By Palak Porwal
In our everyday lives, we have often heard that the ‘universe is expanding’. But have we ever thought about what is the universe expanding into or where exactly is it expanding? Even if we acquire far better telescopes than we use today it will be challenging to explore the edges of our observable universe, because we are limited to information brought to us by light travelling from far off distances.
Many physicist and cosmologists do not allow light to be a drawback for them. From mathematical equations and predictions from pre-existing theories, we have come up with a few outlooks on what may lie beyond the edges of the universe. The most common idea is that our space time is infinitely big with different universes; each with their own las and constants of physics also answers the question of existence of life in our universe. It maybe that in our universe matter combined in just the right proportion for life to exist and in the other universes combination can be different resulting in different configuration of matter and life.
The most discussed idea is that of Bubble universes. Each universe is like bubble floating in a sea of cosmic hyperspace. When these bubbles clash into each other, it may end as a big bang and give rise to a new universe. This is a staggering idea which is testable to some limits. It is believed that past collisions with other bubbles may have left some imprints on the (CMB) cosmic microwave background. Cosmic microwave background is the heat leftover by big bang.
On the other hand, Many worlds theory is the most controversial interpretation. It was proposed by Hugh Everett. It states that each time any choice is made or a quantum measurement ids taken , our universe branches out into several parallel universes, each experiencing its own possible outcome of the decision.
E.g. If you decided to go swimming, at the point of your choice our universe will split into two parallel universes. In one of them you will go swimming and in the other you will not go swimming. According to many worlds theory, there may be a universe where an asteroid did not cause the extinction of the dinosaurs. Propositions like these are extremely questionable as they themselves question the foundations of our physical reality. A theory like this cannot be experimentally approved because the outcome is not in our hands. The reality desired by us maybe portrayed in some other parallel universe. Many worlds may explain the quantum weirdness of the particles, but allowing universe to choose what it wants to show us sounds philosophical and not scientific.
As we have seen, bubble universes and many worlds theory are the leading ideas for what lies beyond the edges of the universe. However, just like quantum mechanics and general relativity, these two are highly incompatible with each other. In bubble universes, new universes are constantly being born through eternal inflation. Inflation was proposed by Alan Guth and later improvised upon by Andrei Linde, which states that within the trillionth part of a second our universe went through exponential expansion and that inflation may slow down in some regions of cosmos but it goes on in the other sections. On the contrary, many worlds theory puts forward that every possibility is materialized. So there might be an alternative of reality here big bang never happened. What are we suppose to believe? If one theory makes big bang the origin of everything that there is and other which proposes that there are alternative sets of realities far from what we can believe.
In 2016, MIW or many interacting worlds was proposed which seems to bridge the gap between Bubble universes and Many worlds theory. It states that our universe is a gigantic number of worlds all together. These parallel worlds are equally real, existing through time with precisely defined properties. The bizarre phenomenon of quantum mechanics arises due to repulsion between nearby parallel worlds. The alternate realities experienced by these parallel worlds are already preexisting. The beauty of this theory is that it allows Newtonian mechanics to stand ground in one universe but gives rise to quantum mechanics when all the universes are combined together.
Reaching into the depth of it, MIW does leave many questions unanswered. In MIW, those physical worlds exist in the same time experiencing the other side of reality. Assuming that they are experiencing the different sides of SAME reality, it means that they have the same origin. Does that mean that one big bang gave rise to those similar parallel universes? Furthermore, these universes behave as if they are connected to one colossal wave function.
How do we imagine these universes? If they are connected to our universe as a result of their origin, then how close are they to us?
There are diverse ways in which these parallel universes can be present in the cosmos. One possibility can be that they are like slices of bread, stacked on top of each other in a loaf of cosmic hyperspace. The repulsive force between them can result in the quantum weirdness in our measurements. Another possibility is that these parallel universes are right here. These universes are hidden from us in dimensions which cannot conceive as our brains our only wired to discern 3 dimensions. It can be that one large dimension contains all these hidden worlds. The repulsive force between these universes separates them and yet binds them together. It also throws light upon the instantaneous effect of this repulsive force on our quantum measurements.
But are forces allowed to cross dimensions? Apparently. Gravity is an example of it. It is present in the 4 dimensional space-time as well as the 3 dimensional world of ours where we notice its effects every day.
The beautiful thing about physics is that through our observations and predictions we come across various forms of information and all we need to do is to connect the dots. Many Interacting worlds and the idea of parallel universes in hidden dimensions is just in its infancy. Scientists at CERN working with the large hadron collider are looking for these hidden worlds. Finding it is like one in a million chances (literally). We are still keeping our hopes up because maybe while hunting for these parallel universes, we come across something even better which helps us to put the pieces of this cosmic puzzle together.
"Confronting the multiverse: What infinite universes would mean?" by Robert Lawrence Kuhn, December 23, 2015 // http://www.space.com/31465-is-our-universe-just-one-of-many-in-a-multiverse.html//
" Many Interacting Worlds theory: Scientists propose existence and interaction of parallel worlds" by the Griffith university , October 30, 2014
"Multiverse collisions my dote the sky" by Jennifer Ouellette, November 10, 2014// https://www.quantamagazine.org/20141110-multiverse-collisions-may-dot-the-sky//
"Quantum World proposed to arise from many Ordinary ones" By Alexandra Witze, October 29, 2014
, March 1985// https://www.scientificamerican.com/article/the-hidden-dimensions-of-spacetime/
”Understanding the hidden dimensions of modern physics through the arts" by Djuna Croon , September 29, 2015