# In zero $g$ would someone inside a water bubble be unable to swim and drown?

I am referring to a scene from the film Passengers where a woman is swimming in a pool on a spaceship with artificial gravity, and suddenly the artificial gravity turns off. She is stuck in the water and is unable to propel herself out of the bubble.
Here is an official clip from the film, though be aware it could be frightening to some:

But, why does this happen? Why can't she just paddle her way out of the bubble? Shouldn't moving the water using her hands and legs towards one direction push her in the opposite direction? Why won’t this work in zero G?

• Without knowing the film or book an answer will be difficult. not everybody has seen a scene which you saw. Aug 21, 2021 at 14:26
• Duplicate of space.stackexchange.com/q/39085 Aug 21, 2021 at 14:29
• This must have been asked before. Aug 21, 2021 at 15:11
• From the title, the question looks like a duplicate, but from the content, it is very different from q39085. Maybe reword the question as: "Is it realistic, that the lady would drown in a huge water bubble after artificial gravity on a spaceship fails?". Aug 21, 2021 at 17:01
• "Aurora flounders in the weightless water." ... "Rippling masses of water float everywhere, dividing and merging. There is no surface. There is no up. In the middle of this chaos, Aurora is trying not to drown. A truck-sized blob of water swallows her up. Inside the jiggling mass she struggles, running out of air. She gathers herself. Lunges through the water. Shoots out of the blob, gasping for breath. She drifts within reach of a railing and grabs hold." imsdb.com/scripts/Passengers.html Aug 22, 2021 at 9:37

The physics in that film isn't very realistic in parts.

She could swim out of the bubble, although the couldn't just float to the 'top'.

One major flaw in that scene is that the bubble would form at all. From memory it's about 5 or 10m diameter, seemingly held together by surface tension.

The surface tension would not be strong enough to hold a bubble that big together, it would break into thousands of smaller pieces.

She would be fine, but it wouldn't be as dramatic for the viewers!

• Yes this is probably right. As discussed here at small sizes (e.g. drops) cohesion due to surface tension is strong, and at large sizes (moons or planets) self-gravitation dominates, but a few tens of meters is at the cross-over point between the two and at the surface the pressure due to either effect is only about $1 \times 10^{-3}$ Pa.
– uhoh
Aug 21, 2021 at 23:09
• I wonder how hard it would be to breath pure air if the whole space is filled with a mixture of air and small floating bubbles everywhere. Aug 22, 2021 at 7:38

If you look at that scene carefully, it was not so much the propelling herself through the water that she had a problem with. She was actually doing exactly that, she was paddling her way out of the bubble. But just before she could reach the end of the bubble ( she had got her hand poking out) , another body of water crashed into the original bubble, increasing the distance she needed to paddle to reach the edge. And since her lungs had run out of air by then, she could not do that any more.

The main difference she had to encounter was that she could not just float to the top. In normal gravity, you do not have to actively paddle to reach the top. As long as you have air in your lungs, buoyancy would push you to the top.

In zero G, there is no buoyancy, so she had to actively expend energy to paddle her way to the edge . And she ran out of air, before she could make it to the edge.

• "In normal gravity, you do not have to actively paddle to reach the top" is not the case for everyone. Lungs full of air and I still end up at the bottom of the pool. Aug 22, 2021 at 3:02
• It sort of depends on the proportion of fat and other stuff in your body, because the density of humans is critically near the density of water ;P Aug 22, 2021 at 6:33
• @Trebor If anything i would assume fat persons would be even more buoyant, because fat is less dense than bone and muscle
– user311852
Aug 22, 2021 at 7:57
• Can confirm: gaining enough body fat makes a person positively buoyant, and losing it makes them negatively buoyant again.
– rob
Aug 22, 2021 at 11:56

The film scene is bad physics in many aspects. For example, surface adhesion would usually keep the girl at the surface of the forming water bubble. She would just need to turn round in the right direction to be able to breath. You probably have seen insects fall into a drink and keep floating at the surface, despite gravity should pull them down (and actually pulls them down, once you push them in). But for the small insects, surface adhesion in water is higher than gravity, and they keep afloat.

In zero gravity in a space ship, the lady would definitely stay at the surface, too.

In reality, with the water being rough after her swimming, a lot of small bubbles would form, after the gravity fails. The question is, if one could breath in this mixture of water droplets and air. I guess, with sneezing and coughing regularly, humans would be able to force out the excess water, unless the water-to-air-mixture gets too extreme. Some instinct movements of the arms and hands will usually help to defend against the water droplets before they even enter the mouth.

• 1) "Surface adhesion" is the term for two surfaces sticking to each other. From your description of insects on the water, you likely meant "Surface tension" 2) Surface tension is negligible at human scale: put a human on water and they get wet. 3) Keeping "afloat" requires buoyancy, and there's no buoyancy in water at zero g, as there's no pressure differential inside the water: it's at atmospheric pressure throughout. 4) When the gravity stopped, she was already underwater as she'd dived in, so no force could "keep" her at the surface, as she wasn't there. Aug 22, 2021 at 7:09
• @DewiMorgan Surface tension is what creates a bubble (though not as big as shown in the movie). And no, I am not talking about buoyancy, either: The insect, that floats on top of the water in a glass, sinks, once it is dipped in, because it has negative buoyancy. But we have no gravity here. What I wanted to say: Surface adhesion keeps the insect afloat despite its (under normal conditions) negative buoyancy. Aug 22, 2021 at 13:43
• "Surface adhesion" is a term only applied to solids, not to liquids, and describes adherence of the surfaces together. All of the things you describe are surface tension (en.wikipedia.org/wiki/Surface_tension). Yes, it makes bubbles and droplets spherical, but also holds insects from passing through the water's surface, and keeps small droplets from breaking up. It applies only to small, hydrophobic, surface objects. It does not apply to already-wet objects, submerged objects, or objects at human scale rather than insect scale; so it is triply irrelevant here. Aug 22, 2021 at 20:44

That's a fun question and when I first saw it, I wondered about the actual physics too. I don't have any "research" except observation to offer: I thought about the space station... and if someone had a plain old cup of coffee and the gravity shut off. We've all seen things "let loose" from videos of astronauts in space. Including water/solids.

The water would stay together initially until some force acted upon it, such as simply moving the cup. At that point the blob of coffee would basically divide and could become many smaller blobs depending on if anything acted upon them. So back to the movie... if she was in the water and gravity went away, all she should need to do is start thrashing and flailing about, which would send the water in all kinds of trajectories and away from her most importantly.

I don't know about adhesion though, and if any water would "cling" to her (i.e. if you pour water down a wall, it also spreads sideways a bit beyond the main pour, despite the pull of gravity downward, so there is some "clinginess" going on related to adhesion (cohesion??)). But even if it clung to her nose/mouth, the simple act of coughing would easily dislodge it into the zero-G area around her. Any physicists out there to confirm?