Why the multiverse is possible according to physics, but not definitely Premium

From the possibility of multiple universes to the concept of cosmic inflation, explore the boundaries of physics and reality.

If a theory about the physical world is experimentally testable and then verifiable, it will stop existing in the realm of metaphysics and become a part of physics. No matter how weird or vague a theory may seem to be, it only needs to be workable in this sense for it to be a theory of reality.

Some examples of theories whose predictions the human sense may not be equipped to understand fully or are altogether counter-intuitive include the bending of light, gravitational waves, black holes, and quantum physics. Scientists noticed the first three possibilities in the theories of Albert Einstein. They were intriguing but at the same time were also unsubstantiated. It took scientists many decades of work to figure out how and why they exist in the universe and how to test them.

There are also some theories that we currently don’t have the methods to test. These theories may be logically consistent and may even arise straightforwardly from the inferences of well-established physical laws. Such ideas are better called ‘speculative science’. Some of them are quite famous. One is string theory, which uses advanced mathematics to explain some of the mysteries of the universe today, such as why the force of gravity is much weaker than the other fundamental forces.

Another example of a speculative theory is the multiverse, which physicists also call ‘bubble universes’. We have a lot of evidence to indicate that an event called the Big Bang created many aspects of our universe as we know it. But there is no reason for us to think that a Big-Bang-like event happened only once or that it won’t happen again in future. Instead, it may have happened many times before and might even be happening still, yielding multiple copies of universes.

The expanse of space – which contains everything both accessible and inaccessible – is infinite. Shortly after the Big Bang, scientists believe our own universe rapidly expanded in volume in a very short time. This phenomenon is called cosmic inflation. It is a popular (but currently unverified) explanation for the fact that some distant parts of the universe have very similar physical characteristics, which would have been possible if they had once been very close together before being suddenly separated. And there are hardly any models of cosmic inflation that don’t also predict the possibility of other universes out there.

Another (unverified) idea that supports the possibility of a multiverse is primordial gravitational waves. It posits that when our universe went through cosmic inflation, some parts of the spacetime fabric could have expanded more quickly than others, creating spacetime ‘bubbles’ that developed into ‘pocket’ universes.

From the point of view of cosmology – the study of the universe’s past, present, and future – we don’t know what there was before the Big Bang, what caused the Big Bang, the sequence of events in the moments preceding it or in fact what went ‘bang’. When physicists discuss our universe, they are effectively discussing things that happened right after the Big Bang. This limitation obviously means we lack a great deal of information. Even so, scientists have overwhelming evidence that an event like the ‘hot’ Big Bang happened.