Who first hypothesized that the universe is accelerating?

Who first hypothesized that the universe is accelerating?

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I couldn't find this answer anywhere. Before 1998, was there a notable physicist who conjectured that the universe is accelerating and perhaps even submitted some equations to support it (and the existence of dark energy). Such a hypothesis would likely have been rejected outright and fallen into oblivion, which is why I have to ask this question to get the answer. And I don't mean Einstein's cosmological constant since he was trying to make the universe static rather than accelerating. Someone who actually believed that the universe's expanding rate was increasing even before there was any evidence of it.

Science isn't concerned with belief. The possibility of a dark energy term and therefore an accelerating universe is implicit in GR and in the consequent Friedmann-Lemaitre equations that govern the dynamics of the universe. When the supernova cosmology teams set out to measure the deceleration of the universe, the models that they fitted to their data explicitly allowed for the possibility that the universe might actually be accelerating.

However, such hypothetical universes had certainly been explored before. The De Sitter universe (proposed by Willem de Sitter in 1917) is an accelerating universe consisting only of a cosmological constant. Our own universe appears to be headed asymptotically towards being described as a De Sitter universe.

The idea of $Lambda$ as a form of "dark energy" that had the potential to cause an accelerating universe was already put forward as an idea by Lemaitre in the late 1920s and early 30s. The picture below shows the evolution of the scale factor for families of solutions and was apparently made by Lemaitre in 1927 (see this science history blog about Lemaitre). The upper 5 curves correspond to a universe that is accelerating today.

The Genius of Albert Einstein: His Life, Theories and Impact on Science

Reference Article: Facts about Albert Einstein, his life and influence on multiple scientific fields.

Albert Einstein is often cited as one of the most influential scientists of the 20th century. His work continues to help astronomers study everything from gravitational waves to Mercury's orbit.

The scientist's equation that helped explain special relativity – E = mc^2 – is famous even among those who don't understand its underlying physics. Einstein is also known for his theory of general relativity (an explanation of gravity), and the photoelectric effect (which explains the behavior of electrons under certain circumstances) his work on the latter earned him a Nobel Prize in Physics in 1921.

Einstein also tried in vain to unify all the forces of the universe in a single theory, or a theory of everything, which he was still working on at the time of his death.

Wary Astronomers Ponder An Accelerating Universe

AT their telescopes in the last few years, astronomers have been searching the heavens for evidence that the expansion of the universe is slowing down. The mutual gravitational attraction of all matter in stars, planets and everything else known or hypothesized should be putting a gradual brake on the outward rush of space since the explosive moment of cosmic creation in the theorized Big Bang.

The preliminary results of the search are now in, and they are stunning. The expansion of the universe appears to be accelerating, instead of decelerating.

''Our observations show that the universe is expanding faster today than yesterday,'' Dr. Adam Riess, a young astronomer at the University of California at Berkeley, said in an interview last week. An analysis by him and an international team of scientists indicated that the cosmic expansion rate is about 15 percent greater now than when the universe was half its current age, about seven billion years ago.

The group including Dr. Riess and another one, led by Dr. Saul Perlmutter of Lawrence Berkeley National Laboratory, used similar techniques of measuring the cosmic expansion rates over time by studying distant exploding stars, called supernovas. At first, the astronomers were not sure they could believe what they were seeing. But as they examined more supernovas and explored sources of possible error or alternative explanations, they have grown bold in describing the implications of their research at recent meetings.

''Try as we might, we have not found any errors,'' Dr. Alexei V. Filippenko, a University of California astronomer who has worked on both teams, told colleagues 10 days ago at a meeting in Marina del Rey, Calif. ''We get a nonzero cosmological constant.''

Translated, that means the astronomers are increasingly confident that they have detected the first strong evidence that the universe is permeated by a repulsive force, the opposite of gravity. The simplest explanation, other astrophysicists agree, is that the force is something called the cosmological constant. As conceived by theorists, this force is a property of the vacuum of space itself, an energy that acts on a large scale to stretch space and thus counteract gravity's restraining power.

If the observations are correct, this is one more case of astronomers handing cosmologists a new piece to a jigsaw puzzle, which is always maddeningly incomplete, and asking them to find a way to fit it into a satisfying theoretical whole. Knowledge of an accelerating expansion could lead to a revised recipe of just what the universe is made of. It could resolve a paradox raised by previous controversial suggestions that the universe appears to be younger than its oldest stars. It could also change thinking about cosmic evolution and the ultimate fate of the universe.

Reflecting the cautious excitement and fervid conjecture touched off by the new findings, Dr. Michael S. Turner, an astrophysicist at the University of Chicago and Fermi National Laboratory, said: ''If it's true, this is a remarkable discovery. It means that most of the universe is influenced by an abundance of some weird form of energy whose force is repulsive.''

If he were alive, no one would be more bemused by this turn of events than Albert Einstein. Soon after he invented his general theory of relativity in 1915, Einstein was unsettled to find it demanded that the universe either expanded or contracted over time. But like nearly all scientists at the time, he assumed the universe was static, neither expanding nor contracting. What to do?

To compensate for what he considered a flaw in his theory, Einstein introduced the idea of the cosmological constant, symbolized in equations by the Greek letter lambda. The repulsive energy force would presumably counteract gravity and make the universe in his theory stand still. Soon after Edwin P. Hubble discovered the expanding universe in 1929, Einstein renounced the cosmological constant as the greatest blunder of his career.

For years, scientists agreed, dismissing lambda as ''that fudge factor.'' In the last decade, however, they reluctantly dusted it off as a means of balancing the books on the matter and other forces that are required to support the favored interpretation of Big Bang theory.

In this model, called the inflationary Big Bang, the universe should contain a critical density of matter, just enough to slow expansion to a halt, given infinite time. Scientists express this condition of critical density as omega equals one. Too little mass -- if omega equals less than one -- and the universe would expand forever, growing ever more tenuous. If omega equals more than one, then the universe would collapse of its own weight, contracting in what is called the Big Crunch.

So far, astronomical observations and other research have established that the mass density of the universe amounts to no more than 30 percent of the preferred critical value. That includes the mass from ordinary matter in galaxies and a large component of mysterious exotic particles, invisible and still hypothetical. Despite this matter deficit, cosmologists clung to inflation theory because it had passed many tests and provided a satisfying explanation for early conditions in the universe.

In 1990, reviewing all the data, Dr. Turner proposed a formula for a '➾st-fit universe'' that accorded with inflation theory. By his calculations, the universe contained 5 percent ordinary matter and 25 percent mass in the form of cold dark matter, invisible and exotic. The cosmological constant, the energy of empty space, would account for the balance of 70 percent, bringing the universe up to critical density.

The new findings appear to make a prophet of Dr. Turner and others who were beginning to share his views. In January, both teams studying supernovas, measuring how fast these stars were rushing outward when they exploded, reported that the cosmic expansion rate had slowed little or not at all over billions of years. The universe's mass, in ordinary and exotic matter, added up to no more than 20 to 30 percent of critical density. The universe, therefore, seemed destined to expand forever.

After more analysis of the observations, the teams realized they were probably seeing the direct evidence for the mysterious background energy known as the cosmological constant. Not only was the universe's expansion not slowing down, it was speeding up.

Dr. Perlmutter's group, the Supernova Cosmology Project, has studied 40 distant supernovas in detail. Describing their results in January, Dr. Perlmutter acknowledged that the evidence strongly suggested a cosmological constant, but went no further. ''We were trying to be very conservative until we had more observations,'' he said last week.

The other group, called the High-Z Supernova Search Team, has examined only 14 supernovas but was less restrained in its more recent report. Dr. Brian Schmidt of the Mount Stromlo and Siding Spring Observatory in Australia, said in an interview reported in the current issue of the journal Science that his team concluded with a statistical confidence of between 98.7 and 99.9 percent that cosmic expansion is receiving an antigravity boost, presumably from energy of the cosmological constant.

''My own reaction is somewhere between amazement and horror,'' said Dr. Schmidt, the team leader. 'ɺmazement, because I just did not expect this result, and horror in knowing that it will likely be disbelieved by a majority of astronomers -- who, like myself, are extremely skeptical of the unexpected.''

Dr. Riess, whose research led to the conclusion of an accelerating expansion, said: ''We are trying not to rush to judgment on the cosmological constant. There could be some other sneaky little effect we have overlooked, something that makes the supernovas dimmer and appear to be farther away than they really are or some variations in the behavior of more distant supernovas that are deceiving us.''

But nothing has emerged to make the astronomers doubt their findings, he said. The accelerating expansion indicates that the repulsive force could account for at least 65 percent of the critical density, thus closing the gap between known mass and the much-admired model in which the universe is characterized as omega equaling one. And if the universe was once expanding more slowly than it is now, this would make it older -- about 14 billion years old, or a billion years or more than new estimates for the age of the earliest known stars.

Dr. Perlmutter saw a need to observe more nearby supernovas for comparison with ones being observed at distances of seven billion light-years. This should produce a more refined measure of differences in the expansion rate over time and perhaps reveal any distorting variations in supernovas then and now.

Still, many astrophysicists and cosmologists are beginning to think that Einstein was on to something, though for the wrong reason. The cosmological constant as a repulsive energy force may exist, after all. Physicists can think of no known principle to forbid it. Indeed, theories of quantum mechanics suggest that the energy of the cosmological constant could come from ''virtual particles,'' which may be winking in and out of existence in empty space.

'➬tually, the cosmological constant is the least interesting explanation, and that's pretty interesting in itself,'' Dr. Turner said.

Astrophysicists conceive of other possible sources of repulsive energy in forms that go by such names as X-matter and quintessence. These are speculative concepts in which mysterious textures in the early universe that created conditions for a cosmic background energy and might even help explain the formation of galaxies. Scientists are likely to venture other ideas if evidence for an accelerating universe continues to mount.

''It gives us confidence that two groups that are very competitive and very good are getting the same results,'' Dr. Turner said.

Who first hypothesized that the universe is accelerating? - Astronomy

Hubble’s Law is a proportional relationship between a galaxy’s distance and that galaxy’s receding velocity. This relationship between an object’s distance and the velocity it is moving away is a direct observation of the expansion of the observable Universe. Hubble’s Law infers that a galaxy that is moving away from an observer twice as fast as another galaxy is twice as far away.

Before Hubble and the early work on modern cosmology, there was much discussion about the size and shape of the Universe. And, questions such as a finite or infinite Universe were often discussed. In 1920, two American astronomers, Harlow Shapley and Heber Curtis, debated over the size of the Universe issue. Shapley thought the Universe was small, about the size of a spiral galaxy. Curtis argued that the Universe was much, much larger. In a few short years after the famous Curtis-Shapley debate, ideas put forth and data collected would begin to resolve these questions.

Even though Hubble’s Law is named after American astronomer Edwin Hubble, others worked on this cosmological concept and relationship before Hubble. In 1922, Alexander Friedmann, a Russian physicist, postulated through a set of equations that the Universe might be expanding, and if so, the equations he developed could explain that expansion. In 1927, Father Georges Lemaître, a Catholic Belgian Priest, proposed the theory that the Universe was expanding and not simply set into place. He also hypothesized the rate at which the Universe is expanding. Lemaître was also responsible for the initial concepts of the Big Bang theory. He drew his work from Einstein’s Law of General Relativity. His 1927 paper was entitled Un Univers homogène de masse constante et de rayon croissant rendant compte de la vitesse radiale des nébuleuses extragalactiques (A homogeneous Universe of constant mass and growing radius accounting for the radial velocity of extragalactic nebulae) . The problem was that few scientists outside of Belgium read Lemaître’s paper.

Lemaître was the first to propose that the expansion of the Universe explains the spectral redshifts being observed in galaxies. There are many who believe Hubble’s Law should be called Lemaître’s Law.

In addition to being a Catholic priest, Lemaître was an astronomer and professor of physics at the Catholic University of Leuven, Belgium.

Georges Lemaître, Belgian priest, astronomer and professor of physics at the Catholic University of LeuvenLemaître by huidig is in the Public Domain

Rediscovering the Scientist-Priest Who Radically Changed Our View of the Universe

In 1917 Albert Einstein, developing the consequences of his general theory of relativity, postulated a homogeneous, static, spatially curved universe. Mass and energy warp space-time, and would tend to make it collapse into a point—but if you add to the equation a positive term that compensates for this tendency towards contraction, the system remains in equilibrium. The beginning of modern cosmology is ushered in with this maneuver. To avoid the catastrophic ending of the universe—the inevitable result if only gravity were present—an arbitrary term was invented. Wanting to maintain the prejudice regarding the stability and persistence of the universe that had lasted for millennia and still evidently held Einstein captive, he forcefully introduced the “cosmological constant,” a kind of vacuum energy which is positive and tends to push everything outwards, thus contrasting with and counterbalancing the gravitational pull and guaranteeing the stability of the whole.

Today, now we know that the universe is made up of 100 billion galaxies, it is shocking to realize that scientists in the first two decades of the last century, among them some of the most brilliant minds of all time, were still convinced that it consisted solely of the Milky Way. It was the slow concentric movement of the bodies belonging to this galaxy that gave the idea of a universe that was like a stationary, harmonious and ordered system. Soon afterwards this was brought into question by new kinds of observation, but a radical break with the old conceptions was also anticipated by the brilliant intuition of a young Belgian scientist.

In 1927 Georges Lemaître was a 33-year-old Catholic priest with a degree in astronomy from the University of Cambridge, and in the process of completing his PhD at the Massachusetts Institute of Technology. He is among the first to grasp that Einstein’s equations can also describe a dynamic universe, a system of constant mass but one that is expanding—with a radius, that is, which gets bigger with the passage of time. When he presents this idea to his older and much more established colleague, Einstein’s response is shockingly negative: “Your calculations are correct, but your physics is abominable.” So deeply rooted is the prejudice which for millennia had conceived of the universe as a stationary system that even the most elastic and imaginative mind of the period rejects the idea that it can be expanding, and that as a consequence of this expansion it must have had a beginning.

It would take years of discussion and fierce argument before this extraordinarily novel idea was generally accepted by scientists, and a great deal more time would have to pass before it became public knowledge.

The key to its success is suggested by Lemaître himself, in an article in which he proposed his new theory, backed up with measurements of the radial speed of extra-galactic nebulae.

At the time, the attention of astronomers was concentrated on those peculiar objects resembling clouds which they conceived of as being groups of stars aggregated together with agglomerations of dust or gas. Today we know that they are in fact galaxies, each containing thousands of stars, but the telescopes of the time were not sufficiently developed to show them in much detail.

In order to calculate the speed at which a star or any other luminous body moved, astronomers had long known how to use the Doppler effect. The same phenomenon that we notice with sound waves from an ambulance siren can be observed with light waves. When the source recedes, the frequency of the waves that we receive is reduced: the sound of the siren gets fainter the further away it is. In the same way, the color of visible light shifts towards red with distance. By analysing the spectrum of luminous frequencies emitted by various celestial bodies, we can measure for each one this shift towards red, precisely the so-called red shift, and work out from this the radial speed with which they are receding from us.

But it was not easy to measure how far away these formations were, or consequently to determine whether they were situated within our galaxy or not. The solution was discovered by Edwin Hubble, a young astronomer working at the Mount Wilson Observatory in California, equipped with what at the time was the world’s most powerful telescope.

The technique employed was based on the study of Cepheids, pulsating stars of variable luminosity or brightness. Hubble begins his work just a few years after the death of Henrietta Swan Leavitt, one of the first American astronomers, a young scientist who had contributed enormously to this field and received, as is often the case, no appropriate recognition. In fact, at the beginning of the twentieth century it was considered unthinkable that a woman could use a telescope, and the extremely rare young female scientists were often deployed in subordinate roles. Leavitt was entrusted with the role of human “computer,” a wholly secondary and badly paid job: her task, in fact, consisted of examining, one after another, thousands of photographic plates containing images taken through telescopes, and recording the characteristics of stars and other celestial objects. She was assigned, in particular, the task of measuring and cataloguing the apparent brightness of these stars.

The young astronomer focused her studies on the stars with variable luminosity belonging to the Small Magellanic Cloud, a nebula which at the time was thought to be part of our own galaxy. It was Leavitt’s incisive observation that the brightest stars were also those with the largest pulsation period. Once this correlation was established, an estimate of the absolute brightness of a star could be obtained, which in turn would allow us to measure its distance from us. The brightness of an object varies according to the inverse square of the distance from the observer, so by knowing its absolute brightness, one need only measure the apparent brightness to calculate the distance.

Leavitt measured the relation between luminosity and period in the Cepheid variables of the Small Magellanic Cloud, and by hypothesizing that the stars were largely at the same distance, she was able to construct a scale of intrinsic luminosity, starting from the visible ones recorded on the plates.

Thanks to the incredible intuition of this brilliant young astronomer, we have at our disposal standard candles, that is to say light sources of known intensity, through which it is possible to deduce an absolute measure of distance.

This is what Hubble did when he used the Cepheids of the Andromeda nebula to reach the conclusion that these celestial bodies are too far away to be part of our Milky Way.

Lemaître was familiar with the first measurements made by Hubble, which not only placed these nebulae beyond our galaxy but also endowed them with an impressive speed of recession. His theory of an expanding universe made it possible to explain these unprecedented observations, as long as it was accepted that an enormous system was involved, immensely bigger than anything previously supposed. A gigantic structure in which there are countless galaxies similar to our own, with everything inclined to move away from everything else.

After having placed the Earth at the centre of the universe for thousands of years, and having reluctantly accepted that it is just one of the many bodies that rotate around the Sun, a further, final illusion suddenly crumbles. The solar system and our beloved Milky Way have no special position. We are an insignificant component of an anonymous galaxy—just one among the myriad of others to be found throughout the universe. And as if this was not enough, the entire system changes over time. Like all material objects it had a point of origin, and it will in all probability also have an end.

Lemaître’s intuition, confirmed by Hubble’s measurements, provided the basis for nothing less than a new vision of the world. In his original article, written in French, the astronomer-priest had gone so far as to predict a relationship of strict proportionality between distance and the speed at which astronomical objects recede. If his idea about the expanding universe was right, the more distant galaxies would have to move away from us at higher speeds, and would consequently exhibit a greater red shift. And this is precisely the result that Hubble obtained as his catalogue of observations grew in complexity and richness. But for a long time, Lemaître’s intuition was ignored because the Belgian journal in which he’d published his article had such a limited circulation. For this reason, until very recently, the scientific world had always referred to this correlation as “Hubble’s law.”

Thanks to a careful work of reconstruction, the contribution of the Belgian scientist has finally been recognized. It took almost a century, but today the relation that made it possible to establish the essentially dynamic nature of the universe is called, appropriately, the “Hubble–Lemaître law.” In the early 1930s, faced with large amounts of experimental data, Einstein also ended up abandoning his initial scepticism. Legend would have us believe that when reluctantly admitting that the Belgian priest and the American astronomer were right, the eminent scientist regretted his previous failure to understand, remarking that the cosmological constant “had proved to be the biggest blunder I have made in my life.”

Starting from an initial state in rapid expansion, there was no need to introduce this ad hoc correction, and so the cosmological constant disappeared for many decades from the fundamental equation of cosmology. By an irony of sorts, however, there would be a further reversal in the second half of the twentieth century when the discovery of dark energy caused the term that had so tormented its inventor to be reintroduced.

It was Lemaître once more who was the first to speculate that the expansion of the universe could actually be accelerating—and who, not by chance, kept Einstein’s cosmological constant in the equation, albeit reduced to a much lower value. Lemaître described the birth of the universe as a process that had taken place some time between 10 and 20 billion years ago, starting from an elementary state which he called the “primeval atom.” His hypothesis drew together the most advanced scientific theories of the period and the numerous mythological narratives that made everything originate from a kind of cosmic egg. But before doing so, he established the connection between microcosm and macrocosm that would prove so very fruitful in the coming decades.

From the outset, the formulation of this groundbreaking theory produced a great deal of perplexity. In truth, world opinion was otherwise engaged: the Wall Street Crash of 1929, the emergence of Fascism and Nazism in Europe, the many indications that the entire planet was about to descend into another global war. But even in scientific contexts where there was interest, the skepticism directed at the new cosmological theory was extremely strong. A good number of the most eminent scientists of the age refused even to countenance the idea of a beginning to space-time, or a birth of the universe. The problem lay in the fact that it bore a terrible resemblance to the biblical Genesis, and to the creation theory advocated by many religions. And if this wasn’t bad enough, the first proponent of the theory happened to be a priest as well as a scientist, and a Roman Catholic one at that.

The idea of an eternal universe, of an uncreated and everlasting stationary state, had first been supported by Aristotle, and it still fascinated many scientists. One of the best known of these was Fred Hoyle, a British astronomer who simply considered the theory proposed by Lemaître to be utterly repugnant. Hoyle remained convinced by his own ideas right up until his death in 2001. In 1949, in a program made for BBC radio, it was Hoyle who coined the term “Big Bang”—a description he intended as derogatory. Ironically, the image of a great explosion that Hoyle had used with the intention of ridiculing the new cosmological theory ended up penetrating so deeply into the collective imagination that it contributed significantly to its success.

One of the bastions of the most tenacious opposition to the theory was provided by Soviet science. For decades, Soviet scientists stigmatized the Big Bang as a pseudoscientific and idealistic theory that hypothesized a form of creationism—far too similar to the religious kind not to be deeply suspect. It mattered little, for them, that Lemaître had scrupulously separated science from faith, to the extent of reacting with horror when in 1951 Pope Pius XII could not resist the temptation of referring to the Big Bang described by scientists as resembling the biblical moment of Creation. It was an attempt by the Pope to provide a sort of scientific basis for creationism, to reinforce the rational basis of faith—and Lemaître strongly objected to it.

It was experimental results, once again, that would determine the definitive success of Big Bang theory. Among the theoretical developments of the new cosmological theory there had been, in the 1950s, the prediction of a radiation diffused throughout the universe: fossil waves, the relics of a moment in which photons had irrevocably separated from matter and that continued to fluctuate around us. These were very weak electromagnetic waves, stretched for billions of years by the expansion of space-time, an attenuated energy that would have given to the interstellar void a typical temperature of a few degrees kelvin.

The stunning discovery that confirmed this was made almost by chance in 1964 by the American astronomers Arno Penzias and Robert Wilson. The pair had been working for weeks to mend an antenna they hoped to use for radioastronomical observations in the microwave region, but they had failed to eliminate an annoying signal that seemed to be coming from every direction at once. At first they had assumed that it was interference caused by a radio station transmitting in the vicinity of the laboratory then they had thought it might be electromagnetic disturbance connected with various activities in nearby New York. After even checking that a pair of pigeons that had nested in the antenna—leaving a coating of whitish dielectric material, also known as pigeon poo—were not responsible, they stopped searching and published their results in a short letter. The discovery of cosmic microwave background (CMB) radiation emanating from all directions and the observation that the universe had a temperature of a few degrees kelvin, that is to say around –270 degrees Celsius, sealed the success of the already indisputable new theory. Penzias and Wilson had effectively recorded the echo of the Big Bang, the mother of all catastrophes, the primal event, the proof that everything had begun 13.8 billion years ago.

Excerpted from Genesis: The Story of How Everything Began by Guido Tonelli, translated by Erica Segre and Simon Carnell. Published by Farrar, Straus and Giroux in April, 2021. Copyright © Giangiacomo Feltrinelli Editore, Milano. Translation copyright © 2020 by Simon Carnell and Erica Segre. All rights reserved.

Who first hypothesized that the universe is accelerating? - Astronomy

Paper Information

Journal Information

International Journal of Astronomy

p-ISSN: 2169-8848 e-ISSN: 2169-8856

The Nature of Dark Energy and Dark Matter

A, Gopal Road, Panbazar, Guwahati, 781001, India

Correspondence to: Ranku Kalita , A, Gopal Road, Panbazar, Guwahati, 781001, India.


Copyright © 2014 Scientific & Academic Publishing. All Rights Reserved.

This work is licensed under the Creative Commons Attribution International License (CC BY).

It is proposed that the accelerating expansion of the universe is due the cosmologicalization of the principle of equivalence – which recognizes momentary equivalence between gravitational force and inertial force – in an expanding spherical distribution of matter, wherein momentary equivalence occurs at a certain radial distance between gravitational force upon the gravitational mass and inertial force – generated by the accelerating frame of reference of spacetime – upon the inertial mass of an object on the surface of the sphere. The principle of equivalence also recognizes momentary equivalence between a freefalling gravitational mass and the impression of acceleration of an inertial mass in an inertial frame of reference with respect to an accelerating frame of reference. Since the acceleration of the inertial mass is impressional, it is conceivable therefore that the inertial mass of the object can be impressional as well. It is proposed that there are objects in nature which possess impressional inertial mass, and that such objects are the dark matter in the universe.

Keywords: Cosmology, Dark energy, Dark matter, Cosmological constant

Top Ten Mysteries of the Universe

1. What Are Fermi Bubbles?

No, this is not a rare digestive disorder. The bubbles are massive, mysterious structures that emanate from the Milky Ways center and extend roughly 20,000 light-years above and below the galactic plane. The strange phenomenon, first discovered in 2010, is made up of super-high-energy gamma-ray and X-ray emissions, invisible to the naked eye. Scientists have hypothesized that the gamma rays might be shock waves from stars being consumed by the massive black hole at the center of the galaxy.

2. Rectangular Galaxy

“Look, up in the sky! It’s a…rectangle?” Earlier this year, astronomers spotted a celestial body, roughly 70 million light-years away, with an appearance that is unique in the visible universe: The galaxy LEDA 074886 is shaped more or less like a rectangle. While most galaxies are shaped like discs, three-dimensional ellipses or irregular blobs, this one seems to have a regular rectangle or diamond-shaped appearance. Some have speculated that the shape results from the collision of two spiral-shaped galaxies, but no one knows for now.

3. The Moon’s Magnetic Field

One of the moon’s greatest mysteries—why only some parts of the crust seem to have a magnetic field—has intrigued astronomers for decades, even inspiring the buried mythical “monolith” in the novel and film 2001: A Space Odyssey. But some scientists finally think they may have an explanation. After using a computer model to analyze the moon’s crust, researchers believe the magnetism may be a relic of a 120-mile-wide asteroid that collided with the moon’s southern pole about 4.5 billion years ago, scattering magnetic material. Others, though, believe the magnetic field may be related to other smaller, more recent impacts.

4. Why Do Pulsars Pulse?

Pulsars are distant, rapidly spinning neutron stars that emit a beam of electromagnetic radiation at regular intervals, like a rotating lighthouse beam sweeping over a shoreline. Although the first one was discovered in 1967, scientists have for decades struggled to understand what causes these stars to pulse—and, for that matter, what causes pulsars to occasionally stop pulsing. In 2008, though, when one pulsar suddenly shut off for 580 days, scientists’ observations allowed them to determine that the “on” and “off” periods are somehow related to magnetic currents slowing down the stars’ spin. Astronomers are still at work trying to understand why these magnetic currents fluctuate in the first place.

5. What Is Dark Matter?

Astrophysicists are currently trying to observe the effects of dark energy, which accounts for some 70 percent of the universe. But it's not the only dark stuff in the cosmos: roughly 25 percent of it is made up of an entirely separate material called dark matter. Completely invisible to telescopes and the human eye, it neither emits nor absorbs visible light (or any form of electromagnetic radiation), but its gravitational effect is evident in the motions of galaxy clusters and individual stars. Although dark matter has proven extremely difficult to study, many scientists speculate that it might be composed of subatomic particles that are fundamentally different from those that create the matter we see around us.

From end to end, the newly discovered gamma-ray bubbles extend 50,000 light-years, or roughly half of the Milky Way's diameter, as shown in this illustration. (NASA's Goddard Space Flight Center) This pulsar captured in an image by the Chandra X-Ray grabbed attention for its eerie similarity to a human hand. (P. Slane et al. / SAO / NASA / CXC) One of the many mysteries baffling astronomers is how galaxies such as the Milky Way are able to form new stars at an unsustainable rate. (NASA / JPL) Why do only some parts of the Moon have a magnetic field? Recent science may indicate that it is a relic of an asteroid collision 4.5 billion years ago. (NASA / JPL / USGS) The galaxy LEDA 074886 appears more or less like a rectangle, but no one knows why. (Shown here in a false-color image) (Image courtesy of Alister Graham, Swinburne University of Technology)

6. Galactic Recycling

In recent years, astronomers have noticed that galaxies form new stars at a rate that would seem to consume more matter than they actually have inside them. The Milky Way, for example, appears to turn about one sun’s worth of dust and gas into new stars every year, but it doesn’t have enough spare matter to keep this up long-term. A new study of distant galaxies might provide the answer: Astronomers noticed gas that had been expelled by the galaxies flowing back in to the center. If the galaxies recycle this gas to produce new stars, it might be a piece of the puzzle in solving the question of the missing raw matter.

7. Where Is All the Lithium?

Models of the Big Bang indicate that the element lithium should be abundant throughout the universe. The mystery, in this case, is pretty straightforward: it doesn’t. Observations of ancient stars, formed from material most similar to that produced by the Big Bang, reveal amounts of lithium two to three times lower than predicted by the theoretical models. New research indicates that some of this lithium may be mixed into the center of stars, out of view of our telescopes, while theorists suggest that axions, hypothetical subatomic particles, may have absorbed protons and reduced the amount of lithium created in the period just after the Big Bang.

8. Is There Anybody Out There?

In 1961, astrophysicist Frank Drake devised a highly controversial equation: By multiplying together a series of terms relating to the probability of extraterrestrial life (the rate of star formation in the universe, the fraction of stars with planets, the fraction of planets with conditions suitable for life, etc.) he surmised that the existence of intelligent life on other planets is extremely likely. One problem: Roswell conspiracy theorists notwithstanding, we haven’t heard from any aliens to date. Recent discoveries of distant planets that could theoretically harbor life, though, have raised hopes that we might detect extraterrestrials if we just keep looking.

9. How Will the Universe End? [Warning, Potential Spoiler Alert!]

We now believe the universe started with the Big Bang. But how will it end? Based on a number of factors, theorists conclude that the fate of the universe could take one of several wildly different forms. If the amount of dark energy is not enough to resist the compressing force of gravity, the entire universe could collapse into a singular point—a mirror image of the Big Bang, known as the Big Crunch. Recent findings, though, indicate a Big Crunch is less likely than a Big Chill, in which dark energy forces the universe into a slow, gradual expansion and all that remains are burned-out stars and dead planets, hovering at temperatures barely above absolute zero. If enough dark energy is present to overwhelm all other forces, a Big Rip scenario could occur, in which all galaxies, stars and even atoms are torn apart.

10. Across the Multiverse

Theoretical physicists speculate that our universe may not be the only one of its kind. The idea is that our universe exists within a bubble, and multiple alternative universes are contained within their own distinct bubbles. In these other universes, the physical constants—and even the laws of physics—may differ drastically. Despite the theory's resemblance to science fiction, astronomers are now looking for physical evidence: Disc-shaped patterns in the cosmic background radiation left over from the Big Bang, which could indicate collisions with other universes.

About Joseph Stromberg

Joseph Stromberg was previously a digital reporter for Smithsonian.

Accelerating universe? Not so fast

Certain types of supernovae, or exploding stars, are more diverse than previously thought, a University of Arizona-led team of astronomers has discovered. The results, reported in two papers published in the Astrophysical Journal, have implications for big cosmological questions, such as how fast the universe has been expanding since the Big Bang.

Most importantly, the findings hint at the possibility that the acceleration of the expansion of the universe might not be quite as fast as textbooks say.

The team, led by UA astronomer Peter A. Milne, discovered that type Ia supernovae, which have been considered so uniform that cosmologists have used them as cosmic "beacons" to plumb the depths of the universe, actually fall into different populations. The findings are analogous to sampling a selection of 100-watt light bulbs at the hardware store and discovering that they vary in brightness.

"We found that the differences are not random, but lead to separating Ia supernovae into two groups, where the group that is in the minority near us are in the majority at large distances -- and thus when the universe was younger," said Milne, an associate astronomer with the UA's Department of Astronomy and Steward Observatory. "There are different populations out there, and they have not been recognized. The big assumption has been that as you go from near to far, type Ia supernovae are the same. That doesn't appear to be the case."

The discovery casts new light on the currently accepted view of the universe expanding at a faster and faster rate, pulled apart by a poorly understood force called dark energy. This view is based on observations that resulted in the 2011 Nobel Prize for Physics awarded to three scientists, including UA alumnus Brian P. Schmidt.

The Nobel laureates discovered independently that many supernovae appeared fainter than predicted because they had moved farther away from Earth than they should have done if the universe expanded at the same rate. This indicated that the rate at which stars and galaxies move away from each other is increasing in other words, something has been pushing the universe apart faster and faster.

"The idea behind this reasoning," Milne explained, "is that type Ia supernovae happen to be the same brightness -- they all end up pretty similar when they explode. Once people knew why, they started using them as mileposts for the far side of the universe.

"The faraway supernovae should be like the ones nearby because they look like them, but because they're fainter than expected, it led people to conclude they're farther away than expected, and this in turn has led to the conclusion that the universe is expanding faster than it did in the past."

Milne and his co-authors -- Ryan J. Foley of the University of Illinois at Urbana-Champaign, Peter J. Brown at Texas A&M University and Gautham Narayan of the National Optical Astronomy Observatory, or NOAO, in Tucson -- observed a large sample of type Ia supernovae in ultraviolet and visible light. For their study, they combined observations made by the Hubble Space Telescope with those made by NASA's Swift satellite.

The data collected with Swift were crucial because the differences between the populations -- slight shifts toward the red or the blue spectrum -- are subtle in visible light, which had been used to detect type Ia supernovae previously, but became obvious only through Swift's dedicated follow-up observations in the ultraviolet.

"These are great results," said Neil Gehrels, principal investigator of the Swift satellite, who co-authored the first paper. "I am delighted that Swift has provided such important observations, which have been made toward a science goal that is completely independent of the primary mission. It demonstrates the flexibility of our satellite to respond to new phenomena swiftly."

"The realization that there were two groups of type Ia supernovae started with Swift data," Milne said. "Then we went through other datasets to see if we see the same. And we found the trend to be present in all the other datasets.

"As you're going back in time, we see a change in the supernovae population," he added. "The explosion has something different about it, something that doesn't jump out at you when you look at it in optical light, but we see it in the ultraviolet.

"Since nobody realized that before, all these supernovae were thrown in the same barrel. But if you were to look at 10 of them nearby, those 10 are going to be redder on average than a sample of 10 faraway supernovae."

The authors conclude that some of the reported acceleration of the universe can be explained by color differences between the two groups of supernovae, leaving less acceleration than initially reported. This would, in turn, require less dark energy than currently assumed.

"We're proposing that our data suggest there might be less dark energy than textbook knowledge, but we can't put a number on it," Milne said. "Until our paper, the two populations of supernovae were treated as the same population. To get that final answer, you need to do all that work again, separately for the red and for the blue population."

The authors pointed out that more data have to be collected before scientists can understand the impact on current measures of dark energy. Scientists and instruments in Arizona will play important roles in these studies, according to Milne. These include projects led by NOAO the Large Synoptic Survey Telescope, or LSST, whose primary mirror was produced at the UA and a camera built by the UA's Imaging Technology Lab for the Super-LOTIS telescope on Kitt Peak southwest of Tucson. Super-LOTIS is a robotic telescope that will use the new camera to follow up on gamma-ray bursts -- the "muzzle flash" of a supernova -- detected by Swift.

The concept of other universes has been proposed to explain how our own universe appears to be fine-tuned for conscious life as we experience it.

If there were a large (possibly infinite) number of universes, each with possibly different physical laws (or different fundamental physical constants), then some of these universes (even if very few) would have the combination of laws and fundamental parameters that are suitable for the development of matter, astronomical structures, elemental diversity, stars, and planets that can exist long enough for life to emerge and evolve.

The weak anthropic principle could then be applied to conclude that we (as conscious beings) would only exist in one of those few universes that happened to be finely tuned, permitting the existence of life with developed consciousness. Thus, while the probability might be extremely small that any particular universe would have the requisite conditions for life (as we understand life), those conditions do not require intelligent design as an explanation for the conditions in the Universe that promote our existence in it.

An early form of this reasoning is evident in Arthur Schopenhauer's 1844 work "Von der Nichtigkeit und dem Leiden des Lebens", where he argues that our world must be the worst of all possible worlds, because if it were significantly worse in any respect it could not continue to exist.

Intercourse and babies in space

Large space stations with hotels and living space for private citizens will likely be the first option for most people to get to space - Image Credit: IllustroArt via Shutterstock

For a civilization to be really free from Earth, the population needs to grow, and that means babies. Living on the Moon or Mars will be arduous and stressful, so the first inhabitants will probably spend only a few years there at a time and are unlikely to start a family.

But once people do take up permanent residency off-Earth, there are still many unknowns. First, little research has been done on the biology of pregnancy and reproductive health in a space or low-gravity environment like the Moon or Mars . It’s possible there will be unexpected hazards to the fetus or mother. Second, babies are fragile, and raising them is not easy. The infrastructure of these bases would have to be sophisticated to make some version of normal family life possible, a process that will take decades.

With these uncertainties in mind, it seems likely that the first off-Earth baby will be born much closer to home. A Dutch startup called SpaceLife Origin wants to send a heavily pregnant woman 250 miles up just long enough to give birth . They talk a good story, but the legal, medical and ethical obstacles are formidable. Another company, called Orbital Assembly Corporation, plans to open a luxury hotel in orbit in 2027 called the Voyager Station. Current plans show that it would hold 280 guests and 112 crew members, with its spinning-wheel design providing artificial gravity. But the breathless news reports omit any discussion of the difficulty and cost of such a project.

However, on April 12, 2021, NASA announced that it is considering allowing a reality TV show to send a civilian to the International Space Station and film them for 10 days. It’s plausible that this idea could be extended, with a wealthy couple booking a long-term stay for the entire process from conception to birth in orbit.

At the moment, there’s no evidence anyone has had intercourse in space. But with about 600 people having been in Earth orbit – including one NASA couple who kept their marriage a secret – one space historian was able to gather plenty of Space Age salacious moments .

My guess is that sometime around 2040, a unique individual will be born. They may carry the citizenship of their parents, or they may be born in a facility operated by a corporation and end up stateless . But I prefer to think of this future person as the first true citizen of the galaxy.