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According to quantum theory, the vacuum contains neither matter nor energy, but it does contain fluctuations, transitions between something and nothing in which potential existence can be transformed into real existence by the addition of energy.(Energy and matter are equivalent, since all matter ultimately consists of packets of energy.) Thus, the vacuum's totally empty space is actually a seething turmoil of creation and annihilation, which to the ordinary world appears calm because the scale of fluctuations in the vacuum is tiny and the fluctuations tend to cancel each other out.
- Mandelshtam, Leonid; Tamm, Igor, The uncertainty relation between energy and time in nonrelativistic quantum mechanics, Izv. Akad. Nauk SSSR (ser. Fiz.), 1945, 9: 122–128. English translation: J. Phys. (USSR) 9, 249–254 (1945).