- PROTONS, NEUTRONS, AND ELECTRONS: THE STUFF OF LIFE:
- Until about thirty years ago, astronomers thought that the universe was composed almost entirely of this “baryonic matter”, ordinary atoms. The familiar material of the universe, known as baryonic matter, is composed of protons, neutrons, and electrons. Dark matter may be made of baryonic or non-baryonic matter.
- Non-baryonic matter, or not:
- The 50-foot in diameter superconducting magnetic ring at the Fermi National Accelerator Laboratory near Chicago was the centerpiece of a recent experiment with muons, tiny particles that could inform our understanding of the universe. If proven, the muon’s identity shift could imply the existence of another, yet-undiscovered fundamental particle, which, in turn, might be responsible for one of the biggest unsolved mysteries in astrophysics today, the identity of dark matter.
- Protons and neutrons are bound together into nuclei and atoms, these nuclei are surrounded by a full complement of electrons. Hydrogen is composed of one proton and one electron. Helium is composed of two protons, two neutrons, and two electrons. Carbon is composed of six protons, six neutrons, and six electrons. Heavier elements, such as iron, lead, and uranium, contain even larger numbers of protons, neutrons, and electrons. Astronomers like to call all material made up of protons, neutrons, and electrons “baryonic matter”.
- More than 95% of the energy density in the universe is in a form that has never been directly detected in the laboratory. 24% of the universe is 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. 71.4% of the universe is Dark Energy. The universe is expanding at an accelerated rate. Fast-moving neutrinos do not play a major role in the evolution of structure in the universe.
- By measuring the motions of stars and gas, astronomers can weigh galaxies. By measuring how the background galaxies are distorted by the foreground cluster, astronomers can measure the mass in the cluster. The mass in the cluster is more than five times larger than the inferred mass of invisible stars, gas, and dust.
- There are a number of plausible speculations on the nature of the dark matter: Brown Dwarfs, Supermassive Black Holes, or WIMPs (for Weakly Interacting Massive Particles) or non-baryonic matter.
- Many cosmologists advocate reviving the cosmological constant term on theoretical grounds, as a way to explain the rate of expansion of the universe. Modern field theory associates this term with the energy density of the vacuum. For this energy density to be comparable to other forms of matter in the universe, it would require new physics theories. So the addition of a cosmological constant term has profound implications for particle physics and our understanding of the fundamental forces of nature. A cosmological constant term added to the standard model Big Bang theory leads to a model that appears to be consistent with the observed large-scale distribution of galaxies and clusters, with WMAP’s measurements of cosmic microwave background fluctuations, and with the observed properties of X-ray clusters.
- Adding a constant to the equations facilitates the correct answer.
