How can one enter a parallel universe? Physicists' answer may surprise you.

Currently, the existence of parallel universes is primarily associated with science fiction. However, there are scientific theories suggesting that other universes may exist. If this is the case, how can one access them? Physicist Paul Sutter believes that such a possibility exists, but it is an incredibly challenging journey, as reported by Space.

Theories Suggesting the Existence of Parallel Worlds

The existence of parallel universes is supported by at least two well-known theories in physics. One of them is known as the inflationary theory, which describes the extremely early universe. Shortly after the Big Bang, not just one but a vast number of universes could have been created, all undergoing rapid expansion. Each of these universes has different physics and distributions of matter. However, accessing other universes is extraordinarily difficult, as they lie beyond the observable cosmos and are moving away from us faster than the speed of light.

The other theory, known as the many-worlds interpretation of quantum mechanics, states that when a random quantum process occurs, one universe experiences one of the possible outcomes while other universes experience different results. This leads to the creation of a multiverse containing all possible quantum outcomes.

How to Access a Parallel Universe?

To enter one of these parallel universes, one would need to create a time machine to travel back to the past. Typically, such time travel leads to various paradoxes. For instance, if you were to go back in time and destroy the time machine, it would no longer exist, making it impossible to travel back in time. Yet the journey would have already taken place.

According to Stephen Hawking's chronology protection conjecture, traveling back in time is impossible. On the other hand, Novikov's self-consistency principle suggests that time travel is possible, but altering the past is not. But how can one travel to the past without changing it?

This is feasible if you travel back in time but not to your own past. Instead, you would find yourself in an alternative history where changes can be made. When you return to the future, the past in that reality remains unchanged.

The many-worlds interpretation of quantum mechanics provides a natural framework for creating such alternative histories. If the universe is constantly splitting, then time travel merely moves you from one reality to another. Conversely, upon returning to the future, a new reality can be created that did not previously exist.

However, no one knows exactly how this works. It remains unclear how this process unfolds or what mechanism gives rise to an alternative history.

What Does Quantum Physics Say?

Efforts to understand this issue through the study of quantum mechanics have yielded ambiguous results. Quantum fields tend to break down when time machines come into play. They can be stabilized by abandoning some fundamental principles of the theory, such as the correspondence principle, which states that quantum processes ultimately lead to macroscopic behavior and that fundamental reactions are reversible. No one is willing to discard these principles, as they seem central to the theory.

However, even classical, non-quantum systems face challenges. Suppose you have a switch that can turn the time machine on and off, for example, by opening or closing a wormhole. We do not know how alternative histories might adapt to such changes in their space-time structures, regardless of the quantum processes occurring at the subatomic level.

If we could build a time machine, it would be easy to verify whether alternative histories are created. All one would need to do is change something in their own past. If that is impossible, it suggests that there is only one timeline. If it is possible, then it indicates the existence of alternative histories and validates the many-worlds interpretation of quantum mechanics.

It is uncertain whether any of this is achievable, but such possibilities cannot be entirely dismissed. Therefore, while traveling to a parallel universe may be an extremely complex process, it cannot be said to be entirely impossible.