this post was submitted on 28 Sep 2025
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If I made a sci-fi game I would just make the currency MWh. They handwave away so much science, why not have a watch sized device that can store insane amounts of power?
Which makes me wonder, is there a physics limit to the density of energy? There has to be, anyone know what it's called?
the physics limit to the density of energy is literally a black hole. it compresses the maximum amount of mass (energy) into a space. but that's technologically useless since you can't extract the energy out of it on-demand.
The densest ways of storing energy that are technologically useful are:
There's also speculative technologies like antimatter (24 * 10^9 kWh/kg) which aren't available today.
Source
The beauty of using uranium as currency is that if anyone hoards too much of it, the problem takes care of itself.
So one gram of antimatter could power a modern city for like three months? That's wild.
There actually is a method that could be used to extract energy out of a black hole. Probably not something you'd build in a watch-sized device though.
it only seems to work for rotating black holes though?
Yeah, that's why you have to wind up your watch every now and then. To spin up its internal black hole again.
just drink more it'll start spinning soon enough
Don't they all spin though? As in any matter falls in one way or another angular momentum is gained.
It is possible, but very unlikely. Maybe two bh merge that has exactly opposite angular momentum.
If the well, event horrizon expands when a blackhole takes more mass, why can't we just figure out how much volume it is compressed into by measuring the event horrizon increase?
We know the matter that goes in is a certain size. Maybe we can deduce the total size it is compressed to? And the size the blackhole gains.
It's impossible to know based on the current understanding of particle physics. A black hole is formed when the inward gravitational force exceeds the outward neutron degeneracy pressure of a sufficiently massive object, which is what keeps neutrons from occupying the same space (not really, it's complicated). Beyond that, only conjecture exists with no evidence, and the information paradox makes it impossible to observe the space inside the event horizon.
Because Hiroshima was leveled by "only" 20 MWh (cost ranges from 120€ in northern Scandinavia to 1010€ in Greece) so having people carry energy wallets with enough to make more around day to day is like paying your groceries bill with C4 (which is perfectly save as long as there is no primary explosive).
Yeah, but they will have a perfect safe containment device, and a way to transfer safely, just like they have FTL.
Stellaris is a space 4x game that uses energy as a universal currency. The Endless Space games are also 4x games that use ancient nanomachines called Dust as currency.
And yes, concentrating energy increases mass. E=MC^2, which means more Energy must necessarily mean more Mass. So basically gravity will be your hard limit, theoretically stuffing enough energy into small enough a place will create a black hole, though I assume if you're talking electricity then there's probably some physical limit you would hit first.
We have technological limits to the storage efficiencies of different types of batteries. Batteries defined as something that can store useable energy. If we are talking just energy, matter "stores" lots of energy, and you can look at the famous Einstein equation to play with numbers. I do know we have something like a matter density limit in black holes.
Matter, expressed in mass, so kilograms or tons.