時間是甚么?

時間是甚么?

本帖最後由 ye1928ye 於 11-4-2013 09:35 編輯

請李博仕談談''時間''.
過霍金的"時間簡史",一知半解.
第四維?
懇請李博仕詳细講觧一下,謝謝!
千祈咪落伍
時間就是金錢
A1a>=a1a>
本帖最後由 ye1928ye 於 3-4-2013 07:25 編輯

2# always9k  謝謝提點.
孺子难教.自願返回浅水池!
千祈咪落伍
pushhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh
Buy when there's blood in the streets, even if the blood is your own
三維是立體空間,舉例﹔你的位置是彌敦道(長)/太子道(濶)/十樓(高),如果加入時間-2013年4月10日下午3時-便構成一個四維空間的位置
skk
"What is time?" is too big a question that I think nobody dares to answer with complete confidence.

However, our understanding of time has progressed enormously since Einstein's proposal of the theory of relativity.

Basically, time is a number we record by a clock. A clock traces a trajectory in 4-dimensional spacetime, called a world line. A clock can measure the time lapse between any two events on its world line, it cannot measure the time lapse between two events not on its world line.

For flat spacetime, if a clock moves according to a geodesic (uniform motion), we can extend its valid region of measurement to the whole space by placing clocks everywhere, synchronizing them, and letting them move parallel to the original clock with the same speed. In this way we get a global inertial frame. A lot of interesting results in special relativity are based on this notion, for example, time dilation and length contraction.

When a clocks accelerates in a flat spacetime, there is no way to construct a global frame out of it, and we need to stick on its world line. This leads to resolution of twin paradox.

If there are huge mass and energy around, the spacetime is curved. One natural way to compare times recorded by clocks at different locations is via light signals. In this way one finds that time runs slower in a strong gravitational field. For example, time runs slower on the surface of the earth than at a satellite orbit. GPS has to take this effect into account, as well as the special-relativistic time dilation due to relative motion.

Our knowledge of time breaks down at the Big Bang and the singularity in black holes. There is so far no consensus on how to solve this problem. Hawking advocates the so-called Euclidean integral method, which can avoid the singularity by go to imaginary time. This method leads to his no-boundary proposal, which asserts that universes with a compact topology are most probable. His idea is not well-established and hasn't been verified yet. I personally don't like that he advocates his personal idea in popular science, in which I think only mainstream scientific results should appear.
A1a>=a1a>
6# always9k 謝謝你的回帖,我会重看幾遍的.
看後, 好像对''時間''这慨念有一点新的認知.
謝謝!
千祈咪落伍
本帖最後由 dick 於 17-4-2013 20:10 編輯

時間不是概念。
你會否有時不察覺時間呢?
過去、現在、將來。它夾著甚麼東西,運動。時間關涉著運動。他很快跑完一百呎;這件工作他需要多點時間完成。
最後,時間不屬於對象(觀察物)的。它是觀察者的表象。外界所有東西都要透過時時間、空間這個主觀者的表象,呈現給觀察者。
請你記著,時間與空間都屬於認知主體,沒有時、空你不能對外物認知。信嗎?
本帖最後由 ye1928ye 於 18-4-2013 04:05 編輯

8# dick 謝謝你的回帖,看了幾次,盡力去理觧,對''時間''一詞好像有新的認知.
但老實說,亦有點''玄之又玄''的感覺.
無論如何,仍希望有''宗教人仕''說說''时間''是甚麼?
千祈咪落伍