Over extremely small timescales, matter can spontaneously appear out of nothing.
From the newscientist.com
Mark claimed that the actions arose spontaneously, without instigation from him.
From the washingtonpost.com
Do melodies come to you spontaneously, or do you work them out on an instrument?
From the time.com
The first step is for everyone to realize that it will not happen spontaneously.
From the dotearth.blogs.nytimes.com
Powdered thorium metal is pyrophoric and will often ignite spontaneously in air.
From the en.wikipedia.org
Many passers-by, including religious Romanian students, spontaneously joined in.
From the en.wikipedia.org
This was disputed by scientists who believed they could spontaneously generate.
From the telegraph.co.uk
News reports had initially suggested Stefanoni turned himself in spontaneously.
From the suntimes.com
He also revved up the fans when he spontaneously jumped into the midst of them.
From the kansas.com
More examples
In a spontaneous manner; "this shift occurs spontaneously"
Ad lib: without advance preparation; "he spoke ad lib"
(spontaneous) ad-lib: said or done without having been planned or written in advance; "he made a few ad-lib remarks"
(spontaneous) Self generated; happening without any apparent external cause; Done by one's own free choice, or without planning; proceeding from natural feeling or native tendency without external constraint; arising from a momentary impulse; controlled and directed internally : self-active : ...
(Spontaneous) An unconstrained form of divination, free from any particular medium, and actually a generalization of all types of divination. The answer comes from whatever object the diviner happens to see or hear. ...
(Spontaneous) Loss of foetus occurring naturally.
(Spontaneous) Not planned but done because you suddenly want to do it/done naturally, without being forced or practised
(Spontaneous) Proceeding from natural feeling, temperament or disposition without restraint.
(Spontaneous) Something that happens all by itself, without any outside stimuli