Einstein was voted "the first man of the century" by Time Magazine, and his special theory of relativity was like a short and strong light that illuminated the vast unknown. The gravitational theory of general relativity combines space-time and matter intact, and our commonly used GPS global positioning system has a relativistic effect in it. But science is falsifiable, is Einstein really right? What did he do? What is special relativity? What are the problems with general relativity?
Produced by: "Gezhi Dao Pulpit" public account (ID: SELFtalks)
The following is the transcript of Shao Lijing's speech by Shao Lijing, a researcher at the Kevili Institute of Astronomy and Astrophysics at Peking University:
Was Einstein right?
If you want to ask Einstein if he is right, you must first know who Einstein is.
You must have heard that he was a very great physicist. But you may not know that he was once named the "first man of the century".
This is a selection organized by Time magazine in 2000 to select the person who has made the greatest contribution to and the most profound impact on humanity in the last century, that is, in the entire 100 years.
Of course, in the last century, there were many things, many people, such as the two world wars, and there were many characters.
After judging, we agreed that Einstein could be the well-deserved first man of the century.
He was named the Person of the Century, the so-called First Man of the Century.
<h1>Einstein's Miracle Year</h1>
What exactly did he do? This has to start in 1905.
At that time, Einstein was actually not very happy, and he did not find a good job, working as a small clerk in a patent office. Usually a little hobby, like to push physical formulas, after work to calculate things.
In 1905, he published several articles for the first time, and people later found that these works were very classic and very important to us.
There are three more important jobs, the first of which is Brownian motion.
He watched some of the pollen in the water drift around, and it was deduced that water was composed of molecules, and matter was composed of molecules and atoms.
It's a great conclusion, a deeper understanding of the world.
The second job is called the photoelectric effect, which is to study light.
Light shines, so is it a wave or a particle?
So Einstein proposed that light can be particles, which are so-called light quanta. This is many years ahead of other physicists at the time, and there are very clear images of quantum physics.
The third very important achievement is called special relativity.
Of these three achievements, the second gave Einstein a "small prize" called the Nobel Prize in Physics.
However, in these three works, the most important thing that everyone thinks is special relativity.
What kind of theory is special relativity? This must start from the historical situation at that time.
At that time, there was an authoritative figure in the physics community called Newton, and Einstein probably went to listen to a report called "Is Newton right?"
Newton had many theories that were very important at the time, but there was a very profound hypothesis behind them, which was his view of space-time.
What is space-time?
TIME: Time goes on and on. Empty: Space, infinite expansion.
Newton thought that time and space were absolute and irrelevant, which is very similar to what we think of as space-time, in which we live in such a space-time, in which we move in space-time.
But Einstein thought that an experiment at the speed of light at that time was a beam of light shining on you, you ran towards the beam, and you ran in the same direction as the beam, running backwards, and the measured speed of light was the same, and the difference could not be detected.
If it is Newton's view of space-time, when running toward the speed of light, the speed of light should be measured, and when running with the speed of light, the measured speed of light will be smaller.
But does experiment tell us that they are the same?
It was on this basis that Einstein was very keenly aware that the speed of light is constant, and that the speed of light is a constant.
When Einstein proposed this, he posed a very great challenge to Newton's view of space-time, which led him to the special theory of relativity.
After special relativity was proposed by Einstein, was it right?
In physics, right or wrong is not up to authority.
Physics is an experimental science, and it is necessary to study whether it is right or wrong by doing experiments, and what is consistent with the experiment may be right, and what does not match the experiment must be wrong.
To take a simple example, there is a famous inference in Einstein's special theory of relativity called the mass-energy conversion relation, that is, mass can be converted into energy. If its mass is large, it may also have a large energy.
But whether this thing is right or not needs to be tested experimentally.
There are many kinds of experimental tests, such as the explosion of nuclear bombs, which actually use the energy mass conversion relationship.
There are also nuclear power plants, which also take advantage of the energy mass relationship. These relationships are now testable with very high precision.
Therefore, special relativity is a more advanced and correct theory than Newton's absolute view of space-time, and it has also been very well evaluated in the physics community.
Mr. de Broglie commented that special relativity was like a brilliant rocket, suddenly drawing a short but very strong light in the dark night sky, illuminating the vast unknown field.
However, Einstein was not satisfied with the special theory of relativity, and he was thinking that the special theory of relativity was very good, but was there any problem?
For example, he found that his special theory of relativity and Newton's theory of gravity were mathematically inconsistent, which needed to be explained. If there is a mismatch, there may be one wrong, or both.
As you know, Newton's theory of gravity is very deeply rooted in the hearts of the people. For example, apples fall from trees to the ground, the moon revolves around the earth, and the affairs of heaven and earth are under its control, which is a theory that governs heaven and earth.
If it is wrong, it needs stronger evidence to illustrate the matter.
Einstein found that special relativity did not correspond to Newton's gravity, and he wanted to explain this contradiction, which was not very optimistic.
There was a man named Planck at that time, and he was equivalent to a senior.
When he met Einstein, he said, "Oh, Einstein, the special theory of relativity you made is so good, so good, I probably use it every day." But now that everything is clear, why are you still busy with another problem?
<h1>Ten years of grinding a sword in the general sense of relativity</h1>
Another problem was the problem of gravity, and Einstein was not frustrated by it, but went on to do research on this area, doing it for 10 years, from 1905 to 1915.
He finally resolved this contradiction and proposed a theory of gravitational force based on general relativity. This theory is very powerful, it combines space-time and matter very completely.
He believes that space-time should have matter, and there is matter to have space-time. This is a theory that very subverts human understanding of time and space.
A better summary of this theory is that space-time tells matter how to move.
As you can see in this picture, because this little ball is matter, it is moving, causing space-time to bend, and in addition, space-time tells matter how to move. This is a set of gravitational theories about the interaction of space-time with matter.
To explain to you one of the most profound ideas of the last century, there is no one, called the equivalence principle.
Einstein was the first person to take this thing very high, and the question goes like this, Einstein stood on a scale trying to weigh it, and he saw that there was a weight count.
Throw a ball and it will fall down because there is gravity, and it may be lighter to put on Mars, but there is also gravity.
One of the good guys did something, he threw Einstein, the scale, and the ball down at the same time.
Einstein was still standing on the scale, and the ball was still falling, but Einstein saw that the ball was not falling down, because he was falling down with the ball, and he saw that the weight gauge did not weigh, because the scale was falling down with him.
At this point, Einstein, the scale, and the ball are in a reference frame called the inertial frame.
Instead, Einstein stood on the ground weighing and weighed the non-inertial frame, then gravity and non-inertial frames were equated.
This is mathematically proven, meaning that space-time is curved.
Of course, Einstein later figured it out, and in his biography, called it the most beautiful time of his life, The happiest moment.
You can think about it, why did this thing shock Einstein so much?
When Einstein celebrated his 76th birthday, someone might have forgotten to prepare a gift and just got something for Einstein.
It could be a disposable paper cup with a paper clip made underneath, then tied to an elastic rope and hung two balls with weight.
This thing is very simple, anyway, put on the table, just like the picture on the left, but this time it is not the most natural state, the rope is stretched, its most natural state should be retracted, how to retract?
Put it down, and in the process of this fall, you can see that the rope quickly retracts the ball, and it is in a most natural state again.
That is to say, when it is gravitationally pulled, it is in a non-inertial frame, and when it does free fall, it is in an inertial frame.
It was a very profound thought, and Einstein was also very satisfied with this gift at the time.
This thing is also reflected in science fiction works, such as space odyssey, someone running on the deck, but shouldn't it be weightless at this time? How can you run on the deck?
Quite simply, there is a circular spaceship to turn it up, and when it is turned up, there will be a force called centrifugal force, which is a non-inertial system, which is called artificial gravity, and with gravity you can run.
Mr. Yang Zhenning once said: There are three major contributions to physics in the twentieth century, two and a half of which are Einstein's. Two refer to special relativity and general relativity, and half refer to the photoelectric effect.
<h1>Science is falsifiable</h1>
Of course, there are many artists who also have their own interpretations of the curvature of space-time, and they have made very beautiful works of art.
However, Einstein's general theory of relativity is not a very simple theory, and I have just told you a core idea. This can be seen in the question a journalist asked Sir Eddington.
Sir Eddington was the first scientist in the world to measure light deflection. At that time, a reporter asked him: Sir Eddington, I heard that there are only three people in this world who understand Einstein's general theory of relativity.
Eddington was stunned, who was the third one besides me and Einstein?
As can be seen from this incident, general relativity is very difficult.
Another interesting question is Feynman's story.
Feynman is a famous American physicist and has also won the Nobel Prize in Physics.
Once, he went to a meeting on relativity, got to the venue, got off the plane and forgot the address.
He found a taxi driver and asked: Have you ever seen such a group of people with their heads held high, who do not care about the things and people around them, and who always say gee-mu-nu, gee-mu-nu,...?
As soon as the driver heard that, he was immediately sent to the right place.
What is gee-mu-nu?
It is the quantity that describes the characteristics of space-time in general relativity, which is a very interesting group.
Science is falsifiable, is Einstein right again?
For example, in the solar system, we can test Einstein's various theories through various experiments. In the solar system, gravity is very weak, and Einstein's theory of gravity differs from Newton's theory of gravity by only one millionth.
But our detection accuracy is very high, we can reach a higher order of magnitude than this accuracy, so we can check for small deviations. On this slight deviation, Einstein's theory of general relativity triumphed over Newtonian gravity.
There is also the GPS global positioning system that everyone often uses, which has a relativistic effect.
If the effects of special relativity are not taken into account, then there will be a deviation of two kilometers in a day, and if the effects of general relativity are not considered, there will be a deviation of 14 kilometers in a day.
So was Einstein right? Is such a high-precision test right? Is he right everywhere?
not necessarily.
We look at the distant starry sky again, and we have to do something a little more extreme, such as we have to investigate something called a neutron star.
The mass of the neutron star is a little larger than the Sun, and its size is as large as the Haidian area, which is very small, so its density is very high.
Take a spoon to hold a spoonful of neutron star material, the weight of this material is more than the weight of the world's people combined, is a very dense class of objects, the gravitational field is also very strong, so it is a very good place to test gravity.
For example, it will rotate in the air like a lighthouse, will be observed by us, and will be observed every turn, which is a very reliable and stable rotating clock.
Our probes need to be seen with large, professional-grade telescopes.
This is the Chinese Sky Eye FAST telescope built in Guizhou, China, where pulsars can be seen, which is a very important scientific research target for it.
Pulsars are a bunch of clocks distributed in space-time, which in turn can be linked through these large radio telescopes to form so-called pulsar timing arrays, which can detect gravitational waves.
Einstein calculated gravitational waves himself in 1916, and a few years later he repented, saying that there were no gravitational waves, and that he had miscalculated.
Einstein asked, was Einstein right?
After a few years, he found out that it was right. And asked, was Einstein right?
It is a very good habit, not only to question authority, but also to question oneself, and this habit is a very important quality in science.
We actually measured gravitational waves now, we measured gravitational waves on September 14, 2015, and I joined their team at that time, and we were very excited, and we spent a lot of time doing this.
This is the telescope that measures gravitational waves, which is a gravitational wave detector in the United States with two arms 4 kilometers long.
This is the first example of a gravitational wave ever seen by humans, and it is very small and requires very precise detection technology to detect it.
In fact, the first example of gravitational wave detection we measured came from a black hole, which is another very magical object predicted by Einstein's general theory of relativity, which is a very distorted state of space-time.
Last year, the Event Horizon Telescope took the first picture of a black hole and was a direct test of Einstein's general theory of relativity.
I'm also a member of the Event Horizon Telescope Collaboration, and I'm very fortunate that we've been able to detect with great precision not only the merger of two black holes, but also the state of the merger of two neutron stars.
This process of union is very important to us because it produces elements that are indispensable to the Earth and the solar system.
Einstein died in 1955 when his executors read a poem in his memory.
He said: We have all benefited a lot, the whole world is grateful for his teachings, and what is exclusive to him has long been spread throughout the masses, and he will be like a comet that is about to perish, radiant and eternally combined with his light.
<h1>Keep your child's curiosity in mind</h1>
Einstein was one such great man of the century. But how does Einstein evaluate himself?
He said very modestly: I don't have a special talent, I'm just very curious.
He dared to challenge authority and had a curious heart, a quality that we are now very scarce.
Was Einstein right?
Einstein's theory has not deviated or deviated from our tests until now, and Einstein was right in the accuracy of the experiment today.
But our technology is also evolving, and he may be wrong at any time, like Newton's gravitational pull, which deviates from Einstein's theory on a very small scale and is eventually replaced by Einstein's theory.
Theoretically, there are still some problems with Einstein's general theory of relativity.
For example, the problem of the singularity of the black hole that it cannot explain, and the problem that it cannot be integrated into quantum space-time, as well as dark matter and dark energy, we don't know what it is.
So we need people in our time who can challenge authority and ask questions. Asking questions is very important, just like we do research people, often see a picture.
This white circle indicates human knowledge, and we do research, which is specifically drilled into a very small point, drilled hard, and finally what can be made?
It may be a very small point drilled, but this point is a completely new knowledge of mankind, and it will be passed down forever.
Curiosity is very important in this process, it drives you to be able to do this thing, this very bad thing to do, it is the original motivation for things that are not easy to do.
Therefore, we must keep the children's curiosity well.
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