How light works

Light is at once both obvious and mysterious. We are bathed in yellow warmth every day and stave off the darkness with incandescent and fluorescent bulbs. But what exactly is light? We catch glimpses of its nature when a sunbeam angles through a dust-filled room, when a rainbow appears after a storm or when a drinking straw in a glass of water looks disjointed. These glimpses, however, only lead to more questions. Does light travel as a wave, a ray or a stream of particles? Is it a single color or many colors mixed together? Does it have a frequency like sound? And what are some of the common properties of light, such as absorption, reflection, refraction and diffraction?

You might think scientists know all the answers, but light continues to surprise them. Here's an example: We've always taken for granted that light travels fasterthan anything in the universe. Then, in 1999, researchers at Harvard University were able to slow a beam of light down to 38 miles an hour (61 kilometers per hour) by passing it through a state of matter known as a Bose-Einstein condensate. That's almost 18 million times slower than normal! No one would have thought such a feat possible just a few years ago, yet this is the capricious way of light. Just when you think you have it figured out, it defies your efforts and seems to change its nature.

Still, we've come a long way in our understanding. Some of the brightest minds in the history of science have focused their powerful intellects on the subject. Albert Einstein tried to imagine what it would be like to ride on a beam of light. "What if one were to run after a ray of light?" he asked. "What if one were riding on the beam? … If one were to run fast enough, would it no longer move at all?"

Einstein, though, is getting ahead of the story. To appreciate how light works, we have to put it in its proper historical context. Our first stop is the ancient world, where some of the earliest scientists and philosophers pondered the true nature of this mysterious substance that stimulates sight and makes things visible.

光是一次明顯和神秘。我們沐浴在黃色溫暖每一天，並且避開黑暗與白熾燈和螢光燈燈泡。到底是什麼光？當陽光角度通過充滿灰塵的房間，當彩虹出現在一場暴風雨之後或在一杯水中的飲用吸管看起來相互脫節，我們抓到瞥見它的性質。然而，這些瞥見，只能導致更多的問題。光能波、 射線或粒子流作為旅行嗎？它是一種單一顏色或多種顏色混合在一起嗎？它有一個像聲音的頻率嗎？和的光，如吸收、 反射、 折射和衍射的共同屬性是什麼嗎？

您可能認為科學家們知道所有的答案，但光繼續給他們個驚喜。下面是一個例子： 我們一直在為理所當然光傳播老子有什麼在宇宙中。然後，在 1999 年，哈佛大學的研究人員們能夠通過傳遞它通過物質稱為玻色-愛因斯坦凝聚狀態慢一束光到 38 英里 （每小時 61 公里） 一小時。這是比正常慢近 18 萬倍!沒有人會想到這種壯舉可能只是幾年前，然而這是反復無常光明之路。只是當你認為你沒有想明白，它違背你的努力，似乎改變它的性質。

儘管如此，我們在我們的理解來很長的路。一些科學的歷史中最聰明的人有其強大的智力重點主題。阿爾伯特 · 愛因斯坦試圖想像會騎著一束光。"如果一個是運行後一束光嗎?"他問。"如果一個騎橫樑上嗎？…如果有人以足夠快的速度運行，將它不再移動在所有嗎?"

不過，在愛因斯坦，超越這個故事。我們要明白如何光亮工程，把它放在其適當的歷史背景。我們第一站就是物質的古代的世界，其中的一些最早的科學家和哲學家沉思這神秘，刺激的視線，使事情可見的真正性質。

What Is Light?

Over the centuries, our view of light has changed dramatically. The first real theories about light came from the ancient Greeks. Many of these theories sought to describe light as a ray -- a straight line moving from one point to another. Pythagoras, best known for the theorem of the right-angled triangle, proposed that vision resulted from light rays emerging from a person's eye and striking an object. Epicurus argued the opposite: Objects produce light rays, which then travel to the eye. Other Greek philosophers -- most notably Euclid and Ptolemy -- used ray diagrams quite successfully to show how light bounces off a smooth surface or bends as it passes from one transparent medium to another.

Arab scholars took these ideas and honed them even further, developing what is now known asgeometrical optics -- applying geometrical methods to the optics of lenses, mirrors and prisms. The most famous practitioner of geometrical optics was Ibn al-Haytham, who lived in present-day Iraq between A.D. 965 and 1039. Ibn al-Haytham identified the optical components of the human eye and correctly described vision as a process involving light rays bouncing from an object to a person's eye. The Arab scientist also invented the pinhole camera, discovered the laws of refraction and studied a number of light-based phenomena, such as rainbows and eclipses.

By the 17th century, some prominent European scientists began to think differently about light. One key figure was the Dutch mathematician-astronomer Christiaan Huygens. In 1690, Huygens published his "Treatise on Light," in which he described the undulatory theory. In this theory, he speculated on the existence of some invisible medium -- an ether -- filling all empty space between objects. He further speculated that light forms when a luminous body causes a series of waves or vibrations in this ether. Those waves then advance forward until they encounter an object. If that object is an eye, the waves stimulate vision.

This stood as one of the earliest, and most eloquent, wave theories of light. Not everyone embraced it. Isaac Newton was one of those people. In 1704, Newton proposed a different take -- one describing light as corpuscles, or particles. After all, light travels in straight lines and bounces off a mirror much like a ball bouncing off a wall. No one had actually seen particles of light, but even now, it's easy to explain why that might be. The particles could be too small, or moving too fast, to be seen, or perhaps our eyes see right through them.

光是什麼？

幾百年來，我們對光的看法發生了巨大的變化。關於光的第一次真正理論來自古希臘人。許多這些理論尋求光形容雷 — — 從一個地方移動到另一條直線。畢，最出名的是定理的直角三角形，提議視覺造成的光線擺脫一個人的眼睛和引人注目的物件。伊壁鳩魯持相反的觀點： 物體產生光線，然後旅行到眼睛。其他希臘哲學家 — — 最明顯的是歐幾裡得和托勒密 — — 用於雷圖相當成功地顯示如何輕彈回光滑的表面或彎曲，它從一個透明介質傳遞到另一個。

阿拉伯學者接受了這些想法和磨練他們更進一步，發展中國家現在稱為幾何光學 — — 將幾何方法應用到的光學鏡片、 鏡像和棱鏡。幾何光學最著名醫生是伊本 · 阿爾海森在當今伊拉克之間西元 965 和 1039年生活。· 伊本 · 阿爾-海森確定人眼的光學元件，並正確描述視覺作為一個過程，涉及彈跳從一個物件到一個人的眼睛的光線。阿拉伯科學家也發明了針孔攝像頭、 發現折射規律和研究了多種基於光的現象，如彩虹、 日食及月食。

到 17 世紀，一些著名的歐洲科學家開始以不同的方式思考光。荷蘭的數學家天文學家惠更斯克利斯蒂安是一個關鍵人物。在 1690 年，惠更斯出版他"論文上輕"，他所描述的波動理論。在這一理論，他推測的一些無形的介質 — — 醚 — — 填充所有空的空間物件之間存在性。他進一步推測那光形式時發光體在這醚導致一系列的波或振動。這些波然後向前推進，直到他們遇到一個物件。如果該物件是眼睛，海浪刺激視覺。

此站為一體的最早和最有口才，波浪理論的光。不是每個人都擁抱它。以撒 · 牛頓是那些人之一。在 1704 年牛頓建議不同 — — 一個描述光作為白血球、 或顆粒。畢竟，光直線傳播的和很像皮球從牆上反彈反彈一面鏡子。沒有人見過粒子的光，但即使是現在，很容易解釋為什麼會這樣。微粒可能太小，或移動太快，將被看見，或也許我們的眼睛看得透。