Can you hide an object from radar while leaving it visible to the naked eye? A document from a U.S. intelligence agency examined that question in 2010. It reviewed experiments in which researchers partially concealed objects from microwaves, which are used by radar, among other things.
This wasn’t a single experiment in which an object vanished in front of a group of observers. The document brought together ideas and results from early experiments, and described their limits: an object can be partially concealed, but perfect concealment is impractical under known physics.
How Do You Hide an Object From Waves?
One way to conceal an object is to make it blend into the background. A stealth aircraft, for example, is designed to reflect fewer radar waves back toward the radar system. Another approach, examined in the document, aims to guide waves around an object.
The idea is similar to water splitting around a rock and flowing on behind it. If waves travel around an object and continue on their way, a device searching for their reflections may have trouble detecting it. The document reviewed several concealment methods, including experiments that had already demonstrated the idea to a limited extent using microwaves.
Why Can’t an Object Disappear Completely?
The experiments did not make objects invisible to people in the room. The concealment they demonstrated was limited and worked across a relatively narrow range of waves. According to the document, perfectly concealing an object would require materials that behave in ways physics does not allow.
In other words, finding a better material or improving the equipment wouldn’t be enough. These methods have limits. The document also estimates that practical concealment from visible light, the light people can see, would require new scientific ideas, not just incremental improvements to existing materials.
What Remains Unknown
The document does not present a practical way to hide an object from visible light. Nor does it describe a specific experiment in which an object can be seen vanishing before someone’s eyes.
Radar waves can pass around an object, at least to some extent. But look at it directly, and it’s still there.
