1. What is the Hubble Constant?

The Hubble constant (H₀) is a measure of the rate of expansion of the universe. It relates the recession velocity of galaxies to their distance from us, providing fundamental insights into cosmology and the age of the universe.

2. How Does the Calculator Work?

The calculator uses Hubble's Law:

Where:

• \( H_0 \) — Hubble constant (km/s/Mpc)
• \( v \) — Recession velocity (km/s)
• \( d \) — Distance to galaxy (Mpc)

Explanation: The equation shows the linear relationship between a galaxy's distance and its recession velocity due to the expansion of the universe.

3. Importance of Hubble's Law

Details: Hubble's Law provides evidence for the expanding universe and is fundamental to modern cosmology. The Hubble constant helps estimate the age of the universe and understand dark energy.

4. Using the Calculator

Tips: Enter recession velocity in km/s and distance in megaparsecs (Mpc). Both values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What is the current accepted value of H₀?
A: There's tension between measurements (~67 km/s/Mpc from CMB vs ~73 km/s/Mpc from local measurements), known as the "Hubble tension."

Q2: Why are the units km/s/Mpc?
A: This shows how many kilometers per second a galaxy recedes for each megaparsec of distance from us.

Q3: How was Hubble's Law discovered?
A: Edwin Hubble observed in 1929 that galaxies' redshifts (indicating velocity) were proportional to their distances.

Q4: What affects the accuracy of H₀ measurements?
A: Distance measurement methods, peculiar velocities of galaxies, and cosmic variance all contribute to uncertainty.

Q5: How does H₀ relate to the age of the universe?
A: The Hubble time (1/H₀) gives a rough estimate, though the actual age depends on the universe's matter/energy content.