Although systems consisting of many interacting small particles can be highly complex and chaotic, some can nonetheless be described using simple theories. Does this also pertain to the world of quantum physics?
Category: particle physics – Page 152
The Fate of Water on Mars: New Findings from Hubble and MAVEN Missions
“In recent years scientists have found that Mars has an annual cycle that is much more dynamic than people expected 10 or 15 years ago,” said Dr. John Clarke.
What happened to all the liquid water on Mars and what can this teach us about Earth-like exoplanets? This is what a recent study published in Science Advances hopes to address as an international team of researchers investigated the atmospheric and atomic processes responsible for Mars losing its water over time. This study holds the potential to help researchers better understand the evolution of Mars, specifically regarding the loss of water, and what implications this holds for Earth-like exoplanets.
For the study, the researchers used a combination of data from NASA’s Mars Atmosphere and Volatile Evolution (MAVEN) and Hubble Space Telescope (HST) spacecraft to measure the ratio of hydrogen and deuterium that escapes from Mars over three Martian years, with each Martian year comprising 687 Earth days. Deuterium is also called “heavy hydrogen” since it is a hydrogen atom with a neutron in its nucleus, making its mass greater than hydrogen.
Since deuterium is heavier, this means hydrogen is lost to space faster, and measuring this present-day loss can help scientists determine how much was lost in Mars’s ancient past. Additionally, Mars’ orbit is more elliptical than Earth, meaning it orbits farther away from the Sun at certain times of the year, and this could also contribute to hydrogen loss, as well. In the end, the team found that this ratio changes as Mars is closer to the Sun and farther away, which challenges longstanding hypotheses regarding Mars’s atmospheric evolution.
Atoms on the edge
Typically, electrons are free agents that can move through most metals in any direction. When they encounter an obstacle, the charged particles experience friction and scatter randomly like colliding billiard balls.
But in certain exotic materials, electrons can appear to flow with single-minded purpose. In these materials, electrons may become locked to the material’s edge and flow in one direction, like ants marching single-file along a blanket’s boundary. In this rare “edge state,” electrons can flow without friction, gliding effortlessly around obstacles as they stick to their perimeter-focused flow. Unlike in a superconductor, where all electrons in a material flow without resistance, the current carried by edge modes occurs only at a material’s boundary.
Now MIT physicists have directly observed edge states in a cloud of ultracold atoms. For the first time, the team has captured images of atoms flowing along a boundary without resistance, even as obstacles are placed in their path. The results, which appear in Nature Physics (“Observation of chiral edge transport in a rapidly rotating quantum gas”), could help physicists manipulate electrons to flow without friction in materials that could enable super-efficient, lossless transmission of energy and data.
NASA Discovers a Long-Sought Global Electric Field on Earth
Discovering Earth’s third global energy Field. 🌀
A NASA-led rocket team has finally discovered the long-sought electric field driving particles from Earth’s atmosphere into space ‼️
First hypothesized over 60 years ago, it is “an agent of chaos” whose impacts are still not fully known: go.nasa.gov/3XcDDLD
An international team of scientists has successfully measured a planet-wide electric field thought to be as fundamental to Earth as its gravity and magnetic fields. Known as the ambipolar electric field, scientists first hypothesized over 60 years ago that it drove atmospheric escape above Earth’s North and South Poles. Measurements from a suborbital rocket have confirmed the existence of the ambipolar field and quantified its strength, revealing its role in driving atmospheric escape and shaping our ionosphere — a layer of the upper atmosphere — more broadly. The paper was published today in the journal Nature.
Quantum Experiment Could Finally Reveal The Elusive Gravity Particle
The graviton – a hypothetical particle that carries the force of gravity – has eluded detection for over a century. But now physicists have designed an experimental setup that could in theory detect these tiny quantum objects.
In the same way individual particles called photons are force carriers for the electromagnetic field, gravitational fields could theoretically have its own force-carrying particles called gravitons.
The problem is, they interact so weakly that they’ve never been detected, and some physicists believe they never will.
How Subjective is Entropy Really?
Physics stack exchange has recently been debating the question of the subjectivity of entropy.
I recommend Andrew Steane answer.
I’m a computer scientist doing some research that touches on basic concepts in statistical mechanics: macrostate, microstate and entropy. The way I’m currently conceiving of it is that the microstate includes all the information to perfectly the describe the state of a system, the macrostate provides some of the information, allowing you to narrow down the possibilities to a subset of states and a distribution over them, and the entropy roughly says how much information is still missing after you specify the macrostate.
From various places online, including this SE thread, I read that the choice of what to put in the macro-description depends on what state variables one is interested in. That SE answer seems to downplay the significance of this, but from my uninformed outsider perspective it seems like a big deal. I could, for example, make the entropy of any system zero if I choose the state variables to be the position and momentum of every particle (let’s just stick to the classical paradigm for now).
From the examples I’ve seen, there are only a few state variables such as temperature and pressure that are even considered, but could/does it ever happen that two different experimenters on the same system have different ‘opinions’ on what the state variables should be, and so calculate totally different values for entropy? If not, is there a satisfying reason why the choice of state variables is not as subjective as it appears?
