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It's about time 黃心穎 returns for cameo appearances 


"It's about time" and "黃心穎 returns for cameo appearances" are 2 separate topics.
For those who missed watching the show, 黃心穎 took time off from searching for the fictitious 挪威的森林蛋糕 and returned in cameo appearances as 魯賓穎。 On to "about time"... For most of us, knowing "when to meet our friends where" is all we need to know about time and space. What more are there to know about time and space? 

We have no idea where time comes from. We don't know if it has a start or an end. Time seems so abstractive as we have not been able to detect it through our five senses. We conveniently use time for tagging events such as "Getting up at 6, lunch at noon and then 八時入席。" We also use time for specifying the duration of events such as "Keep an egg in boiling water for 5 minutes for a soft boiled egg."
How long is 5 minutes? "300 seconds," someone quickly responded. How do we count a second? In grossly simplified terms, by counting 9,192,631,770 cycles (~9 billions) of transitions between two energy levels of the caesium133 atom (Cs133, 銫133.) Through understanding of quantum theory, (but in a substantially technical language,) that is roughly how "a second" is defined by the International System of Units (SI, 國際單位制。) 

Psychologically, "Time flies when you are having fun." In reality (or in relativity theory,) time, as defined, is not able to speed up but can slow down only.
(1) One condition that time may slow down is when subjected to gravitational force. Gravity weights on the atomic activities of the caesium clock (and that of everything else, including Abe's senses.) This means, on a "massive" (with high gravitational pull) planet, Abe holding a clock would see his clock running normal. However, Bea, far away from the influence of that planet, checking against her clock, notices Abe's clock is running slow, and, Abe is acting sluggish and not aging as fast. This phenomenon is known as Gravitational Time Dilation. (Time being stretched and thus taking longer to make a clock tick.) 

(2) The other condition is when Abe is traveling at a constant velocity relative to an observer, Bea, for instance. Bea measures time by bouncing a flash of light left and right between mirrors placing next to her. Knowing the speed of light and the spacing between the mirrors, Bea is able to measure time by calculating the elapse time for the light to bounce between the mirrors. As Abe passes by Bea, Bea hands over the mirror set to Abe. Bea then repeats the measurement with the mirror set now traveling with Abe. Bea observes, in addition to bouncing between the mirrors, the light also has to move along with Abe. The light is now taking a longer travel path than before. Since the speed of light (in vacuum) is universally constant, the longer light path means Bea now measures a longer elapse time between light bounces. From Bea's perspective, the clock with Abe is taking more time to make a tick than when the clock was with her, or, time with Abe is elapsing slower.


Much like watching another train passing by when looking out the window of a smooth riding train, a rider cannot tell which train is the moving one. As long as the relative movement between Abe and Bea are at constant velocity, neither one could tell if one or both are moving. Thus, conversely, from Abe's perspective, Bea could be the one traveling relative to him. Hence, from Abe's perspective, Bea's clock is the one that is running slow.
With relative movements at constant velocity, both persons see the time with the other person is elapsing slower. This phenomenon is known as Relative Velocity Time Dilation. 

What about space (空間，不單是指太空)? With the turning of your head, you can see with your eyes where things are located. With your palm, you can feel the size difference between an iPhone 8 and an iPhone 8 Plus. Ironically, measurement of a meter of length relies on something rather abstract... Time. The SI definition of a meter is the length of the path traveled by light in vacuum during a time interval of 1/299,792,458 (~300 millionth) of a second. (This definition of length is a reflection of the exact speed of light in vacuum, which is the same for all regardless if a person is moving or at rest.) The proper way to measure the distance between points is by measuring the elapse time for light to travel from one point to another outside the influence of gravity.


Do you see the irony? The measurements of the physical space actually relies on the measurements of the abstractive time. Recall the Relative Velocity Time Dilation example earlier, it turns out Abe is traveling from X to Y. Bea may measure the distance between X and Y by measuring the elapse time for Abe to make a round trip from X to Y then back to X. Using the traveling speed reported by Abe, Bea would be able to calculate the distance between X and Y.
Abe would do the same calculation, but, with the clock traveling with him. As mentioned earlier under Relative Velocity Time Dilation, Abe's clock is running slow relative to Bea's clock that is stationary relative to X and Y. Abe would measure a smaller elapse time because of his slower clock. Consequently, Abe would calculate a smaller distance between X and Y with his smaller elapse time measurement. This phenomenon is known as Space Contraction or Length Contraction (along the dimension of motion.) 

As physical as it may seem, the length of an object, or, the spacing between objects, are not universal. Ade and Bea could obtain different length measurements for the same object. (And, neither one is incorrect, by the definitions of time and space.)
We thought the earth was flat. We were wrong. We thought the earth was the center of the solar system. We were wrong. We thought the physical space is absolute. We are not too sure. ¯\_(ツ)_/¯ 

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