If you throw a stone into the water, it will stir up ripples in the water, which are formed by the fluctuations of the water, and no one who is blind has seen it.
But the stone also stirs up another kind of ripple that you can't perceive at all, which is formed by the fluctuations of space-time and travels at the speed of light.
Where it passes, space-time will be stretched, and all objects that exist in space-time will also be stretched, and the name of this ripple has long been familiar to you-
Gravitational waves were originally proposed by Henry Poincaré in 1905, based on the lorentz transformation, according to Poincaré's corollary, all objects produce gravitational waves when they move, so you are always surrounded by gravitational waves.
But gravitational waves, that is, invisible and untouchable, can not find a way to prove it, but in theory, it seems to have, and it is everywhere. Another thing with the same characteristics as it is a ghost, so Poincaré is equivalent to proposing a ghost-like idea.
Henri Poincaré | jules henri poincaré
10 years later, Einstein's "General Theory of Relativity" came out, this great theory more clearly predicted the existence of gravitational waves, but also successfully hyped gravitational waves on the hot search, a large number of mouth cannons... Oh no, a lot of scientists are involved in the study and discussion of gravitational waves.
emmm...... Anyway, it's a war of words over whether there are gravitational waves.
Interestingly, general relativity clearly predicted the existence of gravitational waves, but Einstein himself was once on the line with his own theory.
In 1936, he wrote a letter to his friend, the German physicist Max Born, saying that after careful study with Nathan Rosen, he found that gravitational waves were just a mathematical illusion embodied in the equations of the gravitational field, and did not actually exist at all.
Nathan Rosen
Also in the same year, he submitted a paper in the Physical Review, a scientific journal owned by the American Physical Society, detailing his and Rosen's findings. The general meaning is that once a gravitational wave is formed, it will collapse into a singularity under the action of its own gravitational force, rather than carrying the actual energy in space as predicted by general relativity.
That is to say, Einstein's position at that time was: Although my theory shows that gravitational waves should exist, I personally proved that gravitational waves cannot exist.
However, in the end, this matter did not make others angry, but made Einstein himself angry. Because his paper failed to pass peer review, it was anonymously dismissed by Howard Robertson as soon as it was published. Robertson also attached a note to the original manuscript, saying that the paper had errors, and asked Einstein to take it back to check the revision, quite a general theory of relativity that you know a der, and think about where you are wrong.
As soon as this happened, Einstein was angry, the paper was rejected, and he didn't know who did it, so he vowed never to publish a paper in the Physical Review again.
Fortunately, leopold Infeld, a Polish physicist who was Einstein's assistant at the time, had been in contact with Robertson, so under his mediation and mediation, Einstein finally accepted Robertson's opinion, and after recalculation, agreed with the existence of gravitational waves.
Of course, Einstein never knew that Robertson was the one who rejected his paper, if he had known... belch...... I don't know what to expect.
However, although Einstein acknowledged the existence of gravitational waves, he always thought that gravitational waves were too weak to be detected, and on this issue, Einstein was actually right, and in terms of the degree of weakness of gravitational waves, it was indeed impossible to detect.
I know that I said this, there must be a lot of people who can't help but ask, eh, buddy, are you not connected to the Internet in the village, that thing has not been detected by ligo in 2015? Who says it can't be detected?
It is true that gravitational waves have been detected twice by ligo, but this cannot be said to be that Einstein underestimated the abilities of his descendants too much, but that the physicists who engaged in gravitational waves were really too good, and they really completed a task that was impossible to complete.
Notice that I'm saying "really impossible," meaning that I'm definitely not exaggerating or deliberately rendering.
Because many people know that ligo is composed of two metal pipes perpendicular to each other 4 kilometers long, and the information it detected at that time was the stretch of one of the pipes to the 21st power of 10 at the moment when the gravitational wave passed. This figure means that the length of the pipe that was stretched at that time was only 1/1000th the diameter of a proton.
Ligo Gravitational Wave Observatory
Protons are subatomic particles that make up atomic nuclei, the volume of the nucleus is only one hundred billionth of an atom, and the proton is much smaller than the nucleus, so you think, what is the concept of one-thousandth of its diameter?
If you really can't think of it, then put it this way, even if you stand next to ligo's interference arm and shout, its amplitude is hundreds of billions of times greater than the stretch caused by that gravitational wave.
Such a small change in length, just to measure it is already as difficult as ascending to the sky, and after thinking of a sufficiently sensitive method, it is also necessary to distinguish the signal of gravitational waves from various environmental interferences, which is nothing more than a fool's dream.
For example, if I put you in a barrel and drop a drop of water on the barrel, you need to measure by the vibration of the barrel when the drop fell, and most importantly, the barrel is placed in a heavy rain.
That is, you have to figure out how to measure a specific drop of water through a tiny, almost non-existent vibration while the barrel is constantly drenched in rain – that's what ligo needs to accomplish. So how impossible it seems to be to detect gravitational waves is, it can be seen.
Because of this, when the ligo plan was first proposed, many people said that -
However, this seemingly impossible task was completed by Ligo on September 14, 2015 – and when the news was announced, the whole world boiled over.
What was once a fantasy has now become a reality, and mankind has finally seen the dawn in the matter of capturing gravitational waves, followed by the Einstein telescope program in Europe, the Space Explorer program in the United States, the Kagra plan in Japan, and a series of gravitational wave detection plans such as China's Ali plan, Taiji plan, and Lyra plan.
But the question is, why do we have to go to great lengths to capture such a weak signal?
When we look up at the night sky, except for the bright moon and those brilliant stars, what remains is the endless darkness, but in these seemingly empty spaces, there are many answers that human beings are struggling to find.
Since the day of the Big Bang, some things have happened all the time in the universe, such as the formation of galaxies, the demise of celestial bodies, the collision of black holes, and even the birth of cosmic Buddha-figures.
Some of them just happened, some of them occurred millions of years ago, tens of millions of years, or even billions or billions of years ago, and the information related to these events does not necessarily radiate in the form of electromagnetic waves, or the electromagnetic waves they emit can never come to the earth for various reasons.
For such events, even the most advanced astronomical telescopes we build will not help.
It's like covering your ears and throwing you into a dark cave, and you'll know nothing about anything that happens in the shadows of the cave. But once you have sound, you can rely on another information carrier other than light to glimpse these secrets.
Gravitational waves have exactly the characteristics of sound very similar, it carries information in space, and it is difficult to be blocked by objects like electromagnetic waves, so it can present us with ancient information that many electromagnetic waves cannot bring, giving us the opportunity to spy on more cosmic events.
For example, the first gravitational wave signal detected by Ligo let us know that not only is there a binary black hole system in the universe, but they also merge into a new, larger black hole after collision, and this ancient event that occurred 1.3 billion years ago, only gravitational waves can tell us, because it is the story between two black holes, and electromagnetic waves do not even have a chance to escape from them.
Therefore, the study of gravitational waves has an extraordinary significance, and the breakthrough of gravitational wave detection technology and the establishment of gravitational wave observatories are like letting us have an extra pair of tailwind ears after having the clairvoyance of astronomical telescopes.