According to the Hindu text Śrīmad Bhāgavatam, “there are innumerable universes besides this one.” This concept of multiple universes is well known to Hindus familiar with the scriptures. But modern physicists have also been pondering whether our universe is all that we have or if there are many universes out there.
Throughout much of modern history, our scientific understanding of the universe has been limited by what we could see. As our telescopes have grown more powerful, the size of the universe has increased as well. However, we can only “see” so far, leaving many scientists to wonder what the universe is like beyond the far limits of our technology.
Some scientists even postulate that there may be not just one universe, but many—what’s known as a multiverse. Max Tegmark, a physicist at the Massachusetts Institute of Technology, has proposed four possible types of multiverses.
Level One Multiverse: The Extension of Our Universe
The universe that we actually can see is limited by the strength of our modern telescopes. Few physicists believe the universe ends right at this point, although it’s impossible to know what exists beyond the range of our telescopes.
The first type of multiverse suggests that our universe simply keeps on going, all the way to infinity. If this were true, then an infinite number of possibilities exist out there, such as an infinite number of Earths or Milky Way galaxies. And just as we are limited by our telescopes, other universes would also be isolated by their own.
Level Two Multiverse: Pocket Universes
The second type of multiverse is similar to the first, but it suggests that as the universe expanded, pocket universes were cut off from each other. Unlike the first type of multiverse, where the laws of physics are the same everywhere, in this type they may vary radically among the different pocket universes.
This can be tied to string theory, which has many possible solutions. Each one of these may correspond to a separate universe. This leads to the thought that humans only exist because our universe happens to be ideally suited for life (the “Goldilocks zone”). For example, if another pocket universe did not have gravity, then life might never have started, leaving that universe sterile.
Level Three Multiverse: Many Worlds
Like the first type of multiverse, the third supposes that the laws of physics are consistent across all universes. In this case, though, new daughter universes appear at each moment in time, leading to all possible futures existing somewhere.
Take the case of the Schrödinger’s cat paradox, which supposes that until the box is opened, the cat exists in two states—dead and alive. According to the many worlds multiverse, separate universes exist for each of those states (or wave functions). Of course, an observer in each of those universes would be aware of only one of those outcomes.
Level Four Multiverse: The Mathematical Multiverse
The last type of multiverse moves beyond comprehensible physics and into the realm of metaphysics. Tegmark proposes that each coherent system of mathematics may belong to some kind of physical reality—or separate universe. So a system that does not make sense in our universe might be perfect valid elsewhere.
None of these multiverses has been verified experimentally, but this classification system gives physicists a good scaffolding on which to hang their future multiversal endeavors.
Every universe is covered by seven layers—
earth, water, fire, air, sky, the total
energy and false ego—each ten times
greater than the previous one. There are innumerable universes besides this one,
and although they are unlimitedly large,
they move about like atoms in You.
Therefore You are called unlimited.
Śrīmad Bhāgavatam 6.16.37