We can't stop time. Even in a traffic jam, when time seems to freeze and stop. Saving light during the daytime doesn’t help either; time inevitably moves forward. Why not back? Why do we remember the past and not the future? Physicists...
We can't stop time. Even in a traffic jam, when time seems to freeze and stop. Saving light during the daytime doesn’t help either; time inevitably moves forward. Why not back? Why do we remember the past and not the future? Physicists believe that the answer to this deep and complex question may lie in the familiar gravity we all know.
The basic laws of physics don't care at all which direction time moves. For example, the rules that govern the orbits of the planets apply whether you are moving forward or backward in time. You can view the movements in the solar system in reverse and they will look completely normal, without breaking any of the laws of physics. What distinguishes the future from the past?
"The problem of the arrow of time has always worried people," says Flavio Mercati of the Perimetric Institute for Theoretical Physics in Waterloo, Canada.
Most people who think about the arrow of time say that it is determined by entropy, the amount of disorder (chaos) in a system, be it a bowl of porridge or the universe. According to the second law of thermodynamics, the total entropy of a closed system always increases. While entropy increases, time moves in the same direction.
When the ice cube in your glass melts and dilutes your whiskey and cola, for example, entropy increases. When you break an egg, entropy increases. Both examples are irreversible: you can't freeze an ice cube in a glass of warm cola or reassemble an egg. The sequence of events - and therefore time - moves in only one direction.
If the arrow of time follows an increase in entropy, and if entropy in the universe is always increasing, then entropy must have been low at some point in the past. This is where the mystery arises: why was the entropy of the Universe low at the beginning?
According to Mercati and his colleagues, there was no special initial state at all. Instead, the state that told time to move forward appeared naturally in the universe under the dictation of gravity. The scientists revealed this argument in a recently published paper in Physical Review Letters.
To test their idea, the scientists modeled the Universe as a collection of thousands of particles that interact with each other only through gravity and represent galaxies and stars floating in space.
The scientists found that regardless of starting positions and velocities, at some point the particles inevitably end up grouped together into a ball before scattering again. This moment can be called equivalent to the Big Bang, when the entire universe collapses into an infinitesimal point.
Instead of using entropy, scientists describe their system using a quantity they call “entanglement,” defined as the rough ratio of the distance between two particles that are farther apart than the others to the distance between the two nearest particles. . When all the particles stick together, entanglement is at its lowest value.
The key idea in all of this, as Mercati explains, is that this moment of least entanglement arises naturally from a group of gravitationally interacting particles—no special conditions are required. The entanglement increases as the particles move apart, representing both the expansion of the universe and the forward movement of time.
If that weren't enough, events that took place before the particles clustered together - that is, before the Big Bang - moved in the second direction of time. If you replay events from this point back, the particles will gradually fly away from the cluster. As entanglement increases in this backward direction, this second arrow of time will also point into the past. Which, based on the second direction of time, will actually be the "future" of another universe that exists on the other side of the Big Bang. Quite confusing, you will agree.
The idea is similar to one proposed 10 years ago by physicists Sean Carroll and Jennifer Chen of the California Institute of Technology. They linked the arrow of time to ideas describing inflation, the sudden and rapid expansion of the universe that occurred immediately after the Big Bang.
“What's interesting about this idea is that it makes sense for us,” Carroll said, describing his work as it applied to the arrow of time. “Perhaps the reason we remember yesterday and not tomorrow is due to the conditions associated with the Big Bang.”
Linking the direction of time to a simple system from classical physics is relatively new, says physicist Steve Carlip of the University of California, Davis. What's new here is to abandon entropy in favor of the idea of entanglement. The problem with entropy is that it is defined in terms of energy and temperature, which are measured through an external mechanism like a thermometer. In the case of the universe, there is no external mechanism, so you need a quantity that does not rely on any unit of measurement. Entanglement, by contrast, is a dimensionless relation and fits the bill.
This does not mean that entropy should be abandoned completely. Our everyday experiences - like your cool lemonade - rely on entropy. But when considering the issue of time on a cosmic scale, one must operate in terms of entanglement, not entropy.
One of the main limitations of this model is that it is solely based on classical physics, completely ignoring quantum mechanics. It also does not include Einstein's general theory of relativity. It doesn't contain dark energy or anything else that is needed to create an accurate model of the Universe. But researchers are thinking about how to incorporate more realistic physics into the model, which could then make testable predictions.
“The big problem for me is that there are so many different physical arrows of time,” says Carlip. The forward direction of time most often manifests itself without involving gravity at all. For example, light is always emitted from a lamp - and never towards it. Radioactive isotopes decay into lighter atoms, never the other way around. Why then does the arrow of time, emerging from gravity, push other arrows of time in the same direction?
“This is a big question that remains open. I don’t think anyone has a good answer to this question yet.”
Have you ever wondered why time always moves forward? Everyone knows that, unlike the reinforced concrete and unchanging time of Newtonian mechanics, in the Theory of Relativity time is not absolute, it is plastic and flows slower or faster depending on the observer’s frame of reference, time can be slowed down and accelerated, but it never stops or turns back. No matter how much we accelerate, what rockets we board, what black holes we fly to, time cannot be reversed. It always goes only in one direction, flowing from the past directly through our brain (this is where the tricky and not fully understood moment sits, which we call “present” or “now”) and rushes from there like an arrow into the future. This concept is called in science "arrow of time", because it has a clear direction.
If we take a step back, we can imagine that time is the most natural arrow. Its sharp tip dug into everyone’s skull at the moment of birth (or conception, as you like), and all their lives the long shaft flies through the head, and somewhere in the distance the plumage is already looming. And as soon as the arrow slips between the eyes and leaves the body, leaving the personality, time will also end. And for the individual - for good.
But this is not what I wanted to talk about, but about why time always flows only forward, always in one direction. This phenomenon has a well-known scientific explanation associated with the law of non-decreasing entropy, although it is not without flaws, primarily because scientists still do not fully and precisely know what time is, what its inner essence. This is such a concept that the further you talk, the deeper you dig, the more you begin to repeat yourself, until you go full circle and become convinced that it is impossible to explain what time is until you explain what time is.
But let’s not get into metaphysics and philosophy, this again is not what we’ll be talking about today. I want to devote a post to a not very well-known and even a little unexpected conclusion about why time moves forward, which follows from the laws and phenomena of nature, from where, it seems, well, you wouldn’t expect anything related to time and its direction.
Because we will talk about Ampere's law, known (known, known, although most have forgotten, of course) to everyone since the seventh grade of school. You don’t even need to know any formulas, just remember that if current flows through two conductors in one direction, they begin to attract. Or repel if the current flows in different directions.
There is not very great knowledge, of course. If Ampere at the beginning of the 19th century could frighten uneducated peasants with his discovery, now, at the beginning of the 21st, even the most backward person knows why this happens, and why the compass needle turns when brought to a conductor with current, this example has set everyone’s teeth on edge since childhood. That, they say, a magnetic field appears around the wire, and if you show the socket your thumb, and, it seems, the current enters the right palm, then this is the rule of the right hand and the right gimlet, if in the left, then the left gimlet, and if in both at once palms enters, then 220 Volts will significantly jump away, maybe even to death.
Ampere's law is not some abstract quasars from a galaxy far, far away, not quantum neutrinos or abstruse Big Bangs - everyone can touch it with their hands. And even to deduce it yourself, science is not tricky. I took a conductor (a piece of wire 1 meter long), an electrical source, and a compass. He sent a current of 1 Ampere through the wire (funny pun, right? In the 19th century, one Ampere sent currents of one Ampere through the conductor), measured how many degrees the compass needle deviated, and wrote it down in a notebook. I turned on 2 Amps, “the needle deviated to a larger angle,” I wrote it down in my notebook. Then 3, 4, 5 Amperes, measured the angles, wrote them down, built a graph, derived a formula, checked them with Wikipedia. Business for 30 minutes, not even a schoolchild, here a preschooler can handle it.
ATTENTION! This was a turn of phrase; preschoolers should not be allowed near wires with a current of 1 ampere or more. I'm serious.
Everything is simpler than a steamed turnip; in a nutshell, Ampere’s law says that electric current gives rise to a magnetic field. And the stronger the current, the stronger the magnetic field. This is understandable, everyone knows this, it is not interesting. Everyone still remembers that the principle works just fine the other way around (although in this case it’s called Lorentz’s law) - a magnetic field generates an electric current, it’s not for nothing that the turbines at the stations spin, generating electricity for us, and note that they were spinning as before, and now spin, the Lorentz force does not decrease over time, and tariffs increase every year.
Andre Ampere came up with his own law for direct current; with alternating current everything is approximately the same, although the formula is a little more complicated. Alternating current is variable, i.e. a changing electric field, which in this case also generates a changing magnetic field. But the calculations there are more complicated. In the middle of the 19th century, scientist James Maxwell collected all the formulas describing electricity and magnetism into one pile (there were 20 of them!) and called them by his own name. The result was the famous Maxwell equations, on which all electrodynamics is built, that is, very roughly speaking "all electricity", which in turn means all our progress, all modern civilization.
20 long formulas are very boring and long, scientists after Maxwell sat, pondered, translated them into vector differential form, we shortened the unnecessary coefficients a little, and we got 4 equations. I can’t help but cite them, even if it’s not entirely clear what they are about, all the same, this is one of the peaks of human genius, something that everyone should at least try to understand in life, something that is not ashamed to show to aliens. I will say more, if we didn’t know these 4 formulas, no aliens at all show nothing will work, because contact them on the radio will become a problem.
Formulas can be written in different forms, different versions and systems of units, for example, like this:
I repeat, this is the very essence, the very center, so that the picture fits on the T-shirt, if you start to understand and unfold what is written, each symbol will turn out to be a complex equation or concept, so we will get to the original 20, but we will spend two years on this in higher mathematics of the institute course. Rotors, divergences, integration of the incoming flow over the surface, vortex fields changing in time and space, and other tricky stuff will be used. We won’t even get close to it, I’ll just decipher the letters a little so that it’s at least approximately clear what we’re talking about.
Capital English letter E in all formulas means that we are talking about an electric field. Vector, everything is done, the arrows are in place. Capital English letter B- accordingly, the field is magnetic. Big J- electric current (more precisely, not exactly, but for simplicity we will assume that electric current), small ρ is charge, t is time, s is the speed of light, zero means zero.
The first equation (aloud) reads like this: “The divergence of the electric field is equal to the total charge,” and this expression implies a simple thought - in the world there are small single droplets called electric charge(for example, an electron), which spread an unknown thing around themselves, manifesting itself as an electric field.
The second equation reads like this: “The divergence of the magnetic field is zero,” which means, oddly enough, magnetic monopoles do not exist. Although, you may have heard, the search for hypothetical magnetic monopoles (not monopolies, like Gazprom, but monopoles, like a single charge) today is a very hot topic in science, but this is a completely different, or rather highly advanced, quantum science; in the mid-19th century, magnetic monopoles did not exist for Maxwell, at least this is what his second equation says. This means that magnets always have a pair of poles, north and south, and there is no way to separate them separately.
The third sounds more complicated: “The rotor of the electric field is equal to the rate of change of magnetic flux density.” And also with a minus sign. In human words this means, as I already said, a changing magnetic field generates an electric one.
Fourth: “The rotor of the magnetic field is proportional to the rate of change in the electric flux density,” there is also the speed of light mixed in, plus some additional current with the magnetic permeability of vacuum. Readers with an asterisk (*) recognized it as the so-called “displacement current” but these are insignificant details now; in fact, this is exactly Ampere’s law, with which my story began, only decorated with all sorts of differential bells and whistles.
Equations exist for a reason; they are solved. If we start combining all 4 formulas at the same time, setting all sorts of boundary conditions, equating different sides to zero, bringing them to a common denominator, and so on, we can derive, for example, something like this:
Or the same for the magnetic component, they are completely symmetrical with the electrical one in this case:
This is the formula for an electromagnetic wave in a vacuum. James Maxwell predicted with his equations that if you take an electric field that changes for some reason, it will immediately generate a magnetic field next to it. Which will also turn out to be changing, and since it is changing, it means, in turn, will also begin to generate a changing electric field, which (see the beginning of the sentence) will generate a new magnetic field, which... and so in a circle these fields will begin to generate each other, but at In this case, they will not stand still, but will run away from us into the distance at the speed of light.
The red arrow shows here force electric field E, and blue magnetic field B.
30 years after the start of theoretical research and Maxwell’s formulas, the German scientist Heinrich Hertz, after whom the gigahertz of our Pentiums are named, experimentally discovered electromagnetic radio waves, and after some time it became clear that visible light is exactly the same radio wave, only not “radio.” -”, well, in short. And off we go: radio stations, television, the Internet, cellular communications, interplanetary communication, globalization, as a new stage in the development of mankind.
In general, in fact, 99.9% of what we see, feel, touch, and so on, all that thing that we call surrounding reality Accordingly, our whole life and a little more is nothing more than the manifestation of electromagnetic waves and their interaction with our receptors and sense organs. And not only outside, but also inside us, in our own brain. For each individual person, the entire surrounding world is a set of electrical impulses that recreate the picture of reality and place the subject (oneself) at its center.
All this, as I already said, is perfectly described (except for a few marginal quantum effects) by formulas that were discovered and mathematically solved in the mid-nineteenth century, a few years before the abolition of serfdom in Russia. Well, or a few years before the abolition of slavery in the USA, who is mad about what.
Look again carefully at the electromagnetic wave formula. Let me briefly explain what we are talking about here; it is important for the further narrative.
It can be seen that first the electric field E is divided into x, y and z, which are in squares, and some other number 6, only inverted the other way around - ∂. All together it's called second derivative along the coordinate axes, i.e. shows how our electric field is laid out along the x, y and z axes of space. Do you know what the axes of space are, why our space is three-dimensional, and so on? There are also posts on this topic on your fingers™. And then, if you don’t pay attention to With 2 (speed of light squared), we will see that the electric field is expanded in exactly the same way (albeit with a minus sign) along the t axis, i.e. along the time axis. The speed of light in the formula is only needed so that the dimensions are the same everywhere, so that meters can be added to meters. Even at a quick glance, it is clear, if you do not pay much attention to the plus or minus signs, that the expansion of the electric field along the space axis, like the expansion along the time axis, is approximately the same thing, or at least a very similar matter.
It was then that physicists began to suspect that time this is something very similar to space that they are somehow related to each other, at least when describing the behavior of electromagnetic waves. Although they have not yet ventured to directly combine these concepts into a single whole - you never know what is written in the formula. You know, what is written on something can be very different from the true content hidden behind the inscription or the wall of the barn.
It took half a century and a genius of Einstein's caliber to believe the mathematics and declare unified space-time not a funny incident in the formula for calculating electromagnetic waves, but the basis of the structure of the universe or at least the Theory of Relativity.
On the other hand, it is impossible not to mention that it was not Einstein who personally invented this space-time from his head. I’m telling you, it was already known half a century before that the minds of almost everyone involved in the cutting-edge of science of that time were burning on this topic - Lorentz, Poincaré, Planck, Minkowski, Riemann...
I’ll simplify the above formula a little, get rid of derivatives, and write it with squares. (Attention, you can’t do this mathematically, it’s unacceptable! Teachers at institutes tear off students’ legs for this, I used a similar trick solely as part of an explanation on your fingers™, don’t even think about blurting out something like that somewhere on an exam!) This is not entirely correct, or rather completely wrong, but it will do, the conclusions turn out to be the same, and the explanation is much easier.
E This is our electric field, with a magnetic one B it will be exactly the same formula. But look closely, this is essentially a quadratic equation! A particularly attentive reader may notice that the formula is strikingly similar to the Pythagorean theorem, only not for a flat triangle, but for a three-dimensional, or rather four-dimensional, because time t is also a coordinate, from which it will smoothly move on to the concept invariant interval, but we won’t go there. Also note - the speed of light With she hasn’t gone anywhere, there she is, also in a square, which is not so important now. It is important that it is firmly built into Maxwell’s equations, determining the speed of propagation of electromagnetic waves. And if we move on to Einstein and the Theory of Relativity, this is generally the highest possible speed of information dissemination throughout our Universe.
I will only say one thing about the quadratic equation. Anyone who does not know what a quadratic equation is cannot be called a human being and cannot be allowed into the 21st century. Seriously, there is such an eternal philosophical problem - what is a person and how does he differ from an animal? Well, it is clear that a person is much more complex and highly organized, but where do we draw the line? The dog can be taught to understand words and commands. A trained monkey can speak itself (in the language of the deaf and dumb), dolphins in schools communicate in their own language, they have emotions and feelings, they understand a lot. Even an experimental mouse can be taught to solve simple logical problems, and monkeys can add and subtract objects in their minds, if their number is not much more than ten.
For me personally, the line of the concept of “homo sapiens” lies somewhere around the quadratic equation. No animal can understand what it is - too high a level of abstraction is required. A caveman who is afraid of fire and lightning cannot understand the quadratic equation and also cannot be called a reasonable person. I'll say more... No, I won't say more. Let me just remind you that, after all, the 21st century is here, to be considered a person of our time it is not enough to be able to write and read syllables. The level of Sunday parochial school is no longer enough; you need to finish your studies at least up to the sixth or seventh grade. And there is no need at all to memorize the discriminant formula or calculate the roots in your head; it is enough to at least in principle remember that such equations exist, understand what their meaning is and be developed enough to be able to Google the solution. Otherwise, I'm sorry, but you have no future.
I hope that each of those who have read this far have seen at least one quadratic equation in their lives and are at least roughly aware of how to solve them. But most importantly, he must understand that for any quadratic equation there are always two solutions, two roots. This is the necessary level of logic and abstraction, inaccessible to an animal, but proposed by me to test for humanity and rationality.
Maybe you even remember that at school they deceived us - they say that if a quadratic equation has a discriminant equal to zero, then it has one root, and if it is less than zero, then there are no roots at all, so we will write it down in the answer. The time has come to reveal a terrible secret, accessible only to the elite club of humanity, only to the best of the best - any quadratic equation always has solutions and there are always exactly two of them. This is what mathematics requires, this is what logic requires. True, decisions may not be valid, but vice versa comprehensive, but this does not cancel anything.
Abstract mathematics is a little (in fact, a lot) broader than observable reality. To understand this, you just need to be a little higher than an animal that reacts only to a set of external stimuli. A person must not only react, but also think!
So, the task is to think about it. Let the floor area of a rectangular room be 54 square meters, and one wall is three meters longer than the other. What can you say about the length of the walls of this room?
A person with abstract thinking will say: “One wall will be length x, the second will be x + 3, and their product will be 54.”
x (x + 3) = 54
or the same thing, in a more familiar form:
x 2 + 3x - 54 = 0
We solve the quadratic equation, we get two (and there are always two, remember, right?) roots: 6 and –9.
Let us not forget further that our man is not simple, but reasonable; he will most likely expand his mind and say: “Although our equation has two purely abstract and mathematical roots, we live in real reality, given to us in sensations! And keeping in mind that reality is most often significantly already(in the sense of less) mathematics, we will discard the absurd answer of minus nine meters. Because I’m not just solving some abstract equation, I’m looking for the area and length of the walls of the specific room I’m in right now. And I see that her wall length is not minus nine. This means that by discarding one root, I get the length of the first wall to be six, and the second to be 3 meters longer, that is, 9 meters. Ordinary human ones, not minus meters. In our Universe, in the one where we live, there are no minus meters in rooms."
The situation is exactly the same with the equations of electromagnetic waves. I have already said that this is not quite a quadratic equation, there is actually a second partial derivative, but if you don’t pay too much attention to this and expand the formula, you get the same parsley.
By calculating the equation of an electromagnetic wave (how it behaves in time and space) we get two possible solutions, both of which are absolutely valid from a mathematical point of view. But what are they like in real reality?
One of the solutions describes the following process: The man picked up a match and struck it on the box. The match flared, the flame lit up, and light photons, or in other words, electromagnetic waves of the visible and infrared spectrum, flew in all directions of the dark room (with an area of 54 square meters, yeah). After some time (quite quickly, the speed of light after all) these waves reached the walls of the room and illuminated them. If there were windows in the walls - electromagnetic waves from a lit match leaked through the glass and flew on, ever expanding, setting off on their endless flight through the Universe, until they were stopped by the inquisitive eye of the observer, if anything stopped them at all.
And now another solution to Maxwell’s equations, absolutely acceptable from the point of view of mathematics: Somewhere far away, on the very border of the Observable Universe, it is not clear how and for what reason an electromagnetic wave originated. The wave was barely noticeable, almost imperceptible, but with the flight it grew and gained power, having flown 13.8 billion years, it burst into our window, and immediately merged with exactly the same waves, very successfully and in time emitted by the walls in order to have time to come together and powerfully hit the match, where from sulfur dioxide and phosphorus oxide we get a whole match head, exactly at the moment when we struck it on the box. Wow, what a coincidence!
Both solutions are mathematically correct, both can happen, why not? But you and I are reasonable people. We understand that there is a cause and there is an effect. We may realize that one of the solutions is not a description of our reality, mathematics is mathematics, but one of the solutions will have to be rejected as absurd. In our world, only one solution has physical meaning - electromagnetic waves fly from a lit match, and time only flows forward.
This is the answer to the question in the title of the article. Unexpected, right? You've probably already begun to forget where it all began, did you think I launched into philosophical rantings and mathematical education for sixth-graders, while completely losing the thread of the story?
No. So, while solving Maxwell’s abstract equations, we unexpectedly realized not only that for electromagnetic waves both spatial and temporal coordinates are almost the same thing, only part of a single formula, but they propagate in a common four-dimensional space-time (and this is a serious claim on Einstein !), but also that one of the solutions is absurd from a physical point of view, describes some kind of Universe that is not ours, where the cause is confused with the effect, and therefore our time flows only in one direction, and not in the mathematically possible two.
NB! A short afterword for readers with an asterisk (*). I hasten to apologize to you and admit that the structure of the article is a bit like an illusionist’s trick. I already mentioned at the beginning that in order to explain what time is, we will first have to explain what time is. There is a similar situation here. Although the reasoning itself sounds quite convincing, if you start poking around in mathematics and formulas, it turns out that Maxwell’s equations themselves have a cause-and-effect relationship built into them from the very beginning. And we, supposedly relying on the argument of “cause and effect,” throw away what was obtained with the help of these same “cause and effect.” By rejecting one of the solutions “as absurd,” we are actually acting quite voluntarist, thereby not explaining or clarifying anything.
A much more correct approach to explaining the phenomenon of the arrow (direction) of time lies precisely in thermodynamics, in statistical physics, in the transition to the non-decrease of entropy and ultimately rests on the second law of thermodynamics (which says that it is impossible to build a perpetual motion machine). But more about this sometime next time, if there is such a desire, here I treacherously took advantage of the unexpected result of solving Maxwell’s equations in order to attract the reader’s attention to them and try on your fingers™ explain what they are and why they are so important for modern civilization. Readers with an asterisk (*) of course immediately figured out my not-so-hidden plan, especially for you I prepared this idea to knock you over the head.
In the reality around us, scientists have counted 4 fundamental interactions, which through deft mathematical manipulations can be reduced to two: electromagnetic-strong-weak and gravity. I have already mentioned that 99.9% (or 99.99%, as you like, is still an estimated and approximate figure) of the observed phenomena and, accordingly, the information entering us, is a manifestation of electromagnetic-strong-weak effects, but for simplicity, the last two components can be discard and declare that electromagnetism is the essence that almost completely controls reality on a human-perceivable scale, although we must not forget about gravity either. Gravity - heartless force, and those who are distracted from her even for a second, she will immediately rub their nose into the asphalt, in the most literal sense of the word. Why do you know Maxwell’s equations, have a concept of quantum mechanics, but also don’t make mistakes in the Theory of Relativity (theory of gravity), because it’s fraught.
Another thing is the virtuality surrounding us. Yes, virtuality is already almost a full-fledged reality (a new, additional layer of reality at a minimum), although the detailing is still lame in places and the connection is periodically interrupted. However, please note that the text that you are reading right now, like all other articles on your fingers™, like many, many other things, are exclusively in virtuality, they have never entered the world around us, and, perhaps, will forever remain only a set of bytes, that is, in fact, electromagnetic waves that have no rest mass. They are not subject to the laws of gravity; on the Internet there are no gravitational forces at all, just pure electromagnetism. In any virtual game, you can completely turn off gravity by setting the appropriate parameters, you can change it as you want, or you can not obey it at all. At the same time, electromagnetism is revealed in all its glory, even particle-wave duality is present. Any recorded information is based on bits (essentially quanta), but information is transmitted by electromagnetic waves at the speed of light, anyone playing Dota from Europe on an American server knows what lag is (signal delay), and a significant part of this lag is fundamentally determined by speed propagation of electromagnetic waves through wires.
In virtuality, not 99.9%, but all 100% of surrounding phenomena have an electromagnetic component. Here it is difficult to rely on the centuries-old experience of evolutionary habits, there is no gravity, apples can fall upward, and the seemingly “absurd” discarded second solution of Maxwell’s equation may turn out to be not absurd at all, what do you say to this?
The Universe and the “Arrow of Time”
“Time is what keeps everything from happening at once,” wrote Ray Cummings in his 1922 science fiction story “The Girl in the Golden Atom.” This phrase perfectly describes the whole purpose of time. But how does time do this, why doesn't everything happen at the same time? What mechanism makes time flow forward and only forward?In a recent study published in the journal Physical Review Letters, a team of theoretical physicists once again explored the so-called “arrow of time,” a concept that describes the inexorable forward movement of time. This research was a different way to look at how time behaves on a universal scale.
The traditional "past hypothesis" suggests that any system begins in a state of low entropy and then, due to thermodynamic processes, its entropy increases. That is, any isolated system moves towards increasing entropy.
In our daily life, we can find many examples of increasing entropy, such as a gas filling all the space given to it, or a melting ice cube. In these examples, an irreversible increase in entropy, disorder, and chaos is observed. That is, the past is low entropy, the future is high.
If this is applied to the universal scale, then the Big Bang should have given birth to the Universe precisely in a state of low entropy. As time passed, the Universe expanded and cooled, its entropy increased. Thus, according to this hypothesis, time is inextricably linked with the degree of entropy in our Universe.
But there are several problems with this idea.
All observational evidence indicates that the environment in the Universe formed immediately after the Big One was hot and a complete chaos of primordial particles. As the Universe grew and cooled, gravity created from it a completely different Universe, more ordered and more complex - stars and planets were formed from the cooling clouds of gas, and from them, in turn, galaxies and clusters. In the end, organic chemistry became possible, giving impetus to the emergence of life and us, people who philosophize about time and space. On the scale of the Universe, entropy has decreased, not increased, as the “past hypothesis” suggests.
According to one of the study's participants, Flavio Mercati of the Institute for Theoretical Physics in Ontario, the question is how entropy is measured.
Since entropy is a physical quantity with its own dimensions (like energy and temperature), there must be some kind of framework in relation to which these dimensions can be measured.
“This can be done for the subsystems of the Universe, because the rest of the Universe sets these limits for them, but it itself has no external references for measuring such things, because there is nothing outside of it,” Mercati expressed his opinion to Discovery News.
But if not entropy, then what moves universal time forward?
Complexity is a dimensionless quantity. If you look at our Universe, we can say with confidence that its complexity is directly related to time. Over time, the Universe becomes more structured and complex.
“Our answer is gravity, and its tendency to create order and structure (complexity) out of chaos,” Mercati says.
Mercati and his colleagues tested this idea on computer models that simulated the Universe. And they found that, no matter how you model it, the complexity of universes always increases and never decreases over time.
At the moment of the Big Bang, the Universe began in a state of least complexity. It was a kind of hot “soup” of disordered particles and energy. Then, as it cools, gravity begins to act, gases form stars, stars group into galaxies. The universe is inexorably becoming more complex, and gravity is the driving force behind this complexity.
As the Universe matures, subsystems become isolated enough for the classical “arrow of time” to operate under low entropy conditions. On the scale of the Universe, our perception of time is due to the constant increase in complexity, but in these subsystems the concept of entropy dominates.
“The universe is a construct whose complexity is constantly increasing,” Mercati said in a press release for the study. “It consists of large galaxies separated by huge voids. But in the distant past they were closer. Our assumption is that our perception of time is the result of a law that determines the irreversible increase in complexity.
Imagine that there is a broken egg on your face, and this is not a figure of speech. Trying to juggle eggs results in one of them falling and breaking on your head, and now you have to go to the shower and change clothes. But wouldn't it be easier to turn back time a minute? After all, the egg broke in just a couple of seconds - why can’t you do the same thing, only in reverse? Just put the shell back together, throw in the white and yolk - and that's it... You would have a clean face, clean clothes and no yolk in your hair.
Move only forward
It sounds funny - but why? Why can't this action be undone? In fact, there is nothing impossible about this. There is no natural law that would prohibit doing this. Moreover, physicists report that any moment that happens in everyday life can happen in reverse at any point in time. So why can’t you “reverse-break” eggs, “reverse-burn” a match, or even “reverse-dislocate” a leg? Why don't these things happen every day? Why is the future different from the past? This question seems quite simple, but to answer it we need to go back to the birth of the Universe, turn to the atomic world and reach the boundaries of physics.
Isaac Newton
Like many stories in the world of physics, this one begins with the great physicist Isaac Newton. The bubonic plague swept through Britain in 1666, and it was this that forced Newton to leave Cambridge University and go home to his mother, who lived in rural Lincolnshire. There Newton got bored and, isolated from the outside world, took up physics. He discovered three laws of motion, including the well-known maxim that every action has its reaction. He also came up with an explanation for why gravity works.
The concept of time in physics
Newton's laws are incredibly effective in describing the world around us. They can be used to explain many phenomena, from why apples fall from trees to why the Earth revolves around the Sun. But they have a strange property - they work in exactly the same way and vice versa. If an egg breaks, Newton's laws say that it can return to its original state. Obviously this is wrong, but virtually every theory that has been developed by scientists since Newton has this exact same problem. The laws of physics simply do not take into account whether time flows forward or backward. They care about this as much as they care about whether you write with your right hand or your left. But you definitely care! As far as you know, time has an arrow that indicates its direction, and it always faces the future. You may confuse east and west, but you will never confuse yesterday and tomorrow. However, the fundamental laws of physics do not distinguish between the past and the future.
Ludwig Boltzmann
The first person to seriously confront this problem was the Austrian physicist Ludwig Boltzmann, who lived in the second half of the 19th century. In those days, all ideas that are now accepted as an axiom were controversial. In particular, physicists were not as convinced as they are today that everything in the world is made of particles called atoms. According to most physicists, the idea of atoms could not be proven, it could not be verified by practical methods. Boltzmann believed that atoms actually existed, so he used this idea to explain all everyday things, such as the flame of a fire, the functioning of the lungs, and why tea cools when you blow on it. He thought that he could understand all these things using the concept that was so close to him - the theory of atoms.
Negation
Some physicists were impressed by Boltzmann's work, but most rejected it. He was soon ostracized by the scientific community for his ideas. However, it was he who showed how atoms are related to the nature of time. At that time, the theory of thermodynamics appeared, which describes how heat behaves. Boltzmann's opponents insisted that the nature of heat could not be described; they said that warmth is just warmth. Boltzmann decided to prove that they were wrong, and heat is caused by the chaotic movement of atoms. He was right, but he had to spend the rest of his life defending his point of view.
One-way process
Boltzmann began by trying to explain something strange - "entropy". According to the laws of thermodynamics, everything in the world has a certain amount of entropy, and when something happens to that object, the entropy increases. For example, if you put ice cubes in a glass of water, they will melt and the entropy in the glass will increase. And the growth of entropy is different from everything in physics - the process moves in one direction. Physicists have long wondered whether the way time passes is determined by an increase in entropy. As you already understood, Boltzmann was the first to raise this question, but then many other scientific minds began to study this issue. And in the end, it became clear that time could potentially flow in the opposite direction - but only if entropy decreases, which is simply impossible.
To European people, time seems like a straight line. The past is behind you, the future is ahead, and life moves forward. A familiar picture... But not for everyone. There are peoples who are confident that time flows in a completely different way: from front to back, in a circle, or even uphill. This suggests that modern lifestyles have greatly changed our understanding of time. Recent research into “non-standard” perception of time led scientists to Papua New Guinea, to the village of Gua, a settlement of the Yupno tribe.Rafael Nunez, an employee of the University of California at San Diego (USA), and his colleagues went to the slopes of the Finisterre ridge in the northeast of the country. There are no roads, electricity or even pastures in this area. The tribe's way of life remains virtually untouched for centuries. Communicating with local residents, American researchers paid attention to the gestures of the aborigines at the moment when the conversation turned to the passage of time, events of the past, present or future. The gestures of the interlocutors seemed quite unusual to Nunez and his colleagues.
If the conversation took place on the street, then when mentioning the past, the aborigines pointed down to the foot of the local mountains and the mouth of the river, and when talking about the future, they pointed up to the tops of the mountains, where the source of the river was hidden. Gestures were repeated regardless of where the person’s gaze was directed. All the natives were sure: the future was up in the mountains, and the past was in the valley.
Inside the hut, geographical landmarks are lost, and there the time line becomes more direct. However, natives point towards the door when talking about the past and away from the entrance when talking about the future, regardless of the orientation of the house. This may be due to the fact that the entrance of the hut is raised above ground level, the researchers speculate. Thus, the past, like the exit from the house, is located “down the slope”, and the space inside the hut is at the top, which means in the future.
Researchers have put forward a historical hypothesis that explains this picture of the world: the ancestors of the Yupno arrived in these places by sea and then rose to a height of 2500 meters. Perhaps that is why the lowland seems like a thing of the past to them. What seemed most surprising to scientists was that the time line repeated the surrounding landscape. “This is the first time that everyday concepts of time have topographical properties,” Nunez concluded.
However, the Yupno have almost like-minded people. For the Australian Pormpuraau tribe, time flows from east to west. The ideas about time of some tribes living in the remote corners of the planet make us think about many things. For example, that the picture of the world we are accustomed to is not universal.
For example, in Quechua, the language of the tribal group that in ancient times created the state we know as the Inca Empire, time was inseparable from space: both concepts were denoted by the same word "pacha". Moreover, the Quechuas did not distinguish between the past and the future: in their opinion, there were only two types of time-space: the one that is here and now, and the one that is “not now” and not here. Such a past-future in the Quechua language was called “navya-pacha”.
In some languages of Ancient India, including Hindi, yesterday and tomorrow are also denoted by the same word “kal”. Only by the nearby verb can you understand whether we are talking about the past or future tense. The languages of these peoples reflect the cyclical perception of time that was characteristic of our ancestors. The harvest, the alternation of seasons, the cycles of nature - the usual events went in a circle, repeating over and over again.
One might assume that the modern idea of progress and personal achievement and striving forward would not appeal to them. Success in their understanding was rather not to fall out of the usual circle of time - to sow and harvest on time, not to die of illness in youth, to give birth and raise children who will continue the life cycle.
There are also amazing peoples who believe that time flows backwards. This is the opinion, for example, of the Aymara who live on the slopes of the Andes. For them, the future is behind their backs, and the past is in front of their eyes. The logic is simple: we remember and saw the past, but we know nothing about the future. And for the Chinese, the past is at the top and the future is at the bottom. Here, most likely, it’s a matter of the habit of writing in a column from top to bottom. In terms of the “horizontal” nature of time, the Chinese agree with the Europeans, but they show a slightly different direction: they perceive “forward” as “top to bottom.”