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自然科學：普及篇 – 開欄文
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我是物理系畢業生，有了自然科學的基本常識；容易讀懂科學新知的報導，同時也有興趣接觸它們。
過去《中華雜誌》雖是政論性和人文學術性刊物，但有時會介紹一些自然科學的研究結果；每年也都會刊登有關諾貝爾獎得主的消息。我唸大學時就替《中華》翻譯過一篇報導天文學脈動星的文章。
同窗好友王家堂兄在1980前後，介紹我進入高能物理的「普及科學」世界；此後常常讀一些這方面的書籍。因此，我一直保持著對物理學的興趣，之後自然而然的進入宇宙學領域。
以上三點是這個部落格過去經常轉載自然科學方面報導/論文的背景。
本文於 修改第 3 次
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破解生命起源奧秘：過去5年的5個突破性發現 – S. Jordan/L. G. de Chalonge
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Unravelling life’s origin: five key breakthroughs from the past five years
Seán Jordan/Louise Gillet de Chalonge, 05/02/24
There is still so much we don’t understand about the origin of life on Earth.
The definition of life itself is a source of debate among scientists, but most researchers agree on the fundamental ingredients of a living cell. Water, energy, and a few essential elements are the prerequisites for cells to emerge. However, the exact details of how this happens remain a mystery.
Recent research has focused on trying to recreate in the lab the chemical reactions that constitute life as we know it, in conditions plausible for early Earth (around 4 billion years ago). Experiments have grown in complexity, thanks to technological progress and a better understanding of what early Earth conditions were like.
However, far from bringing scientists together and settling the debate, the rise of experimental work has led to many contradictory theories. Some scientists think that life emerged in deep-sea hydrothermal vents, where the conditions provided the necessary energy. Others argue that hot springs on land would have provided a better setting because they are more likely to hold organic molecules from meteorites. These are just two possibilities which are being investigated.
Here are five of the most remarkable discoveries over the last five years.
Reactions in early cells
What energy source drove the chemical reactions at the origin of life? This is the mystery that a research team in Germany has sought to unravel. The team delved into the feasibility of 402 reactions known to create some of the essential components of life, such as nucleotides (a building block of DNA and RNA). They did this using some of the most common elements that could have been found on the early Earth.
These reactions, present in modern cells, are also believed to be the core metabolism of LUCA, the last universal common ancestor, a single-cell, bacterium-like organism.
For each reaction, they calculated the changes in free energy, which determines if a reaction can go forward without other external sources of energy. What is fascinating is that many of these reactions were independent of external influences like adenosine triphosphate, a universal source of energy in living cells.
The synthesis of life’s fundamental building blocks didn’t need an external energy boost: it was self-sustaining.
Volcanic glass
Life relies on molecules to store and convey information. Scientists think that RNA (ribonucleic acid) strands were precursors to DNA in fulfilling this role, since their structure is more simple.
The emergence of RNA on our planet has long confused researchers. However, some progress has been made recently. In 2022, a team of collaborators in the US generated stable RNA strands in the lab. They did it by passing nucleotides through volcanic glass. The strands they made were long enough to store and transfer information.
Volcanic glass was present on the early Earth, thanks to frequent meteorite impacts coupled with a high volcanic activity. The nucleotides used in the study are also believed to have been present at that time in Earth’s history. Volcanic rocks could have facilitated the chemical reactions that assembled nucleotides into RNA chains.
Hydrothermal vents
Carbon fixation is a process in which CO₂ gains electrons. It is necessary to build the molecules that form the basis of life.
An electron donor is necessary to drive this reaction. On the early Earth, H₂ could have been the electron donor. In 2020, a team of collaborators showed that this reaction could spontaneously occur and be fuelled by environmental conditions similar to deep-sea alkaline hydrothermal vents in the early ocean. They did this using microfluidic technology, devices that manipulate tiny volumes of liquids to perform experiments by simulating alkaline vents.
This pathway is strikingly similar to how many modern bacterial and archaeal cells (single-cell organisms without a nucleas) operate.
The Krebs Cycle
In modern cells, carbon fixation is followed by a cascade of chemical reactions that assemble or break down molecules, in intricate metabolic networks that are driven by enzymes.
But scientists are still debating how metabolic reactions unfolded before the emergence and evolution of those enzymes. In 2019, a team from the University of Strasbourg in France made a breakthrough. They showed that ferrous iron, a type of iron that was abundant in early Earth’s crust and ocean, could drive nine out of 11 steps of the Krebs Cycle. The Krebs Cycle is a biological pathway present in many living cells.
Here, ferrous iron acted as the electron donor for carbon fixation, which drove the cascade of reactions. The reactions produced all five of the universal metabolic precursors – five molecules that are fundamental across various metabolic pathways in all living organisms.
Building blocks of ancient cell membranes
Understanding the formation of life’s building blocks and their intricate reactions is a big step forward in comprehending the emergence of life.
However, whether they unfolded in hot springs on land or in the deep sea, these reactions would not have gone far without a cell membrane. Cell membranes play an active role in the biochemistry of a primitive cell and its connection with the environment.
Modern cell membranes are mostly composed of compounds called phospholipids, which contain a hydrophilic head and two hydrophobic tails. They are structured in bilayers, with the hydrophilic heads pointing outward and the hydrophobic tails pointing inward.
Research has shown that some components of phospholipids, such as the fatty acids that constitute the tails, can self-assemble into those bilayer membranes in a range of environmental conditions. But were these fatty acids present on the early Earth? Recent research from Newcastle University, UK gives an interesting answer. Researchers recreated the spontaneous formation of these molecules by combining H₂-rich fluids, likely present in ancient alkaline hydrothermal vents, with CO₂-rich water resembling the early ocean.
This breakthrough aligns with the hypothesis that stable fatty acid membranes could have originated in alkaline hydrothermal vents, potentially progressing into living cells. The authors speculated that similar chemical reactions might unfold in the subsurface oceans of icy moons, which are thought to have hydrothermal vents similar to terrestrial ones.
Each of these discoveries adds a new piece to the puzzle of the origin of life. Regardless of which ones are proved correct, contrasting theories are fuelling the search for answers. As Charles Darwin wrote:
False facts are highly injurious to the progress of science for they often long endure: but false views, if supported by some evidence, do little harm, for everyone takes a salutary pleasure in proving their falseness; and when this is done, one path towards error is closed and the road to truth is often at the same time opened.
Seán Jordan, Associate professor, Dublin City University
Louise Gillet de Chalonge, PhD Student in Astrobiology, Dublin City University
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三體互動問題：從天文物理到人際關係 – Avi Loeb
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應該是因為功力不夠，讀完這篇文章後我頗有「丈二金剛」的感覺。標題有「人際互動」，但涉及此議題文字可能頂多只有全文的1/8。
婁布博士寫這篇文章的目的，大概只是為了說出以下這段話：
Four years ago, I recommended this novel to the creators of a new series on Netflix, which recently came to fruition.
劉慈欣先生這部大作《三體》和根據它拍成的電影，也被此欄04/12/24關於文革的貼文引用，做為該談話節目的「引子」。所以，雖然我沒搞懂作者此文要表達什麼主旨，還是給它轉載，湊個熱鬧；並替劉先生和Netflix打打廣告。
THE THREE-BODY PROBLEM: FROM CELESTIAL MECHANICS TO HUMAN INTERACTIONS
AVI LOEB, 04/04/24
There are striking analogies between the interpersonal relationships of humans and the gravitational interaction of physical bodies in space. Consider a two-body system. In both realms, the systems can have stable configurations, leading to long-lived marriages or stellar binaries. But when a third body interacts strongly with these systems, a non-hierarchical three-body system often displays chaos with one of the members ejected and the other two remaining bound. This brings up analogies with interpersonal relationships when a third body is added to a non-hierarchical two-body system.
The chaotic gravitational dynamics in a system of three stars inspired the storyline for the novel “The Three-Body Problem” by the Chinese science fiction writer Cixin Liu. The book describes a planet in the triple star system, Alpha-Centauri, whose unpredictable chaotic dynamics motivate a civilization born there to travel towards Earth, which possesses a stable orbit around the Sun. Four years ago, I recommended this novel to the creators of a new series on Netflix, which recently came to fruition.
The restricted three-body problem involves a stable orbit of two large bodies accompanied by a small third body. In this case, the satellite resembles a child living with two parents, a configuration that often, but not always, displays stability.
In 1975, the Scottish astronomer Douglas C. Heggie wrote a paper in which he simulated the evolution of pairs of stars embedded in a star cluster. Heggie compared the binding energy per unit mass of each stellar binary to the characteristic energy of the background cluster members. He found that binaries, which are more tightly bound than the background average, tend to get tighter as a result of interactions with the background stars. Conversely, binaries which are more loosely bound than the background, get wider and eventually detach. This resulted in Heggie’s law: “Hard binaries get harder, and soft binaries get softer.” This law rings a bell regarding married couples in a closed society of background people who interact intensely with them.
The above-mentioned analogies are surprising, given that gravity is attractive, whereas human interactions are both attractive and repulsive. In electromagnetism, charges of equal sign repel each other, whereas charges of opposite sign are attracted to each other. This is different from human interactions, where people with aligned views are attracted to each other, and those with opposite views repel each other.
The main difference between a collection of charged particles, a so-called plasma, and a collection of gravitating bodies is that electric interactions can be screened. An embedded charge tends to attract opposite charges around it, resulting in the so-called Debye sphere, outside of which this charge has no influence. The neutralization of embedded charges makes a plasma behave like a neutral fluid on scales much larger than the Debye scale. In contrast, gravity cannot be screened because all known gravitating masses are positive.
The long-range nature of gravity, with no screening, allows it to dominate the evolution of the Universe. All other known forces, including electromagnetism and the weak and strong interactions, are much stronger than gravity on small scales, but they do not reach the cosmic scales on which gravity is most effective.
Another difference between a plasma and a collection of gravitating bodies is that the latter is dynamically unstable. The core of a star cluster, with more binding energy per star than its envelope, tends to transport energy outwards, just like a hot object embedded in a cold environment. As energy is drained from the core, it condenses to a higher density where it becomes even “hotter”. This results in a gravothermal instability, during which the collapse process accelerates as the interaction time among the stars gets shorter as the cluster core gets denser.
In 1957, the Austrian-British astrophysicist Herman Bondi wrote a paper in which he considered the existence of negative masses in Albert Einstein’s theory of gravity. A negative mass would repel a positive mass away from it and attract another negative mass towards it. Given that, a pair of positive and negative masses of equal magnitude could accelerate together up to the speed of light. The negative mass would push away the positive mass, which in turn would pull the negative mass for the ride. The runaway pair would accelerate indefinitely without any need for fuel or a propulsion system. Energy conservation would not be violated because the sum of the two masses is zero. Does the real Universe contain runaway pairs of positive and negative masses that accelerate close to the speed of light over billions of years?
A runaway pair of equal and opposite-sign masses would not exert a net-gravitational influence at large distances because the two components sum up to a zero total mass. However, if the runaway pair passes close to a gravitational wave observatory, like LIGO-Virgo-KAGRA, it could induce a brief gravitational signal that could be detected at distances comparable to the separation between the positive and negative masses. The signal will be characterized by a pulse of gravitational attraction followed by a pulse of gravitational repulsion or the other way around.
Given that the net gravitational effect of runaway pairs is zero, they have no effect on the mass budget of the Universe or its expansion history. However, it would be intriguing to search for them. If we ever find material with a negative mass, we could use it for gravitational propulsion. Alternatively, if we ever encounter an alien spacecraft that maneuvers with no associated engine or fuel, we should check whether its creators used negative mass to propel it.
After all, we know that the expansion of the universe is accelerating due to the repulsive gravity generated by an unknown substance called “dark energy.” If we could bottle this substance in a thin enclosure, we might possess a negative mass object that could enable our future exploration of interstellar space.
Avi Loeb is the head of the Galileo Project, founding director of Harvard University’s – Black Hole Initiative, director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics, and the former chair of the astronomy department at Harvard University (2011-2020). He is a former member of the President’s Council of Advisors on Science and Technology and a former chair of the Board on Physics and Astronomy of the National Academies. He is the bestselling author of “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth” and a co-author of the textbook Life in the Cosmos”, both published in 2021. His new book, titled “Interstellar”, was published in August 2023
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關於暗能量的新數據及其導致的推論 -- Dennis Overbye
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A Tantalizing ‘Hint’ That Astronomers Got Dark Energy All Wrong
Scientists may have discovered a major flaw in their understanding of that mysterious cosmic force. That could be good news for the fate of the universe.
An interactive flight through millions of galaxies mapped using coordinate data from the Dark Energy Spectroscopic Instrument, or DESI. Credit...By Fiske Planetarium, University Of Colorado Boulder And Desi Collaboration (請至原網頁查看圖片)
Dennis Overbye, 04/04/24
On Thursday, astronomers who are conducting what they describe as the biggest and most precise survey yet of the history of the universe announced that they might have discovered a major flaw in their understanding of dark energy, the mysterious force that is speeding up the expansion of the cosmos.
Dark energy was assumed to be a constant force in the universe, both currently and throughout cosmic history. But the new data suggest that it may be more changeable, growing stronger or weaker over time, reversing or even fading away.
“As Biden would say, it’s a B.F.D.,” said Adam Riess, an astronomer at Johns Hopkins University and the Space Telescope Science Institute in Baltimore. He shared the 2011 Nobel Prize in Physics with two other astronomers for the discovery of dark energy, but was not involved in this new study. “It may be the first real clue we have gotten about the nature of dark energy in 25 years,” he said. (卜凱：B.F.D. = big fucking deal)
That conclusion, if confirmed, could liberate astronomers — and the rest of us — from a longstanding, grim prediction about the ultimate fate of the universe. If the work of dark energy were constant over time, it would eventually push all the stars and galaxies so far apart that even atoms could be torn asunder, sapping the universe of all life, light, energy and thought, and condemning it to an everlasting case of the cosmic blahs. Instead, it seems, dark energy is capable of changing course and pointing the cosmos toward a richer future.
The key words are “might” and “could.” The new finding has about a one-in-400 chance of being a statistical fluke, a degree of uncertainty called three sigma, which is far short of the gold standard for a discovery, called five sigma: one chance in 1.7 million. In the history of physics, even five-sigma events have evaporated when more data or better interpretations of the data emerged.
This news comes in the first progress report, published as a series of papers, by a large international collaboration called the Dark Energy Spectroscopic Instrument, or DESI. The group has just begun a five-year effort to create a three-dimensional map of the positions and velocities of 40 million galaxies across 11 billion years of cosmic time. Its initial map, based on the first year of observations, includes just six million galaxies. The results were released today at a meeting of the American Physical Society in Sacramento, Calif., and at the Rencontres de Moriond conference in Italy.
DESI has generated the largest-ever 3-D map of the universe. Earth is depicted at the bottommost point of one magnified section.Credit...Claire Lamman/DESI collaboration; Custom Colormap Package by cmastro (請至原網頁查看圖片)
“So far we’re seeing basic agreement with our best model of the universe, but we’re also seeing some potentially interesting differences that could indicate that dark energy is evolving with time,” Michael Levi, the director of DESI, said in a statement issued by the Lawrence Berkeley National Laboratory, which manages the project.
The DESI team had not expected to hit pay dirt so soon, Nathalie Palanque-Delabrouille, an astrophysicist at the Lawrence Berkeley lab and a spokeswoman for the project, said in an interview. The first year of results was designed to simply confirm what was already known, she said: “We thought that we would basically validate the standard model.”
But the unknown leaped out at them.
When the scientists combined their map with other cosmological data, they were surprised to find that it did not quite agree with the otherwise reliable standard model of the universe, which assumes that dark energy is constant and unchanging. A varying dark energy fit the data points better.
“It’s certainly more than a curiosity,” Dr. Palanque-Delabrouille said. “I would call it a hint. Yeah, it’s not yet evidence, but it’s interesting.”
But cosmologists are taking this hint very seriously.
Wendy Freedman, an astrophysicist at the University of Chicago who has led efforts to measure the expansion of the universe, praised the new survey as “superb data.” The results, she said, “open the potential for a new window into understanding dark energy, the dominant component of the universe, which remains the biggest mystery in cosmology. Pretty exciting.”
Michael Turner, an emeritus professor at the University of Chicago who coined the term “dark energy,” said in an email: “While combining data sets is tricky, and these are early results from DESI, the possible evidence that dark energy is not constant is the best news I have heard since cosmic acceleration was firmly established 20-plus years ago.”
In an artist’s rendering, light from quasars passes through intergalactic clouds of hydrogen gas. The light offers clues to the structure of the distant cosmos.Credit...NOIRLab/NSF/AURA/P. Marenfeld and DESI collaboration (請至原網頁查看圖片)
Dark energy entered the conversation in 1998, when two competing groups of astronomers, including Dr. Riess, discovered that the expansion of the universe was speeding up rather than slowing, as most astronomers had expected. The initial observations seemed to suggest that this dark energy was acting just like a famous fudge factor — denoted by the Greek letter Lambda — that Einstein had inserted into his equations to explain why the universe didn’t collapse from its own gravity. He later called it his worst blunder.
But perhaps he spoke too soon. As formulated by Einstein, Lambda was a property of space-itself: The more space there was as the universe expanded, the more dark energy there was, pushing ever harder and eventually leading to a runaway, lightless future.
Dark energy took its place in the standard model of the universe known as L.C.D.M., composed of 70 percent dark energy (Lambda), 25 percent cold dark matter (an assortment of slow-moving exotic particles) and 5 percent atomic matter. So far that model has been bruised but not broken by the new James Webb Space Telescope. But what if dark energy were not constant as the cosmological model assumed? (卜凱：L.C.D.M. = Lambda cold dark matter)
At issue is a parameter called w, which is a measure of the density, or vehemence, of the dark energy. In Einstein’s version of dark energy, this number remains constant, with a value of –1, throughout the life of the universe. Cosmologists have been using this value in their models for the past 25 years.
But this version of dark energy is merely the simplest one. “With DESI we now have achieved a precision that allows us to go beyond that simple model,” Dr. Palanque-Delabrouille said, “to see if the density of dark energy is constant over time, or if it has some fluctuations and evolution with time.”
The DESI project, 14 years in the making, was designed to test the constancy of dark energy by measuring how fast the universe was expanding at various times in the past. To do that, scientists outfitted a telescope at Kitt Peak National Observatory with 5,000 fiber-optic detectors that could conduct spectroscopy on that many galaxies simultaneously and find out how fast they were moving away from Earth.
An animated 3-D model of DESI’s focal plane. The movement of the 5,000 robotic positioners is coordinated so that they don’t bump into one another. Credit Credit...By David Kirkby/desi Collaboration (請至原網頁查看圖片)
As a measure of distance, the researchers used bumps in the cosmic distribution of galaxies, known as baryon acoustic oscillations. These bumps were imprinted on the cosmos by sound waves in the hot plasma that filled the universe when it was just 380,000 years old. Back then, the bumps were a half-million light-years across. Now, 13.5 billion years later, the universe has expanded a thousandfold, and the bumps — which are now 500 million light-years across — serve as convenient cosmic measuring sticks.
The DESI scientists divided the past 11 billion years of cosmic history into seven spans of time. (The universe is 13.8 billion years old.) For each, they measured the size of these bumps and how fast the galaxies in them were speeding away from us and from each other. (卜凱：關於宇宙年齡，請見本欄2024/03/19貼文)
When the researchers put it all together, they found that the usual assumption — a constant dark energy — didn’t work to describe the expansion of the universe. Galaxies in the three most recent epochs appeared closer than they should have been, suggesting that dark energy could be evolving with time.
“And we do see, indeed, a hint that the properties of dark energy would not correspond to a simple cosmological constant” but instead may “have some deviations,” Dr. Palanque-Delabrouille said. “And this is the first time we have that.” But, she emphasized again, “I wouldn’t call it evidence yet. It’s too, too weak.”
Time and more data will tell the fate of dark energy, and of cosmologists’ battle-tested model of the universe
“L.C.D.M. is being put through its paces by precision tests coming at it from every direction,” Dr. Turner said. “And it is doing well. But, when everything is taken together, it is beginning to appear that something isn’t right or something is missing. Things don’t fit together perfectly. And DESI is the latest indication.”
Dr. Riess of Johns Hopkins, who had an early look at the DESI results, noted that the “hint,” if validated, could pull the rug out from other cosmological measurements, such as the age or size of the universe. “This result is very interesting and we should take it seriously,” he wrote in his email. “Otherwise why else do we do these experiments?”
Dennis Overbye is the cosmic affairs correspondent for The Times, covering physics and astronomy. More about Dennis Overbye
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宇宙學ABC和「『第一因』問題」何以無解-Marcelo Gleiser
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The Big Bang’s mysteries and unsolvable “first cause” problem
The “first cause” problem may forever remain unsolved, as it doesn’t fit with the way we do science.
Marcelo Gleiser, 04/05/24
KEY TAKEAWAYS
* The quest to understand the Universe’s origin has evolved from mythic narratives to the quantitative insights of modern cosmology, sparked by Einstein’s theory of relativity and its implications for understanding the cosmos’s structure and expansion.
* Key discoveries, such as the expanding Universe through Hubble’s observations and the Big Bang theory’s predictive success, have grounded our cosmic understanding in observable phenomena, revealing a Universe that was once hotter, denser, and more uniform.
* Despite significant advances, the earliest moments and the fundamental cause of the Universe’s inception remain shrouded in mystery — perhaps forever so.
If there’s one question that has been present throughout human history across all cultures, it’s the question of the origin of all things. Why is there a Universe? How come we exist in it to be able to ask this question? Across millennia, different cultures offered mythic narratives to address the mystery of existence. But with the development of modern science, the focus has shifted to a more quantitative approach — a scientific narrative of the origin and history of the Universe, the focus of modern cosmology.
It all started in 1915 when Albert Einstein proposed his new theory of gravity, the general theory of relativity. Einstein’s brilliant innovation was to treat gravity not as a force acting at a distance, as did Newton, but as the curvature of space due to the presence of mass. Thus, according to Einstein, the orbital motions of celestial objects are caused by the spatial curvature of their surroundings. A way of visualizing this is by throwing marbles across a mattress. If no weight bends the mattress, the marbles will move along straight lines. But if you place a heavy lead ball on the mattress, the marbles that roll nearby will trace curved paths. If you practice your throws, you can get the marbles to circle the lead ball, somewhat like planets circle the Sun. Einstein’s theory allows physicists to calculate the geometry of the bent space around an object. He demonstrated his theory’s validity by both showing how Mercury’s orbit wobbles about the Sun (the precession of Mercury’s perihelium；《水星最接近太陽位置時的旋進軌道》) and by computing how starlight gets bent as it travels near the Sun.
Two years after he launched his new theory, Einstein took a bold step, moving from solar system applications to the whole Universe. He figured that he could solve his equations to estimate the geometry of the Universe as it is bent by the matter inside. To do this, he made three simplifying assumptions: that the Universe is spherical, that it is static, and that matter is, on average, distributed equally everywhere in space (this latter assumption became known as the “cosmological principle”). To his surprise, his imaginary Universe wasn’t stable: perturb it a bit and the whole thing collapses into a point due to its own gravity. Disappointed but not defeated, Einstein added an extra term to his equations to act as a counterbalance to gravity’s attraction: the so-called “cosmological constant.” Adjusting its value, Einstein managed to find his static spherical solution. Hence modern cosmology was born.
Einstein’s pioneering work inspired many theoretical physicists to build their own desktop Universes — mathematical models that changed his assumptions to see what would happen. In 1917, the same year of Einstein’s model, the Dutch Willem De Sitter solved the equations for an empty Universe (one with no matter at all) with the cosmological constant. His solution, not surprisingly, described a space where two points would exponentially move away from one another. In 1922, the Russian Alexander Friedmann abandoned Einstein’s assumption of a static Universe and found, to his delight, solutions for a Universe that would grow with time. How fast it would grow depended on the value of the cosmological constant and on the type of matter that filled all of space.
While theoreticians were imagining different desktop Universes, the American astronomer Edwin Hubble was pointing the 100-inch telescope at Mount Wilson to determine whether the Milky Way was the only galaxy in the Universe or whether there were many galaxies out there — “island Universes” spread across space. In 1924, 100 years ago this year, he hit on the solution: The Milky Way is but one of billions of galaxies out there. The Universe suddenly became enormous, beyond what we humans could contemplate. Five years later, Hubble dropped the real bomb: Not only were there countless galaxies in the cosmos, but the vast majority were moving away from one another. The Universe, Hubble concluded, is expanding. This remarkable discovery changed everything. If the Universe is growing in volume and galaxies are moving apart, that means that in the past they were closer together. Using some coarse approximations, Hubble estimated that some 2 billion years back, galaxies would all be squeezed into a very tiny volume. This would represent the beginning of the comic history. The Universe, it turns out, had a beginning at some distant point in the past.
The Big Bang model
In the late 1940s, the Russian American physicist George Gamow worked with Ralph Alpher and Robert Herman to figure out what could be the story of an expanding Universe. The essential point is that if the Universe was expanding now, then in the past it was smaller, hotter, and denser. Before galaxies, stars, and planets existed, matter was crunched up and broken down into its most basic constituents. Mixing atomic and nuclear physics, the trio arrived at a few stunning conclusions. The first was that a Universe originating in a hot, dense state should now be suffused with microwave radiation, a relic from the era of recombination when hydrogen atoms first formed as protons and electrons joined, thereby releasing photons to traverse the cosmos freely. In modern numbers, that happened about 380,000 years after the Big Bang, the event that marked the beginning of time, the time that clocks the expansion of the Universe. In 1965, the radiation predicted by Gamow, Alpher, and Herman was discovered by Robert Wilson and Arnold Penzias, two radio astronomers working for Bell Labs in New Jersey.
The second prediction from Gamow, Alpher, and Herman was that going even further back in time, the Universe would be so hot and dense that protons and neutrons would roam free, unable to combine to form the first atomic nuclei. As recounted in Steven Weinberg’s classic book The First Three Minutes, the synthesis of the lightest nuclei — or primordial nucleosynthesis — happened when the Universe was about one second to three minutes old, as protons and neutrons combined to form deuterium and tritium, isotopes of hydrogen with one and two neutrons attached to the proton, respectively, and also helium-4 (two protons and two neutrons) and its isotope helium-3 (two protons and one neutron), and, finally, lithium-7 (three protons and four neutrons). Combining the rules of nuclear physics with the thermodynamics of an expanding and cooling Universe, it was possible to estimate the abundances of these elements and compare them to observations. The concordance was another great success for the Big Bang model. By the late 1960s, there was no doubt that the narrative of a Universe that started hot and dense and with matter dissociated into its simplest constituents correctly described the cosmic infancy. The question in everyone’s minds then was: What about earlier times? How far closer to the beginning of time could physics get? This is where things start to get both more exciting — and murkier.
Toward the beginning of time
As we try to push the reach of our theories to earlier times, we move up in energy from atomic and nuclear physics to particle physics. After all, the earlier you look at the Universe, the hotter and denser it was, and so the particles that filled up space had higher energies. Thus, to dive deeply into the cosmic infancy, physicists must use concepts from high-energy physics, going beyond experimental results. With some confidence, we could push the clock back to one-hundred-thousandth of a second after the bang, when the Universe had energies comparable to those when protons and neutrons got broken down into a quark-gluon plasma, a state of matter that has been studied in the past two decades or so with great success but also with some serious conceptual limitations. Still, we have good reason to believe that this state actually existed in the early Universe, presenting a wall behind which matter was dissociated into its simplest known constituents. That is, before this, we can really talk about a primordial soup of elementary particles filling up space.
The spectacular discovery of the Higgs boson in 2012 confirmed that we could study different forces of nature under the same framework. We know of four fundamental forces: the gravitational, the electromagnetic, and the strong and weak nuclear forces. The two latter forces are only active at subnuclear distances, explaining why we are not familiar with them in our everyday lives. What the discovery of the Higgs confirmed was that the electromagnetic and weak forces tend to behave in similar ways at very high energies, at the limit of what our current experiments can probe. If we map these energies to the early Universe, we are talking about one-trillionth of a second after the bang, or 10-12 seconds (10的12次方). We don’t understand exactly how particles interact at these energies, but what we do understand, summarized in the Standard Model of particle Physics, indicates that the whole Universe went through a sort of phase transition. This transition resembles the process where cooling liquid water crystallizes into ice, breaking the fluid’s uniform symmetry—where molecules are evenly dispersed—into a rigid, ordered lattice. Similarly, we say that the Universe went through a phase transition at about this early time when the “electroweak” force split into the electromagnetic and the weak forces. Details are missing but that’s the overall picture.
At this juncture, cosmology hits a conceptual barrier, as it needs to navigate backward in time without experimental guidance. Despite decades of efforts across the globe, we have not gathered any information from the very early Universe that could guide us. The solution, of course, is to extrapolate and propose models of the early Universe that are compelling for different reasons. For example, they may offer explanations to current challenges to the Big Bang model, as in the inflationary model; they may open new avenues for research in very high energy physics — as in theories of quantum gravity; or they may inspire experimental work in novel directions — as in, for instance, searches for dark matter and primordial gravitational waves.
Inflationary models were proposed during the early 1980s as potential solutions to several issues plaguing the Standard Big Bang model. For example, observations tell us that the geometry of space is very nearly flat, and we don’t know why. We also don’t know why the temperature of the microwave background mentioned above is so homogeneous, to one part in one hundred thousand. We also don’t know how the matter clumping needed to form galaxies and large cosmic structures originated. Somehow, matter gathered in various spots and attracted more matter. Inflation was proposed originally by MIT’s Alan Guth to address these issues. To do so, it invokes a sort of Higgs-like field assumed to be part of some unknown particle physics model describing the physics of the very early Universe. In the same way that the Higgs field drove the split between the electromagnetic and weak forces at 10-12 sec, the “inflaton field” drove the dynamics of the very early Universe at…10-35 sec. That’s a lot of zeroes into the unknown.
Guth’s model, along with the many alternatives proposed since his pioneering work, rely on this extrapolation, assuming that a primordial field caused the Universe to expand exponentially fast for a very short period of time. As the field loses energy, it relaxes to its lowest energy state and decays into a plethora of particles with explosive effectiveness, causing an ultrafast heating of the Universe. Some cosmologists call this the real Big Bang, though this is a matter of taste. One of the challenges here is to uncover an even earlier history of the Universe, one that actually determines what kind of field this hypothetical inflation was and where it came from. Compelling as cosmic inflation is, we don’t really have either a believable model nor any evidence that it truly happened, apart from concordance with current observations. A handful of models nicely describe the Universe that we see (flat, homogeneous, crumpled up) but we still need a mother theory to give it more fundamental validity. What this theory might be requires even more adventurous extrapolations.
Even if we assume that we can push back our models even further in time, we soon hit a monumental conceptual barrier. As we approach the highest energies that we can still make sense of, the Universe may require a different way to be described, borrowing from quantum physics: the physics of the very small. The point is that in the quantum world, everything is jittery and everything fluctuates. If we carry this notion into the force of gravity — and its relation to space and time — we need to consider the possibility that at very early times, there was no time and space as we know them but some sort of vague quantum foam, where space and time bubbled in different ways here and there (though “here” and “there” become very murky ideas). Unfortunately, our current attempts to describe such quantum spacetime foam in theories known as string theories and loop quantum gravity have been only partially successful or not at all successful, at least in providing a compelling scenario for the origin of the Universe. We seem to be fundamentally stuck when it comes to the question of the origin of all things.
The problem of the first cause
And this is not surprising, once we pay attention to the history of philosophy and the nature of science. The origin of the Universe pushes the boundaries of what we can understand. Simply put, most of science is based on two things: objectivity and causality. Objectivity asks for a clear separation between the observer and what is being observed. Causality assumes an ordering in time whereby an effect is preceded by a cause. As I pointed out in a recent book with my colleagues Adam Frank and Evan Thompson, the origin of the Universe brings both causality and objectivity to a halt. And it does so in a very different way from quantum physics, where both principles are also challenged. Quantum mechanics blurs the separation between observer and observed and substitutes deterministic evolution by probabilistic inference. It is, however, still a causal theory since an electron will respond to, say, an electromagnetic force in ways dictated by well-known dynamical causes (with, for a technical example, a Coulomb potential in Schrödinger’s equation). There are known forces at play that will induce specific dynamical behaviors.
But when it comes to the origin of the Universe, we don’t know what forces are at play. We actually can’t know, since to know such force (or better, such fields and their interactions) would necessitate knowledge of the initial state of the Universe. And how could we possibly glean information from such a state in some uncontroversial way? In more prosaic terms, it would mean that we could know what the Universe was like as it came into existence. This would require a god’s eye view of the initial state of the Universe, a kind of objective separation between us and the proto-Universe that is about to become the Universe we live in. It would mean we had a complete knowledge of all the physical forces in the Universe, a final theory of everything. But how could we ever know if what we call the theory of everything is a complete description of all that exists? We couldn’t, as this would assume we know all of physical reality, which is an impossibility. There could always be another force of nature, lurking in the shadows of our ignorance.
At the origin of the Universe, the very notion of cause and objectivity get entangled into a single unknowable, since we can’t possibly know the initial state of the Universe. We can, of course, construct models and test them against what we can measure of the Universe. But concordance is not a criterion for certainty. Different models may lead to the same concordance — the Universe we see — but we wouldn’t be able to distinguish between them since they come from an unknowable initial state. The first cause — the cause that must be uncaused and that unleashed all other causes — lies beyond the reach of scientific methodology as we know it. This doesn’t mean that we must invoke supernatural causes to fill the gap of our ignorance. A supernatural cause doesn’t explain in the way that scientific theories do; supernatural divine intervention is based on faith and not on data. It’s a personal choice, not a scientific one. It only helps those who believe.
Still, through a sequence of spectacular scientific discoveries, we have pieced together a cosmic history of exquisite detail and complexity. There are still many open gaps in our knowledge, and we shouldn’t expect otherwise. The next decades will see us making great progress in understanding many of the open cosmological questions of our time, such as the nature of dark matter and dark energy, and whether gravitational waves can tell us more about primordial inflation. But the problem of the first cause will remain open, as it doesn’t fit with the way we do science. This fact must, as Einstein wisely remarked, “fill a thinking person with a feeling of humility.” Not all questions need to be answered to be meaningful.
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Michio Kaku: Quantum computing is the next revolution
SPECIAL COLLECTION
The Universe. A History.
What was it like when human beings transformed the Earth?
What was it like when humans first arose on planet Earth?
What was it like when mammals appeared and thrived?
What was it like when life on Earth became complex?
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「大爆炸」一詞淵源 -- Helge Kragh
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下文之所以有趣，不只是它敘述了「大爆炸」理論以及該名稱的演變；也在於它描繪出語言 – 這裏指「指號」和「概念」-- 在日常生活中演變的例子。
索引：
denigrate：抹黑，貶低，詆毀
derogatory：貶損的，貶低的，瞧不起的
entail：蘊含，意味
entrenched：牢不可破的，根深柢固的，積重難返的
harpoons：鉤形頭的叉或標槍，捕鯨叉
misnomer：不適當或錯誤的名稱
nomenclature：術語，命名系統
primeval：太古的，原始的，早期的
sitcom：situation comedy的簡稱：以同一群角色在不同有趣情境和情節下的搞笑廣播劇或電視劇
How did the Big Bang get its name? Here’s the real story
Astronomer Fred Hoyle supposedly coined the catchy term to ridicule the theory of the Universe’s origins — 75 years on, it’s time to set the record straight.
Helge Kragh, 03/25/34
“Words are like harpoons,” UK physicist and astronomer Fred Hoyle told an interviewer in 1995. “Once they go in, they are very hard to pull out.” Hoyle, then 80 years old, was referring to the term Big Bang, which he had coined on 28 March 1949 to describe the origin of the Universe. Today, it is a household phrase, known to and routinely used by people who have no idea of how the Universe was born some 14 billion years ago. Ironically, Hoyle deeply disliked the idea of a Big Bang and remained, until his death in 2001, a staunch critic of mainstream Big Bang cosmology.
Several misconceptions linger concerning the origin and impact of the popular term. One is whether Hoyle introduced the nickname to ridicule or denigrate the small community of cosmologists who thought that the Universe had a violent beginning — a hypothesis that then seemed irrational. Another is that this group adopted ‘Big Bang’ eagerly, and it then migrated to other sciences and to everyday language. In reality, for decades, scientists ignored the catchy phrase, even as it spread in more-popular contexts.
The first cosmological theory of the Big Bang type dates back to 1931, when Belgian physicist and Catholic priest Georges Lemaître proposed a model based on the radioactive explosion of what he called a “primeval atom” at a fixed time in the past. He conceived that this primordial object was highly radioactive and so dense that it comprised all the matter, space and energy of the entire Universe. From the original explosion caused by radioactive decay, stars and galaxies would eventually form, he reasoned. Lemaître spoke metaphorically of his model as a “fireworks theory” of the Universe, the fireworks consisting of the decay products of the initial explosion.
However, Big Bang cosmology in its modern meaning — that the Universe was created in a flash of energy and has expanded and cooled down since — took off only in the late 1940s, with a series of papers by the Soviet–US nuclear physicist George Gamow and his US associates Ralph Alpher and Robert Herman. Gamow hypothesized that the early Universe must have been so hot and dense that it was filled with a primordial soup of radiation and nuclear particles, namely neutrons and protons. Under such conditions, those particles would gradually come together to form atomic nuclei as the temperature cooled. By following the thermonuclear processes that would have taken place in this fiery young Universe, Gamow and his collaborators tried to calculate the present abundance of chemical elements in an influential 1948 paper1.
Competing ideas
The same year, a radically different picture of the Universe was announced by Hoyle and Austrian-born cosmologists Hermann Bondi and Thomas Gold. Their steady-state theory assumed that, on a large scale, the Universe had always looked the same and would always do so, for eternity. According to Gamow, the idea of an ‘early Universe’ and an ‘old Universe’ were meaningless in a steady-state cosmology that posited a Universe with no beginning or end.
Over the next two decades, an epic controversy between these two incompatible systems evolved. It is often portrayed as a fight between the Big Bang theory and the steady-state theory, or even personalized as a battle between Gamow and Hoyle. But this is a misrepresentation.
Both parties, and most other physicists of the time, accepted that the Universe was expanding — as US astronomer Edwin Hubble demonstrated in the late 1920s by observing that most galaxies are rushing away from our own. But the idea that is so familiar today, of the Universe beginning at one point in time, was widely seen as irrational. After all, how could the cause of the original explosion be explained, given that time only came into existence with it? In fact, Gamow’s theory of the early Universe played almost no part in this debate.
Rather, a bigger question at the time was whether the Universe was evolving in accordance with German physicist Albert Einstein’s general theory of relativity, which predicted that it was either expanding or contracting, not steady. Although Einstein’s theory doesn’t require a Big Bang, it does imply that the Universe looked different in the past than it does now. And an ever-expanding Universe does not necessarily entail the beginning of time. An expanding Universe could have blown up from a smaller precursor, Lemaître suggested in 1927.
An apt but innocent phrase
On 28 March 1949, Hoyle — a well-known popularizer of science — gave a radio talk to the BBC Third Programme, in which he contrasted these two views of the Universe. He referred to “the hypothesis that all the matter in the universe was created in one big bang at a particular time in the remote past”. This lecture was indeed the origin of the cosmological term ‘Big Bang’. A transcript of the talk was reproduced in full in the BBC’s The Listener magazine, and Hoyle mentioned it in his 1950 book The Nature of the Universe, which was based on a series of BBC broadcasts he made earlier the same year.
How dwarf galaxies lit up the Universe after the Big Bang (請至原網頁查看圖片)
Although Hoyle resolutely dismissed the idea of a sudden origin of the Universe as unacceptable on both scientific and philosophical grounds, he later said that he did not mean it in ridiculing or mocking terms, such as was often stated. None of the few cosmologists in favour of the exploding Universe, such as Lemaître and Gamow, was offended by the term. Hoyle later explained that he needed visual metaphors in his broadcast to get across technical points to the public, and the casual coining of ‘Big Bang’ was one of them. He did not mean it to be derogatory or, for that matter, of any importance.
Hoyle’s ‘Big Bang’ was a new term as far as cosmology was concerned, but it was not in general contexts. The word ‘bang’ often refers to an ordinary explosion, say, of gunpowder, and a big bang might simply mean a very large and noisy explosion, something similar to Lemaître’s fireworks. And indeed, before March 1949, there were examples in the scientific literature of meteorologists and geophysicists using the term in their publications. Whereas they referred to real explosions, Hoyle’s Big Bang was purely metaphorical, in that he did not actually think that the Universe originated in a blast.
The Big Bang was not a big deal
For the next two decades, the catchy term that Hoyle had coined was largely ignored by physicists and astronomers. Lemaître never used ‘Big Bang’ and Gamow used it only once in his numerous publications on cosmology. One might think that at least Hoyle took it seriously and promoted his coinage, but he returned to it only in 1965, after a silence of 16 years. It took until 1957 before ‘Big Bang’ appeared in a research publication2, namely in a paper on the formation of elements in stars in Scientific Monthly by the US nuclear physicist William Fowler, a close collaborator of Hoyle and a future Nobel laureate.
Before 1965, the cosmological Big Bang seems to have been referenced just a few dozen times, mostly in popular-science literature. I have counted 34 sources that mentioned the name and, of these, 23 are of a popular or general nature, 7 are scientific papers and 4 are philosophical studies. The authors include 16 people from the United States, 7 from the United Kingdom, one from Germany and one from Australia. None of the scientific papers appeared in astronomy journals.
Among those that used the term for the origin of the Universe was the US philosopher Norwood Russell Hanson, who in 1963 coined his own word for advocates of what he called the ‘Disneyoid picture’ of the cosmic explosion. He called them ‘big bangers’, a term which still can be found in the popular literature — in which the ultimate big banger is sometimes identified as God.
A popular misnomer
A watershed moment in the history of modern cosmology soon followed. In 1965, US physicists Arno Penzias and Robert Wilson’s report of the discovery of the cosmic microwave background — a faint bath of radio waves coming from all over the sky — was understood as a fossil remnant of radiation from the hot cosmic past. “Signals Imply a ‘Big Bang’ Universe” announced the New York Times on 21 May 1965. The Universe did indeed have a baby phase, as was suggested by Gamow and Lemaître. The cosmological battle had effectively come to an end, with the steady-state theory as the loser and the Big Bang theory emerging as a paradigm in cosmological research. Yet, for a while, physicists and astronomers hesitated to embrace Hoyle’s term.
It took until March 1966 for the name to turn up in a Nature research article3. The Web of Science database lists only 11 scientific papers in the period 1965–69 with the name in their titles, followed by 30 papers in 1970–74 and 42 in 1975–79. Cosmology textbooks published in the early 1970s showed no unity with regard to the nomenclature. Some authors included the term Big Bang, some mentioned it only in passing and others avoided it altogether. They preferred to speak of the ‘standard model’ or the ‘theory of the hot universe’, instead of the undignified and admittedly misleading Big Bang metaphor.
Nonetheless, by the 1980s, the misnomer had become firmly entrenched in the literature and in common speech. The phrase has been adopted in many languages other than English, including French (théorie du Big Bang), Italian (teoria del Big Bang) and Swedish (Big Bang teorin). Germans have constructed their own version, namely Urknall, meaning ‘the original bang’, a word that is close to the Dutch oerknal. Later attempts to replace Hoyle’s term with alternative and more-appropriate names have failed miserably.
The many faces of the metaphor
By the 1990s, ‘Big Bang’ had migrated to commercial, political and artistic uses. During the 1950s and 1960s, the term frequently alluded to the danger of nuclear warfare as it did in UK playwright John Osborne’s play Look Back in Anger, first performed in 1956. The association of nuclear weapons and the explosive origin of the Universe can be found as early as 1948, before Hoyle coined his term. As its popularity increased, ‘Big Bang’ began being used to express a forceful beginning or radical change of almost any kind — such as the Bristol Sessions, a series of recording sessions in 1927, being referred to as the ‘Big Bang’ of modern country music.
In the United Kingdom, the term was widely used for a major transformation of the London Stock Exchange in 1986. “After the Big Bang tomorrow, the City will never be the same again,” wrote Sunday Express Magazine on 26 October that year. That use spread to the United States. In 1987, the linguistic journal American Speech included ‘Big Bang’ in its list of new words and defined ‘big banger’ as “one involved with the Big Bang on the London Stock Exchange”.
Today, searching online for the ‘Big Bang theory’ directs you first not to cosmology, but to a popular US sitcom. Seventy-five years on, the name that Hoyle so casually coined has indeed metamorphosed into a harpoon-like word: very hard to pull out once in.
Nature 627, 726-728 (2024)；doi: https://doi.org/10.1038/d41586-024-00894-z
References
1. Gamow, G. Nature 162, 680–682 (1948). Article PubMed Google Scholar
2. Fowler, W. A. Sci. Mon. 84, 84–100 (1957). Google Scholar
3. Hawking S. W. & Tayler, R. J. Nature 209, 1278–1279 (1966). Article Google Scholar
COMPETING INTERESTS：The author declares no competing interests.
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暗物質並不存在 ---- Bernard Rizk
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下面是奧他瓦大學新聞室發佈的研究報告；奧他瓦通譯為「渥太華」。我離開學校已經50多年，看不懂它不稀奇。
我推測：這位辜仆達教授提出了一個可以不需要假設「暗物質」存在來解釋觀測到某些宇宙現象的理論。至於他的理論是否足以否定「暗物質」的存在，或是否能解釋所有觀測到的宇宙現象；我相信還兩說。
以宇宙年齡而論，如下文所報導，根據辜仆達教授的計算大約是267億年(03/2024)；但在2022年之前，該計算則大約是137.87億年。過個三、五年在我掛掉以前，很可能又有新數字。
New research suggests that our universe has no dark matter
Bernard Rizk, Media Relations Office, Univ. of Ottawa, 03/15/24
The current theoretical model for the composition of the universe is that it’s made of ‘normal matter,’ ‘dark energy’ and ‘dark matter.’ A new uOttawa study challenges this.
A University of Ottawa study published today challenges the current model of the universe by showing that, in fact, it has no room for dark matter.
In cosmology, the term “dark matter” describes all that appears not to interact with light or the electromagnetic field, or that can only be explained through gravitational force. We can’t see it, nor do we know what it’s made of, but it helps us understand how galaxies, planets and stars behave.
Rajendra Gupta, a physics professor at the Faculty of Science, used a combination of the covarying coupling constants north_east external link (CCC) and “tired light north_east external link” (TL) theories (the CCC+TL model) to reach this conclusion. This model combines two ideas — about how the forces of nature decrease over cosmic time and about light losing energy when it travels a long distance. It’s been tested and has been shown to match up with several observations, such as about how galaxies are spread out and how light from the early universe has evolved.
This discovery challenges the prevailing understanding of the universe, which suggests that roughly 27% of it is composed of dark matter and less than 5% of ordinary matter, remaining being the dark energy.
Challenging the need for dark matter in the universe
“The study's findings confirm that our previous work (“JWST early Universe observations and ΛCDM cosmology north_east external link”) about the age of the universe being 26.7billion years has allowed us to discover that the universe does not require dark matter to exist,” explains Gupta. “In standard cosmology, the accelerated expansion of the universe is said to be caused by dark energy but is in fact due to the weakening forces of nature as it expands, not due to dark energy.”
“Redshifts” refer to when light is shifted toward the red part of the spectrum. The researcher analyzed data from recent papers on the distribution of galaxies at low redshifts and the angular size of the sound horizon in the literature at high redshift.
“There are several papers that question the existence of dark matter, but mine is the first one, to my knowledge, that eliminates its cosmological existence while being consistent with key cosmological observations that we have had time to confirm,” says Gupta.
By challenging the need for dark matter in the universe and providing evidence for a new cosmological model, this study opens up new avenues for exploring the fundamental properties of the universe.
The study, Testing CCC+TL Cosmology with Observed Baryon Acoustic Oscillation Featuresnorth_eastexternal link,was published in the peer-reviewed Astrophysical Journal.
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另一個修正演化論企圖的盲點 - Jerry Coyne
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廓因教授這篇文章批評婁博教授的觀點；後者請見本欄2024/02/14的貼文。廓因教授也是生物學家，內容自然充實有料。熟悉相關領域的網友可以慢慢品味。我的《短評》則針對婁博教授的「論述前提」(本欄2024/02/15貼文)。
如我指出，婁博教授的許多思考「盲點」，來自他具有爭議「論述前提」所導致的「認知偏差」。廓因教授似乎苟同我的看法；例如，下文中這段話：”This is a matter of ignorance that will eventually be solved.”，和我《短評》中1.1小節最後一段文字是同樣的意思。其次，廓因教授也批評了我提到婁博教授的「目的論」傾向。
Yet another misguided attempt to revise evolution
Jerry Coyne, 02/12/24
What we have below (click on headline for free access) is a review in Nature by Denis Noble of a new book by Philip Ball, How Life Works: A User’s Guide to the New Biology, which has garnered good reviews and is currently #1 in rankings of books on developmental biology. The Amazon summary promises that the book will revise our view of life:
A cutting-edge new vision of biology that will revise our concept of what life itself is, how to enhance it, and what possibilities it offers.
Biology is undergoing a quiet but profound transformation. Several aspects of the standard picture of how life works—the idea of the genome as a blueprint, of genes as instructions for building an organism, of proteins as precisely tailored molecular machines, of cells as entities with fixed identities, and more—have been exposed as incomplete, misleading, or wrong.. . .
I haven’t read it yet, though I will (I have several books ahead of it, including the galleys of Richard Dawkins’s new book, for which I’m to provide a blurb (“正面的”簡介，摘要). Instead, I will review a review: Denis Noble’s review published a few days ago. (That’s the screenshot below. 請至原網頁查看；該文即《自然科學：普及篇》2024/02/14貼文) Admittedly, it’s a review of a review, but Noble gives his take on the book’s importance, and in so doing reveals his own idea that neo-Darwinism is not only impoverished, but misguided in important ways. And, as usual, Noble proves himself misguided.
In some ways it’s unfortunate that Noble was chosen as a reviewer, as the man, while having a sterling reputation in physiology and systems biology, is largely ignorant of neo-Darwinism, and yet has spent a lot of the last decade trying to claim that neo-Darwinism is grossly inadequate to explain the features and evolutionary changes of organisms. You can see all my critiques of Noble here, but I’ll just quote briefly from the latest to give you a flavor of how he attacks modern evolutionary theory:
In an earlier post I wrote, “Famous physiologist embarrasses himself by claiming that the modern theory of evolution is in tatters“, I emphasized five assertions Noble made in a 2013 paper in Experimental Physiology, and then I criticized them as being either deeply misguided or flat wrong. Noble’s claims:
* Mutations are not random
* Acquired characteristics can be inherited
* The gene-centered view of evolution is wrong [This is connected with #2.]
* Evolution is not a gradual gene-by-gene process but is macromutational.
* Scientists have not been able to create new species in the lab or greenhouse, and we haven’t seen speciation occurring in nature.
I then assessed each claim in order:
* Wrong, partly right but irrelevant, wrong, almost completely wrong, and totally wrong (speciation is my own area).
* And yet Noble continues to bang on about “the broken paradigm of Neo-Darwinism,” which happens to be the subtitle of his new article (below) in IAI News, usually a respectable website run by the Institute of Art and Ideas.
And yes, Noble’s banging persists in his review of Ball’s book. The criticisms I level will be against Noble’s claims, as I can’t verify whether he’s accurately characterizing Ball’s views or spouting his (Noble’s) own misguided views.
The problem with Noble;s review is twofold: the stuff he says is new and revolutionary is either old and well known, or it’s new and unsubstantiated. Here are a few of his quotes (indented “以下以*號顯示” and in italics) and my take (flush left):
First, Noble’s introduction to the book, which is okay until Noble tries to explicate it:
* So long as we insist that cells are computers and genes are their code,” writes Ball, life might as well be “sprinkled with invisible magic”. But, reality “is far more interesting and wonderful”, as he explains in this must-read user’s guide for biologists and non-biologists alike.
On to Noble’s asseverations:
* When the human genome was sequenced in 2001, many thought that it would prove to be an ‘instruction manual’ for life. But the genome turned out to be no blueprint. In fact, most genes don’t have a pre-set function that can be determined from their DNA sequence.
Well, the genome is more or less a blueprint for life, for it encodes for how an organism will develop when the products of its genome, during development, interact with the environment—both internal and external—to produce an organism. Dawkins has emphasized, though, that the genome is better thought of as “recipe” or “program” for life, and his characterization is actually more accurate (you can “reverse engineer” a blueprint from a house and engineer a house from a blueprint—it works both ways—but you can’t reverse engineer a recipe from a cake or a DNA sequence from an organism.) The DNA of a robin zygote in its egg will produce an organism that looks and behaves like a robin, while that of a starling will produce a starling. You can’t change the environment to make one of them become the other. Yes, the external environment (food, temperature, and so on) can ultimately affect the traits of an organism, but it is the DNA itself, not the environment, that is the thing that changes via natural selection. It is the DNA itself that is passed on, and is potentially immortal. And the results of natural selection are coded in the genome. (Of course the “environment” of an organism can be internal, too, but much of the internal environment, including epigenetic changes that affect gene function are themselves coded by the DNA.)
As for genes not having a “pre-set function that can be determined from their DNA sequence,” this is either wrong or old hat. First, it is true that at this point we don’t always know how a gene functions from its DNA sequence alone, much less how it could change the organism if it mutates. This is a matter of ignorance that will eventually be solved. As for “pre-set function”, what does Noble mean by “pre-set”? A single gene can participate in many developmental pathways, and if it mutates, it can change development in unpredictable ways, and in ways you couldn’t even predict from what that gene “normally” does. The gene causing Huntington’s chorea, a fatal neurodegenerative disease, has a function that’s largely unknown but is thought to affect neuron transport. But it also has repeated sections of the DNA (CAGCAGCAG. . . . .), and mutations that increase the number CAG repeats can cause the disease when they exceed a certain threshold.
But the “Huntington’s gene” is not there to cause disease, of course. It interacts with dozens or even hundreds of other genes in ways we don’t understand. What is its “pre-set” function? The question is meaningless. And was does “pre-set” mean, anyway?
The second sentence in the bit above is garbled and ambiguous, and at any rate doesn’t refute the notion that the genome is indeed the “instruction manual for life.”
But wait: there’s more!
* Instead, genes’ activity — whether they are expressed or not, for instance, or the length of protein that they encode — depends on myriad external factors, from the diet to the environment in which the organism develops. And each trait can be influenced by many genes. For example, mutations in almost 300 genes have been identified as indicating a risk that a person will develop schizophrenia.
* It’s therefore a huge oversimplification, notes Ball, to say that genes cause this trait or that disease. The reality is that organisms are extremely robust, and a particular function can often be performed even when key genes are removed. For instance, although the HCN4 gene encodes a protein that acts as the heart’s primary pacemaker, the heart retains its rhythm even if the gene is mutated.
“Polygeny,” or the view that traits can be affected by many genes, is something I learned in first-year genetics in 1968. But some “traits” or diseases are the product of single genes, like the trait of getting Huntington’s Chorea of sickle-cell disease. But many diseases, like high blood pressure and heart disease, can be caused by many genes. And it’s not just diseases. Whether your earlobes are attached to your face or are free is based on a single gene, and eye color, to a large extent, is too (see this list for other single-gene alternative traits).
As far as the HCN4 gene goes, mutations may allow it to have a rhythm, but many mutations in that gene cause abnormal rhythms.and can even bring on death through heart attacks. No, the gene is not robust to mutations, and I can’t understand where Noble’s statement comes from. It appears to be wrong. (I am not attributing it to Ball here.)
More:
* Classic views of evolution should also be questioned. Evolution is often regarded as “a slow affair of letting random mutations change one amino acid for another and seeing what effect it produces”. But in fact, proteins are typically made up of several sections called modules — reshuffling, duplicating and tinkering with these modules is a common way to produce a useful new protein.
This is not a revision of the “classic” view of evolution because we’ve known about domain-swapping for some time. For example, the “antifreeze” proteins of Arctic and Antarctic fish can involve changes in the number of repeats in the enzyme trypsinogen, which normally has nothing to do with preventing freezing. Or, antifreeze proteins can arise via the cobbling together of bits of different known genes, or from bits of the unknown genes, or even be transferred via horizontal acquisition from other species. Yes, this happens, but it’s not the only way by a long shot that evolution occurs. In fact, now that we can sequence DNA, we’ve found that many adaptive changes in organisms are based in changes in single genes or their regulatory regions, and not swapping of modules. Here’s a figure from a short and nice summary by Sarah Tishkoff from 2015 showing single genes involved in various adaptations that have occurred in one species—our own. The traits are given at the top, and the genes involved are by the symbols. For example, though several genes can involve skin pigmentation, mutations in just one of them can make a detectable change.
Global distribution of locally adaptive traits. Adaptation to diverse environments during human evolution has resulted in phenotypes that are at the extremes of the global distribution. Fumagalli et al. have integrated scans of natural selection and GWAS to identify genetic loci associated with adaptation to an Arctic environment. ILLUSTRATION: A. CUADRA/SCIENCE AND MEAGAN RUBEL/UNIV. OF PENNSYLVANIA (請至原網頁查看圖片)
At any rate, we can nevertheless regard shuffling of domains (or even horizontal gene transfer from other species) as mutations, and the new mutated gene then evolves according to its effect on the replication of the gene. No revision of neo-Darwinism or its mathematics is involved. New ways of changing genes haven’t really revised our view of how evolution works, even when we’re talking about the “neutral theory” instead of natural selection.
These mutations, by the way, contra Noble, are still “random”—that is, they occur irrespective of whether they’d be useful in the new environment—and although they can make big changes in the organism’s physiology or appearance, can nevertheless evolve slowly. A gene with a big effect need not evolve quickly, for the rate of evolution depends not on the effect on the organism’s appearance, physiology, and so on, but on its effect on the organisms’s reproductive capacity. And these things need not be correlated.
* Later in the book, Ball grapples with the philosophical question of what makes an organism alive. Agency — the ability of an organism to bring about change to itself or its environment to achieve a goal — is the author’s central focus. Such agency, he argues, is attributable to whole organisms, not just to their genomes. Genes, proteins and processes such as evolution don’t have goals, but a person certainly does. So, too, do plants and bacteria, on more-simple levels — a bacterium might avoid some stimuli and be drawn to others, for instance. Dethroning the genome in this way contests the current standard thinking about biology, and I think that such a challenge is sorely needed.
* Ball is not alone in calling for a drastic rethink of how scientists discuss biology. There has been a flurry of publications in this vein in the past year, written by me and others2–4. All outline reasons to redefine what genes do. All highlight the physiological processes by which organisms control their genomes. And all argue that agency and purpose are definitive characteristics of life that have been overlooked in conventional, gene-centric views of biology.
This passage verges on the teleological. For surely organisms don’t have “goals” when they evolve. If a mutation arises that increases the rate of replication of a gene form (say one increasing tolerance to low oxygen in humans living in the Himalaya), it will sweep through the population via natural selection. If it reduces oxygen binding, it will be kicked out of the population. Can we say that increased oxygen usage is a “goal”? No, it’s simply what happens, and I suspect there are other ways to adapt to high altitude, like getting darker skin. To characterize organisms as evolving to meet goals, as Noble implies here, is a gross misunderstanding of the process.
Yes, the organism is the “interactor”, as Dawkins puts it: the object whose interaction with its environment determines what gene mutations will be useful. But without the “replicator”—the genes in the genome—evolution cannot occur. The whole process of adaptation, involving the interaction of a “random” process (mutation) and a “deterministic” one (natural selection), is what produces the appearance of purpose. But that doesn’t mean, at least in any sense with which we use the word, that “purpose” is what makes organisms alive.
But the appearance of “purpose” as a result of natural selection brings up another point, one that Dawkins makes—or so I remember. I believe that he once defined life as “those entities that evolve by natural selection.” I can’t be sure of that, but it’s as good a definition of life as any, as it involves organisms having replicators, interacting “bodies”, and differential reproduction. (According to that definition, by the way, viruses are alive.) So if you connect natural selection with purpose, one might say, “Life consists of those organisms who have evolved to look as if as if they had a purpose.” But I prefer Dawkins’s definition because it’s more fundamental.
At the end, Noble says that this “new view of life” will help us cure diseases more readily:
* This burst of activity represents a frustrated thought that “it is time to become impatient with the old view”, as Ball says. Genetics alone cannot help us to understand and treat many of the diseases that cause the biggest health-care burdens, such as schizophrenia, cardiovascular diseases and cancer. These conditions are physiological at their core, the author points out — despite having genetic components, they are nonetheless caused by cellular processes going awry. Those holistic processes are what we must understand, if we are to find cures.
I haven’t heard anybody say that “genetics alone can help us treat complex diseases”. You don’t treat heart disease by looking for genes (though you can with some cancers.) But genetics can surely help! For genetic engineering is on the way, and at least some diseases, like sickle-cell anemia, will soon be “curable” by detecting the mutated genes in embryos or eggs and then fixing the mutation with CRISPR. And advances in genetics are surely helping us cure cancer—see this article. But of course some diseases, even those with a genetic component, need environmental interventions: so called “holistic” cures. There may, for example, be a genetically-based propensity to get strep throat. But if you get it, you don’t worry about genes, you take some penicillin or other antibiotic. (Curiously, the form of Streptococcus that causes strep throat doesn’t seem to have evolved resistance to the drug!)
Overall, I don’t see much new in Noble’s take on evolution—just a bunch of puffery and regurgitation of what we already know. Perhaps people need to know about this stuff in a popular book, but, after all, Noble’s piece was written for scientists, for it appears in Nature.
Despite repeated claims in the last few years that neo-Darwinism is moribund or even dead, it still refuses to lie down. Happy Darwin Day!
Addendum by Greg Mayer: For those interested in the distinction between the blueprint (wrong) and recipe (on the right track) analogies for the genome, I wrote a post explicating the difference, citing and quoting Richard, here at WEIT; the post also explains why the Wikipedia article about “Epigenetics” is definitionally wrong; see especially the link to this paper by David Haig.
Development is epigenetic
by Greg Mayer One of the points I stress to students in my evolution class is that development is epigenetic: organisms develop from a less differentiated state to a more differentiated state. In modern terms, genes, the intraembryonic environment, and the extraembryonic environment interact to produce the organism through a sequence of stages going from an undeveloped to a mature state. . .
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《基因並非生物成長的藍圖》短評
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0. 前言
這篇文章有論點，但也相當有趣(請見本欄上一篇)。前者指婁博教授提出了他的主張，也列舉了支持他這些主張的依據；後者指婁博教授的文章有濃厚的哲學意味，卻不幸包含了至少兩個邏輯謬誤。略抒拙見於下。
1. 哲學立場
這篇文章不到1,000字，婁博教授把重點放在生物學和基因學的相關論述；對他立論背後的哲學立場僅僅一筆帶過；後者請參考上一節關於他生平超連接中的簡短介紹。
1.1 綜觀論
婁博教授的綜觀論傾向，可從原文倒數第二段中，他使用了 “holistic processes” 一詞看出。這個立場通常跟構成論相對。我並不排斥「綜觀論」，尤其在社會科學理論及其應用上；但就我略有所知的自然科學各領域而言，我都傾向「構成論」。
婁博教授在本文中沒有提到另一個相關領域：環境遺傳學(或稱擬遺傳學)；這個領域可參見環遺學1和環遺學2。
我認為：綜觀論和綜合性質論兩者，是目前人類還沒有掌握到全部知識前的過渡理論；也就是說，在我們沒有能力以現有理論解釋某些現象前，一種類似OK繃功能的觀點。
1.2 目的論
婁博教授的目的論傾向，可從以下兩段文字看出。
“Genes, proteins and processes such as evolution don’t have goals, but a person certainly does.”
這句話是原書作者博爾教授的文字；婁博教授認同並引用。
“… And all argue that agency and purpose are definitive characteristics of life that have been overlooked in conventional, gene-centric views of biology.”
對「目的論」有興趣的朋友，請參考此文。
在以上引用的第二段文字中有「行動能力」一詞，此概念的用法可參見我剛發表的《我對「文革/紅衛兵」的看法》(該文第2.1小節)。
我認為：一般來說，自然、社會、和人文三大科學領域中的「目的論」都站不住腳。但是，每一個人在她/他的生命歷程中，可以「選擇」和/或「改變」自己生活的「目的」。這個立場來自我所了解的意識、「自由意志」、與「行動能力」(特別是該欄《主動性》一文)。
2. 邏輯謬誤
1) 前後矛盾
請比較這三段文字：
a. “Genes, proteins and processes such as evolution don’t have goals, …”
b. “… reshuffling, duplicating and tinkering with these modules is a common way to produce a useful new protein.”
c. “… organisms control their genomes.”
分析如下：
b段的 “to produce a useful new protein.” 中， ”useful new protein” 應該解讀為一種 “goal” ，故b段與a段矛盾。
c段中的 “organisms” 一字，依脈絡應該解讀為”genes” 或相應的人體結構/組成物質，而不是指「人」。「控制」蘊含「目的」；因此，c段也與a段矛盾。
2) 結論不能從前提導出
請參考以上我對綜觀論以及目的論的一般性批評。
婁博教授今年88歲，且不論他注意力或關照力是否已經難以周全；從他執著於上述的「哲學立場」來看，其思路中多多少少有些「認知偏差」也就不足為怪了。
3. 結論
雖然婁博教授引用了一些研究報告支持他的論點，整篇文章的嚴謹度和說服力不足。
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基因並非生物成長的藍圖 ---- Denis Noble
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(請參見本欄下一篇《短評》)。
t’s time to admit that genes are not the blueprint for life
The view of biology often presented to the public is oversimplified and out of date. Scientists must set the record straight, argues a new book.
Denis Noble, 02/05/24
How Life Works: A User’s Guide to the New Biology, Philip Ball, Pan Macmillan (2024)
For too long, scientists have been content in espousing the lazy metaphor of living systems operating simply like machines, says science writer Philip Ball in How Life Works. Yet, it’s important to be open about the complexity of biology — including what we don’t know — because public understanding affects policy, health care and trust in science. “So long as we insist that cells are computers and genes are their code,” writes Ball, life might as well be “sprinkled with invisible magic”. But, reality “is far more interesting and wonderful”, as he explains in this must-read user’s guide for biologists and non-biologists alike.
When the human genome was sequenced in 2001, many thought that it would prove to be an ‘instruction manual’ for life. But the genome turned out to be no blueprint. In fact, most genes don’t have a pre-set function that can be determined from their DNA sequence.
Instead, genes’ activity — whether they are expressed or not, for instance, or the length of protein that they encode — depends on myriad external factors, from the diet to the environment in which the organism develops. And each trait can be influenced by many genes. For example, mutations in almost 300 genes have been identified as indicating a risk that a person will develop schizophrenia.
It’s therefore a huge oversimplification, notes Ball, to say that genes cause this trait or that disease. The reality is that organisms are extremely robust, and a particular function can often be performed even when key genes are removed. For instance, although the HCN4 gene encodes a protein that acts as the heart’s primary pacemaker, the heart retains its rhythm even if the gene is mutated1.
Another metaphor that Ball criticizes is that of a protein with a fixed shape binding to its target being similar to how a key fits into a lock. Many proteins, he points out, have disordered domains — sections whose shape is not fixed, but changes constantly.
This “fuzziness and imprecision” is not sloppy design, but an essential feature of protein interactions. Being disordered makes proteins “versatile communicators”, able to respond rapidly to changes in the cell, binding to different partners and transmitting different signals depending on the circumstance. For example, the protein aconitase can switch from metabolizing sugar to promoting iron intake to red blood cells when iron is scarce. Almost 70% of protein domains might be disordered.
Classic views of evolution should also be questioned. Evolution is often regarded as “a slow affair of letting random mutations change one amino acid for another and seeing what effect it produces”. But in fact, proteins are typically made up of several sections called modules — reshuffling, duplicating and tinkering with these modules is a common way to produce a useful new protein.
Later in the book, Ball grapples with the philosophical question of what makes an organism alive. Agency — the ability of an organism to bring about change to itself or its environment to achieve a goal — is the author’s central focus. Such agency, he argues, is attributable to whole organisms, not just to their genomes. Genes, proteins and processes such as evolution don’t have goals, but a person certainly does. So, too, do plants and bacteria, on more-simple levels — a bacterium might avoid some stimuli and be drawn to others, for instance. Dethroning the genome in this way contests the current standard thinking about biology, and I think that such a challenge is sorely needed.
Ball is not alone in calling for a drastic rethink of how scientists discuss biology. There has been a flurry of publications in this vein in the past year, written by me and others2–4. All outline reasons to redefine what genes do. All highlight the physiological processes by which organisms control their genomes. And all argue that agency and purpose are definitive characteristics of life that have been overlooked in conventional, gene-centric views of biology.
This burst of activity represents a frustrated thought that “it is time to become impatient with the old view”, as Ball says. Genetics alone cannot help us to understand and treat many of the diseases that cause the biggest health-care burdens, such as schizophrenia, cardiovascular diseases and cancer. These conditions are physiological at their core, the author points out — despite having genetic components, they are nonetheless caused by cellular processes going awry. Those holistic processes are what we must understand, if we are to find cures.
Ultimately, Ball concludes that “we are at the beginning of a profound rethinking of how life works”. In my view, beginning is the key word here. Scientists must take care not to substitute an old set of dogmas with a new one. It’s time to stop pretending that, give or take a few bits and pieces, we know how life works. Instead, we must let our ideas evolve as more discoveries are made in the coming decades. Sitting in uncertainty, while working to make those discoveries, will be biology’s great task for the twenty-first century.
Nature 626, 254-255 (2024)；doi: https://doi.org/10.1038/d41586-024-00327-x
References
Noble, D. Prog. Biophys. Mol. Biol. 166, 3–11 (2021)., Article PubMed Google Scholar
Noble, R. & Noble. D. Understanding Living Systems (Cambridge Univ. Press, 2023)., Google Scholar
Vane-Wright, R. I. & Corning, P. A. Biol. J. Linn. Soc. 139, 341–356 (2023)., Article Google Scholar
Corning, P. A. et al. (eds) Evolution “On Purpose”: Teleonomy in Living Systems (MIT Press, 2023)., Google Scholar
Download references
COMPETING INTERESTS：The author declares no competing interests.
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10個科學家目前還沒有答案的問題 -- Marcelo Gleiser
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objectivity：客觀性
reductionism：簡化論或簡化觀
10 of the most mystifying open questions in science
From how life emerged on Earth to why we dream, these unanswered questions continue to perplex scientists.
Marcelo Gleiser, 12/21/23
KEY TAKEAWAYS
* With the end of 2023 approaching, it’s time to revisit some of the toughest questions in science.
* Here's my (admittedly biased) list of the top ten. Each entry is briefly explained and accompanied by references to current books and articles on the topics.
* As you'll see, some of these questions have been with us for quite some time, and they may be unanswerable — at least through the usual scientific methodology.
To celebrate (with a sigh perhaps?) the end of this turbulent year, there’s nothing better than diving into some of the biggest open questions in science — those that have long kept scientists up at night. Though confounding, these questions point to an essential fact in science: the more we know, the more there is to know. There is no end to knowledge as long as we keep asking questions (and receive funding to try to answer them). Even more interestingly, some of these questions simply can’t be answered, at least not through the usual scientific methodology that combines objectivity and reductionism: the notions, respectively, that we can separate ourselves from the objects we are studying, and that it is possible to break complex systems into smaller ones to study their behavior and then infer the behavior of the whole from the behavior of the parts.
Every list of “most important” questions has a dose of arbitrariness, given the author’s subjectivity. However, I would venture to say that these rank among the toughest open questions — and for sure among the more mysterious and attention-grabbing. So, here it goes, in no particular order:
1. What is the Universe made of? We know only 5% of the composition of the Universe. This 5% is made of the familiar atoms of the periodic table, their molecular aggregates, or the components of the atoms: protons, electrons, and neutrons. There are also neutrinos — the elusive particles that can traverse matter as if nothing was there, including the whole of Earth. The mystery is the other 95%, composed of dark matter (roughly 27%) and dark energy (roughly 68%). Dark matter doesn’t shine and is found around galaxies and clusters of galaxies, like an invisible cloak. We know it’s there because it has mass and hence gravity: It pulls on the familiar 5% we can see, and we can measure this effect. Dark energy is much more mysterious, an ether-like medium filling up space with the bizarre property of pushing it apart, making galaxies accelerate away from one another. We don’t know what dark matter or dark energy are, and there are hypothetical explanations that try to modify Einstein’s theory of gravity to accommodate the observations and do away with the darkness. But after decades of searching, we remain quite ignorant.
2. How did life come about? Life appeared on Earth some 3.5 billion years ago, perhaps earlier. The mystery here is how aggregates of nonliving atoms gathered into progressively more complex molecules that eventually became the first living entity, a chemical machine capable of metabolism and reproduction. The fact that living matter is matter with intentionality remains a profound mystery.
3. Are we alone in the Universe? This question is really two questions, given that we want to know not only whether any extraterrestrial life exists but also whether it is intelligent. Ultimately, we would like to know how common life is. We also need to know why, if intelligent life is not so rare, we haven’t yet heard from “them”? On the question of aliens, I recommend the recent book by Big Think columnist Adam Frank, The Little Book of Aliens, for an up-to-date synopsis of the search for life in the cosmos. As I pointed out in my recent book, this question has a direct impact on how we relate to our own future and the planet we call home.
4. What makes us human? We have three times more neurons than a gorilla, but our DNAs are almost identical. Many animals have a rudimentary language, can use tools, and recognize themselves in mirrors. So, what exactly differentiates us from them? The thicker frontal cortex? The opposing thumb? The discovery of fire and the ability to cook? Our culture? When did language and tool-making appear? An excellent intro to this is Jeremy DeSilva’s book, First Steps.
5. What is consciousness? We’ve confronted this question before in these pages, wondering about the nature of consciousness, and even its possible connection with quantum physics, a trendy topic in some circles. How is it that the brain generates the self of self, the unique experience that we have of being unique? Can the brain be reversed-engineered to be modeled by machines or is this a losing proposition? And why is there a consciousness at all? What is its evolutionary purpose, if any?
6. Why do we dream? Even though we spend about a third of our lives sleeping, we still don’t know why we dream. Do dreams have an essential function, physiological and/or psychological? Or are they simply random images of a brain in partial rest? Was Freud right about his theory that dreams are some sort of expression of repressed desires? Or is that all bogus?
7. Why does matter exist? According to the laws of physics, matter shouldn’t exist on its own; each particle of matter — each electron, proton, neutron — should have a companion of antimatter, like twins. So, there should be positrons, antiprotons, and antineutrons in abundance. But there aren’t. The problem is that when matter and antimatter meet, they disintegrate in a puff of high-energy radiation. If you shook hands with your antimatter other, a good chunk of the U.S. would blow up in smoke. So, the mystery is what happened to this antimatter. Clearly, if the Universe had equal amounts of both earlier on, something happened to favor matter over antimatter. What? Was the Universe “born” this way, with a huge asymmetry between matter and antimatter? Maybe some primordial asymmetry evolved to do the job, selecting matter? If so, when did it act in cosmic history, and what would this asymmetry be? We’ve been trying to figure this one out for decades with no great success.
8. Are there other universes? Or is our Universe the only one? Believe it or not, modern theories of cosmology and particle physics predict the existence of other universes, potentially with different properties to our own. Are they there? How would we know, if we could? If we can’t confirm this hypothesis, is it still part of science? I have argued here before that the multiverse hypothesis is profoundly problematic and not particularly useful, even if fun to think about.
9. Where will we put all the carbon? With the global vamping up of industrialization, we are putting more and more carbon (and methane) up in the atmosphere, accelerating global warming. What can be done to change our impact on the environment? And what happens if we don’t? Models of global warming offer a range of predictions, from somewhat mild to dire. But clearly, time is running out to ponder about the issue and do nothing. It’s time to take this seriously at a global scale, for the benefit of the next generation and even just the next decade or so. Politicians are moving too slowly. We need to take this one into our own hands and act individually as well.
10. How can we get more energy from the Sun? We have based our explosive growth mainly on fossil fuels. Nevertheless, we have a remarkable energy source up in the sky, waiting to be explored more efficiently. Also, can we reproduce the solar engine here on Earth, fusing hydrogen into helium in a controllable and viable way to solve the energy problem for the foreseeable future? Progress is coming, but slower than we’d like. Or need.
What was it like when the very first stars died?
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