For many years, cosmologists have claimed the Universe is 13.8 billion years old. A new paper says no, it’s 26.7 billion. How do we decide?
Perhaps the greatest achievement of late-20th and early-21st century astrophysics is the arrival of a “consensus model” of the entire Universe: Lambda-CDM (ΛCDM) cosmology. For countless generations of humans, we’ve marveled at questions such as:
- What is the Universe?
- What makes it up?
- How far, to the limits of what it’s possible to observe, does it go on for?
- How did it come into existence, and how long ago?
- How did it grow up to be the way it is today?
- And what will its ultimate fate be?
Today, after unprecedented measurements of galaxies all throughout cosmic history, all-sky imaging of the Universe at microwave wavelengths, and thousands upon thousands of supernovae and other transient events all across the Universe, we finally have our answers to these questions. Our Universe, made of 68% dark energy, 27% dark matter, and just 5% “normal stuff,” began from a small, dense, nearly-perfectly-uniform state some 13.8 billion years ago in a hot Big Bang, and has been expanding, cooling, and gravitating ever since.
At least, that’s the consensus picture. Recently, a challenge to that picture has gotten some popular attention, based on a recently published paper claiming that the Universe is actually 26.7 billion years old, not 13.8 billion years old. Let’s look at these two theories side-by-side, and unpack what’s true versus what we’d need to be true in order to truly determine the age of the Universe.
Different assumptions
Anytime you’re given a scientific theory, you have to ask yourself, “what assumptions are behind it?” In the case of the standard model of cosmology, ΛCDM, the assumptions are that:
- the laws of physics are given by General Relativity (for gravity) and…