BLOCKCHAIN & WEB3 FUNDAMENTALS - Chapter 9, Exercise 2 Solution ========================================================== Paying Someone With No Direct Lightning Channel PROBLEM ------- Explain, in your own words, how two people who have never directly opened a Lightning Network channel with each other can still send a payment to one another through the network. SOLUTION -------- The Lightning Network isn't just a collection of isolated, two-party channels - it's a real network of many interconnected channels, and a payment can route across a path of multiple existing channels rather than needing one direct channel between the sender and the final recipient. Concretely: if person A has an open channel with person B, and person B separately has an open channel with person C, then A can pay C by routing the payment through B - the payment effectively hops from the A-B channel to the B-C channel, with B's own node forwarding it along (typically earning a small routing fee for doing so). Neither A nor C ever needed to open a channel directly with each other; they just needed to be connected through some path of existing channels across the wider network. This is exactly why this chapter describes the real network as having roughly 17,000 public nodes and around 40,000 public channels - that density of interconnection is what makes it likely that a workable route exists between most pairs of participants, even ones who've never transacted with each other before, without every possible pair needing its own dedicated, individually funded channel. ANSWER: The payment routes across a path of existing, already-open channels between intermediate nodes, rather than requiring a direct channel between the two parties - much like how a message can pass through several people who each know the next person along a chain, even if the first and last person in that chain have never met directly. ---- WHY THIS WORKS AS AN ANSWER This correctly describes routing across a chain of existing channels as the actual mechanism (rather than, say, incorrectly assuming a direct on-chain settlement is needed for every new pair of users), and ties the explanation to the chapter's own real network-size figures as evidence for why this routing generally works in practice.