Schwinger effecteffect
Julian Schwinger, one of the creators of quantum electrodynamics, realized in 1951: if the electric field exceeds a fantastic value of about 10^18 V/m, the vacuum becomes unstable. Quantum fluctuations — virtual particle pairs — will be torn apart by the field and become real. Schwinger derived a formula showing that pair production is similar to tunneling: exponentially small in a weak field and catastrophically increasing at the critical value. This phenomenon is a close relative of Hawking radiation and particle production in the early Universe.
How it works
The effect explains what can happen near magnetars or in the focus of ultra-powerful lasers. In the laboratory, its analogue is created in graphene: due to the negligible effective mass of charge carriers, the critical field is reduced by orders of magnitude, allowing the study of quantum breakdown on a table.
💡 Physicists hope to 'boil' the vacuum with next-generation X-ray lasers, and for now reproduce a mini-Schwinger in graphene, obtaining an avalanche of electrons and holes.
E_c = \frac{m_e^2 c^3}{e\hbar}
E_c — critical electric field strength (Schwinger limit), m_e — electron mass (≈9.109×10⁻³¹ kg), c — speed of light in vacuum (≈2.998×10⁸ m/s), e — elementary charge (≈1.602×10⁻¹⁹ C), ħ — reduced Planck constant (≈1.0546×10⁻³⁴ J·s)
P \propto \exp\left(-\frac{\pi m_e^2 c^3}{e\hbar E}\right)
P — probability of creating an electron-positron pair per unit volume per unit time (for a constant uniform field), m_e, c, e, ħ — as above, E — actual electric field strength