The Simplest Solution To The Expanding Univers…

The Simplest Solution To The Expanding Universe’s Biggest Controversy

“This is how dark energy was first discovered, and our best methods of the cosmic distance ladder give us an expansion rate of 73.2 km/s/Mpc, with an uncertainty of less than 3%. 

However. 

If there’s one error at any stage of this process, it propagates to all higher rungs. We can be pretty confident that we’ve measured the Earth-Sun distance correctly, but parallax measurements are currently being revised by the Gaia mission, with substantial uncertainties. Cepheids may have additional variables in them, skewing the results. And type Ia supernovae have recently been shown to vary by quite a bit — perhaps 5% — from what was previously thought. The possibility that there is an error is the most terrifying possibility to many scientists who work on the cosmic distance ladder.”

We live in an expanding Universe that’s 13.8 billion years old, full of two trillion galaxies, containing dark energy, dark matter, normal matter and radiation. For decades, we’ve been refining and better-understanding this cosmic picture, with one of the goals of modern astrophysics to measure the rate of expansion. Right around the year 2000, results from the Hubble key project, the scientific reason the Hubble space telescope was built, indicated that the expansion rate was 72 km/s/Mpc, with an uncertainty of around 10%. Now, we have multiple independent ways to measure that rate to even greater precision, but the problem is that two different groups no longer agree. One claims a rate of 73.2 km/s/Mpc, and the other claims a rate of 67.4 km/s/Mpc. The claimed uncertainties are small, and do not overlap.

Is this a crisis for cosmology? Or is one group simply mistaken due to an unidentified error? Is this a loose OPERA cable all over again? Here’s the big question keeping scientists up at night.