The full-field image of MACSJ0717.5+3745 shows many thousands of galaxies in four separate sub-clusters within the large cluster. The blue contours show the inferred mass distribution from the gravitational lensing effects on background objects. Not shown in this diagram is the X-ray data, which shows an offset between the X-ray emitting gas, which traces the normal matter distribution, and these blue contours, which map out the total mass, including dark matter. (Credit: NASA, ESA, D. Harvey (École Polytechnique Fédérale de Lausanne, Switzerland), R. Massey (Durham University, UK), Harald Ebeling (University of Hawaii at Manoa) & Jean-Paul Kneib (LAM))
There are a wide variety of theoretical studies that call our standard model of cosmology into question. Here’s what they really mean.
Perhaps the pinnacle of scientific achievement is the fact that, at a fundamental level, from subatomic scales up to the largest cosmic ones, humanity has come to understand the Universe more completely and comprehensively than ever before. The Standard Model of particle physics accounts for the interactions, presence and properties of normal matter and radiation in the Universe, including atoms, ions, light, and neutrinos, while General Relativity accounts for gravitation. Cosmically, the Big Bang plus the ingredients of inflation, dark matter, and dark energy explain the Universe’s evolution and structure, allowing us to piece together the most powerful explanatory picture of our cosmos ever concocted.
But you wouldn’t know it by reading the news about science these days. You’d think that dark matter, dark energy, and inflation were all ad hoc fixes that were destined to be wrong, that astronomy discoveries about distant galaxies, cosmic expansion, and black holes have demonstrated that our view of the Universe is fundamentally broken, and that new scientific discoveries continuously…
In the very early Universe, there were tremendous numbers of quarks, leptons, anti-quarks, and anti-leptons of all species. After only a tiny fraction-of-a-second has elapsed since the hot Big Bang, most of these matter-antimatter pairs annihilate away, leaving a very tiny excess of matter over antimatter. How that excess came about is a puzzle known as baryogenesis, and is one of the greatest unsolved problems in modern physics. (Credit: E. Siegel/Beyond the Galaxy)
You can only create or destroy matter by creating or destroying equal amounts of antimatter. So how did we become a matter-rich Universe?
Everywhere we look in the Universe, we find structure of some sort: planets, stars, gas, dust, plasma, and galaxies galore. Every indication we have is that each one of those structures we see is overwhelmingly composed of normal matter, like quarks and leptons, with only trace amounts of antimatter, made of things like antiquarks and antileptons. And yet, when we perform our particle experiments here on Earth, at low energies and at high energies, using particles from colliders as well as particles from cosmic rays, we always find the same thing: that our reactions, while they can create and destroy matter, can only do so at the expense of creating and destroying an equivalent amount of antimatter.
So how, then, did all the matter, and not an equal amount of antimatter, come to exist in our Universe? That’s the topic of this week’s Ask Ethan question thanks to Mateen Khan, who writes in wanting to know:
“Can you help me understand, how matter came to existence from almost nothing (at the moment of big bang) to it’s vast abundance everywhere in the universe and still growing. I am puzzled with the fact that matter is not a living organism so how come it has multiplied in a sense to keep growing?”
Although it isn’t quite the case that the matter abundance is growing or multiplying with time, it is true that our Universe must have generated a matter-antimatter asymmetry, somehow, in the distant past. Here’s what science knows about that puzzle as of today.
The early Universe was full of matter and radiation, and was so hot and dense that it prevented all composite particles, like protons and neutrons from stably forming for the first fraction-of-a-second. There was only a quark-gluon plasma, as well as other particles (such as charged leptons, neutrinos, and other bosons) zipping around at nearly the speed of light. This primordial soup consisted of particles, antiparticles, and radiation: a highly symmetric state. (Credit: Models and Data Analysis Initiative/Duke University)
To start thinking about how matter came into existence, you have to understand that “almost nothing” is not a good description of what the Universe was like at the start of the hot Big Bang. In fact, it was likely just the opposite, as “almost everything,” at least in terms of what is allowed by the incredibly high energies and temperatures present at the start of the hot Big Bang, is…
One of the very first spherules collected off of the ocean floor by Avi Loeb’s expedition to try to recover fragments of a suspected interstellar meteor. The actual nature of these spherules is almost certainly terrestrial, not extraterrestrial, and has nothing to do with the alleged meteor Loeb is chasing. (Credit: The Galileo Project)
Harvard astronomer Avi Loeb claimed to track down and find alien spherules on the ocean bottom. The sober truth is an utter embarrassment.
One of the most common, and unfortunately well-deserved, tropes is that of an arrogant physicist who shamelessly wanders into a field that’s new to them. Armed with their knowledge, experience, and problem solving abilities, they falsely believe that their lack of familiarity with an entire field of science is no obstacle to making meaningful contributions that the “mediocre” scientists working in that inferior field would have no chance at making. It’s such a common theme that xkcd made a brilliant comic years ago whose text reads:
“You’re trying to predict the behavior of <complicated system>? Just model it as a <simple object>, and then add some secondary terms to account for <complications I just thought of>.
Easy, right?
So, why does <your field> need a whole journal, anyway?”
Rarely is someone with this attitude humble enough to make any meaningful contributions in this new field, as they lack the fundamental attitude of being ready to learn what they don’t know while simultaneously being willing and eager to let go of their incorrect, previously-held misconceptions in favor of a more correct way of thinking. Instead, they typically stand in the way of the very good science being done by the experts in that field, and instead confuse an ill-informed general public even further, damaging the entire enterprise of science.
Continuing the long and storied traditions of physicists without shame in exactly this fashion, Harvard astronomer Avi Loeb dubiously claimed that:
an interstellar meteor struck Earth in 2014,
that meteor was possibly made of alien technology,
it landed in a specific place in the ocean,
and that his expedition recovered those fragments and determined that they are of alien origin from beyond our Solar System.
Here to help us explore these objects and their impact this month is Skylar Grayson, a PhD candidate at the School of Earth and Space Exploration at Arizona State University. Skylar works at the intersection of theory and computational astrophysics, and helps simulate the Universe while focusing on the inclusion and modeling of this type of galactic activity, and is one of the people helping uncover just how profound of a role these galaxies play in shaping the Universe around them. Buckle up for another exciting 90 minute episode; you won’t want to miss it!
The 25-meter Giant Magellan Telescope is currently under construction, and will be the greatest new ground-based observatory on Earth. The spider arms, seen holding the secondary mirror in place, are specially designed so that their line-of-sight falls directly between the narrow gaps in the GMT mirrors, creating a view of the Universe without sharp corners to its mirrors or diffraction spikes around its stars. As one of the two US Extremely Large Telescopes proposed by astronomers and currently in development, it is an essential part of bringing about a new generation in cutting-edge ground-based astronomy facilities. (Credit: Giant Magellan Telescope/GMTO Corporation)
Ground-based facilities enable the greatest scientific production in all of astronomy. The NSF needs to be ambitious, and it’s now or never.
If you want to push the frontiers of science, you don’t just need brilliant minds with first-rate educations, you also need cutting-edge facilities to support them. When it comes to the science of astronomy and astrophysics, the next generation of necessary facilities — in the ground and in space, across all wavelengths of light, and even extending beyond light to particles and gravitational waves — were just recently agreed-upon by the National Academies of Sciences in a decadal report known as Astro2020. With a truly balanced portfolio between:
ground-based and space-based endeavors,
small, medium, large, and flagship missions,
various fields of astronomy, from within our Solar System to exoplanets to stars and galaxies to cosmology,
and a series of new and upgraded facilities, including two extremely large telescopes, the next-generation Very Large Array, and upgrades to the IceCube facility for detecting neutrinos at the south pole,
as well as investments in the next generation of scientists,
many have written at length about this ambitious but doable plan to secure a bright future for the United States in this profoundly important area of fundamental science.
These recommendations were adopted, across-the-board, by federal agencies such as NASA and the Department of Energy, and were expected to be (but have not been, to date) adopted by the National Science Foundation as well. However, with one penny-pinching and short-sighted resolution, the NSF has decided that instead of building two extremely large telescopes, the United States will only contribute towards one, and even that is only to the tune of a maximum of $1.6 billion, as recommended by the National Science Board. The truth is we need these facilities, as manyhave argued, and perhaps the best way to understand why is to debunk the most common myths associated with arguing why we don’t.
Initially, at left, the Universe is filled with neutral, light-blocking matter back before any stars have formed. When stars begin to form, however, they create ionizing ultraviolet photons, which lead to pockets that behave as though they’re transparent to visible light, as shown in red. Over time, as we move to the right, more and more of the Universe becomes reionized, until reionization completes around 550 million years after the Big Bang. (Credit: Thesan Collaboration)
JWST has puzzled astronomers by revealing large, bright, massive early galaxies. But the littlest ones pack the greatest cosmic punch.
This image shows the full imaging field of the JWST UNCOVER Treasury Survey, which takes up about 0.007 square degrees in the sky. In this tiny patch of space, some ~50,000 objects are revealed, with the majority of them not associated with the imaged cluster, Abell 2744, at all, but rather as background galaxies that are affected by the gravity of the cluster itself. No signs of matter-antimatter annihilation are seen here, indicating that all stars and galaxies shown are made of matter, not antimatter. However, many gravitationally lensed background galaxies are among the most distant ever discovered. (Credit: R. Bezanson et al., ApJ submitted, JWST UNCOVER Treasury Survey, 2023)
At early times (left), photons scatter off of electrons and are high-enough in energy to knock any atoms back into an ionized state. Once the Universe cools enough, and is devoid of such high-energy photons (right), they cannot interact with the neutral atoms, and instead simply free-stream, since they have the wrong wavelength to excite these atoms to a higher energy level. (Credit: E. Siegel/Beyond the Galaxy)
The overdense regions that the Universe was born with grow and grow over time, but are limited in their growth by the initial small magnitudes of the overdensities, the cosmic scale on which the overdensities are found (and the time it takes the gravitational force to traverse them), and also by the presence of radiation that’s still energetic, which prevents structure from growing any faster. It takes tens-to-hundreds of millions of years to form the first stars; small-scale clumps of matter exist long before that, however. Until stars form, the atoms in these clumps remain neutral, requiring ionizing, ultraviolet photons to render them transparent to visible light. (Credit: Aaron Smith/TACC/UT-Austin)
Energetic, ultraviolet photons are required to reionize atoms.
An artist’s conception of what a region within the Universe might look like as it forms stars for the first time. As they shine and merge, radiation will be emitted, both electromagnetic and gravitational. But the conversion of matter into energy does something else: it causes an increase in radiation pressure, which fights against gravitation. Surrounding the star-forming region is darkness, as neutral atoms effectively absorb that emitted starlight, while the emitted ultraviolet starlight works to ionize that matter from the inside out. (Credit: Pablo Carlos Budassi/Wikimedia Commons)
Determining how early stars and galaxies reionized the Universe is a cosmic challenge.
One of the science goals of the JWST UNCOVER survey is to track galaxy evolution across cosmic time. Here, a selection of nine galaxies pulled from the survey itself are highlighted in context with the cosmic time from which their light was emitted. JWST is shedding a whole new light on the story of galaxy evolution within our Universe, and is also helping us determine which types of galaxies, and when, helped our Universe transition from an opaque state to one transparent to light. (Credit: R. Bezanson et al., ApJ submitted, JWST UNCOVER Treasury Survey, 2023)
The galaxies that compose Pandora’s Cluster, Abell 2744, are present within the three separate cluster components easily visually identifiable, while the remaining background sources are scattered all throughout the Universe, including many from the first ~1 billion years of cosmic history. This field of view is now known to contain many of the earliest galaxies ever found, as well as the youngest proto-cluster of galaxies ever discovered to date: just 650 million years after the Big Bang. (Credit: R. Bezanson et al., ApJ submitted, JWST UNCOVER Treasury Survey, 2023)
This gravitational lensing map shows the reconstructed magnification contours from JWST data owing to the lensing profile of the three bright components of Abell 2744, Pandora’s Cluster. All galaxy clusters have their own unique lensing magnification properties, providing maximum enhancement along specific contours. (Credit: L.J. Furtak et al., MNRAS Submitted/arXiv:2212.04381, 2022)
This huge mass collection bends and distorts the surrounding spacetime.
From whatever pre-existing state started it, inflation predicts that a series of independent universes will be spawned as inflation continues, with each one being completely disconnected from every other one, separated by more inflating space. One of these “bubbles,” where inflation ended, gave birth to our Universe some 13.8 billion years ago. Today, dark energy dominates the Universe and causes space to expand exponentially as well. Could these scenarios be related? (Credit: Nicolle Rager Fuller)
When cosmic inflation came to an end, the hot Big Bang ensued as a result. If our cosmic vacuum state decays, could it all happen again?
From Peter Pan to Battlestar Galactica, one of the most famous notions in all of fiction is the idea of cyclic repetition: all of this has happened before, and it will all happen again. But does that apply to the cosmos itself? The Universe as we know it began with the hot Big Bang, which itself was set up and caused by a prior state known as cosmic inflation, where the Universe was expanding rapidly and relentlessly for an unknown period of time. When inflation came to an end, the energy throughout space — which had previously been in the form of field energy, or energy inherent to space itself — got converted into the various quanta, kicking off the hot Big Bang.
Today, however, billions of years later, we still have a form of energy inherent to space itself: dark energy. Could this someday trigger a similar scenario, leading to a new sort of Big Bang? That’s the question of Sara Wright, who inquires:
“If I understand this correctly, the big bang occurred when the inflationary field energy was suddenly converted into all the particles and radiation that are present today. But there is also the false vacuum decay scenario, where the zero point energy of space may reach an even lower state than it is now. Are these two events related to each other in any way? If so, is it possible that the same big bang that gave rise to us is still propagating far beyond the cosmic horizon of our observable universe?”
This is a really big question and a fascinating possibility that, to be honest, no one knows whether it describes our Universe’s future or not. Here’s the big idea, and why it’s worth pondering.
In the top panel, our modern Universe has the same properties (including temperature) everywhere because they originated from a region possessing the same properties. In the middle panel, the space that could have had any arbitrary curvature is inflated to the point where we cannot observe any curvature today, solving the flatness problem. And in the bottom panel, pre-existing high-energy relics are inflated away, providing a solution to the high-energy relic problem. This is how inflation solves the three great puzzles that the Big Bang cannot account for on its own. (Credit: E. Siegel/Beyond the Galaxy)
In order to admit the most promising students across all socioeconomic backgrounds, an approach that includes, rather than excludes, standardized testing leads to more equitable outcomes. (Credit: NAACP)
There are many problems with relying on SAT and ACT scores for college admissions. But removing them entirely creates less opportunity.
One of the most stressful times in a young person’s life occurs when they’re still a teenager: when they make their decisions surrounding applying to college. Should they apply, and is college right for them? Where should they apply, and what steps should they take and avoid taking in the application process? In recent years, that second question has also included the notion of whether or not those prospective college students should take a standardized test — such as the SAT or ACT — as those tests:
However, the goal of the college admissions process is for admissions officers to make distinctions between applicants who are likely to meet with academic success in college (and beyond) and those who are likely to struggle in college. Although it is true that standardized test scores alone tend to favor wealthy applicants, those tests remain a unique and powerful way for colleges and universities to identify students from schools without deep resources that nevertheless have the potential for extraordinary academic success. Here’s why colleges should — responsibly — include standardized testing as part of their admissions process.
During the 1940s, Einstein himself gave a number of lectures to students who would have, in the past, never have had access to a speaker such as himself. Einstein made it a point to be generous with his time and with affording others access to him, and was a prominent supporter of civil rights for all. Today, it is generally recognized that humans of all races and colors have similar potentials, but that individuals, because of socioeconomic concerns and other factors, are often denied equal opportunity in education. (Credit: Lincoln University of PA/Langston Hughes Memorial Library)
If the light from a parent star can be obscured, such as with a coronagraph or a starshade, the terrestrial planets within its habitable zone could potentially be directly imaged, allowing searches for numerous potential biosignatures. In the far future, it’s these longest-lived, lowest-mass stars that might be the last locations where life persists in the Universe. (Credit: NASA/JPL-Caltech)
There are plenty of life-friendly stellar systems in the Universe today. But at some point in the far future, life’s final extinction will occur.
One of the most humbling aspects of our Universe is the knowledge that, in enough times, all things will eventually pass away. New stars and stellar systems, while they’re expected to keep forming for many billions or even trillions of years to come, are on the decline, with the current star-formation rate only about 3% of what it was at its peak some 11 billion years ago. Planets like Earth around stars like the Sun, while relatively common today, will be extremely rare in the far future. And the longest-lived stars, even if they have Earth-sized planets around them, might be poor candidates for supporting life due to their incredibly active behavior.
At some point in the far future, the last living world in the Universe will encounter its demise, signifying an end to what we know as biological activity within our cosmos. But when will this occur? And when and where will the last chances for intelligent life persist? That’s what Terry Dunn wants to know, writing in as follows:
“My question is about the likelihood of intelligent life in billions of years. M-Class stars are extremely hostile to life (as we know it). Planets in the Goldilocks zone are so close that they are tidally locked like our Moon and always show one side towards the Sun. So one side is blazing hot and the other is freezing cold, and M-Class stars give off huge amounts of dangerous radiation lethal to life (as we know it). So while there is certainly life in universe now (but not nearby), is it likely there will be life in billions of years time?”
Although there are a healthy amount of uncertainties still involved, here’s the best story science has to tell about the answers at present.
Although more than 5,000 confirmed exoplanets are known, with more than half of them uncovered by Kepler, there are no true analogues of the planets found in our Solar System. Jupiter-analogues, Earth-analogues, and Mercury-analogues all remain elusive with current technology. The overwhelming majority of planets found via the transit method are close to their parent star, are ~10% the radius (or, equivalently, ~1% the surface area) of their parent star or more, and are orbiting low-mass, small-sized stars. (Credit: NASA/Ames/Jessie Dotson and Wendy Stenzel; annotated by E. Siegel)
Ingredients for a habitable planet
If you want to have life arise in the Universe, a planet (or world, in the case of a habitable moon, for example)…
