Ask Ethan: What Is The Fine Structure Constant And Why Does It Matter?
“When we do our best to measure the Universe — to greater precisions, at higher energies, under various conditions, at lower temperatures, etc. — we often find details that are intricate, rich, and puzzling. It’s not the devil that’s in those details, though, but rather that’s where the deepest secrets of reality lie.
The particles in our Universe aren’t just points that attract, repel, and bind together with one another; they interact through every subtle means that the laws of nature permit. As we reach greater precisions in our measurements, we start uncovering these subtle effects, including intricacies to the structure of matter that are easy to miss at low precisions. Fine structure is a vital part of that, but learning where even our best predictions of fine structure break down might be where the next great revolution in particle physics comes from. Doing the right experiment is the only way we’ll ever know.“
This week, I was asked to explain the fine structure constant as simply as possible. It’s actually a story more than a century in the making, as the previously-observed fine structure of matter let us know that Niels Bohr’s model of the atom was insufficient from the outset! Today, our understanding of how the spin of matter, the relativistic effects that come from moving close to the speed of light, and the inherently fluctuating nature of the quantum fields permeating the Universe come together enables us to probe the structure and nature of matter more deeply than ever before.
The fine structure constant is so much more than almost anyone realizes. Come open your eyes to its wonders today.
What Would Happen If You Became Dark Matter?
“What if, instead of being made out of Standard Model particles, which experience the full suite of all the fundamental forces, we transitioned to being made out of particles which, to the best of our knowledge, interact only gravitationally? The first thing that would happen to you is that you’d no longer be bound together in any way whatsoever, and that anyone watching you would immediately see you disappear. The nuclear forces that hold your nuclei and protons together would vanish; the electromagnetic forces that caused atoms and molecules to stay together (and light to interact with you) would disappear; your cells and organs and entire body would cease to hold together.”
Here on Earth, everything we know of is made of normal matter, almost exclusively in the form of atoms. But if our understanding of the Universe is correct, there’s five times as much dark matter out there as there is normal matter. Have you ever wondered what would happen to you, a human being, if you spontaneously converted from normal matter into dark matter? Dark matter is fundamentally different from normal matter in a myriad of ways, perhaps most notably for the interactions it doesn’t have. Without the strong, weak, or electromagnetic forces acting on it, it’s effectively invisible to all types of matter and energy, including other dark matter particles. But it continues to interact gravitationally, even as the normal matter making up Earth, the solar system, and the galaxy is affected by everything else. If you gave it enough time and could watch them closely enough, you’d start to see the particles that once made you illustrate this difference.
Come find out what would happen to the particles that once made you if they instantaneously converted to dark matter. You might be surprised!
Ask Ethan: If Matter Is Made Of Point Particles, Why Does Everything Have A Size?
“Many sources state that quarks are point particles… so one would think that objects composed of them — in this instance, neutrons — would also be points. Is my logic flawed? Or would they be bound to each other in such a way that they would cause the resulting neutron to have angular size?”
When we consider things like molecules, atoms, or even protons and neutrons, they all have finite, measurable sizes. Yet the fundamental particles that they’re made out of, like quarks, electrons, and gluons, are all inherently points, with no physical size to them at all. Why, then, does every composite particle not only have a size, but some of them, like atoms, grow to be relatively huge almost immediately, even with only a few fundamental particles involved? It’s due to three factors that all work together: forces, the quantum properties of the particles themselves, and energy. Since the strong and electromagnetic forces work against each other, quarks and gluons can form finite-sized protons; protons and neutrons assemble into nuclei larger than the protons and neutrons combined would make; electrons, with their low mass and high zero-point energy, orbit around nuclei only at great (relative) distances.
Matter doesn’t need to be made of finite-sized particles to wind up creating the macroscopic Universe we know and love. Find out how on this week’s Ask Ethan!
Ask Ethan: Can Normal Stars Make Elements Heavier (And Less Stable) Than Iron?
“Iron has been called stuff like solar fusion ash that collects inside stars, as the last of the elements that fuse w/o consuming more energy than the fusion creates. I have read about the r-process and others that lead to heavier elements in novas and supernovas. My Q is if any elements heavier than iron fuse anyway in normal stars, even if it does consume more energy then it generates.”
When you have a star, perhaps its most defining characteristic is that it fuses lighter elements into heavier ones, releasing energy. While all stars fuse hydrogen into helium, the more massive ones will undergo helium fusion, with the most massive also fusing carbon, oxygen, and eventually silicon, producing iron in the end. By time you get to iron, the most stable element of all, you would lose energy if you fused anything further, so iron’s the end-of-the-road, with a supernova as the next inevitable step. Except, perhaps that picture is a bit oversimplified! Iron isn’t the only thing that gets produced in the silicon-burning phase, and once your star contains iron from previous generations of stars, there are a couple of different processes that can help you build elements very far up the periodic table, without needing to have a supernova or other cataclysmic event at all. When you talk about consuming versus producing energy, that’s a major factor, but arguably isn’t even the most important one when it comes to which elements you produce.
Find out what it’s all about, and how literally half of the heavier-than-iron elements in the Universe are made in stars after all!
The Scientific Story Of How Each Element Was Made
“Neutron star mergers create the greatest heavy element abundances of all, including gold, mercury, and platinum.
Meanwhile, cosmic rays blast nuclei apart, creating the Universe’s lithium, beryllium, and boron.
Finally, the heaviest, unstable elements are made in terrestrial laboratories.
The result is the rich, diverse Universe we inhabit today.”
When the Big Bang first occurred, the Universe was filled with all the various particles and antiparticles making up the Standard Model, and perhaps still others yet to be discovered. But missing from the list were protons, neutrons, or any of the atomic nuclei key to the life-giving elements in our Universe today. Yet the Universe expanded, cooled, antimatter annihilated away, and the first elements began to take shape. After billions of years of cosmic evolution, we arrived at a Universe recognizable today: full of stars, planets, and the full complement of elements populating the periodic table. More than 100 elements are known today, 91 of which are found to occur naturally on Earth. Some were formed in the Big Bang, others were formed in stars, still others were formed in violent cosmic cataclysms or collisions. Yet every one has an origin whose story is now known, giving rise to all we interact with today.
Come get the full story behind how all the elements were made in some fantastic pictures, visuals, and no more than 200 words on this edition of Mostly Mute Monday!