|
宇宙膨脹可能是幻象-Robert Lea
|
瀏覽831 ｜回應2｜推薦1 |
|
|
|
朗布萊瑟教授在一篇今年06/02發表的論文中提出新理論；根據這個理論他認為：
宇宙其實是平坦的和靜態的；「宇宙膨脹」可能是個幻象。
朗布萊瑟教授同時認為他的新理論可以：
a. 解釋「宇宙常數」的理論值和觀察值之間巨大差異的問題；以及
b. 免除假設「暗能量」存在的需要。
朗布萊瑟教授新理論的核心點在於：
以「基本粒子質量」隨時間發展的「變化」來解釋以上三個宇宙學中的問題。
目前這個新理論當然還只有「姑妄聽之」的身份和地位。是否「說得通」尚待下會分解。請參考《宇宙到底擴張得有多快？》一文。
我想借此機會再次提醒一些喜歡把「真理」一詞掛在嘴邊的人：
到目前為止，即使在自然科學領域，所有的「理論」都只有能解釋多少觀察到現象的分別。沒有一個理論能解釋所有人類已經觀察到的現象。更別提我們還沒有觀察到的現象。從而，任何一個認為自己找到了「真理」的人，其實只是搞不清楚什麼是「真理」，或等而下之，她/他找到的只是個「幻象」。
The expansion of the universe could be a mirage, new theoretical study suggests
Robert Lea, 06/20/23
The expansion of the universe could be a mirage, a potentially controversial new study suggests. This rethinking of the cosmos also suggests solutions for the puzzles of dark energy and dark matter, which scientists believe account for around 95% of the universe's total energy and matter but remain shrouded in mystery.
The novel new approach is detailed in a paper published June 2 in the journal Classical and Quantum Gravity, by University of Geneva professor of theoretical physics Lucas Lombriser.
Scientists know the universe is expanding because of redshift, the stretching of light's wavelength towards the redder end of the spectrum as the object emitting it moves away from us. Distant galaxies have a higher redshift than those nearer to us, suggesting those galaxies are moving ever further from Earth.
More recently, scientists have found evidence that the universe's expansion isn't fixed, but is actually accelerating faster and faster. This accelerating expansion is captured by a term known as the cosmological constant, or lambda.
The cosmological constant has been a headache for cosmologists because predictions of its value made by particle physics differ from actual observations by 120 orders of magnitude. The cosmological constant has therefore been described as "the worst prediction in the history of physics."
Cosmologists often try to resolve the discrepancy between the different values of lambda by proposing new particles or physical forces but Lombriser tackles it by reconceptualizing what's already there.
"In this work, we put on a new pair of glasses to look at the cosmos and its unsolved puzzles by performing a mathematical transformation of the physical laws that govern it," Lombriser told Live Science via email.
In Lombriser's mathematical interpretation, the universe isn't expanding but is flat and static, as Einstein once believed. The effects we observe that point to expansion are instead explained by the evolution of the masses of particles — such as protons and electrons — over time.
In this picture, these particles arise from a field that permeates space-time. The cosmological constant is set by the field's mass and because this field fluctuates, the masses of the particles it gives birth to also fluctuate. The cosmological constant still varies with time, but in this model that variation is due to changing particle mass over time, not the expansion of the universe.
In the model, these field fluctuations result in larger redshifts for distant galaxy clusters than traditional cosmological models predict. And so, the cosmological constant remains true to the model's predictions.
"I was surprised that the cosmological constant problem simply seems to disappear in this new perspective on the cosmos," Lombriser said.
A recipe for the dark universe
Lombriser's new framework also tackles some of cosmology's other pressing problems, including the nature of dark matter. This invisible material outnumbers ordinary matter particles by a ratio of 5 to 1, but remains mysterious because it doesn't interact with light.
Lombriser suggested that fluctuations in the field could also behave like a so-called axion field, with axions being hypothetical particles that are one of the suggested candidates for dark matter.
These fluctuations could also do away with dark energy, the hypothetical force stretching the fabric of space and thus driving galaxies apart faster and faster. In this model, the effect of dark energy, according to Lombriser, would be explained by particle masses taking a different evolutionary path at later times in the universe.
In this picture "there is, in principle, no need for dark energy," Lombriser added.
Post-doctoral researcher at the Universidad ECCI, Bogotá, Colombia, Luz Ángela García, was impressed with Lombriser's new interpretation and how many problems it resolves.
"The paper is pretty interesting, and it provides an unusual outcome for multiple problems in cosmology," García, who was not involved in the research, told Live Science. "The theory provides an outlet for the current tensions in cosmology."
However, García urged caution in assessing the paper's findings, saying it contains elements in its theoretical model that likely can't be tested observationally, at least in the near future.
Related:
—Dark energy could lead to a second (and third, and fourth) Big Bang, new research suggests
—Something is wrong with Einstein's theory of gravity
—Da Vinci understood key aspect of gravity centuries before Einstein, lost sketches reveal
—Are black holes wormholes?
本文於 修改第 3 次
|
|
宇宙其實年齡大一倍？ - Mike Mcrae
|
|
|
推薦0 |
|
|
|
《科學快報》這篇報導再度顯示；到目前為止，即使在自然科學領域，人類只有「假說」、尚待進一步證實的「理論」；並無「真理」可言(請參見本欄《宇宙膨脹可能是幻象》一文)。
The Entire Universe Could Be Twice as Old as We Thought
MIKE MCRAE, 《科學快報》SPACE, 07/13/23
A retired cosmological theory should be given a second chance at explaining anomalies in our Universe, according to theoretical physicist Rajendra Gupta from the University of Ottawa in Canada.
By marrying the existing expanding Universe theory with a fringe explanation called the tired light hypothesis, Gupta has found the Big Bang could have taken place an astonishing 26.7 billion years ago. That's twice as old as current models predict.
Those added years could explain why the most distant galaxies observed look surprisingly mature for star-cities that ought to have only been around for half a billion years.
Estimating the age of the Universe isn't unlike guessing a child's birthday based on their height. Objects in the distance – in every direction – look a little redder than their signature patterns of light might have us expect. The most likely explanation is that space expands, stretching those light waves apart like a pulled spring.
As light takes time to travel, redder light is older light, having been pulled over a greater distance. Working backward on this estimated growth rate, it's possible to use expansion to determine when the Universe was a compact volume seething with concentrated energy.
However, this hasn't been the only attempt to explain why light in the distance looks redder. In 1929, Swiss astronomer Fritz Zwicky suggested light simply lost its puff over such vast stretches of space. Less energy means lower frequency and longer wavelengths, shifting the spectrum of bright, distant objects.
Basically, the light got 'tired'.
While Zwicky would later land upon a landmark discovery establishing the great mystery of dark matter, his tired light hypothesis suffered too many problems to make the grade, leaving the expanding Universe model as the theory of choice.
As Gupta puts it in his recently published proposal, that doesn't mean the two concepts are mutually exclusive. A combination might even help resolve why the earliest quasars and galaxies appear to be billions of years old.
It might also help explain why they look smaller than expected despite their well-developed masses.
Gupta's hybrid hypothesis presumes the Universe really is as big as we believe, having expanded to its size from a Big Bang event in the past. He starts with two expanding Universe models: one based on standard assumptions about the evenness and flatness of the cosmos and a second one that introduces some tweaks involving what's known as a coupling constant.
Coupling constants describe interactions of forces between particles, such as the way the electromagnetic fields of two protons held in close proximity will affect each other's behavior in specific ways.
All forces have a coupling constant, which isn't necessarily constant at all, changing with energy. This leaves room for coupling constants to vary enough to affect how light behaves. If this constant has changed over time, our calculations on the age of the Universe could be out by a significant amount.
"Our newly-devised model stretches the galaxy formation time by several billion years, making the universe 26.7 billion years old, and not 13.7 as previously estimated," says Gupta.
One of the problems with tired light theory is that a loss of energy in a light wave would correspond with a loss of momentum, affecting the appearance of far distant objects. With ancient galaxies looking unusually petite, this conflict might actually be a reason to reconsider the hypothesis.
As happens whenever observations don't quite align with expectations, scientists throw every idea they can think of at the problem to see what sticks. Some are mundane, some quirky, and some dig up the corpses of dead hypotheses to see if they have heartbeats after all.
Whatever explanation is left standing in the end, it will almost certainly change how we look at our Universe, and its dazzling contents, evolve.
This research was published in the Monthly Notices of the Royal Astronomical Society.
本文於 修改第 3 次
|
|
宇宙膨脹真的可能是幻象嗎? - Ethan Siegel
|
|
|
推薦0 |
|
|
|
希苟教授這篇文章深入的批判開欄文所報導的新數學理論。他是【以一次巨響開始】部落格的版主；經常發表對宇宙學和天文物理學方面的觀點。
希苟教授的文章一向圖文並茂，請至原網頁參考附圖。在風格上我覺得他有些強勢，近於主觀。
Could the expanding Universe truly be a mirage?
A cute mathematical trick can "rescale" the Universe so that it isn't actually expanding. But can that "trick" survive all our cosmic tests?
Ethan Siegel, 06/27/23
KEY TAKEAWAYS
* In a new paper just accepted for publication in the journal Classical & Quantum Gravity, theoretical physicist Lucas Lombriser showed that one can reformulate the Universe to not be expanding, after all.
* Instead, you can rescale your coordinates so that all of the fundamental constants within your Universe change in a specific fashion over time, mimicking cosmic expansion in an actually non-expanding Universe.
* But could this approach actually apply to our real Universe, or is it a mere mathematical trick that the observations we already have rule out? The smart money is on the latter option.
Back in the 1920s, two side-by-side developments occurred that paved the way for our modern understanding of the Universe. On the theoretical side, we were able to derive that if you obeyed the laws of General Relativity and had a Universe that was (on average) uniformly filled with matter-and-energy, your Universe couldn’t be static and stable, but must either expand or collapse. On the observational side, we began to identify galaxies beyond the Milky Way, and quickly determined that (on average) the farther away they were observed to be, the faster they were observed to be receding from us.
Simply by putting theory and observation together, the notion of the expanding Universe was born, and has been with us ever since. Our standard model of cosmology — including the Big Bang, cosmic inflation, the formation of cosmic structure, and dark matter and dark energy — is all built upon the basic foundation of the expanding Universe.
But is the expanding Universe an absolute necessity, or is there a way around it? In an interesting new paper that’s recently gotten some publicity, theoretical physicist Lucas Lombriser argues that the expanding Universe can be “transformed away” by manipulating the equations of General Relativity. In his scenario, the observed cosmic expansion would merely be a mirage. But does this stand up to the science we already know? Let’s investigate.
Every once in a while, we recognize that there are multiple different ways to look at the same phenomenon. If these two ways are physically equivalent, then we understand there’s no difference between them, and which one you choose is simply a matter of personal preference.
* In the science of optics, for example, you can either describe light as a wave (as Huygens did) or as a ray (as Newton did), and under most experimental circumstances, the two descriptions make identical predictions.
* In the science of quantum physics, where quantum operators act on quantum wavefunctions, you can either describe particles with a wavefunction that evolves and with unchanging quantum operators, or you can keep the particles unchanging and simply have the quantum operators evolve.
* Or, as is often the case in Einstein’s relativity, you can imagine that two observers have clocks: one on the ground and one on a moving train. You can describe this equally well by two different scenarios: having the ground be “at rest” and watching the train experience the effects of time dilation and length contraction as it’s in motion, or having the train be “at rest” and watching the observer on the ground experience time dilation and length contraction.
As the very word “relative” implies, these scenarios, if they give identical predictions to one another, then either one is just as equally valid as the other.
The latter scenario, in relativity, suggests to us that we might be interested in performing what mathematicians refer to as a coordinate transformation. You’re probably used to thinking of coordinates the same way René Descartes did some ~400 years ago: as a grid, where all the directions/dimensions are perpendicular to one another and have the same length scales applying equally to all axes. You probably even learned about these coordinates in math class in school: Cartesian coordinates.
But Cartesian coordinates aren’t the only ones that are useful. If you’re dealing with something that has what we call axial symmetry (symmetry about one axis), you might prefer cylindrical coordinates. If you’re dealing with something that’s the same in all directions around a center, it might make more sense to use spherical coordinates. And if you’re dealing not only with space but with spacetime — where the “time” dimension behaves in a fundamentally different way from the “space” dimensions — you’re going to have a much better time if you use hyperbolic coordinates to relate space and time to one another.
What’s great about coordinates is this: they’re just a choice. As long as you don’t change the underlying physics behind a system, you’re absolutely free to work in whatever coordinate system you prefer to describe whatever it is that you’re considering within the Universe.
There’s an obvious way to try to apply this to the expanding Universe. Conventionally, we take note of the fact that distances in bound systems, like atomic nuclei, atoms, molecules, planets, or even star systems and galaxies, don’t change over time; we can use them as a “ruler” to measure distances equally well at any given moment. When we apply that to the Universe as a whole, because we see distant (unbound) galaxies receding away from one another, we conclude that the Universe is expanding, and work to map out how the expansion rate has changed over time.
So, why not do the obvious thing and flip those coordinates around: to keep the distances between (unbound) galaxies in the Universe fixed, and simply have our “rulers” and all other bound structures shrink with time?
It might seem like a frivolous choice to make, but oftentimes, in science, just by changing the way we look at a problem, we can uncover some features about it that were obscure in the old perspective, but become clear in the new one. It makes us wonder — and this is what Lombriser explored in his new paper — just what we’d conclude about some of the biggest puzzles of all if we adopted this alternative perspective?
So instead of the standard way of viewing cosmology, you can instead formulate your Universe as static and non-expanding, at the expense of having:
* masses,
* lengths,
* and timescales,
all change and evolve. Because the goal is to keep the structure of the Universe constant, you can’t have expanding, curved space that has growing density imperfections within it, and so those evolutionary effects need to be encoded elsewhere. Mass scales would have to evolve across spacetime, as would distance scales and timescales. They would have to all coevolve together in precisely such a way that, when you put them together to describe the Universe, they added up to the “reverse” of our standard interpretation.
Alternatively, you can keep both the structure of the Universe constant as well as mass scales, length scales, and timescales, but at the expense of having the fundamental constants within your Universe coevolve together in such a way that all of the dynamics of the Universe get encoded onto them.
You might try to argue against either of these formulations, as our conventional perspective makes more intuitive sense. But, as we mentioned earlier, if the mathematics is identical and there are no observable differences between the predictions that either perspective makes, then they all have equal validity when we try to apply them to the Universe.
Want to explain cosmic redshift? You can in this new picture, but in a different way. In the standard picture:
* an atom undergoes an atomic transition,
* emits a photon of a particular wavelength,
* that photon travels through the expanding Universe, which causes it to redshift as it travels,
* and then, when the observer receives it, it now has a longer wavelength than the same atomic transition has in the observer’s laboratory.
But the only observation that we can make occurs in the laboratory: where we can measure the observed wavelength of the received photon and compare it to the wavelength of a laboratory photon.
It could also be occurring because the mass of the electron is evolving, or because Planck’s constant (ℏ) is evolving, or because the (dimensionless) fine-structure constant (or some other combination of constants) is evolving. What we measure as a redshift could be due to a variety of different factors, all of which are indistinguishable from one another when you measure that distant photon’s redshift. It’s worth noting that this reformulation, if extended properly, would give the same type of redshift for gravitational waves, too.
Similarly, we could reformulate how structure grows in the Universe. Normally, in the standard picture, we start out with a slightly overdense region of space: where the density in this region is just slightly above the cosmic mean. Then, over time:
* this gravitational perturbation preferentially attracts more matter to it than the surrounding regions,
* causing space in that region to expand more slowly than the cosmic average,
* and as the density grows, it eventually crosses a critical threshold triggering conditions where it’s gravitationally bound,
* and then it begins gravitationally contracting, where it grows into a piece of cosmic structure like a star cluster, galaxy, or even larger collection of galaxies.
However, instead of following the evolution of a cosmic overdensity, or of the density field in some sense, you can replace that with a combination of mass scales, distance scales, and time scales evolving instead. (Similarly, Planck’s constant, the speed of light, and the gravitational constant could evolve, alternatively, instead.) What we see as a “growing cosmic structure” could be a result not of cosmic growth, but of these parameters fundamentally changing over time, leaving the observables (like structures and their observed sizes) unchanged.
If you take this approach, however unpalatable it may seem, you can try to reinterpret some of the presently inexplicable properties our Universe seems to possess. For example, there’s the “cosmological constant” problem, where for some reason, the Universe behaves as though it were filled with a field of constant energy density inherent to space: an energy density that doesn’t dilute or change in value as the Universe expands. This wasn’t important long ago, but appears to be important now only because the matter density has diluted below a certain critical threshold. We don’t know why space should have this non-zero energy density, or why it should take on the value that’s consistent with our observed dark energy. In the standard picture, it’s just an unexplained mystery.
However, in this reformulated approach, there’s a relationship between the value of the cosmological constant and — if you have mass scales and distance scales changing according to the new formulation — the inverse of the Planck length squared. Sure, the Planck length changes as the Universe evolves in this new formulation, but it evolves biased toward the observer: the value we observe now has the value that it has now simply because it is now. If times, masses, and lengths all evolve together, then that eliminates what we call the “coincidence problem” in cosmology. Any observer will observe their effective cosmological constant to be important “now” because their “now” keeps evolving with cosmic time.
They can reinterpret dark matter as a geometric effect of particle masses increasing in a converging fashion at early times. They can alternately reinterpret dark energy as a geometric effect as particle masses, at late times, increase in a diverging fashion. And, quite excitingly, there may be ties between a different way to reinterpret dark matter — where cosmic expansion is reformulated as a scalar field that winds up behaving like a known dark matter candidate, the axion — and couplings between the field causing expansion and the matter in our Universe introduces CP violation: one of the key ingredients needed to generate a matter-antimatter asymmetry in our Universe.
Thinking about the problem in this fashion leads to a number of interesting potential consequences, and in this early “sandbox” phase, we shouldn’t discourage anyone from doing precisely this type of mathematical exploration. Thoughts like this may someday be a part of whatever theoretical foundation takes us beyond the well-established current standard picture of cosmology.
However, there’s a reason that most modern cosmologists who deal with the physical Universe we inhabit don’t bother with these considerations, which are interesting from the perspective of pure General Relativity: the laboratory also exists, and while these reformulations are okay on a cosmic scale, they conflict wholeheartedly with what we observe here on Earth.
Consider, for example, the notion that either:
* fundamental particle properties, such as masses, charges, lengths, or durations are changing,
* or fundamental constants, such as the speed of light, Planck’s constant, or the gravitational constant are changing.
Our Universe, observably, is only 13.8 billion years old. We’ve been making high-precision measurements of quantum systems in the lab for several decades now, with the best-precision measurements revealing properties of matter to within about 1.3 parts in ten trillion. If either the particle properties or the fundamental constants were changing, then our laboratory measurements would be changing as well: according to these reformulations, over a ~14 year timescale (since 2009 or so), we would have noticed variations in the observed properties of these well-measured quanta that are thousands of times larger than our tightest constraints: of about 1-part-per-billion.
The electron magnetic moment, for example, was measured to very high precision in 2007 and in 2022, and showed less than a 1-part-in-a-trillion variation (the limits of the earlier measurement’s precision) between them, showing that the fine-structure constant hasn’t changed.
The spin-flip transition of hydrogen, which results in an emission line of a precise wavelength of 21.10611405416 centimeters, has an uncertainty on it of just 1.4 parts-per-trillion and has not changed since it was first observed in 1951. (Although we’ve measured it better over time.) That shows Planck’s constant hasn’t changed.
And the Eötvös experiment, which measures the equivalence of inertial mass (which isn’t affected by the gravitational constant) and gravitational mass (which is) has shown these two “types” of mass are equivalent to a remarkable 1-part-per-quadrillion as of 2017.
This is a remarkable feature about our Universe under the standard way of looking at things: the very same laws of physics that apply here on Earth apply everywhere else in the Universe, at all locations and times throughout our cosmic history. A perspective applied to the Universe that fails here on Earth is far less interesting than one that applies successfully over the full range of physically interesting systems. If the conventional expanding Universe also agrees with physics on Earth and an alternative to it describes the larger Universe well but fails here on Earth, we cannot say the expanding Universe is a mirage. After all, physics here on Earth is the most real and most well-measured and well-tested anchor we have for determining what’s actually real.
That isn’t to say that journals that publish this type of speculative research — Classical and Quantum Gravity, the Journal of High-Energy Physics, or the Journal of Cosmology and Astroparticle Physics, to name a few — aren’t reputable and high-quality; they are. They’re just niche journals: far more interested in these types of early-stage explorations than they are with a confrontation with our experimentally and observationally driven reality. By all means, keep playing in the sandbox and exploring alternatives to the standard cosmological (and particle physics) pictures of reality. But don’t pretend that throwing out all of reality is a viable option. The only “mirage” here is the notion that our observed, measured reality is somehow unimportant when it comes to understanding our Universe.
本文於 修改第 5 次
|
|
|
本城市首頁
看回應文章
等級：8
