Imagine you suddenly came across a black hole the size of a coin. You've got no idea how it got there, where it came from… oops you're dead. But there are a number of ways this could go, depending on how the black hole was formed. As the video above by German design studio Kurz Gesagt explains, your fate rests on whether the black hole has the mass of a coin, or the width of a coin.
Let's tackle the black hole with a mass of about 5 grams first. It would have a radius of 10-30 m, and by comparison, the radius of a hydrogen atom is about 10-11 m. "So the black hole compared to an atom, is as small as an atom compared to the Sun," says the video. Which is unimaginably small.
So what other properties would this miniscule black hole have? Well, it would have to have an incredibly short lifespan to decay according to the Hawking Radiation theory - it would decay away to nothing in about 10-23 seconds. So way, way before you've even had a chance to contemplate its existence. But it won't disappear into nothingness - all that decaying activity will produce a whopping 450 terrajoules of energy. All from just 5 grams of mass.
And you know what happens when 450 terrajoules of energy is released? Just an explosion three times more powerful than the atomic bombs dropped on Hiroshima and Nagasaki combined. Ouch. Also, you're dead.
Okay, but what if the black hole was the size of a coin, width-wise? That thing would be considerably more massive than the 5-gram black hole, and just slightly more massive than Earth, and it would have a surface gravity 8 billion billion times than our planet. All that gravity would rip you, cell from cell, before you even realise there was a black hole. Ouch. And not only that, but the nature of this gravity means that everything around you will also be sucked up and scattered into countless pieces. "The black hole is now a dominant gravitational piece of the Earth-Moon-Black-Hole-of-Death system," says the video. Good one.
So why wouldn't a black hole that massive instead sink into the centre of Earth and rapidly consume it from the inside out? I'll leave the video above to run through the gory details, but let's just say our planet is way too orbity for that to ever happen. Keep on being you, Earth. We're going to go empty out our pockets, just in case.