What Are the Scientific Flaws in the Movie Downsizing?

[BillTre]

I recently ran across a review of the new movie "Downsizing" (starring Matt Daman and Kristen Wigg (together again from "The Martian")).
The main issue in the movie seems to be shrinking people will reduce their environmental load on the planet (smaller people use less stuff). However, as any biologist knows, smaller size means a larger surface area to volume ratio, which means more heat lose from the body among other things.

I am not concerned about the movie itself but thought it raised some interesting implications. Similar issues could have arisen with other shrinking things movies, but I am "being here now".

1)
Here are some questions I have about being small in this way:
How big would their iPhones be? If they were also shrunk, would they be able to still work? (I figure the electronic elements are approaching limits of current technology, so a reduction in size by >10x might exceed what is possible). Maybe they just would not have iPhones and such things (not clear to me from the trailer).

2)
What about their brains? Either they would be smaller, but with the same size cells, resulting in brains with significantly fewer cells, or their cell would also be shrunk to maintain cell number.
Presumably the shrunken people would maintain human's advantageous brain to body size ratio.
If they had fewer cells, how would they affect them mentally? Lose memories?
If their cells were smaller would they still be able to work on a molecular level? Cells are probably pretty size optimized by evolution.
I suspect that extremely smallified people would have some kind of reduction in brain function, but I also don't think such a question has any obvious answers.

 

[.Scott]

You might also ask how procreation would work. Has their DNA changed? If not, they would give birth to full size people.
If their DNA has been modified, would they still be able to procreate?
I think it's best to just enjoy the movie - and suspend disbelief.

 

[BillTre]

You might also ask how procreation would work. Has their DNA changed? If not, they would give birth to full size people.
If their DNA has been modified, would they still be able to procreate?
I think it's best to just enjoy the movie - and suspend disbelief.

I wondered about that just after I made the post.
For biology to work, the DNA information function would have to be maintained in some way.
But, yeah, it looks like its a movie more for fun than deep analysis.

 

[davenn]

I think it's best to just enjoy the movie - and suspend disbelief.

Agreed ... as with all SciFi

But, yeah, it looks like its a movie more for fun than deep analysis.

again ... of course it is, as with all SciFi

just enjoy the movie.

Dave

 

[Janus]

I recently ran across a review of the new movie "Downsizing" (starring Matt Daman and Kristen Wigg (together again from "The Martian")).
The main issue in the movie seems to be shrinking people will reduce their environmental load on the planet (smaller people use less stuff). However, as any biologist knows, smaller size means a larger surface area to volume ratio, which means more heat lose from the body among other things.

I am not concerned about the movie itself but thought it raised some interesting implications. Similar issues could have arisen with other shrinking things movies, but I am "being here now".

1)
Here are some questions I have about being small in this way:
How big would their iPhones be? If they were also shrunk, would they be able to still work? (I figure the electronic elements are approaching limits of current technology, so a reduction in size by >10x might exceed what is possible). Maybe they just would not have iPhones and such things (not clear to me from the trailer).

2)
What about their brains? Either they would be smaller, but with the same size cells, resulting in brains with significantly fewer cells, or their cell would also be shrunk to maintain cell number.
Presumably the shrunken people would maintain human's advantageous brain to body size ratio.
If they had fewer cells, how would they affect them mentally? Lose memories?
If their cells were smaller would they still be able to work on a molecular level? Cells are probably pretty size optimized by evolution.
I suspect that extremely smallified people would have some kind of reduction in brain function, but I also don't think such a question has any obvious answers.

There's the rub. If you assume that they decrease the number of atoms per person, then you run into problems with certain things not working (including cell metabolism) due to over-simplification. If you try to say that their atoms themselves are shrunk, then they would not be able to process food, air. water etc. with normal sized atoms.

You mentioned the surface area to volume issue already, but that also applies to muscle cross-section to body mass. Cross-section decreases by the square and volume by the cube. A person's muscles would be way stronger than they would need to be at that scale.

Then there is the gravity issue. The scenes from the trailer all make it look like life at small scale would be like life at normal scale. But the acceleration due to gravity would be the same. If we drop an object from 1.5 meters, it will take ~0.4 sec to fall to the ground, at 1/10 scale for instance, this would be dropping it from 0.15m and it would take only 0.175 sec to fall to the ground. Objects would seem to fall faster for someone at that scale than it does at normal scale. I'm not too sure how well our reflexes would handle it. The distance the nerves impulses have to travel will be shorter, but nerve impulse speed is proportional to axon diameter, so the two may well cancel out. We might end up being very clumsy at that scale.

 

[StoneTemplePython]

You mentioned the surface area to volume issue already, but that also applies to muscle cross-section to body mass. Cross-section decreases by the square and volume by the cube. A person's muscles would be way stronger than they would need to be at that scale.

Regarding scaling as height goes up of down, volume actually grows at a sub-cubic rate with humans but the exponent is strictly greater than 2.

I liked your comment though for a couple reasons. The disparity between volume (linked to weight) and surface area (linked to muscle cross-section and strength) is a simple but deep issue that my physicist friends immediately understand but practically everyone else I know does not understand. Most non-physicists (e.g. some CS people I spoke with about this 2 weeks ago) tend to get it better when I give analogies about how high grasshoppers and fleas can jump.

The typical physics response also reminds me of the old joke where a student asks for help estimating the volume of a cow, and the professor responds "that's easy. Let's assume the cow is shaped like a sphere...". Even though it's wrong, one can still get quite good insights with this approach.

In particular this kind of thing is on my mind as a tall guy, I'm quite aware that certain bodyweight exercises like pullups are harder for me, and BMI calculations are misleading by design.
- - - - -
Here's some info on the matter from Nick Trefethen, Professor of numerical analysis at Oxford.

http://www.ox.ac.uk/news/science-blog/does-my-bmi-look-big

Body Mass Index (BMI) is derived from a simple mathematical formula, devised by Belgian scientist Adolphe Quetelet in the 1830s, that divides a person's weight in kilograms by their height in metres squared to arrive at an estimate of an individual's body fat.

It's supposed to provide an approximate measure to help judge if someone has a healthy weight – and indicate, for instance, if they are obese. But as Nick Trefethen of Oxford University's Mathematical Institute pointed out in a recent letter to The Economist the basic formula BMI relies on is flawed:

'If all three dimensions of a human being scaled equally as they grew, then a formula of the form $\frac{\text{weight}}{\text{height}^3}$ would be appropriate. They don't! However, $\frac{\text{weight}}{\text{height}^2}$ is not realistic either,' Nick tells me.

'A better approximation to a complex reality, which is the reform I wish could be adopted, would be $\frac{\text{weight}}{\text{height}^{2.5}}$. Certainly if you plot typical weights of people against their heights, the result comes out closer to $\text{height}^{2.5}$ than $\text{height}^2$.'

Sticking with the current formula, he says, leads to confusion and misinformation: 'Because of that $\text{height}^2$ term, the BMI divides the weight by too large a number for short people and too small a number for tall people. So short people are misled into thinking they are thinner than they are, and tall people are misled into thinking they are fatter than they are.'

- - - -
I saw previews for this movie a couple days ago and wasn't that impressed.

 

[Callista Whyte]

This might sound stupid but would time go faster for a shrunken person?

 

[ZapperZ]

This might sound stupid but would time go faster for a shrunken person?

What makes you think "size" has anything to do with "time"? Do ants experience time differently than us?

Zz.