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Introduction
In the last few centuries, our understanding of universe has grown by leaps and bounds. Before seventeenth century, people generally believed that the Earth is at centre of the universe and all heavenly bodies move around the Earth. Galileo challenged the idea and published his papers in support of Copernican heliocentric theory that the Earth and other planets move around the Sun. Our understanding of universe grew further. We realized that the Sun is not unique and there are hundreds of billions of stars in the galaxy, which are brighter and bigger than the Sun. We came to know that there are many galaxies in the universe beside the Milky Way. Hubble’s law first showed that our universe is expanding. With the Hubble Space Telescope and the Very Large Telescope on Paranal Mountain in Chile, astronomers look into farthest reaches of the sky. The Large Hadron Collider at CERN provides new insight to subatomic particles and untangles the riddles of quantum world. Brain Greene, while introducing the concept of multiverse at World Science Festival on June 13, 2013, explained that the key concepts behind all these concepts are gravitational force. Newton gave inverse square law of gravitations through simple equation in seventeenth century. The law describes force of attraction between two bodies but fails to explain how the objects exert the attractive force. Einstein explained that through General Theory of Relativity in 1915. He proposed that space-time is curved by matter, and that free falling objects move along locally straight paths in curved space-time.
The Big Bang theory describes beginning of the universe. In its simple form, it explains that the universe started with a small singularity and then it inflated over 13.8 billion years to present state. It is based on mathematical theory and models. The temperature was very high in the range of 5.5 billion Celsius in the first second after the universe began. It was made up of neutrons, protons, electrons, positrons, photons, and neutrinos. As the early universe expanded, the gas, which made it up, started to cool. The temperature dropped and eventually reached the state where electrons combined with nuclei to form neutral atoms. The afterglow of the Big Bang known as cosmic background radiation can be detected today (Wallack 2014). The cosmic microwave background radiation reveals the state of universe at a very early stage. The Wilkinson Microwave Anisotropy Probe (WMAP), a NASA Explorer mission, has measured the difference in temperature of the CMB. It has found that the CMB radiation has almost exactly the same temperature in all directions over the sky. The Big Bang theory describes expansion and cooling of the early universe, formation of light chemical elements and formation of stars, galaxies and cluster of galaxies. It does not explain the cause of the expansion and source of matter. Cosmic Inflation explains both these phenomena. The general relativity and modern particle theories predict that gravitational repulsion is created at extremely high energies. A patch of repulsive gravity material that existed in the early universe created the gravitational repulsion required for the Big Bang. The expansion was exponential and lasted probably 10-35 seconds. The repulsive material being unstable decayed. Expansion of the repulsive gravity material caused more and more material/ energy to appear. As the energy of a gravitational field is negative, total energy was conserved (Alan Guth 2013).
The light energy reaching us gives the clue to the creation and existence of universe. NASA’ space telescope SWIFT detected strong gamma ray burst (GRB) in April 2009, which is estimated to be 13.1 light years away. This means the event that is being observed now, occurred 13.1 billion years ago. Considering age of the universe as 13.7 billion years, this is the farthest incident of universe that has been seen (Mathew 2014, 28). We can almost look back to the beginning shortly after the Big Bang happened 13.7 billion years ago to the edge of the observable universe but we can see no further to the space beyond that distance known as Hubble radius. Actually, because of expansion of space after the Big Bang, the astronomers are able to see out to a distance of about forty two billion light years. Anything located beyond that is unknown. However, that does not mean there is nothing beyond, rather the universe goes far beyond our observable range (The Economist 2015).
Max Tegmark, one of the leading proponents of multiverse, has suggested four levels of multiverse. First level multiverse is extension of observable universe. Some theories suggest that the universe extends far beyond the Hubble radius, may be billions times further. Some theories suggest it stretches to infinity and there are numerous isolated universes cut from one another by their Hubble radius. Each of the Level I universes are same as our universe and same physical constants and physical laws govern these universes. They only differ in initial arrangements of matters.
Level II multiverse emerges from the theory of cosmological inflation. The universe is expanding exponentially. Inflation once starts never stops. The inflating volume increases with time. However, the inflating material decays and pocket or bubble universes are produced that grow exponentially. Each of them evolves into Level I multiverse. One inflating bubble develops other inflationary bubbles in never ending chain reaction. Thus, infinite number of bubble universes are formed (NOVA PBS 2014). Bubbles are separated by empty space and are disconnected. Level II multiverses are more dissimilar than level I multiverses. Beside initial conditions, level II multiverses differ in qualities of elementary particles, physical constants used in physical laws and dimensionality (Tegmark 2003a, 44). They may have different gravity or periodic table of elements.
In level III multiverse, laws of physics are same as in the first level. However, component universes are separated not by distance but by time. At every moment within such a multiverse, all of the possible future allowed by the uncertainties of quantum mechanics is actually happening. Quantum mechanics is not a predictive theory. It is a probabilistic theory. It says, for example, a photon strikes a polarizer at 45 degrees to the angle of polarization. It has a 50 percent chance of going through or a 50 percent chance of not going through. There is no way of knowing, which possibility is going to happen. One interpretation of quantum mechanics explains that when the photon hits the polarizer at 45 degrees, there is actually two futures that can happen. One in which it goes through the polarization and one in which it does not. One treats as it continues as if the other future is not there. In the many worlds theory of the multiverse, the entirety of the universe act like the quantum photon but instead of having two potential future states, every possible outcome is manifested. Our entire universe and everything within it including us will be constantly undergoing multiple fissions into daughter universes each with its own reality and future. Any given observer though would only see one outcome.
Level IV is mathematical multiverse. Dr. Tegmark proposes that all coherent mathematical systems describe a physical reality of some sort. Those different systems are of necessity for different universes. Tegmark rests level IV parallel universe on two separate assumptions: one that the physical world is mathematical structure and second that all mathematical structures exist in physical sense (Tegmark 2003b, 14). Many scientists are not comfortable with this idea. How the idea translates into practice is hard to conceive of and seems more to be in the realm of metaphysics. Other three type of multiverse push the boundary of physical theory, but it did not overstep them. Observational data supporting the theory of inflation has convinced some scientists that a multiverse is possible. However, the idea of multiverse remains highlyl controversial. It may be impossible to ever directly observe the multiverse but some scientists hope to gather enough data supporting the theory (The Economist 2015).
Multiverse can be explained from four perspectives: scientific, Philosophical, theological and fictional prospective. Each perspective has been described below.
Scientific Perspective:
Applying the idea of Quantum mechanics, Hugh Everett first suggested the notion of multiverse in his doctoral thesis in 1973. In the last two decades, much theoretical works have been carried out in this direction to make multiverse one of the most exciting and debatable topic of cosmology. As per Dr. Tegmark, multiverse is not theory rather it comes out from prediction of certain theories (Vilenkin, and Tegmark 2011). Level I multiverse is produced by inflation. Level II multiverse is produced by adding string theory with a landscape as possible solutions. Quantum mechanics in its simplest form gives Level III multiverse. If these theories are proved false, these multiverses will collapse. Inflationary model of universe has solved the shortcomings of the Bing Bang model of evolution of universe. The cosmic background radiation has been found to be almost uniform in temperature. CBM was released when universe was about 400,000 years old. Standard cosmology can not explain this. In inflationary model, the universe starts extremely small for uniformity to establish. Inflation stretches the region to be large enough so that visible universe is part of it. Small-scale non-uniformity has been observed in the cosmic background radiation. Inflation attributes these ripples to quantum fluctuations. CMB observations has also found space to be flat. Inflation by rapid stretching of space makes the space flat and uniform like an expanding balloon.
There is one idea of string theory that attempts to unify general theory of relativity and quantum mechanics. All of the solutions produced by string theory that do not match up with what we can see in our own universe, may actually represent reality in other universe. Basic idea behind level II multiverse is that the different solutions of string theory control the environment in these different regions. If we are in the multiverse where the different constituencies are governed by different physical laws, a concept of anthropic selection has to be introduced. Most of the multiverses would be sterile or stillborn because the laws governing them would not allow complexity to emerge. The anthropic principle is the idea that our universe is fine-tuned to allow humans to live. As an example, a small change in the strength of gravity and life as we know, would not exist. We are living in one within the infinite number of universes.
The existence of level III multiverse is based on one crucial assumption that evolution of the time of the wave function is unitary (Tegmark 2003b, 9). This crucial assumption have been tested and no violation has been detected. Presently, quantum computers are being built employing this principle. Their success will provide further evidence of level III multiverse. Level IV multiverse has been conceptualized unifying general relativity and quantum field theory. Developments in this field may proof or disproof the assumptions of level IV.
Philosophical Perspective
Before scientific revolution, the separation between science, philosophy, and theology were not well distinguished. However, the Copernican heliocentric theory came into direct contradiction to Biblical interpretation of universe. Since then, the separation between science and religion has grown and they have moved into separate domains. Science tries to solve for mystery of nature by the process of induction and deduction supported by empirical evidence. Science is also prone to overstepping its boundaries and that is where philosophy steps in. Philosophy tries to expose the flaws in the scientific processes employed.
George Ellis questions the absence of scientific evidence behind the theories of multiverse (Ellis 2011, 6). As per him, multiverse is more of a concept than theory. Scientists have provided theoretical explanation in place of observational testing. In last few centuries, science has made phenomenon progress because it has grown on solid evidence. As of now there no solid evidence to proof existence of multiverse. Multiverse may exist or may not exist. Ellis says this as “scientifically based philosophical speculation” (2011, 6). Many physicists have also questioned its legitimacy as scientific inquiry in the light of its exclusion from experimental verification. This could damage the study of fundamental physics.
Science is rational and explains the world in objective terms. The laws of nature limit it. The idea of many universes has traditionally been subject of philosophical discussions. However, physical cosmology has made rapid progress in last hundred years and in view of Tegmark, the line separating philosophy and physics has shifted drastically and parallel universe has now come under realm of physical discussion (Kragh 2009). The debate on multiverse has been related to relationship between physical cosmology and philosophy. It centres around the criteria of testability of multiverse theories. Many physicists including cosmologists argue that though these theories are beyond falsifiability test, they qualify good science.
Theological Perspective
Proponents of multiverse believe in the idea of natural theology and consider it as an alternative to the belief that God created the world. Some theists consider that the multiverse stands in sharp contrast to Christian belief. It has also been argued that almighty God is creator of all the universes. Mormon theology that differs from traditional Christian theology, has found the concept of multiverse in consonance to their beliefs (Halvorson, and Kragh 2013).
The concept of multiple universes has been mentioned in Hindu mythology. Purana, Hindu scripture written in Sanskrit, describes coexistence of different worlds. Human beings are ruled by kings on the material earth. Gods live in different worlds that are situated in different planes. Brahma, Vishnu and Shiva, the triumvirate, have the highest hierarchy among divinity. Brahma is the creator, Shiva is the destroyer of the world, and Vishnu upkeeps the world. The human world is not real. It is the dream of the Brahma. All things emanate from Brahman and finishes in Brahman. Brahman is not created, nor destroyed. It is infinite and all embracing. In Hindu philosophy, universe is in a state of never ending evolution where cycle of creation and destruction continues ceaselessly (Mathew 2014, 24-25). Vishnu Purana describes Vishnu as sleeping in his heavenly abode. There are bubbles rising around him and each bubble is a universe. Bhagavata Purana also contains lines that mention of innumerable universes.
Frictional Perspective
The concepts behind the multiverse or parallel universe, the big bang, or string theory are very difficult to comprehend for general people. However, now kids as well as grown up are not intimidated by these terms since books, comics, television serials, or movies have made these terms and concepts popular among us. In most of cases, especially TV serials and movies have provided us with superficial knowledge. They may be based on scientific knowledge but most of the time, deviate to the realm of absurdity from scientific perspectives. Do these harm in growth of scientific temperament? No, they help in growth of scientific temperament. Instead from being apprehensive, they make us inquisitive to know more about these concepts. Science behind the Big Bang theory may be very difficult to understand but term ‘big bang’ has become popular from the TV series of the same name.
We read about Alice falling through a rabbit hole into a fantasy world in the novel ‘Alice’s Adventure in the Wonderland’. The rule of law in this fantasy world is different from our real world. When we read about parallel world, we imagine the story of Alice though science says we cannot move between parallel universes. Bulukiya in ‘One thousand and one nights’ goes to alternative worlds, which are similar but distinct from his own world. ‘The Chronicles of Narnia’ is a series of popular fantasy novels written by C S Lewis where main protagonists are transported to other world of talking animals. Children as well as adults get to know about alternative or parallel world through fantasies.
There have been many sci-fi television serials where parallel universe has been depicted. Take the episode of Inferno from television serial Doctor Who. Doctor Who visits alternate universe in his Tardis. Alternate world is similar to original world but there are subtle differences like Hitler has won the war or there is no monarchy in Britain. In the television serial Sliders, a group of people slides in and out of different universes. Each alternate universe has some differences to original world like the Earth’s rotation around the Sun is slower.
The parallel world has been depicted in more scientific basis in science fiction books. H.G.Wells wrote ‘Men Like Gods’ based on multiverse theory. In ‘The Gods Themselves’, Asimov creates a condition where small amount of material is imported from an alternate universe where physical laws are different with disastrous consequences. In the ‘The End of Eternity’ Asimov creates multiple interacting universes separated by time. The eternals can time travel to different universes and make changes. Any change made in the earlier universe affects future universes.
Conclusion
Recent discovery of a transient gravitational waves signal produced by two colliding black holes has far-reaching implication on understanding the universe. We can see back of universe forming to around 13 billion years. We cannot see first few million years after the origin of universe, as the early universe was not transparent to light. Further, light interacts with matter and gets distorted by refraction and reflection. Propagation of gravitational waves through cosmos is unhindered of any interference. Thus, discovery of gravitational waves will allow new insight into the formation of the origin.
The scientific theories of parallel universe are highly controversial. Impressive improvement in cosmological measurements is expected in coming decades. The new findings will support or refute the theories that predict a multiverse. The four level of multiverse are hierarchical. If level I is found to be false, all subsequent levels will also fail. Observational evidence against chaotic inflation may be found, or mathematical or empirical inconsistency may force theorists to abandon the landscape of string theory. The multiverse theory is still in its infancy and is evolving. Future holds lot of promises. New evidence will prove or rule out the multiverse theories.
References
Ellis, George F.R. August 2011. “Multiverse Really Exist?” Scientific American. www.sciam.com. Accessed March 20, 2016. http://www.scientificamerican.com/article/does-the-multiverse-really-exist/.
Guth, Alan. 5 September 2013.” Is Our Universe Part Of A Multiverse.” YouTube video, 1:11:30 Posted 11 Nov 2013, https://www.youtube.com/watch?v=dhGRV8cD_tY.
Kragh, Hedge. April 2009. “Contemporary History of Cosmology and the Controversy over the Multiverse”. Annals of Science, 66: 529-551. Accessed March 20, 2016. DOI:10.1080/00033790903047725.
Mathew, S. 2014. Essays on the Frontiers of Modern Astrophysics and Cosmology. Springer Praxis Books, Accessed March 20, 2016. DOI 10.1007/978-3-319-01887-4_2.
NOVA PBS. 2014. “4 Multiverses You Might Be Living In.” YouTube Video, 5:02, Posted 3 Oct 2014, https://www.youtube.com/watch?v=CIf_z0o0-Hc.
Tegmark, Max. 2003a. “Parallel Universes.” Scientific American. www.sciam.com. Accessed March 20, 2016. http://space.mit.edu/home/tegmark/PDF /multiverse_sciam.pdf.
Tegmark, Max. 2003b. “Parallel Universes.” Accessed March 20, 2016. http://space.mit.edu/home/tegmark/multiverse.pdf.
The Economist. 2015. “Do we live in a multiverse?”, YouTube video, 8:57, Posted 14 August 2015, https://www.youtube.com/watch?v=Rx7erWZ8TjA.
Halvorson, Hans and Kragh, Helge. 2013. "Cosmology and Theology". The Stanford Encyclopedia of Philosophy, Edward N. Zalta (ed.). Accessed March 21, 2016. http://plato.stanford.edu/archives/fall2013/entries/cosmology-theology/
Vilenkin, Alexander, and Max Tegmark. July 2011. “The Case for Parallel Universes.” Scientific American. www.sciam.com. Accessed March 21, 2016. http://www.scientificamerican.com/article/multiverse-the-case-for-parallel-universe/.
Wallack, Dr.Edward J. 2014. “Tests of Big Bang: The CMB”. National Aeronautics and Space Administration. Accessed March 22, 2016. http://map.gsfc.nasa.gov/ universe/bb_tests_cmb.html.
World Science Festival 2013. “Multiverse: One Universe or Many”, YouTube video, 1:33:19, Posted 15 Jun 2013, https://www.youtube.com/watch?v=2Qt-eGKa34M.
