百科知識視頻之煎蛋小學(xué)堂49 物理中常見的混淆概念[v]

Imagine learning for the first eighteen years of your life that the earth is flat,All through elementary school and high school you grow up,Hearing about the flat earth we live on,And doing boring flat-earth physics homework and then,If you're lucky enough you get to college and PSYCH!For the first time they show you a globe and say,"sorry for lying,the earth is actually round"Well this is unfortunately exactly what we do with。

想象一下你人生的頭18年里一直學(xué)到的都是地球是平的 從幼稚的小學(xué)生一直成長到高中生 聽到的都是我們生活的地球是平的 蛋疼的糾結(jié)著關(guān)于平面地球的物理作業(yè) 然后有一天你幸運的上了大學(xué) 我擦!他們第一次給你拿出了個地球儀 然后說 “很抱歉騙了你 但地球其實是圓的” 這是個殘酷的真相 我們對引力的學(xué)習(xí)也是這樣

1.Gravity：

一、引力

You probably learned that objects attract each other based on their mass,So you probably grew up thinking that light can't possibly be affected by gravity,Because light is massless,I know I did,Well guess what?The source of gravity is not mass!It's energy and momentum which light certainly has,Of course regular matter does too,So not only does light get bent passing by a star or planet or black hole.But light attracts the planet or star or black hole in return.To be sure,it's only a very very small amount,But a small amount is not zero,Anyway the point is that Newton's law of gravitation is just an approximation,Good enough to get us to the moon,but not perfect,General relativity is better.

或許你學(xué)過物體是因為質(zhì)量而相互吸引的 所有長大后你就會納悶光應(yīng)該是不會被吸引的吧 應(yīng)為光沒有質(zhì)量啊 我就是這么想的 可你猜這么著?引力的來源不是質(zhì)量!是能量和動量 顯然光也有這些 別的物質(zhì)就更有了 所以不僅光在經(jīng)過恒星，行星還是黑洞時會被彎曲 光反過來同樣還會吸引行星，恒星還有黑洞 準確的說 這種吸引雖然很小很小 但小并不代表沒有 所有重點就是 牛頓萬有引力只是一個近似的法則 這足夠人們登月用的 但并不是完美法則 廣義相對論才更準確一些

2.Special Relativity：

二、狹義相對論

Speaking of the moon,you probably also learned that:If a sheep is moving 2 mph relative to a train,And that train is moving 2 mph in the same direction relative to the ground,Then the sheep is moving 4 mph relative to the gound,2mph plus 2mph equals 4mph,right? FALSE!Experments in special relativity have confirmed,That velocities don't simply add together,And so the sheep will in fact be moving Very very ever-so-slightly slower.than 4mph relative to the ground.

說起月球君 或許你會記起這道題：如果一只小羊相對火車的速度是2英里/時 而火車相對于地面也是2英里/時同向運動 則小羊相對于地面的速度就是4英里/時 2英里/時 +2英里/時 =4英里/時 ，對吧?錯了!關(guān)于狹義相對論的實驗已經(jīng)證明 計算速度不能簡單地直接相加 所有這只小羊相對于地面的速度實際上要比4英里/時 稍微小那么一點點點

And the formula that correctly predicts this deviation from just adding,the velocities is (V1+V2)/(1+V1×V2/C^2),It's not a very big effect,But then again,the earth looks pretty flat,doesn't it? But the earth isn't flat.If I walk 10,000 km away from my cat,And you continue on walking 10,000 km more,You're NOT 20,000 km away from my cat,You're just 12,750 km away.

而消除這種誤差的準確疊加速度的 公式是(V1+V2)/(1+V1×V2/C^2) 雖然影響不大 但話說回來 地球看起來也和平面差不多是吧?但地球卻不是平的 如果我遠離喵星人走了10000千米 然后你繼續(xù)又走了10000千米 你和我家喵星人的距離可不是20000千米呢 你們的距離只有12750千米

In fact:The farthest on earth you can get from ANYTHING on earth is 12,750 km,It's the "earthly distance-limit"Though we normally call it the diameter of the earth,And similarly when you try to add two velocities together,There's a "cosmic speed limit"of 300,000,000 m/s.That is the speed of light.

真相是 你能跑過地球上最遠的一段距離不過12750千米 這是地球君的距離限制 也就是我們常說的地球的直徑 同樣的當(dāng)你想要疊加兩個速度的時候 有一個30億米/秒的“宇宙速度極限” 這就是光速

So just because to our eyes the earth looks flat,Velocities look like they simply add together,And light looks like it doesn't attract gravitationally,Is that an excuse to mislead ourselves and our children,About the true nature of things? NO

所以我們能夠因為地球看上去是平的 或者速度看似能簡單地相加 又或是光線看起來沒有萬有引力 就可以找理由誤導(dǎo)我們自己和祖國的花朵 不告訴他們自然的真相嗎?不。