What if bubbles could last forever?

You blow a bubble. It floats and shines with rainbow colors.

Then, pop! It's gone. What if bubbles never popped?

Blow a soap bubble and it drifts away, shimmering with swirls of color. A few seconds later, pop! It's gone. Some bubbles last longer than others, but they all pop in the end.

So what if bubbles could last forever? Would the sky fill up with them? What would it take to make one that never popped? In this lab we follow three clues: what a bubble's skin is made of, why it dries out, and what happens when a bubble freezes.

A soap bubble is a thin liquid film enclosing a pocket of gas, and its lifetime is set by how long that film can hold its liquid. In the words of researchers at the University of Lille, ordinary bubbles are fragile and ephemeral: they burst after just a few moments because of gravity-induced drainage and/or evaporation of the liquid.

This thought experiment imagines bubbles that never burst. To reason about it, we look at the structure of a soap film, the two ways it loses water, a 2022 study that pushed a bubble's life past a year, and what happens to a bubble at freezing temperatures.

A bubble's skin is like a sandwich. There is soap on the outside and water in the middle.

When the water dries up, the bubble pops.

Science World, a science center in Vancouver, describes a bubble's skin as a sandwich. Two layers of soap molecules are the bread, and a thin layer of water is the filling. The bubble lasts as long as that water stays trapped between the soap layers.

It pops when the water is lost. Bubbles dry out quickly in the sun or in very dry air. A puff of wind can pop them. And if a bubble touches your dry finger, the water is pulled toward your skin and the bubble bursts.

A soap film has the structure of a sandwich: two layers of soap molecules enclosing a thin layer of water. Science World explains that the film survives as long as its water filling is trapped, and fails when that water is lost.

The routes to failure are evaporation, which is fastest in sunlight and dry air; mechanical disturbance such as wind; and contact with a dry surface, which draws water out of the film. The Lille researchers add the other main mechanism: gravity drains liquid downward through the film, thinning its top until it ruptures.

Imagine bubbles that never pop. They would float and float.

You could keep a bubble on your shelf, like a glass ball!

Now imagine bubbles that lasted forever. You could blow a bubble and keep it on a shelf. Every bubble ever blown at a birthday party might still be floating somewhere, drifting in the wind or piling up in corners.

To last forever, a bubble's skin would have to stop its water from draining away and stop it from drying out, forever. Scientists have come close for one of those problems and part of the other, but not for 'forever'. Everything about a never-popping world is an idea, not a fact.

An everlasting bubble would need to defeat both failure modes indefinitely: no net drainage and no net evaporation. It would also need to survive knocks, dust and anything that might grow on it.

If ordinary bubbles behaved like that, the consequences would be odd: foams in sinks and drinks might never collapse, and bubbles might accumulate wherever they drifted. These are speculative. In practice, researchers are interested in long-lived bubbles less for toys than for stable foams, which the Lille team suggested their results could help create.

Scientists made a special bubble. It lasted 465 days!

That's more than a whole year. Tiny plastic beads and a sweet, sticky liquid helped it.

In 2022, a team at the University of Lille in France reported a bubble that lasted 465 days, more than a year. It was about 8 millimeters across. Two ingredients made it so long-lived.

First, tiny plastic beads covered its skin and stopped the water from draining away. On their own, bubbles like that lasted only a few tens of minutes. Second, the team added glycerol, a sweet, thick liquid that soaks up moisture from the air. That made up for the water that dried away. The team thinks mold feeding on the glycerol probably helped finally pop it.

Aymeric Roux, Alexis Duchesne and Michaël Baudoin of the University of Lille published their results in Physical Review Fluids in 2022. Their 'gas marbles' were bubbles with shells of plastic microparticles, which form capillary bridges that stop water draining from the walls. Water-based gas marbles alone survived only a few tens of minutes.

Adding glycerol, which absorbs moisture from the air, compensated for evaporation. The team's models showed an equilibrium between water lost and water absorbed, and an 8 mm water-glycerol bubble lasted 465 days, which the university describes as a record for a bubble in a standard atmosphere. Molds feeding on the glycerol probably hastened its end.

On a very cold day, a bubble can freeze!

Tiny ice crystals swirl across it, like a snow globe.

On a freezing day, a bubble that lands on a cold surface can freeze. Researchers at Virginia Tech filmed it happening. The bottom freezes first. Freezing gives off a little heat, which warms the nearby water and makes it flow up the bubble. That flow breaks off tiny ice crystals that swirl across the bubble like snow in a snow globe, until the whole bubble is frozen.

A frozen bubble doesn't last forever, though. It is still very thin and fragile.

A 2019 study in Nature Communications from Jonathan Boreyko's team at Virginia Tech, reported by PBS NOVA, explained the 'snow globe effect' seen when a bubble freezes on a cold surface. The bottom freezes first, and the freeze front releases latent heat into the adjacent film, warming it and driving a flow toward the top of the bubble.

As more latent heat is released, the flow strengthens, stressing the freeze front and breaking off tiny ice crystals that slide across the surface and grow, so it looks as though many freeze fronts form at once. As Boreyko put it, it is actually only one freeze front. Freezing changes a bubble's film, but does not make it everlasting.