The universe began with a violent and striking explosion, its body dense and foggy orange as the plasma bubbled with an immense amount of heat. In this bright sea that was the beginning of everything, protons and electrons came into contact to create a blinding glow very different from the dark skies we see today.
It wasn’t until 380,000 years later that the first atoms began to form in the cooler temperatures, allowing for the birth of hydrogen and helium which would eventually give way to stars, the beautiful points of light in the universe where carbon, oxygen, and iron are made.
That is, looking back at the broiling, glaring beginning of it all, things were very different from the cooler and tamer space where we live today. But it’s the energy from this chaotic time just a few hundred thousand years after the Big Bang that could be pointing us to something even more extraordinary.
Mapped out, the energy is called the CMB or the Cosmic Microwave Background. This radiation is quite uniform, usually varying no more than 20 microkelvin on any point on the map.
While it was a scorching 3,000 degrees Kelvin when atoms first formed, over 13 billion years of expansion later have left it closer to 2.725 degrees above absolute zero (-454 degrees Fahrenheit or -270 Celsius) across the cosmos.
Expansion has also led to the wavelengths of the light shifting from infrared to microwave, leaving outer space looking transparent and genuinely black to the human eye. But there’s an area of the CMB, called the Cold Spot, that deviates much more than the usual 20 microkelvin. In fact, it’s 150 microkelvin colder than average and spans 1 billion light years across.
The Cold Spot was observed both by WMAP (NASA’s Wilkinson Microwave Anisotropy Probe) and by the Planck satellite, meaning that it wasn’t the product of mere instrumental error.
The Cold Spot is seen here mapped by Szapudi using PanSTARRS and then later as mapped by the Planck satellite. Image by ESA Planck Collaboration.
Is doctor strange in the multiverse of madness same?
Up until early 2017, one of the leading theories as to the cause of the Cold Spot had to do with supervoids. Voids in space aren’t entirely empty; they can host several galaxies themselves but they are much less dense than surrounding regions.
Around the voids, galaxies will come together in enormous walls known as superclusters — the largest objects in the universe. Matter is then drawn to these structures and away from the empty pockets we know as cosmic voids. The Cold Spot could have formed as the CMB radiation traversed one of the supervoids and its properties were then affected by the ISW effect.
This would give the impression that a cold spot existed when there was really none there. The ISW (Integrated Sachs-Wolfe) effect has to do with photons passing through matter-rich or matter-lacking regions of space.
As a photon approaches an area rich in matter, it will receive more energy from the gravity of the matter. Because expansion will have weakened the gravitational pull of the matter dense area by the time the photon is leaving, the photon will then have an energy gain and we’ll see this on the CMB as an increase in temperature.
On the contrary, when photons enter a void they lose energy because the matter-rich regions are pulling them back. While they should regain the energy as they’re leaving, expansion makes the void bigger as the photons are making their way across and so they are ultimately left with less energy and leave that area of the CMB looking much cooler.
So the supervoid theory was based on CMB photons losing energy when they pass through a void, leading this area of the map to appear cold.
Multiverse more on it :
It was a theory first proposed in 2006 and one that seemed to be gaining evidence as in 2015 a study from the University of Hawaii claimed to have discovered a 1.8 billion lightyear void in the direction of the Cold Spot.
However, other teams have since had trouble replicating those results. In a 2017 study, the supervoid theory was refuted by a research group from Durham University who conducted a redshift survey and were able to map 7,000 galaxies in the direction of the Cold Spot.
The survey found 3 large voids — and a possible fourth — but even these voids would only have reduced the temperature by 32 microkelvin and not the 150 microkelvin observed at the Cold Spot. The study from Durham University (led by Ruari Mackenzi and Tom Shanks) gathered spectroscopic data, regarded as more accurate than the photometric data gathered by the team from the University of Hawaii.
Before the switch from analog to digital, a portion of the static seen on TV was CMB radiation. Some in-between stations on FM radios can also pick this radiation up in the form of white noise. Image by DBB.
If it isn’t a supervoid causing this anomaly in the CMB, what is?
It could just be pure chance. According to simulations, a spot like the one observed can happen to 1 in every 50 universes, meaning that we might just happen to exist in a rather special universe. The paper by Mackenzi and Shanks places the odds of such a cold region at 1–2% according to our standard model of cosmology.
But there is a more exciting theory that hasn’t been ruled out: that of the multiverse. This particular idea of the multiverse stems from inflation, the moment soon after the Big Bang when the universe increased rapidly and magnificently in size, a process which scientists use to account for the awe-inspiring size and shape of the universe we see today.
Many versions of inflation say that it is eternal. Once it starts, it continues forever except in small pockets. Our universe would be an example of one of the small pockets — or bubbles — where inflation has stopped.
These normal universes stem from inflation once they have stable vacuum energy. At this point it will begin expanding at a normal rate. If early on our universe bubble bumped into another bubble, it could have left a mark on the CMB, or what we consider to be the Cold Spot. These two universes will merge once they collide and they will exchange energy.
Depending on how distant from us the merger took place, it could look like either a cold or hot spot on the map of the CMB.
According to Professor Tom Shanks, “The craziest sounding of the exotic models of the explanation of the Cold Spot, the multiverse, is actually the most standard in terms of our current model of the universe.”
Random quantum fluctuations could have caused the small variations in temperature seen on the CMB. These will then have blown up in size during inflation.
One of the criticisms against the multiverse theory is that the universe is likely much bigger than what we realize. This puts the odds of another universe colliding into us at an observable part of the sky as incredibly small. Then there is the possibility of human error. Because of the statistical algorithms needed to measure variations in the CMB, anomalies could be due to noisy data. Further observation and data analyzation, namely from the Planck satellite, will either support or disprove theories on the Cold Spot in the future.
For now we exist without answers, peeking out at the radiation all around us and wondering what might’ve formed that cool, lurking spot. Whether caused by a multiverse or not, it exudes a mystery and a challenge to our current cosmological model. While it lends us far more questions than answers, it also allows for our imaginations to run free, presenting us with the wild possibility that yes, maybe we are not alone after all.