The Mummy struggles with the chemistry but gets the physics right with a crash

It’s been 18 years since the cheesy but fun 1999 incarnation of The Mummy, and we were long due for another reboot. To meet that need, along came Tom Cruise accompanied by Russell Crowe and relative newcomers Sofia Boutella and Annabelle Wallis, in The Mummy.

Sofia plays Ahmanet, a cursed Egyptian princess who was cast aside by her family and sought revenge in the worst way possible. For her crimes, she was entombed for eternity and erased from history.

Enter soldier of fortune Nick Morton (Tom Cruise), who unwittingly awakens Ahmanet from a 5,000-year slumber. It’s up to Morton, archaeologist Jenna Halsey (Annabelle Wallis), and Henry Jekyll (Russell Crowe) to stop her from reclaiming her stolen kingdom.

The film is clearly setting up Universal’s “Dark Universe” alternative to the Marvel universe, with a host of famous monsters to be rebooted including Frankenstein, Dracula and the Invisible Man. The film also introduces the secret organisation Prodigium, led by Dr Jekyll, who find, examine and destroy evil manifestations in the world.

So let’s take a light-hearted cross-examination of the science behind some of the action scenes in the film. But beware, we’ll be letting some mild spoilery secrets out of the sarcophagus.

Shooting down an aircraft with birds

While still inside her sarcophagus on board a military transport plane, Ahmanet summons an immense flock of ravens, who smash through the engines and front windshield, and take out the pilots for good measure.

But could the Mummy have taken down an aircraft with birds?

Bird strikes are a regular problem for aircraft of all varieties, with more than 65,000 incidents reported from 2011-2014. High-profile recent incidents include US Airways Flight 1549, which hit a flock of geese shortly after takeoff, prompting an emergency water landing nicknamed the “Miracle on the Hudson”.

In that incident, birds took out both engines but they can also hit the windshield.

Here come the birds. (Universal Pictures)

The aircraft in the film is a Lockheed C-130 Hercules, with a cruise speed of 540km/h. Let’s say a raven can speed for short periods at 80km/h. This gives us a net closing speed of 620km/h between plane and bird, because it is aiming for the plane head-on.

For example, in this learjet collision from 1981, the plane was at low altitude and likely travelling at a relatively low speed of perhaps 400km/h.

Let’s assume that bird wasn’t malicious and hence wasn’t flying head on at the aircraft - so the net closing speed would just be the 400km/h.

Impact energy scales with the square of the speed, so an increase in impact speed from 400km/h to 620km/h results in an increase in impact energy of 2.4 times, meaning a single bird impact in the film is much more damaging.

Some airframe standards mandate being able to withstand a single hit from a 1.8kg bird. Indeed the windshield does seem to handle the first few impacts. But given a few thousand birds flying into the plane all at the same point, it seems highly realistic that the windshield would give way and the plane would be doomed.

This same principle applies to repeated bullet impacts with bulletproof glass.

Verdict: It’s highly plausible that so many bird strikes would break the windshield, if you allow for magical undead-mummy bird-corralling capabilities.

Working with mercury

Superman has his Kryptonite: for The Mummy, the element mercury does the job. Ahmanet is both entombed in a massive bath of mercury and injected directly with it later to disable her, making use of its property of being the only metal that is liquid at room temperature.

The film’s production notes suggest this may have some origin in Egyptian beliefs: perhaps it was just used as a pigment.

The plan is to inject Ahmanet with liquid mercury, then cool it down to -38℃ (which is the correct temperature at which mercury transitions from solid to liquid) to “solidify” Ahmanet, then dissect her for study. One of the potential issues with this plan is that solid mercury is relatively soft (like lead or tin) and can be easily manipulated.

So instead of a stiff Wolverine-like corpse, the Prodigium crew may just enrage her even more, which is exactly what happens.

Verdict: Nice chemistry, but a little soft.

Eating your way to a better body

Princess Ahmanet starts the film as a weak skeleton, but rapidly regains her original physique by consuming multiple human victims.

Her consumed victims become skeletal servants themselves. If we assume her normal weight is 60kg, approximately 15% of that weight is her skeleton, so around 9kg. She needs to gain about 51kg of mass.

I lost count during the film but I think she “consumed” about six people to regain her original physique. That’s about 8.5kg of flesh-eating transfer per victim.

But her (mostly larger male) victims are clearly mostly defleshed, suggesting they may have lost up to half their bodyweight, say 40kg per victim, or a total of 240kg.

That means either her consumption process is inefficient - with only a 21% mass transfer rate - or the directors thought it would be nice to have her suck the flesh off more than one victim for effect.

Verdict: Something doesn’t add up.

Sarcophagus suffocation

As punishment, Ahmanet is entombed alive in her sarcophagus (a common theme in Mummy films), and then dipped into a well filled with mercury. This is a nightmare scenario, but how long might a normal human survive before suffocating?

A big sarcophagus might measure about 2 metres by 1 metre by 0.5 metres - for a total volume of approximately 1m³, or 1,000 litres of air if we ignore the walls. Subtract a small female body - about 60 litres - and you’re left with 940 litres of air, which is initially 21% oxygen - 197.4 litres.

You breathe in air containing oxygen, but the air you exhale isn’t completely devoid of oxygen either. We can use an approximate net oxygen consumption rate of 0.4 litres per minute to work out how long you’d survive:

Time to suffocate = oxygen content / consumption rate

= 197.4 litres / 0.4 litres/minute

= 493.5 minutes

= 8 hrs 13 minutes 30 seconds

This assumes you can completely use all the oxygen available, which is the optimal case. In reality, you’d probably pass out and die before you’d completely sucked all the last bits of oxygen out of the air.

Luckily Ahmanet is cursed, presumably to live forever, so she likely has other concerns, like trying not to go insane being stuck for 5,000 years in her pitch-black sarcophagus.

Verdict: Painfully plausible: she either suffocates 5 million times over or the curse “protects” her from dying.

Behind the scenes: filming in zero gravity

If you don’t have access to a film studio in orbit, your only other filming options are faking it underwater or using robot arms like in Gravity, a drop tower, or what they did for The Mummy: zero-gravity parabolic plane flights, a technique previously used in classic films like Apollo 13.

Filming in zero gravity with parabolic aircraft loops (123rf.com/Lars Christnsen/Universal Pictures/Michael Milford)

Zero Gravity Corporation provided the flights wherein a modified Boeing 727 flies repeated parabolic arcs that alternate between zero gravity for about 20 to 30 seconds (at the top of the parabola) and about 1.8 normal gravity at the bottom of the trajectory - where an 80kg adult will feel like they weigh 144kg.

NASA also uses a KC-135 aircraft to do essentially the same thing, also known as the “Vomit Comet”.

The crew did 16 parabolic flights within a two-hour period, twice a day, for two days - for a total of 64 weightlessness sessions. Talk about dedication. The actors performed inside a C-130 interior reconstruction encased within the larger plane.

Cruise talks about how hard it is to fake weightless action scenes, so the fact that they actually filmed in genuine zero gravity means the film gets an A+ there for scientific realism!

Verdict: You can’t fake real science.

The overall verdict

The Mummy is a welcome revisit to the classic monster film of old, paying the right amount of homage to the classics, while introducing the modern world of 2017 and setting up a new universe within which to entertain film goers.

In terms of the science, we get a heap of physics and a side of chemistry, some okay, some a bit dodgy.

That’s all more than redeemed for by the fact that the plane crash physics involve the real thing: more than half a billion dollars worth of actors and crew doing it for real, over 64 weightless, vomit-inducing loops through the sky.