Edwin Powell Hubble was an American astronomer who changed our understanding of our universe and our place in it. During a series of cold nights in October 1923, Hubble observed the night sky using the powerful Hooker telescope, looking for clues about the mysteries of our universe.
This is where he first spotted a star flaring up in a nova in the M31 nebula in the constellation of Andromeda. But there was something wrong. The astronomical object M31 appeared to be much further away than was believed possible, sitting a staggering 2.5 million light-years away.
This was strange because, at the time, astronomers had estimated that our galaxy was only about 200,000 light-years across. Using the help of his "computer" (someone tasked with examining photographic plates in order to measure and catalog the brightness of stars), the astronomer Henrietta Swan Leavitt, Hubble would later discover that M31 was a galaxy, which would eventually be dubbed the Andromeda Galaxy.
This discovery demonstrated that there were galaxies outside our own. (If you haven't guessed it already, the Hubble Telescope was named after the astronomer.)
More recently, we have come to understand that there may potentially be trillions of galaxies in our universe. It is no secret that our universe is unimaginably large. However, there are some scientists out there that still think we may be thinking a little too small. Welcome to the Multiverse.
You are probably familiar with the idea of a multiverse. Aside from time travel, it has to be one of science fiction's favorite tropes. Though, at times it seems like merely a fascinating plot device, like a lot of science fiction, some of the ideas behind it are based on real science. However, the multiverse theory is not as straightforward as you think, and in some cases may be even stranger than in the movies.
A little thought experiment; A journey to the edge of the universe
Imagine Elon Musk has given you the ability to live 1000 years into the future. Thanks to his Neuralink device, you have left your human body for an eternal robotic one. Death is a thing of the past, and you can instantly 3D-print new robotic parts when things become faulty. With your unlimited life at hand, you decide to hop into an interstellar spaceship and journey to the edge of the universe. After traveling billions of years, (or maybe less), you finally reach the end of the universe.
What do you find? Would you see that there is just much more universe to be discovered? Or, would you fly out of our own universe into another? Would you be surrounded by a host of other "bubble" universes, each just as big as our own? These are valid questions because, at the moment, our understanding of the universe is expanding.
What exactly is a multiverse?
Let's define a multiverse. Think about the word "universe." When people use this term, they tend to refer to all that exists. However, if you use the term universe as "everything we can ever see," this implies there is more than one universe out there. We will be using the later to describe our universe, with the assumption that we are part of a multiverse.
Though the idea of a multiverse is very controversial, at its core, it is a relatively simple concept to wrap your head around. In short, our entire universe is only a small part of a much larger number of universes. The alternative universes are part of an unobservable area of space-time. Our universe is just one of many universes. Some have speculated that in the multiverse, each universe could have its own separate laws of physics.
However, the concept of the Multiverse is not a scientific theory in and of itself. Instead, it is a theoretical consequence based on our current understanding of the laws of physics: if you have an inflationary Universe governed by quantum physics, you may well be bound to wind up with a multiverse. But the theory of a multiverse also has some big problems.
For example, it doesn't predict anything we have observed and can't explain without it, and it also doesn't predict anything definitive we can go and look for.
There are multiple explanations out there for our Multiverse.
Sadly, we cannot see outside our own universe, and we may never get the chance. Nevertheless, there are multiple theories that could explain why a multiverse might be possible. So if there are multiple universes out there, how many are we talking exactly? One line of thought is that there could be infinite universes out there. Think Spider-Man Into the Spider-Verse.
This idea is born out of the fact that researchers are not certain about the shape of space-time. However, the general consensus is that it stretches on forever. But, because there are a finite number of ways particles can be arranged in space and time, they should start repeating at some point. If you were able to look across this infinite plane, you might see copies of yourself or even different versions. Still with me?
The Big Bang might be the first clue
You are probably very familiar with the concept of the Big Bang.
Astronomers know the Universe is expanding, they can measure the distance of galaxies from us, and how fast they appear to be moving away. The farther away they are, the faster they appear to recede, which General Relativity tells us means the Universe is expanding. And if the Universe is expanding, that means it was smaller and denser in the past, as well as more uniform and hotter. This leads us to the Big Bang, which has been postulated to have occurred some 13.8 billion years ago.
However, what happened before the big bang? If we go back far enough in time, we find that there are things which can be observed in the Universe but which the Big Bang can't explain.
So, astronomers have come up with another theory - cosmic inflation. This tells us that before the Big Bang, it was filled with energy. That energy caused space to expand very rapidly. When inflation ended, the energy was converted into matter and energy, which then led to the Big Bang.
The universe may have siblings
This is where Hollywood takes most of their script ideas. The supporting theory of the multiverse centers around the idea that multiple universes follow the physics of quantum mechanics. Dubbed the daughter universe theory, this is an idea driven by the laws of probability. A fun thought experiment would be to imagine all of the choices that you made today. Now sit back and think about just one of those choices.
Why did you make that choice? What other choices could you have made? With a potentially infinite amount of options out there, the daughter theory demonstrates that within the Multiverse, there are infinite versions of yourself, each making different choices. In one universe, you could have a different job, blue hair, be born in a different country, and so on. Trippy right?
Our current simulation could the second clue.
We have been down this rabbit hole before. Aside from talking about multiple universes, people love to discuss the idea that we are living in a simulation. Swedish philosopher Nick Bostrom published a paper called The Simulation Argument, a paper that would go on to question the nature of our reality. A controversial idea, Bostrom's simulation theory centers around three assumptions at least one of which needs to be true:
(1) the human species is very likely to go extinct before reaching a "posthuman" stage; (2) any posthuman civilization is extremely unlikely to run a significant number of simulations of their evolutionary history (or variations thereof); (3) we are almost certainly living in a computer simulation. It follows that the belief that there is a significant chance that we will one day become posthumans who run ancestor‐simulations is false, unless we are currently living in a simulation.
If you want to learn more about simulation theory, be sure to stop by here.
However, some people have taken this idea even further. What if our universe is currently being simulated alongside many other universes. The thinking goes that, if our future ancestors do possess the power to simulate our universe, what is stopping them from simulating multiple universes at once?
There might not be parallel universes out there
As mentioned, one popular idea to come out of multiverse theory is the concept of parallel universes. However, most astrophysicists are not on board the parallel universe train. In one of many examples, Astrophysicist Ethan Siegal has been vocal about the limitations with the theory. He does believe that space-time could possibly go on forever. But, are there alternate realities out there similar to our own? Not so much.
According to Siegal, "Even setting aside issues that there may be an infinite number of possible values for fundamental constants, particles, and interactions, and even setting aside interpretation issues such as whether the many-worlds-interpretation actually describes our physical reality."
"The fact of the matter is that the number of possible outcomes rises so quickly — so much faster than merely exponentially — that unless inflation has been occurring for a truly infinite amount of time, there are no parallel universes identical to this one."
The Multiverse is everywhere
Multiverse theory appears everywhere in popular entertainment, and even plays a role in the epic finale of the Marvel Infinity Saga. You see it in video games, like Final Fantasy and the legendary game Half-Life.
Pop culture is fascinated by the ideas of living in a multiverse, the promise of an alternative version of you living a different life, and experiencing different events. Perhaps we are comforted by this idea. The biggest challenge with multiverse theory is testing the theory. At the very least, it is a fun thought experiment.
There are plenty of researchers who are considering the theory, like the late Stephen Hawking. Although, his idea of a multiverse is much simpler. He stated in his final published study, "We are not down to a single, unique universe, but our findings imply a significant reduction of the multiverse, to a much smaller range of possible universes.”
Do you think we are living in a multiverse? What about a simulation? Leave your comments below.