薛定谔的猫和量子力学有什么关系

薛定谔的猫和量⼦⼒学有什么关系Consider throwing a ball straight into the air.
竖直地向上扔⼀个球。

Can you predict the motion of the ball after it leaves your hand? Sure, that's easy.
你能预测当球离开你的⼿以后的运动吗？当然，这很简单。

The ball will move upward until it gets to some highest point,
在到达某个最⾼点之前，这个球将⼀直上升，
then it will come back down and land in your hand again.
之后它将下落，⼜⼀次回到你的⼿上。

Of course, that's what happens, and you know this because you have witnessed events like this countless times.
当然，事情就是这样的。

你之所以知道，是因为你已经⽆数次⽬击过这样的事情发⽣。

You've been observing the physics of everyday phenomena your entire life.
你⼀直在整个⽣命的⽇常现象⾥观察到物理。

But suppose we explore a question about the physics of atoms,
但是，假设我们去探索⼀个关于原⼦物理的问题，
like what does the motion of an electron around the nucleus of a hydrogen atom look like?
就像是，⼀个电⼦绕氢原⼦核的运动是什么样？
Could we answer that question based on our experience with everyday physics? Definietly not. Why?
我们能依据⽇常的物理经验去回答吗？肯定不⾏。

为什么？
Because the physics that governs the behavior of systems at such small scales
因为，微观系统运⾏的物理定律
is much different than the physics of the macroscopic objects you see around you all the time.与宏观物理--就是那些你见到或是围绕在你⾝边的物理--的定律有很⼤不同。

The everyday world you know and love behaves according to the laws of classical mechanics.每天，你所见到和所深爱的被经典⼒学定律所掌控着。

But systems on the scale of atoms behave according to the laws of quantum mechanics.
但是，原⼦规模的系统被量⼦⼒学定律所掌控。

This quantum world turns out to be a very strange place.
这种量⼦世界被证明是个⼗分奇怪的地⽅。

An illustration of quantum strangeness is given by a famous thought experiment: Schrodinger's cat.
⼀个有名的思想实验给出了⼀个说明量⼦世界奇怪的例⼦：薛定谔的猫。

A physicist, who doesn't particularly like cats, puts a cat in a box,
⼀个实际上并不特别喜欢猫的物理学家，将⼀只猫放进盒⼦中，
along with a bomb that has a 50% chance of blowing up after the lid is closed.
⼀同放进去的还有⼀颗炸弹，在盖⼦盖上后，有50%的机率爆炸。

Until we reopen the lid, there is no way of knowing whether the bomb exploded or not,
除⾮我们我们重新打开盖⼦，我们没有办法得知炸弹有没有爆炸，
and thus, no way of knowing if the cat is alive or dead.
因此，也⽆法知道猫是活着还是死了。

In quantum physics, we could say that before our observation the cat was in a superposition state.
在量⼦物理中，我们可以说在观测之前，那只猫处于叠加态。

It was neither alive nor dead but rather in a mixture of both possibilities, with a 50% chance for each.
既不是活着也不是死亡，⽽是两种可能性的混合，每种可能都有50%的可能性。

The same sort of thing happens to physical systems at quantum scales, like an electron orbiting in a hydrogen atom.
在量⼦规模中，同样的事情发⽣在物理系统上，就像⼀个电⼦绕氢原⼦核运⾏。

The electron isn't really orbiting at all.
电⼦不是真正的绕轨道运⾏。

It's sort of everywhere in space, all at once,
就像是空间中的任何地⽅，都在⼀瞬间，
with more of a probability of being at some places than others,
存在某处⽐其他地⽅有更⼤的可能性，
and it's only after we measure its position that we can pinpoint where it is at that moment.
并且只有在我们测量过它的位置之后，我们才可以精确的知道那个时刻它在哪。

A lot like how we didn't know whether the cat was alive or dead until we opened the box.
很多现象，像是我们不知道这只猫是死是活，直到打开盒⼦。

This brings us to the strange and beautiful phenomenon of quantum entanglement.
这些把我们带⼊奇怪⽽⼜美丽的量⼦缠绕现象。

Suppose that instead of one cat in a box, we have two cats in two different boxes.
假设，现在我们有两只猫，在两个不同的盒⼦⾥，
If we repeat the Schrodinger's cat experiment with this pair of cats,
如果我们对这⼀对猫重复“薛定谔的猫”的实验，
the outcome of the experiment can be one of four possibilities.
这个实验的结果有四种可能。

Either both cats will be alive, or both will be dead,
两只猫都活着或是都死了，
or one will be alive and the other dead, or vice versa.
亦或是，⼀只猫活着⼀只死了，或者反⼀下。

The system of both cats is again in a superposition state, with each outcome having a 25% chance rather than 50%.
这个两只猫的系统⼜存在于叠加态，每种结果都有25%的可能性，⽽不是50%。

But here's the cool thing: quantum mechanics tells us
但是，这⾥有很有棒的事，量⼦⼒学告诉我们，
it's possible to erase the both cats alive and both cats dead outcomes from the superposition state.
有可能去清除叠加态中的结果，即两只猫都活着或死去。

In other words, there can be a two cat system, such that the outcome will always be one cat alive and the other cat dead.
换⾔之，可以是两只猫的系统，这个的结果将总是⼀只猫活着，另⼀只猫死去。

The technical term for this is that the states of the cats are entangled.
这个科学术语就是猫的纠缠态。

But there's something truly mindblowing about quantum entanglement.
但是，关于量⼦纠缠有些真正吸引⼈的事情。

If you prepare the system of two cats in boxes in this entangled state,
如果你在这种纠缠态中，准备两只在盒⼦中猫的系统，
then move the boxes to opposite ends of the universe, the outcome of the experiment will still always be the same.
然后把盒⼦移到宇宙的另⼀端，实验的结果将总是相同。

One cat will always come out alive, and the other cat will always end up dead,
⼀只猫总是活着，⽽另⼀只总是以死亡结束。

even though which particular cat lives or dies is completely undetermined before we measure the outcome.
尽管在观测结果前，具体哪只猫死亡或活着是完全不确定的。

How is this possible? How is it that the states of cats on opposite sides of the universe can be entangled in this way?
这怎么可能？宇宙两端的猫的状态怎能这样被纠缠？
They're too far away to communicate with each other in time,
它们相隔太远以⾄于不能及时沟通，
so how do the two bombs always conspire such that one blows up and the other doesn't?
那么，两个炸弹怎么能总是策划好⼀个爆炸⽽另⼀个⽆恙？
You might be thinking, 'This is just some theoretical mumbo jumbo. This sort of thing can't happen in the real world.'
你⼀定在想，这只是⼀些理论上的胡⾔乱语，这种事情不可能在真正的世界上发⽣。

But it turns out that quantum entanglement has been confirmed in real world lab experiments.但是，这证明了，量⼦纠缠已经在真实世界的实验室被证实了。

Two subatomic particles entangled in a superposition state,
两个亚原⼦的颗粒在叠加态纠缠，
where if one spins one way then the other must spin the other way, will do just that,
在这种状态下，如果⼀个颗粒以⼀个⽅向旋转，另⼀个颗粒必定以反⽅向旋转，事实就是这样，
even when there's no way for information to pass from one particle to the other
甚⾄，当没有办法将信息从⼀个颗粒传给另⼀个，
indicating which way to spin to obey the rules of entanglement.
去暗⽰怎么服从缠绕的法则旋转。

It's not surprising then that entanglement is at the core of quantum information science,
纠缠是量⼦信息科学的核⼼，这⼀点也不奇怪，
a growing field studying how to use the laws of the strange quantum world in our macroscopic world,
这是⼀个正在发展的领域，研究在我们的宏观世界怎样应⽤奇怪的量⼦世界的定律，
like in quantum cryptography, so spies can send secure messages to each other, or quantum computing, for cracking secret codes.
就像量⼦密码，间谍可以互相发送安全信息，或者量⼦计算，去破解密码。

Everyday physics may start to look a bit more like the strange quantum world.
⽇常的物理可能开始看上去有点像奇怪的量⼦世界。

Quantum teleportation may even progress so far,
量⼦远距离传送甚⾄可能发展的⼗分迅速，
that one day your cat will escape to a safer galaxy, where there are no physicists and no boxes.
以⾄于某天你的猫可能逃脱去了另⼀个星系，那⾥既没有物理学家，也没有盒⼦。