Home > Clement's Game > Science Fiction Round 73: More Guardians, More Galaxies

Science Fiction Round 73: More Guardians, More Galaxies


I saw Guardians of the Galaxy Vol. 2 last weekend, and it was a fun film.

Of course, from the perspective of physics, it was a travesty.  Rather than banging on the usual obvious things not done right (Faster than light travel won’t work!  That’s not what happens when you’re exposed to vacuum!), I’ll try to touch on a couple of more subtle issues.

There are spoilers here, but seriously, they’re basically all for things you should have seen coming.

The characters in this poster were all in the movie. The movie was also at least as colorful as the poster.

Those Vines Are As Big As Groot

Conservation of mass.

Does nobody ever care about conservation of mass?

I’m going to ignore most of the other physical impossibilities in the film, but my attention was drawn directly to this one by the intense cuteness of baby Groot.

Specifically: where’s he getting all the mass for those vines he keeps flinging around?  I wouldn’t be so bothered if they retracted back into himself, or some such.  But, no.  When he’s done with them, he leaves them behind with the landscape.  Worse, those vine-whip-tendril-things are pretty big relative to the tiny adorableness that is Groot.

Basically, he should be down to zero mass by the end of it.  Or he’s doing an awful lot of eating off-screen (relative to his body size, that is).

Maybe Rocket should have let him eat the bug.

I Don’t Think You Understand The Gravity Of The Situation

The final battle scene is (apparently) in the core of Ego’s Planet, and everyone is flying or jumping around shooting things at each other.  People not in ships or wearing jetpacks walk around on the ground.

And that’s a problem.

Because gravity doesn’t work like that.

If the core battle really is at the center of the planet, there should be no gravity at all.

Why, might you ask?  It’s a fun property of gravity (in the Newtonian approximation) following a 1/r^2 drop off in strength with distance.  As you move away from the Earth’s surface, the strength of the Earth’s pull falls.  But, as you move into the Earth, the gravity you feel decreases, until you reach about zero at the center.  Intuitively, this is because the half of the Earth to your right is pulling you right, the half to your left is pulling you left, and those two things cancel each other out.  In-between depths have in-between amounts of gravity.

I would have loved to see the effects of varying gravity as they go deeper, culminating in a cool low-to-zero g finale.

Unfortunately, not having gravity makes it a lot more challenging to film, and would have removed some perlious possibilities.  Besides, they clearly have Earth-strength gravity on the surface of the planet, despite being smaller than the Moon, probably because Ego has cosmic powers, so… pff, who needs physics?

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