What is Cosmology and the Big Bang Theory for BeginnersCosmology is the study of the history, structure, and dynamics of the universe including how the universe started and how it will end.
This article is part of a series of articles. Please use the links below to navigate between the articles.
- What is Cosmology and the Big Bang Theory for Beginners
- The Big Bang - The Beginning of the Universe As We Know It
- What is the Cosmic Microwave Background Radiation?
- Expansion of the Universe, Cosmic Scale Factor and Hubble's Law
- The Physics Governing the Universe - Interactions, EM, Gravity
- What is Light? How To Measure the Speed of Light?
- Redshift and Blueshift Explained - How We Know Disance to Far-Off Objects
The word cosmology is derived from two Greek words, "kosmos", meaning the world, and "logos", meaning knowledge or science.
Cosmology has experienced extensive changes over the past centuries, growing from a purely philosophical path to a modern science relying on accurate astronomical measurements. It has become an extremely complex science, including the study of particles on scales tinier than an atom and the formation and evolution of stars, galaxies and structures on scales as large as the observable Universe.
The first question usually asked in cosmology is this:
When did the Universe start and how will it end?
Only in the last century has it been possible for scientists to establish that the Universe is expanding. The remaining challenges for cosmology are to determine:
- How fast the Universe is expanding?
- How long this expansion will last?
- Will the expansion will ever stop or even reverse?
How Fast is the Universe Expanding?
To answer the first question, we can measure the average mass density of the Universe and find out whether there is sufficient mass for the gravitational force to stop the current expansion, or secondly, by observing the expansion velocities of galaxies at great distances and therefore, earlier times, to measure the rate at which the Universe is expanding is changing.
The second method includes a promising approach using observations of supernovae and gravitational lenses. Both methods are being actively pursued, and results are hoped for shortly.
The expansion of the Universe can be interpreted as understanding that, at one point, the Universe must have been enormously dense and hot. So hot that it consisted almost entirely of radiation. As the Universe expanded, it cooled. This idea is known as the Hot Big Bang model.
For decades, it remained untested and controversial. Today, observational data like the Cosmic Background Radiation (CBR) and the abundance of light elements, such as helium, deuterium and lithium, are in good agreement with the predictions of the Hot Big Bang model.
How Long will the Universe Expand For?
The second question is also the subject of extensive research and involves investigations into what dark matter is and what cosmological role it plays.
Details of the statistical properties of the expected structures (galaxies, clusters, superclusters in the Universe) are dependent on the amount of mass present in the Universe. There is strong observational evidence that apart from the luminous objects which radiate enough energy to be detected using modern technology, there is a vast amount of invisible matter, the so-called dark matter.
Scientists think that Dark matter may account for more than 80% of the total mass in the Universe. Despite the proposed models' range, dark matter's nature and exact distribution are still a mystery. The most obvious candidate for this dark matter is ordinary matter in the form of old, burned-out stars or stars that are too small to shine. However, the predictions of the abundance of the conventional matter, obtained by the measurement of several light elements, show that it can account for only a small fraction of the dark matter. Something other than ordinary matter must be present - exotic particles.
Exotic particles would be a relic of some process in the very early Universe. It is very important to identify this exotic dark matter by direct search and accelerator experiments, with particle theory guiding the development of the experiments. The best-accepted candidates for exotic dark matter are weakly interacting particles (WIMPs), axions, and neutrinos with finite mass. Of these, only neutrinos are known to exist; the rest is purely theoretical.
Will the Expansion of the Universe Ever Stop or Reverse?
Maps of the distribution of galaxies in the current Universe reveal a network of thin, filamentary structures of galaxies separated by quasi-spherical voids. When looking at objects at large distances, we observe the Universe's past because of the time light takes to reach us. Detecting large-scale structures at very large distances provides strong observational constraints on the models of structure formation. The early Universe contained small density irregularities, as measured today by fluctuations in the CBR, and the amplitude of these small bumps grew via their self-gravity to make the overall structure seen today. By carefully measuring changes in the overall expansion at ever-increasing distances, hence back time, we can create mathematical models for the Universe's expansion rate and propose theories on what will happen.
Recent observations made by the COBE and WMAP satellites observing and accurately measuring the Cosmic Background Radiation have effectively transformed cosmology from a highly speculative science into a predictive science. This has led many to refer to modern times as the "golden age of cosmology".
In this series, we will cover the above topics in more detail and look at how the large-scale structure of matter formed in the early Universe, the nature of zero point energy, the sub-atomic particles, and much more.
