The remaining light from 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 largely agree it's worth investigating.
The cosmic microwave background (CMB) was created 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 Kelvin (17,500 degrees Fahrenheit or 9,700 degrees Celsius), meaning all the gas was plasma. If the universe expanded, cooled and the plasma became neutral. This released a flood of white-hot light. Over the billions of years since, that light has cooled and stretched to a temperature of about 3 Kelvin (minus 454 F, or minus 270 C), putting that radiation firmly in Earth's microwave band. electromagnetic spectrum.
The CMB is almost perfectly uniform, but there are small temperature differences up to about 1 part per million, and those imperfections, which look like spots of different shapes and sizes, are the juiciest part of it. We cannot predict exactly what the fluctuations will be, which exact spots will be cold and which spots will be hot. That's because the light we see comes from a part of the universe that is now hidden from observable view.
Related: The first light that floods the universe could help unravel the history of the cosmos. Here's how.
This means we have to rely on statistics to understand the CMB. We can't tell which spots will appear where; we can only use physics to understand the average size of spots and how warm or cold they can be on average.
The cold place
Just about everything with the CMB is fine and dandy. We understand where the spots come from and over the decades we have built increasingly sophisticated telescopes satellites to see it better. In fact, the detection and measurement of the CMB is one of the greatest success stories in science.
And then there's the cold spot.
Now there are many cold spots in the CMB. But there is one - the cold spot - that stands out. Visually it is even noticeable. 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 is down and a bit 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 is about 70 microkelvins colder than average, compared to the average regular cold spot which is only 18 microkelvins colder than average. In the deepest parts it is 140 millikelvin colder than average.
It's also big: about 5 degrees across, which doesn't sound like much, but that's about 10 degrees. full moons arranged next to each other. The average spot on the CMB is less than 1 degree. So it is not only strangely cold, but also strangely large.
This is where it gets tricky. It's easy to see the cold spot. Astronomers noticed it for the first time NASA's Wilkinson Microwave Anisotropy Probe in the early 2000s, and the European Space Agency 's Planck satellite confirmed the existence of the cold spot. So it wasn't just a fluke of the instrument, a measurement error or some strange alien interference - it's real.
This leads to another question: do we care?
We cannot say with certainty which spots on the CMB will appear where; we only receive statistical information. There has been a lot of back and forth on this, but the general consensus is that we should not reasonably expect the cold spot to be so large and so cold merely by random chance, based on our understanding of physics. of the past universe, it's just way too excessive.
Yes, big and cold spots should appear randomly every now and then, but the chance of us seeing one purely randomly is less than 1% (and could be much lower depending on who you ask). So while we can just say we've been super unlucky and caught a cold spot, it's rare enough that it requires a little more attention.
So it is not a measurement error and probably not a coincidence. So what is it?
The hot debate
The favored explanation for the strange nature of the cold spot is that it is due to a gigantic cosmic void that lies between us and the CMB in that direction. Cosmic voids are large chunks of almost nothing. But despite that, they do not affect the CMB light, and that is because the cavities evolve.
When light from the CMB first enters a void, 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 as it leaves the other side. But because the voids change, when the light first enters the void can be relatively small and shallow time it leaves, the emptiness is large and deep.
This leads to an overall energy loss from CMB light traversing the void - a process known as the integrated Sachs-Wolfe effect.
So a gigantic void could possibly explain the cold spot, but there's one problem: we don't know for sure if there actually is a gigantic void in that direction. We have maps and surveys of galaxies in that part of the sky, but they are all incomplete in some way; they do not include every galaxy, or they do not cover the entire volume of the supposed void. Again, there has been a lot of back and forth in the literature, with some groups claiming to identify a supervoid, while others said there was nothing special going on.
And even if there were a supervoid in that direction, it's not clear that it would have a strong enough effect to create the cold spot we see.
This ambiguity leaves room for some out-of-the-box proposals, such as the idea that the Cold Spot is a remnant intersection between our universe and a neighboring universe. But even that hypothesis cannot explain all the properties of the cold spot.
Related stories:
- 'Wiggles' of energy waves across the Earth could hold the history of the universe
- Listen to the void: why the cosmic nothingness has so much to say
-The History of the Universe: The Big Bang to Now in 10 Easy Steps
Makes the cold spot the Big bang? Absolutely not. Is it worth watching? Almost certainly. Will we ever finally find out what it is? Maybe not.
That's what science is like. It's never perfect, and there's always a thorn in the side of a given theory. Sometimes those thorns bloom to reveal new forms of TK, sometimes those thorns simply wither away as scientists slowly fall away from them, and sometimes they just sit there, never fully resolved, never fully answered, but never rising to the level that they are more need. attention.
Anyway, it's okay for me. Why? Because nothing is perfect in this universe, not even our descriptions of it.
