The remaining light of the young universe has a major flaw and we don’t know how to fix it. This is 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 investigating.
THE cosmic microwave background (CMB) was generated when our universe was only 380,000 years old. At the time, our cosmos was about a million times smaller than it is today and had a temperature of more than 10,000 kelvins (17,500 degrees Fahrenheit or 9,700 degrees Celsius), meaning that all the gas was plasma. As the universe expanded, it cooled and the plasma became neutral. As he did so, he released a flood of white-hot light. Over the next billion years, this light cooled and stretched to a temperature of about 3 kelvins (minus 454 F or minus 270 C), placing this radiation firmly in the band of microwaves from the atmosphere. 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 various shapes and sizes, are the juiciest part. We cannot predict exactly what the fluctuations will be, which specific places will be cold and which places will be hot. This is because the light we see comes from a part of the universe that is now removed from observable view.
Related: The first light that floods the universe can help elucidate the history of the cosmos. here’s how.
This means we need to rely on statistics to understand CMB. We cannot say which spots will appear where; we can only use physics to understand the average size of spots and how hot or cold they are on average.
The cold spot
Pretty much everything with the CMB is fine. We understand where the spots come from, and over the decades we have built more and more advanced telescopes and telescopes. satellites To see better. In fact, the detection and measurement of the CMB constitutes one of the greatest scientific achievements.
And then there is the cold spot.
There are now many cold spots in the CMB. But there is one… THE cold spot – this stands out. It even stands out visually. If you look at a map of the CMB – where the entire sphere of the sky is compressed into a strange, vaguely oval shape – it’s down and a little to the right. In the sky, it is towards the constellation Eridanus.
The cold spot is strangely cold. Depending on how you define the edge of the spot, it’s about 70 microkelvins colder than average, compared to the regular average cold spot which is only 18 microkelvins colder than average. In its deepest parts, it is 140 millikelvins cooler than average.
It’s also large – about 5 degrees in diameter, which doesn’t sound like much, but it’s about 10 degrees. full moons lined up side by side. The average spot on the CMB is less than 1 degree. So it’s not only strangely cold, but also strangely big.
This is where things get complicated. It’s easy to see the cold spot. Astronomers first spotted it with NASAof Wilkinson Microwave Anisotropy Probe in the early 2000s, and the European Space AgencyThe Planck satellite confirmed the existence of the cold spot. So this wasn’t just a fluke of the instrument, a measurement error, or some strange extraterrestrial interference – it’s a real thing.
This brings us to another question: do we care?
We cannot say for sure which spots on the CMB will appear and where; we only obtain statistical information. There’s been a lot of back and forth on this, but the general consensus is that yes, we shouldn’t reasonably expect the cold spot to be this large and this cold simply by chance, but based on of our understanding of physics. from the previous universe, it’s just too off.
Yes, random large, cold spots should appear from time to time, but our chances of seeing one by pure chance are less than 1% (and can be much lower, depending on who you ask). So while we can just say we were very unlucky and had a cold spot, it’s rare enough that it requires more attention.
This is therefore not a measurement error, and it is probably not the result of chance. So what is it?
The burning debate
The preferred explanation for the strange nature of the cold spot is that it is due to a gigantic cosmic void located between us and the CMB in that direction. Cosmic voids are large patches of almost nothing. But despite this nothingness, they influence CMB light, and that’s because voids evolve.
When CMB light first enters a vacuum, it gains some energy as it transitions from a high-density environment to a low-density environment. In a perfectly static universe, light would lose an equivalent amount of energy on its way out the other side. But because voids change, when light first enters, the void may be relatively small and shallow, and therefore, time it leaves, the void is big and deep.
This results in an overall loss of energy from CMB light passing through the vacuum – a process known as the integrated Sachs-Wolfe effect.
So a giant void could potentially explain the cold spot, but there’s a problem: we don’t know if there actually is a giant void in that direction. We have maps and studies of galaxies in this part of the sky, but they are all incomplete in one way or another; Either they do not capture all the galaxies or they do not cover the entire volume of the supposed void. This too has been the subject of considerable discussion in the literature, with some groups claiming to identify a supervacuum and others claiming there is nothing special about it.
Additionally, even if there were a supervacuum in that direction, it’s not clear that it would produce a strong enough effect to create the cold spot we see.
This ambiguity leaves room for original proposals, such as the idea that the cold spot would be a residual point of intersection between our universe and a neighboring universe. But even this hypothesis fails to explain all the properties of the cold spot.
Does the cold spot invalidate the big Bang? Absolutely not. Is this worth investigating? Almost certainly. Will we ever be able to definitively understand what it is? Maybe not.
This is what science is like. It’s never perfect, and there’s always a little thorn in the side of a theory. Sometimes these thorns bloom to reveal new types of traditional knowledge, sometimes these thorns wither as scientists slowly gnaw at them, and sometimes they just sit there, never fully resolved, never fully answered, but never reaching the level where they need more. attention.
Either way, I’m fine with it. For what? Because nothing is perfect in this universe, not even our descriptions.