Approximately how old is the universe?

• A. 13.8 Billion Years
• B. 4.6 Billion Years
• C. 1.3 Billion Years
• D. 100 Billion Years

Answer: (A)

Understanding the age of the universe comes from looking at how space has expanded since the Big Bang and the faint glow left from that early era. The best estimate, supported by measurements of the cosmic microwave background and the current expansion rate, puts the universe’s birth at about 13.8 billion years ago. By combining how fast galaxies are moving away now with the observed density and energy content of the cosmos, cosmologists work backward in time and converge on this age. The other numbers don’t fit what we observe: the Earth itself formed about 4.6 billion years ago, so 4.6 is only Earth’s age, not the universe’s; 1.3 billion years is far too young to account for the large-scale structure and the CMB we see; 100 billion years would imply an expansion history that conflicts with cosmic background radiation data and distant supernova measurements.