Using the currently accepted rate of expansion of the Universe, how much of the observable universe becomes part of the unobservable universe every earth year?
The rate at which parts of the observable universe become unobservable depends on the Hubble constant (H₀) and the current rate of expansion of the universe. The Hubble constant is roughly 70 kilometers per second per megaparsec (km/s/Mpc), meaning that objects farther than a certain distance are receding from us faster than the speed of light due to cosmic expansion. This boundary is known as the cosmic event horizon. Key Steps to Calculate
Here:
Plugging in values, this gives:
ΔV∼3.2×1021 cubic light-years per year. Interpretation
Each year, about 3.2 sextillion cubic light-years of the observable universe's boundary shifts into the unobservable region. This represents vast regions of space becoming permanently inaccessible to us due to the accelerating expansion of the universe.
Go ahead. Wrap your brain around that!
The rate at which parts of the observable universe become unobservable depends on the Hubble constant (H₀) and the current rate of expansion of the universe. The Hubble constant is roughly 70 kilometers per second per megaparsec (km/s/Mpc), meaning that objects farther than a certain distance are receding from us faster than the speed of light due to cosmic expansion. This boundary is known as the cosmic event horizon. Key Steps to Calculate
- Cosmic Event Horizon: The distance to this boundary depends on the Hubble constant and the current cosmological model. For the Lambda Cold Dark Matter (ΛCDM) model, the cosmic event horizon is approximately 16 billion light-years (though exact values depend on assumptions like dark energy density).
- Expansion of the Horizon: The observable universe's radius grows every year because light from previously unobservable regions reaches us. However, due to the accelerating expansion driven by dark energy, regions that were observable may eventually become unobservable.
- Critical Rate of Expansion: The rate at which the event horizon expands corresponds to a certain fraction of the Hubble constant. Each year, the volume of space just beyond the event horizon expands due to this cosmic acceleration, causing regions of space to effectively "move beyond" our ability to observe them.
- Hubble radius: The current Hubble radius is about 1/H0, which corresponds to ∼14.4 billion light-years.
- Rate of expansion: Every year, the event horizon increases by c/H0, where c is the speed of light. This corresponds to about 1 light-year per year for the boundary itself.
- Volume becoming unobservable: To calculate the amount of space becoming unobservable, consider a spherical shell around the cosmic event horizon. The thickness of this shell grows annually, and its volume can be estimated as:
Here:
- R is the cosmic event horizon radius (∼16 billion light-years),
- ΔR is the rate of horizon expansion (∼1 light-year per year).
Plugging in values, this gives:
ΔV∼3.2×1021 cubic light-years per year. Interpretation
Each year, about 3.2 sextillion cubic light-years of the observable universe's boundary shifts into the unobservable region. This represents vast regions of space becoming permanently inaccessible to us due to the accelerating expansion of the universe.
Go ahead. Wrap your brain around that!
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