The Most Unexplained Anomalies in the Universe

There are things in the universe that actually shouldn't exist, things that according to our best models are either extremely unlikely or shouldn't be there at all. Let's get straight into it. After the Big Bang, the universe was opaque for several hundred thousand years. Too hot, too dense. Then, after about three hundred eighty thousand years, the universe cooled down enough. Matter and radiation separated. The radiation that was released during this process has been traveling through space ever since. Today, it is measurable everywhere, as a faint microwave hum coming from every direction in the sky. The Cosmic Microwave Background, or CMB for short. It is the oldest light in the universe, a snapshot of the state of the universe when it was just 380,000 years old, and it is almost perfectly uniform. In 2003, the WMAP satellite provided data on small temperature fluctuations in the CMB. Tiny variations that allow conclusions to be drawn about the structure of the early universe. In one region, something unexpected appeared. A spot that is significantly colder than the rest. The cold spot. There are natural fluctuations in the CMB. Tiny temperature differences that trace back to density. Differences in the early universe. That is normal and well understood. The cold spot doesn't fit in there. It is larger than expected. Colder than expected. And it lies in a direction where no known structure would explain such a deviation. Statistical analyses have shown that a spot of this size and temperature has a probability of less than 0.2% within the framework of the standard model. One possible explanation. In the foreground of the cold spot, between us and this region of the CMB, lies a massive cosmic void. A so-called supervoid, an area where there are hardly any galaxies. When microwave radiation passes through such a void, it loses a bit of energy. This could at least partially explain the cold spot. In fact, such a void is known to exist exactly there. About 1.8 billion light-years across. One of the largest known voids in the universe. The problem. This void alone explains only a fraction of the observed temperature deviation. Another idea. The cold spot could be the imprint of a collision. A collision of our universe with another universe, early in the development of the cosmos. In the context of certain inflationary models, our universe could be part of a larger multiverse. If two such universes came into contact with each other, some kind of dent or cooling effect in the CMB would be conceivable. Not a completely far-fetched idea, but evidence for it is lacking, and the hypothesis is difficult to test, which makes it unsatisfying from a scientific standpoint. The cold spot has been known for over 20 years. It has been confirmed by several satellites and telescopes. The void does not fully explain it. The multiverse is speculation. There is no consensus. No satisfying one, at least. What is certain? Something is there. In the oldest light of the universe, in a region that actually shouldn't be conspicuous, there is an anomaly that no one has really explained after two decades. Galaxies move. That is known. The universe is expanding. Galaxies are moving away from each other. That is the Hubble expansion. But superimposed on this expansion, there is another movement. One that cannot be explained by the expansion. Our Milky Way, the Andromeda galaxy, and the dozens of smaller galaxies in our neighborhood, the so-called local group, are moving at a speed of about 600 kilometers per second in a specific direction, relative to the background radiation. That is no small thing. 600 kilometers per second. Something is pulling. In the 1980s, the movements of galaxies were systematically measured. What became visible during this? Hundreds of galaxies, spread over millions of light-years, are all moving in the same direction. Toward a single point, the Great Attractor. Gravity explains in principle that masses attract other masses. That is not the problem. The problem is the scale. To explain the observed movement, the Great Attractor would need a mass equal to the mass of thousands of galaxies like ours, concentrated in one region. And the reason why this was difficult to investigate for so long. The Great Attractor lies behind the Milky Way. The disk of our own galaxy is packed with gas, dust, and stars. Visible light cannot get through. Astronomers call this area the zone of avoidance. The region of the sky in which our own galaxy blocks the view of everything behind it. X-rays and radio waves can partially penetrate the disk. Through these wavelengths, the picture has gradually sharpened over the last few decades. What is known today? The Great Attractor is not a single source. Probably a complex structure made of several overlapping structures. Part of the gravitational pull comes from the Norma Cluster. One of the densest known galaxy clusters, right in the zone of avoidance. But that is not enough. Behind it presumably lies the Shapley Supercluster. One of the largest known concentrations of mass in the universe, several hundred million light-years away. It could explain a significant part of the observed movement. Whether it explains everything is not yet certain. The zone of avoidance simply makes complete clarity impossible, with the means currently available. Across more than 1.3 billion light-years, galaxies arrange themselves into a ring structure. It's called the Big Ring. It has a diameter of 1.3 billion light-years. That is hard to wrap your head around. So here is another scale. Our entire Milky Way is about 100,000 light-years wide. The Big Ring is roughly 13,000 times as large as the galaxy we live in. It is located around 9.2 billion light-years away. The light we are currently receiving from there was already on its way before Earth even existed. And here is the problem. The standard model of cosmology, which describes how the universe is structured and how it developed, clearly states structures of this scale should not exist. The universe simply did not have enough time to form them. After the Big Bang, matter distributed itself. Gravity pulled it together. Galaxies formed, then galaxy clusters, then filaments. That is known. But this process has limits. There is a maximum size up to which such structures can form. The Big Ring lies significantly above it. The cosmological principle is one of the fundamental assumptions of modern astrophysics. It states, on large scales, the universe is uniformly distributed. If you look far enough, it looks the same everywhere. No lumps, no structures, just uniformity. This limit is at just under 300 million light-years. The Big Ring measures 1.3 billion light-years. It is therefore almost four times as large as what, according to theory, is even allowed to exist. The probability of this ring structure forming by chance is about 1 in 140,000, which is 0.0005%. What exactly the Big Ring is, nobody knows. A remnant from the early development of the universe? Or a hint that our standard model has a blind spot somewhere that we haven't found yet? To this day, it cannot be fully explained. The Big Ring. Over a billion light-years in size. The cold spot. Hundreds of millions of light-years in diameter, in the oldest radiation of the universe. The Great Attractor. An attraction source, stretching across hundreds of millions of light-years. All three lie where the cosmological standard model actually ends. Uniformity should prevail on these scales. These three anomalies were found independently of one another, using different methods. And all three show the same thing. The universe, on very large scales, does not behave entirely the way the model predicts. In addition, there is a fundamental problem. We sit at a single point in the universe. Structures behind the Milky Way are difficult or impossible to measure directly. Objects that are further away than light could travel in the lifetime of the universe simply lie outside the observational horizon. If an observation does not fit the model, that is initially no proof of a wrong model. It could be a measurement error, a statistical fluctuation. But when anomalies pile up, when several independent findings point in the same direction, then the question shifts. The cosmological standard model is extraordinarily precise. It explains the formation of galaxies, the distribution of matter, the expansion of the universe. It has made predictions that were confirmed, whether the anomalies point to a fundamental problem in the model or to missing physics beyond our knowledge. Or whether they will eventually turn out to be explainable, cannot be said. I hope you enjoyed the video and we'll see each other next time.