5% of the Universe is Normal Matter, What About the Other 95%?
Posted on April 29, 2011 Comments (5)
Great discussion and illustration of the state of our understanding of physics, matter, dark matter and the rest of the stuff our universe has from PhD comics. What is the universe made of? 5% of it is normal matter (the stardust we are made of), 20% dark matter and the other 75% – we have no idea!
Dark Cosmos is a nice book on some of these ideas. It is 5 years old so missing some of the latest discoveries.
Related: Why do we Need Dark Energy to Explain the Observable Universe? – The Mystery of Empty Space – Friday Fun, CERN Version
NASA puts the values of what the universe is made of at:
4.6% atoms – normal matter, the stardust that our planet and we are made of.
23% cold dark matter – dark matter is likely to be composed of one or more species of sub-atomic particles that interact very weakly with ordinary matter. Particle physicists have many plausible candidates for the dark matter, and new particle accelerator experiments are likely to bring new insight in the coming years.
72% dark energy – the first observational hints of dark energy in the universe date back to the 1980’s when astronomers were trying to understand how clusters of galaxies were formed. Their attempts to explain the observed distribution of galaxies were improved if dark energy was present, but the evidence was highly uncertain. In the 1990’s, observations of supernova were used to trace the expansion history of the universe (over relatively recent times) and the big surprise was that the expansion appeared to be speeding up, rather than slowing down! In 2003, the first Wilkinson Microwave Anisotropy Probe (WMAP) results came out indicating that the universe was flat and that the dark matter made up only ~23% of the density required to produce a flat universe. If 72% of the energy density in the universe is in the form of dark energy, which has a gravitationally repulsive effect, it is just the right amount to explain both the flatness of the universe and the observed accelerated expansion. Thus dark energy explains many cosmological observations at once.