 In astronomy, we've hit plenty of hurdles on our quest to comprehend the wonderful cosmos we cherish residing in. Some hurdles, such as putting the first satellite in space or putting a man on the moon or a rover on Mars, have been overcome, so kudos to us for that. However, despite all our victories, we still fall short in many areas, such as understanding dark matter, dark energy, and especially what we're going to be looking at today, dark flow. A couple of years back, scientists were studying a group of galaxy clusters. The observation involved looking at the photon residue left behind from the X-ray emissions of the galaxy interacting with the cosmic background radiation that has permeated our universe since the Big Bang. What they found surprised them. Upon closer inspection, the scientists learned that the galaxy clusters were trekking a 2 million miles per hour towards southern constellations, such as Centaurus, Hydra, and Vela. A complete deviation from the normal paths other galaxies took due to the outward expansion of the universe. And so, scientists named this abnormality in galaxy cluster motion, dark flow. So, what exactly causes dark flow? Well, we don't have a definite explanation that we know for sure is true. We do have an interesting speculation which does involve other universes. You see, scientists theorize that throughout all space permeates an energy field that scientists believed was always there since the beginning of time itself. What scientists speculate is that a fluctuation in this field resulted in the Big Bang, which eventually grew to become our universe. But the theory says it doesn't just end there. You see, according to the theory, fluctuations would have occurred in other pockets of space, billions or even trillions of light-years from our universe, thereby giving rises to other universes. So, how exactly does this tie back to explaining dark flow? Well, scientists who propose the theory say that the matter in these other universes, such as galaxies, stars and planets, exerts a gravitational pull on the galaxy clusters in our universe, thereby knocking them off their usual course under the expansion of the universe. Even more astounding this theory was the fact that scientists discovered that the dark flow effect could be observed within a 2.5 billion light-year radius of Earth. However, as amazing as this dark flow theory is, we must still proceed with caution. As intriguing as the idea of dark flow is, it doesn't come without some controversy. You see, in addition to studying galaxy clusters, scientists also analyzed some data collected from supernova. What they found was astonishing and a bit contradictory. Inspecting the supernova data revealed that some matter in the universe was veering off course on the normal path of expansion at about 500,000 miles per hour, a bit slower than the galaxy clusters. But wait, there's more. Scientists then realized that slower flow could not be attributed to gravitational forces exerted by masses in other universes, but rather a byproduct of the gravitational tug from matter within our own universe, thereby raising the question, is dark flow attributable to tugs from matter in other universes or from within our own universes? So in this case of the brawl of the universes, which one wins? The multiverse explanation or the intra-universe explanation? Well, the answer may shock you. It's a draw. You see, both explanations are equally compelling. The intra-universe explanation stems from well-gathered data from which a fairly logical conclusion was drawn, and the multiverse theory, while I admit shouldn't be taken without doubt, is still in my eyes pretty convincing. As stated earlier, the data observed by scientists revealed that some galaxy clusters were not only traveling away from their expected path from the expansion of the universe, but accelerating too. And as per the basic law of physics, an object only accelerates when a force is applied to it, and it can't be from dark energy since, once again, the cluster isn't traveling in its normal path as the other clusters do in the expansion of our universe. So it does seem highly logical based on this, to come to the conclusion that there might be some matter outside our universe, which could be at play here. So, which dark flow theory resonates better in your mind? The multiverse theory or the intra-universe theory? And feel free to disagree and add your own thoughts on what could be the motive for dark flow, as I myself am teeming with curiosity, and I'm eager to consider other possibilities. Also, if there's anything in this subject you want me to cover more in depth, or any other subject for that matter, be sure to let me know in the comments below. Anyways, that's all for today. I hope you enjoyed this video, and if you did, be sure to leave a like and subscribe, and don't forget to stay tuned for more science videos.