If a Spoon Forgets It Is a Spoon

Consider the spoon: a sturdy, reliable object whose whole job is to keep its shape while you stir. It is hard to imagine one simply forgetting what it is. Yet the question is less silly than it sounds, because the shape of a metal object is not guaranteed. It depends on what the metal is made of and how warm it gets, and a few unusual metals behave in ways that look remarkably like forgetting or, stranger still, like remembering.

The short answer

An ordinary steel spoon cannot forget, at least not at any temperature a kitchen can reach. One metal forgets easily: gallium, which melts at about 30 degrees Celsius, so a gallium spoon would slump away in a cup of tea, as our article on gallium explains. The more interesting metals are the ones that do the opposite. Bend them out of shape, warm them a little, and they go back to the shape they were given in the first place.

What people get wrong about metal

We tend to think of a solid metal as settled: bend it and it stays bent, because the bending has pushed its atoms into new positions for good. For ordinary spoon steel that is true. For the metals called shape-memory alloys, the most famous being nickel titanium, it is not. Their memory is not a trick of the surface. It comes from the fact that the same solid metal can arrange its atoms in two different ways, depending on the temperature.

How a metal remembers

A 2025 review of shape-memory alloys in the journal RSC Advances describes the two arrangements. One, called austenite, is stable at higher temperatures. The other, called martensite, is stable at lower temperatures. In the cool martensite form, the crystal is made of small twinned regions that can shift and flip against each other, so the metal can be bent a long way without any atomic bonds breaking. Warm it up, and the metal turns back into austenite, which has only one way to fit, and the original shape returns with it.

There is a second trick at warmer temperatures, called superelasticity. When the metal is already in its austenite form, a strong enough push turns part of it into martensite on the spot, and the moment the push stops, it turns back. The metal stretches much further than ordinary steel could and then springs back to its shape, with no heating needed at all.

Where the memory is put to work

NASA has used exactly this in a superelastic tyre developed for future vehicles on the Moon and Mars. According to NASA, the alloys it uses can take up to about eight percent reversible strain without permanent damage, a remarkable amount of stretch for a metal to recover from. The tyre needs no air, so it cannot be punctured, and because the metal springs back instead of staying dented, it can flex over rough ground and keep its shape.

So can a spoon forget it is a spoon? A gallium one forgets almost at once, and nobody should drink the tea afterwards. A shape-memory spoon could be twisted into something unrecognisable at breakfast and, with a little warmth, find its way home before lunch. Somewhere between the two is the quiet spoon in your drawer, doing what it has always done: staying exactly the shape it was made.