Black holes are among the most destructive objects in the universe. Anything that gets too close to the central singularity of a black hole, be it an asteroid, planet, or star, risks being torn apart by its extreme gravitational field. And if the approaching object happens to cross the black hole’s event horizon, it’ll disappear and never re-emerge, adding to the black hole’s mass and expanding its radius in the process. There is nothing we could throw at a black hole that would do the least bit of damage to it. Even another black hole won’t destroy it– the two will simply merge into a larger black hole, releasing a bit of energy as gravitational waves in the process. By some accounts, it’s possible that the universe may eventually consist entirely of black holes in a very distant future. And yet, there may be a way to destroy, or “evaporate,” these objects after all. If the theory is true, all we need to do is to wait.
黑洞是宇宙中 最有毀滅性的物體之一。 任何東西,如果太靠近 黑洞的中心奇點, 不論是小行星、行星、恆星, 都有很高的風險可能會因為 它的極端重力場而四分五裂。 如果靠近黑洞的物體 剛好穿過了黑洞的事件視界, 它就會消失,永遠不會再出現, 在過程中,還會增加 黑洞的質量並擴大它的半徑。 不論我們朝黑洞丟什麼, 都無法對它造成一點損傷。 就連另一個黑洞也無法摧毀它, 兩個黑洞只會融合成 一個更大的黑洞, 在過程中以重力波的 形式釋放出一點能量。 有人說, 最終,宇宙有可能滿滿都是黑洞, 發生在非常遙遠的未來。 但,也許還是有辦法可以摧毀 或「蒸發」這些物體。 如果理論沒錯, 我們要做的就是等待。
In 1974, Stephen Hawking theorized a process that could lead a black hole to gradually lose mass. Hawking radiation, as it came to be known, is based on a well-established phenomenon called quantum fluctuations of the vacuum. According to quantum mechanics, a given point in spacetime fluctuates between multiple possible energy states. These fluctuations are driven by the continuous creation and destruction of virtual particle pairs, which consist of a particle and its oppositely charged antiparticle.
在 1974 年,史帝芬霍金 推論出一個過程, 可能會導致黑洞漸漸失去質量。 它就是漸漸被大家 所知的霍金輻射, 它的基礎是一個已被大家接受的 現象,叫做真空量子漲落。 根據量子力學, 在時空中給定的一個點 會在數種可能的能態間起伏漲落。 驅動這些起伏漲落的是 虛粒子對的不斷創造和摧毀, 虛粒子對包含了一個粒子 和一個帶相反電荷的反粒子。
Normally, the two collide and annihilate each other shortly after appearing, preserving the total energy. But what happens when they appear just at the edge of a black hole’s event horizon? If they’re positioned just right, one of the particles could escape the black hole’s pull while its counterpart falls in. It would then annihilate another oppositely charged particle within the event horizon of the black hole, reducing the black hole’s mass. Meanwhile, to an outside observer, it would look like the black hole had emitted the escaped particle.
正常情況下,這兩者出現後 沒多久,就會相撞並毀滅, 總能量維持不變。 但,當它們出現在黑洞事件視界 邊緣時,會發生什麼事? 如果把它們放對位置, 其中一個粒子可以 逃離黑洞的引力, 另一個粒子則會掉進去。 接著,它就會在黑洞的事相面內, 摧毀另一個帶相反電荷的粒子, 因而減少黑洞的質量。 此時,從外部觀察者來看, 就像是黑洞放射出了 逃離的那個粒子。
Thus, unless a black hole continues to absorb additional matter and energy, it’ll evaporate particle by particle, at an excruciatingly slow rate. How slow? A branch of physics, called black hole thermodynamics, gives us an answer.
因此,除非黑洞持續 吸收額外物質和能量, 不然它就會以極緩慢的速度, 一個粒子一個粒子地蒸發。 多慢?物理有一個分支 叫做黑洞熱力學, 它就可以給我們答案。
When everyday objects or celestial bodies release energy to their environment, we perceive that as heat, and can use their energy emission to measure their temperature. Black hole thermodynamics suggests that we can similarly define the “temperature” of a black hole. It theorizes that the more massive the black hole, the lower its temperature. The universe’s largest black holes would give off temperatures of the order of 10 to the -17th power Kelvin, very close to absolute zero. Meanwhile, one with the mass of the asteroid Vesta would have a temperature close to 200 degrees Celsius, thus releasing a lot of energy in the form of Hawking Radiation to the cold outside environment. The smaller the black hole, the hotter it seems to be burning– and the sooner it’ll burn out completely.
當日常的物體或是天體 釋放能量到它們的環境中時, 我們會感受到熱能, 並能用它們放出的能量 來測量它們的溫度。 黑洞熱力學指出, 我們可以用類似的方式, 定義黑洞的「溫度」。 它的理論是,黑洞的質量越大, 它的溫度就越低。 宇宙中最大的黑洞 發出的絕對溫度會是 10 的 -17 次方, 非常接近絕對零度。 如果黑洞的質量 和灶神星(小行星)一樣, 溫度就會接近攝氏 200 度, 因此會以霍金輻射的形式 釋放許多能量 到寒冷的外在環境。 黑洞越小, 它似乎燃燒得越熱—— 也會更快完全燒盡。
Just how soon? Well, don’t hold your breath. First of all, most black holes accrete, or absorb matter and energy, more quickly than they emit Hawking radiation. But even if a black hole with the mass of our Sun stopped accreting, it would take 10 to the 67th power years– many many magnitudes longer than the current age of the Universe— to fully evaporate. When a black hole reaches about 230 metric tons, it’ll have only one more second to live. In that final second, its event horizon becomes increasingly tiny, until finally releasing all of its energy back into the universe. And while Hawking radiation has never been directly observed, some scientists believe that certain gamma ray flashes detected in the sky are actually traces of the last moments of small, primordial black holes formed at the dawn of time.
有多快?不用期待了。 首先,大部分的黑洞長大 或是吸收物質和能量的速度, 都比它們發散 霍金輻射的速度更快。 但,即使質量和我們太陽 一樣大的黑洞停止成長了, 也需要花上 10 的 67 次方年—— 比宇宙目前的壽命還要長許多—— 才會完全蒸發。 當黑洞達到大約 230 公噸時, 它就會只剩下一秒鐘可以活。 在那最後一秒鐘, 它的事件視界會越來越小, 直到最後,將它所有的 能量釋放回宇宙。 雖然從來沒有人 直接觀察到霍金輻射, 有些科學家相信,在空中 偵測到的某些伽瑪射線閃光 其實就是在時間之初 所形成的小型原始黑洞 在其最後時刻留下的蹤跡。
Eventually, in an almost inconceivably distant future, the universe may be left as a cold and dark place. But if Stephen Hawking was right, before that happens, the normally terrifying and otherwise impervious black holes will end their existence in a final blaze of glory.
最終,在幾乎無法 想像的遙遠未來, 宇宙可能會變成只是 一個寒冷、黑暗的地方。 但,如果史帝芬霍金 是對的,在那發生之前, 平常十分嚇人,且在其他情況 都不會受到影響的黑洞, 在發出最後的光輝之後, 將不復存在。