Interference happens when two or more waves, signals, or pieces of information overlap and either strengthen or weaken each other. The concept applies across physics, electronics, psychology, and biology, but the underlying principle is the same: something gets in the way of something else, changing the outcome. Here’s how interference works in the contexts that matter most.
Wave Interference in Physics
All wave interference stems from a single rule called superposition: when two waves meet at the same place and time, their effects add together. Each wave creates a disturbance, each disturbance exerts a force, and all the forces combine. If the waves travel along the same line, you simply add their heights (amplitudes) at every point.
This addition produces two classic results. When two identical waves arrive perfectly in sync, their crests line up and their troughs line up. The combined wave has twice the height of either wave alone. This is constructive interference. When two identical waves arrive perfectly out of sync, every crest lines up with a trough. The heights cancel to zero, and the waves effectively erase each other. This is destructive interference.
What determines whether waves add or cancel? The path difference between them. If one wave travels slightly farther than the other to reach the same point, the two waves arrive at different points in their cycle. When that extra distance equals a whole number of wavelengths (one wavelength, two wavelengths, three, and so on), the waves are back in sync and reinforce each other. When the extra distance equals a half wavelength, one and a half wavelengths, two and a half, and so on, the waves are perfectly out of sync and cancel. Most real-world interference falls somewhere between these extremes, producing partial reinforcement or partial cancellation.
You can see wave interference in ripples on a pond, hear it in the “beats” between two slightly mistuned guitar strings, and observe it in the shimmering colors on a soap bubble, where light waves reflecting off the front and back surfaces of the thin film interfere with each other.
Electromagnetic Interference in Electronics
Electromagnetic interference, commonly called EMI, occurs when unwanted electromagnetic energy disrupts the normal operation of an electronic device. Natural sources include the sun and thunderstorm activity, but the overwhelming majority of EMI in modern life comes from human-made devices: motors, power lines, LED dimmers, Wi-Fi routers, cellphones, and countless other electronics that radiate energy as they operate.
One specific form of EMI is crosstalk, which happens inside circuit boards and cables when signals leak between closely spaced wires or traces. The electrical field around one wire induces a small current in an adjacent wire, creating noise that distorts the intended signal. Crosstalk is one of the most common sources of signal degradation in electronics. It can reduce data transmission speed and, in severe cases, cause a communication link to fail entirely. Designers minimize it by spacing traces farther apart, adding shielding, and placing grounding structures near signal paths.
5G and Aircraft Altimeters
A high-profile example of EMI involves 5G wireless signals and aircraft radio altimeters, the instruments planes use to measure altitude during landing. The 5G C-band frequencies sit close to the frequencies altimeters use, and that proximity creates a risk of interference. As of August 2025, the FAA had received 659 reports of potential C-band interference, and after analyzing most of them, identified 118 events where 5G signals were the likely cause. The FAA is now proposing that all aircraft in the contiguous United States upgrade to altimeters with better interference rejection, with compliance deadlines expected between 2029 and 2032.
Medical Devices in Hospitals
EMI is a particular concern in healthcare settings, where electronic monitors, infusion pumps, and implanted devices like pacemakers can be disrupted by nearby radio transmitters. Cellphones, two-way radios, and electrosurgery equipment are all potential sources. The FDA recommends that hospitals designate zones where portable transmitters are restricted and test critical care devices for electromagnetic compatibility before purchase.
Memory Interference in Psychology
Your brain experiences interference too, and it’s one of the main reasons you forget things. In cognitive psychology, interference-based forgetting happens when information learned at different times competes for space in memory. There are two directions this can go.
Proactive interference occurs when something you already know makes it harder to learn something new. If you memorized your old phone number years ago, it may keep intruding when you try to recall your new one. The original memory is so firmly stored that it blocks consolidation of the new information.
Retroactive interference works the other way: new learning disrupts older memories. If you study French vocabulary and then immediately study Spanish vocabulary, the Spanish words can weaken your recall of the French ones. The newer memory effectively overwrites or competes with the older one during the vulnerable period when the original memory is still being solidified.
Similarity makes both types worse. When two sets of information are closely related (two similar languages, two similar motor skills, two courses in the same subject), they compete more directly for the same mental pathways. Research on motor skill learning found that contextual interference effects were strongest when the tasks being practiced were dissimilar, while highly similar tasks created a different kind of memory representation that was more vulnerable to confusion. This is why students often mix up closely related concepts more than unrelated ones.
RNA Interference in Biology
Cells have their own version of interference, and it serves as a defense mechanism. RNA interference is a natural process that silences specific genes by destroying their messenger molecules before those molecules can be used to build proteins.
Here’s how it works. When a cell detects double-stranded RNA (a molecular form that doesn’t normally appear in healthy cells and often signals a viral invader), an enzyme called Dicer chops it into small fragments roughly 21 to 25 units long. These fragments are loaded into a protein complex that separates the two strands and keeps one as a guide. That guide strand then scans the cell’s messenger RNA, looking for a matching sequence. When it finds one, the protein complex cuts the messenger RNA apart, preventing it from being read. The complex then releases the broken pieces and moves on to find and destroy more copies using the same guide.
This system originally evolved to fight viruses and silence rogue genetic elements, but scientists have turned it into a powerful research and medical tool. By designing synthetic RNA fragments that match a specific gene, researchers can selectively shut that gene off to study its function or, potentially, to treat diseases caused by overactive genes.
Why Interference Matters Across Fields
Whether you’re looking at ocean waves, radio signals, memory formation, or cellular biology, interference follows the same basic logic: when two similar things occupy the same space or pathway, they interact. Sometimes the result is amplification. Sometimes it’s cancellation. The outcome depends on timing, similarity, and proximity. In physics, the timing is measured in wavelengths. In psychology, it’s measured in how closely two learning events occur and how similar the material is. In electronics, it’s measured in frequency separation and physical distance between conductors. Understanding what causes interference in your specific context is the first step toward either harnessing it or preventing it.