Do we live in a giant dark void?

What if the key to understanding one of the biggest mysteries in cosmology lies in nothing? Literally, the vast expanses of empty space between galaxies. Recent research has proposed that a gigantic void, a region of under dense matter in our local universe, could be causing the expansion rate of the cosmos to appear faster than expected from observations of the cosmic microwave background radiation or CMB. Now the CMBB is how the bread gets buttered around the Keing household. So this discrepancy known as the Hubble tension is of particular importance to me and my cosmologist friends. It's been a thorn in our sides for more than a decade now. What is the Hubble tension? It revolves around the famous Hubble constant which is a measurement of how fast the universe is expanding. We can calculate this rate using two primary methods. observations of the cosmic microwave background which originated from the formation of hydrogen 380,000 years after the big bang and the second method are measurements of type 1A supernova bright exploding stars in the relatively modern local universe the problem is these two different methods give conflicting results for the value of the Hubble constant the difference may seem small about 9% but it's a huge deal in cosmology because each methodology has about a 1% % chance of being a fluke, meaning that these things don't agree at over the five sigma level. Now, this reminds me of what many parents get to experience when their kid is about 2 years old. When you take your child to the pediatrician at age two, the pediatrician measures their height and their weight. And from their height at age two, they can basically predict, usually they just double it, but they predict based on millions or billions of samples, namely every human being that's ever been measured in this way, how tall they'll be at the end of their life or when they finish growing. And so it be as if using the baby method, we got a very different method than if you measured a kid right before he or she was done with puberty, local more recently, and those two values disagreed wildly. They were off by almost a foot in some cases. This would be quite startling. Now enter the void hypothesis as a method of explaining and resolving the Hubble tension. A team of researchers has found that the massive underdense region called the Kenan Barger Kawi or KBC void which stretches across some 700 million lighty years could be responsible for the Hubble tension. The model that is being proposed shows that continuous outflows of matter from this vast void region towards us could make the expansion rate appear faster in our local patch of the universe compared to the cosmic average from the early universe. It's like being on a rowboat on a river. The flow of the river makes it seem like you're moving faster relative to the river banks when you add it to the velocity of your canoe. So, what evidence and what are the implications for this hypothesis? Remarkably, this local void model can explain both the higher local Hubble constant values and the observed bulk motions of galaxies streaming away from the void without needing to tweak any parameters precisely. If confirmed, this could mean we don't necessarily need to modify our theories of gravity or cosmic expansion. Those would be more exotic explanations that would require new physics. This is good old-fashioned ordinary galactic physics, the kind that we've been practicing for literally a hundred years now and understand quite well. The effect arises from the inhomogeneous distribution of matter in our universe. We're in a sort of special part of the universe that's not exactly representative of the entirety of the universe as a whole. However, the model depends on a specific void profile assumed, and it may not account for interactions with other large scale structures beyond the local void. There are also open questions about the scale of such voids and its impacts on previously measured data. Now, are there any other competing solutions? Why yes, the local void hypothesis isn't the only game in town for resolving the Hubble tension. Other proposed solutions include so-called early dark energy models that affect the early expansion rate of the universe in a way that's very different than the later expansion rate that we're experiencing now. There are theories of modified Newtonian dynamics called man that change gravity that could cause a variation of the Hubble constant from age zero basically to age much later. The influence of primordial magnetic fields on the cosmic microwave background has also been proposed as a solution to the Hubble tension. Each of these solutions has its own strengths and the predictions to be tested against future observations. So what's the cosmic perspective in all this? What this really highlights is that the vast emptiness of space can have a profound consequence on our understanding of the cosmos. The cosmic model we've constructed may need revisions to account for the complex inhomogeneous structure of matter we observe. Now, as we continue to probe the depths of space with ever more powerful telescopes like the James Webb Space Telescope, the secrets of cosmic voids and the true nature of the universe's expansion may be finally resolved. And this Hubble tension could go away when astronomers like me will no longer have anxiety nor need for special psychotherapists because sometimes studying the emptiness, the void and screaming into it is the key to seeing the bigger picture. If you enjoyed this video, please click on this video with my recent interview with Wendy Freriedman, who also thinks she may have found a solution involving somewhat less exotic stars called Tip of the Red Giant branch stars. And don't forget to subscribe.