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The arrow of time, also called time's arrow, is the concept positing the "one-way direction" or "asymmetry" of time. It was developed in 1927 by the British astrophysicist Arthur Eddington, and is an unsolved general physics question. This direction, according to Eddington, could be determined by studying the organization of atoms, molecules, and bodies, and might be drawn upon a four-dimensional relativistic map of the world ("a solid block of paper").

The arrow of time, also called time's arrow, is the concept positing the "one-way direction" or "asymmetry" of time. It was developed in 1927 by the British astrophysicist Arthur Eddington, and is an unsolved general physics question. This direction, according to Eddington, could be determined by studying the organization of atoms, molecules, and bodies, and might be drawn upon a four-dimensional relativistic map of the world ("a solid block of paper").

'''<font color="#ff8000"> 时间之箭The arrow of time</font>'''是一种概念，假定时间是“单向方向”或“不对称”的。此概念于1927年由英国天体物理学家亚瑟·爱丁顿提出的一个普通物理学问题，至今尚未解决。按照爱丁顿的说法，研究原子、分子和物体的组织可以确定时间的方向，也可以绘制在一张四维的相对论世界地图上(“一整块纸”)。  

'''<font color="#ff8000"> 时间之箭The arrow of time</font>'''是一个假定时间是“单向方向”或“不对称”的概念。此概念于1927年由英国天体物理学家亚瑟·爱丁顿提出的一个普通物理学问题，至今尚未被解决。按照爱丁顿的说法，研究原子、分子和物体的组织既可以确定时间的方向，又可以把它绘制在一张四维的相对论世界地图上(“一整张纸”)。  

<ref>{{cite book|title=The scientist as philosopher: philosophical consequences of great scientific discoveries

<ref>{{cite book|title=The scientist as philosopher: philosophical consequences of great scientific discoveries

<ref>{{cite book|title=The scientist as philosopher: philosophical consequences of great scientific discoveries

<ref>{{cite book|title=The scientist as philosopher: philosophical consequences of great scientific discoveries

【书籍：The scientist as philosopher: philosophical consequences of great scientific discoveries《作为哲学家的科学家: 伟大科学发现的哲学后果》】

【书籍：The scientist as philosopher: philosophical consequences of great scientific discoveries《作为哲学家的科学家: 伟大科学发现的哲学影响》】

|first1=Friedel

|first1=Friedel

Physical processes at the microscopic level are believed to be either entirely or mostly time-symmetric: if the direction of time were to reverse, the theoretical statements that describe them would remain true. Yet at the macroscopic level it often appears that this is not the case: there is an obvious direction (or flow) of time.

Physical processes at the microscopic level are believed to be either entirely or mostly time-symmetric: if the direction of time were to reverse, the theoretical statements that describe them would remain true. Yet at the macroscopic level it often appears that this is not the case: there is an obvious direction (or flow) of time.

人们通常认为，微观层面上的物理过程认为是全部或部分时间对称的: 如果时间的方向逆转，描述它们的理论仍然正确。然而，在宏观层面上，情况往往并非如此， 时间存在明显的方向(或流动)。

通常，人们认为，微观层面上的物理过程是全部或部分时间对称的: 即使时间的方向逆转，描述它们的理论仍然正确。然而，在宏观层面上，情况往往并非如此， 时间存在明显的方向(或流动)。

The symmetry of time (T-symmetry) can be understood simply as the following: if time were perfectly symmetrical, a video of real events would seem realistic whether played forwards or backwards. Gravity, for example, is a time-reversible force. A ball that is tossed up, slows to a stop, and falls is a case where recordings would look equally realistic forwards and backwards. The system is T-symmetrical. However, the process of the ball bouncing and eventually coming to a stop is not time-reversible. While going forward, kinetic energy is dissipated and entropy is increased. Entropy may be one of the few processes that is not time-reversible. According to the statistical notion of increasing entropy, the "arrow" of time is identified with a decrease of free energy.<ref>{{cite journal

The symmetry of time (T-symmetry) can be understood simply as the following: if time were perfectly symmetrical, a video of real events would seem realistic whether played forwards or backwards. Gravity, for example, is a time-reversible force. A ball that is tossed up, slows to a stop, and falls is a case where recordings would look equally realistic forwards and backwards. The system is T-symmetrical. However, the process of the ball bouncing and eventually coming to a stop is not time-reversible. While going forward, kinetic energy is dissipated and entropy is increased. Entropy may be one of the few processes that is not time-reversible. According to the statistical notion of increasing entropy, the "arrow" of time is identified with a decrease of free energy.<ref>{{cite journal

'''<font color="#ff8000"> 时间对称性The symmetry of time</font>'''可以简单地理解为: 如果时间是完全对称的，那么一段真实事件的视频，无论从前往后播放还是从后往前播放，都会显得很真实。例如，重力是一种时间可逆的力。一个球被抛起，减速到停止，然后下降，在这种情况下正放和倒放看起来同样真实。该系统具有'''<font color="#ff8000"> 时间对称性The symmetry of time</font>'''。然而，球反弹并最终停止的过程是不可逆的。在前进过程中，动能耗散，熵增加。熵可能是少数几个处于时间不可逆的过程之一。根据熵增的统计概念，时间的“箭头”被确定为自由能的减少。

'''<font color="#ff8000"> 时间对称性The symmetry of time</font>'''可以简单地理解为: 如果时间是完全对称的，那么一段真实事件的视频，无论从前往后播放还是从后往前播放，都会显得很真实。例如，重力是一种时间可逆的力。一个球被抛起，然后下降、减速直至停止，在这种情况下正放和倒放看起来同样真实。该系统具有'''<font color="#ff8000"> 时间对称性The symmetry of time</font>'''。然而，球反弹并最终停止的过程是不可逆的。在前进过程中，动能耗散，熵增加。熵可能是少数几个处于时间不可逆的过程之一。根据熵增的统计概念，时间之箭被确定为自由能的减少。

<ref>{{cite journal| author=Tuisku, P. |author2=Pernu, T.K. |author3=Annila, A. | title=In the light of time

<ref>{{cite journal| author=Tuisku, P. |author2=Pernu, T.K. |author3=Annila, A. | title=In the light of time