在物理學最令人驚訝的事實就是：
Quantum physics
宇宙中的一切，從光到電子、原子，
其行為同時具備粒子及波動的特性，
所有其他怪異的東西， 你可能在量子物理中聽過，
「薛丁格的貓」、「上帝玩骰子」 及「鬼魅般的交互作用」
這一切皆因
萬物同時具備粒子及波動的特性而來。
這聽起來似乎很瘋狂，
如果環顧四周，你看到 海浪與岩石上的顆粒，
兩者之間沒有一絲相似之處，
那麼，為什麼會把它們混為一談？
物理學家並不是隨隨便便 就將這些東西混在一起看，
相反的，通過簡單的步驟，
它們被推導到宇宙的雙重性。
配合上大量的證據，就像一個拼圖。
第一個認真看待雙重性的人
Albert Einstein
是1905年的愛因斯坦，
但他的理論源於 馬克斯•普朗克早期的想法。
普朗克嘗試解釋高溫物體發出的色光，
像是燈泡的燈絲，
但要做到這一點，他運用 一招看似無望的絕招：
他說物體是由振盪的粒子組成，
振盪的粒子只會發出特定顏色的光，
能量的大小由光的頻率決定。
普朗克從來沒有對這點高興過， 但愛因斯坦將它拿來運用並發揚光大。
他運用普朗克的想法，認為光本身，
這大家都知道是一個波，其實是光子流，
愛因斯坦宣稱每個光子 都有一個單獨的能量。
愛因斯坦本人宣稱這是他 唯一真正做到的科學革命，
但它可解釋可光照射金屬表面 產生電子的現象(光電效應)。
即使憎恨這種想法的人 都不得不承認，它真的很管用。
Rutherford
接下來的拼圖來自英國的拉塞福。
1909年，歐內斯特•馬士登 與漢斯•蓋革為拉塞福工作，
他們對金原子發射α粒子，
並震驚地發現， 一些α粒子會反彈向後飛。
這顯示，原子的質量集中 在一個很小的核中。
Rutherfords atom
在小學你看到原子卡通影片，
原子的電子軌道就像一個微型的太陽系，
這是拉塞福的原子模型。
古典物理學告訴我們，
繞圈運動的電子必定發出光(電磁波)，
當我們發出無線電波和X射線時， 一直運用到此現象。
所以拉塞福的原子會短暫射出X射線，
在電子以螺線前進至 原子核之前就會崩潰。
Bohr model
不過，丹麥理論物理學家 尼爾斯•玻爾拉塞福與合作，
他指出，原子明明就存在沒有崩潰，
所以也許是物理學規則需要修改。
玻爾提出理論指出電子 位於某些特殊的軌道，
所以能不發出任何光線。
只有當電子改變軌道時， 才會吸收和發射光，
而光的頻率則取決於軌道的能量差。
就這樣，普朗克和愛因斯坦起的頭，
玻爾的原子說修正了拉塞福的問題，
並解釋了為什麼原子 只會發出特定顏色的光。
每一個元素都有其特殊的軌道，
因而其自身獨特的一組頻率。
玻爾原子模型有一個小小的問題：
無法解釋特殊軌道的形成機制。
De Bruit
為這一切都帶來完美的解答。
他指出如果光，這大家都知道是一種波，
行為像粒子，
比如說電子，這大家都知道是一個粒子，
行為也像波一般。
如果電子也具有波動性，
就很容易解釋玻爾特殊軌道的規則了。
一旦你想像電子的行為像波動，
你就可以去尋找它的波動性。
都觀察到電子的波動性。
Wave behavior
至今我們已可以非常清楚的演示這一現象：
在拍攝個別電子通過狹縫的情形，
每個被檢測到的電子都是 在特定時間出現在特定位置，
這像是粒子的行為。
但是，當你多次重複實驗，
所有的電子會形成干涉條紋，
這是波動的行為特徵。
電子的行為像波又像粒子，
這是物理學中最奇特且最強大的一點。
理查•費曼說過一句名言：
這說明了量子力學中最神秘的核心。
萬物皆遵循此一特點，
於是最後一塊拼圖就定位。
particle and wave -- TED_ed Chad Orzel
One of the most amazing facts in physics is this: Quantum physics everything in the universe, from light to electrons to atoms, behaves like both a particle and a wave at the same time. All of the other weird stuff you might have heard about quantum physics, Schrodinger's Cat, God playing dice, spooky action at a distance, all of it follows directly from the fact that everything has both particle and wave nature. This might sound crazy. If you look around, you'll see waves in water and particles of rock, and they're nothing alike. So why would you think to combine them? Physicists didn't just decide to mash these things together out of no where. Rather, they were led to the dual nature of the universe through a process of small steps, fitting together lots of bits of evidence, like pieces in a puzzle. The first person to seriously suggest the dual nature of light Albert Einstein was Albert Einstein in 1905, but he was picking up an earlier idea from Max Planck. Planck explained the colors of light emitted by hot objects, like the filament in a light bulb, but to do it, he needed a desperate trick: he said the object was made up of oscillators that could only emit light in discrete chunks, units of energy that depend on the frequency of the light. Planck was never really happy with this, but Einstein picked it up and ran with it. He applied Planck's idea to light itself, saying that light, which everybody knew was a wave, is really a stream of photons, each with a discrete amount of energy. Einstein himself called this the only truly revolutionary thing he did, but it explains the way light shining on a metal surface knocks loose electrons. Even people who hated the idea had to agree that it works brilliantly. Rutherford The next puzzle piece came from Ernest Rutherford in England. In 1909, Ernest Marsden and Hans Geiger, working for Rutherford, shot alpha particles at gold atoms and were stunned to find that some bounced straight backwards. This showed that most of the mass of the atom is concentrated in a tiny nucleus. Rutherfords atom The cartoon atom you learn in grade school, with electrons orbiting like a miniature solar system, that's Rutherford's. There's one little problem with Rutherford's atom: it can't work. Classical physics tells us that an electron whipping around in a circle emits light, and we use this all the time to generate radio waves and X-rays. Rutherford's atoms should spray X-rays in all directions for a brief instant before the electron spirals in to crash into the nucleus. Bohr model But Niels Bohr, a Danish theoretical physicist working with Rutherford, pointed out that atoms obviously exist, so maybe the rules of physics needed to change. Bohr proposed that an electron in certain special orbits doesn't emit any light at all. Atoms absorb and emit light only when electrons change orbits, and the frequency of the light depends on the energy difference in just the way Planck and Einstein introduced. Bohr's atom fixes Rutherford's problem and explains why atoms emit only very specific colors of light. Each element has its own special orbits, and thus its own unique set of frequencies. The Bohr model has one tiny problem: there's no reason for those orbits to be special. De Bruit But Louis de Broglie, a French PhD student, brought everything full circle. He pointed out that if light, which everyone knew is a wave, behaves like a particle, maybe the electron, which everyone knew is a particle, behaves like a wave. And if electrons are waves, it's easy to explain Bohr's rule for picking out the special orbits. Once you have the idea that electrons behave like waves, you can go look for it. And within a few years, scientists in the US and UK had observed wave behavior from electrons. Wave behavior These days we have a wonderfully clear demonstration of this: shooting single electrons at a barrier with slits cut in it. Each electron is detected at a specific place at a specific time, like a particle. But when you repeat the experiment many times, all the individual electrons trace out a pattern of stripes, characteristic of wave behavior. The idea that particles behave like waves, and vice versa, is one of the strangest and most powerful in physics. Richard Feynman famously said that this illustrates the central mystery of quantum mechanics. Everything else follows from this, like pieces of a puzzle falling into place.
授課教師
陳永忠 [email protected]