物理抽象概念

1、物理抽象概念最廣泛被接受關(guān)于時間的物理理論是愛因斯坦的相對論。在相對論中，時間與空間一起組成 四維時空，構(gòu)成宇宙的基本結(jié)構(gòu)。時間與空間都不是愛因斯坦愛因斯坦絕對的，觀察者在不同的相對速度或不同時空結(jié)構(gòu)的測量點，所測量到時間的流逝是不同的。 廣義相對論預(yù)測質(zhì)量產(chǎn)生的重力場將造成扭曲的時空結(jié)構(gòu)，并且在大質(zhì)量（例如：黑洞）附 近的時鐘之時間流逝比在距離大質(zhì)量較遠(yuǎn)的地方的時鐘之時間流逝要慢。現(xiàn)有的儀器已經(jīng)證 實了這些相對論關(guān)于時間所做精確的預(yù)測，并且其成果已經(jīng)應(yīng)用于全球定位系統(tǒng)。另外，狹 義相對論中有“時間膨脹”效應(yīng)：在觀察者看來，一個具有相對運動的時鐘之時間流逝比自 己參考系的（靜止的）時鐘之時間流

2、逝慢。就今天的物理理論來說時間是連續(xù)的，不間斷的，也沒有量子特性。但一些至今還沒有被證 實的，試圖將相對論與量子力學(xué)結(jié)合起來的理論，如量子重力理論，弦理論，M理論，預(yù) 言時間是間斷的，有量子特性的。一些理論猜測普朗克時間可能是時間的最小單位。史提芬霍金（Stephen W. Hawking）史提芬霍金（Stephen W. Hawking）根據(jù)史提芬霍金（Stephen W. Hawking）所解出廣義相對論中的愛因斯坦方程式，顯示宇 宙的時間是有一個起始點，由大霹靂（或稱大爆炸）開始的，在此之前的時間是毫無意義的。 而物質(zhì)與時空必須一起并存，沒有物質(zhì)存在，時間也無意義。時間定義：人類在生活中

3、總結(jié)出時間的觀念，其根源來自于日常生活中事件的發(fā)生次序。當(dāng) 然人們在生活中得到的絕不僅僅是事件發(fā)生次序的概念，同時也有時間間隔長短的概念，這 個概念來源于對兩個過程的比較一一比如兩件事同時開始，但一件事結(jié)束了另一件事還在進(jìn) 行，我們就說另一件事所需的時間更長。這里我們可以看到，人們運用可以測量的過程來測 量抽象的時間。在物理學(xué)中也是類似，時間是通過物理過程來定義的，首先在一個參考系（要求是慣性系， 或者是非慣性系，但過程發(fā)生的空間范圍無窮?。┲?，取定一個物理過程，設(shè)其為時間單位， 然后用這個過程和其他過程比較，以測定時間。但測量時間（即上述比較過程）必須有同時性概念。過程開始有一個同時性問題，

4、過程結(jié)束 也有一個同時性問題最簡單的例子：我們要求運動員在發(fā)令槍開槍同時起跑，同時計時 員開始計時，并在運動員抵達(dá)終點線時計時員必須同時停止計時。這個問題具體見各類相對論書籍。同時性問題，使得古典牛頓力學(xué)、狹義相對論和廣義相對 論有著不同的“時間”。直觀概念告訴我們：任何人在事件是否同時上是可以達(dá)成一致意見 的（也許某些人會欺騙別人，造成類似偵探小說或政治小說中的情形，不過這是人類“高智 商”的表現(xiàn)，我們完全可以用測量用的儀器來代替：），所以我們之后不說人，而說觀察者） 在相對論中，觀察者的運動狀態(tài)引起同時性的變化，或者說觀察者1以v1運動，認(rèn)為同時 的兩件事，以v2運動的觀察者2可能會認(rèn)為不

5、同時一一這導(dǎo)致時間測量的相對性。從數(shù)學(xué)上說，古典牛頓力學(xué)中時間參數(shù)只有一個，所有參考系共享此時間參數(shù)。這其實就是 假設(shè)所有參考系，所有空間位置可以共享同一個同時性定義。而狹義相對論認(rèn)為不同參考系就不同時了，即不同參考系有各自的時間參數(shù)t，其間關(guān)系由 洛倫茲變換決定。廣義相對論認(rèn)為不同地點也會不同時，廣義相對論中關(guān)于時間有比較復(fù)雜 的內(nèi)容，參見廣義相對論書籍。當(dāng)然請注意：嚴(yán)格說這不是簡簡單單的“認(rèn)為”，而是基于兩個假設(shè)：狹義相對論是光速不 變原理。廣義相對論是引力本質(zhì)為時空彎曲等。而這兩個假設(shè)得到了實驗的廣泛驗證。 上面我們說完了時間間隔測量的問題。但前面也提到：時間的先后次序是人們在日常生活中

6、 對時間的第一印象。古典牛頓力學(xué)中，這一點很容易理解：我們有唯一的時間參數(shù)t，所以 任意兩事件（一個發(fā)生在t1，另一個發(fā)生在t2）也就有確定的先后次序。那么相對論中呢？ 相對論中同地兩事件先后順序的確定的，這可以從洛倫茲變換直接看出。但可以肯定，相對 論中不同地兩事件的先后次序也是隨參考系（我很愿意這么說：儀器的運動狀態(tài)不同，這樣 能夠把事情的本質(zhì)說出來）不同而不同的。但這里就有一個問題：會不會有可能在參考系1 中事件a先于事件b發(fā)生，且事件a的發(fā)生影響了事件b的發(fā)生（最極端的情況，使得b 無法發(fā)生，譬如一個孩子殺死了他年輕的祖父），而在參考系2中正好反過來？如果是這樣， 物理學(xué)乃至一切原理中

7、最重要的一個基本原理一一因果律將轟然倒塌。所以這個問題是非常 重要的。讓我們嚴(yán)格敘述這個問題：事件a發(fā)生，并發(fā)出信號（廣義的信號，涵蓋一切可以 影響到b的方式，但由于a，b不同地，這個信號就需要一定時間的傳播），影響b。另一個 參考系中正好相反。值得慶幸的是：可以用洛倫茲變換證明，只要信號速度不超過光速（最 多使用光，光速），信號就不可能先于b的發(fā)生傳遞到b所在位置。另外說一句：狹義的另一個假設(shè)：任何物理系中物理定律有著相同形式，也是廣義相對論所 服從的。換句話說，參考系1中對一個物理過程加以測量，得到I1=v1t1。參考系2中加以 測量同樣也會得到I2=v2t2，盡管可能11，v1，t1和1

8、2, v2, t2都不相等。當(dāng)然嚴(yán)格說這個 例子不合適，因為v的定義位置矢量導(dǎo)數(shù)。但是對一些復(fù)雜的物理學(xué)定律，如麥克斯韋方程 組，這個假設(shè)就很重要了。時間箭頭自古以來人類就知道時間是不可逆的，人出生，成長，衰老，死亡，沒有反過來的。玻璃瓶 掉到地上摔破，沒有破瓶子從地上跳起來合整的。從經(jīng)典力學(xué)的角度上來看，時間的不可逆 性是無法解釋的。兩個粒子彈性相撞的過程順過來反過去沒有實質(zhì)上的區(qū)別。時間的不可逆 性只有在統(tǒng)計力學(xué)和熱力學(xué)的觀點下才可被理論地解釋。粗略地說，熱力學(xué)第二定律說在一 個封閉的系統(tǒng)中（我們可以將宇宙看成是最大的可能的封閉系統(tǒng)）熵只能增大，不能減小。 宇宙一直在朝熵增大的方向演化，這

9、給出了宏觀的時間箭頭。下面說說時間箭頭。在以上的討論中，我們從時間間隔和先后次序兩方面討論了時間，卻忽 略了時間很重要的一個特性：時間箭頭。子曰：逝者如斯夫，不舍晝夜。人生百年，逝去就 沒有重生的余地。但覆水難收的又何嘗僅僅是人生！物理學(xué)理論告訴我們：凡是與熱現(xiàn)象相 關(guān)的物理過程，都是不可逆的。這里的不可逆，不是絕對意義上的不可恢復(fù)，而是說：這些 物理過程產(chǎn)生的結(jié)果不可能在不造成其他影響的情況下完全恢復(fù)。這就是大名鼎鼎的熱力學(xué) 第二定律。下面給出兩個熱力學(xué)第二定律的表述：低溫?zé)嵩床豢赡軐崃孔园l(fā)傳遞給高溫?zé)嵩矗ɑ虿豢赡軓牡蜏責(zé)嵩磳崃總鬟f給高溫?zé)嵩矗?并不產(chǎn)生其他變化）時間的表現(xiàn)時間的表現(xiàn)不可

10、能從單一熱源吸熱完全轉(zhuǎn)化為機(jī)械功，并不引起其他任何變化?？梢宰C明兩表述等價。后一個表述有明顯的工程痕跡這來源于對蒸汽機(jī)一類將熱轉(zhuǎn)化為 功的工程機(jī)械的研究。這些研究大都與當(dāng)時那個工業(yè)革命的時代相聯(lián)系，在今天已經(jīng)沒有太 多純理論的價值，但卻有一種東西，雖然主流研究已經(jīng)基本絕跡，還是有非專業(yè)學(xué)者前仆后 繼地加以研究，那就是第二類永動機(jī)。第二類永動機(jī)是這樣一種機(jī)器一一給它一定能量，讓 它開始運行，接下來它可以將由于摩擦等耗散因素耗散掉的能量全部吸收，接著再將這些能 量投入回機(jī)械的能量循環(huán)。這樣的一個永動機(jī)如果造出，就意味著我們有辦法用今天開采出 的能源維持機(jī)械的永恒運動（因為一切耗散掉的能量都可以重新

11、利用），使得世界以現(xiàn)今的 能耗速度運行到世界末日！但熱力學(xué)第二定律很明確地告訴我們：這是不可能的。耗散掉的 能量（內(nèi)能）絕不能完全轉(zhuǎn)化為耗散前的形式（機(jī)械功），這破壞了無論古典牛頓力學(xué)還是 相對論中的，基本原理的無時間方向性。那么這是為什么呢？ 熵為了理解這一點，我們必須引入熵的概念。由于在經(jīng)典熱力學(xué)中，引入熵的概念需要很多技 術(shù)性內(nèi)容，這里不加贅述，可以參見任何熱學(xué)教本。這里只給出熵的一個性質(zhì)：任何絕熱（也 就是孤立，不被外界所影響）熱力學(xué)過程，只要初始狀態(tài)和末態(tài)是平衡態(tài)（經(jīng)典熱力學(xué)中熵 對平衡態(tài)才能定義，對于這一點的誤解，曾導(dǎo)致了熱寂說），末態(tài)的熵一定大于初態(tài)的熵。 簡單說，孤立體系向著熵

12、增加的方向發(fā)展。注意，一般熱學(xué)書中會說：不可逆絕熱過程熵增， 可逆絕熱過程熵是不變的。但其實可逆過程不是真實存在的過程一一真實存在的宏觀過程， 只要其中分子有熱運動，過程就是不可逆的。（在超流等現(xiàn)象中，存在可逆宏觀過程，但這 時超流部分沒有熱運動）但熵究竟是什么？玻爾茲曼用一個公式告訴了我們S=klnw，其中k為常數(shù)，w為熱力學(xué)概率 （關(guān)于物質(zhì)的分子、原子運動的量，在經(jīng)典熱力學(xué)的情況表征體系混亂程度的量）。他用統(tǒng) 計方法證明了，平衡態(tài)下這個公式給出了前面所說的熵。也就是說，在經(jīng)典熱力學(xué)的意義下， 熵意味著事物朝混亂的方向發(fā)展。當(dāng)然需要指出的是，并非所有情況下，這種發(fā)展都可以稱 之為“混亂”。比

13、如宇宙從遠(yuǎn)古的濃湯狀態(tài)演化到現(xiàn)今的星系結(jié)構(gòu)。Physical abstractionThe most widely accepted theory about the time of the physical is Einsteins theory of relativity.In the theory of relativity, time and space to make up the four-dimensional space-time, constitute the basic structure of the universe. Time and space are not Ei

14、nsteinEinsteinAbsolute, and the observer at different relative speeds or different spatial and temporal structure of the measuring point, the measured lapse of time is different. General relativity predict the quality of the gravity field will distort the space-time structure, and in the large mass

15、（for example: a black hole） near the clock time goes by slower than clock time in places farther distance massive passage of time. Existing instruments have confirmed these relativistic done about the time accurate predictions, ,and the results have been applied to the Global Positioning System. In

16、addition, the special theory of relativity, time dilation effect: the observer, a clock of the relative motion of the clock of the passage of time than their reference system （still） the slow passage of time.Physical theory is a continuous, uninterrupted, there is no quantum properties. But has yet

17、to be confirmed, trying to combine the theory of relativity and quantum mechanics, quantum theory of gravity, string theory, M theory, prophecy time discontinuous quantum properties. Some theoretical speculation that the Planck time might be the smallest unit of time.Steven Hawking （Stephen W. Hawki

18、ng）Steven Hawking (Stephen W. Hawking)According to Einsteins equations of general relativity Steven Hawking (Stephen W. Hawking) solution, the time of the universe is a starting point, or by the Big Bang (Big Bang) began this Time is meaningless. The material time and space, must work together to co

19、-exist, there is no material existence, time is meaningless.Time Definition: human life summed up the concept of time, from its roots in the order of occurrence of the events of daily life. Of course, people get more than just an event in life occurs concept of order, but also the concept of interva

20、l length, this concept comes from the comparison of the two processes - such as two things at the same time, but one thing to the end The other thing is still going on, we say another thing needed for a longer time. Here we can see that people can measure measuring abstract time.Is also similar in p

21、hysics, time is defined by physical processes, first of all, in a reference system (requirements inertial system, or a non-inertial reference frame, but the spatial extent of the process occurs infinitely small), whichever is given a physical process, set its unit of time, and then use this process

22、and other processes compared to the measurement time.Measuring time (i.e., the above-mentioned comparison process) must have the concept of simultaneity. The process begins with a simultaneous end of the process, a simultaneity problem -the most simple example: We require athletes starting at the sa

23、me time the starting gun shot, simultaneously begin timing timekeeper, and athletes arrive at the finish line timekeeper must stop timing.The this specific see all kinds of relativistic books. Issues, classical Newtonian mechanics, special relativity and general relativity has a different time. Intu

24、itive concept tells us: anyone in the events are on can agree on (maybe some people will deceive others, resulting in similar detective novels or political novel situations, but this is the performance of mankind highly intelligent We measurement instrument can use instead :), so we do not say, say

25、observers) caused by simultaneous changes in the theory of relativity, the state of motion of the observer or observers v1 movement that while two things, the v2 sports observer may not at the same time - which led to a relative time measurement.Mathematically speaking, the time parameters of classi

26、cal Newtonian mechanics is only a reference system to share this time parameter. In fact, this is the assumption that all reference systems, all the spatial location can share the same simultaneity defined.And the special theory of relativity that different reference system is not at the same time,

27、different reference systems each time parameter t, during which the relationship is determined by the Lorentz transformation. General relativity that different locations will not at the same time, about the time in general relativity complex, HYPERLINK , see the books of the general theory of relati

28、vity.Course Note: Strictly speaking, this is not simple, think, but is based on two assumptions: the special theory of relativity is the speed of light the same principle. General relativity is gravitational nature of time and space bending. These two assumptions have been extensive verification of

29、the experiment.Above finished the interval measurement problem. But also mentioned earlier: the priorities of the time, people in their daily lives, the first impression of the time. Classical Newtonian mechanics, which is easy to understand: we have only the time parameter t, so any two events occu

30、rred at t1 (a, another t2) will determine priorities. So the theory of relativity? The order determined by the theory of relativity in the same place in both events, which can be seen directly from the Lorentz transformation. To be sure, however, that the theory of relativity in a different manner a

31、nd the sequence of events is also with the reference system (I am willing to say: the state of motion of the instrument, so that the nature of the matter to say it) vary. But here there is a question: will likely reference system in the event a b occur prior to the event, and the event of the occurr

32、ence of a impact (the most extreme circumstances of the occurrence of the event b such that b can not occur, such as a child killed his young grandfather), while the reference system just turn? If this is the case, the most important physics even all principle a basic principle - the law of causalit

33、y collapsed. Therefore, this problem is very important. Let rigorous description of this problem: Event occurs, and send a signal (a generalizeds signal covers everything that can affect the way to b, a, b to the signal you need a certain time of dissemination), HYPERLINK , affecting b. Another refe

34、rence system is the opposite. The good news is: can prove with a Lorentz transformation, as long as the signal speed does not exceed the speed of light (up to the light, the speed of light), the signal can not be prior to the occurrence of b passed to the b location.Also to say: the narrow sense ano

35、ther assumption: any of the Department of Physics of the laws of physics have the same form, but also the general theory of relativity obey. In other words, the reference system of a physical process to be measured, to give L1 = v1t1. The reference system will be measured in the same get l2 = v2t2,

36、despite the possibility of l1, v1, t1 and l2, v2, t2 are not equal. Of course, strictly speaking, this case is not appropriate, because the definition of the position of the v vector derivative. But the complex laws of physics, such as the Maxwell equations, this assumption is very important.Arrow o

37、f timeSince ancient times, humans have know time is irreversible, birth, growth, aging, death, and did not turn. The bottles dropped smashes, no broken bottles together the whole jump up from the ground. From the point of view of classical mechanics point of view, the irreversibility of time can not

38、 be explained. Elastic collision of two particles smooth over the reversal of the past no practical difference. The irreversibility of time is available only in the point of view of statistical mechanics and thermodynamics theory to explain. Roughly speaking, the second law of thermodynamics in a cl

39、osed system (the universe as the largest closed system) entropy can only increase, not decrease. The evolution of the universe has been moving in the direction of entropy increase, which gives the macroscopic arrow of time.Here to talk about the arrow of time. In the above discussion, we discussed t

40、he time, from the time interval and priorities while ignoring the very important characteristics: the arrow of time. Confucius said: ,lost time, around the clock. Life for centuries, the dead would be no room for rebirth. But is it just spilled a life! Physics theory tells us that: all physical proc

41、esses related thermal phenomena are irreversible. Irreversible unrecoverable, not in an absolute sense, but rather that: the result of these physical processes is not possible in the case of do not otherwise affect full recovery. This is the famous second law of thermodynamics.Here are two of the se

42、cond law of thermodynamics expressed:Low heat source is impossible to heat spontaneously passed to the high temperature heat source (or impossible from a low temperature heat source to transfer heat to the high temperature heat source, does not produce other changes) Time performanceTime performance

43、2 impossible from a single heat source endothermic completely converted into mechanical work, and does not cause any other changes.You can prove equivalence of two expressions. After a representation there are obvious signs of engineering - this comes from a class steam engine heat into power engine

44、ering machinery. Most of these studies linked to the era of the industrial revolution at that time, not too pure theory of value in today, but there is one thing, although the mainstream research has basically disappeared, or non-professional scholars fought to be studied, and that is the first The

45、two types of perpetual motion. The second type of perpetual motion machine is such a machine - a certain energy to it, it began to run, HYPERLINK , then it can be due to friction and other dissipative factors dissipate the energy of all the absorption can then back to mechanical energy input energy

46、cycle. If you create a perpetual motion, it means that we have to maintain the perpetual motion of the mechanical (because all the energy is dissipated can re-use), making the world run to the energy consumption rate mined todays energy end of the world! But the second law of thermodynamics tells us

47、 very clearly: this is impossible. Dissipated energy (internal energy) must not be completely converted to the form before the dissipation (mechanical work), which destroys Whether classical Newtonian mechanics or relativity, the basic principles of the direction of time. So this is why?EntropyTo understand this, we must introduce the concept of entropy. Need a lot of technical content in classical thermodynamics, ,the introduction of the concept of entropy, without repeat, can see any thermal