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This article comes from the official account of Wechat: ID:fanpu2019, author: Ethan Siegel

Traditionally, the standard model of cosmology holds that the universe began with a big bang, followed by continuous expansion and cooling. However, a new study finds that based on an ingenious mathematical technique, we can "scale" the universe, and inflation may be an illusion. Can this idea stand up to scrutiny?

Write article | Ethan Siegel

Translation | Liu Hang

Source: geralt / pixabay back in the 1920s, there were two parallel studies that paved the way for our modern understanding of the universe. In theory, if we follow the general theory of relativity, we can deduce a universe uniformly filled with matter and energy, which will not be static and stable, and will either expand or collapse. In terms of observation, we are beginning to be able to observe galaxies outside the Milky way, and we can be sure (on average) that the farther away they are from us, the faster they will move away from us.

Simply combining theory with observation, the concept of an expanding universe was born and has been with us to this day. Our standard cosmological model-- including the Big Bang, cosmic inflation, the formation of cosmic structures, and dark matter and dark energy-- is based on an expanding cosmic model.

But is an expanding universe absolutely necessary and is there any other possibility? Recently, an interesting new paper [1] has attracted some attention. Theoretical physicist Lucas Lombriser (Lucas Lombriser) believes that the expansion of the universe can be "disappeared" by making some changes to the equations of general relativity. In his vision, the observed expansion of the universe is just an illusion. But is this consistent with what we know about science?

In a vacuum, all light, regardless of its wavelength or energy, travels at the same speed: the speed of light in the vacuum. When we look at light from distant stars, the light we see has actually completed the journey from the light source to the observer. Figure source: the equivalence of Lucas Vieira / Wikimedia Commons physics sometimes we can realize that there are many different ways to understand the same phenomenon. If the two methods are physically equivalent, then we know that there is no difference between them, and which way to choose is only a matter of personal preference.

In optics, for example, you can describe light as waves (as Huygens did) or rays (as Newton did), and in most experiments, both descriptions make the same prediction.

In the field of quantum physics, quantum operators act on quantum wave functions. You can choose to use wave functions to describe particles and make them evolve, while the quantum operators remain the same, or you can keep the wave functions of particles unchanged and let the quantum operators evolve.

Or, as often happens in Einstein's theory of relativity, imagine two observers with clocks: one on the ground and the other on a moving train. This phenomenon can be described equivalently from two different perspectives: making the ground "static", the observer on the train experiencing the effect of time expansion and length contraction in motion, or making the train in a "static" state. The observer on the ground experiences the effect of time expansion and length contraction.

As the word "relative" implies, if these scenarios give the same prediction to each other, then any one of them is equivalent to the other.

The revolutionary idea of the theory of relativity founded by Einstein (similar mathematical expressions were derived by Lorentz, George Francis FitzGerald and others before Einstein) is that fast-moving objects appear to contract in space and expand in time. The faster you move relative to the stationary observer, the more your length will seem to shrink, while to the outside world, time will look more inflated. For the observer standing on the ground, the train shrinks and the time inside the train expands; for the observer on the train, the outside world experiences length contraction and time expansion. Source: C. Renshaw, IEEE, 1996 the latter scenario in the theory of relativity suggests that the coordinate transformation commonly used by mathematicians may give us some inspiration. We may be used to thinking about coordinates in the Cartesian way of Rene about 400 years ago: the directions / dimensions are perpendicular to each other, and the axes have the same scale, that is, the Cartesian coordinate system that we have all learned.

But Cartesian coordinates are not the only coordinate system that works. For example, when dealing with objects with axial symmetry, we may prefer to use cylindrical coordinates; when dealing with objects with symmetry about the central point, it may be more reasonable to use spherical coordinates. If you are dealing not only with space, but with space-time-where the "time" dimension essentially behaves differently from the "space" dimension-it is more convenient to use hyperbolic coordinates to connect space and time.

The greatness of coordinate methods is that they are just a choice. As long as you do not change the basic physics behind the system, you are free to choose any coordinate system you like to describe anything in the universe.

Once the critical point for the formation of a black hole is crossed, everything in the event horizon will be squeezed into a singularity, at most one-dimensional. No three-dimensional structure can survive completely. However, an interesting coordinate transformation shows that every point inside a black hole corresponds to an external point, which raises the mathematically interesting possibility that a small universe is born inside each black hole. Image source: vchalup / Adobe Stock redefines coordinates: there is an obvious way to try to apply to an expanding universe. Traditionally, we have noticed that the distances in bound systems (such as nuclei, atoms, molecules, planets, and even star systems and galaxies) remain constant over time; we can use them as a "yardstick". Distance can be well measured at any given moment. When we apply it to the entire universe, because we see distant (unbound) galaxies away from each other, we conclude that the universe is expanding and try to find a relationship between the rate of expansion and time.

So why not reverse thinking and redefine these coordinates: keep the distance between the (unbound) galaxies in the universe fixed, while our "rulers" and other bound structures shrink over time?

This choice may seem rash, but in science, by changing the way we look at things, we can reveal features that are not obvious in the original perspective, which may become clear in the new perspective. The method of redefining coordinates makes us look forward to it-which is what Lombriser explores in his new paper. From this reverse perspective, what conclusions will we draw on the biggest puzzles?

This is a clip of a medium-resolution simulation of the structure of the universe shrinking in proportion to the expansion of the universe, showing the gravitational growth of the dark matter-rich universe for billions of years. It is worth noting that at the intersection of filamentous structures, filamentous matter and rich clusters of galaxies are mainly produced by dark matter; normal matter plays only a small role. As the scale of the simulation increases, the smaller-scale structure will essentially be underestimated or "smoothed" more seriously. Image source: Ralf Kaehler and Tom Abel (KIPAC) / Oliver Hahn is different from the traditional cosmological point of view, we can rebuild the universe as static and non-expansive, at the cost of mass, length and time scale, will change and evolve. Because our goal is to keep the structure of the universe constant, there can be no room for expansion and bending (which contains growing density inhomogeneity), so these evolutionary effects need to correspond elsewhere. The mass scale will have to evolve with the evolution of space-time, and so will the distance scale and time scale. They must co-evolve in a precise way so that when they are combined to describe the universe, they can constitute the "inverse" of the standard interpretation.

Another way is to keep the structure of the universe constant, as well as the mass scale, length scale and time scale at the same time, but the cost is that the basic constants of the universe evolve together in some way, so that all the dynamics of the universe can be "encoded" on them.

You may try to object to these two statements because our traditional view is more intuitive. But as we mentioned earlier, if mathematics are the same and there are no observable differences between the predictions of any point of view, then they all have the same validity when trying to apply them to the universe.

What is the universe like when it is not expanding? Want to explain the redshift in the universe? In this new image, it can be explained in a different way. In a standard image:

Atoms undergo atomic transitions

Release photons with specific wavelengths

The photon passes through the expanding universe and has a redshift during the journey.

When the observer receives it, its wavelength is longer than the wavelength of the same atomic transition in the observer's laboratory.

There are many energy levels in iron atoms, and there are different electron transition selection rules. Although many quantum systems can be controlled to achieve efficient energy transfer, there are no examples of biological systems operating in the same way. Image source: Daniel Carlos Leite Dias Andrade et al., Conference: 25 °CSBMM-Congresso da Sociedade Brasileira de Microscopia e Microan á lise, 2015 in the laboratory, the only observation we can make is to measure the observed wavelength of the received photon and compare it with the wavelength of the laboratory photon. The evolution of electron mass, the Planck constant (ℏ), and the (dimensionless) fine structure constant (or combination of other constants) may occur in this process. The redshift of distant photons that we measure may be caused by many different factors, which are indistinguishable. It is worth noting that with proper expansion, these multiple factors will also bring the same type of redshift to gravitational waves.

When the balloon is inflated, the coins glued to its surface seem to move away from each other, and coins that are "farther away" move away faster than coins that are closer. Any light will have a redshift, similar to the expansion of a balloon, the wavelength of light will be "stretched" to a larger value. This image explains the redshift of the universe very well. Image source: E. Siegel / Beyond the Galaxy similarly, we can reconstruct the way structures in the universe grow. Usually, in a standard image, we start with a slightly overdense region of space that is slightly higher than the average density of the universe. And then over time:

The gravitational disturbance in this area attracts more matter than the surrounding area.

As a result, the spatial expansion of this region is slower than the average expansion of the universe.

As the density increases, it will eventually cross the threshold and trigger the conditions of gravitational bondage.

This region begins to contract gravitationally and form part of the cosmic structure, such as star clusters, galaxies, and even larger clusters of galaxies.

Instead of tracking the evolution of the overdense region of the universe (in a sense, tracking the evolution of the density field), we can also consider replacing it with a combination of mass scale, distance scale and time scale. Similarly, the evolution of Planck constant, speed of light and gravitational constant can be taken into account. The "growing structure of the universe" we see may not be the result of the growth of the universe, but that these parameters fundamentally change over time, keeping observable measurements (such as the structure and its observed dimensions) unchanged.

The typical or "ordinary" overdense areas will gradually form rich structures, while the lower density "Void" regions will have less structure. However, the early small-scale structures were dominated by the densest regions (marked here as "Rarepeak"), which grew fastest and details could only be observed in the highest resolution simulations. Source: J. McCaffrey et al., Open Journal of Astrophysics (submitted), 2023 if we take this approach, no matter how unnatural it may seem, we can try to reinterpret some currently unexplained features of our universe. For example, in the case of the "cosmological constant", for some reason, the universe seems to fill space with a field of inherent constant energy density: this energy density does not dilute or change as the universe expands. This problem was not important a long time ago, but it is important now because the density of matter has been diluted below a certain critical threshold. We do not know why space has this non-zero energy density, nor do we know why it presents a value consistent with the dark energy we have observed. In standard images, this is an inexplicable mystery.

However, in this reconstruction method, if the mass scale and distance scale change according to the new structure, there is a relationship between the value of the cosmological constant and the reciprocal of the square of Planck length. Moreover, Planck length varies with the evolution of the universe, which evolves from the point of view of the observer: the value we are observing now is the observation at this moment. If time, mass and length all evolve together, then the so-called "coincidence problem" in cosmology is eliminated. Any observer will observe the effective cosmological constant of their "present", which is important because their "present" moment is constantly evolving with cosmic time.

A schematic diagram of photon radiation density (red), neutrino density (black dotted line), matter density (blue), and dark energy density (dotted line) over time. In a new model proposed a few years ago, dark energy is replaced by the black solid line in the picture, which is observably indistinguishable from our hypothetical dark energy. By 2023, the dark energy in the expanding universe can differ from the "constant" by about 7% in the equation of state; more differences are strictly limited by the data. Image source: F. Simpson et al., Physics of the Dark Universe, 2018 in this case, they can reinterpret dark matter as the geometric effect of an early increase in particle mass in a convergent manner. They can also reinterpret dark energy as a geometric effect in which particle mass increases in a divergent manner at a later stage. Excitedly, there are different ways to reinterpret dark matter-in which cosmic expansion is reinterpreted as the result of the interaction of the axon scalar field (as a known candidate for dark matter) with the field. The coupling of the axon scalar field with other fields introduces CP destruction, which is one of the key elements of matter-antimatter asymmetry in our universe.

Real "hallucinations" thinking in this way can lead to many interesting potential conclusions. In the early stage of "sandboxie", we should not prevent anyone from carrying out this type of mathematical exploration. One day, such an idea could become part of a theoretical basis that goes beyond the currently accepted standard model of cosmology.

However, even if this is interesting from the perspective of pure general relativity, most modern cosmologists do not bother to consider these issues. Because even if it is observed experimentally and proved to be acceptable on a cosmic scale, it is completely contradictory to what we have already observed on Earth.

When hydrogen atoms are formed, the spin parallelism and antiparallelism of electrons and protons have the same probability. If they are antiparallel, no further transitions will occur, but if they are parallel, they can enter lower energy states through quantum tunnels and emit photons of specific wavelengths over a long time scale. The accuracy of this transition measurement has reached 1/1000000000000 and has remained unchanged for decades, limiting the Planck constant, the speed of light, the electron mass and their combination. Image source: Tiltec / Wikimedia Commons for example, consider the following point of view:

Changes in the properties of elementary particles, such as mass, charge, length, or lifetime

Or fundamental constants, such as the speed of light, Planck constant, or gravitational constant, change.

Our universe, from an observable point of view, is only 13.8 billion years old. We have made high-precision measurements of quantum systems in the laboratory for decades, and the most precise measurement results show that the accuracy of electron magnetic moment is 1.3 parts per trillion [2]. If the properties or basic constants of the particles change, our laboratory measurements will also change. According to the reconstructed theory of Lucas Lombriser et al., in about 14 years since 2009, we should be able to observe changes in these precise measurements thousands of times that of our finest measurements: a difference of about 1/1000000000.

The magnetic moments of electrons were measured with extremely high precision in 2007 and 2022, and the variation between them was less than 1/10000000000000 (the limit of early measurement accuracy), indicating that the fine structure constant had not changed.

The spin-flip transition of the hydrogen atom results in a ray with an exact wavelength of 21.10611405416 cm with an uncertainty of only 1.4 parts per trillion and has not changed since it was first observed in 1951. Over time, physicists measured it more accurately, indicating that the Planck constant had not changed.

The E ö tv ö s experiment, which measures the equivalence between inertial mass (which is not affected by the gravitational constant) and gravity mass (affected), has shown that the mass equivalence of the two "types" is very significant by 2017, reaching 1/1000000000000.

The principle of equivalence holds that there should be no difference between the acceleration of gravity in the universe and the acceleration caused by any other force. One of them depends on the gravitational constant while the other does not. The most accurate test of the equivalent principle is done by the MICROSCOPE satellite, with an accuracy of 10 to the negative 15th power, which is a method to constrain the variation of the gravitational constant with time. Image source: a remarkable feature of APS / Carin Cain's study of the universe from a standard point of view is that throughout the history of the universe, all the laws of physics that apply to the earth apply to any place and moment in the universe. A cosmological point of view that fails on earth is far less interesting than a view that works successfully in all physical systems. The traditional view of the inflated universe is consistent with physics on Earth, while another alternative view does well in describing the larger universe but fails on Earth, so we cannot say that the expanding universe is an illusion. After all, physics on Earth is the most authentic anchor point for us to carry out the most accurate measurement and strict inspection.

This is not to say that journals that publish such speculative and exploratory research-such as Classical and Quantum Gravity (Classical and Quantum Gravity), Journal of High Energy Physics (Journal of High Energy Physics) or Journal of Cosmology and Cosmic Particle Physics (Journal of High Energy Physics)-do not have a reputation and high quality; in fact, they are very prestigious. They are specialized journals in a particular field-they are more interested in early theoretical exploration than in the analysis and understanding of experiments. In any case, continue to explore realistic alternatives to standard cosmology (and particle physics). But don't pretend that abandoning all reality is a viable option. The only illusion here is the reality we observe and measure, which is very important in understanding our universe.

reference

[1] Lucas Lombriser 2023 Class. Quantum Grav. 40 155005, DOI: https://doi.org/10.1088/1361-6382/acdb41

[2] Phys. Rev. Lett. 130,071801 DOI: https://doi.org/10.1103/PhysRevLett.130.071801

A brief introduction to the author

Ethan Siegel, astrophysicist, writer and science communicator, teaches physics and astronomy. Since 2008, its blog "from the Big Bang" (Starts With A Bang!) He has won many science writing awards, including the Best Science blog Award from the British Physics Research Association. There are Treknology:The Science of Star Trek from Tricorders to Warp Drive,Beyond the Galaxy and so on.

This article is translated from Ethan Siegel, Could the expanding Universe truly be a mirage? Original address: https://bigthink.com/starts-with-a-bang / expanding-universe-mirage/, published in "return to Park" authorized by the author.

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