The universe has a beginning and continues to expand today. Advances in observation technology are gradually revealing its full nature.
Basic Knowledge
The universe is thought to have begun approximately 138億 years ago from an extremely hot and dense state called the Big Bang. At first, the universe contained only elementary particles. As it cooled, protons, electrons, and atoms formed, and 38万 years later, light was able to travel freely (recombination). The remnant of this light is called the cosmic microwave background (CMB), which was accidentally discovered by Penzias and Wilson in 1965.
Evidence that the universe is expanding is that more distant galaxies have greater redshift (the phenomenon in which light is stretched and becomes red). Hubble’s law (1929), which was discovered by Hubble, is the starting point of the Big Bang theory.
Observation technology:
① Optical telescopes (Hubble Space Telescope・James Webb Space Telescope).
② Radio telescopes (ALMA Telescope・Chile).
③ Gravitational-wave detectors (LIGO・KAGRA), which made the first detection in 2015.
Big Bang（The beginning of the universe approximately 138億 years ago）
Cosmic background radiation (CMB)（A remnant of the light from recombination. Approximately 2.7K)
Redshift（The phenomenon in which light is stretched. Evidence of the expansion of the universe）
Hubble’s law（The more distant a galaxy is, the faster it is moving away. 1929）
Hubble Space Telescope（Launched in 1990・orbits Earth・visible light）
James Webb Space Telescope (JWST)（Launched in 2021・infrared・observes the early universe)
Further Exploration (Background・Significance)
The expansion rate of the universe is accelerating over time, and dark energy is thought to be the cause. The composition of the universe is estimated to be approximately 5% ordinary matter, 27% dark matter, and 68% dark energy. What we know accounts for only 5% of the universe.
In September 2015, humanity detected gravitational waves for the first time. Waves of spacetime distortion predicted by Einstein in 1916 were captured as signals from merging black holes. This can be said to have added “sound” as a new method of observation in astronomy.
JWST released its first images in 2022 and is observing galaxies from the early universe approximately 135億 years ago. This corresponds to about 3億 years after the birth of the universe. Advances in observation technology are enabling us to approach the origin of the universe ever more closely.
- Age of the universe = approximately 138億 years
- Big Bang = beginning from an extremely hot and dense state
- CMB = light from recombination・approximately 2.7K
- Redshift = evidence of the expansion of the universe
- Hubble’s law (1929)
- Composition of the universe: ordinary matter 5%・dark matter 27%・dark energy 68%
- First detection of gravitational waves = 2015
Points to Note (Easily Confused)
① The Big Bang was not an “explosion” but “the beginning of expansion.” Space itself is expanding. ② Dark matter (a source of gravity) and dark energy (a source of accelerated expansion) are different. ③ Redshift = moving away (light stretches), while blueshift = moving closer (light contracts). ④ A light-year is a distance. “The universe 138億 years ago” refers to time, while “a galaxy 138億 light-years away” refers to distance.
Practice
- Approximately how old is the universe thought to be?
- What phenomenon provides evidence that the universe is expanding?
- What is the name of the space telescope launched in 2021 that observes the early universe using infrared light?