BLOCKCHAIN & WEB3 FUNDAMENTALS - Chapter 5, Exercise 3 Solution
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Why the Shrinking Block Reward Is a Genuinely Open Question

PROBLEM
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Explain why this chapter treats the shrinking block reward as a
genuinely open question for Bitcoin's long-term security, rather than
a problem that's already been solved — connect your answer back to
Chapter 4's own 51%-attack cost reasoning.

SOLUTION
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Chapter 4 established that Bitcoin's real security against attacks
like a 51% attack comes directly from the total amount of honest
mining power securing the network - the more real computing power
miners collectively point at the network, the more expensive it
becomes for an attacker to out-mine everyone else and rewrite history.
That real 2025 estimate (around $6 billion for a week-long attack) is
only that high because so much genuine mining power currently competes
honestly for the block reward.

Miners only keep dedicating that much real hardware and electricity to
the network if doing so remains profitable. Today, most of a miner's
income comes from the block reward itself (newly issued bitcoin), with
transaction fees as a comparatively small supplement. As this chapter
describes, that block reward keeps halving roughly every four years and
is expected to shrink to zero around 2140 - meaning miner income will
increasingly have to come from transaction fees alone.

The genuinely open question is whether transaction fees, on their own,
will actually be large enough to keep total honest mining power at a
level that preserves something like today's real 51%-attack cost. If
fee revenue turns out to be too low, less mining power might stay
dedicated to the network, which per Chapter 4's own reasoning would
lower the real cost of a 51% attack - a real, direct link between this
chapter's own supply mechanics and Chapter 4's own security economics.
Nobody can point to decades of already-observed experience at that
future, reward-free state to confirm this works out, since it hasn't
happened yet - which is exactly why this chapter calls it an open
question rather than a solved one.

ANSWER: The block reward's real, mechanical decline toward zero
directly threatens the same mining-power-based security Chapter 4
described, since miner participation depends on profitability, and it
remains genuinely unverified whether transaction fees alone will be
enough to keep that level of honest mining power (and therefore that
level of 51%-attack cost) high once the reward is negligible - a real,
unresolved question rather than something already settled by decades
of lived experience.

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WHY THIS WORKS AS AN ANSWER

This draws the explicit causal chain between Chapter 5's own halving
mechanics and Chapter 4's own mining-power-based security argument,
rather than treating the two chapters' material as unconnected facts.