Earlier in this module, we came to understand how event horizons work by drawing an analogy to a fish falling over a waterfall. At a certain point in its descent, the falling fish can no longer communicate with its friend above because the water is flowing downwards at a greater speed than the speed of sound. Luckily, in the story, we rescued our fishy friend using a rocket pack. This was possible because the speed of sound is not a universal limit.
소리의 속도가 우주의 한계가 아니기 때문 소리의 지평선(sonic horizon)에서 탈출할 수 있었다.
The speed of light on the other hand is. Were we to drop our fishy friend into a real black hole, a rocket pack would be of little use because once you're beyond the event horizon of a real black hole, escape is no longer possible. But don't worry, no fish were harmed in the making of this course.
[중력에 의해 가속되는 폭포수를 블랙홀이 끌어 들이는 에너지로 비유해 봤다. 강력한 블랙홀이라면 가속된 속도가 빛의 속도를 넘을 수도 있지 않을까?] 빛의 속도는 우주의 한계속도다. 실제 블랙홀 이었다면 물고기는 탈출할 수 없다.
We also learned about a revolution in physics which began in the early 1900's. Einstein, in a single year and with four extraordinary papers, turned physics on its head. One of the results of these papers was that space and time are no longer absolutes and in their place was this amalgamation called space-time.
1900년대 초에 아인슈타 인이 발표한 네개의 논문으로 물리학을 완전히 뒤집어 놓았다. 이제 시간과 공간이 절대 적이지 않다.
In this framework, relative motion is what matters and many of our traditional notions about how the universe works no longer apply. Some truly weird things start happening like length contraction, time dilation, and relative simultaneity.
이체제를 시공간(spacetime)이라고 하자. 전통적인 물리학이 더이상유효하지 않다. 빛의 속도는 우주의 상수 이며 빠른 속도로 움직이는 기준 관성 좌표계는 시간의 지연과 거리의 단축을 격게 된다. 그로 인해 '동시성'도 상대적이 된다.
When Einstein went about generalizing his theory of relativity, he realized that there ought to be an equivalence between gravitational fields and the acceleration of a reference system, meaning, if we stuff you in a windowless rocket, you can't tell the difference between a rocket sitting at rest on the surface of the earth or a rocket that is accelerating uniformly upwards at a rate equal to the acceleration due to gravity on Earth's surface.
Under these two conditions, the two are indistinguishable. In addition, general relativity comes with its own quirks, one of which being that mass deforms space-time.
가속에 의해 작용하는 힘과 질량에 의한 중력이 같다는 등가의 원리를 제시하고 이를 일반화한 일반 상대론을 펼쳤다. 질량이 시공간을 왜곡 시킨다.
This is what causes the effect known as gravitational lensing, something not exclusive to black holes but something they are nonetheless known for, that is their ability to bend light rays. In the next module, we'll explore black holes in more detail and learn how to weigh a black hole.
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