What would work in real life (chemistry wise) so that we can have Spiderman climbing skills? originally appeared on Quora, the place to gain and share knowledge, empowering people to learn from others and better understand the world. You can follow Quora on Twitter, Facebook, and Google Plus.

What would work in real life (chemistry wise) so that we can have Spiderman climbing skills?

The problem isn’t just chemistry. It’s biology and chemistry and physics.

Physics:

Human beings are “large” as animals go. The reason this matters is because of the Square Cube Law. Essentially, this means that if you make an animal twice as “big”, you get a surface area that is 4 times bigger (roughly - the square of 2) but a mass that is 8 times bigger (roughly - the cube of 2).

Let’s look at a simplified example. Let’s take a spider and approximate it as a cube 1cm x 1cm x 1cm and a density of 1 g/cm^3 (the density of water). A spider might hang 100 times its body length from a branch (that’s a meter in this case). This spider has a surface area of 6 cm^2 and a mass of 1 g. To hold up a mass of 1g, you need a force equivalent to about 9.8 mN, something easily provided by a string of silk so thin that you can’t see it. The amount of liquid silk necessary for this is likely measured in the micrograms.

Now, let’s look at a simplified human. We’ll approximate that human as a cube 50cm x 50cm x 50cm and a density of 1g/cm^3. The human is going to hang just 50 meters - about 160 feet. This is 100 times the body length, just like the spider. This human has a surface area of 15,000 cm^2 and a mass of 125,000 g. To hold up a mass of 125 kg, you need a force equivalent to about 1,225N. This force would need to be provided by a string that will absolutely be visible. The amount of liquid required to make such a string would likely weigh kilograms.

And here’s the problem: a human would have to carry enormous weights of liquid silk to move short distances like a spider.

There are two ways to fix this:

1. Make humans much lighter

2. Make the rope much lighter

Making humans much lighter is possible (technically) but it’s not going to be easy. Lots of genetic engineering might make us 20–30% lighter, but we’re not going much lower than that. The reason is that we simply must have a certain amount of water in our bodies. Birds have a density of around .75 g/cm^3, and evolution has lowered their densities for millions of years.

That won’t make enough of a difference - we’ll still need to carry more than our own weight of liquid silk to move around.

But what about making the rope lighter?

Chemistry:

Let’s talk about carbon nanotubes, which are probably the strongest possible “rope” (or at least in that ballpark). They have a strength of roughly 100 GPa, which is to say they can support 100 billion Newtons per square meter of rope cross sectional area. That’s around 100 times stronger than spider silk. To support our 1,225N, we’ll need a rope with an area of 1.225E-8 square meters. That’s a round strand with a thickness of just 0.062mm in radius. That’s astonishing.

So, even if we humans stay our regular weight, carbon nanotubes are strong enough to allow us to hang from a fiber that we could conceivably carry.

But what about strength? Are we strong enough to be pulled around by one arm like that?

Biology:

Generally, no. Repeatedly being yanked by one arm is going to lead to tendon/joint damage and dislocation. Again, genetic modification could make this possible - orangutans are about as heavy as we are, and they climb and hang from their arms all the time.

So, to sum up:

1. Humans are really too heavy for this sort of thing.

2. Spider silk is way too heavy for this, but if you could find a way to “spin” carbon nanotubes, then it’s conceivable we could carry the fluid necessary to do this.

3. Our arms couldn’t take this kind of punishment - see point 1.

But, if you’re willing to genetically engineer humans and you can master the difficulties of spinning carbon nanotubes on demand, then you might just make this possible.

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