Call it irreversibility, call it time's arrow
, call it the second law of thermodynamics. Fact is that everything evolves in such a way that things get more messy. Disorder rises. Entropy
increases. We do not observe the opposite happening. Heat flows from from hot to cold, not the other way around. Fluids mix but don't unmix. Shattered pieces of crystal don't reassemble into a vase.
Detailed balance is a simple and powerful rule to describe the dynamics of two-state systems.
If you know the probability of a transition from a state A to the other state B of a physical system (in some appropriate time unit), and you also know the probability of the reverse reaction
, then you automatically know what is equilibrium condition for N bodies distributed in the two states:
Previously thought to be indivisible, with negative charge for all, the electron is one of the fundamental building blocks of nature. A new experiment, however, has shown that electrons, if crowded into narrow wires, are seen to split apart.
The electron is responsible for carrying electricity in wires and for making magnets. These two properties of magnetism and electric charge are carried by electrons which seem to have no size or shape and are impossible to break apart.
Besides the usual share of random readers who google something and get directed here by mere chance (to be read: by the sheer amount of valuable information I have posted here), this blog is read by an interesting mix of particle physicists, students, experts in other fields of Physics, and Science amateurs -plus a small number of science reporters looking for news.
Of course I love each and every one of my faithful readers like good teachers love their pupils, but among the varied crowd, the readers which I am most happy to host here are students and amateurs, because they provide me with true motivation for spending my time writing popularization articles. Without them, many of my posts would lose their meaning.
Time for a quick compare-and-contrast. Here is what "Physics Today" lists as their top stories and most popular articles for July 2009:
Scientists at Penn State University, in collaboration with institutes in the US, Finland, Germany and the UK, have figured out the long-sought structure of a layer of C60 – carbon buckyballs – on a silver surface. The results in Physical Review Letters and Physics could help in the design of carbon nanostructure-based electronics.
Ever since the 1985 discovery of C60, this molecule, with its perfect geodesic dome shape has fascinated scientists, physicists, and chemists alike. Like a soccer ball, the molecule consists of 20 carbon hexagons and 12 carbon pentagons. The electronic properties of C60 are very unusual, and there is a massive research effort toward integrating it into molecular scale electronic devices like transistors and logic gates.
One year ago, a paper
by a distinguished group of theorists announced first evidence of new physics
from measurements of the properties of B_s mesons performed at the Tevatron by the CDF
experiments. They had combined all the available information, obtaining a result which disagreed with the Standard Model (SM) prediction by more than three standard deviations.
in the latest (August 2009
) edition of Scientific American describes an astronaut floating motionless with respect to his distant spaceship. He is not tethered to the spaceship and has no objects available that can be hurled away or can in some other way create a thrust.
How is he ever going to make it back to his spaceship?
A new paper on the ArXiV
caught my attention this evening for several reasons. First of all, because two of its five authors (J.Ellis, J.R.Espinosa, G.F.Giudice, A.Hoecker, and A.Riotto) are (or have been) my colleagues in Padova University; second, because the title is quite catchy; third, because indeed the results it presents are valuable food for thought.
"Other people's data ntuples are a bit like their genitals. You may occasionally be allowed to play with them, but you should not expect to be granted unhindered access."
Unknown (the previous attribution to M. F. is fallacious)