The remaining light of the early universe has a major flaw, and we don’t know how to fix it. It’s the cold spot. It’s just way too big and way too cold. Astronomers aren’t sure what it is, but they mostly agree that it’s worth studying.
The cosmic microwave background (CMB) was formed when our universe was only 380,000 years old. Back then, our cosmos was about a million times smaller than it is today and had a temperature of over 10,000 Kelvin (17,500 degrees Fahrenheit or 9,700 degrees Celsius), meaning all the gas was plasma. As the universe expanded, it cooled and the plasma became neutral. It released a flood of white-hot light. Over billions of years, this light has cooled and expanded to a temperature of about 3 Kelvin (minus 454 F or minus 270 °C), putting this radiation firmly in the microwave band of the universe electromagnetic spectrum.
The CMB is almost perfectly uniform, but there are tiny temperature differences of about 1 part per million, and these imperfections, which look like spots of different shapes and sizes, are the juiciest part of it. We cannot predict exactly how strong the fluctuations will be, which exact spots will be cold and which will be hot. That’s because the light we see comes from a part of the universe that is now hidden from observable view.
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This means we have to rely on statistics to understand the CMB. We cannot say which stains will appear where; Using physics we can only understand how big the spots are on average and how hot or cold they might be on average.
The cold spot
Almost everything is fine with the CMB. We know where the spots come from, and over the decades we have built increasingly sophisticated telescopes Satellites to be able to see better. In fact, detecting and measuring CMB is one of science’s greatest success stories.
And then there is the cold spot.
Now there are many cold spots in the CMB. But there is one – The Cold Spot – that’s what stands out. It also stands out visually. If you look at a map of the CMB – where the entire celestial sphere is compressed into a strange, vaguely oval shape – it’s down and a little to the right. In the sky it shows the direction of the constellation Eridanus.
The cold spot is strangely cold. Depending on how you define the edge of the spot, it will be about 70 microkelvins colder than average, compared to an average common cold spot, which is only 18 microkelvins colder than average. At its lowest points it is 140 millikelvin colder than average.
It’s also big – about 5 degrees in diameter, which doesn’t sound like much, but that’s about 10 Full moons lined up next to each other. The average point on the CMB is less than 1 degree. So it’s not only incredibly cold, but also incredibly big.
Now it’s getting difficult. The cold spot is easy to spot. Astronomers discovered it for the first time NASAWilkinson Microwave Anisotropy Probe in the early 2000s and the European Space AgencyThe Planck satellite confirmed the existence of the cold spot. So it wasn’t just a fluke of the instrument, a measurement error, or a strange extraterrestrial disturbance – it’s a real thing.
This leads to another question: Do we care?
We cannot say with certainty which spots will appear where on the CMB; We only receive statistical information. There has been a lot of back and forth about this, but the general consensus is that based on our understanding of physics we shouldn’t reasonably expect the cold spot to be so large and so cold, just by chance of the past universe it’s just way too inappropriate.
Yes, occasionally large and cold spots should appear randomly, but our chance of seeing one purely by chance is less than 1% (and can be much lower, depending on who you ask). While we can easily say that we were very unlucky and got a cold spot, it’s rare enough that a little more attention is needed.
So it is not a measurement error and probably not a coincidence either. So what is it?
The hot debate
The preferred explanation for the strange nature of the cold spot is that it is due to a vast cosmic void located in that direction between us and the CMB. Cosmic voids are large patches of almost nothing. But despite this nothingness, they influence the CMB light, and that is because the cavities continue to evolve.
When light from the CMB first enters a cavity, it gains some energy as it passes from a high-density environment to a low-density environment. In a completely static universe, light would lose the same amount of energy as it exited the other side. However, because the cavities change, the cavity may be relatively small and flat when the light first enters Time it works, the emptiness is big and deep.
This results in a total energy loss of the CMB light passing through the cavity – a process known as the integrated Sachs-Wolfe effect.
So a giant cavity could potentially explain the cold spot, but there’s a problem: we’re not sure there’s actually a giant cavity in that direction. We have maps and galaxy surveys in this part of the sky, but they are all somehow incomplete; Either they don’t cover every galaxy or they don’t cover the entire volume of the supposed void. Again, there has been considerable controversy in the literature, with some groups claiming to have identified a supervoid while others saying there was nothing special there.
And even if there were a supervoid in this direction, it’s not clear whether it would be strong enough to produce the cold spot we see.
This ambiguity leaves room for some unconventional suggestions, such as the idea that the Cold Spot is a leftover intersection between our universe and a neighboring one. But even this hypothesis cannot explain all the properties of the cold spot.
Does the cold spot invalidate this? Big Bang? Absolutely not. Is it worth taking a look? Pretty sure. Will we ever finally find out what it is? Maybe not.
That’s how science is. It’s never perfect and there’s always a little thorn in the side of a theory. Sometimes these thorns blossom to reveal new types of TK, sometimes these thorns simply wither as scientists slowly work on them, and sometimes they just stay there, never fully resolved, never fully answered, but never to the point where they are more need attention.
Both are fine for me. Why? Because nothing in this universe is perfect, not even our descriptions of it.