Introduction to Cosmology

I work on Cosmology — “a subject that has the modest aim of understanding the entire Universe and all its contents” [J. Peacock].



  • All the known

All the known galaxies and galaxy clusters which you can observe them by most powerful telescopes make only 4.9% of the physical universe.

  • What we think we know

The following diagram made by Planckteam shows our picture of the history of the known cosmos. In the beginning, the Universe emerged out of an initial singularity (the big bang), after which it was in a high-energy plasma state. Some mechanism, often called inflation, then rapidly stretched it exponentially in a short time, creating curvature (temperature) perturbations out of the quantum fluctuations of the plasma, and cooling it down to “normal” energy scales, where the elementary particles could combine to form nuclei and then atoms.

cosmic timeline

After the formation of hydrogen atoms (recombination), radiation decoupled from matter. This means that photons, not finding any more free electrons around to scatter off, could for the first time propagate freely through space: the Universe became at this point transparent, and the cosmic microwave background radiation(CMBR) was formed as the snapshot of the Universe at this time, about 380,000 years after the big bang.
The following period of time is called the dark ages: the expanding Universe was empty of structure, and its matter content was slowly accreting around the overdense regions… until somewhere the density became high enough for the first stars to ignite: the Universe became populated and eventually, with the progress of structure formation, assumed its present form.


  • Puzzles come out

According to recent results of Planck our Universe is made of 4.9% baryonic matter (luminous matter) and 26.8% unknown matter (Dark Matter). Also we know there is another component of the Universe called Dark Energy. Just 4.9% of our cosmic pie is observable and we just know there are other components of the Universe which we couldn’t observe directly.

Dark matter and dark energy are the most important puzzles of the Cosmology. We can’t detect them directly but we have robust evidences from CMB , SN type Ia , LSS, Gravitational Lensing and other observations to believe in the existence of such weird components of the Universe.