The leftover light from the young universe has a big flaw, and we don’t know how to fix it. It’s a cold place. It’s just too big and too cold. Astronomers aren’t sure what it is, but they mostly agree that it’s worth investigating.
The cosmic microwave background (CMB) was created when our universe was only 380,000 years old. At that time, our cosmos was about a million times smaller than it is today and had a temperature of more than 10,000 Kelvin (17,500 degrees Fahrenheit, or 9,700 degrees Celsius), meaning that all the gas was plasma. How The universe expanded, cooled, and the plasma became neutral. In the process, he released a stream of red-hot light. In the billions of years since then, this light has cooled and stretched to a temperature of about 3 Kelvin (minus 454 F or minus 270 C), bringing this radiation firmly into the microwave range. electromagnetic spectrum.
The CMB is almost perfectly uniform, but there are tiny differences in temperature down to about 1 part per million, and these imperfections, which look like blobs of various shapes and sizes, are the juiciest part of it. We cannot predict exactly what the fluctuations will be, which places will be cold and which will be hot. This is because the light we see comes from a part of the universe that is now removed from observation.
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This means we have to rely on statistics to understand the CMB. We cannot tell where the spots will appear; we can only use physics to understand the average size of the spots and how hot or cold they might be on average.
Cold point
Pretty much everything about CMB is great. We understand where the spots come from, and for decades we’ve been building ever more advanced telescopes and satellites to look better. In fact, the discovery and measurement of the CMB is one of the greatest success stories in science.
And there is also a cold place.
There are many cold spots in the CMB now. But there is one – in the cold spot is what stands out. It even stands out visually. If you look at the CMB map – where the entire sphere of the sky is compressed into a strange, vaguely oval shape – it’s at the bottom and slightly to the right. In the sky, it is in the direction of the constellation Eridan.
The cold place is surprisingly cold. Depending on how you define the edge of the spot, it’s about 70 microkelvins cooler than average, compared to the average regular cold spot, which is only 18 microkelvins cooler than average. The deepest parts are 140 millikelvins cooler than average.
It’s also big, about 5 degrees across, which doesn’t sound like much, but it’s about 10 full moon lined up next to each other. The average patch on the CMB is less than 1 degree. So not only is it surprisingly cold, but it’s also surprisingly large.
Now this is where things get complicated. It’s easy to see a cold spot. Astronomers first noticed it with NASAWilkinson Microwave Anisotropy Probe in the early 2000s and European Space AgencyThe Planck satellite confirmed the existence of the cold spot. So it wasn’t just an instrument fluke, a measurement error, or some weird alien intervention—it was a real thing.
This leads to another question: do we care?
We cannot say exactly where the spots will appear on the CMB; we only receive statistical information. There’s been a lot of thinking about this, but the general consensus is that yes, we shouldn’t reasonably expect a cold spot to be so big and so cold just by chance, that based on our understanding of the physics of the early universe, it’s just too farfetched.
Yes, by chance large and cold spots should appear from time to time, but our chances of seeing just one by pure chance are less than 1% (and could be much lower, depending on who you ask). So while we can just say we got unlucky and got a cold spot, it’s rare enough that it warrants more attention.
So this is not a measurement error and probably not a coincidence. So what is it?
Hot debate
The favored explanation for the strange nature of the cold spot is that it has to do with the giant cosmic void that lies between us and the CMB in that direction. Cosmic voids are large patches of almost nothing. But despite this nothingness, they affect the light of the CMB, and this is because voids develop.
When light from the CMB first enters the void, it gains a small amount of energy as it passes from a high-density medium to a low-density medium. In a completely static universe, light would lose an equivalent amount of energy as it exited the other side. But because voids change when light first enters, the void can be relatively small and shallow, and time she leaves, the void is great and deep.
This results in a total loss of energy from the CMB light traversing the void, a process known as the complex Sachs-Wolf effect.
So a giant void could potentially explain the cold spot, but there’s one problem: we’re not sure if there really is a giant void in that direction. We have maps and surveys of galaxies in this part of the sky, but they are all in some ways incomplete; they either do not capture every galaxy or they do not cover the entire volume of the supposed void. As such, this has also seen considerable variation in the literature, with some groups claiming to identify the supervoid and others saying there is nothing special about it.
Also, even if there were a supervoid in that direction, it’s unclear whether it would have a strong enough effect to create the cold spot we see.
This ambiguity leaves room for some unconventional proposals, such as the idea that the cold spot is the remnant of a point of intersection between our universe and a neighboring one. But even this hypothesis cannot explain all the properties of the cold spot.
A cold place invalidates Big explosion? Definitely not. Is it worth considering? Almost certainly. Will we ever finally find out what it is? Maybe not.
This is the science. It’s never perfect, and there’s always a little thorn in one theory or another. Sometimes these spikes bloom to reveal new kinds of TK, sometimes these spikes simply bloom as scientists slowly chip away at them, and sometimes they just sit there without a full solution, without a full answer, but never rising to the level of needing more attention.
I like it anyway. why? Because nothing in this universe is perfect, not even our descriptions of it.