时间为何不同于其他维度？

Why is time different from other dimensions?

似乎所有人都知道时间的特殊性,但物理学——迄今最精密、最成功的科学怎么处理它?梳理2000多年来物理学的基本运动理论的发展,一个初步的脉络呈现在我们面前.亚里士多德认为时间维度与空间维度是互不影响的,空间维度可能更为重要——天上和地面的运动规律是不一样的.牛顿引入绝对时间与绝对空间的概念,在经典力学中时间维度是与空间维度地位平等的.牛顿提出三大运动定律以后,物理学的基本运动理论一分为三:爱因斯坦的(狭义)相对论力学、量子力学和演化力学.三个力学理论分别引入一个普适物理常数:真空中光速c、普朗克常数h和玻尔兹曼常数k,各自界定了对物理世界认识的一个极限:光速不变性、不确定性和不可逆性.对时间的认识也一分为三:量子力学基本沿用经典力学的时间概念;基于相对论,力学时间与空间统一了,可以在一定程度相互转换,但基本的时序是相对性不变的,时间与空间有所不同;基于热力学第二定律和耗散-涨落定理所代表的不可逆性,演化力学给予了时间一个特别地位.这些显然还不是最后答案.三种普适力学若是统一,以后时间的作用怎样?

Through the development of fundamental equation of motion in physics,from Aristotle,via Newton and Einstein,to present,it is clear that time is a special dimension.Currently there are three fundamental dynamical frameworks after Newton＇s classical mechanics：（special） relativistic mechanics,quantum mechanics and evolution mechanics.Each has brought a fundamental constant into physics： speed of light in vacuum c,Planck constant h,and Boltzmann constant k.At present there is no valid empirical evidence against the predictions from each of three fundamental mechanics.In this sense all three of them can be regarded as ＂universal dynamics＂.Each has also brought a limit on our quantitative description of Nature： invariance of light speed,uncertainty principle,and irreversibility.Two of those limits are explicitly related to time： the invariance of light speed and irreversibility：one is implicitly related to time： due to the uncertainty principle reversible quantum paths exist during a quantum process.In both quantum mechanics and evolution mechanics the time is of essentially of Newtonian type,though latter has explicitly embedded irreversibility as adopted from ＂the second law＂ of thermodynamics,because ＂the second law＂ is it＇s a special limit.In relativistic mechanics,though time and space can be transformed into each other,nevertheless such transformation is not arbitrary.Time ordering still has a strong physical meaning—specifically space-like,time-like,and light-like events are invariant under space-time transformation.Time may ultimately be related to an essential structure in Nature： causality,which we are far from a complete understanding.Similar to general relativity breaks down the philosophical belief of a prior or transcendental concept of space and time,it may be likely we are going to break another generally beholding concept of causal relation as a human construction,and time is ＂real＂.It is evident that we may be in the same position as physics before 1905： a profound conceptual consistent problem exists among those three fundamental mechanics.Maybe a unification of current three fundamental dynamical frameworks is a best route to gain deeper assessment on time and through a light on the consistent problem.Before such grand vision may be realized,there are a few smaller goals which appear within our immediately experimental exploration ability.The one-to-three classification of relativistic mechanics,quantum mechanics and evolution mechanics requires us to test its new experimental predictions,particularly those from evolution mechanics.Indeed,evolution mechanics predicts the existence of a new mathematical structure on stochastic integration,beyond the usual Ito and Stratonovich integration.In a small manner this choice of mathematical structure for stochastic processes in physics is similar to that of Euclidean vs.Riemannian geometry.Also,evolution mechanics predicts the existence of a relationship between the friction matrix and diffusion matrix as the accompanying property of the existence of Boltzmann-Gibbs distribution function.This relationship is an extension of the Einstein relation to nonlinear regime without detailed balance—a surprising simple relation.