 In 1935, two physicists named Albert Einstein and Nathan Rosen proposed the idea of tunnels through space-time that could connect two distant points in the infinite universe, which would come to be known as an Einstein-Rosen bridge or a wormhole. For decades, they have been a subject of fascination in both the science and science fiction community, yet we haven't made much progress with creating and stabilizing a wormhole of our own. So today, we're going to be taking a look at what exactly is holding us back from turning our greatest science fiction fantasy into reality. Imagine it's the year 12,000 and you're aboard your starship. You wish to visit your extended family living on the planet S252015, which is in the neighboring Andromeda Galaxy 2.5 million light years away. You wave goodbye to the blue marble behind you, which has been your home for the entirety of your life, and look ahead to the wormhole which will take you to your destination in the blink of an eye. But as you enter the wormhole, something seems off, and then you realize that the wormhole is collapsing with you and your dreams of an interplanetary trip in it. Leaving you wondering, why is this happening? Now, before we go any further, it's important that we understand that there are many different types of wormholes. However, for most physicists, the main two are Lorentzian wormholes and Euclidean wormholes. Euclidean wormholes, often noted as being the weirder of the two, exist in an imaginary time scale. Imaginary time is kind of an odd concept to imagine itself. Let's pretend this line represents our time. This point at the origin represents the present, and to the right of the origin we have the future, and to the left of the origin we have the past. But let's shake things up a bit and say that we had a second line which ran perpendicular to the one on screen. This line is basically the result of multiplying the real-time coordinates by the imaginary number i, which is the square root of negative 1, a process called Wicks rotation. In this perpendicular scale, we now have what is called imaginary time. Unlike our time, where only one moment of an event can happen at a given point in time, every moment of the given event can happen at once in imaginary time. This means there is no such thing as a beginning in imaginary time as imaginary time is something which has always existed. Crazy, right? Imaginary time itself is a very abstract concept, which will certainly come in handy in later videos as we take a look at events such as the Big Bang. But for trying to analyze the viability of a wormhole in our very real world with very real time, maybe we should avoid wormholes which get us entangled with imaginary time. So with that being said, let's focus more on Lorentzian wormholes. Lorentzian wormholes are probably the type of wormholes that pop into your head upon the mere mention of the word. This version of a wormhole in theory are traversable, forming a cosmic bridge between two distant points of our universe, an unstable bridge that is, as no matter in real life would be able to go through these wormholes. Even a photon attempting to go through one of these wormholes would result in the wormhole collapsing at the speed of light. Now if you have seen the previous videos in our wormhole series, you would know that negative energy is basically the solution to this. And it is worth noting if you don't know what negative energy is and what its properties are, then check out our exotic matter video and then come right back to this one. Assuming you've done that and now have a basic understanding of exotic matter and negative energy, the next question is how exactly do we get negative energy since it's not exactly an easily obtainable item that you can just buy on Amazon. On top of that, classical physics kind of forbids the idea of negative energy. There is one way through what physicists dubbed the Casimir effect. Let's pretend that we are inside a room full of empty space, a vacuum if you will. Then imagine we took two mirrors and brought them closer and closer to each other in this room. Now contrary to what you might believe, empty space is not empty. It's filled with fluctuating particles and electromagnetic waves. As we bring the mirrors closer, the electromagnetic waves with a longer wavelength will not be able to fit between them. As a result, the energy of the space between the mirrors is much less than the energy of the surrounding space, thus making it negative energy and pushing the mirrors apart in the process. This negative energy has a repulsive effect as opposed to the normal attractive gravitational pull of normal matter, which is why it can be used to keep a wormhole open. Now that's all fine and dandy with just one small problem. This Casimir effect, as mentioned, would only produce about 10 to the negative 4 joules of energy per cubic meter of space. This is a very insufficient amount to even stabilize a decent sized wormhole. In order to understand just how miniscule this amount is, a 1 kilogram mass in the same volume of space has an energy density of roughly 9 x 10 to the 16 joules per meter cubed. Quite disappointing indeed. This doesn't mean all is lost, as there is another potential way. You remember from earlier how we mentioned empty space was also full of fluctuating particles? Well, these fluctuating particles consist of a pair of particles, with one being composed of matter, and the other being composed of antimatter, both of which pop in and out of existence constantly. Now let's say we travel near the event horizon of a black hole, where these particle fluctuations would also be taking place. The difference here is one of the particles will escape from the clutches of the black hole, while the other particle will be gobbled up. What's interesting is that the intense gravitational field of the black hole can create scenarios where the particle absorbed from the duo has negative energy. The mechanism behind this is far too complex for the scope of this video, but this may be good news as there is a certain type of wormhole called a Schwartz child wormhole, which consists of a black hole and a white hole, and lucky for us, exists as a viable solution to some of Einstein's equations that could make use of this production of negative energy, right? I mean, after all, maybe we could harness these quantum fluctuations to produce enough exotic matter to stabilize a Schwartz child wormhole. Well, before we get all giddy, it's worth mentioning there are some caveats. First of all, the negative energy produced by the particle pair actually causes the black hole to evaporate. The thermal radiation released by this process is called Hawking Radiation, and unfortunately till date, there has been no direct observations of Hawking Radiation. Also, because of the immense gravity of a black hole, this can lead to the elongation of the wormhole throat, an eventual collapse of the wormhole. And to put the cherry on top, white holes themselves haven't been proven to exist so far. By now, the pattern should become clear to you. It seems like the main problem with all these wormholes is that either we don't have enough of a specific component to make them, or the component itself hasn't been discovered yet, or they do exist as some wacky abstract concept which bends your mind. So have we hit a dead end? Well, the answer to that is it's too early to decide. I mean, we still have a lot of breakthroughs in physics every day, so it doesn't mean all hope is lost, especially with that Schwartzschild wormhole. But how exactly would that work in real life, and what exactly are the mechanisms behind a white hole, and more importantly, where can we find one? Those questions itself are way too complex for a brief gloss over in this video, and require a separate video of their own. So that is why you should stick around for part two, where we will continue to unlock the mysteries behind wormholes. Before ending this video, it's imperative to reiterate, just because the solutions to the problems outlined today exist, doesn't mean in the future some daring physicists won't come up with a solution. Whether or not interplanetary and intergalactic voyages will be no different than a family trip one day is something which only time can tell. Meanwhile, you should keep yourself entertained and informed about our wacky universe by subscribing and hitting that notification bell. And as always, don't forget to stay tuned for more science videos.