 It's hard not to ask ourselves, is this all there is when we stare up at the night sky? Surely, beyond all these stars, planets, black holes, and galaxies that comprise what we have come to know as the universe, there are other universes? Or are we truly alone in an infinite black void? Stick around with me and Willie from Canubis to find out. The idea of there being a multiverse is one of the hot spots of debate in science, so let's try and contemplate this controversy by diving into some of the arguments and seeing just how strong they are. Our first case for the existence of a multiverse is a theory of inflation, which states that for a fraction of a second following the Big Bang, our universe expanded at an exponentially increasing rate from the size of a subatomic particle to well, a pretty large size to say the least. During this period of expansion, it's believed some parts of space expanded faster than others, creating these sort of bubbles of space-time that went on to become separate universes where the laws of physics may differ from our own. Some speculate that this expansion and formation of new universes is non-stop, meaning these other bubbles are constantly forming in a proposed phenomena called eternal inflation. Evidence for eternal inflation is proposed to come from analyzing cosmic microwave background radiation, leftover electromagnetic radiation from the Big Bang permeating our bubble universe. Should our bubble universe collide with another bubble universe, this would cause a disturbance in the fabric of space-time, which we would detect through fluctuations in CMB readings. Unfortunately, we haven't discovered any statistically significant fluctuations yet that hint at a possible collision with another universe, and while there is an acceleration in the expansion of the universe, it's too slow for what is predicted by inflation theories. It seems like the idea of eternal inflation won't do for now, due to lack of sufficient evidence. Perhaps then, we should look at some fairly decent arguments for the multiverse on a quantum mechanical level. Now when I say the word gravity, the Einsteinian definition of the fabric of space-time work by the presence of matter and energy comes to mind. However, there may be more to gravity than what meets the eye. In recent decades, some scientists speculate that gravity may consist of subatomic particles called gravitons. It's hypothesized that when two bodies are massed, such as this planet and this alien meat, they exchange gravitons thereby exerting their gravitational pull on each other, with the planet of course winning this tug of war. On a larger scale, this means if our universe were to come into contact with other universes, they would exchange gravitons, which we would detect assuming we had the technology to do so. Unfortunately, this method is invalid, since we haven't even verified the existence of gravitons themselves, meaning that for now gravitons grab a meter hypothesis due to insufficient evidence. So we're just going to say this graviton method is currently untestable and move on to our final argument for this video, the many-worlds interpretation. In quantum mechanics, when we want to find out the state of a quantum system, such as the location of a particle at a given time, we figure out its wave function, which is the probability of finding an entity at a given state at any given time. At times, a particle is believed to be in superposition or multiple states at once. However, when someone makes an observation on the particle, it somehow ends up in only one quantum state, which is a phenomena called wave function collapse. The many-worlds interpretation states that instead of the wave function collapsing, other universes are created where the other possible quantum states become reality. In other words, for every event that occurs in our universe, an alternate universe exists where that event may have taken a different turn. Still not clear enough? Let's demonstrate this principle using one of the most famous examples in physics, Schrodinger's Cat. Let's say we had a cat in a box and wanted to see if it was dead or alive. Well, until we opened the box to check, the cat is in its state of superposition where it's both dead and alive. However, the moment we open the box, the near-act of our observation causes the cat to go from a state of superposition to one defined state, which in this scenario is dead, sadly. However, the many-worlds hypothesis states that there is an alternative universe where we open the box to find the cat alive. This idea doesn't just apply to cats, as there are many scenarios in our universe that can have infinite outcomes, like what you choose to eat for breakfast, which means there could be an infinite amount of alternative universes out there where all possible outcomes for a given event occurred. An interesting thought, really, but unfortunately, like the other scenarios, the many-worlds hypothesis is just a proposal and has no hard evidence to back it up. So does the multiverse exist? Though no hardcore evidence exists, there are some promising theories, and we never know what we may find, which is why we must always keep an open mind towards the possibility of a multiverse. But let's say the multiverse existed, how would that work out? Well, that's what my friend, Canubis, will be looking at in this two-part collaboration. So hop onto his channel and check out his video to learn more about the multiverse. And be sure to leave your thoughts on the multiverse below, as well as other theories you want me to cover. But before you do, be sure to hit that subscribe button and notification bell, and stay tuned for more science videos.