Category: SCIENCE

The first stars took tens or even hundreds of millions of years to form, and then died in the cosmic blink of an eye. Here’s how.

The cosmic story that gave rise to us is a story rife with creation and destruction. At the start of the hot Big Bang, energetic particles, antiparticles, and quanta of radiation were created. Fractions-of-a-second later, most of the particle-antiparticle pairs had annihilated away. Protons and neutrons formed within the first second, and then over the subsequent minutes, atomic nuclei fused together, creating the first elements. Over the next several hundred thousand years, neutral atoms finally formed, and gravitation pulled matter together into clumps. Eventually, some of the largest clumps gravitationally collapsed, creating the first stars.

But these stars, made up of the pristine material forged in the hot Big Bang, would not remain the only luminous objects in the Universe for very long. As these stars were overwhelmingly massive, 25 times the typical mass of stars created during modern times, they burned through their fuel rapidly, causing them to evolve through their life cycles extremely quickly. The more massive a star is, the shorter its lifespan, meaning that these very first stars didn’t live for long at all. The death of the first stars was absolutely necessary to give rise to the Universe as we know it today. Here’s the cosmic story you haven’t heard.

In order to form stars, the gas you’re going to make it out of needs to collapse. But gravitationally collapsing means you have to radiate energy away; the very act of collapsing is one of energy transfer, where gravitational potential energy gets turned into kinetic energy, and where the kinetic energy of matter (i.e., the energy of motion) causes that material to heat up. Today, heavy elements are the best and most efficient energy-radiators that exist, which means that clouds of gas can collapse efficiently, and form all sorts of stars, from the rare ones that come in at hundreds of solar masses down to very small, faint ones at the low-mass end…

The Universe is an amazing place. Under the incredible, infrared gaze of JWST, it’s coming into focus better than ever before.

Although it might seem that the world changed long ago from the Hubble era to the JWST era, the reality is that humanity’s greatest space-based observatory of all-time is less than two years old. It launched on Christmas Day, 2021, and required six months of deployment, commissioning, and calibration operations before it was ready to begin the primary phase of its life: full-time science operations. Since those milestones were achieved in July of 2022, JWST has been our cosmic workhorse, revealing the Universe in a whole new light, with unprecedented resolution and wavelength coverage to view the cosmos.

While its first sets of spectacular images were released during 2022, this past year, 2023, represents the very first year that we had this remarkable observatory operating full-time, surveying the Universe near and far to reveal some of the most incredible views, plus many unexpected scientific discoveries, that pretty much no one could have anticipated. Here, without further ado, are my favorite JWST science images released in 2023.

1.) Our most distant black hole ever. It was only last month, while combining Chandra X-ray data with JWST’s deep, infrared views of galaxy cluster Abell 2744, that scientists revealed a tiny, distant, early galaxy with only around 10-to-100 million solar masses worth of material in it, but that was incredibly X-ray luminous, indicating an active black hole of around 9 million solar masses. Not only is this the most distant black hole ever discovered, it’s also our first example of such an extreme mass ratio, where the central black hole is right around as massive as all the stars in the host galaxy combined. Our understanding of black hole-galaxy formation and coevolution will never be the same.

In our Universe, matter is made of particles, while antimatter is made of antiparticles. But sometimes, the physical lines get real blurry.

Here in this Universe, there are certain laws of physics that never appear to be broken. No information-carrying signal, for instance, can ever move faster than the speed of light. Energy, if you account for all of the different types that exist, can never be created or destroyed: only conserved. Electric charge, linear momentum, and angular momentum are all similarly conserved. And, to the best of our knowledge, the only way to create new matter particles is to create an equal number of new antimatter particles, as we’ve never observed a single reaction that has either created or destroyed a net amount of matter over antimatter, or the other way around.

But are all of the entities in our Universe either “matter” or “antimatter” in some sense, or are there particles out there that don’t have antiparticles at all? That’s the question of David Wiser, who wants to know:

“I was wondering if there are any elementary particles that do not have corresponding antiparticles? The only two that seem to fit this category are the photon and graviton. Are there others? Is there any significance to not having an antiparticle? Is this related to their traveling at the speed of light?”

There’s a lot to unpack here, but the short answer is yes: not every elementary particle has a corresponding, distinct antiparticle. The long answer is even more interesting. Let’s dive in and find out!

Above, you can see the particles of the Standard Model. These represent all of the presently-known and discovered fundamental particles that make up the Universe, and they still don’t account for two of the greatest mysteries in all of physics: dark matter and dark energy. The particles within the Standard Model come in a few different varieties:

• there are quarks, which have masses, color charges, electric charges, spins, and come in six flavors (up…

Atomic nuclei form in minutes, atoms form in hundreds of thousands of years, but the “dark ages” rule thereafter, until stars finally form.

When it comes to our cosmic history, it’s incredible to realize how impactful the earliest moments were in creating the conditions that would allow for our very existence many billions of years later. The earliest stages we can say anything meaningful about actually occurred even prior to the start of the hot Big Bang. Cosmic inflation took place and then ended, seeding the Universe with quantum fluctuations and then giving rise to the hot Big Bang. The Universe cooled and expanded from its hottest, densest stages to produce more matter than antimatter, then stable protons and neutrons, then atomic nuclei, and eventually even neutral atoms, all amidst a background sea of radiation and neutrinos.

You might think that once neutral atoms form, the next step would be driven by gravitation: the formation of stars. But the timescales required to form them are immense compared to everything that came before. By the time just half-a-million years have passed, the Universe is dominated by matter, the radiation sea is cool enough that atoms cannot become ionized, and gravitation gets to work in earnest. Even with those ingredients, it will still take somewhere between 50 and 100 million years for even the very first star in the Universe to form. For all the time in between, the Universe experiences the darkest part of the era known as the cosmic dark ages. Here’s what it was like back then.

The formation of neutral atoms isn’t simply important for setting into place the building blocks of all the complex chemical structures that can arise from molecules, ions, and any combination of atoms bound together. It’s also very important for “freeing” the photons, or particles of light, left over from the hot Big Bang. When neutral atoms first formed, that marks the time when photons stopped scattering off of free electrons, since free electrons are only present when your atoms are ionized in the form of a plasma. Once all…

On December 9, 2023, Halley’s Comet reached aphelion: its farthest point from the Sun. As it returns, here are 10 facts you should know.

On December 9, 2023, Halley’s comet achieved aphelion, reaching its greatest distance.

These 10 fantastic facts celebrate its impending return.

1.) Its first recording was 240 B.C.E.

Spotted in China, records describe a “Broom Star.”

2.) Halley’s questioning Newton led to the Principia.

Newton offhandedly told Halley a central, ~1/r² force law would create elliptical orbits, then proved it.

3.) Halley identified 3 prior returns.

Previous comet arrivals in 1531, 1607, and 1682 portended Halley’s 1705 prediction.

For generations, physicists have been searching for a quantum theory of gravity. But what if gravity isn’t actually quantum at all?

The two greatest leaps of 20th century physics still leave physicists grappling to understand how it’s possible, at a fundamental level, that they can coexist. On the one hand, we have Einstein’s general theory of relativity (GR), which treats space as a continuous, smooth background that’s deformed, distorted, and compelled to flow and evolve by the presence of all the matter and energy within it, while simultaneously determining the motion of all matter and energy within it via the curvature of that background. On the other hand, there’s quantum physics, governed at a fundamental level by quantum field theory (QFT). All the quantum “weirdness” is encoded in that description, including ideas like quantum uncertainty, the superposition of states, and quantum indeterminism: fundamentally anti-classical notions.

Traditionally, approaches to unify the two have focused on quantizing gravity, attempting to place it on the same footing as the other quantum forces. But a series of new papers, led by Jonathan Oppenheim, takes a very different approach: creating a “postquantum” theory of classical gravity. It’s led to questions by many, including Patreon supporters Cameron Sowards and Ken Lapre:

“I’d love to see your thoughts about the just published postquantum theory of classical gravity.”

“[A]ny chance you have the time and inclination to explain this paper in English so non-physicists could take a stab at understanding it?”

It’s a big idea that, importantly, is still in its infancy, but that doesn’t mean it doesn’t deserve consideration. Let’s first look at the problem, and then, the proposed solution inherent to this big idea.

It’s often said that General Relativity (GR) and Quantum Field Theory (QFT) are incompatible, but it’s difficult for many to understand why. After all, for problems are only concerned with gravity, using GR…

The brilliant mind who discovered the spacetime solution for rotating black holes claims singularities don’t physically exist. Is he right?

Here in our Universe, whenever you gather enough mass together in a small enough volume of space, you’re bound to eventually cross a threshold: where the speed at which you’d need to travel to escape the gravitational pull within that region exceeds the speed of light. Whenever that occurs, it’s inevitable that you’ll form an event horizon around that region, which looks, acts, and behaves exactly like a black hole as seen from the outside. Meanwhile, inside, all that matter gets inexorably drawn towards the central region inside that black hole. With finite amounts of mass compressed to an infinitesimal volume, the existence of a singularity is all but assured.

The predictions for what we should observe outside the event horizon match extraordinarily well with observations, as we’ve not only seen many luminous objects in orbit around black holes, but have even now imaged the event horizons of multiple black holes directly. The theorist who laid the foundation for how realistic black holes form in the Universe, Roger Penrose, subsequently won the Nobel Prize in Physics in 2020 for his contributions to physics, including for the notion that a singularity must exist at the center of every black hole.

But in a surprising twist, the legendary physicist who discovered the spacetime solution for rotating black holes — Roy Kerr, way back in 1963 — has just written a new paper challenging that idea with some very compelling arguments. Here’s why, perhaps, singularities may not exist within every black hole, and what the key issues are that we should all be thinking about.

Making an ideal black hole

If you want to make a black hole, in Einstein’s General Relativity, all you have to do is take any distribution of pressureless mass — what relativists call “dust” — that starts in the same vicinity and is initially at rest, and let…

In General Relativity, the matter and energy present curve spacetime, which we experience as gravity. Why can’t there be an “antigravity” force?

Although there are four known fundamental forces to the Universe, there’s only one that matters on the largest cosmic scales of all: gravitation. The other three fundamental forces:

• the strong nuclear force, which holds protons and neutrons together,
• the weak nuclear force, responsible for radioactive decays and any “species change” among quarks and leptons,
• and the electromagnetic force, which causes neutral atoms to form,

are all largely irrelevant on cosmic scales. The reason why is simple: the other forces, when you gather large sets of particles together, all balance out at large distances. Matter, under those three forces, appears “neutral” at large scales, and no net force exists.

But not so with gravitation. In fact, gravitation is unique in this sense. With gravitation, there are only “positive” charges: things with positive amounts of mass and/or energy. Between those things, the gravitational force is only attractive, and so cumulatively, it can really add up. But why is it this way, and not any other? That’s what Alex Gebethner wants to know, writing in to ask:

“The common model used to explain spacetime to laymen like me is the bowling ball on a bedsheet. The weight of the ball deforms the flat sheet and draws in smaller objects nearby. But it seems logical that the bedsheet could be deformed in the other direction (upwards, to continue with the bedsheet analogy) by a very similar object, pushing objects away from the point of deformation. However, we never observe this occurring. Why? Why does spacetime only bend in one direction (that of gravity)?”

It’s a profound question, and one that deserves a quality answer.

Above is the “classic” illustration of General Relativity: the notion that space (and spacetime) is simply a fabric, and that…

In the early stages of the hot Big Bang, matter and antimatter were (almost) balanced. After a brief while, matter won out. Here’s how.

Things happen fast in the earliest stages of the Universe. In the first 25 microseconds after the start of the hot Big Bang, a number of incredible events have already occurred. The Universe created all the particles and antiparticles — known (as part of the Standard Model) and unknown (including whatever makes up dark matter) — it was ever capable of creating, reaching the highest temperatures it ever attained. Through a still-undetermined process, it created an excess of matter over antimatter: just at the 1-part-in-a-billion level. The electroweak symmetry broke, allowing the Higgs to give mass to the Universe. The heavy, unstable particles decayed away, and the quarks and gluons bound together to form protons and neutrons.

But that only gets us so far. At these early stages, there may be protons and neutrons in the Universe, as well as a high-energy bath of photons and neutrinos-and-antineutrinos, but we’re still a long way from the Universe as we recognize it today. In order to get there, a number of other things must occur. And the first of those, once we have protons and neutrons, is to get rid of the last of our antimatter, which is still incredibly abundant.

You can always make antimatter in the Universe, so long as you have the energy for it. Einstein’s most famous equation, E = mc², works two ways, and it works equally well for both applications.

1. It can create energy from pure matter (or antimatter), converting mass (m) into energy (E) by reducing the amount of mass present, such as by annihilating equal parts matter with antimatter.
2. Or it can create new matter from pure energy, so long as it also makes an equivalent amount of the antimatter counterparts for each matter particle it creates.

These annihilation-and-creation processes, so long as there’s enough energy for creation to proceed smoothly, balance…

For a substantial fraction of a second after the Big Bang, there was only a quark-gluon plasma. Here’s how protons and neutrons arose.

The story of our cosmic history is one of an expanding and cooling Universe. As we progressed from a hot, dense, uniform state to a cold, sparse, clumpy one, a number of momentous events happened throughout our cosmic history. At the moment of the hot Big Bang, the Universe was filled with all sorts of ultra-high energy particles, antiparticles, and quanta of radiation, moving at or close to the speed of light.

On the other hand, today, we have a Universe filled with stars, galaxies, gas, dust, and many other phenomena that are too low in energy to have existed in the early Universe. Once things cooled enough so that the Higgs gave mass to the Universe, you might think that protons and neutrons would have immediately formed thereafter.

But under the hot, dense conditions that were present in the young, post-Big Bang Universe, they couldn’t exist right away. It took time, and the right set of conditions, before even something as fundamental to our Universe as a proton or neutron could stably form for the first time. Here’s the story of how those essential building blocks of atoms first came to be.

In the hot, dense environment of the early Universe, but after the fundamental particles have obtained a rest mass, the Universe was teeming not only with high-energy radiation, but also with several species of fast-moving, relativistic particles. In fact, the Universe possesses every particle-antiparticle combination that’s energetically possible in great numbers, continuously popping in-and-out of existence as particle-antiparticle pairs emerge from the collisions of other quanta. The particles that exist at this time include:

• quarks and antiquarks,
• leptons and antileptons,
• neutrinos and antineutrinos,
• as well as the gauge bosons.