Cosmology is facing again some troubles. Some estimations of the Hubble parameter differ up to four standard deviations from the accepted value. Even when a few km/s/Mpc are not quite a huge difference, it turns than they can provide anomalies … Continue reading

# Tag Archives: dark energy

What is dark energy? Where does it come from? Is it constant? Is it a quantum field? Is it vacuum energy? Nobody knows what is the 70% of the Universe! In the beginning of Physics as Science, Aristotle himself introduced … Continue reading

Hi, folks! Before the upcoming series of thematic blog posts (they are on their way, eager readers), I found a very interesting paper to discuss. The paper is this http://arxiv.org/abs/1408.1820 and the pdf file can be found here http://arxiv.org/pdf/1408.1820v1.pdf . The author of … Continue reading

Warm Dark Matter candidates: neutrinos, axions, extra relativistic species currently unknown. Cold Dark Matter candidates: many. Pick one (or many!): Z primes, the lightest supersymmetric particle (LSP), gravitino, gaugino, neutralino, ELKO fields, Majorana spinors, the infinite component Majorana field, unparticles, … Continue reading

Some conclusions of this fascinating subject and thread about the mythical spacetime foam: (1) CDM(Cold Dark Matter) and MOND seems to be complementary descriptions of the same dynamics and phenomenology. (2) MOND force law works at galactic scales. This can … Continue reading

The second post in this thread is completely speculative. 1) Suppose that Dark Energy is some kind of “fluid” made of some long wavelength “particles” or “exotic stuff”. 2) How different are those “Dark Energy particles” from the particles we … Continue reading

Some weeks ago, I was studying some papers and talks by Jack Ng. I am going to share with you what I have learned from them, about the wonderful subject of the “quantum spacetime foam”. Some topics and ideas I … Continue reading

2) I recommend you not to use Internet Explorer. It seems that Explorer does not scale the images very well. Moreover, Explorer seems to be bad working with LaTeX code I use here. So, please, use any other web browser … Continue reading

Evolution of the Universe: the scale factor The Universe expands, and its expansion rate is given by the Hubble parameter (not constant in general!) Remark (I): The Hubble “parameter” is “constant” at the present value (or a given time/cosmological age), … Continue reading

The next thread is devoted to Cosmology. I will intend to be clear and simple about equations and principles of current Cosmology with a General Relativity background. First of all…I will review the basic concepts of natural units I am … Continue reading