Our Universe Has Two Different Sides, Physicists Confirm

ruticker 02.03.2025 12:34:31

Recognized text from YouScriptor channel Sabine Hossenfelder

Recognized from a YouTube video by YouScriptor.com, For more details, follow the link Our Universe Has Two Different Sides, Physicists Confirm

The universe is an odd place, and it just became even odder because the new analysis confirmed an anomaly that everyone ignored because they thought it would go away. Well, it didn't. It seems that the universe looks noticeably different on one side of us than on the other. Let's have a look. This anomaly is called the **hemispherical power symmetry**. It's been around since 2003, when the WMAP data showed that the cosmic microwave background (CMB) has more fluctuations on one side of the universe than on the other. If that makes no sense to you, it's because it makes no sense. This asymmetry quite simply shouldn't be there. In fact, I don't know any good explanation for it, which is probably why physicists have largely ignored it. There isn't even a theory for it; it's just weird. The cosmic microwave background (CMB) radiation is the leftover radiation from the hot plasma in the early universe, and that's now all around us. The radiation was once hot but has since dropped to an average temperature of just about **2.7 Kelvin**. However, the temperature isn't exactly the same in all directions in the sky. This is because, in this hot plasma in the early universe, some places were a tiny little bit hotter and others a tiny little bit colder. So, the cosmic microwave background has temperature fluctuations around the average. This is what you see in this image: the blue spots are a little colder, and the red ones are a little hotter. Physicists have studied these temperature fluctuations intensely because they're our best clue to what was going on after the Big Bang. Loosely speaking, they count how many patches of what size are hidden in this image. What you can see by eye is that there are a lot of patches that are kind of this size, which is about one degree in angular size. But really, there are fluctuations of any size; it's just that they're difficult to see. If you do a data analysis and plot the sizes of fluctuations as a function of their number, then you get what's called the **power spectrum** of the cosmic microwave background. In this figure, the large patches are counted on the left with a small L, and the small ones are counted towards the right. This big peak here—that's the many small sprinkles we readily see by eye. The hemispherical power symmetry is now the observation that one side of the universe seems to have more temperature fluctuations than the other side. This is not about the CMB temperature itself; it's about the fluctuations. The CMB temperature itself is also somewhat larger in one direction than in the other, but this is because of our own motion through the universe. It's called the **CMB dipole** and is more or less well understood. But the hemispherical power symmetry is something different altogether. It means, loosely speaking, that there is more texture or detail on one side of the universe than on the other, even if the average is the same. By the way, this video comes with a quiz that lets you check how much you remember. However, 20 years ago, the data wasn't particularly good. The new paper now looked for the anomaly again in a much newer data set from the **Planck mission**. For their analysis, they divided up the entire sky into increasingly smaller patches and then calculated the typical size of fluctuations in them. From this, they then extracted the two directions that are most different and also calculated how different they are. There are two interesting things about this. One is that you can see in this image that in some ranges, that is, for certain sizes of the patches, the discrepancy is around **3 Sigma**. The other interesting finding is that the direction in which the fluctuations are larger is nowhere near the CMB dipole. They find their largest in this direction, but the CMB dipole is somewhere up here. What does this mean? For one thing, as we just saw, the statistical significance is not particularly large. Depending on how you look at it, it's somewhere between **two and three sigma**—that's about a one in a few hundred chance of something like this happening coincidentally. So, it could be just coincidence. The other two options are that either the data is biased because of the way we make our observations, or our location in the universe isn't as random as it seems. Both of these options would require a major rethinking of all we know about the cosmos. Another way to think of it is that the CMB measurements are like the universe's first selfie, and like most selfies, it's showing us more details than we wanted to know. Did you know there's a free and easy way to learn more about the science behind all the videos that you've been watching? Yes, there is! Have a look at **Brilliant**. 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