People like to think of black holes and white holes as gateways through the universe. You fall into a black hole, zoom across spacetime, and are flung out of a white hole at some distant location. It would be pretty nice if this was how physics actually worked (it may make intergalactic travel a whole lot easier).
But unfortunately, this isn't exactly how physics works.
White holes, to be clear, are entirely theoretical. As of this moment, we don't have any evidence for them. In fact, most scientists think that they don't exist. However, they are handy mathematical constructs that allow us to talk about the space surrounding a black hole in meaningful ways.
In short, if black holes deal with an amazing amount of mass, white holes deal with none at all. Theoretical models say that that a white hole cannot be entered from the outside. This is, of course, the complete opposite of what we know black holes to be (supermassive objects that cannot be exited).
Learn more about them with the video below, and if you like the video, you can support us and get cool stuff.