If I had a machine that allowed me to suddenly… transport myself elsewhere, the air filling

會急速填滿剛才我消失之處留下的真空， 力量大到足以轟爆耳膜，

the vacuum where I used to be would collapse with enough force it would burst the eardrums

並讓站在旁邊的人感到反胃。

and cause nausea in anyone standing nearby.

遠距傳送聽起來很酷，但對於「聽」而言就相當危險。

Teleportation may sound like a cool idea, but thanks to sound itself, it's a pretty dangerous proposition.

聲波是機械性的，需要有介質才能傳播，

[MUSIC]

現在我講話的聲音使空氣前後搖動，

A sound wave is mechanical, it needs a medium to travel through.

製造高壓區和低壓區。

Right now, the wave created by my voice is wiggling the air back and forth, creating

當我們說到聲音大小，實際上再說空氣壓力波

areas of higher and lower pressure.

的強度。聲音越大，則波動越強。

When we talk about how loud a sound is, we’re really talking about the intensity of that

不似池塘漣漪，聲音從來源以球形傳播出去。

pressure wave. The louder the sound, the more intense the wave.

就像泡泡越大表面越薄，越遠離音源

Unlike ripples on a pond, sound moves out from its source in the shape of a sphere.

則同樣面積的聲波壓力越小，

Just like a bubble gets thinner as it gets bigger, the farther we are from the source

也就是離聲源兩倍遠處，聲音強度僅四分之一。

of a sound, the less pressure there is on a given area of the sound sphere.

可聽見的最小聲音，導致我們耳膜振動的幅度

This means that if we move twice as far from a sound, it will be at one-fourth the intensity.

小於一個氧分子寬度！ 我們可以安然聽到十億倍強度的聲響。

The smallest sound pressure wave we can hear vibrates our eardrum less than the width of

聽覺是已知感官中接收強度範圍最廣者， 因此我們需要更寬的指標

a single oxygen molecule! Yet we can comfortably hear sounds a billion times more intense.

以便測量。為此我們使用分貝(dB)。

Hearing has the widest range of any of our senses, by far, so we need a wide scale to

分貝是指數性的，某聲響大十分貝，其強度就大十倍。 三十分貝？

measure it. To do that we use decibels.

就是一千倍強。讓人耳朵作痛的界線

dBs are logarithmic. Something 10 decibels louder is ten times as intense. 30 decibels?

比我們能聽到最小的聲音大十兆倍。

A thousand times as intense. Our threshold for pain comes at sounds 10

高速公路大約有90分貝。

trillion times more intense than the quietest sound we can hear.

槍聲可達130分貝以上。

Highway traffic is about 90 decibels.

1883年，南太平洋喀拉卡托火山爆發， 煙塵噴上大氣17英里高，

[gunshots]

發出沙皇炸彈的四倍能量，

[jet noise]

即世上最強的核爆。喀拉卡托爆發的聲音近180分貝， 爆炸足以震破

In 1883, the island of Krakatoa in the South Pacific erupted, sending ash nearly 17 miles

40英里外的耳膜，空氣震波繞行地球四圈。

into the atmosphere, with a force four times more powerful than the Tsar Bomba, the most

想像你聽到這個......而人在三千英里外。如果

powerful nuclear weapon ever detonated. At nearly 180 dB, this explosion shattered

你靠得夠近，這會是你一輩子聽到最後一聲巨響。

eardrums 40 miles away, and pushed a wave of air around the globe four times.

但聲音大小有個上限，提示：不是「刻度11」。

Imagine hearing this… BANG! only three thousand miles away. Get close

聲音在波峰推擠耳膜，在波谷放開耳膜。

enough to that, and it'll be the last sound you never hear.

要是波谷達到真空，就無法再更大聲，此一上限

But there’s an upper limit to how loud a sound can be, and, hint: It’s not “11”.

是194分貝，它將扭曲、加熱並超越音速。

Sound waves push air together at their peak, and leave low pressure in the valleys. Once

更強大的聲波只能轉化成衝擊波。

this part reaches a vacuum, the sound can’t get any louder. Push the wave any harder than

NASA的農神五號火箭可以發出750萬磅推力，

194 dB, then it distorts, heats up, it’s moving faster than the speed of sound.

高達200~220分貝。這力量足以點燃1.5公里內的草，

We can go higher, only then it's stopped being sound and has become a shock wave.

並殺光數百公尺內的一切生物。

NASA’s Saturn V rocket was capable of shooting out 7.5 million pounds of space-fire thrust

為了發射火箭，NASA每分鐘把九十萬加侖的水

at 200-220 dB. That’s enough pressure to ignite grass a kilometer and a half away and

倒入發射台下方的池子，才讓聲波不至於拆掉發射器。

kill everything within a few hundred meters.

倒入發射台下方的池子，才讓聲波不至於拆掉發射器。

For Space Shuttle launches, NASA dumped water at a rate of 900,000 gallons per minute into

當然，大氣更濃厚的行星，可以維持更強大的

a pool underneath the launch pad to keep the sound waves from literally ripping the shuttle

聲波，更高的分貝數。

apart.

我不禁思考，土星上的雷暴聽起來是怎樣？

Of course, planets with more dense atmospheres, like Venus or Saturn, could sustain more intense

事實上，我真的想要找到答案。

sound waves, and even higher decibel levels.

保持好奇心吧。

It makes me wonder, what would a lightning storm on Saturn sound like?

In fact, I’d like to find out.

Stay curious!

BANG! [ringing sound]