What is nothing? When most of us think of 'nothing,' we think of empty space, devoid of absolutely anything. But to a physicist, "nothing" can still have quite a lot in it.

If that sounds strange to you, you're not alone. Here's PBS Space Time to explain it:

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When we think of 'nothing,' we typically think of a space with nothing in it. A space that has zero particles, no particle at every place where a particle could be. Physicists call this the 'vacuum state,' and thanks to quantum mechanics, it has some weird properties.

One of the deepest underlying principles in quantum mechanics is Heisenberg's uncertainty principle—that it's impossible to know both a particle's exact position and its exact momentum. The more you know about one variable, the less you know about the other.

But the uncertainty principle works for other quantities, too. The same principle applies to energy and time. The more you know about a particle's energy, the less you know about when it is, and vice versa. Here, something weird happens: If you know that there will never be a particle at a particular point, suddenly that point could have any amount of energy, sometimes enough to create a particle anyway.

These particles are called 'virtual particles,' and they're basically quantum fluctuations. Once you make enough 'nothing,' the universe starts trying to find a way to fill it, even if that means creating particles out of thin air to do it.

There's also the possibility that the entire universe is just one big virtual particle. The 'vacuum genesis' hypothesis theorizes that the entire universe began as a big fluctuation in the 'nothing' that came before it. While it hasn't been proven, it sure is an interesting idea to think about: that in the end, all we—you, me, the whole universe—add up to is a big bunch of nothing.

Source: PBS Space Time

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