Does time exist? - Education and Training Encyclopedia

Does time exist?

Does time exist? You may scoff at this question: "of course time exists!" " Otherwise, the alarm clock won't pull me out of bed early in the morning, a class won't last 45 minutes, my parents won't be old, and I'm not young ... "

Indeed, time is passing, and we need to bear the influence it imposes on us. So, what is "time"? An hour? As early as 4000 years ago, the Egyptians and Babylonians divided the day into 24 hours according to the trajectory of the sun in the air, which is actually the surface caused by the rotation of the earth.

Until 1960, 1 sec is equivalent to 1/86400 of the average solar day. However, the problem arises: this means that the earth has been rotating at a constant speed. However, this is not the case. With the development of observation and measurement technology, astrophysicists realize that the rotation speed of the earth is not constant. Under the gravity of the moon, the rotation speed of the earth slows down by 0.00 164 seconds every hundred years on average. Very small.

But after centuries of accumulation, a day will become longer and longer, and the length of each second will change accordingly. Please ... can you imagine 1m becoming 1.0 1m and 1kg becoming 1.2kg over time? Absolutely not! In order to accurately measure time, 1 sec should be 1 sec at any time! Physicists began to look for the phenomenon of 1 second to solve the problem. It must be completely stable and has nothing to do with the earth's rotation. Thus, in the 1960s, 1 sec became "radiation oscillation of 9 19263 1770 period between two ultra-fine energy levels of cesium-133 ground state".

People define the length of 1 second according to atomic oscillation. Laser-excited strontium atoms are more accurate than the current official standard cesium atomic clock.

Simply put, it is ... when you apply energy to an atom, such as cesium-133, it immediately absorbs energy and releases energy in the form of electromagnetic waves. This kind of electromagnetic wave can be regarded as a series of waves propagating on the water surface, with peaks and valleys. Well, when you have counted 9 19263 1770 peaks and valleys, 1 second has just passed. Since atoms do not change with time, the length of 1 sec will never change.

Follow the rhythm of atoms

However, can this definition tell us what time is? I can't. For example, when we measure the length of a board with a meter ruler, our eyes can intuitively perceive the length, and then we can get the value. When we talk about the quality of an article, we clearly know that the quality of an article depends on its constituent substances.

But when? Can't see or touch. So what are we measuring? It's nothing. Whether our reference object is the rotation of the earth or the rotation of the pointer, we only compare it between different durations. If the minute hand of the watch moves 1/6 times when washing dishes, we can infer that it took 10 minutes; If the sun moves 15 in the sky during a nap, it means that we have slept 1 hour ... whenever we take a nap, we always evaluate the duration of an action by comparing it with another exercise.

We saw the pointer moving, so we said "time is up" ... but in the eyes of physicists, this is obviously not enough. They want to "see" time, such as the basic particles that make up time, just like the Higgs boson they have captured.

The Higgs boson candidate events observed in the Large Hadron Collider due to proton collision: the dense photon coil experiment at the top shows the event of decay to two photons (yellow dotted line and green solid line), and the torus instrument experiment at the bottom shows the event of decay to four muons (red trajectory).

It's just that the more physicists want to determine the time, the more elusive the latter is ... "Is time unpredictable? Why, at least some concepts are certain for us, such as past, present and future ... "Do you really think so? Now let's talk about it. The so-called "now" is the moment when you read these two words, and this moment seems to be universal, right? But you will find that things are not that simple.

For example, you want to know "what is happening on Neptune at the moment". This question is difficult to answer accurately.

Let's just say. Suppose people set up a base on the satellite of this gas giant planet 4.5 billion kilometers away from the sun. Friends stationed there use ultra-modern Skype to keep in touch with you. You can meet him in his room if he wants. So is he.

Equation of time; equation?of?time;?time?difference

At 9 o'clock in the morning, you go to your room, turn on your computer and want to know what your friends are doing at the same time. On the computer screen, you see him sitting in bed reading a book. The conclusion is that your friend was reading when you turned on the computer. So he must be able to see what you are doing now. At the same time, if your friend puts down his book and sits on the bed watching the computer, will he see you come to the computer? No. He will see that your bedroom is dark.

It takes four hours for light to reach Neptune from the earth, so you saw your friend on Neptune's satellite on the earth, and that was him four hours ago. Similarly, he saw you four hours ago! The so-called "now" is really difficult to define. ...

This is normal: it's 1 in the morning, and of course you're sleeping. 1 am？ That's right, because information transmission also takes time, and the speed can't exceed the speed of light (slightly less than 300,000 km/s). It took this image about 4 hours to walk the distance from the earth to Neptune.

So, the picture you saw about your friend at 9 am was actually recorded four hours ago. On your computer screen, it takes 4 hours in the morning to see what your friends are looking at you. Two 4 hours is the time difference of 8 hours. What a coincidence! Because of distance, three different moments exist at the same time in the so-called "present". This is embarrassing enough for an "obvious" concept. ...

Everyone has his own time.

This is not over. Distance not only makes it impossible for us to define a * * * present, but also the length of time on different planets is inconsistent! This is one of Einstein's important discoveries, which is discussed in his special theory of relativity.

If you fly around the moon in a high-speed spaceship, you will feel that the clock on the spaceship is running normally. Your relatives on earth feel the same way. It's just ... when you return to earth, they will scold you: "I thought you said you were only going for three days." Why did you go for a week! " "You protested," No, I went for three days! "

Strange things have happened! You take out your watch to prove it. The watch proves that you are not talking nonsense ... For your relatives and you, time is passing normally. However, the duration is different. What's going on here? Because your movement is close to the speed of light, the watch is no longer synchronized. To understand this strange thing, just read the contents of the photonic clock and you will find that the truth is not mysterious. Besides, readers who have seen Interstellar already know that there is time dilation, which is an important setting in movies.

In the movie Interstellar, the protagonists Cooper and Brand stay on a planet near a black hole for a few minutes, and then return to a distant spaceship. After boarding the spaceship, they found that their companions were more than 20 years older! The expansion of time is simply appalling. But this time it was not the speed that disturbed the clock, but gravity that started it. According to Einstein's general theory of relativity, gravity can be regarded as a distortion of space and time.

Therefore, even if we can establish real-time contact with Neptune, there will still be time difference due to the different rotational speeds of the planets. Einstein once proved that it is impossible for two observers in relative motion to agree on the concept of "simultaneity".

Of course, the results of special relativity can only be perceived when it is close to the speed of light, but the earth and Neptune, which revolve around the sun, do not belong to this situation. In practice, we can create a certain "simultaneity" between Neptune and the earth, but this is only approximate and far from the authentic "simultaneity" in the eyes of physicists.

Therefore, the existence of the so-called giant cosmic clock can uniformly time the Andromeda galaxy (2.5 million light years away from us) and the Milky Way, thus defining "past", "present" and "future" for everyone, which is beautiful.

Andromeda galaxy

There is no cosmic time, and time varies from person to person. Only in a small corner of the universe, on our earth, the role of relativity is minimal. We have the illusion that the world time really exists, just because we haven't studied this problem deeply enough. ...

There are no particles of the past and the future.

The trip to space just now changed your view of time? Don't expect roaming to the material core to bring more comfortable answers! Can protons in the nucleus hear the ticking of time? No ... the river of time flows through them, just like water flows through duck feathers, leaving no trace. Protons do not age. Protons don't die. It is conservatively estimated that its life span is 10 33 years, which is much longer than the age of the universe. The same is true of electrons revolving around protons. They are eternal. Time will not affect them.

Simple schematic diagram of proton quark structure, the color of each single quark can be set at will, but three different colors must be used and mixed into white.

Well, to be honest, these are exceptions. Many particles have lifetimes ranging from one trillionth of a second to several hours, and then decay into other particles or pure energy. Ah! Finally, something seems normal ... just on the surface. Because the relationship between particles and time is a little active. They easily confuse "the past" with "the future"! Imagine playing a movie backwards, and you can immediately understand what is going on.

When physicists watch one of their favorite "blockbusters"-proton collisions, they can see the beginning from the end and the end from the beginning without any difficulty. According to the laws of physics, only one condition needs to be met: the movie played backwards should be viewed through a special mirror, which can not only reverse the image, but also reverse its quantum characteristics, thus making it exactly the same as the movie being played.

For us, even in the mirror, it is incomprehensible to play the movie backwards. But in the field of particle physics, time can pass in two different directions. You will find that this theory can take us very far. Have you ever heard of antimatter? Every particle has its antimatter: the same mass, but the opposite charge (and other quantum properties). Antimatter particles are like the reflection of particles in a "special" mirror.

Although Star Trek made antimatter a household name (Captain Kirk's Enterprise spacecraft used antimatter as fuel), it actually existed!

Star trek poster

Positrons, as antiparticles of electrons, have been detected by detectors many times. However, one of the characteristics of antimatter and matter is that they cannot exist. Once positron and electron meet, they will disappear and become two photons.

Times of chaos.

However, there is another explanation for this "encounter": electrons encounter photons that are retrograde in time, not positrons! The whole process is like two particles exchanging their own travel routes.

Retrograde photons then descend along the river of time (this will not change its nature: a photon is its own antiparticle, and it is impossible to distinguish a photon going back in time from a photon descending along the river of time), while electrons begin to ascend along the river of time. In our eyes, it is a particle with the same mass as an electron, but all its characteristics are just the opposite, that is, the so-called positron, the antimatter of an electron.

This argument about antimatter explains why all particles have their own antiparticles, with the same mass and opposite characteristics. Because each particle may hit a photon that goes back in time, it also goes against time. But you have to understand that this is only an explanation of antimatter, and even some physicists think it is ridiculous.

Whatever. From the point of view of pure mathematics, when we use equations to describe the encounter between particles and antiparticles, the passage of time is unbiased, and the past and the future have no meaning.

Faced with such a strange phenomenon, some physicists even doubt the existence of time! At present, a major focus of physics is to reconcile general relativity with quantum mechanics. The former describes the universe dominated by gravity, while the latter describes the particle world. Relativity knows nothing about particles, and gravity completely ignores the laws of quantum physics. Therefore, physicists are committed to developing an alternative theory that can realize the unity of micro-physics and macro-physics.

This is a picture taken by the Large Hadron Collider at CERN. Two lead nuclei collide and produce a beam of emitted particles. Some of these particles can exist forever, and some can go back in time.

This effort has not yet succeeded, but some ideas seem promising. One of them is the theory of loop quantum gravity. You can tell how complicated it is just by looking at the name, and it is not clear in a few words. But this theory's view of time interests us. It's simple: time does not exist, it's just an illusion!

Scientists who study this theory try to rewrite the laws of physics and delete the time variable t from their equations. So far, there is no indication that they will fail. there is little time left ...

A huge illusion?

Time, hallucination? It's hard to believe, because this "illusion" makes our life orderly. Where does the illusion come from? A simple experiment can give us a hint ... take a glass full of water and drop a drop of ink into it. At first, you can see a drop of ink in a transparent liquid. The ink gradually melted, and soon, the whole glass of water became the color of ink.

The ink droplets eventually completely dissolve in water. At this time, the entropy (chaos of ink painting system) reached the maximum. Entropy will not weaken, so we think there is a difference between "before" and "after", and we think that time has passed.

You can repeat this experiment 10 times, and eventually you will get a cup of diluted ink. From the point of view of a single molecule, there is no "reason" for ink to be mixed into water. No laws of physics force molecules to mix. However, according to the second law of thermodynamics, an independent system (in this case, the contents of a glass filled with water and ink) will spontaneously evolve into an equilibrium state, which is more stable and disorderly.

Explained in physical language is that "entropy" has increased. Haven't you heard of this word? Remember, "entropy" refers to the degree of chaos in the system. Yes, chaos can be measured … that is, the amount of information needed to describe a system completely. The more information, the more confusion.

Melting Ice: A Classic Example of Entropy

If your bedroom only has a bed, a wardrobe and a desk, you can easily describe the layout of the bedroom to your friends. On the contrary, if the bed is not made properly, smelly socks are littered and books are spread on the desk, you should provide more information so that your friends can have an accurate impression of your bedroom. In the latter case, "entropy" is higher.

According to the laws of thermodynamics, the entropy of all independent systems will increase spontaneously. This gives time a "directional arrow" ... a one-way arrow. Yes, entropy can make some experiences irreversible and define the past and the future. For example, ink drops will never regroup in a water cup.

Theoretically, nothing can stop the ink molecules from re-polymerizing. But overall, ink molecules have no chance to recombine into ink droplets. Mixtures are always more difficult to describe than systems composed of two different substances. Re-gathering ink droplets means reducing the entropy in the system, which is impossible! It's unheard of. You can clean your bedroom and reduce the entropy of the bedroom. But once involved, the bedroom is no longer an independent system.

Your efforts to tidy your room are also releasing energy and heat energy, thus increasing the entropy of the whole universe. In the end, the increase of overall entropy will offset the decrease of local entropy, and the two are inseparable. All systems are developing towards chaos. The remains of ancient civilization are proof of this. ...

Chaos is inevitable.

You may have inadvertently noticed that the involvement of entropy is only used to describe a complex system full of various particles, but at the level of a single particle, entropy has no meaning, so particles seem to have escaped the clutches of time. What about us? As a complex system, we certainly have to bear the influence of entropy.

However, you may ask: a fresh life is a small miracle, which can organize all kinds of cells and organs in an orderly way and has nothing to do with chaos! But be careful, don't forget the precise definition of entropy: the increase of entropy is aimed at independent systems. If an organism is completely isolated without food and breathing gas, it will die and decompose ... isn't this a sign of chaos!

We can keep the body in order because we constantly get energy through air and food. We limit the entropy inside the body, but increase the entropy of the whole universe. Our bodies will involuntarily yield and gradually fail until they die. Entropy finally defeated the body and ushered in victory. The time we feel is not the ticking of the clock, but the doomed struggle: our bodies can't fight against chaos.

Shoushan

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