For decades, astrophysicists have studied various aspects of the universe. From black holes to the origin of the universe itself. But some have gone even further to know the unknown or the incomprehensible. Is it possible that something exists even outside the universe?
To answer this question, we must first define the universe. In most cases, the word "Universe" means the observable Universe, the region with all the matter that can be observed from Earth at the present time. It is determined by the speed of light.
The word "observable" here does not mean the ability of modern instruments to detect light from a distant object, but a physical boundary determined by the speed of light itself. Since nothing can travel faster than light, we cannot observe anything further from the Earth than the light that has reached us since the beginning of the universe (13.7 billion years).
According to calculations, the diameter of the observable universe is about 93 billion light years, or 28.5 gigaparsecs. Now the question arises, how the diameter of the universe can be 93 billion light years if the age of the universe is only 13.8 billion years?
Let's figure it out … According to Hubble's law, the most distant regions of the universe are expanding faster than the speed of light. On the other hand, special relativity tells us that objects cannot move faster than the speed of light relative to each other. It turns out that not objects move faster than the speed of light, but the very space between them.
Thus, if you move faster than the speed of light in a straight line to the edge of the universe, will you see the edge of the universe? The answer is no, because the universe has no boundaries. We know that our universe is isotropic and expanding, but where is it expanding?
Multiverse theory
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Imagine that our cosmos is actually one universe in the multiverse, where each universe is like a soap bubble floating in the void of the multiverse. Each bubble expands from its own Big Bang, and they also have their own laws of physics. It may sound crazy, but..
If by chance two of these soap bubble universes come close enough and begin to interact with each other in such a way that the second universe is discovered from within the first universe, we can obtain evidence of this hypothesis. Astronomers have actually watched the cosmos looking for any sign that might confirm our universe is interacting with another universe, and they have indeed found something special.
After examining the cosmic microwave background, scientists noticed temperature fluctuations in different regions. While most of these temperature fluctuations are attributed to modern cosmological theories, there is one region known as the "cold spot" that does not fit any of all existing theories.
Relic Cold Spot or Eridanus Supervoid.
For some strange reason, the “cold spot” is about 70 MCK (microkelvin) colder than the average temperature of 2.7 K. While this may be the norm in a small area of space, the cold spot covers a huge region that is one billion light years … It is located in the Southern Hemisphere (do not confuse it with the southern hemisphere of the Earth) in the direction of the constellation Eridanus. Many researchers call this the "cosmic axis of evil"
To explain the "cold spot", astronomers have come up with several theories or hypotheses. One such hypothesis is the Supervoid hypothesis, which suggests that this anomaly is caused by the presence of a huge void between us and the cosmic microwave background in this direction. Another possible explanation is the cosmic texture hypothesis.
But the most fantastic and most controversial of all hypotheses is that the “cold spot” is actually caused by a collision between our universe and another universe, and the spot is located exactly where the universes interact with each other. Recently, this hypothesis has received some justification …
In 2017, Professor Tom Shanks of Durham University stated in his article that Supervoid is unlikely to explain a “cold spot” of this size. He added that while we cannot rule out other explanations provided by the Standard Model, in a situation where they too cannot provide answers, we should consider a more exotic explanation - the collision of our universe and another bubble universe.