Dec 11, 2024 05:53 PM
(This post was last modified: Dec 12, 2024 05:53 PM by C C.)
The quantum reason behind the solidity of matter
https://bigthink.com/starts-with-a-bang/...ty-matter/
KEY POINTS: One of the most puzzling facts that most of us learn is that atoms, despite being made of very small quanta like protons, neutrons, and electrons, are actually quite enormous: around 10^-10 meters across. Meanwhile, protons and neutrons are only 10^-15 meters apiece, and electrons are even smaller, point-like particles as far as we can tell. Atoms, seemingly, are mostly empty space. If this is the case, then you’d expect that matter, being made from atoms, would be mostly empty as well, and two objects composed of atoms would be able to pass through each other. But matter is instead solid, and quantum physics explains why.
EXCERPT: . . . The Pauli Exclusion Principle doesn’t only explain why matter is solid, but also why it occupies the amount of space that it does. Again: it isn’t just the uncertainty principle and electrostatic repulsion that’s responsible for volume; if matter were made of bosons, it wouldn’t occupy space in the same fashion that it does when it’s made of fermions. As I wrote earlier this year:
“The hydrogen atom is small because its electron is in the lowest-energy state allowable, the ground state, and only has one electron. Heavier atomic nuclei, however — like carbon, oxygen, phosphorus, or iron — have more protons in their nuclei, requiring greater numbers of electrons within them. If the lower-energy quantum states are all full of electrons, then subsequent electrons must occupy higher-energy states, leading to larger electron orbits (on average) and “puffier” atoms that occupy greater volumes. […] The more protons you have at the core of your atom, the more electrons you have orbiting within the outskirts of your atom. The more electrons you have, the greater the number of energy states that must be occupied. And the higher the energy state of the highest-energy electrons within your atom, the greater the amount of physical volume your atom must occupy.”
As long as matter is made up of fermions, it’s impenetrable to other objects that are also made up of the same type of fermionic matter. To those of you who thought that the Pauli Exclusion Principle wasn’t such a big deal, remember this: if it weren’t for that principle, and the fermionic nature of matter, something as simple as “sitting in a chair” would be a physical impossibility! (MORE - missing details)
Particle that only has mass when moving in one direction observed for first time
https://www.eurekalert.org/news-releases/1067793
INTRO: For the first time, scientists have observed a collection of particles, also known as a quasiparticle, that's massless when moving one direction but has mass in the other direction. The quasiparticle, called a semi-Dirac fermion, was first theorized 16 years ago, but was only recently spotted inside a crystal of semi-metal material called ZrSiS. The observation of the quasiparticle opens the door to future advances in a range of emerging technologies from batteries to sensors, according to the researchers.
The team, led by scientists at Penn State and Columbia University, recently published their discovery in the journal Physical Review X.
“This was totally unexpected,” said Yinming Shao, assistant professor of physics at Penn State and lead author on the paper. “We weren’t even looking for a semi-Dirac fermion when we started working with this material, but we were seeing signatures we didn’t understand — and it turns out we had made the first observation of these wild quasiparticles that sometimes move like they have mass and sometimes move like they have none.”
A particle can have no mass when its energy is entirely derived from its motion, meaning it is essentially pure energy traveling at the speed of light. For example, a photon or particle of light is considered massless because it moves at light speed. According to Albert Einstein’s theory of special relativity, anything traveling at the speed of light cannot have mass. In solid materials, the collective behavior of many particles, also known as quasiparticles, can have different behavior than the individual particles, which in this case gave rise to particles having mass in only one direction, Shao explained.
Semi-Dirac fermions were first theorized in 2008 and 2009 by several teams of researchers... (MORE - details, no ads)
https://bigthink.com/starts-with-a-bang/...ty-matter/
KEY POINTS: One of the most puzzling facts that most of us learn is that atoms, despite being made of very small quanta like protons, neutrons, and electrons, are actually quite enormous: around 10^-10 meters across. Meanwhile, protons and neutrons are only 10^-15 meters apiece, and electrons are even smaller, point-like particles as far as we can tell. Atoms, seemingly, are mostly empty space. If this is the case, then you’d expect that matter, being made from atoms, would be mostly empty as well, and two objects composed of atoms would be able to pass through each other. But matter is instead solid, and quantum physics explains why.
EXCERPT: . . . The Pauli Exclusion Principle doesn’t only explain why matter is solid, but also why it occupies the amount of space that it does. Again: it isn’t just the uncertainty principle and electrostatic repulsion that’s responsible for volume; if matter were made of bosons, it wouldn’t occupy space in the same fashion that it does when it’s made of fermions. As I wrote earlier this year:
“The hydrogen atom is small because its electron is in the lowest-energy state allowable, the ground state, and only has one electron. Heavier atomic nuclei, however — like carbon, oxygen, phosphorus, or iron — have more protons in their nuclei, requiring greater numbers of electrons within them. If the lower-energy quantum states are all full of electrons, then subsequent electrons must occupy higher-energy states, leading to larger electron orbits (on average) and “puffier” atoms that occupy greater volumes. […] The more protons you have at the core of your atom, the more electrons you have orbiting within the outskirts of your atom. The more electrons you have, the greater the number of energy states that must be occupied. And the higher the energy state of the highest-energy electrons within your atom, the greater the amount of physical volume your atom must occupy.”
As long as matter is made up of fermions, it’s impenetrable to other objects that are also made up of the same type of fermionic matter. To those of you who thought that the Pauli Exclusion Principle wasn’t such a big deal, remember this: if it weren’t for that principle, and the fermionic nature of matter, something as simple as “sitting in a chair” would be a physical impossibility! (MORE - missing details)
Particle that only has mass when moving in one direction observed for first time
https://www.eurekalert.org/news-releases/1067793
INTRO: For the first time, scientists have observed a collection of particles, also known as a quasiparticle, that's massless when moving one direction but has mass in the other direction. The quasiparticle, called a semi-Dirac fermion, was first theorized 16 years ago, but was only recently spotted inside a crystal of semi-metal material called ZrSiS. The observation of the quasiparticle opens the door to future advances in a range of emerging technologies from batteries to sensors, according to the researchers.
The team, led by scientists at Penn State and Columbia University, recently published their discovery in the journal Physical Review X.
“This was totally unexpected,” said Yinming Shao, assistant professor of physics at Penn State and lead author on the paper. “We weren’t even looking for a semi-Dirac fermion when we started working with this material, but we were seeing signatures we didn’t understand — and it turns out we had made the first observation of these wild quasiparticles that sometimes move like they have mass and sometimes move like they have none.”
A particle can have no mass when its energy is entirely derived from its motion, meaning it is essentially pure energy traveling at the speed of light. For example, a photon or particle of light is considered massless because it moves at light speed. According to Albert Einstein’s theory of special relativity, anything traveling at the speed of light cannot have mass. In solid materials, the collective behavior of many particles, also known as quasiparticles, can have different behavior than the individual particles, which in this case gave rise to particles having mass in only one direction, Shao explained.
Semi-Dirac fermions were first theorized in 2008 and 2009 by several teams of researchers... (MORE - details, no ads)
