No, really.



Before clocks, telling time was simple: look up, find the sun in the sky, and call it a day. After a while, despite the simplicity and elegance, we humans decided to create devices to help break up the day into smaller, more distinct parts — enter sundials and water clocks.



Now most of us rely on the clocks in our phones, watches, and devices. Communicating a shared time between two people in the same timezone is easy: all we have to do is look at our clocks and say the time.



But how do our devices tell time? And, more importantly, how do our devices communicate a sense of time between each other?



The answer is more complex than it seems. Many, if not most computers rely on a trusted source — an atomic clock, for example — to order events. Because of this, a computer in Cambodia can trust that a computer in London is synchronized to the same time, right?



Not quite.



Because of network delays, effects of relativity, and time dilation (differences between someone on an airplane and someone on the ground), the changes, however small, can prevent accurate synchronicity of time across a network.



This discrepancy is critical when constructing a decentralized payments network; nodes can't rely on a third party system like an atomic clock. To prevent a user from spending the same amount of money twice, a network needs a reliable system that can order transactions.



Proof of work — the enabling mechanism of the Bitcoin protocol — solves this problem through a SHA-256 brute force search. This solution, although monumental, is slow and clumsy. Bitcoin can only handle a max of 7 transactions per second.

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Solana is the world’s first blockchain built for web-scale because it solves the distributed time problem without significant overhead.

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The core innovation that makes this possible is Proof of History—a mechanism for continuous ordering that acts as a global clock for the Solana network.



Proof of History creates a record that proves that an event has occurred at a specific moment in time.

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Whereas other networks require participants to communicate in order to agree that time has passed, each Solana node maintains its own clock by encoding the passage of time in a sequential series of events.



With the help of sand, let's learn how this works.