The Universe is a vast, diverse, and interesting place, full of matter and energy, in various forms, playing out on the stage of spacetime, in accordance with the laws of physics. This is exemplified by this Hubble space telescope image of galaxy cluster IDCS J1426.5+3508. How much do you need to take away, though, before you’re truly left with nothing? Image credit: NASA, ESA, and M. Brodwin (University of Missouri).

The Four Scientific Meanings Of ‘Nothing’

If you want to know how we get something from nothing, you’d better understand what we mean!

When we look around at our world and Universe today, we talk and think about all the things that are in it. These range from particles, atoms, and human beings to planets, stars, galaxies, and the largest structures of all. Depending on what we’re interested in, we might discuss gas, dust, radiation, black holes, or even dark matter. But all the things we see, observe, or infer the existence of today might not have been there forever. Some of these arose from some pre-existing matter that was around previously, but others seemingly came from nothing. Unsurprisingly, not everyone agrees about what we mean, scientifically, when we talk about what “nothing” actually is. Depending on who you ask (or when you ask them), you might get one of four separate meanings. Here’s why they’re all relevant.

The loneliest galaxy in the Universe, which has no other galaxies in its vicinity for 100 million light years in any direction. Still, this is not a true realization of empty space. Image credit: ESA/Hubble & NASA and N. Gorin (STScI); Acknowledgement: Judy Schmidt.

1.) A time when your “thing” of interest didn’t exist. How did the Universe make planets? How about stars? How about a matter asymmetry? These things didn’t always exist, but rather had to be created. When the mechanism is known, we normally…