What could microscopic people use for fire? ( series )

Question

Since fire is a staple of civilization and intelligent life , I though that my microscopic people ( 200 μm - 220 μm ) ought to have it too , but upon researching , I realized that fire can not exist at such small sizes

So my question is : what could these microscopic people use / harness in place of fire?

As a checklist of sorts , the replacement must -

• Produce heat ( of course )

• Be sustainable

• Not be Extremely difficult to produce or obtain

• Be Transportable

All help is greatly appreciated Thanks

Answer 1

There are 2 main properties of fire: warmth, light.

Warmth

At a microscopic scale, you can get the warmth directly by respiration. By respiration, I mean processing food (glucose) with oxygen to produce energy. In fact all living organisms have a fire burning in them. Only very very slowly. In fact SE has a very quick check on that too: https://physics.stackexchange.com/questions/116960/how-much-energy-in-form-of-heat-does-a-human-body-emit which states that an average adult male dissipates about 120 watts per hour. Which is nearly equivalent to burning 4 kgs of coal per hour.

So then. In order to get warmth at microscopic scale equivalent to fire, you oxidise high-energy chemicals into oxides and derive energy from them. If you want an even higher energy compound than glucose, try respiring with ethyne (acetylene) and oxygen instead of glucose and oxygen. Trust me, you (as a microscopic organism) would NOT regret this!

LIGHT

For light, you are going to use bioluminescence as a living organism. Vertebrates (fish) do that. Marine invertebrates do that. Even bacteria and fungi do that! Why can't you, an intelligent microscopic life form, can do likewise? And if your bodies are unfit for that, you can always domesticate some bioluminescent bacteria or grow a few molds of that fungus. Then harvest it and carefully seal the shiny part (probably some compound of phosphorus) in a non reactant microscopic bag (probably some membrane or something) and carry it wherever you want.

Answer 2

Great question, but I am not convinced that microscopic people would need fire. Cooking with fire played a role in human evolution by allowing us to spend far less time chewing and digesting. This more efficient transformation of incoming food into energy to grow and run our bodies increased the evolutionary payoff for "spending" energy on brain growth. It also simply freed up time to do other evolutionarily successful things. However microscopic intelligent beings would presumably take in food in a completely different way (absorption?), with a completely different evolution.

The other main roles for fire, warmth and repelling predators, could still apply, but at the scale these people live at their world must be so granular, so much subject to violent buffeting, and generally so utterly different from ours, that there is no reason to suppose any close analogue of fire would be necessary to them. In particular, there is no reason why defence and warmth should be provided the same way.

The third significant role of fire for early humans - to clear and fertilize land in "slash and burn" agriculture - is also unlikely to have a parallel at that scale.