新的实验发现时间有两个方向!(中英文)

科学家发现在平行宇宙中时间有可能回到过去!

了解时间对于物理学来说，是其中一个最大的开放性问题，历史之中哲学家们一直以来也备感困惑。时间是什么？为什么它有方向？这个概念被定义为「时间之矢」(arrow of time)，通常直指时间的不对称性，虽然宇宙中大多数的定律是绝对地对称。

这个问题现在有了更进一步具可能性的解释。加州理工学院物理学家Sean Carroll以及麻省理工学院宇宙学家Alan Guth做了一个模拟实验，发现时间箭头可以自然地来自一个完美对称的方程式系统。

时间之矢的发现，是来自于观察到时间似乎的确是从我们身上经过，而那个时间的方向也与宇宙中的熵(Entropy)一致。而熵是用来测量发生在世界上的失序现象。一颗完整的蛋比起一颗破碎的蛋有更少熵，因此若我们看到一颗破碎的蛋时，我们就会知道它已经破了。我们的经验告诉我们，已经破碎的蛋就像冰块融化一般，无法再归位回来，也就是说，整理一个房间，要比弄乱一个房间耗费更多的能量。

Carroll和Guth的实验结果尚未发表，但他们终于在《New Scientist》中提出讨论。在他们的模拟实验中，包含了大量的粒子在引力之下相互作用，并任意方向的移动。有些粒子自然的聚集在一起，而这个聚集区的熵值低，且之后会在特定的时间方向分开和扩张。而出人意外的是，当你把整个系统镜像化时，熵值仍然在增加，而这也显示出时间的两个方向都是可行的。

像这样的研究调查已经不是第一次，2014年一个国际性的物理学家团队研发出一个简易模式，透过它可以呈现出物理对称定律而只有「明显的」时间之矢。他们的调查结果刊登在《物理评论快报》(Physical Review Letters)当中。他们注意到有时间之矢，但这仅只是从这个系统中的粒子的观点而来，而对于外部观察者而言，时间里则没有特别的方向。

这些科学家公布的内容，当研究出版后，定会受到热烈的争论。而这个模式提供了有趣的观点，不过它无法提供更接近的答案，告诉我们时间是什么；如果有的话，也只是增加了我们对于时间本质及其复杂性的疑问。在此情况下，我同意道格拉斯·亚当斯(Douglas Adams)的诠释：「时间是幻象，午餐时间更是加倍如此。」

How Time Could Move Backwards In Parallel Universes

Understanding time isone of the big open questions of physics, and it has puzzled philosophersthroughout history. What is time? Why does it appear to have a direction? Theconcept is defined as the “arrow of time,” which is used to indicate that timeis asymmetric – even though most laws of the universe are perfectlysymmetric.

Apotential explanation for this has now been put forward. Physicist Sean Carrollfrom CalTech and cosmologist Alan Guth from MIT created a simulation that showsthat arrows of time can arise naturally from a perfectly symmetric system ofequations.

The arrow of time comes from observing thattime does indeed seem to pass for us and that the direction of time isconsistent with the increase in entropy in the universe. Entropy is the measure of the disorder ofthe world; an intact egg has less entropy than a broken one, and if we see abroken egg, we know that it used to be unbroken. Our experience tells us thatbroken eggs don’t jump back together, that ice cubes melt, and that tidying upa room requires a lot more energy than making it messy.

Carrolland Guth’s work is still unpublished but they discuss it at length in New Scientist. Their simulation includes alarge number of particles interacting under gravity and moving in randomdirections. Some particles naturally assemble into a clump, an area of lowentropy and then separate and expand in a specific time direction.Surprisingly mirroring the entire system, the entropy still increases, whichshows that both directions of time are a viable solution.

Thisis not the first time something like this has been shown. In 2014, an internationalgroup of physicists developed a simple model that shows you can have symmetriclaws of physics and an only “apparent” arrow of time. Their findings werepublished in Physical Review Letters. They noticedthat there was an arrow of time, but only from the point of view of theparticle in the system – for an external observer, there was nospecial direction in time.

Whatthe scientists have announced will definitely become hotly debated once theresearch is published. The model offers intriguing ideas, but it doesn’t get uscloser to answering what time is; if anything, it increases thequestions we have about its nature and complexity. In this situation, Isubscribe to the Douglas Adams’ interpretation: “Time is an illusion, lunchtimedoubly so.”

http://hssszn.com/?p=9083

http://www.iflscience.com/physics/time-moving-forward-illusion

（来源：网络）

系统培训——量化实战特训营

3月18-20日，北京

建模编程——策略实战——资金管理——绩效评价