Infinite realities: the multiverse hypothesis

Over the past century, scientists have begun to question whether the universe we know is the only one. Could there be others, perhaps with different laws of physics, or even copies of ourselves, living out different versions of reality? This is the central idea behind the multiverse theory, which proposes that our universe may be just one of many. Let’s dive into the science behind the fascinating hypothesis of the multiverse.

What is the Multiverse Theory?

The multiverse theory suggests that the universe we inhabit may be only one of an infinite number of universes, all existing in parallel. These universes could vary in size, shape, and even in the physical laws that govern them. This idea has quickly captured the imagination of scientists and philosophers but remains one of the more speculative areas of modern physics.

There are multiple interpretations of the multiverse theory, each with its own reasoning and implications:

• Bubble Universes (Eternal Inflation Theory): This version of the multiverse comes from the inflationary theory of the universe’s expansion. After the Big Bang, the universe underwent a rapid expansion. According to the eternal inflation theory, this process didn’t stop uniformly across space. Instead, pockets of space stopped inflating, forming “bubble universes”, while inflation continued elsewhere. Each of these bubbles could represent its own universe with its own physical laws. “Our observable universe is just one such bubble”, explains physicist Alan Guth, one of the pioneers of inflation theory

Bubble universe. / © Double A Studios

• Quantum Multiverse (Many-Worlds Interpretation): According to quantum mechanics, particles can exist in multiple states simultaneously until observed. The Many-Worlds Interpretation of quantum mechanics takes this idea a step further, proposing that for every possible outcome of a quantum event, a new universe is created. This means that every time a decision is made, or an event occurs, the universe splits into parallel realities. “All possible outcomes happen, but in different worlds”, notes physicist Hugh Everett, who first suggested the Many-Worlds theory in 1957. (Hugh Everett, The Many-Worlds Interpretation of Quantum Mechanics, 1957)
  

Many-worlds interpretation. / © Double A Studios

• String Theory and the Multiverse: String theory, which attempts to unify all the fundamental forces of physics, also leaves the door open to the possibility of multiple universes. According to string theory, our universe could be one of many that exist in higher-dimensional space. These universes may be “branes” (short for membranes) floating in a higher-dimensional space. A collision between such branes could explain the Big Bang itself.

String theory multiverse. / © Double A Studios

The Evidence for the multiverse

Despite its intriguing premise, the multiverse theory remains speculative because it’s extremely difficult to test. However, some indirect evidence has given scientists reasons to consider the multiverse seriously.

• Cosmic Microwave Background Radiation (CMB): The afterglow of the Big Bang, known as the CMB, provides a snapshot of the early universe. Some anomalies in the CMB, such as cold spots, have led some researchers to speculate that they might be the result of other universes interacting with ours. However, these interpretations remain controversial, and most cosmologists agree that more evidence is needed. (Laura Mersini-Houghton, 2007)
  
  
• Mathematical Models: Mathematical theories like string theory and quantum mechanics inherently suggest the existence of the multiverse. These models are mathematically consistent, and although they haven’t been empirically proven, they fit within the framework of our current understanding of physics. (Brian Greene, The Elegant Universe, 1999).
  
  
• Inflation Theory: The idea that our universe rapidly expanded after the Big Bang is well-supported by observational evidence. However, inflation theory also predicts the existence of other “pockets” or bubble universes. As noted by Alan Guth, the inflationary model “almost inevitably predicts the existence of a multiverse”. (A. Guth, The Inflationary Universe: The Quest for a New Theory of Cosmic Origins, 1997)

Inflationary multiverse. / © Double A Studios

Implications of the multiverse

If the multiverse theory is correct, it would fundamentally change our understanding of reality. Here are some of the most interesting implications:

• Alternate Realities: In the quantum multiverse interpretation, every possible outcome of every event in history has already happened – in a parallel universe. This means that there could be other versions of you living out completely different lives based on the different decisions you (or others) made.
  
  
• Different Laws of Physics: Some universes might operate under physical laws that are entirely different from those of our universe. There could be universes where gravity is weaker or stronger, or where time flows in reverse.
  
  
• The Anthropic Principle: One explanation for why our universe is so perfectly suited for life is that out of an infinite number of universes, we happen to live in one where conditions are just right. In other universes, life might not be possible, but with infinite possibilities, it’s statistically inevitable that at least one universe – ours – would have the right conditions for life to exist. (Leonard Susskind, The Cosmic Landscape: String Theory and the Illusion of Intelligent Design, 2005)

Criticism of the multiverse

While the multiverse theory is extremely exciting, it’s also highly controversial. A large portion of the scientific community points out that, because we currently lack the means to test for other universes, the theory verges on philosophical speculation rather than empirical science. As physicist Paul Steinhardt says, “The multiverse is not falsifiable – there’s no experiment we can do to confirm it”. (P. Steinhardt, “The Inflation Debate: Is the Theory at the Heart of Modern Cosmology Deeply Flawed?”, Scientific American, 2011)

Parallel worlds. / © Geralt / Pixabay

Additionally, critics argue that invoking the multiverse to explain phenomena like the fine-tuning of our universe feels more like a metaphysical “escape hatch” than a genuine scientific solution. They believe we should first exhaust other explanations before accepting such a bold and untestable theory.

Should one day be proven right, the multiverse theory could open up a vast range of possibilities about the nature of reality. As our understanding of physics deepens, we may one day uncover the answers to this fascinating mystery. Until then, the idea of infinite realities remains a tantalizing thought, one that continues to inspire both scientific inquiry and our imagination.

Reference list:

1. Alan Guth, The Inflationary Universe: The Quest for a New Theory of Cosmic Origins (1997)
2. Hugh Everett, The Many-Worlds Interpretation of Quantum Mechanics (1957)
3. Brian Greene, The Elegant Universe (1999)
4. Paul Steinhardt, "The Inflation Debate: Is the Theory at the Heart of Modern Cosmology Deeply Flawed?" Scientific American (2011)
5. Laura Mersini-Houghton, studies on the CMB cold spot hypothesis (2007)
6. Leonard Susskind, The Cosmic Landscape: String Theory and the Illusion of Intelligent Design (2005)

Adriano Anfuso is a photographer and digital creator who is passionate about capturing the awe-inspiring beauty of the cosmos and Earth's wonders. You can check out his work here.