[mabbo]

Tiny machines that extract energy and material from their environment in order to replicate themselves... isn't that bacteria? Life? Isn't that all around us already? Aren't we that?

The only way I can imagine gray goo being a real threat is if we can design such a machine that is more efficient and resilient at extracting energy and matter into copies of itself better than 4 billion years of evolution has made the existing life on Earth. And while, yes, we are often able to do better than life at certain tasks, I have a hard time believing on a large scale of time and space we can win that arm wrestle.

Life is optimized in every direction and has tried most of the tricks. It's hard to beat.

[gallerdude]

Life is really good at finding a local maximum, but not a global maximum. Cheetah's were evolved to be really fast, but they're still slower than a motorcycle.

[cwp]

Cheetahs evolved to chase down prey. They are much better at that than a motorcycle. (Or even a person on a motorcycle!)

[mabbo]

> Cheetah's were evolved to be really fast, but they're still slower than a motorcycle

A good kick can permanently disable a motorcycle such that it can no longer move faster than a cheetah. Less so for cheetahs- they can heal from wounds. A cheetah is also carrying with it all the needed equipment to turn many forms of raw matter (meat) into fuel to power a cheetah. And many cheetahs carry with them a fully functional cheetah factory.

My point is that humans are great at optimizing one dimension, but to build something that is better optimized in enough dimensions to outdo life is very unlikely.

[kleer001]

Let me know when motorcycles can reproduce. Then I'll be scared.

[DagAgren]

Motorcycles are not self-sufficient. On a timescale of longer than a day, they will lose to any cheetah.

Humans have yet to design a machine that could even outcompete a fluffy kitten.

[Symmetry]

Rewrites in how living cells work at a fundamental level is really hard. It took a billion years to go from prokaryotic cells to eukaryotic ones and that was a pretty simple change - just move the energy extracting membrane inside to get out of the squre/cube culs-de-sac bacteria were stuck in. But at the same time it's the sort of thing that would be obvious to an intelligent designer. I'm not sure that microscopic diamondoid self-replicators are possible but I wouldn't rule out the idea that similar improvements are easy pickings in synthetic biology and that's a pretty scary thought.