The fundamentals of space-time: Part 3 - Andrew Pontzen and Tom Whyntie

Translator: Connie Zhao Reviewer: Thomas Tam

Gravity. It controls the universe.

重力掌控住宇宙。

Everything attracts everything else.

萬物相互吸引。

Ouch!

哎喲！ 包括你在內。

Including you.

Ow!

In this final lesson,

喺最後嘅課題度，

we'll explore what gravity means for space-time,

我哋將會探索 重力對時空嘅意義，

or rather what space-time means for gravity.

或者更準確噉講， 時空對重力嘅意義。

Until now, we've been dealing with things moving

直到而家，我哋都係處理緊 以恆定速度移動嘅事物，

at constant speeds,

同埋時空度嘅直線世界線。

with straight world lines in space-time.

But once you add gravity,

但一旦你加入重力，

if you measure a speed at one moment,

如果喺某個時刻測量速度，

then again a bit later,

稍後再測量多一次，

the speed may have changed.

嗰個速度可能已經改變咗。

In other words, as I discovered,

換句話講，正如我所發現嘅，

gravity causes acceleration,

重力會導致速度增加，

so we need the world line to look different

所以我哋需要世界線 喺下一刻睇落唔同。

from one moment to the next.

As we saw in the last lesson,

正如我哋喺上一課所見到， 傾斜物體世界線嘅正確方法

the correct way to tilt an object's world line

is using a Lorentz transformation:

係用洛倫茲變換：

Einstein's stretch and squash trick.

愛因斯坦嘅伸展同壓縮技巧。

So, to map out what gravity is doing to Tom's motion,

所以，要搞清楚 重力對湯姆運動做緊啲咩，

we need to create a whole load of little patches of space-time,

我哋需要創建一大堆 小塊嘅時空，

each transformed by different amounts.

每小塊都係由唔同嘅量轉化。

噉，我嘅世界線同每條嘅角度都會唔同。

So that my world line is at a different angle in each one.

And then, we're ready to stitch everything together.

然後，我哋準備 將所有嘢合併埋一齊。

We assemble a cozy quilt of space-time

我哋組裝咗一張 舒適嘅時空被子，

where world lines look curved.

喺呢度，世界線睇落係彎曲嘅。

Where the world lines join, the objects collide.

喺世界線嘅交匯處， 物體就會碰撞。

By making these connections between the patches,

將呢啲小塊嘅時空連結，

a curvature gets built into space-time itself.

建立時空本身嘅曲率。

But Einstein's true genius

但愛因斯坦真正天才 係精確描述每個時空小塊

was to describe precisely how each patch

is stretched and squashed

係點樣根據附近嘅質量 同能量去伸展同壓縮。

according to nearby mass and energy.

單單有啲嘢嘅存在 就會令到時空彎曲，

The mere presence of stuff curves the space-time,

and curving space-time moves the stuff around.

而彎曲嘅時空 就會令到啲嘢周圍移動。

This is gravity, according to Einstein.

呢個就係愛因斯坦所講嘅重力。

Previously, Isaac Newton had explained gravity

先前，艾薩克·牛頓用力量 同增加速度嘅概念去解釋引力，

using the ideas of force and acceleration,

without any wibbily wobbly space-time,

而冇任何摇摆不定嘅時空；

and that did pretty well.

已經解釋得相當好。

But Einstein's theory does just slightly better

但愛因斯坦嘅理論 喺預測方面做得好少少，

at predicting, for example,

例如水星圍繞太陽嘅軌道，

the orbit of Mercury around the Sun,

or the way that light rays are deflected by massive objects.

或者光線被大質量物體 偏轉嘅方式。

More importantly, Einstein's theory predicts things

更重要嘅係， 愛因斯坦嘅理論預測咗

that simply don't exist in older theories

一啲喺舊有理論入面 根本唔存在嘅嘢，

where space, time and gravity were separate.

空間、時間同重力係分開嘅。

The stitching can leave wrinkles in the space-time material.

縫合會喺時空材料入面 留下咗皺紋。

These are called gravitational waves,

呢啲叫做重力波，

which should be detectable as tiny, repetitive,

佢哋應該可以喺太空中被檢測到

subtle squashes and stretches in space.

係微小、重複、 微妙嘅壓縮同延伸。

So we're building experiments to check if they are there.

所以我哋建立緊實驗 嚟檢查佢哋係咪存在。

In the meantime, indirect evidence,

與此同時，間接證據，

most recently in the polarization patterns of light

最近喺大爆炸剩低嘅光 嘅偏振模式，

left over from the Big Bang,

strongly suggest that they are.

強烈表明佢哋確實存在。

But despite Einstein's successes,

但儘管愛因斯坦取得咗成功，

when too much stuff gets concentrated

當太多物質集中 喺一個太細嘅空間入面，

in too small a space,

like in a black hole,

好似黑洞噉，

the curvature of space-time becomes so large,

時空嘅曲線就會變得好大，

that his equations collapse.

令到佢嘅方程式崩潰。

我哋需要一幅 新嘅時空圖像，

We need a new picture of space-time

將量子力學納入

that incorporates quantum mechanics

to unlock the secret at the heart of black holes.

去解開黑洞中心嘅秘密。

噉，即係話，未來仲有

Which means there's plenty more to be discovered

about space, time, and space-time in the future.

好多關於太空、時間 同時空嘅嘢要發現。