1 Parallel Universe
Is there another article you are reading exactly like this one? That guy is not you, but lives on a planet with mist-shrouded mountains, endless wilderness, noisy cities, and 8 other planets orbiting a star, also called "Earth"? His or her life experience is the same as yours every second. However, maybe she is about to put down the article at this moment and you are planning to read on.
This idea of ??a "double" sounds strange and unbelievable, but it seems that we have to accept it because it has been supported by the results of various astronomical observations. Today's most popular and simplest universe model points out that there is a galaxy exactly like our Milky Way about 10^ (10^28) meters away from us, and there is exactly the same you in it. Although this distance is far beyond people's imagination, it does not affect the authenticity of the existence of your "clone". The idea originally originated from a very simple "natural possibility" rather than the assumption of modern physics: the universe is infinite in size (or at least large enough) and - as astronomical observations indicate - evenly distributed in matter. In this case, according to the laws of statistics, it can be concluded that all events (no matter how similar or identical) will happen countless times: there will be countless planets that breed human beings, and among them there will be people exactly like you - one They have the same appearance, name, memory, and even the same actions and choices as you - there is more than one such person, to be precise, there are infinitely many.
2. Bubble theory
The term "bubble state", to put it casually, means that the price of one or a series of assets suddenly increases in a continuous process. The initial price increase will This creates expectations that prices will rise, thus attracting new buyers - these people generally just want to make profits through buying and selling, but are not interested in the use of these assets themselves and their ability to generate profits. With price increases often a reversal of expectations, they are followed by a collapse in prices, culminating in a financial crisis. Typically, a "boom" lasts longer than a bubble, with more modest increases in prices, production, and profits. It may be followed by a crisis in the form of a crash (or panic), or it may end with the gradual fading of the boom. without a crisis occurring.
Kindleberger's definition of bubble is relatively vivid, but it is difficult to operate in theoretical research. Modern economic research usually defines a bubble as a persistent deviation of asset prices from their fundamental value. This definition simplifies the judgment of bubbles. There are two tasks that need to be done. One is to determine the basic value of the asset, and the other is to see whether the deviation of the asset price is sustainable or disappears in a short period of time.
P.S.
[Popular Science] Parallel Universe (Full text completed) (Updating)
Original work: (U.S.) Max Ironmark
Original publication: "Scientific American" 2003.5
Translation: focus
Parallel Universe
Is there another article you are reading that is exactly the same as this one? article? That guy is not you, but lives on a planet with mist-shrouded mountains, endless wilderness, noisy cities, and 8 other planets orbiting a star, also called "Earth"? His or her life experience is the same as yours every second. However, maybe she is about to put down the article at this moment and you are planning to read on.
This idea of ??a "double" sounds strange and unbelievable, but it seems that we have to accept it because it has been supported by the results of various astronomical observations. Today's most popular and simplest universe model points out that there is a galaxy exactly like our Milky Way about 10^ (10^28) meters away from us, and there is exactly the same you in it. Although this distance is far beyond people's imagination, it does not affect the authenticity of the existence of your "clone". The idea originally originated from a very simple "natural possibility" rather than the assumption of modern physics: the universe is infinite in size (or at least large enough) and - as astronomical observations indicate - evenly distributed in matter.
In this case, according to the laws of statistics, it can be concluded that all events (no matter how similar or identical) will happen countless times: there will be countless planets that breed human beings, and among them there will be people exactly like you - one They have the same appearance, name, memory, and even the same actions and choices as you - there is more than one such person, to be precise, there are infinitely many.
The latest cosmological observations show that the concept of parallel universes
is not a metaphor. Space seems infinite. If this is the case,
everything that can happen will definitely happen, no matter how
absurd they are. In places far beyond the reach of our astronomical observations
there is a universe exactly like ours. Astronomers have even calculated
their average distance from the Earth
You will probably never see your "shadows". The farthest distance you can observe is the farthest light has traveled since the Big Bang: about 14 billion light-years, or 4X10^26 meters - the radius of a sphere that exactly defines the size of our observable horizon , or simply, the size of the universe, also called the Hubble volume. Similarly, the other universe you are in is also a sphere of the same size. The above is the most intuitive explanation of "parallel universe". Each universe is a small part of the larger "multiverse".
With such a definition of "universe", people may think that this is just a metaphysical way. But the difference between physics and metaphysics is whether the theory can be tested experimentally, not whether it seems weird or contains something imperceptible. Over the years, the frontiers of physics have expanded to incorporate abstract (and once metaphysical) concepts such as a spherical Earth, invisible electromagnetic fields, time slowing down at high speeds, quantum overlap, the curvature of space, black holes, and more. wait. In recent years the concept of the "multiverse" has joined the above list, joining previously tested theories such as relativity and quantum mechanics, and meeting at least one basic criterion of an empirical scientific theory: making predictions. Of course, the conclusions made may also be wrong. Scientists have so far discussed as many as four types of independent parallel universes. The key question now is not whether multiverses exist, but how many levels they have.
The first level: beyond the horizon
All parallel universes form the first level multiverse. --This is the least controversial level. Everyone accepts the fact that although we cannot see the other self at the moment, we can observe it later by moving to another place or simply waiting in place long enough. It's like looking at an approaching ship beyond the horizon of the sea - it's similar to looking at objects outside the horizon. As light travels, the radius of the observable universe expands by one light-year every year, so just sit there and wait and see. Of course, you probably won’t be able to wait until the day when the light from another you in another universe reaches here, but theoretically speaking, if the theory of universe expansion is tenable, your descendants may be able to see it with super telescopes they.
So, the concept of a Level 1 multiverse sounds mundane? Isn't space infinite? Who could imagine a sign somewhere saying "Space ends here, watch out for the ditch below"? If so, everyone will instinctively question: What is "outside" at the end? In fact, Einstein's gravity field theory turned our intuition into a problem. It is possible that space is not infinite, as long as it has some degree of curvature or is not topological (i.e., interconnected) as we intuitively think.
A spherical, donut-shaped or horn-shaped universe may have limited size but no boundaries. Observations of the cosmic microwave background radiation can be used to test these hypotheses. See another article "Is the Universe Finite?" ” by Jean-Pierre Luminet, Glenn D. Starkman and Jeffrey R. Weeks; Scientific American, April 1999 However, observations so far seem to contradict them. The model of the endless universe is consistent with the observational data, and there are strong restrictions.
Another possibility is that space itself is infinite, but all matter is limited to a limited area around us - the once popular "island universe" model.
What's different about this model is that matter is distributed in fractal patterns at large scales and is constantly dissipated. In this case, almost every universe in the first level multiverse will eventually become empty and dead. However, recent observations on the three-dimensional galactic distribution and microwave background have pointed out that the organization of matter appears to be vaguely uniform on large scales, and no clear details can be observed on scales greater than 10^24 meters. Assuming this pattern continues, the space beyond our observable universe will also be filled with planets, stars, and galaxies.
There is data supporting the theory that space extends beyond the observable universe. The WMAP satellite recently measured fluctuations in the microwave background radiation (left). The strongest amplitude exceeds 0.5 kelvin, suggesting that space is very large, perhaps even infinite (middle image). In addition, WMAP and 2dF galaxy redshift detectors found that matter is uniformly distributed in space at very large scales
Observers living in different parallel universes of the first level multiverse will perceive that they are different from ours Same physical laws, but different initial conditions. According to the current theory, matter was thrown out with a certain degree of randomness at a moment in the early days of the Big Bang. This process includes all possibilities for the distribution of matter, and each possibility is not 0. Cosmologists assume that our original universe with an approximately uniform distribution of matter and an initial wave state (one of 100,000 possibilities) is quite typical (at least among all parallel universes that have produced observers). typical) individual. Then the nearest person who is exactly like you will be 10^(10^28) meters away; and only 10^(10^92) meters away will there be an area with a radius of 100 light years, and everything in it It is exactly the same as the space we live in, which means that everything that happens in our world in the next 100 years will be completely reproduced in this area; and the area will only increase to 10^(10^118) meters away. Bo is so big, in other words, there will be a universe exactly like ours.
The above estimate is extremely conservative. It only enumerates all quantum states in a space with a temperature below 10^8 degrees and a size of one Hubble volume. One step in the calculation is this: How many protons can fit in a Hubble volume at that temperature? The answer is 10^118. Each proton may exist or not exist, which is a total of ***2^(10^118) possible states. Now all it takes is a box that can hold 2^(10^118) Hubble spaces to exhaust all possibilities. If the box is larger - for example, a box with a side length of 10^ (10^118) meters - the arrangement of the protons will inevitably repeat according to the drawer principle. Of course, the universe has more than just protons and more than two quantum states, but a similar method can be used to estimate the total amount of information the universe can hold.
The average distance of another universe that is exactly the same as ours
The "doppelg?nger" closest to you may not be as far away as theoretically calculated, but may be much closer. Because the way matter is organized is also subject to other physical laws. Given some laws such as planet formation processes and chemical equations, astronomers suspect that there are at least 10^20 planets inhabited by humans within our Hubble volume alone; some of them may be very similar to Earth.
The framework of the Level 1 multiverse is often used to evaluate modern cosmological theories, although the process is rarely articulated. Consider, for example, how our cosmologists use the microwave background to try to derive the geometry of the universe as "spherical space." With the difference in the radius of curvature of space, the size of those "hot areas" and "cold areas" on the cosmic microwave background map will show certain characteristics; and the observed areas indicate that the curvature is too small to form a spherical closed space. However, it is important to maintain statistical rigor. The average size of these regions in each Hubble space is completely random. So it's possible that the universe is fooling us - it's not that the curvature of space is insufficient to form a closed sphere making the observed area smaller, but rather that the average area of ??our universe is inherently smaller than others. So when cosmologists swear that their spherical space model is 99.9% reliable, what they really mean is that our universe is so unsociable that only one in 1,000 Hubble volumes looks like that. of.
The key point of this class is: even if we cannot observe other universes, the multiverse theory can still be verified in practice.
The key is to predict the uniqueness of each parallel universe in the first-level multiverse and point out its probability distribution - what mathematicians call a "metric." Our universe should be one of those "most likely universes." Otherwise - and we unfortunately live in an unlikely universe - then the previously hypothesized theory would be in big trouble. As we will discuss next, how to solve this measurement problem will become quite challenging.
Schematic diagram of the second layer of the multiverse.
Second level: bubbles left after expansion
If the concept of the first level multiverse is not easy to digest, then try to imagine the next level 1 multiverse with infinite sets The structure of the universe: Groups are independent of each other and even have different space-time dimensions and physical constants. These groups make up the second layer of the multiverse—predicted by a modern theory called "disordered expansion."
As an inevitable extension of the Big Bang theory, "inflation" is closely related to many other corollaries of the theory. For example, why is our universe so big yet so regular, smooth and flat? The answer is that "space has undergone a rapid stretching process," which not only explains the above question, but also explains many other properties of the universe. See "The Expanding Universe" by Alan H. Guth and Paul J. Steinhard; Scientific American, May 1984; "The Self-Reproducing Expanding Universe" by Andrei Linde, November 1994 The "inflationary" theory is not only the language of many theories of elementary particles, but And it has been confirmed by many observations. "Disordered persistence" refers to behavior on the largest scales. The space as a whole is being stretched and will continue to do so forever. However, certain areas stopped pulling, creating individual "bubbles" like those inside a puff of toast. There are countless such bubbles. Each of them is a Level 1 multiverse: infinite in size and filled with matter that has been precipitated by fluctuations in energy fields.
For the Earth, the other bubble is infinitely far away, so far away that you can never reach it even if you travel at the speed of light. Because the space between Earth and "the other bubble" is stretching faster than you can travel. If there is another you in another bubble, even your descendants will never be able to observe it. For the same reason that space is expanding at an accelerating rate, the disheartening observation is that even the other self in the first layer of multidimensional space will no longer be visible.
The second level of the multiverse is very different from the first level. Not only do the initial conditions of each bubble differ, but their appearance is also vastly different. The mainstream view in physics today is that the dimensions of space and time, the properties of elementary particles, and many so-called physical constants are not part of the basic physical laws, but are just the result of a process called "symmetry breaking." For example, theoretical physicists believe that our universe once consisted of nine equal dimensions. In the early history of the universe, only three of the dimensions participated in the expansion of space, forming the three-dimensional universe we observe now. The remaining 6 dimensions are now unobservable because they are curled up into very tiny scales, and all matter is distributed on the "surface" of these three fully stretched dimensions (for 9 dimensions, the third dimension is a It’s just a surface, or a “membrane”).
We live in 3+1-dimensional space-time, and we are not particularly surprised by this. When the
partial differential equations describing nature are elliptic or hyperbolic equations, that is, one of space or time is 0-dimensional or
multi-dimensional at the same time, to the observer , the universe is impossible to predict (purple and green parts).
In other cases (hyperbolic equation), if n>3, atoms cannot exist stably, and n<3, the complexity is too low to allow observers who cannot produce self-awareness
(Without gravity, topology is a problem).
Thus, we say that the symmetry of space is destroyed. The uncertainty in quantum waves causes different bubbles to disrupt their equilibrium in different ways as they expand. And the results will be all kinds of strange. Some of them may stretch into 4-dimensional space; others may only form two generations of quarks instead of the three we are familiar with; and some of them may have basic physical constants larger than ours.
Another way to create a second level multiverse is to go through the complete cycle of the universe from creation to destruction. In the history of science, this theory was proposed by a physicist named Richard C in the 1930s. Recently, two scientists, Paul J. Steinhardt of Princeton University and Neil Turok of Cambridge University, elaborated on it. Steinhardt and Turok proposed a model of a "secondary three-dimensional brane" that is fairly close to our space, with some translation in higher dimensions. see "Been There, Done That," by George Musser; News Scan, Scientific American, March 2002 This parallel universe is not truly an independent universe, but the universe as a whole - past, present and future - forms multiple universe, and can be shown to contain just as much diversity as the disorderly expanding universe. In addition, physicist Lee Smolin of Waterloo has proposed another theory with similar diversity to the Level 2 multiverse, in which the universe is created and mutated through black holes rather than through membrane physics.
Although we cannot interact with other things in the Level 2 multiverse, cosmologists can still indirectly point to their existence. Because their existence can be used to explain the randomness of our universe. Here’s an analogy: Imagine you walk into a hotel and find a room with the door number 1967, the year you were born. What a coincidence, you marveled at that moment. But you soon realized that this was no coincidence at all. There are hundreds of rooms throughout the hotel, and it's normal to have one of them share your birthday. However, if what you see is another number that has nothing to do with you, it will not trigger the above thinking. What does this mean? Even if you don’t know anything about hotels, you can use the above method to explain many accidental phenomena.
Let’s take a more relevant example: examine the mass of the sun. The Sun's mass determines its luminosity (i.e., the amount of radiation it emits). Through basic physical calculations, we know that only when the mass of the sun is within a narrow range of 1.6X10^30~2.4X10^30 kilograms, can the earth be suitable for life. Otherwise the Earth would be hotter than Venus or colder than Mars. The mass of the sun is exactly 2.0X10^30 kilograms. At first glance, the Sun's mass appears to be an astonishing stroke of luck and coincidence. The masses of most stars are randomly distributed in the huge range of 10^29 to 10^32 kilograms. Therefore, if the mass of the Sun is randomly determined at birth, the chance of falling into the right range will be very slim. However, with the hotel experience, we understand that this apparent chance is actually the result of inevitable selection in a large system (in this case, many solar systems) (because we are here, the mass of the sun has to be). This observer-dependent selection is called the "anthropic principle." Although it is understandable how controversial it has been, physicists have widely accepted the fact that this selection effect cannot be ignored when testing basic theories.
What applies to hotel rooms also applies to parallel universes. What's interesting is: when the symmetry of our universe is broken, all (at least most) properties are "adjusted" just right. If even a very small change is made to these properties, the entire universe will be completely different - No living thing can exist in it. If the mass of protons increases by 0.2%, they immediately decay into neutrons, and the atoms cannot exist stably. If the electromagnetic force were reduced by 4%, there would be no hydrogen and no stars. If the weak interactions were weaker, hydrogen would also not be able to form; on the contrary, if they were stronger, those supernovae would not be able to spread heavy element ions into the interstellar space. If the universe had a larger constant, it would blow itself apart before galaxies could form.
While the jury is still out on how well-regulated the universe is, each of the examples above implies that there are many parallel universes containing every possible state of regulation.
see "Exploring Our Universe and Others," by Martin Rees; Scientific American, December 1999 The Level 2 multiverse suggests that it will be impossible for physicists to determine the theoretical values ??of those constants. They can only calculate the probability distribution of expected values, after selection effects are taken into account.
The third level: quantum parallel world
The parallel worlds predicted by the first and second level multiverses are so far apart that they are beyond the reach of astronomers. But the next level of the multiverse is all around you and me. It stems directly from the famous and controversial interpretation of quantum mechanics - that any random quantum process causes the universe to split into multiples, one for each possibility.
Quantum parallel universe. When you roll a die, it appears to randomly result in a specific result. However, quantum mechanics points out that in that instant
you actually rolled every state, and the dice came to rest at different points in different universes. In one universe, you rolled a 1, in the other universe you rolled a 2... Yet we can only see a small part of the total reality - one universe.
In the early 20th century, the success of quantum mechanical theory in explaining phenomena at the atomic level set off a revolution in physics. In the atomic realm, the movement of matter no longer obeys the laws of classical Newtonian mechanics. While quantum theory has achieved remarkable success in explaining them, it has also triggered explosive and heated debates. What does it mean? Quantum theory points out that the universe is not determined by the position and speed of all particles as described by classical theory, but by a mathematical object called a wave function. According to Schr?dinger's equation, this state evolves over time in a manner that mathematicians call "unity," meaning that the wave function evolves in an infinite-dimensional space called a "Hilbert space." Although quantum mechanics is described as random and uncertain most of the time, the way the wave function itself evolves is completely deterministic and there is no randomness at all.
The key question is how to relate the wave function to what we observe. Many reasonable wave functions lead to seemingly absurd and illogical states, such as the cat that is simultaneously dead and alive in what is called quantum superposition. To explain this weird situation, in the 1920s, physicists made a hypothesis: when someone tries to observe it, the wave function immediately "collapses" into a certain state in classical theory. This additional hypothesis can solve the problems discovered by observation, but it makes the originally elegant, harmonious and unified theory patchwork and loses its unity. The nature of randomness often attributed to quantum mechanics itself is the result of these unpalatable assumptions.
As years passed, physicists gradually abandoned this hypothesis and began to accept a view proposed by Princeton University graduate Hugh Everett in 1957. He pointed out that the assumption of "collapse of the wave function" was completely redundant. Pure quantum theory does not actually create any contradictions. It heralds a situation in which a state of reality will gradually split into many overlapping states of reality, and the observer's subjective experience during the splitting process is only to experience the completion of a slight possibility that is exactly equal to the previous "wave function collapse hypothesis result" random events. This overlapping traditional world is the third level multiverse.
For more than 40 years, the physics community has been hesitant about whether to accept Everett's parallel world and has gone back and forth several times. But if we divide it into different perspectives and look at it separately, it will be easier to understand. Physicists who study its mathematical equations stand from an external perspective, like a bird flying in the sky surveying the ground; while observers living in the world described by the equations stand from an internal perspective, like a bird being overlooked by a bird. frog.
From the bird's perspective, the entire third level multiverse is very simple. It can be described by just a smoothly evolving, deterministic wave function without any splitting or parallelism. The abstract quantum world described by this evolving wave function contains a large number of parallel classical worlds. They are constantly splitting and merging, like a bunch of quantum phenomena that cannot be described by classical theory. From the frog's perspective, the observer perceives only a small part of the total truth. They can observe the first layer of the universe in which they live, but an effect called "decoherence" that imitates the collapse of the wave function while retaining unity prevents them from observing other parallel universes.
Every time an observer is asked a question, makes a decision, or answers a question, the quantum interactions in his brain lead to compound outcomes such as "continue reading this article" and "give up reading." This article". From the bird's perspective, the act of "making a decision" causes the person to split into two, with one continuing to read the article and the other doing something else. From the frog's perspective, the two clones of the person were unaware of each other's existence, and their perception of the split just occurred was only a slight random event. They only know what decision "they" made, but they don't know that there was another "he" who made a different decision at the same time.
Although it sounds strange, this kind of thing also happens in the first layer of the multiverse mentioned earlier. Apparently, you just made the decision to "continue reading this article," yet another you in another galaxy far, far away put down the magazine after reading the first paragraph. The only difference between the first universe and the third universe is where the "other you" is. In the first level of the universe, he is located far away from you - "far" in the usual concept of dimensional space. In the third level of the universe, your clone lives in another quantum branch, separated by a Hilbert space with infinite dimensions.
The existence of the third-level multiverse is based on a crucial assumption: the unity of the evolution of the wave function over time. Fortunately, none of the experiments so far deviate from the unity hypothesis. Over the past few decades we have demonstrated unity in a variety of larger systems: including carbon-60 buckyballs and kilometers of optical fiber. On the theoretical flip side, unity is also supported by the discovery of a "decoherence" effect. see "100 Years of Quantum Mysteries," by Max Tegmark and John Archibald Wheeler; Scientific American, February 2001 Only some theoretical physicists in quantum gravity have questioned the unity, one of which is that evaporating black holes might disrupt the unity. Sex should be a non-unity process. But a recent string theory research result called "AdS/CFT consensus" suggests that the field of quantum gravity is also unified. Black holes do not erase information, but transmit them elsewhere.
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If physics were to be unified, the standard picture of how quantum fluctuations worked in the early days of the Big Bang would have to be rewritten. Instead of randomly generating a certain initial condition, they generate all possible initial conditions that overlap and exist simultaneously. Then, the "decoherence" effect ensures that they evolve in their respective quantum branches like traditional theories. This is the key point: the distribution results of the evolution of different quantum branches (i.e., the third level multiverse) in one Hubble volume are the same as the distribution results of the evolution of the same quantum branch (i.e., the first level multiverse) in different Hubble volumes. There is no difference. This property of quantum fluctuations is called "ergodicity" in statistical mechanics.
The same principle can also be applied to the second level multiverse. The process of breaking symmetry does not produce just one unique outcome, but the superposition of all possible outcomes. These results then develop in their own direction. Therefore, if the physical constants, space-time dimensions, etc. are different in the quantum branches of the third-level multiverse, those second-level parallel universes will also be different.
In other words, the Level 3 multiverse does not add anything new to Level 1 and Level 2, but is just a more indistinguishable copy of them - the same old story in different quantum states. This is happening over and over again in branching parallel universes. The once fierce skepticism about Everett's theory disappeared after it was discovered that it was essentially the same as other less controversial theories.
Schematic diagram of the difference between the third layer and the first layer
There is no doubt that this connection is quite deep, and the research by physicists is only in its infancy. For example, consider the long-standing question: Will the number of universes expand exponentially over time? The answer is a surprising "no." From the bird's perspective, the entire world is described by a single wave function; from the frog's perspective, the number of universes does not exceed the total number of all distinguishable states at a given moment - that is, the total number of Hubble volumes containing different states. Things like planets moving to new positions, marrying someone, or whatever, these are new states.
Below the temperature of 10^8 Kelvin, the total number of these quantum states is approximately 10^ (10^118), that is, at most this many parallel universes. This is a huge number, but it is very limited.
From the perspective of the frog, the evolution of the wave function is equivalent to jumping from one of these 10^ (10^118) universes to another. Now you are in universe A - the universe in which you are reading this sentence at this moment. Now you jump to universe B - the universe where you are reading another sentence. There is an observer in universe B who is exactly the same as universe A, with only a few seconds of extra memory. All possible states exist at every moment. So the "passage of time" is likely to be the transition between these states - an idea first proposed by Greg Egan in his 1994 science fiction novel [Permutation City] and later adopted by Oxford University physicist David Deutsch and Free Physics. Scientist Julian Barbour et al.