The Multiverse Is (Un)Real
How is our universe fine-tuned for life? Is it just a random occurrence or is our universe an isolated entity in the multitude of bustling universes?
You might have wondered about the vastness of space, whether it has an edge, how far it extends, and what lies beyond it. With the recent focus and discussions in contemporary science and mainstream media, the term “multiverse” is no longer a science fiction but conventional wisdom.
What about another “you” in an alternate reality? He would have started reading this article at the same time as you. But, unlike you, that person has reached this web page accidentally and is now thinking to move on, not wanting to know in detail about the multiverse, and is not even bothered to finish this sentence. On the other hand, this earthly “you” has decided to continue reading.
Your alternate reality persona also resides in the same city, same country, and the same planet, revolving around the same 4.5 billion-year-old yellow dwarf star. He/ She is identical to you in almost every aspect till the moment you decided to continue reading this article while that person chose otherwise. That exact moment branched out into two separate universes with their own unique realities.
I can understand this to be baffling.
Astonishingly, it is a prediction of the fusion of two widely accepted theories in physics – String Theory and Eternal Inflation. Eternal inflation is a concept that emphasizes the ever-growing and expanding universe without coming to a halt, thereby creating different regions of space or pocket universes.
On the other hand, String Theory draws attention to the local physics being different in all those regions. For example, there could be different kinds of elementary particles, different values of fundamental forces, or different fundamental forces altogether, and where even life could be grossly dissimilar or may not exist at all.
A Historical Perspective of the (Expanding) Universe
In 1920, a debate took place at the Natural History Museum in Washington D.C. The focus was determining the scale of the universe. At the center stage were two astronomers, Harlow Shapley, and Heber Curtis. Shapley opinioned that the universe was much smaller, and the spiral nebulae were nearby gas clouds. Along with all the stars in the Milky Way, they comprised the entire universe.
Curtis, on the other hand, argued that the universe was much larger in size, and the spiral nebulae were other galaxies light-years away. In their respective models, Shapley put the Sun far away from the center of the Milky Way, while Curtis placed the Sun near its center.
Along came Edwin Hubble, who in the mid-1920s was studying the Cepheid variable stars in the Andromeda Galaxy. A Cepheid variable star is a star whose brightness varies with a regular beating pattern. Fainter stars beat rapidly while brighter stars beat slowly. By observing those stars, Hubble was able to determine the time taken by them to beat, which, in turn, helped in deducing their luminosity, thereby calculating how far they were.
This observation helped in determining that the Andromeda galaxy was far more distant than what Shapley had proposed. Accordingly, the viewpoint shifted towards the universe being much vast, containing many galaxies located far out in space.
Multiverse as a Consequence of Inflationary Cosmology & String Theory
Edwin Hubble also discovered a major event in cosmology – the universe was expanding and accelerating more than the speed of light itself! The farther away the galaxies were, the faster they were receding.
Anything that expands follows from a natural progression of being smaller and denser than in the past. Extrapolating farther back, we reach a point in time that was uniform and hotter than the present situation, famously known as the Big Bang.
Unfortunately, there is a limit up to which the backward extrapolation works beyond which the predictions of the Big Bang start breaking down. A theory proposed by Alan Guth called “Inflation” overcomes the shortcomings of the Big Bang theory.
According to Inflation, the Universe did not contain matter or radiation before the Big Bang. Rather, it was brimming with enormous energy - energy in its pristine form inherent to space itself. That energy density was about 10^25 times greater than what dark energy is today. It caused the universe to expand at a colossal rate. At some point, the inflation ended and all the energy got transformed leading to the Big Bang.
An important point to note here is that Inflation, as a whole, does not come to a halt everywhere at once. It surely ends at locations that are separated from other regions, among which the space continues to expand. Any two such regions are physically disconnected from each other and hence cannot be in contact. However, Inflation, in itself, whenever and wherever it starts, continues for an eternity, and wherever it ends, it culminates into a Big Bang. This is the scenario of the “Eternal Inflation” theory. So, in summary, there could be multiple Big Bangs occurring in separate regions of space, each one leading to a universe of its own.
String Theory, which removes the mathematical inconsistencies between the theory of the large entities (governed by the Theory of Relativity) and the theory of the small things (governed by Quantum Mechanics), postulates that the entire universe can be explained in terms of “minute strings”. These “strings” can vibrate in a total of 11 dimensions – ten of space and one of time. Since we are limited by the four dimensionalities of spacetime, we cannot observe or interact with higher dimensions. It also predicts a multitude of spacetime instances, amounting to more than 10^500, popularly known as the “String Theory Multiverse” or the “String Theory Landscape”.
Life and Multiverse
Our universe seems to be fine-tuned for the formation of life, at least in this part of the galaxy (life in other regions of the observable universe is still to be discovered). The numerical constants present in the laws of nature make one wonder about their values being what they are and not any other number.
For example, the gravitational force which holds together larger bodies, if it was too weak, planets, stars, and galaxies would not have formed. If it was too strong, stars would have burned up too quickly. The electromagnetic force, if it was much stronger or weaker, any chemical bond would have ceased to exist. If the strong nuclear force was weaker, the universe would not have stable chemical elements essential to life. Similarly, if the weak nuclear force was stronger or weaker, stars could not have formed.
The cosmological constant which limits the expansion of the universe needs to be close to zero, balancing out the attractive force of gravity with the repulsive force of space (dark energy). It needs to be fine-tuned to something like 1 part in 10^120. If it was slightly less, the universe would collapse, if slightly more, the universe would fly apart.
These constants point us to a fundamental statistical question – What is the probability for the aforementioned constants to have the value that they possess for complex life to form and evolve? Well, in a single universe, the probability is almost negligible. But in a sea of universes, the probability becomes significant. In an eternally inflating universe, there is a chance that one of the universes would be similar to ours.
Consider this analogy – shuffle a deck of cards and you arrive at a combination of cards in a particular order. Given enough time and infinite permutations, it is almost certain that the same combination, in the same order will appear again. So, given infinite universes, a universe in which life can form will form. The multiverse inherently explains the reason for our existence, and our existence, in turn, makes the multiverse conceivable.
Is Multiverse Real?
Considering the theories and their probable predictions, the multiverse seems inevitable. But here comes the beauty of science. It has always relied on testability – the grueling process of undergoing numerous tests, hypothesis generation, being reviewed by peers and institutes of repute, and then culminating into a law. These steps entail legitimate proof in place rather than following some wild speculations.
However, this doesn’t mean that the present theories can be falsified based on the absence of any evidence. About 100 years ago, a black hole was also a prediction of mathematics of Relativity theory and we had to wait for a century to finally have proof of it and consider it in mainstream physics. Likewise, the multiverse too can be a figment of our reality, it’s just that we might have to wait for some time, maybe much longer, for any evidence to support its existence.
Until then, keep on doing what you need to do in this reality, as your doppelganger would already be doing things you could not have done because of the splitting of the universe every time a conscious decision was made. And if you have loved and lost in this reality, in a parallel world, you have loved and won too – and this can be soothing as love, like the universe, cannot be bounded, is eternal, and it just requires perseverance.
This post was originally published on https://primitiveproton.com/