What is the sharpest thing in the world?

Defining the "sharpest thing in the world" is tricky because "sharpness" isn't a single, easily measurable property. It depends on several factors, including the angle of the tip, the material's hardness, and the atomic structure at the very tip. There's no single universally agreed-upon champion. However, we can discuss some contenders for incredibly sharp objects:

• Ultrasharp silicon needles: Researchers have created incredibly sharp silicon needles using advanced fabrication techniques like focused ion beam milling. These needles can achieve apex radii of just a few nanometers, meaning they're sharper than any conventional blade. Their sharpness is often defined by the radius of curvature at the tip. However, it's important to note that even these incredibly sharp needles will eventually blunt with use.

• Diamond tipped tools: Diamonds are incredibly hard, and specialized diamond tools used in micromachining and nanotechnology can achieve extremely sharp points. Their sharpness is dictated both by the cutting edge's geometry and the hardness of the diamond itself, allowing for incredibly precise cutting and shaping of materials at a microscopic scale. Again, the sharpness is relative to the application.

• Atomically sharp tips of Scanning Probe Microscopes (SPMs): The tips used in Scanning Tunneling Microscopes (STMs) and Atomic Force Microscopes (AFMs) are often described as atomically sharp. While not "sharp" in the way a knife is, their apex consists of only a few atoms, providing incredibly high resolution for imaging surfaces at the atomic level. These aren't "sharp" for cutting, but for incredibly fine-scale interaction.

It's crucial to remember that the sharpness of these objects is context-dependent. A silicon needle might be sharper in terms of radius of curvature than a diamond tip, but the diamond's hardness might allow it to maintain its sharpness for longer and cut harder materials. The atomic tip of an SPM is sharp on an atomic scale, but utterly useless for any conventional cutting task.

Therefore, there's no single definitive answer to the question. The "sharpest" object depends on how you define and measure sharpness.