One of the foundational principles of special relativity is that light always travels at the same constant speed. The speed of light is fast, but it still takes 8.3 minutes to travel the enormous distance from the Sun to the Earth. This means that if the sun were just suddenly change brightness, there would be a delay of 8.3 minutes before we would see the change here on Earth.
특수 상대론의 주장중 하나가 빛의 속도는 불변이다. 태양에서 불발한 광자가 지구에 도착하는데 8.3분 걸린다.
Suppose that powerful aliens with advanced technology managed to change the Sun's gravity, maybe by removing a big blob of hot gas.
어느 발전된 외계인이 태양의 가스 일부를 날려버렸다고 하자.
Removing the gas also causes the Sun to dim at the same time. If we calculate the gravitational traction between the Sun and the Earth.
태양은 질량이 줄어들고 아울러 빛도 약해진다.
Newton's equations had no time dependents. If the sun's mass suddenly changes as it were, if aliens removed a large portion of gas. Newton would have predicted that the earth would feel a different force due to gravity instantaneously, with no delay.
뉴튼의 만유인력 법칙은 시간 의존성이 없다. 태양의 질량이 줄어듬과 동시에 지구에서 만유인력이 변했다는 것을 알아챌수 있다.
If gravity changes instantaneously, as Newton predicted, it would still take the photons emitted by the Sun 8.3 minutes to reach the Earth, revealing the alien's actions as the Sun becomes dimmer. This means that we could receive information about changes to the Sun at a speed faster than light by using gravity. This instantaneous transmission of information is sometimes called action at a distance.
태양의 중력이 변했더라도 빛을 발할 테고 광자가 지구까지 도달하는데 여전히 8.3분 걸린다. 외계인이 태양을 어둡게 만들었다는 사실은 8.3분후에 알아 채게된다. 뉴튼의 만유인력은 태양질량이 줄어든 사실을 빛보다 빨리 알 수 있다는 뜻이기도 하다. 뉴튼은 이렇게 즉각적인 정보전달을 멀리있는 변화(action at a distance)라고 했다.
Einstein realized that Newton's theory of gravity was wrong because it implies that action at a distance takes place and that gravity could transmit information faster than the speed of light.
아인슈타인은 뉴튼의 이론에 의문을 제기했다. 중력 변화가 빛보다 빠르게 전달 될 수는 없기때문이다.
Although there were no experiments Einstein could conduct that show that action at a distance is incorrect, Einstein knew that it would imply that there could be ways to transmit information at speeds faster than light which would contradict the principles of special relativity.
아인슈타인은 실험으로 증명할 수는 없지만 빛보다 빠르게 정보가 전달 될 수 있는 원인은 다른데 있을 것이라고 생각했다.
아인슈타인은 실험으로 증명할 수는 없지만 빛보다 빠르게 정보가 전달 될 수 있는 원인은 다른데 있을 것이라고 생각했다.
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Einstein theorized that gravity could be made compatible with special relativity if changes in gravitational fields are transmitted by gravitational waves that obey the speed of light limit in the universe. Gravitational waves, also called gravitational radiation, are an important part of Einstein's general theory of relativity.
아인슈타인은 빛의 속도에 관한 특수상대론에 배치되지 않으면서 중력에 관한 이론을 세웠다. 중력장의 변화에 의해 발생하는 중력파 혹은 중력복사는 우주의 기본 원칙인 빛의 속도 한계를 따른다는 것이다. 일반 상대론의 중요 부분중 하나다.
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Let's return to the aliens who are changing the Sun's mass and brightness. Einstein theories predicts that it takes 8.3 minutes for the gravitation force felt by the Earth to change, so changes in gravity travel at the same speed as light.
The relationship between the force of gravity and gravitational radiation is similar to the relation between electrostatic forces and the emission of electromagnetic radiation or light.
중력과 중력파의 관계를 정전기력과 전자기파의 관계와 같다고 이해해보자.
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An electron or a proton are just two examples of charged particles, which create an electrostatic field. Electrostatic fields can be attractive if the force is between opposite charges, or repulsive if the force is between same charges.
전자나 양성자는 하전된 입자다. 전정기 장은 하전된 입자 사이에 작용하는 인력 혹은 척력이다.
By grabbing a balloon against your head you cause negative charges or electrons from your hair to migrate to the balloon, leaving your head positive charges. If you then hold the negatively charge balloon near your positively charged head your hairs would stand up. Following electrostatic field lines.
The word static, means that the system doesn't change with time. Positive charge, like some hair, will feel and attractive electrostatic force that will feel a force toward the negatively charged balloon. The electric field of the balloon influences nearby objects, but in a static system, there is no electromagnetic radiation or light emitted in this situation.
'정(static)'이라는 말은 시간의 변화를 고려하지 않은 시스템이라는 뜻이다. 전하들이 전기장을 형성하여 인력 혹은 척력을 발휘하지만 복사가 잃어나고 있지 않다.
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If we want to produce electromagnetic radiation, we need to create periodic changes in the static charges. This can be accomplished by changing the position of a charged balloon, say by waving it back and forth rapidly. Positively charged hair will be attracted first in one direction, then the other, and so on. This is situation which produces a time changing electric and magnetic field that causes a disturbance called electromagnetic radiation, also known as light.
전자기 복사를 일으키려면 정전하들이 주기적으로 변해야 한다[위치 혹은 전하량]. 머리를 문지른 풍선을 한 방향에서 주기적으로 흔들면 전기장이 흔들리고 이로인해 자기장이 생겨 전자기 복사(방출=radiation)이 일어난다.
For example, if the balloon is moved back and forth once per second, it generates a changing electric field that moves away from the source at the speed of light. One complete cycle of the balloon corresponds to one cycle of the light wave. So if the balloon moved at one hertz, it produces a photon with a wave length equal to the distance light travels in one second. That's 299,792 kilometers of photon at the very long end of the wave length spectrum in the radio frequencies.
예를 들어 머리에 문지른 풍선을 1초에 한번씩 움직이면 1헤르츠짜리 전자기파가 방출된다. 아주 파장이 긴 빛이다. 이 빛도 속도는 299,792 킬로미터다.
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This electromagnetic wave travels at the speed of light perpendicular to the motion that the balloon is being waved. Information about the changing balloons position reaches your hair after a time equal the distance divided by the speed of light. When the wave passes by a charged particle, the particle will feel a time changing force. That will cause it to oscillate back and forth in a direction perpendicular to the direction the wave travels in.
Normally, we don't use balloons to create electromagnetic waves. Instead, we might have an alternating current traveling through a dipole antenna to create radio waves, a long wavelength form of light.
The important thing to know is that light is only emitted when there are time-changing electric charges or magnets.
중요한 점은 빛은 전하나 자기가 시간 변화를 일으킬 때 빛의 복사가 발생된다는 점을 기억해 두자.
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A star or planet has a gravitational field that doesn't change with time, and unlike electrostatic forces, gravity is only attractive. A small mass place near a heavy planet will feel an attractive gravitational force that will pull it towards the surface. If there is no motion of the masses, there will be no gravitational radiation emitted. Just like the electrostatic example, in order to excite gravitational waves, we're going to need a gravitational field that changes with time.
중력은 끄는 힘만 있다. 그래서 만유인력이다. 두 질량체의 질량변화가 없다면 인력은 존재하나 중력 복사는 없다. 전자기파와 마찬가지로 중력파가 나오려면 질량에 시간 상 변화가 있어야 한다.
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When gravitational waves are created, they move away from their source at the speed of light and, as the wave moves. It distorts space time by stretching and compressing spacial dimensions periodically in the two directions perpendicular to the direction that the wave travels.
생성된 중력파는 전자기파와 마찬가지로 빛의 속도로 움직인다. 시공간이 압축과 이완을 시간상 주기적 변화를 일으키면 중력변화의 수직방향으로 파동이 전달된다. [전자기파의 이동방향은 전자기장의 변화에 대해 수직이다.]
These waves are called transverse waves and can be understood in a simplified sense by the analogy of a transverse wave on this rope that Curtis and Ross are playing with. In this video, we see Ross waving the rope up and down, which is sort of like a gravitational wave source. The wave travels along the rope horizontally from left to right and then from right to left. At each point between Ross and Curtis, the rope is forced to move up and down at the same frequency as Ross's hand.
In a transverse wave, the movement of the medium is in a different direction than the direction that the wave travels in. A gravitational wave is a wave in space-time, which means that instead of moving objects a gravity wave compresses and decompresses space-time.
중력파는 횡파(transverse wave)인데 파동의 진행과 메질의 진동이 서로 수직이다. 중력파는 시공간에서의 파동 물체의 움직임 대신 시공간이 앞북되었다 이완되기를 반복한다.
Suppose that a gravitational wave travels from the ceiling to the floor through my body. Focus on my arms. The affect of the gravitational wave will be to stretch one arm out outwards and compress the other arm inwards. Then the second part of the wave's periodic motion will cause the opposite changes in each arm. Periodic motions of my arm will then occur when the wave travels through my body.
If a gravitational wave were to pass by your ear, it would cause your eardrum to start vibrating, so that you could in principle hear a gravitational wave if you had sensitive enough ears. For this reason, scientists often convert gravitational waves into equivalent sound waves, which is how we got the chirp sound of two merging black holes.
중력파가 사람의 기를 통과하면서 고막을 두드린다. 고막이 충분히 민감하다면 중력파 소리를 들을 수도 있다. 과학자들이 두 블랙홀이 충돌하면서 생성되었던 중력파를 엄청 증폭해서 들려주는 소리를 들어봤을 것이다.
In reality the wave are very weak and changing arm lengths are microscopic. In the Star Trek: The Next Generation episode called Hero Worship, the Enterprise is violently rocked by gravitational waves. This is rather difficult to understand since in reality the waves are very weak, and the Enterprise would have had to have been right next to a ridiculously strong explosive event, in order to get such a strong rocking event.
Scientists on Earth have been working hard for decades to build detectors, sensitive enough to detect gravitational waves, and directly detected them for the first time in 2015.
과학자들이 지난 수십년간 각고의 노력끝에 2015년 처음으로 미세한 중력파를 감지해 냈다.
과학자들이 지난 수십년간 각고의 노력끝에 2015년 처음으로 미세한 중력파를 감지해 냈다.
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[인터뷰] [커세라 페이지]
How do binary pairs of black holes form?
Interview with Dr. Tyrone Woods, Researchers at Monash University
So I think something that is fascinating everybody in the Black Hole community right now is the recent discovery by LIGO, demonstrating the existence of binary pairs of black holes. How these objects actually form still remains a mystery, although we have a lot of ideas.
Generally, one major picture is that a pair of stars born together eventually die together, one forming a black hole and then the other.
Another idea is that to get around some of the complicating factors in terms of trying to actually make a binary pair of black holes together starting from scratch is to form these objects initially born separately in a globular cluster, a very dense system of stars. And then many of which orbit our own Milky Way.
These are sort of the building blocks of galaxies. These systems move around within their den system and interact far more often than they would in a lower density stellar environment like our Milky Way. And they can swap partners and maybe in this way bring together two black holes in a close enough orbit that they eventually merge but we don't know which is the right answer.
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