### quantum tunneling

**(tunneling, barrier penetration)**
(quantum mechanical effect of particles passing through a barrier)

**Quantum tunneling** (or just **tunneling**, or **barrier penetration**)
is a quantum-mechanical effect demonstrating some strangeness of the
**Heisenberg uncertainty principle**, which states that there is a minimum
possible product of the certainty of a particle's momentum
and the certainty of that particle's position. If a particle
is sufficiently close to a sufficiently thin wall (barrier),
this uncertainty says there's a chance the
particle could be on the other side.
A particle approaching one side of the wall
could ultimately be found to be on the other side,
a phenomenon termed *tunneling* or *barrier penetration*.
Since there is a finite chance that this happens,
with sufficient repeated attempts,
the odds of a particle getting through rises to virtual inevitability.

The Heisenberg uncertainty principle is
not merely "not knowing where the particle is",
but that a "particle's exact location" doesn't always exist.
As weird as the effect seems, it is ubiquitous,
being an integral part of **fusion** (thus the shining of the Sun),
of radioactivity,
and of electronic components including the **tunnel diode**,
which clearly do their function in common consumer devices.

In astronomy, models of stellar structure
depend upon a calculation of the fusion rate in a
specific plasma according to its temperature and pressure,
calculations that include the effect of this tunneling,
and stars basically wouldn't shine very much without it.

(*physics,quantum mechanics,radioactivity*)
**Further reading:**

http://en.wikipedia.org/wiki/Quantum_tunnelling

**Referenced by pages:**

Gamow peak

Hawking radiation

quantum mechanics (QM)

superconducting tunnel junction (STJ)

Heisenberg uncertainty principle

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