Hubble Time Calculator

Hubble's Law

Hubble Time Formula:

\[ t_H = \frac{1}{H_0} \]

Hubble Time (seconds):

Hubble Time (years):

1. What is Hubble Time?

Definition: Hubble time (t_H) is the inverse of the Hubble constant (H₀), representing the time since the Big Bang in a simple cosmological model.

Purpose: It provides a rough estimate of the age of the universe based on the current expansion rate.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ t_H = \frac{1}{H_0} \]

Where:

\( t_H \) — Hubble time (seconds)
\( H_0 \) — Hubble constant (s⁻¹)

Explanation: The Hubble constant measures the current expansion rate of the universe. Its inverse gives a characteristic time scale for the expansion.

3. Importance of Hubble Time

Details: While not exactly equal to the age of the universe (due to changing expansion rates), Hubble time provides a fundamental timescale in cosmology.

4. Using the Calculator

Tips: Enter the Hubble constant in inverse seconds (default 2.27×10⁻¹⁸ s⁻¹, approximately 70 km/s/Mpc). The calculator shows results in both seconds and years.

5. Frequently Asked Questions (FAQ)

Q1: Why isn't Hubble time exactly equal to the age of the universe?
A: The expansion rate has changed over time due to the influence of matter, dark energy, and radiation.

Q2: What's the current best estimate of the Hubble constant?
A: Current measurements range between 67-74 km/s/Mpc (about 2.17-2.40×10⁻¹⁸ s⁻¹).

Q3: How is the Hubble constant measured?
A: Through observations of Cepheid variables, supernovae, and cosmic microwave background.

Q4: What units are typically used for the Hubble constant?
A: Often expressed in km/s/Mpc (kilometers per second per megaparsec) which is converted to s⁻¹ for this calculation.

Q5: Why does the calculator show two results?
A: The primary result is in seconds (SI units), with a conversion to years for easier interpretation.