Measuring and Understanding the Universe

This is the last article that I have read from, also (like the previous one) a 2003 article:


Title: “Measuring and Understanding the Universe”

Authors: Wendy L. FreedmanMichael S. Turner


Revolutionary advances in both theory and technology have launched cosmology into its most exciting period of discovery yet. Unanticipated components of the universe have been identified, promising ideas for understanding the basic features of the universe are being tested, and deep connections between physics on the smallest scales and on the largest scales are being revealed.


I have decided to underline the most relevant ideas or terms that I consider are worth keeping in mind. As I have mentioned somewhere else in this blog (in case I haven’t, this is the moment), I want to note down the important concepts, key words, ideas, etc., that interest me. Again, this blog site is not intended to be a place where every single concept will be explained. For that, there are many other webs… and, as I always say, in any case Wikipedia (like Google Translator, if needed) is our friend.

(I’ll try not to repeat this kinda disclaimer in future posts, I promise 😉

Some the ideas / key items that I have underlined are:

  • Inflation: enormous expansion of the Universe that took place in a tiny fraction of a second during the early history of the Universe. A concept introduced by Alan Guth in 1980.
  • Ordinary matter (baryonic): the kind of matter that accounts for a 4% of the total-mass density in the Universe. Neutrons and protons.
  • Dark Matter: about the total 30% of the total-mass energy of the Universe, composed of particles most likely formed in the early Universe. Something fundamentally different from the ordinary matter we are made of.
  • Dark Energy: 2/3 of the total mass-energy of the Universe whose repulsive gravitational effects began causing the expansion of the Universe to speed up. If it didn’t exist, it is thought that the flat Universe we live in (yeah, it is supposed to be flat!) would decelerate its expansion by its own self-gravity and recollapse (Have you heard of the Big Crunch? It was one of the possibilities for the evolution of the Universe, when I was studying GR at university… Now we know more of the story… The Universe is expanding, but not only expanding… It is expanding faster and faster and faster each time…).
  • Friedmann-Lemaitre-Robertson-Walker (FLRW) cosmological model: an exact solution of Einstein’s field equations of general relativity that explains quite well our Universe. It assumes that in large scales the Universe is homogeneous and isotropic.
  • Currently known components of the Universe: ∑ (ordinary matter of baryons + cold dark matter + massive neutrinos + cosmic microwave background and other forms of radiation + dark energy).
  • Expansion of the Universe: discovered in 1929 by Edwin Hubble.
  • Hubble constant: slope of the relation between distance and recession velocity, a relation that Hubble established when he measured the distance to some nearby galaxies. There have been many measures of this constant, as the one obtained from the results of the WMAP satellite that estimated a value of : Ho ~= 71 km/sec/Mpc (Mpc stands for megaparsec, a unit of length). Here is a picture to give some color to this post: a well-known image obtained by the WMAP (I bet you have seen this one before).
7 year WMAP image of background cosmic radiation (2010)

7 year WMAP image of background cosmic radiation (2010). Image from the Wikimedia Commons.

  • Big-Bang Nucleosynthesis (BBN): early phase of the Universe in which light elements were formed by means of protons and neutrons combination.
  • Measurements of the CMB (Cosmic Microwave Background): the CMB is the resulting radiation left over from an early stage in the development of the Universe. It provides the best explanation for the accounting of ordinary matter in the Universe.
  • Cold Dark Matter (CDM): descriptive theory that tries to explain how the structure of the Universe plausibly arose. CDM is a hypothetical form of matter that interacts very weekly with electromagnetic radiation. Leading candidates for the CDM particle are axions and neutralinos.
  • Axion: a CDM hypothetical particle a trillion times smaller in mass than that of the electron.
  • Neutralino: a hypothetical particle predicted by supersymmetry that might fit well as the CDM hypothetical particle. It is supposed to be a hundred times more massive than the proton.
  • Baryogenesis: the three conditions proposed by Sakharov necessary for the Universe to develop a slight excess of baryons over antibaryons: i) action of microscopic forces that do not conserve the net number of quarks; ii) breaking of the symmetry between particles and antiparticles; iii) departure from the thermal equilibrium.


WELL, that’s all for know, folks. ‘See’ you in future posts!

Development of the Universe and New Cosmology

In later posts I will mention the latest books (or audiobooks) that I have read or listened to, or videos that I have visualized on the Internet, related to Physics. Now, I want to start noting down a 2003 article that I’ve recently read:


Title: “Development of the Universe and New Cosmology

Authors: A.S. SakharovH. Hofer


Cosmology is undergoing an explosive period of activity, fueled both by new, accurate astrophysical data and by innovative theoretical developments. Cosmological parameters such as the total density of the Universe and the rate of cosmological expansion are being precisely measured for the first time, and a consistent standard picture of the Universe is beginning to emerge. Recent developments in cosmology give rise the intriguing possibility that all structures in the Universe, from superclusters to planets, had a quantum-mechanical origin in its earliest moments. Furthermore, these ideas are not idle theorizing, but predictive, and subject to meaningful experimental test. We review the concordance model of the development of the Universe, as well as evidence for the observational revolution that this field is going through. This already provides us with important information on particle physics, which is inaccessible to accelerators.