Age, Size and Fate of the Universe
The age of the universe
Definition
The age of the universe is the elapsed cosmic time since the hot early phase described by the Big Bang model. The observable universe is the region from which signals have had enough cosmic time to reach us.
Hubble Time
A simple characteristic time is: **tH = 1H₀ It gives a rough cosmological timescale. The actual age depends on the expansion history and cosmic contents. Current standard cosmological measurements give an age close to: 13.8 billion years**.
Observable Universe
We can only observe regions whose signals can reach us. Because the universe has expanded during photon travel, present distances to the most distant observable regions can be much greater than the simple product `c × age`.
Fate
The universe's future depends on its contents and expansion behavior. In the standard dark-energy-dominated picture, continued expansion is expected.
Formula / Key Relation
Approximate characteristic Hubble time: **tH≈1H₀** If `H₀` is in SI units, `t_H` is in seconds.
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Age, Size and Fate of the Universe
Sticky Notes · Quick Revision
Age:
- ≈13.8 billion years
- Hubble time:
- `tH≈1H₀`
- Observable universe:
- limited by cosmic horizons
- Future:
- depends on cosmic components
60-second revision
- Age, observable size and fate depend on the universe's expansion history.
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