you are not understanding what the nothingness is.

before the big bang theory a pure vacuum was thought to contain nothing. what that meant was that a pure vacuum does not contain any matter an hence contains nothing.

this has been found to not really be the case. even though there is no matter there is still something there.

so if you have a pure vacuum and wait a while it will spontaneously begin to fill with elementary particles.

see this link [link to the-great-learning.com]