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%.
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.
Why Cosmology’s Expanding Universe Controversy Is An Even Bigger Problem Than You Realize
“The question of how quickly the Universe is expanding is one that has troubled astronomers and astrophysicists since we first realized that cosmic expansion was a necessity. While it’s incredibly impressive that two completely independent methods yield answers that are close to within less than 10%, the fact that they don’t agree with each other is troubling.
If the distance ladder group is in error, and the expansion rate is truly on the low end and near 67 km/s/Mpc, the Universe could fall into line. But if the cosmic microwave background group is mistaken, and the expansion rate is closer to 73 km/s/Mpc, we just may have a crisis in modern cosmology.
The Universe cannot have the dark matter density and initial fluctuations that such a value would imply. Until this puzzle is resolved, we must be open to the possibility that a cosmic revolution may be on the horizon.”
Ever since we first learned that the Universe was expanding, scientists have worked hard to measure just how fast that expansion rate is. From that, combined with what makes up the Universe, we can learn how old the Universe is and what it was like in the past, as well as what it’s fate will be in the future. Yet the two groups that make independent measurements of that rate, from the cosmic microwave background and the cosmic distance ladder, have gotten inconsistent results. If the distance ladder team has made a mistake, everything will be fine with cosmology. But if that team is right and the microwave background team is wrong, there should be a crisis coming.
Why is that? Come find out why the biggest controversy in modern cosmology might be an even bigger problem than almost everyone realizes!