Physicists have long studied the nature of the universe, but some theorists are more interested in understanding the unknown (and perhaps unknowable) realm of what matter is beyond the boundaries of the universe. Could there be other matter out there? The answer is: probably. Here are five theories about the possible existence of "something."
"Beyond the universe" has always been an extremely tricky question, because first you have to define the universe, you have to understand the universe. From this, a common answer emerges, which is called the observable universe, defined by the speed of light. This is defined because our naked eyes can only see light, and nothing in the universe can travel faster than the speed of light.
Because the speed of light is finite, the size of the universe becomes unfathomable. But we can define it using the speed of light, the distance that the most distant beam of light travels to earth. In addition, the redshift phenomenon, which proves that the observable universe is still expanding, is also finite -- because optical telescopes can provide us with the farthest reaches of the universe, a limit sometimes called the Hubble volume. We'll never get beyond the Hubble volume boundary, so for all intents and purposes, it's the only universe we can interact with.
Artists of the observable universe logarithmic scale, with the sun as the center, outward is planets and outer planets in the solar system, the kuiper belt and oort cloud, south gate 2, Orion arm, the Milky Way and Andromeda galaxy, nearby galaxies, fibrous structure of the universe, the cosmic microwave radiation, and is not visible on the edge of the big bang plasma.
Beyond Hubble volume
We certainly know, though, that there are "more universes" beyond Hubble's volume boundary. Astronomers think space may be infinite because the distribution of "matter" (energy, galaxies, etc.) is almost identical to that in the observable universe. If so, it could have some very strange effects on the outer space. Beyond the Hubble volume, you can not only find many more different planets, but eventually everything possible.
If you go far enough, you'll find that humans on Earth in another solar system are just like us in every way, except that you had cereal for breakfast this morning instead of eggs, or that there's one place you skipped breakfast. In fact, cosmologists think that if you go far enough, you'll find another Hubble that's exactly the same size as ours. Maybe there's another version of you, where every move you make affects you 10 to 10^188 meters away. It seems unlikely, but infinity is extremely infinite.
The large-scale structure of the universe in three-dimensional space visualized by the Hubble Volume (sphere). Each tiny dot of light on this scale represents a supercluster. The Virgo supercluster - home to our galaxy - lies at the center of our Hubble volume, but is too small to see in the image.
In 2008, astronomers discovered something very strange and unexpected - star clusters in the Milky Way galaxy flowing in the same direction at a rate of more than two million miles per hour. New observations in 2010 confirmed the phenomenon, which became known as the cosmic undercurrent. This movement defies all predictions about the distribution of mass in the universe after the Big Bang.
One possible reason is that the gravitational pull of a huge structure beyond Hubble's volume exerts a certain influence on the cluster, creating dark currents. This means that the structure of the infinite universe beyond our view is not uniform. As for the structures themselves, they can be virtually any matter, the aggregation of matter and energy on a scale that we can barely imagine, the bizarre distortions of gravity leaking from other universes.
Bubble universe theory
Talking about matter beyond Hubble's volume requires a bit of cheating, because it might still be the same universe, but this part of it might not be visible to us. This part may have the same laws and constants of physics as our universe. In another version of the universe, the expansion of the universe after the Big Bang caused "bubbles" to form in the fabric of space.
Each bubble is a region that stops expanding with the rest of space and forms its own universe, with its own laws of physics. In this scenario, the space is infinite, and so is each bubble (because you can store an infinite number of infinite values in a single infinite body). Even if you could somehow breach the boundaries of our bubbles, the space between them is still expanding, so no matter how fast you go, you'll never get to the next bubble.
Fertility of black holes
A theory developed by physicist Lee Smalling, known as the multiple universe theory, suggests that each black hole in our universe could lead to the formation of a new universe. Each universe has slightly different laws of physics. In this way, Smalling suggests some kind of natural selection for the universe, since the law of the frequent formation of black holes leads to the creation of more universes than the ones of black hole formation, and such universes "die out." This theory has since been disproved (by Smalling himself and others).
There are many theories about parallel universes, but the most popular string theory involves an evolution of string theory ideas involving branes that vibrate in other dimensions. A detailed explanation of string theory or brane theory is beyond the scope of this article, but the conclusion of the whole event is that these corrugated branes in the 11th dimension are whole other universes, and that when the ripples collide with each other, a new universe is formed.
The effects of the ripple motion help explain the distribution of matter in the universe as we now observe it. One of the strangest elements of the theory is that all the gravity we experience in the universe is actually leaking out from another universe in another dimension (which explains why gravity here seems so weak compared to other fundamental forces).