Photons Explain Dark Energy

 

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When it comes to the Universe, there are some things we can be confident are out there based on what we observe. 

We know that the Universe was hotter, denser, and more uniform in the distant past. We know that the stars and galaxies in the Universe have grown up and evolved as the Universe has aged. 

We know that gravitation has formed the large-scale structure in the Universe, and that structure has grown more complex over time. 

And we also know how much normal matter, altogether, is present in the Universe, and that it isn’t sufficient to explain the full suite of the gravitational effects that we see on its own.  READ MORE...

A Society Too Complex to Survive

Homo sapiens evolved as a separate species about 300,000 years ago. Measured in generations (with each generation lasting 20 years), that means there are about 15,000 great-great-etc. grandparents separating you from the earliest human ancestors. 

While that’s a remarkable fact in itself, what’s really remarkable is how the world each of those generations experienced was remarkably static. Of course, there were natural disasters and wars. In general, however, the “techno-social” universe your 9,045th great-grandparent lived in was not very different from the one your 9,046th one inhabited. The same holds true for the vast majority of generations after them.  READ MORE...

US Scored Low on Human Rights

Americans like to think their country is exceptional — an unequaled bastion of freedom and opportunity. However, when it comes to human rights, a new report suggests the United States is anything but exceptional. Compiled by the Global Rights Project (GRIP) at the University of Rhode Island and the CIRIGHTS data project, the 2023 GRIP Annual Report assesses and ranks 195 countries on their dedication to 25 individual human rights. 

These are divided into four categories:

• Physical integrity: the right of citizens to not be unnecessarily harmed by state agencies
• Empowerment: the right to live and speak freely
• Worker rights: the right to decent-paying and safe work
• Justice rights: the right to fair laws

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Exploring the Quantum Universe

After a multi-year review, the U.S. particle physics community has announced its vision for research spanning the next five to ten years. The various projects could, if funded, help researchers develop a much better understanding of the laws of nature.

The recommendations were released in a report called “Exploring the Quantum Universe: Pathways to Innovation and Discovery in Particle Physics.” It was written by the Particle Physics Projects Prioritization Panel (P5), a sub-panel of the High Energy Physics Advisory Panel (HEPAP), and will be submitted to funding agencies like the U.S. Department of Energy Office of Science and the Natioce Foundation to guide their funding decisions over the next decade.  READ MORE...

The Physics of Immortality

From your own experiential perspective, the laws of physics are stacked against you if you ever hope to achieve immortality. From a thermodynamic perspective, every system tends toward increasing entropy-and-disorder, and the only way you can combat that is by constantly inputting an external source of energy; in other words, your body and mind will eventually break down. 

And although you might try to leverage the power of relativity to dilate time and slow its passage, that will never work from your individual perspective; time only dilates or slows relative to an observer in a different reference frame from your own.

While this may confine a human’s dream of immortality to solutions that rely on technological enhancements or science-fiction level technology that relies on novel physical laws and/or phenomena, there’s still plenty for relativity to say about living forever: at least, relative to the rest of the Universe. 

While nearly all of us living today will certainly be dead in another century, should we all remain on Earth, the lessons from both special and general relativity teach us that there are a few physical situations that we should strive for if we truly want to maximize the amount of time that we can spend as living creatures within our Universe. Here’s the key insight we all need to understand.

The foundation of relativity: spacetime

Even though we normally credit Einstein with overcoming the disparate ideas of space and time that had held sway since the time of Newton and coming up with the revolutionary concept of a four-dimensional fabric that weaves them both together — spacetime — it wasn’t Einstein at all that came up with that key insight. 

It’s true that 1905 was indeed a banner year for Einstein, with the two key insights that powered special relativity key among them:

1. That the laws of physics are invariant, or that they do not change, in all non-accelerating frames of reference.
2. And that the speed of light in a vacuum, c, is identical for all observers, regardless of their motion or of the motion of the light source in question.

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Quantum Universe Inside an Atom

In many ways, the quest for what's truly fundamental in our Universe is the story of probing the Universe on smaller scales and at higher energies.

By going inside the atom, we revealed the atomic nucleus, its constituent protons and neutrons, and the quarks and gluons inside, plus many other spectacular features.

It's through this investigation of the subatomic world that we've revealed the elementary building blocks of our Universe and the rules that allow them to bind together to compose our cosmic reality.

If you wanted to uncover the secrets of the Universe for yourself, all you’d have to do is interrogate the Universe until it revealed the answers in a way you could comprehend them. 

When any two quanta of energy interact — irrespective of their properties, including whether they’re particles or antiparticles, massive or massless, fermions or bosons, etc. — the result of that interaction has the potential to inform you about the underlying laws and rules that the system has to obey. 

If we knew all the possible outcomes of any interaction, including what their relative probabilities were, then and only then would we claim to have some understanding of what was going on. Being quantitative in precisely this fashion, asking not only “what happens” but also “by how much” and “how often,” is what makes physics the robust science that it is.

Quite surprisingly, everything that we know about the Universe can, in some way, be traced back to the most humble of all the entities we know of: an atom. 

An atom remains the smallest unit of matter we know of that still retains the unique characteristics and properties that apply to the macroscopic world, including the physical and chemical properties of matter. And yet, an atom is a fundamentally quantum entity, with its own energy levels, properties, and conservation laws. 

Moreover, even the humble atom couples to all four of the known fundamental forces. In a very real way, all of physics is on display, even inside a single atom. Here’s what they can tell us about the Universe.   READ MORE...

Defining Our Physical Universe

On the smallest of physical scales, we have the fundamental, elementary particles, which build up to assemble nuclei, atoms, molecules, and even larger structures. 

On larger scales, we have planets, stars, stellar systems, galaxies, clusters of galaxies, and vast voids between them, all contributing to the enormous cosmic web.

Overall, there are many different scales to view the Universe on. Here's the grand cosmic tour, from the extremely tiny to the unfathomably large.



Our Universe spans from subatomic to cosmic scales.
The journey from macroscopic scales down to subatomic ones spans many orders of magnitude, but going down in small steps can make each new one more accessible from the previous one. Humans are made of organs, cells, organelles, molecules, atoms, then electrons and nuclei, then protons and neutrons, and then quarks and gluons inside of them. This is the limit to how far we’ve ever probed nature.Credit: Magdalena Kowalska/CERN/ISOLDE team

All told, 13 different scales are presently known.
On the right, the gauge bosons, which mediate the three fundamental quantum forces of our Universe, are illustrated. There is only one photon to mediate the electromagnetic force, there are three bosons mediating the weak force, and eight mediating the strong force. This suggests that the Standard Model is a combination of three groups: U(1), SU(2), and SU(3), whose interactions and particles combine to make up everything known in existence. With gravity thrown into the mix, there are a total of 26 fundamental constants required to explain our Universe, with four big questions still awaiting explanation.Credit: Daniel Domingues/CERN

1.) Fundamental, elementary particles. Down to 10-19 meters, these quanta have never been divided.
When two protons, each one made of three quarks held together by gluons, overlap, it’s possible that they can fuse together into a composite state dependent on their properties. The most common, stable possibility is to produce a deuteron, made of a proton and a neutron, which requires the emission of a neutrino, a positron, and possibly a photon as well.Credit: Keiko Murano

2.) Nuclear scales. On femtometer (~10-15 m) scales, individual nucleons, composed of quarks and gluons, bind together.
Although you yourself are made of atoms, what you experience as “touch” doesn’t necessarily require another, external atom to come in actual overlapping contact with the atoms in your body. Simply getting close enough to exert a force is not only enough, it’s what most commonly occurs.        READ MORE...

Spacetime - Is It Real?

An illustration of heavily curved spacetime, outside the event horizon of a black hole. As you get closer and closer to the mass’s location, space becomes more severely curved, eventually leading to a location from within which even light cannot escape: the event horizon. At large distances, the spatial curvature is indistinguishable for equal mass black holes, neutron stars, white dwarfs, or any other comparably massed object. Credit: JohnsonMartin/Pixabay




When most of us think about the Universe, we think about the material objects that are out there across the great cosmic distances. Matter collapses under its own gravity to form cosmic structures like galaxies, while gas clouds contract to form stars and planets. Stars then emit light by burning their fuel through nuclear fusion, and then that light travels throughout the Universe, illuminating anything it comes into contact with. 

But there’s more to the Universe than the objects within it. There’s also the fabric of spacetime, which has its own set of rules that it plays by: General Relativity. The fabric of spacetime is curved by the presence of matter and energy, and curved spacetime itself tells matter and energy how to move through it.

But what, exactly, is the physical nature of spacetime? Is it a real, physical thing, like atoms are, or is it merely a calculational tool that we use to give the right answers for the motion and behavior of the matter within the Universe?


It’s an excellent question and a tough one to wrap your head around. Moreover, before Einstein came along, our conception of the Universe was very different from the one we have today. Let’s go way back to the Universe before we even had the concept of spacetime, and then come forward to where we are today.

The journey from macroscopic scales down to subatomic ones spans many orders of magnitude, but going down in small steps can make each new one more accessible from the previous one. Humans are made of organs, cells, organelles, molecules, atoms, then electrons and nuclei, then protons and neutrons, and then quarks and gluons inside of them. This is the limit to how far we’ve ever probed nature.Credit: Magdalena Kowalska/CERN/ISOLDE team

At a fundamental level, we had long supposed that if you took everything that was in the Universe and cut it up into smaller and smaller constituents, you’d eventually reach something that was indivisible. Quite literally, that’s what the word “atom” means: from the Greek ἄτομος: not able to be cut. 

The first record we have of this idea goes back some 2400 years to Democritus of Abdera, but it’s plausible that it may go back even farther. These “uncuttable” entities do exist; each one is known as a quantum particle. Despite the fact that we took the name “atom” for the elements of the periodic table, it’s actually subatomic particles like quarks, gluons, and electrons (as well as particles that aren’t found in atoms at all) that are truly indivisible.   READ MORE...

The Big Bang Means Something Different Now

If there’s one hallmark inherent to science, it’s that our understanding of how the Universe works is always open to revision in the face of new evidence. 

Whenever our prevailing picture of reality — including the rules it plays by, the physical contents of a system, and how it evolved from its initial conditions to the present time — gets challenged by new experimental or observational data, we must open our minds to changing our conceptual picture of the cosmos. 

This has happened many times since the dawn of the 20th century, and the words we use to describe our Universe have shifted in meaning as our understanding has evolved.

Yet, there are always those who cling to the old definitions, much like linguistic prescriptivists, who refuse to acknowledge that these changes have occurred. 

But unlike the evolution of colloquial language, which is largely arbitrary, the evolution of scientific terms must reflect our current understanding of reality. 

Whenever we talk about the origin of our Universe, the term “the Big Bang” comes to mind, but our understanding of our cosmic origins have evolved tremendously since the idea that our Universe even had an origin, scientifically, was first put forth. 

Here’s how to resolve the confusion and bring you up to speed on what the Big Bang originally meant versus what it means today.  READ MORE...

Rare Ring Galaxies

Almost every galaxy can be classified as a spiral, elliptical, or irregular galaxy. Only 1-in-10,000 galaxies fall into the rarest category of all: ring galaxies.  With a dense core consisting of old stars, and a circular or elliptical ring consisting of bright, blue, young stars, the first ring was only discovered in 1950: Hoag's object.  After decades of wondering how these objects form, we've seen enough of them, capturing them in various stages of evolution, that we finally know where they come from.

When we look out into deep space, beyond the confines of the Milky Way, we find that the Universe isn’t quite so empty. Galaxies — small and large, near and far, in rich clusters and in near-total isolation — fill the abyss of space, with the Milky Way being just one of approximately two trillion such galaxies within the observable Universe. 

Galaxies are collections of normal matter, including plasmas, gas, dust, planets, and most prominently, stars. It’s through the examination of that starlight that we’ve learned the most about the physical properties of galaxies, and been able to reconstruct how they came to be.

In general, there are four classes of galaxies that we see. Spirals, like the Milky Way, are the most common type of large galaxy in the Universe. Ellipticals, like M87, are the largest and most common type of galaxy in the rich, central regions of galaxy clusters. Irregular galaxies are a third ubiquitous type, usually distorted from a prior spiral or elliptical shape by gravitational interactions. 

But there’s a very rare type that’s striking and beautiful: ring galaxies. They make up only 1-in-10,000 of all the galaxies out there, with the first one, Hoag’s object, only discovered in 1950. After more than 70 years, we’ve finally figured out how the Universe makes them.  READ MORE...

Laniakea Destroyed by Dark Energy

On the largest cosmic scales, planet Earth appears to be anything but special. Like hundreds of billions of other planets in our galaxy, we orbit our parent star; like hundreds of billions of solar systems, we revolve around the galaxy; like the majority of galaxies in the Universe, we’re bound together in either a group or cluster of galaxies. 

And, like most galactic groups and clusters, we’re a small part of a larger structure containing over 100,000 galaxies: a supercluster. Ours is named Laniakea: the Hawaiian word for “immense heaven.”

Superclusters have been found and charted throughout our observable Universe, where they’re more than 10 times as rich as the largest known clusters of galaxies. Unfortunately, owing to the presence of dark energy in the Universe, these superclusters ⁠— including our own ⁠— are only apparent structures. In reality, they’re mere phantasms, in the process of dissolving before our very eyes.

The Universe as we know it began some 13.8 billion years ago with the Big Bang. It was filled with matter, antimatter, radiation, etc.; all the particles and fields that we know of today, and possibly even more. 

From the earliest instants of the hot Big Bang, however, it wasn’t simply a uniform sea of these energetic quanta. Instead, there were tiny imperfections ⁠— at about the 0.003% level ⁠— on all scales, where some regions had slightly more or slightly less matter and energy than average.

In each one of these regions, a great cosmic race ensued. The race was between two competing phenomena:

1. the expansion of the Universe, which works to drive all the matter and energy apart
2. gravitation, which works to pull all forms of energy together, causing massive material to clump and cluster together

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Violating Speed of Light

Just 13.8 billion years after the hot Big Bang, we can see 46.1 billion light-years away in all directions. Doesn't that violate...something?

A visual history of the expanding Universe includes the hot, dense state known as the Big Bang and the growth and formation of structure subsequently. The full suite of data, including the observations of the light elements and the cosmic microwave background, leaves only the Big Bang as a valid explanation for all we see. (Credit: NASA/CXC/M. Weiss)

The cardinal rule of relativity is that there's a speed limit to the Universe, the speed of light, that nothing can break.And yet, when we look at the most distant of objects, their light has been traveling for no more than 13.8 billion years, but appears much farther away.Here's how that doesn't break the speed of light; it only breaks our outdated, intuitive notions of how reality ought to behave.

If there’s one rule that most people know about the Universe, it’s that there’s an ultimate speed limit that nothing can exceed: the speed of light in a vacuum. If you’re a massive particle, not only can’t you exceed that speed, but you’ll never reach it; you can only approach the speed of light. If you’re massless, you have no choice; you can only move at one speed through spacetime: the speed of light if you’re in a vacuum, or some slower speed if you’re in a medium. The faster your motion through space, the slower your motion through time, and vice versa. There’s no way around these facts, as they’re the fundamental principle on which relativity is based.

And yet, when we look out at distant objects in the Universe, they seem to defy our common-sense approach to logic. Through a series of precise observations, we’re confident that the Universe is precisely 13.8 billion years old. The most distant galaxy we’ve seen so far is presently 32 billion light-years away; the most distant light we see corresponds to a point presently 46.1 billion light-years away; and galaxies beyond about 18 billion light-years away can never be reached by us, even if we sent a signal at the speed of light today.

Still, none of this breaks the speed of light or the laws of relativity; it only breaks our intuitive notions of how things ought to behave. Here’s what everyone should know about the expanding Universe and the speed of light.  READ MORE...

The Big Band IS NOT the Beginning

The Big Bang teaches us that our expanding, cooling universe used to be younger, denser, and hotter in the past...

However, extrapolating all the way back to a singularity leads to predictions that disagree with what we observe...

Instead, cosmic inflation preceded and set up the Big Bang, changing our cosmic origin story forever...

Where did all this come from? In every direction we care to observe, we find stars, galaxies, clouds of gas and dust, tenuous plasmas, and radiation spanning the gamut of wavelengths: from radio to infrared to visible light to gamma rays. No matter where or how we look at the universe, it’s full of matter and energy absolutely everywhere and at all times. 

And yet, it’s only natural to assume that it all came from somewhere. If you want to know the answer to the biggest question of all — the question of our cosmic origins — you have to pose the question to the universe itself, and listen to what it tells you.

Today, the universe as we see it is expanding, rarifying (getting less dense), and cooling. Although it’s tempting to simply extrapolate forward in time, when things will be even larger, less dense, and cooler, the laws of physics allow us to extrapolate backward just as easily. 

Long ago, the universe was smaller, denser, and hotter. How far back can we take this extrapolation? Mathematically, it’s tempting to go as far as possible: all the way back to infinitesimal sizes and infinite densities and temperatures, or what we know as a singularity. 

This idea, of a singular beginning to space, time, and the universe, was long known as the Big Bang.

But physically, when we looked closely enough, we found that the universe told a different story. Here’s how we know the Big Bang isn’t the beginning of the universe anymore.  READ MORE...