Comment by not_kurt_godel
8 days ago
Sometimes I have a hard time wrapping my head around reconciling that with the estimated number of protons in the observable universe which is "only" ~10^80 (https://en.m.wikipedia.org/wiki/Eddington_number). Seems like it "should" be much higher, but orders of magnitude are sometimes deceptive to our intuition.
Unrelated, but I moved to a more rural area a while back and I’m surrounded by orchards and fields a fair amount of time, and my mind just can’t wrap itself around the scale of agriculture.
One avocado tree can produce around 200 avocados per year, and the orchards around here are probably around 150 trees/acre, so 30k avocados/acre/year.
Each avocado has about 250 calories (and that is just the parts that we eat, the tree has to put energy and mass into the pit and skin etc). These are food calories / kcal, so that’s 250k calories per avocado, or ~7.5 billion calories per year per acre.
7.5B calories/year is just about exactly 1kW, so that orchard is converting sunlight (and water, air, and trace minerals) to avocado calories at a continuous rate of 1kW. It’s incredible. The USDA says that as of 2022 there were about 880M acres of farmland in the United States alone.
1 acre is about 4,050 m^2, and incident sunlight has an average intensity of 1kW/m^2.
So your avocado orchard is converting incident sunlight to food calories with an efficiency of about 0.025%.
(This ... isn't wildly inefficient for photosynthesis, though typical values range from 1--3% AFAIU, though I've not computed this on a per-acre / per-hectare basis.)
Mind too that you're getting more than just avocado meat, there are also the skins and pits as you note, as well as leaves and wood, all of which could be used as fuel should we really want to.
Ecologists look at the net total energy conversion of ecosystems, often expressed not in terms of energy but as carbon fixation --- how much CO2 is captured from the atmosphere and converted to biomass.
And that amount is ... surprisingly limited. We'll often hear that humans use only a small fraction of the sunlight incident on the Earth's surface, but once you start accounting for various factors, that becomes far less comforting than it's usually intended. Three-quarters of Earth's surface is oceans (generally unsuitable for farming), plants and the biosphere require a certain amount of that activity, etc., etc. It turns out that humans already account for about 40% of net primary productivity (plant metabolism) of the biosphere. Increasing our utilisation of that is ... not likely, likely greatly disruptive, and/or both.
Another interesting statistic: In 1900, just as the Model T Ford was being introduced, and local transport (that is, exclusive of inter-city rail and aquatic transport) was principally dependent on human feet or horse's hooves, twenty percent of the US grain crop went to animal feed. (And much of that ended up on city streets.) We had a biofuel-based economy, and it consumed much of our food supply.
(Stats are for the US but would be typical of other countries of the time.)
This isn't an argument that fossil fuels are "good", or that renewables are "bad". It does point out, however, that changing our present system is hard, and any solution will cause pain and involve compromises.
It takes a bit to accept your (10^0 m) place in the universe on the length scale between the Planck length (10^-35 m), the width of a proton (10^-15 m) and the diameter of the observable universe (10^27 m).
I wonder if there's any reason we're roughly in the middle.
Well the ratio of the strong force, vs electromagnetism and the speed of light define the size of the atom. Life requires machinery to self replicate and the distance between a DNA base pair is a sugar molecule attached in a chain so that's about as small as possible. Intelligence requires a certain amount of complexity of something like a brain, and it has to be made of cells and doubtful it could be made more than an order of magnitude smaller.
Could intelligent life exist based on some other physical phenomena than a self-replicating string of atoms? Maybe some unknown quantum phenomena inside neutron stars or something big and slow on galactic scales or something new which fills the dark matter gap...
But otherwise it's physics driving where units of "stuff" can exist, and the correct scales for long term complexity/turbulence can happen, like the thin film of goo on the outside of the frozen crust of a molten rock we are.
"Roughly" still being off by a factor of 10^5 means an amoeba, or bacteria in general, would be acing the "middle" better than us though.
My brain says that's only 4 times as many.