Bitcoin: Digital Gold

:::section{mins=2} What Is Bitcoin :::

:::lead [[gloss:bitcoin|Bitcoin]] is the first decentralized digital currency that operates without banks, governments, or intermediaries. The network launched in January 2009 and has been running almost continuously ever since. :::

:::p [[gloss:bitcoin|Bitcoin]] combines two things at once: it is both a payment network and a digital asset. The network enables direct value transfer between participants anywhere in the world without any intermediaries. The BTC asset itself has a hard-capped supply — only 21 million coins will ever be created, and not a single one more. As of April 2026, about 19.87 million of those have been mined, which amounts to nearly 95% of the maximum. :::

:::p{html} The protocol was launched on January 3, 2009 by an anonymous creator working under the pseudonym [[gloss:satoshi-nakamoto|Satoshi Nakamoto]]. Consensus is based on [[gloss:proof of work|Proof of Work]] — a mechanism we covered in detail in 1.3 §2: miners spend computational resources searching for a valid hash, and the winner earns the right to record a [[gloss:block|block]] and claim the associated BTC reward. A new block appears approximately every 10 minutes, with base-layer throughput sitting at around 7 [[gloss:transaction|transactions]] per second. :::

:::p As of April 2026, [[gloss:bitcoin|Bitcoin]]'s market cap stands at around $1.33 trillion, making it the largest crypto asset by a wide margin. Its [[gloss:bitcoin-dominance|dominance]] (Bitcoin dominance — Bitcoin's share of total crypto market cap) holds around 55–60%. The current [[gloss:block-reward|block reward]] of 3.125 BTC was set after the fourth [[gloss:halving|halving]] in April 2024. :::

:::p{html} [[gloss:bitcoin|Bitcoin]] was the first working answer to the "Byzantine Generals Problem" — how strangers on the internet can agree on a shared database state without an intermediary when some of them may be dishonest. We discussed this problem in 1.1 §1 and its solution mechanism in 1.3 §1. Practically, this delivers three key properties: censorship resistance (no government can block a [[gloss:transaction|transaction]], unlike PayPal or SWIFT), immutability (after 6 confirmations — about an hour — a transaction is practically impossible to reverse, which we cover in 1.3 §7), and transparency (all transactions are public and verifiable via a blockchain explorer). :::

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:::callout{icon=💡} [[gloss:bitcoin|Bitcoin]] is often called digital gold, and the parallel runs deeper than it first appears. Supply is capped (21 million coins against the Earth's gold reserves), coins must be "mined" through computational work rather than extracted from shafts and ore, they cannot be forged thanks to cryptography rather than physical properties, and no central authority — no government, no central bank — controls emission. :::

:::keypoints{label="Key Points"}

• The first working decentralized digital currency in history
• Hard-capped supply: 21 million BTC forever, no exceptions
• Works without intermediaries, banks, or central authorities
• Largest crypto asset by market cap (~$1.33T as of April 2026) :::

:::details{badge=Advanced title="Bitcoin as a Schelling Point"} :::p [[gloss:bitcoin|Bitcoin]] is the [[gloss:schelling-point|Schelling point]] of the entire crypto industry. The same protocol has been running since 2009 with minimal changes, and this is a deliberate stance: there is no premine (no pre-mined allocation for creators), no VC funding, and no foundation with the power to push through changes. Maximum decentralization is achieved through several mechanisms working simultaneously — about 20,000 full [[gloss:node|nodes]] run around the world, network [[gloss:hashrate|hashrate]] holds around 700–900 exahashes per second, which makes attacks economically pointless, and no single company or mining pool controls more than 3–4% of the total computing power. :::

:::p Closely related to this is the [[gloss:lindy-effect|Lindy effect]] — the observation that the expected lifespan of a non-perishable phenomenon (a technology or an idea) is proportional to its current age. For [[gloss:bitcoin|Bitcoin]] this means something simple: the longer it runs without critical failures, the more reliable it appears to investors and users. Seventeen years of nearly uninterrupted operation is an argument that no other crypto asset can offer. :::

:::p The absence of a leader isn't a bug — it's a critical feature. No one can step onto the stage and announce that "the rules are changing now." Any change to the protocol requires agreement from the entire community of miners, developers, and users, and that's precisely what makes [[gloss:bitcoin|Bitcoin]] the most conservative protocol in the industry. ::: :::

:::further{label="Further Reading"}

• Bitcoin Whitepaper (Satoshi Nakamoto, 2008) | bitcoin.org
• mempool.space — live Bitcoin network dashboard | mempool.space :::

:::quiz{id=q-2-1-s1 correct=2 explanation="Correct. The 21M cap is coded into every [[gloss:bitcoin|Bitcoin]] node. Changing it would require virtually every node operator, miner, and exchange to agree and upgrade to modified software — practically impossible given the protocol's consensus-driven nature. Fiat currencies, by contrast, can be inflated by central bank decision alone."} What makes Bitcoin's 21 million cap fundamentally different from fiat currencies?

• Bitcoin has a large supply, so it's more valuable
• Central banks can increase the cap if needed
• The cap is built into the protocol and requires consensus of the entire network to change
• Satoshi can personally authorize additional issuance :::

:::section{mins=2} Satoshi Nakamoto and Bitcoin's Birth :::

:::lead [[gloss:satoshi-nakamoto|Satoshi Nakamoto]] is the pseudonymous creator of [[gloss:bitcoin|Bitcoin]], whose true identity remains unknown to this day. He published the whitepaper on October 31, 2008, launched the network on January 3, 2009, and vanished from public view in April 2011, leaving the project to live on its own. :::

:::p [[gloss:bitcoin|Bitcoin]]'s history begins with a nine-page document titled "Bitcoin: A Peer-to-Peer Electronic Cash System", published on a cryptography mailing list on October 31, 2008. The context was the global financial crisis, when the largest US and European banks stood on the brink of collapse due to risky mortgage-related bets, and governments began massively bailing them out at taxpayers' expense. On January 3, 2009, Satoshi created the genesis block (block #0, the network's first block), embedding in it a newspaper headline from The Times of that same day: "Chancellor on brink of second bailout for banks" — a direct ideological statement that the financial system could be built differently, so that it couldn't be rescued with a printing press in principle. :::

:::p On January 12, 2009, the first [[gloss:bitcoin|Bitcoin]] [[gloss:transaction|transaction]] took place: Satoshi sent 10 BTC to Hal Finney, a cryptographer and one of the project's earliest participants. On May 22, 2010, Bitcoin Pizza Day happened: programmer Laszlo Hanyecz bought two pizzas for 10,000 BTC (around $41 at the time). At April 2026 prices, those coins would be worth around $740 million — a frequently cited example of how cryptocurrencies work in their early stages. :::

:::p In April 2011, [[gloss:satoshi-nakamoto|Satoshi]] sent his final public message on the mailing list and vanished forever. His wallets — identified through what is known as the Patoshi pattern, a distinctive pattern in the nonce fields of early blocks that points to a single miner — hold approximately 1.1 million BTC. Not a single one of these coins has moved since 2010. As of April 2026, their combined value stands at around $80 billion, which makes Satoshi the largest known BTC holder in the world. :::

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:::callout{icon=💡} As if someone invented the internet, launched it, and walked away — no patents, no company, no profit motive. It works precisely because no one can claim it. :::

:::keypoints{label="Key Points"}

• The whitepaper came out during the 2008 financial crisis as a response to bank [[gloss:bailout|bailouts]]
• The genesis block contains an ideological statement from a Times newspaper headline
• Satoshi's wallets hold 1.1M BTC ($80B), none moved since 2010
• The unknown identity is an important feature making [[gloss:bitcoin|Bitcoin]] truly ownerless :::

:::details{badge=Advanced title="Bitcoin's Predecessors and Satoshi Candidates"} :::p [[gloss:bitcoin|Bitcoin]] didn't emerge from a vacuum — it had several intellectual predecessors that laid down individual building blocks of the eventual design. David Chaum created DigiCash in 1989, which used blind signatures — digital signatures where the signer never sees the content being signed. Adam Back proposed the [[gloss:proof of work|Proof of Work]] concept in his 1997 Hashcash project, where it was used to fight email spam. Wei Dai described b-money in 1998 — the idea of decentralized digital money with no central issuer. Finally, Nick Szabo in 2005 published his Bit gold concept, considered the closest direct predecessor to Bitcoin: a chain of computational proofs serving as money. Satoshi's real genius was in combining all these scattered ideas into a single working system, while adding the [[gloss:blockchain|blockchain]] and economic incentives for miners within a P2P network. :::

:::p Satoshi candidates are discussed with remarkable regularity. Craig Wright publicly claimed for years that he was the creator of [[gloss:bitcoin|Bitcoin]], but in 2024 a UK court definitively ruled against him. Hal Finney — the first recipient of a Bitcoin transaction and a long-standing candidate — sadly passed away in 2014, and his involvement was never confirmed nor disproved. Nick Szabo and Adam Back both categorically deny any involvement. The community has long settled on a consensus on this question: the identity of the creator doesn't matter, because the protocol works without him, and that's exactly where its strength lies. :::

:::p What can be said about Satoshi himself with confidence is fairly limited. He wrote in British English, actively posted on forums during hours convenient for European and American time zones, and clearly had expert-level understanding of C++, cryptography, and economics. Everything else is speculation. ::: :::

:::further{label="Further Reading"}

• Genesis Block (#0) on blockchain.com explorer | blockchain.com
• The Complete Satoshi — all writings and emails | nakamotoinstitute.org :::

:::quiz{id=q-2-1-s2 correct=2 explanation="Correct. The Times headline from January 3, 2009 ("Chancellor on brink of second bailout for banks") was deliberately chosen by Satoshi to anchor [[gloss:bitcoin|Bitcoin]]'s ideological purpose: a response to the 2008 financial crisis and uncontrolled fiat money creation. The headline also doubled as proof that block #0 wasn't pre-mined before that date."} Why is the text embedded in the genesis block important?

• It's a technical comment explaining how the code works
• It proves block #0 is the oldest block
• It's an ideological statement about why Bitcoin was created — the 2008 crisis and bank bailouts
• It's a cryptographic proof-of-work checksum :::

:::section{mins=2} UTXO: The Transaction Model :::

:::lead [[gloss:bitcoin|Bitcoin]] doesn't store "balances." It stores a list of Unspent Transaction Outputs ([[gloss:utxo|UTXOs]]). Your "balance" is the sum of all UTXOs addressed to you. :::

:::p The [[gloss:utxo|UTXO]] model differs fundamentally from the familiar banking approach. Instead of recording "Alice has 0.8 BTC," Bitcoin stores two separate outputs — one for 0.5 BTC and another for 0.3 BTC — each with its own recipient address. These "outputs" are the result of some past transfers to Alice, and from her perspective they are essentially sitting "in her wallet" waiting to be spent. When Alice wants to send 0.6 BTC to Bob, the protocol takes both of her UTXOs as inputs to a new [[gloss:transaction|transaction]] (0.5 + 0.3 = 0.8) — in other words, what was an output in older transactions becomes an input in the new one. Then the protocol creates two new outputs: 0.6 BTC for Bob and 0.2 BTC back to Alice as "change," minus the miner's fee. The old UTXOs are destroyed, and new ones are created in their place. :::

:::p Put differently, "input" and "output" are not two different types of coins — they are two different moments in the life of the same coin. It is born as an output of the transaction that created it, and it dies when it becomes an input of another transaction that spends it. :::

:::p Every [[gloss:transaction|transaction]] in [[gloss:bitcoin|Bitcoin]] consumes (spends) existing [[gloss:utxo|UTXOs]] as inputs and creates new ones as outputs. The only exception is the [[gloss:coinbase-transaction|coinbase transaction]] — a miner's reward for successfully mining a [[gloss:block|block]] — which has no inputs, only outputs, because the new BTC are literally created out of thin air by this transaction. This approach gives Bitcoin two important advantages. First, parallel processing: different UTXOs are independent of each other, so transactions involving them can be validated simultaneously. Second, better privacy compared to [[gloss:ethereum|Ethereum]]'s account model, which we'll cover in 2.2: a fresh address can be used for every change output, making it harder to trace ownership. :::

:::callout{icon=💡} [[gloss:utxo|UTXOs]] = physical cash. You have bills in your pocket: $500 + $200 + $100 = $800. You pay $600: hand over $500 + $200, receive $100 in change. The $500 bill "leaves" your pocket as a whole — you can't send part of a bill. Your balance = the sum of all your bills. :::

:::keypoints{label="Key Points"}

• [[gloss:bitcoin|Bitcoin]] doesn't store balances but a list of unspent "coins" ([[gloss:utxo|UTXOs]]) with owner addresses
• Each [[gloss:transaction|transaction]] consumes old UTXOs entirely and creates new ones, including "change"
• This model enables parallel processing and better privacy than account model
• The full UTXO set describes the network's current state — around 180M records, ~10 GB :::

:::details{badge=Advanced title="Bitcoin Script: The Transaction Locking Language"} :::p Every [[gloss:utxo|UTXO]] in the network is "locked" by a cryptographic script called scriptPubKey, or the public script. To spend such a UTXO, a user must provide an input script (scriptSig) that satisfies the locking conditions. Over the years, Bitcoin has seen several main types of these scripts emerge. The earliest is P2PKH (Pay to Public Key Hash), which requires providing a public key and a signature. Built on top of it is P2SH (Pay to Script Hash), which enables [[gloss:multisig|multisig]] and time-locked spending. Later came more compact and cheaper variants: P2WPKH is the SegWit version of P2PKH, and P2TR is based on Taproot and uses Schnorr signatures for improved privacy and efficiency. :::

:::p An important property of Bitcoin Script is that it is deliberately not Turing-complete. It has no loops, no recursion, and only a limited set of available opcodes. This isn't a technical limitation but a deliberate design choice by the developers — favoring safety over flexibility. The impossibility of writing an infinite loop guarantees that validation of any [[gloss:transaction|transaction]] will complete in finite, predictable time. For comparison: [[gloss:ethereum|Ethereum]] and its smart contracts can face out-of-gas attacks, where a malicious contract attempts to exhaust all resources of the validating [[gloss:node|node]]. :::

:::p{html} [[gloss:bitcoin|Bitcoin]] address types are easy to distinguish by the prefix at the beginning of the string. An address starting with 1... is a legacy P2PKH address, the oldest format. The 3... prefix indicates P2SH. Modern bech32 addresses start with bc1q... for SegWit and bc1p... for Taproot. Modern wallets default to bech32 or Taproot because they offer lower fees and better privacy. ::: :::

:::further{label="Further Reading"}

• Learn Me a Bitcoin — UTXO explained | learnmeabitcoin.com
• Bitcoin Optech — technical topics index | bitcoinops.org :::

:::quiz{id=q-2-1-s3 correct=1 explanation="Correct. [[gloss:utxo|UTXOs]] are spent whole, not partially — just like physical bills. The 0.5 BTC UTXO is entirely consumed as input; the protocol creates two new outputs: 0.4 BTC to Bob and 0.1 BTC change back to Alice (usually to a fresh address for privacy). The 0.3 BTC UTXO isn't touched because 0.5 already covers the 0.4 payment."} Alice has two UTXOs: 0.5 BTC and 0.3 BTC. She sends 0.4 BTC to Bob (ignore fees). What happens?

• Her 0.5 BTC UTXO becomes 0.1 BTC, Bob gets 0.4 BTC
• The 0.5 BTC UTXO is consumed entirely, creating two new UTXOs: 0.4 BTC for Bob and 0.1 BTC back to Alice
• Both UTXOs are consumed: Bob gets 0.4 BTC and 0.4 BTC, totaling 0.8 BTC
• The transaction is invalid — UTXO amounts don't match 0.4 exactly :::

:::section{mins=3} Mining, Difficulty, and Halving :::

:::lead Miners compete to find a nonce — a random number added to the [[gloss:block|block]] header such that the resulting hash falls below a specified target. The winner earns the right to record the block in the chain and claims the BTC reward. Roughly every four years, this reward is cut in half — an event called a [[gloss:halving|halving]], and it's what defines [[gloss:bitcoin|Bitcoin]]'s entire monetary policy, already mapped out a century ahead, all the way to 2140. :::

:::p{html} We covered the [[gloss:proof of work|Proof of Work]] mechanism in detail in 1.3 §2, so here we'll focus on Bitcoin specifics. The mining process looks like this. A miner gathers unconfirmed [[gloss:transaction|transactions]] from the [[gloss:mempool|mempool]] — the queue of transactions waiting to be included in a block — assembles a block from them, and starts iterating through different nonce values in the header. For each value, a double [[gloss:sha-256|SHA-256]] hash of the block header is computed. If the result falls below the current target, the block is found and the miner wins the round. If not, the next nonce value is tried. This process repeats hundreds of quintillions of times per second across the entire network simultaneously. :::

:::p Network [[gloss:difficulty|difficulty]] automatically adjusts every 2,016 blocks, which corresponds to roughly two weeks. When blocks are found faster than the target 10 minutes, difficulty rises; when they're found slower, it falls. This is a self-correcting mechanism: since 2009 the network [[gloss:hashrate|hashrate]] has grown more than a million-fold (from megahashes to exahashes per second), yet the average block time has stayed close to 10 minutes. :::

:::p [[gloss:halving|Halving]] is a programmed event that occurs every 210,000 blocks, which corresponds to roughly four years. This mechanism is precisely what creates [[gloss:bitcoin|Bitcoin]]'s predictable deflationary monetary policy. At network launch in 2009, the reward was 50 BTC per block; after the fourth halving in April 2024, it dropped to 3.125 BTC. The next halving is expected around 2028 and will reduce the reward to 1.5625 BTC. The final satoshi — Bitcoin's smallest indivisible unit — will only be mined around 2140. :::

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:::callout{icon=💡} Imagine a gold mine that, on a strict schedule, cuts its output exactly in half every four years. All market participants know this schedule a century in advance, and no one can deviate from it. When demand for such a metal keeps rising while supply steadily drops, theory says this should push the price up. That logic is exactly what sits at the core of [[gloss:bitcoin|Bitcoin]]'s economic model. :::

:::keypoints{label="Key Points"}

• Mining is searching for a nonce that produces a hash below the target, reward to the winner
• [[gloss:difficulty|Difficulty]] auto-adjusts every ~2 weeks, maintaining the 10-minute block time
• [[gloss:halving|Halving]] every 4 years cuts the reward in half, creating predictable deflation (~0.8% annually)
• 21 million BTC is the absolute cap, last satoshi to be mined around 2140 :::

:::details{badge=Advanced title="Energy Debates, Attack Costs, and the Long-Term Security Budget"} :::p Critics often repeat the claim that "[[gloss:bitcoin|Bitcoin]] consumes energy like Argentina" — and in absolute numbers this is true, around 170 TWh per year as of April 2026. But this claim comes with serious counterarguments. Per data from the Bitcoin Mining Council and Cambridge Centre, about 55% of all mining energy comes from renewable sources — hydro, solar, and stranded gas (associated gas that would otherwise simply be flared at oil fields). Miners are economically forced to seek the cheapest possible energy, and that often turns out to be excess or wasted generation. Meanwhile, this energy expenditure secures over $20 billion annually in network security, which makes attacks economically irrational. :::

:::p Let's calculate the cost of a 51% attack on [[gloss:bitcoin|Bitcoin]] today. To capture more than half of the [[gloss:hashrate|hashrate]] even for a single hour, an attacker would need to deploy over 400 EH/s of new hardware — that's $15–20 billion in [[gloss:asic|ASIC]] investment plus $5–10 million per hour in electricity. Economically, such an attack makes no sense: even if a double-spend succeeded, the resulting market panic would instantly crash the BTC price, and the attacker would lose far more than they could possibly steal. :::

:::p A far more interesting long-term problem is the security budget after block rewards become negligible (this will start to bite after the 2040s). When the [[gloss:block-reward|block reward]] effectively drops to zero, the network will need to run almost entirely on transaction fees. Today, fees make up only 2–5% of total miner revenue, and unless they grow several-fold, hashrate will start to fall and security along with it. Possible solutions have long been under discussion: mass adoption driving fee growth; protocols like [[gloss:ordinals|Ordinals]] and [[gloss:runes|Runes]] that create artificial demand for block space; and [[gloss:lightning-network|Lightning Network]], which offloads the L1 but also reduces potential fees. This remains the main open question in Bitcoin's long-term economics. ::: :::

:::further{label="Further Reading"}

• Cambridge Bitcoin Electricity Consumption Index | ccaf.io
• Hashrate Index — mining economics dashboards | hashrateindex.com :::

:::quiz{id=q-2-1-s4 correct=2 explanation="Correct. Every 2,016 blocks (about every 2 weeks), the [[gloss:bitcoin|Bitcoin]] protocol compares the actual time taken to produce those blocks against the target (2,016 × 10 min = ~2 weeks). If blocks were found faster — [[gloss:difficulty|difficulty]] rises. If slower — it drops. This self-correction has kept the average block time remarkably close to 10 minutes for 17 years, regardless of [[gloss:hashrate|hashrate]] changes."} Why does Bitcoin's block time stay around 10 minutes even though hashrate has grown a million-fold since 2009?

• Miners coordinate manually to keep the block time steady
• 10 minutes is hardcoded and the network waits if blocks arrive faster
• The protocol auto-adjusts difficulty every 2,016 blocks to maintain the 10-minute target
• Satoshi personally fine-tunes difficulty in major releases :::

:::section{mins=2} Lightning Network and Scaling :::

:::lead [[gloss:lightning-network|Lightning Network]] is a network of payment channels built on top of [[gloss:bitcoin|Bitcoin]]. It enables instant micropayments for fractions of a cent, without recording every [[gloss:transaction|transaction]] on the main chain. In essence, this is Bitcoin's Layer 2 (L2, second layer). :::

:::p [[gloss:bitcoin|Bitcoin]]'s base layer handles about 7 transactions per second — critically insufficient for a global payment system when compared to Visa, which handles up to 65,000 TPS at peak. [[gloss:lightning-network|Lightning Network]] solves this problem: the bulk of everyday payments happens off the main chain, while Bitcoin's security is preserved through cryptographic guarantees. :::

:::p The principle behind Lightning is rather elegant. Two participants open a channel by locking some amount of BTC in a [[gloss:multisig|multisig]] address — an address that requires signatures from multiple parties in order to move funds. Once the channel is open, they can exchange a nearly unlimited number of payments within it — instantly and almost for free, without recording each transaction on the [[gloss:blockchain|blockchain]]. When the channel eventually closes, the final balance is written to L1 as a single transaction. :::

:::p What makes Lightning truly powerful is routing. If Alice has an open channel with Bob, and Bob has one with Charlie, then Alice can pay Charlie through Bob without needing a direct channel between them. A network of thousands of interconnected channels makes it possible to send payments to nearly any participant. Meanwhile, Bob cannot steal funds mid-route — the [[gloss:htlc|HTLC]] (Hash Time-Locked Contract) mechanism makes the entire payment chain atomic: either everyone receives their funds, or no one does. :::

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:::callout{icon=💡} [[gloss:lightning-network|Lightning]] is like opening a tab at a bar. You leave a deposit with the bartender, order drinks all night "on the tab," and settle up with a single final transaction at the end. Each individual order doesn't require a card swipe — it's fast and nearly free. The flip side: your deposit stays locked up until "the night ends" — that is, until the channel closes. :::

:::keypoints{label="Key Points"}

• [[gloss:lightning-network|Lightning]] moves payments off-chain, recording only channel open and close on L1
• Opening a channel requires locking BTC in a [[gloss:multisig|multisig]] address — capital acting as liquidity
• Routing through intermediate nodes is safe thanks to [[gloss:htlc|HTLC]] — all or none
• Network capacity as of April 2026: 5,000 BTC locked in channels ($370M) :::

:::details{badge=Advanced title="HTLC, Taproot, and Lightning Privacy"} :::p [[gloss:htlc|HTLC]] (Hash Time-Locked Contract) is the safe routing mechanism on which the entire Lightning network rests. Imagine an Alice→Bob→Charlie route. Alice generates a random secret and then sends its hash across the network. Charlie ultimately receives the actual secret only once the payment physically reaches him. By revealing this secret, Charlie claims his BTC from Bob; Bob in turn reveals the same secret to claim his BTC from Alice. The entire chain operates atomically: if anyone along the route fails to reveal the secret within N blocks, all the funds automatically return to the senders. No one can steal funds mid-route — the mathematics simply doesn't allow it. :::

:::p The Taproot activation in 2021–2022 brought a serious upgrade to [[gloss:lightning-network|Lightning]]. Schnorr signatures make channel opens and closes indistinguishable from ordinary on-chain transactions — a significant privacy improvement. Currently under active development are PTLCs (Point Time-Locked Contracts), which will replace HTLCs in the future and make privacy even stronger. Developing alongside them is splicing (2025–2026) — the ability to add or remove funds from a channel without closing it, which significantly reduces on-chain footprint and user costs. :::

:::p [[gloss:lightning-network|Lightning]] also has real limitations worth being aware of. To receive incoming payments, a [[gloss:node|node]] must remain constantly online — otherwise it can miss a malicious channel close attempt. Watchtowers — third-party services that monitor channels while the owner is offline — exist to address this problem. Another pain point is UX complexity for beginners: concepts like channels, inbound liquidity, and routing don't yet fit into an ordinary user's intuition. Developers are actively working on all these issues, and Lightning becomes noticeably more user-friendly with each passing year. ::: :::

:::further{label="Further Reading"}

• Lightning Network Whitepaper (Poon, Dryja, 2016) | lightning.network
• 1ML — real-time Lightning Network statistics | 1ml.com :::

:::quiz{id=q-2-1-s5 correct=2 explanation="Correct. [[gloss:htlc|HTLC]] makes routing cryptographically atomic. Bob holds Alice's payment in escrow and can only claim it by revealing the secret. He can only get that secret by forwarding the payment to Charlie successfully. If he tries to pocket the funds mid-route, he simply can't unlock them — the protocol forces the chain to resolve either completely or not at all."} Why can't Bob steal funds when routing a Lightning payment from Alice to Charlie through his node?

• Because Bob has publicly staked reputation he doesn't want to lose
• Because all payments are recorded on L1 blockchain in real time
• The HTLC mechanism makes the payment atomic: Bob can only claim Alice's BTC after revealing a secret he gets from Charlie
• A government regulator verifies every routed payment :::

:::section{mins=2} Bitcoin as an Asset: ETFs and Institutions :::

:::lead [[gloss:bitcoin|Bitcoin]] is increasingly viewed as "digital gold" — a store-of-value asset. [[gloss:spot-etf|Spot ETFs]] have been approved in the US since January 2024, institutional investors are actively entering the market, and corporations are starting to hold BTC as part of their treasury reserves. All of this represents the structural shift of 2024–2026. :::

:::p The transformation of [[gloss:bitcoin|Bitcoin]]'s perception from speculative instrument into a full-fledged macro asset began in 2020, when MicroStrategy (renamed [[gloss:strategy-company|Strategy]] in 2025) under CEO Michael Saylor began systematically converting corporate treasury into BTC. By April 2026, Strategy had accumulated 815,061 BTC with a combined value of approximately $61.5 billion. The average purchase price sits at around $75,500 per BTC. The company funds its purchases through issuance of its own stock and convertible notes, and MSTR has effectively become a Bitcoin proxy on the stock market: its price moves with BTC but with additional leverage. :::

:::p The key turning point came in January 2024, when the [[gloss:sec-regulator|SEC]] approved 11 spot Bitcoin [[gloss:etf|ETFs]] at once. [[gloss:blackrock-ibit|BlackRock's IBIT]] became the fastest-growing ETF in history: by April 2026, its [[gloss:aum|AUM]] (assets under management) stands at around $54 billion, giving it approximately 49% of the entire US spot Bitcoin ETF market. In second place is Fidelity FBTC with over $15 billion. Total Bitcoin ETF inflows in Q1 2026 reached $12.4 billion. This is precisely a structural shift: institutional investors have finally received a familiar regulated instrument for Bitcoin exposure that isn't tied to crypto exchanges. :::

:::p The 2024–2026 cycle showed unusual dynamics. [[gloss:bitcoin|Bitcoin]] hit its all-time high in October 2025 — around $107,000 — and then corrected by about 30%. As of April 2026, the price sits around $74,000–$75,000. Interestingly, this level nearly matches [[gloss:strategy-company|Strategy]]'s average purchase price, meaning the largest corporate holder is currently sitting close to break-even. :::

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:::callout{icon=💡} Gold has five thousand years of human trust behind it; [[gloss:bitcoin|Bitcoin]] has just seventeen. But there are important differences running the other way: gold can't be sent across the internet in a single second, it can't be divided into one hundred million parts (while Bitcoin divides into satoshis), and its authenticity can't be verified in milliseconds without an intermediary — a jeweler or a bank. :::

:::keypoints{label="Key Points"}

• [[gloss:spot-etf|Spot Bitcoin ETF]] (January 2024) is the biggest structural shift for institutional adoption
• [[gloss:blackrock-ibit|BlackRock IBIT]]: fastest-growing ETF in history (~$54B [[gloss:aum|AUM]], ~49% of spot BTC-ETF market)
• [[gloss:strategy-company|Strategy]] (former MicroStrategy): largest corporate holder — 815,061 BTC (~$61.5B)
• [[gloss:bitcoin|Bitcoin]] remains a risk asset short-term and is seen as a store of value long-term :::

:::details{badge=Advanced title="Macro Correlations and Valuation Models"} :::p [[gloss:bitcoin|Bitcoin]]'s macro correlation with traditional markets has shifted noticeably across eras. In 2020–2022, Bitcoin correlated strongly with the Nasdaq index, with a correlation coefficient of 0.6–0.8 — typical behavior for a classic risk asset. In 2023–2024, the correlation dropped noticeably, down to 0.3–0.5. And in 2025–2026, Bitcoin's correlation with gold has begun rising, which some analysts interpret as a gradual transition of Bitcoin into store-of-value territory. The main thesis among serious investors today goes like this: short-term, Bitcoin still behaves like a risk asset, but long-term, it increasingly resembles digital gold. :::

:::p One of the more interesting valuation models is the power law model. According to it, BTC price over long timeframes follows a power law with remarkable precision (R² above 0.95 on a log-log scale). The model predicts a range of $100,000–$1,000,000 during 2025–2030. It also has its critics: they accuse it of overfitting (too closely fitting historical data), of survivor bias (only one asset with such a history, Bitcoin, has survived), and of not accounting for future demand shocks. Another important metric is the [[gloss:mvrv|MVRV ratio]] (Market Value to Realized Value) — the ratio of market cap to "realized" cap, where each [[gloss:utxo|UTXO]] is counted at the price of its last movement. Historically, MVRV above 3 has signaled market overheating, while MVRV below 1 has signaled a potential bottom. :::

:::p The famous Stock-to-Flow model from analyst PlanB, which was very popular before 2021, has in fact proven unreliable. Its loud predictions — $100,000 by the end of 2021 and $1 million by 2025 — simply didn't come true. The model completely ignores the demand side, and today it's viewed more as a historical curiosity than as a real forecasting tool. ::: :::

:::further{label="Further Reading"}

• BlackRock IBIT — iShares Bitcoin Trust fact sheet | blackrock.com
• Glassnode Studio — on-chain metrics dashboards | glassnode.com :::

:::quiz{id=q-2-1-s6 correct=2 explanation="Correct. Individuals could always buy [[gloss:bitcoin|Bitcoin]] on exchanges. What the [[gloss:spot-etf|ETFs]] changed is access for the institutional capital pool — pension funds, endowments, and financial advisors who can't custody crypto themselves or deal with unregistered securities. [[gloss:blackrock-ibit|IBIT]] alone drew $54B in [[gloss:aum|AUM]] in two years, reflecting demand that couldn't previously be expressed through existing products."} What makes the January 2024 approval of spot Bitcoin ETFs a structural shift rather than just another news event?

• ETFs pushed the price up, which is always good for Bitcoin
• ETFs finally allowed ordinary people to buy Bitcoin
• They gave institutional investors a regulated, familiar wrapper — pension funds, RIAs, and allocators could finally include BTC without custody complexity
• The SEC now guarantees Bitcoin's price :::

:::section{mins=3} Limitations, Ordinals, and Bitcoin Philosophy :::

:::lead [[gloss:bitcoin|Bitcoin]] is slow (just 7 TPS), energy-intensive, and lacks smart contracts. But its supporters see all of these as features deliberately chosen, not bugs. The attempts to turn Bitcoin into "more than just money" — the [[gloss:ordinals|Ordinals]] and [[gloss:runes|Runes]] protocols — were a vivid chapter in 2023–2024, but by 2026 much of that hype has faded. :::

:::p On closer examination, every one of [[gloss:bitcoin|Bitcoin]]'s "weaknesses" turns out to have a flip side. Slowness is the price paid for security: the 10-minute interval between [[gloss:block|blocks]] gives the network enough time for global synchronization and makes chain forks far less frequent. The absence of smart contracts is also a deliberate choice favoring simplicity: a smaller attack surface, fewer bugs, fewer unexpected ways to lose money. And the energy cost is simply the price of security: over $20 billion per year spent on electricity makes attacks on the network economically pointless. :::

:::p Volatility is arguably Bitcoin's most real problem — but even it has been dropping with each market cycle. From swings of ±90% in 2013–2014, the network has moved to far more moderate ±40–50% in 2024–2025. As capitalization grows and institutional participation expands, volatility continues to fall. The common claim that "Bitcoin is used by criminals" also deserves attention — the data doesn't support it. Per Chainalysis reports, less than 1% of all [[gloss:bitcoin|Bitcoin]] [[gloss:transaction|transactions]] are tied to illicit activity, whereas cash is used for crime tens of times more often. On top of that, [[gloss:blockchain|blockchain]] transparency makes Bitcoin a poor choice for any illegal activity: all transactions are public and remain traceable forever. :::

:::p Attempts to expand [[gloss:bitcoin|Bitcoin]]'s functionality went through a vivid episode with [[gloss:ordinals|Ordinals]] and [[gloss:runes|Runes]]. In January 2023, developer Casey Rodarmor introduced the Ordinals protocol — a way to "number" individual satoshis and "inscribe" arbitrary data into them: images, text, JSON. In effect, this gave Bitcoin the ability to host NFTs directly in the blockchain. In April 2024, the same Rodarmor launched Runes — a standard for fungible tokens (interchangeable, unlike NFTs) built on the [[gloss:utxo|UTXO]] model. At the peak of the 2023–2024 hype, Ordinals and [[gloss:brc-20|BRC-20]] tokens drove network fees up 10–50x and brought miners around $2.5 billion — roughly eight times normal fee revenue. But by 2026 the hype has largely passed: in February 2026, Magic Eden, the largest NFT marketplace, dropped support for Bitcoin Ordinals and Runes to focus on Solana. Trading volumes collapsed from billions to tens of millions of dollars per month. The experiment showed something important: Bitcoin can technically host more than money, but it doesn't want to become "an Ethereum for everything." :::

:::p{html}

:::callout{icon=💡} Criticizing [[gloss:bitcoin|Bitcoin]] for being slow is a bit like criticizing gold for being heavy. It isn't a bug or a technological limitation, but an inseparable property that provides reliability. Fast, lightweight gold — the kind you could instantly forge or bake up at home — would simply be less valuable. :::

:::keypoints{label="Key Points"}

• Slowness and lack of smart contracts are deliberate design choices, not technical limitations
• Energy consumption secures the network with $20B+ per year in security
• Volatility decreases with each market cycle thanks to institutionalization
• The [[gloss:ordinals|Ordinals]] and [[gloss:runes|Runes]] experiment (2023–2024) showed: Bitcoin can host tokens, but is meant to be money :::

:::details{badge=Advanced title="Bitcoin Governance: From SegWit to Covenants"} :::p Bitcoin governance operates on the principle of "rough consensus plus working code." There is no formal voting, no foundation making decisions, no official CEO. The main mechanism for documenting and discussing changes is [[gloss:bip|BIPs]] (Bitcoin Improvement Proposals). All disputes eventually resolve through a complex combination of three forces: developers (primarily Bitcoin Core), miners (who signal their support by including specific flags in the blocks they mine), and economic [[gloss:node|nodes]] — users and exchanges running full nodes, which ultimately determine which version of the protocol counts as canonical. :::

:::p The most telling examples of contentious changes are the SegWit activation in 2017 and the block size war of 2015–2017. SegWit was a soft fork — a backward-compatible upgrade that activated after 95% miner signaling, extensive negotiations, and a real threat of UASF (User Activated Soft Fork): a strategy where user nodes begin rejecting blocks that don't support SegWit, effectively forcing miners to comply. The block size war was fought between "big blockers," who wanted larger block sizes for more throughput, and "small blockers," who insisted on solving the problem through L2 and [[gloss:lightning-network|Lightning]]. In the end, small blockers won, and big blockers forked off into a separate chain — Bitcoin Cash. The broader outcome of this whole history: [[gloss:bitcoin|Bitcoin]] cemented its position as the most conservative protocol in the industry, where any changes are rare and pass through years of debate. :::

:::p Taproot was activated in November 2021 after a surprisingly smooth process — Schnorr signatures and MAST (Merkelized Abstract Syntax Trees) significantly improved both privacy and network efficiency. The active debates of 2025–2026 are centered around [[gloss:covenants|Covenants]] (OP_CTV, OP_CAT) — the ability to set conditions on how a [[gloss:utxo|UTXO]] can be spent in the future. Such constraints could enable vaults (crypto storage with withdrawal delays), contention control mechanisms, and complex [[gloss:multisig|multisig]] schemes. The main controversy around covenants is that they modify Bitcoin's base layer, potentially opening up new attack vectors, and many in the community argue the protocol's current functionality is already sufficient for its mission. ::: :::

:::further{label="Further Reading"}

• Bitcoin Magazine — Technical articles | bitcoinmagazine.com
• Ordinal Theory Handbook (Casey Rodarmor) | docs.ordinals.com :::

:::quiz{id=q-2-1-s7 correct=1 explanation="Correct. Bitcoin Script is intentionally not Turing-complete — no loops, no recursion, a small opcode set. Every [[gloss:transaction|transaction]] must validate in finite, predictable time. History has shown how costly Turing-complete contracts can be: The DAO hack on [[gloss:ethereum|Ethereum]] ($60M), countless DeFi exploits, reentrancy bugs. [[gloss:bitcoin|Bitcoin]] maintainers made a conscious trade-off: less expressiveness in exchange for dramatically reduced attack surface."} Why has Bitcoin deliberately avoided adding smart contracts like Ethereum's?

• Satoshi's original code simply cannot support them technically
• Simplicity is a security feature — less attack surface, fewer bugs, easier verification. Complex contracts lead to catastrophic losses
• The SEC prohibits smart contracts on Bitcoin
• Miners would lose money on them :::