We have long thought that time had only one dimension, but what if we were wrong, asks Miriam Frankel
PHYSICISTS aren’t known for playing fast and loose with the rules of reality. But when it comes to the concept of space, some take a remarkably permissive attitude. For most of us, it would seem there are just three dimensions of space. Yet string theory, for instance, postulates there are at least nine.
The same attitudes don’t tend to apply to time. For almost all physicists, time has just one dimension, period. Yet some dare to wonder if there might be more to time than meets the eye.
It is a dangerous game – mess with time, and you can end up scrambling the laws of cause and effect. But then again, we know physics has plenty of problems. Maybe a drastic step is exactly what is needed to solve them? “Everything in reality can come out from a theory with two times,” says Itzhak Bars at the University of Southern California, who has been wondering about this for decades.
With his ideas and those of others now hinting at what might lie inside black holes and even suggesting a possible solution to one of the biggest mysteries in quantum mechanics, perhaps this wild idea deserves the time of day.
The edifice of modern physics is supported by two great pillars. Quantum theory describes the world of particles and three of the four fundamental forces, while general relativity explains the remaining force, gravity, as the curvature of space-time. Yet nearly every deep problem in physics is a crack along the same fault line: these theories paint incompatible pictures of how reality works.
Broadly speaking, physicists suspect a deeper picture underlies both theories. Trying to work out what that is has led them to ideas like string theory, with its many extra dimensions of space. But few think we are anywhere near the true answers yet.
So, what about time, then? At first blush, Albert Einstein’s ideas about relativity do at least teach us that time is far stranger than everyday experience suggests. We know that distances and durations aren’t fixed properties of the world, but depend on how fast you are moving. Two observers whizzing at different velocities close to the speed of light can disagree about how far apart two events were and how much time elapsed between them, without either being wrong.
Even so, Einstein insisted they had to share an objective reality – which he hinged upon the speed of light.
米里亚姆·弗兰克尔提出：长久以来，我们都认为时间只有一个维度，但倘若我们错了呢？
物理学家向来不会随意对待现实世界的法则。但谈及空间这个概念时，一部分学者的包容度却相当高。对大多数人而言，空间似乎就只有三个维度。例如弦理论就假定，空间至少存在九个维度。
但这套开放思路一般不会用在时间上。几乎所有物理学家都认定，时间只有一个维度，仅此而已。不过仍有学者大胆猜想：时间或许比我们看到的更加复杂。
这是一场冒险的探索：一旦改动时间的设定，因果定律就可能被打乱。但从另一方面看，物理学本身尚存大量难题。或许，我们正需要这样颠覆性的思路来破解困局。南加州大学的伊扎克·巴尔斯说：“现实中的一切，都可以从一个包含双时间维度的理论推导得出。”数十年来，他一直在研究这个构想。
如今，他与其他学者的理论，不仅暗示了黑洞内部可能存在的景象，甚至有望解开量子力学中最大谜题之一。或许这个看似天马行空的猜想，值得我们认真审视。
现代物理学的大厦由两大支柱支撑。量子理论描述粒子世界以及四种基本力中的三种；广义相对论则把剩下的引力解释为时空的弯曲。然而物理学几乎所有深层难题，都源于同一条裂痕：两套理论对现实运行方式的描述互不相容。
大体而言，物理学家猜想两套理论背后，存在一套更底层的统一规律。为探寻这个规律，科学家提出了弦理论等假说，引入了大量额外的空间维度。但很少有人认为，我们已经接近最终答案。
那么时间呢？乍看之下，阿尔伯特·爱因斯坦的相对论至少告诉我们：时间远比日常感受更加诡异。我们知道，距离与时长并不是世界固定不变的属性，而是和观测者的运动速度相关。两名以接近光速、不同速度飞驰的观测者，对于两件事件之间的距离、间隔时长会得出不同结论，而双方的观测结果都没有错误。
即便如此，爱因斯坦坚持认为，所有人共享同一个客观现实，而这一结论建立在光速不变原理之上。
