The mind-bending physics of time | Sean Carroll

Summary

视频脚本探讨时间的本质,分析熵增原理如何催生生命的复杂性,讨论箭头时间的起源,并提出生命起源这一科学难题尚待解答。

Takeaways

• 😀 时间这个词是英语中使用频率最高的名词。我们每天都在谈论时间。
• 😯 时间本身可能不是一个难题,真正的困惑在于时间的属性,例如过去、现在和未来之间的关系。
• 😕 从物理学的角度来看,我们最好的物理理论并不区分过去和未来。
• 🤔 时间是否有方向性,这是一个深奥的哲学问题。我们感觉时间是有方向的,但从物理学角度来看,时间可能本质上没有方向。
• 😶 时间的方向性可能是因为我们生活在一个有影响力的事件之后——大爆炸之后。
• 🧐 熵的增加解释了为什么时间会有方向性。从一个低熵的状态发展到一个高熵的状态是宇宙的一个基本规律。
• 😊 生命不是抵抗熵的增加,而是依靠熵的增加才能存在。如果熵不增加,就没有任何有趣的事情发生。
• 🤨 我们不完全了解为什么会出现复杂的结构,例如生命。这是一个活跃的科学研究领域。
• 😃 熵从低增加到高,为复杂性的出现提供了空间。复杂的系统利用了熵的增加。
• 😀 如果熵不增加,宇宙就会无聊至极,没有生命的出现。

Q & A

时间的本质是什么?

时间本质上只是一个在宇宙中不同事件的标签和度量。时间帮助我们区分一个时刻和另一个时刻,但时间本身并没有固有的方向性。

为什么我们感觉时间是有方向的?

我们感觉时间有方向性是因为我们生活在一个熵在持续增加的宇宙中。熵的增加造成了从过去到未来的时间方向感。

熵是什么?

熵是衡量一个系统的混乱程度和无序程度的物理量。一个有序的系统熵较低,一个混乱的系统熵较高。根据热力学第二定律,孤立系统的熵随时间增加。

为什么我们只有过去的记忆而没有未来的记忆?

这与宇宙的低熵起源有关。我们只有过去的记忆是因为过去的事件对现在有影响。但未来还没有发生,所以我们对未来没有记忆。

我们如何解释时间的方向性?

通过过去假说。它认为我们的宇宙起源于一个低熵的状态,从那时起熵不断增加,这造成了从过去到未来的时间方向感。

生命与熵的关系是什么?

生命存在要依赖于宇宙中熵的增加。熵增加提供了可能的复杂性。生命利用熵的增加而存在,但生命的目的不是反对熵增加。

为什么会出现复杂的生命结构?

熵从低增加到高为复杂结构提供了可能性。尽管熵的增加是必然的,但复杂结构的出现还有其他原因,需要深入研究信息和化学方面的问题。

如果熵不增加会怎样?

如果熵不增加,宇宙将停滞不前,处于平衡状态。没有因果关系,也不会有任何有趣的事发生。

时间旅行可能吗?

目前看来,根据我们的物理定律,时间旅行不太可能。时间没有固有的方向性,但因熵增加导致的时间方向感,使得回到过去变得不可能。

时间的本质最终能被完全理解吗?

关于时间的本质和方向性,许多问题仍未完全解答。我们需要更深入地研究熵的性质和复杂系统的形成。这是一个活跃的科学研究领域,还需要进一步探索。

Outlines

00:00

⏰时间的概念

第一段讨论了时间这个词语在语言中的广泛应用。我们在日常对话中频繁使用时间,但并不会对时间概念本身感到困惑。时间主要是用于区分不同时刻的标签。时间的本质并不神秘,真正的困惑在于我们对时间性质的讨论,例如过去、现在和未来等不同时间属性之间的关系。

05:02

⏱️物理学角度看时间

第二段从物理学的角度分析时间。 根据我们最好的物理学理论,时间没有固有的方向性。但在日常生活中,时间的方向性显而易见。这需要有心理训练才能认识到时间可以没有方向性。可以类比空间没有固有方向性,但地球的引力给地球空间带来了方向性。时间也是一样,没有固有方向,但大爆炸事件确定了时间的方向。

Mindmap

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Keywords

💡时间

时间是一个非常常用的名词,它描述事件发生的顺序和持续的长短。视频说时间这个词在英语中使用频率非常高。时间让我们能够区分不同时刻发生的事件,也让我们能够计划和安排生活。视频讨论了时间的特性,例如过去、现在和未来的不同,时间是否有方向性等概念。

💡熵

熵是描述一个系统的混乱程度和随机性的物理量。熵越高,系统越混乱。视频说,宇宙有着从低熵到高熵的趋势,这被称为热力学第二定律。低熵状态下事物更有序,高熵状态下事物更混乱。

💡过去假说

过去假说是一个由物理哲学家大卫·阿尔伯特提出的概念,用来解释时间的方向性。该假说认为,宇宙起源于一个低熵状态的大爆炸,从那时起熵就持续增加。所以我们观测到时间的方向性,可以归因于宇宙的低熵起源。

💡热力学第二定律

热力学第二定律阐述了孤立系统的熵必然随时间增加,这是时间方向性的一个来源。视频说,由于这个定律,宇宙整体上处于从低熵到高熵的演化过程中。

💡因果关系

视频说,如果熵不增加,将不会有因果关系。因为高熵状态意味着时间的流逝,我们的过去行为才会对未来产生影响。如果熵不增加,过去、现在和未来就没有区别。

💡复杂性

视频讨论了复杂性的产生需要依赖于熵的增加。因为在最大熵状态下,宇宙非常简单,没有复杂性。只有在从低熵到高熵的演化过程中,才有可能出现复杂的结构。

💡生命

视频否定了“生命与增加的熵作斗争”的观点。相反,生命得益于熵的增加,在熵增过程中出现。如果熵不增加,将不会出现生命。

💡信息

视频说复杂性的产生与信息有关。熵增过程中,信息的传递和转换创造了可能的复杂模式。这是一个科学研究的课题。

💡起源

视频讨论了复杂性的起源问题,认为这需要研究信息、化学和地质学等过程,也许在其他行星上也可能出现生命。这个问题仍有许多未解之谜。

💡简单性

视频说,宇宙起源于一个简单的低熵状态,未来最终也将是简单的高熵状态。在这两个简单状态之间,复杂性得以出现。

Highlights

时间这个词是英语中使用最频繁的名词

物理理论没能区分过去和未来

时间存在一个方向性

我们感知时间的方向性是因为我们生活在一个有影响力的事件之后:大爆炸

熵表示一个系统的混乱、无序和随机程度

第二定律的热力学:宇宙总是从低熵向高熵发展

低熵状态可以解释之后发生的一切

复杂的结构需要依靠熵的增加才能存在

生命不应视为抵抗熵增加的斗争

如果熵不增加,什么有趣的事情都不会发生

复杂性存在于从简单低熵状态向简单高熵状态的过程中

研究复杂结构如何出现是一个活跃的科研领域

生命依赖于熵的增加才出现

我们还不完全理解复杂性的起源

如果熵不增加,什么也不会发生

Transcripts

- Lexicographers will tell you that time,

the word, "T-I-M-E,"

is the most used noun in the English language.

We can't get through the day

without talking about time all the time.

I think about how we use time,

when we actually talk about it.

If you say, "Meet me at 7 p.m.,"

no one panics.

No one says like, "Oh my God, what are you talking about

with these esoteric concepts about 7 p.m.?"

We all know what to do operationally.

Time, in some sense,

is just a label on different events in the Universe.

The Universe happens over and over again

at different things we call moments,

and time helps us tell the difference

between one moment and another.

So what time is, I don't think is the problem.

The issue-

the real puzzles-

come about when we talk about the properties

that time has.

We have a past, we have a present, we have a future.

How are they different?

Are we moving through it?

We have memories of the past,

but we have no memories of the future.

Why is that?

Where does that asymmetry come from?

Why are we all born young?

Why do we all inevitably age?

Why do we think

that we can affect the future but not the past?

Could we possibly travel back into it?

Anyway, there's a lot of questions about the nature

of time that are really confusing

and many of them we don't know the answer to,

but what time is,

I don't think it's one of them.

One of the most noticeable features

of time is that it has a direction, right?

That there's a difference between the past and future.

Sometimes we think about this

as just an intrinsic feature of reality.

Like the past already happened, it's in the books-

the future is up for grabs.

It hasn't happened yet, and the present is where we live.

But then, along comes physics.

And what people notice about our best theories

of physics is that those theories do not distinguish

between the past and the future.

But in our everyday lives, nothing is more obvious.

It really requires a bit of mental discipline to say,

"Well, time could exist without an arrow."

And one way of thinking

about that is there is no intrinsic arrow of space,

but there's still space, okay?

We live in a three-dimensional world-

up, down, left, right, forward, backward-

at the level of the fundamental laws of physics,

there's no special direction in space.

And how you perceive that is imagine you're an astronaut:

you're flying around in your little spacesuit.

There wouldn't be any difference

between any direction you could look.

There's no experiment you could do

in physics that would point

out a direction in the universe, but space still exists.

Likewise, time would still exist even

if there wasn't an arrow.

But here on Earth, we do have an arrow of space.

If I pick up a coffee cup and let it go,

it will always fall down.

There's clearly a distinction between up and down.

No one is tempted to think that's a fundamental feature

of the Universe.

It's not because downness is embedded

in the laws of physics.

It's because we live

in the vicinity of an influential object-the Earth.

The arrow of time is exactly the same way.

We in our everyday lives, perceive an arrow of time

because we live in the aftermath of an influential event:

the Big Bang.

And that gets us

into a realm of the concept of 'entropy.'

Entropy is how messy, how disorganized,

how random a system is.

When things are nice and neat and tidy,

they are low entropy.

When they're all messy

and all over the place, they're high entropy.

And there's a natural tendency of things

in the Universe to go from low entropy to high entropy.

This is called the 'second law of thermodynamics.'

The real question is:

Why was the world ever low

entropy to begin with?

Why was the world lower entropy yesterday than it is today?

The explanation is not completely satisfying, to be honest.

The explanation is the following:

because it was even lower entropy the day before yesterday.

And why was the Universe even lower entropy the day

before yesterday?

Because it was even lower entropy the day before that.

And this chain of reasoning goes back 14 billion years

to the Big Bang, to the origin of our observable universe;

in a hot, dense state, a very low-entropy state,

and the Universe has been increasing in entropy ever since.

And this is called the 'Past hypothesis' by philosophers-

David Albert, who's a philosopher of physics,

gave it this name.

So now we say, "If you know that the world is made of atoms,

and you know what entropy is,

in terms of rearranging all those atoms,

and you know the past hypothesis-

that the entropy of the universe started really low-

then you can explain everything that happened after that.

There's a way of talking

about human life and entropy, which I think is misguided,

which is that we should think about life.

You know, literally living, being a biological organism,

taking in food and everything,

as a fight against increasing entropy.

I think that's wrong.

I think that we owe life

to the fact that entropy is increasing,

because what would it mean if entropy were not increasing?

It would mean that nothing is happening.

Nothing interesting is taking place.

Without entropy increasing,

there's no memory of the past.

Without entropy increasing,

there's no causal effect that we have on the future.

You'd just be in what we call 'thermal equilibrium.'

Everything would be the same everywhere.

It would be the maximally boring universe.

But what we do have as a scientific question is:

'Why do complicated complex structures come

into existence at all?'

It's clear that they need increasing entropy to exist,

because if entropy were already maxed out,

there would be no complexity.

But that doesn't mean they have to come

come into existence.

Think about a famous example there:

The perfume is all in little bottle.

It's in a big room.

You open it, and it all floats through the room.

The entropy of the perfume increases.

But if you think about it,

when the perfume is all in the bottle, it's very simple.

Once it's all spread through the room

it's also very simple.

It went from low entropy to high entropy,

but it went from simple to simple.

It's the journey from the simple, low-entropy starting point

to the simple, high-entropy ending point,

that there's a large space

of possibilities where things can be intricate.

There's more perfume here over there.

There can be swirls caused by the motion

of the wind in the room and so forth.

The Universe is just like that.

Our Universe started out simple and low entropy.

In the future, the stars will die,

the black holes will evaporate.

It'll be dark, empty, and again, simple, but high entropy.

It's in between that things like us-

complicated, intricate systems that feed

off of the increasing entropy

of the Universe-

can and do come into existence.

We don't know the whole story there.

I think it's a very fun, active, scientific research area:

Why did complex structures like living beings come

into existence and exactly the way we did?

What is the role of information?

What is the down-to-Earth chemistry that is going on here?

What is the geology that is going on here?

Could it happen on other planets?

Very interesting questions- but one thing I do know

is that if entropy weren't increasing along the way,

none of it would've come to pass.