，花儿绽放的源泉；是 让积雪融化，候鸟归家的动力；是让希望重燃，温暖心灵的良药。
参考阅读：Thomas Young’s double-slit experiment (杨氏双孔干涉实验)
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I’ve got a question for you. What is light? If you're standing out on the field you're surrounded by light. What are you surrounded by? You can feel it hitting your skin. You can feel the sun as it moves through the day and you know at night it's going to be dark you won't be able to see as well. But what's the sun doing? Is it creatingwaves 波浪? Is it shootingparticles 粒子? What's happening? This is an important question and in the mid-1800s physicists didn't really know but they knew a couple of things about it. They knew that light had afinite 有限的speed and they knew that light had aconstant 恒定的speed. That meant that as it was traveling it stayed the same speed and that its speed was ameasurable 可测量的number. It didn't just travelinstantaneously 瞬间地. This was a good firstclue线索. But if we're trying tofigure out 弄明白what it actually is this doesn't really answer everything. Let's think about this. If it's a wave let's think about other waves that we know.
Let's talk first about water because we know water has waves. We’ve seen it. We can kind ofvisualize 想象it and we know that if we see water passing a small opening like this when it hits thatbarrier 障碍 and it goes to the opening then it will kind of curve around it it'lldiffract 衍射. And then you get it traveling in all of these directions all at once. Okay that's pretty good. Let’s just kind of do a little quickthought experiment 思想实验. If we add a second opening here what happens? Well you're gonna get the same effect and you'll get theselayers 层forming or this curving around thebarrier 障碍. But at each of theseintersection points 交叉点 you're gonna haveinterference 干涉. Now sometimes it will be constructive sometimes it'll be destructive but if you measure it at a point further along what you'll see if you measure the height of the water is you'll get thisinterference pattern干涉图样forming were actually the highest peak would be at the center of the twoslits 狭缝. But this is a really good demonstration of waveproperties 性质. So why not try it with light? Why not use this as a test to see if light behaves as a particle or as a Wave? Because surely if it was a particle what would happen is it would pass through these and you just get collections of the light at two points. You wouldn't get aninterference pattern 干涉图样forming it’ll be simple. It’ll be as though you were shooting balls through these little openings. So physicists did this experiment. They tried it out. What did they see? So they sent a plain wave along like this and what happened was on aprojection screen 投影屏幕on the other side they actually saw the interference pattern. They saw the same thing that they would have seen with water but after using light. So that seems prettydefinitive 决定性的. Light behaves as a wave! Okay! problem solved right? Not quite!
You know a water wave is just waving through the water. You know that sound waves are just waving through the air. What's a light waving through? What is themedium 介质that's carrying the light? Let'srecall 回忆a couple of things that we said a while back. We said that light has afinite 有限的speed and that it has aconstant 恒定的speed. So that means that as light is traveling through space it travels at one speed and we know that earth moves around the Sun. So what if we could take onebeam of light 光束 andsplit 劈开it into two and send them on differenttrajectories 轨道? So we send them one along with atrajectory 轨道that follows the motion of the earth and one that’sperpendicular 垂直的to the motion of the earth so that it would beunaffected不受影响的by the Earth's motion. It wouldn't see any change in its path length as the earth moves along. Well if there was amedium介质that the light was waving through then you would have a change in the path length that the light sees. This would result in interference when yourecombine 重组the beams. So they tried this and this experiment showed nothing. It showed nointerference干涉when theyrecombined 重组thebeams 光束. That meant that the light wasn't being caught up in this in thisother以太 (曾被假想成为光的传播介质)that they called it. What does that mean? Does that mean that light can't be a wave if it's not waving through anything? Does that mean that light is a particle that just travels along with the samemomentum动量as the Earth?
I'll leave you with one final thought. Maybe you've seen it in a movie. They use a device called aGeiger counter 盖革计数器 (一种探测X射线强度的计数仪器). What aGeiger counter盖革计数器is is that it counts x-rays. X-rays are kind of like a high-energy light and so you know that when you shine an x-ray on aGeiger counter 盖革计数器 it's gonna click and it'll click for each x-ray that it counts. But this is an interestingconcept 概念. TheGeiger counter盖革计数器is clicking once for a wave. If it was clicking once for a wave how would that be? That means you're taking an entire wave front andcollapsing瓦解it down to just onedetection探测? Well that’s kind ofcurious奇怪的. So maybe then the light is actually a particle? Maybe it's both of these things? And that was the bigrevelation被揭露的真相that light wasn't just a wave or a particle. We said it was both. It was both at the same time and itexhibited 展示bothproperties 性质. And this was very important in understanding and developingquantum mechanics 量子力学. Well we’ll talk more about that next time!
1.Which experiment showed that light behaves as a Wave? Briefly describe this experiment.
2.What did the example of a Geiger counter demonstrate?
3.What medium does light travel on?
4.In conclusion is light a wave or a particle?
a beam of light 光束
figure out 弄明白
projection screen 投影屏幕
thought experiment 思想实验
ether 以太 (曾被假想成为光的传播介质)
Geiger counter盖革计数器 (一种探测X射线强度的计数仪器)
intersection points 交叉点
quantum mechanics 量子力学
It was a big revelation that light wasn't just a wave or a particle. It was both at the same time.
It was a big revelation∧thatlightwasn'tjust a wave∧or a particle.〡It wasboth∧at thesametime.
连读：was a just a
失去爆破：it was big revelation that light light wasn’t wasn’t just at the