If you’re one of the many fans of the Marvel Cinematic Universe, you’ll know that Dr. Strange has the power to explore the multiverse. He can travel to other worlds and meet alternate versions of himself, maybe even one that isn’t inexplicably charming. In comic books and science fiction, the multiverse refers to a collection of different universes that include our own.

But what about real science? Surely, the idea of the multiverse is purely limited to fantasy and imagination, right? Well, it might surprise you to know that the idea of the multiverse is actually part of scientific theory, and its existence would actually help explain some phenomena we already know about.

That being said, the science and theory behind the multiverse gets really complicated really quickly. If you’re still committed to trying to untangle this multiverse madness, there are a bunch of terms you’ll need to learn first before you can begin your multidimensional journey.

## dimension

In science and math, a dimension is a property of space. You probably know that our spatial movement involves three dimensions: height, width, and depth. You can move forward and back, left and right, and up and down. There is also a fourth dimension: time. On Earth, time only moves forward at a constant rate. However, the measurement of time starts to behave oddly once you start moving really fast or decide to hang out around a black hole–more on them later. So, scientists tend to describe outer space in terms of both time and space. Speaking of which …

## space-time

Space-time, also known as the space-time continuum, refers to the four-dimensional space that our reality exists in. This includes the three spatial dimensions together with time. Understanding space-time is important to getting a grip on the idea of the multiverse and where—and even when—other worlds might exist. Given how huge the universe is, we would need to better understand space-time and develop technology for traveling through both space and time to possibly discover worlds and universes beyond our own.

## 🔭 Turn your gaze to this quiz

The universe is full of infinite possibilities, including the chance to take our quiz on these “cosmic” words. Try it now or wait until you’ve reviewed all the words first. And when you’re in the mood to plunge into deep space—er, I mean thought!—you can always visit our word list, with learning tools to practice these words.

## cosmology

Cosmology is a branch of science that studies the nature of the universe. Cosmology often combines astronomy and physics when describing celestial phenomena. Basically, cosmology is concerned with studying where our universe came from and how it works. In practice, this involves a lot of extremely complicated math and experiments. The term cosmology also refers to a branch of philosophy that theorizes how the universe works, what our place in it is, and whether or not there might be other universes out there somewhere.

## metaphysics

Metaphysics is a branch of philosophy that asks questions about the nature of reality and the universe. Unlike the science of physics, the philosophy of metaphysics relies solely on theory and speculation to explain how our reality works or might work. Because many theories focused on the multiverse or parallel universes are currently impossible to test or find supporting evidence for, they are often considered to be part of metaphysics rather than a natural science. For example, the idea of modal realism, which states that all possible worlds physically exist, is considered to be philosophy rather than science since it is impossible to prove and doesn’t align with our current understanding of reality.

## quantum

Without getting too technical, the word quantum is used in physics to describe really small quantities of energy. Quantum mechanics, also known as quantum physics, is a subscience of physics that studies subatomic particles and matter. Based on our current understanding of science, quantum mechanics seems to be the most likely route through which we may be able to explore whether or not the multiverse is scientifically possible.

Once you start looking at things at the subatomic level, the normally impossible seems to become possible. For example, the study of quantum mechanics has proven it is entirely possible for an atom to exist in two different places at the same time. Scientifically, this would suggest the idea of multiple identical universes existing simultaneously may be possible, and most multiverse theories rely on quantum mechanics to support the argument that the multiverse is possible.

## the many-worlds interpretation

The many-worlds interpretation, also known as the Many-Worlds Theory, is a theory about the existence of other worlds or a multiverse. According to this idea, every possible event that could happen exists in another world. For example, if you roll a six-sided die and it comes up as a four, the MWI theorizes that there exist five other worlds where the other five rolls happened.

Out of all multiverse theories, this one is especially tempting to scientists because it doesn’t imply that many random universes somehow exist. Randomness is a problematic concept in science, and this theory addresses it by suggesting all the universes exist. Also, it is possible to test this theory–albeit using methods that are much too complicated to go into here. Still, even this multiverse explanation remains entirely theoretical until we make new discoveries in quantum mechanics.

## the big bang

The big bang, according to the big bang theory, was a sudden massive burst of matter and energy that created the universe billions of years ago. This theory is the most prevalent origin story of the universe and has supporting evidence such as the presence of cosmic microwave background, space radiation whose only scientific explanation is that it is leftover from when the big bang occurred.

Some multiverse theories speculate that the expansion that began with the big bang never stopped and that the universe is still expanding. Based on this inflation theory, it might be possible that the universe will continue to expand infinitely. This possibility leads to a multiverse theory in which “randomness” repeats and infinite “Earths” with infinite duplicates of “You” exist or will exist somewhere as the universe continues to grow indefinitely.

Another multiverse theory based on the big bang is the bubble theory. This theory speculates that different parts of space-time expanded at different rates. According to the theory, these “bubbles” of space-time resulted in bubble universes with different laws of physics. This multiverse theory suggests that our universe is just one of the many bubble universes out there.

## observable universe

The term observable universe is used to refer to the portion of the universe we can see or could possibly see. Basically, the observable universe is everything we can see using devices like telescopes, probes, or other astronomical equipment. When discussing the possibility of a multiverse, the answer seems to lie outside the observable universe. As far as we know, there are no “bizarro Earths” out there or galaxies with different laws of physics. So, a multiverse theory may suggest that parallel worlds, galaxies, or universes exist beyond the limits of the observable universe that we can see.

## string theory

Without getting too confusing, string theory is a theory in physics that suggests that subatomic particles in quantum mechanics are string-like objects rather than points. String theory also supposes that space-time actually consists of more than three spatial dimensions. The theory states that these dimensions are simply so small that we are unable to detect them.

If string theory is true, these extra dimensions would make the multiverse scientifically possible. In one interpretation of string theory, for example, it is theorized that our universe exists on a membrane, called a brane. Our world exists on a three-dimensional brane alongside other branes which may have more dimensions and thus different laws of physics. If we could somehow reach those other branes, we may discover entirely new worlds and universes.

## black holes

Black holes are extremely dense celestial objects whose gravity is so intense that not even light can escape them. This means that we can’t even “see” them with astronomical equipment and must detect them using the area around them. Black holes are mysterious parts of our universe where the laws of physics break down and normal scientific rules don’t apply. So, what would happen if someone entered a black hole?

The assumption is that a person would simply be destroyed by gravity. However, another theory among physicists is that black holes might be tunnels or wormholes that lead to other universes. If this theory is true, it is assumed that our own universe resembles a black hole in other universes as well.

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