Having recently posted a general piece about spin in general (https://physbang.com/2024/11/24/what-is-spin/) I thought it would be useful to discuss one particular use of spin in a practical context; cooling. Suppose we have a material with a single unpaired electron in each of its atoms. The lone electrons can either be spin-up or spin-down and on … Continue reading Spin Cooling
Death and Data Analysis
It sounds like an unlikely scientific challenge but a recent BBC Radio 4 program about dismembered feet that have been washed-up on Canadian and US shores is a great puzzle to tax inquisitive brains. Despite what may appear to be an off-topic context (for the usual range of physbang items) the story's challenge to make … Continue reading Death and Data Analysis
What is Spin?
Spin, when applied to fundamental particles, is a property rather than a description. The basic components of matter are not tiny spinning tops, like coins that are stood on edge then flicked on opposite sides to make them rotate. Instead, spin is a physical property that can be demonstrated and also a numerical value that … Continue reading What is Spin?
Kepler: Greater than Copernicus
Copernicus is generally credited with having first described the “true” arrangement of the solar system at a time when Science was being reborn after the Dark Ages. So revolutionary was his book De Revolutionibus that he withheld it for more than 10 years before finally publishing a small number of copies in 1543. As he … Continue reading Kepler: Greater than Copernicus
What is the Strong Nuclear Force?
When thinking about atoms, one of the obvious puzzles is how a nucleus stays together when it is packed with positively charged particles (protons). Why don't the positive protons simply repel each other, causing the nucleus to disintegrate? The fact that there are also neutral particles (neutrons) in the nucleus may “dilute” the positive charge … Continue reading What is the Strong Nuclear Force?
Mammoth effort to image our galaxy in infra-red
Astronomers working on the European Southern Observatory's (ESO's) Visible and Infra-Red Telescope for Astronomy (VISTA) have today published the biggest ever dataset of infra-red images of the Milky Way. A few of the images captured by the ESO VISTA project. Full details about this composite can be found at https://www.eso.org/public/images/eso2413a/ Importantly, capturing images using infra-red … Continue reading Mammoth effort to image our galaxy in infra-red
What causes aurorae?
As the nights draw in and skies get darker we approach the time of year when aurorae become easier to observe, especially at times (like now) of high sunspot activity. But the link between aurorae and events happening on the surface of the Sun is not immediately obvious and was initially deduced only indirectly. Subject … Continue reading What causes aurorae?
Active Reading
Little is made of the fact that the skills required to read a textbook are different from those used when reading a consumer magazine or a work of fiction. The reasons for this difference are the greater density of information and sequencing of concepts that occur in non-fiction publications. As a result, skimming is best … Continue reading Active Reading
The coldest exoplanet ever seen
Most exoplanets (planets that are outside the Solar System) are detected indirectly. Either a temporary and regular dimming is measured as they pass in front of the host star or their orbit causes a wobble that produces a periodic red-shift in the star's spectrum. Only a small number of planets have then gone on to … Continue reading The coldest exoplanet ever seen
Chandra: the Universe as seen in X-rays
Chandra is the unsung hero of space telescopes. Far better known is the Hubble Space Telescope, which is rightly famous for the spectacular images it has produced. But Hubble was only ever intended to be one arm of a four-pronged approach to astronomical observations, another of which is provided by Chandra. Whereas Hubble produces images … Continue reading Chandra: the Universe as seen in X-rays
Mr Tarrant's physbang 'blog 