Approximately how long ago did the Big Bang occur?

The correct answer indicates that the Big Bang occurred approximately 14 billion years ago, which is supported by extensive astronomical observations and calculations. This timeframe aligns with findings from the cosmic microwave background radiation, the distribution of galaxies, and the observed expansion of the universe.

When scientists measure the universe's age, they focus on the rate of expansion (described by Hubble's Law) and factor in observations from telescopes and satellites that have provided detailed insights into the early universe's conditions. These measurements suggest the universe has been expanding since the Big Bang, supporting the estimate of around 13.8 billion years.

The other options propose significantly different timescales. A duration of 10 billion years is less than the established consensus and does not reflect the current scientific understanding. Likewise, 20 billion years greatly exceeds the estimated age of the universe, indicating an incorrect interpretation of cosmological data. The timeframe of 4.5 billion years more accurately corresponds to the age of the Earth rather than the universe itself, further illustrating why 14 billion years is the most accurate estimate for when the Big Bang occurred.