At one point or other in our lives, we have wondered whether our universe is the only one there is or are there other universes forming a Multiverse? Here I will introduce and describe a multiverse theory and try to convince you, however speculative or comic this idea or theory may seem, to take it seriously as it might actually be true! The text may be a bit long, but by the end of it, you might be convinced of the theory.
In the 1990s, two teams of astronomers found, through painstakingly long and tedious observations of many galaxies, that the expansion of our universe is actually speeding up instead of slowing down. This discovery surely won them a Nobel Prize but they raised an associated but difficult question: What force is there that pushes all those galaxies apart at an ever-quickening speed?
Well, the most promising answer comes from Einstein’s theory of general relativity. The generic idea of gravity is the force that brings everything together as an attractive force. However, according to the theory and the corresponding math, if there is an invisible lump of energy like a uniform invisible mist, then the gravity generated by the mist would be repulsive.
REPULSIVE GRAVITY!! This would be precisely what we need to explain the observations! As the astronomers call it dark energy, this invisible energy should be what causes the galaxies to rush away from each other faster and faster. When the astronomers calculated the amount of dark energy that must be infusing the space’ they found a certain but exact number, i.e., 1.38 x 10-123; it posed another question: Does this minuscular technical detail be the gateway to some uncharted realms of reality? Now, the only theory that has come even close to explaining this is the String Theory.
Well, the central idea of string theory is quite simple. When you examine things at the microscopic level, first you’ll find atoms, then protons, electrons, and even further, you find quarks! But if you approach even smaller, the theory says you will find little tiny vibrating filaments of energy. Just like the strings in a violin, these filaments can vibrate in different patterns producing different musical notes that we call particles. All the particles, electrons, quarks, bosons, everything comprises of small vibrating energy filaments. Everything in the world is a part of a Cosmic Symphony that these tiny strings play. It is a very compelling picture, but there is a cost to this elegant unification.
The mathematics of String Theory has internal inconsistencies unless we allow for a totally bizarre idea. Extra dimensions of space! We know about our usual three spatial dimensions: length, breadth, and width. But string theory suggests that on incredibly small scales, there are additional dimensions crumpled to such a tiny size that we cannot observe them. But even if the dimensions are hidden, they can impact the things we can observe because the shape of the extra dimensions constraints how the string vibrates. This vibration determines everything in string theory, including the mass of particles, the strength of forces, and, ultimately, dark energy. So, the total amount of dark energy can be determined by the shape of the extra dimensions! There rises another problem. We don’t know the shape of extra dimensions.
When this idea was first developed, the math allowed for about five shapes for the extra dimensions. But gradually, this list increased to thousands to millions of shapes. Until recently, the list has soared to an incredible number, 10500. Looking at this number, many scientists gave up, saying the string theory would never give definitive test results. But some brave and crazy scientists turned this over the head.
Here comes the idea of a Multiverse Theory. It suggests that maybe all these candidates are on equal footing and are as real as the other, in the sense that there are many universes, each with a different shape for the extra dimensions. However radical this theory may be, it profoundly impacts that mysterious number of dark energy observed by the astronomers. If there are other universes, and if they have a different shape for the extra dimensions, then each universe’s physical features will be fundamentally different, including the amount of dark energy. This means there is not just one number that we are trying to solve using our laws of physics, but there are many numbers, each corresponding to a different universe. Hence, the pertinent question is: Why do we humans find ourselves in a universe with a particular amount of dark energy that we have measured but not any other universe with a different amount of dark energy?
Now since we are speculating the possibility of other universes, we need a mechanism that generates these universes. Cosmologists have found such a mechanism while trying to understand the Big Bang. The Big Bang theory provides many clues about how the universe evolved after the “Bang” but doesn’t give any insights on what powered the “Bang” itself. This gap can be filled by an upgraded version of the big bang theory called inflationary cosmology. It identifies a particular kind of fuel that would naturally generate an outward rush of space, based on the concept of quantum fuel. The fuel is supposed to be so efficient that there is no possible way to use it all up. Thus, the big bang of our universe was not likely a one-time event! The fuel not only generated our big bang, but it would also generate countless other “big bangs,” each giving rise to its own separate universes with our universe becoming one bubble within a grand cosmic bubble bath of universes!
Now the last and big question remains, that is, will we ever be able to confirm the existence of these other universes? Well, here’s an idea of how we can detect other universes. After the big bang, when the universe expanded quickly, small tiny quantum jitters from the micro-world stretched into the macro-world, leaving a particular radiation print. Cosmologists have already discovered this and call it the Cosmic Microwave Background. As the inflationary theory predicts, there are countless bubbles of universes; it is very likely for these bubbles to collide with each other. This collision would generate a subtle pattern of radiation and temperature variations across space that we might, one fateful day, be able to detect. If you ask me, who knows, the “Cosmic Microwave Background” we detected might already be the energy print of collision between our and another universe with no way to prove its confirmation.