Is it possible to create something out of nothing? Or, more precisely, can energy be made into matter? Yes, but only when it comes together with its twin, antimatter. And there's something pretty mysterious about antimatter: there's way less of it out there than there should be. Let's start with the most famous physics formula ever: E equals m c squared. It basically says that mass is concentrated energy, and mass and energy are exchangeable, like two currencies with a huge exchange rate. 90 trillion Joules of energy are equivalent to 1 gram of mass. But how do I actually transform energy into matter? The magic word is <i>energy density</i>. If you concentrate a huge amount of energy in a tiny space, new particles will come into existence. If we look closer, we see that these particles always come in pairs, like twins. That's because particles always have a counterpart, an antiparticle, and these are always produced in exactly equal amounts: 50/50. This might sound like science fiction, but it's the daily life of particle accelerators. In the collisions between two protons at CERN's Large Hadron Collider, billions of particles and antiparticles are produced every second. Consider, for example, the electron. It has a very small mass and negative electric charge. It's antiparticle, the positron, has exactly the same mass, but a positive electric charge. But, apart from the opposite charges, both particles are identical and perfectly stable. And the same is true for their heavy cousins, the proton and the antiproton. Therefore, scientists are convinced that a world made of antimatter would look, feel, and smell just like our world. In this antiworld, we may find antiwater, antigold, and, for example, an antimarble. Now imagine that a marble and an antimarble are brought together. These two apparently solid objects would completely disappear into a big flash of energy, equivalent to an atomic bomb. Because combining matter and antimatter would create so much energy, science fiction is full of ideas about harnessing the energy stored in antimatter, for example, to fuel spaceships like Star Trek. After all, the energy content of antimatter is a billion times higher than conventional fuel. The energy of one gram of antimatter would be enough for driving a car 1,000 times around the Earth, or to bring the space shuttle into orbit. So why don't we use antimatter for energy production? Well, antimatter isn't just sitting around, ready for us to harvest. We have to make antimatter before we can combust antimatter, and it takes a billion times more energy to make antimatter than you get back. But, what if there was some antimatter in outer space and we could dig it out one day from an antiplanet somewhere. A few decades ago, many scientists believed that this could actually be possible. Today, observations have shown that there is no significant amount of antimatter anywhere in the visible universe, which is weird because, like we said before, there should be just as much antimatter as there is matter in the universe. Since antiparticles and particles should exist in equal numbers, this missing antimatter? Now that is a real mystery. To understand what might be happening, we must go back to the Big Bang. In the instant the universe was created, a huge amount of energy was transformed into mass, and our initial universe contained equal amounts of matter and antimatter. But just a second later, most matter and all of the antimatter had destroyed one another, producing an enormous amount of radiation that can still be observed today. Just about 100 millionths of the original amount of matter stuck around and no antimatter whatsoever. "Now, wait!" you might say, "Why did all the antimatter disappear and only matter was left?" It seems that we were somehow lucky that a tiny asymmetry exists between matter and antimatter. Otherwise, there would be no particles at all anywhere in the universe and also no human beings. But what causes this asymmetry? Experiments at CERN are trying to find out the reason why something exists and why we don't live in a universe filled with radiation only? But, so far, we just don't know the answer.
有可能無中生有嗎? 或更精確的說 能量可以轉換成物質嗎? 可以,但只會和雙胞胎兄弟— 反物質,一起出現 關於反物質,有件很神秘的事: 它存在的量,遠比它應有的量少 讓我們從最有名的物理公式說起: 能量 = 質量 x 光速的平方 基本上是說,質量是濃縮的能量 而質量和能量是可以互換的 就像是匯率極高的兩種貨幣 90 兆焦耳的能量 等於 1 公克的質量 要怎樣才能把能量轉換成物質呢? 關鍵是「能量密度」 如果你把巨大的能量 集中到很小的空間 新的粒子就會出現 如果我們更仔細看 我們會看到 這些粒子總是成對出現 就像是雙胞胎 因為每個粒子都有對應的夥伴 叫做反粒子 它們總是依照 50 比 50 等量出現 這聽起來像是科幻小說 但對粒子加速器來說,卻稀鬆平常 當兩個質子 在歐洲核子研究中心的 大型強子對撞機中相撞 每秒會產生數十億個 粒子與反粒子 比如說,像是電子 質量很小,而且帶負電 它的反粒子,也就是正電子 質量完全相同 但是帶正電 除了電荷相反以外 兩種粒子一模一樣,而且完全穩定 這對於它較重的表兄弟也成立 也就是質子與反質子 因此,科學家相信 反物質組成的世界 看起來、摸起來、聞起來 都像我們的世界 在反世界中 我們可以找到反水、 反金、 或是,比如說 反彈珠 現在想像一下,彈珠和反彈珠 放在一起 這兩個看似堅固的物體 會完全消失 變成巨大的能量閃光 相當於一顆原子彈 因為將物質與反物質結合 會產生極大的能量 科幻小說裡面有許多 用反物質儲存能量的想法 例如《星際爭霸戰》裡 太空船的燃料 畢竟,反物質所含的能量 是傳統燃料的十億倍 一公克反物質的能量 足夠開車繞地球一千圈 或讓太空梭進入軌道 為什麼我們不用反物質產生能量呢? 這個嘛,反物質並不會坐著 等我們開採 我們必須先製造反物質 才能燃燒反物質 而要製造反物質 得先花十億倍 未來可回收的能量 但若外太空裡有些反物質 有一天我們可從某處的 反行星上開採呢? 幾十年前,許多科學家相信 這是有可能的 現今,觀測結果顯示 在已觀察到宇宙的任何地方 都找不到大量的反物質 這是很詭異的,如我們先前所說 反物質的數量應該要 和宇宙中物質的數量相等 因為反粒子和粒子 存在數目應該相等 反物質到哪裡去了? 這真是一個謎 要了解可能發生了什麼事 我們必須回到大霹靂 在宇宙誕生的瞬間 大量的能量被轉換成質量 最初的宇宙包含了 等量的物質與反物質 但僅僅一秒之後 大部份的物質,及所有的反物質 就互相破壞消失了 產生大量的輻射 我們至今仍觀測得到 只有約一億分之一的 原始物質留了下來 沒有任何反物質倖存 「等等!」你可能會這麼說: 「為什麼所有的反物質都不見了, 而只有物質留下來?」 我們好像還蠻幸運的 有一點點的不對稱 存在於物質和反物質之間 否則,這宇宙中 將會沒有任何粒子 也不會有人類 是什麼造成這樣的不對稱呢? 歐洲核子研究中心的實驗 正試著找出答案 為什麼有些東西留下來了? 為什麼我們的宇宙 不是只充斥著輻射? 至今,我們還是不知道答案