展示時間對稱性蹺蹺板
它最後將導向何方？？
物理系統的『時間對稱性』T-symmetry，是說『物理定律』在『時間反向變換』time reversal transformation 
下保持不變。比方說『牛頓第二運動定律』 ![\vec{F} = m \frac{d}{d[-t]} \frac{d}{d[-t]} \vec{r} = m \frac{d}{dt} \frac{d}{dt} \vec{r}](http://www.freesandal.org/wp-content/ql-cache/quicklatex.com-fb0feeef88a994b9773cc30a9c7e7a6a_l3.png "Rendered by QuickLaTeX.com")
具有『時間對稱性』。假使一個粒子從『初始態』 
沿著軌跡往『終止態』 
運動，如果『時間逆流』，此粒子將逆向由『終止態』 沿著軌跡向『初始態』 運動。
於是在『理化系統』中，就有了『微觀可逆性』原理︰
Corresponding to every individual process there is a reverse process, and in a state of equilibrium the average rate of every process is equal to the average rate of its reverse process.
。然而這個『微觀可逆性』原理，到了『巨觀世界』後，卻是與『熱力學』的『最大熵』 Maximum entropy 理論衝突。一八七二年時，玻爾茲曼提出了『 H 理論』︰
![H(t) = \int \limits_0^{\infty} f(E,t) \left[ \log\left(\frac{f(E,t)}{\sqrt{E}}\right) - 1 \right] \, dE](http://www.freesandal.org/wp-content/ql-cache/quicklatex.com-5c2388f11732c013df3a0d6c7767f6e3_l3.png "Rendered by QuickLaTeX.com")
，此處 
就是在 
時間的『能量分布』函數，而那個 
是『動能』在 
與 
間之『粒子數』。據聞，玻爾茲曼是想用著『統計力學』的辦法，能夠推導出『最大熵』 
的『不可逆性』。
馬克士威妖
可以如是描述成︰假使一個絕熱容器被分成兩塊，中間有『妖』所控制之『門』，那個容器中的『粒子』到處亂撞時，總會碰到『門』上，此『妖』喜歡將『快‧慢』之『粒子』分別為『兩半』，因此，其中的一半就會比另外一半的『溫度』要高。
由於更早五年前，『馬克士威』設想了一個『想像實驗』︰
… if we conceive of a being whose faculties are so sharpened that he can follow every molecule in its course, such a being, whose attributes are as essentially finite as our own, would be able to do what is impossible to us. For we have seen that molecules in a vessel full of air at uniform temperature are moving with velocities by no means uniform, though the mean velocity of any great number of them, arbitrarily selected, is almost exactly uniform. Now let us suppose that such a vessel is divided into two portions, A and B, by a division in which there is a small hole, and that a being, who can see the individual molecules, opens and closes this hole, so as to allow only the swifter molecules to pass from A to B, and only the slower molecules to pass from B to A. He will thus, without expenditure of work, raise the temperature of B and lower that of A, in contradiction to the second law of thermodynamics.
也就有人『Johann Loschmidt』反對玻爾茲曼的『 H 理論』之說法︰if there is a motion of a system from time t0 to time t1 to time t2 that leads to a steady decrease of H (increase of entropy) with time, then there is another allowed state of motion of the system at t1, found by reversing all the velocities, in which H must increase. This revealed that one of Boltzmann’s key assumptions, molecular chaos, or, the Stosszahlansatz, that all particle velocities were completely uncorrelated, did not follow from Newtonian dynamics.
這件事，聽說是由有『熱力學之父』之稱的『卡爾文男爵威廉‧湯姆森』 ── 絕對溫標的創造者 ── 最早所說的。其後一九二八年『 愛丁頓』在《The Nature of the Physical World》說到了現今大眾所知『時間之箭』一詞︰ Let us draw an arrow arbitrarily. If as we follow the arrow we find more and more of the random element in the state of the world, then the arrow is pointing towards the future; if the random element decreases the arrow points towards the past. That is the only distinction known to physics. This follows at once if our fundamental contention is admitted that the introduction of randomness is the only thing which cannot be undone. I shall use the phrase ‘time’s arrow’ to express this one-way property of time which has no analogue in space.
之後美國物理學家 Edwin Thompson Jaynes ，一生始終致力於推動『機率就是邏輯之擴展』，在他百年後，二零零三年， G. Larry Bretthorst 受其請託編輯了《Probability Theory: The Logic of Science 》一書，起頭其中有一段說︰
The thinking computer
Models have practical uses of a quite different type. Many people are fond of saying, “They will never make a machine to replace the human mind – it does many things which no machine could ever do.” A beautiful answer to this was given by J. von Neumann in a talk on computers given in Princeton in 1948, which the writer was privileged to attend. In reply to the canonical question from the audience (‘But of course, a mere machine can’t really think, can it?’), he said: You insist that there is something a machine cannot do. If you will tell me precisely what it is that a machine cannot do, then I can always make a machine which will do just that! In principle, the only operations which a machine cannot perform for us are those which
we cannot describe in detail, or which could not be completed in a finite number of steps.
也許到底『機率』是什麼？還有得說吧！！