There are certain physical processes in nature that seem impossible by basic rules but can still happen under the right conditions. Scientists call these “forbidden mechanisms.” They’re processes that basic physics says can’t happen, but higher-level physics allows them at reduced rates.
One clear example is phosphorescence. It’s what makes some materials glow in the dark for minutes or hours. These materials release light slowly through what scientists call “forbidden decays.” Each additional unit of spin change beyond one slows the decay rate by about 100,000 times.
Phosphorescence glows in the dark because forbidden decays slow light release to a crawl, stretching seconds into hours.
Rare earth atoms like erbium and neodymium also use forbidden shifts. They stay in excited energy states for a long time without releasing energy. Scientists use them as dopants in solid-state lasers. Their long-lived excited states make it easier to build up the energy needed for laser light.
Forbidden shifts also appear in outer space. In low-density gases, atoms rarely collide with each other. This gives them time to release energy through forbidden shifts. Scientists have spotted these “forbidden emission lines” in nebulae and plasmas. Nitrogen, sulfur, and oxygen all produce these special lines at specific wavelengths. Meta-stable states are commonly found in these environments, allowing atoms to remain in excited conditions long enough to emit substantial amounts of photon energy.
Quantum tunneling is another forbidden-seeming process. A particle can enter a region where its energy is lower than the barrier blocking it. That sounds impossible. But the uncertainty principle saves the day. It creates uncertainty in the particle’s momentum. That uncertainty adds enough energy to avoid a contradiction. When a particle is detected within this barrier region, position measurement increases momentum uncertainty enough that the total energy meets or exceeds the barrier height, resolving any apparent contradiction.
Scientists have also found ways to boost forbidden shifts using graphene. Graphene can carry plasmons, which are waves of light energy that travel through electrons. These plasmons have wavelengths hundreds of times shorter than regular light. That smaller scale matches atomic sizes better. It increases the chances of forbidden shifts happening.
This opens the door to unusual effects. These include emitting two plasmons at once or releasing light in two steps. It also supports creating pairs of entangled photons, which are useful for quantum cryptography.
Forbidden physics isn’t really forbidden. It’s just harder to observe under everyday conditions.
