Physicists have been discussing spacetime since the early 1900's. A very smart person, by the name of Albert Einstein, modeled space as 4 dimensions rather than just 3. The axis were then X, Y, Z and .... time.
Fortunately, you don't need to understand Relativity Theory in order to grasp Proof of Spacetime!
Fast forward 100 years or so and two researchers, Ilan Orlov and Tal Moran, proposed a new consensus mechanism where users staked space in their storage systems as a proof of value.
PoST is very similar to other consensus mechanisms where storage space is used as a stake in the mining process.
But, as you may have noticed, PosT adds one additional ingredient to Proof of Space : Time!
In a Proof of Spacetime system, the amount of time the space is used in your local storage adds to the value you can prove to the network.
For example, whereas in a pure Proof of Space you would prove 3 terabytes of storage, in a PoST system you could prove 3 terabytes-month. That'd mean you proved that 3 TB of storage was allocated to the network for a month.
PoST guarantees that a certain resource was locked for an amount of time. This adds another guarantee that stakers won't just allocate space until a block is minted and then turn their machines off for the rest of the month, for example.
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