What Are They? Do They Exist? How Do We Find Out?
by Larry Klaes, space exploration enthusiast, science journalist, SF aficionado. The article first appeared at Science That.
Two physicists decide to visit Las Vegas to try their luck at gambling. One of the pair plays craps, where he proceeds to rapidly lose their limited funds as he continually throws one poor roll of the dice after another. His companion, none too pleased at watching their money disappear, demands to know from his friend why he keeps playing this game despite losing every time.
“I may be losing at craps in this universe,” replies the first physicist, “but in an alternate reality, my duplicate is making a fortune!”
Among the biggest mysteries of modern cosmology is the question of whether other universes beyond our own exist in the Cosmos, or Multiverse, as it would be called should they prove to be real.
The general public is aware of the concept of parallel or alternate universes largely through popular science fiction, where they have been a plot device for a long time. Perhaps the best known of those imagined alternate existences is the Mirror Universe of the Star Trek series, where we meet the “bad” versions of the main characters from our universe – or their own fictional “reality” parallel to our real reality.
But do parallel universes truly exist? Are they composed largely of varying degrees of the people and places we know from this reality? Or could they be something far more complex and vast than most science fiction has ever attempted to portray?
If certain physicists who study this concept are correct, then parallel universes exist on a number of “flavors” or levels. Max Tegmark, a professor of physics at the Massachusetts Institute of Technology (MIT) says there are four levels of parallel universes. They range from the first level, where alternate realities exist at distances well beyond the observable Universe we live in, to the fourth, where all mathematically possible universes can and do exist. Many if not most of those universes would not resemble ours at all, obeying entirely different laws of physics. The universes envisioned by Tegmark would be virtually impossible to visit, barring some breakthrough in physics and technology.
Another type of alternate universe is known as the Many Worlds Interpretation (MWI). This theory was first proposed by Hugh Everett III in 1957 and later became the Level Three type of alternate universe in Tegmark’s catalog of parallel existences. Utilizing quantum physics, MWI claims that every action by every person and object creates an infinite number of alternative actions that branch off into their own universe. In this scenario, every possible history and future becomes reality in its own existence separate from our own. This idea was the plot device for the science fiction television series Sliders, which had a group of people travel to alternate Earths every week from 1995 to 2000 via a machine that generated a wormhole.
Could we ever detect or visit these parallel universes? If the theories of current physics are proven true, then the answer would be not any time soon in most cases. However, there has been speculation that four “cold spots” or “bruises” in the cosmic microwave background (CMB) radiation – the surviving remnant of the Big Bang which began our universe some 13.8 billion years ago – are alternate universes which either once quantum entangled with or “bumped” into our reality at some point in the distant past.
If there were parallel universes which collided with our own Universe, one has to ask why they did not create a new Big Bang as predicted by the ekyprotic cosmological model: In this scenario, a physical property in string theory called branes has the branes of several universes collide perhaps once every one trillion years or so. Their collision releases huge amounts of energy to create a new universe. This is what some scientists say is what brought about our Universe in contrast to the current Big Bang model of creation.
There are those who disavow the idea of other universe beyond our own. They correctly state that there is no scientifically empirical evidence for their existence, only theories and mathematical models. While these skeptics are correct in their reasoning, one also has to ask if they need to take another look at our perspectives on the Cosmos over the centuries. Not too many centuries ago, only a few people dared to speculate there were any worlds beyond our Earth or that the Sun was just a very close member of those myriads of twinkling stars in the night sky.
As late as 1920, astronomers were still debating whether the Milky Way galaxy was the ultimate cosmic structure or just one of many billions of stellar islands in the Universe. We now know the latter to be true, adding to our list of cosmic “demotions” from thinking we were the literal focus of existence to just being residents of a rather small world circling a typical star in a galaxy of hundreds of billions of suns, all of which is part of an immense and ancient Universe with at least one hundred billion galaxies if not more.
So are we part of a vast, singular Universe, or is our reality just one of an infinity of alternate existences on a scale far beyond what even our current knowledge can determine? Just as with the possibility of there being extraterrestrial life now that we know many billions of worlds exist in our Milky Way alone, or the historical precedent of Copernicus and others claiming that Earth is just one planet orbiting its sun and not the other way around, it is very tempting to conclude that even something as massive as the Universe might not be the only one in reality. However, we must temper our conclusions on this exciting possibility until the day science determines their existence – or lack thereof.