Empty Block

DEFINITION

A block that contains no user transactions — only the coinbase transaction paying the miner who found it. It is fully valid under consensus rules. It is empty because it was found in the brief window before the miner had a full list of transactions to include.

Every block must contain at least one transaction: the coinbase, which creates the new bitcoin and pays the fees to the miner. Everything else is optional. A block with only that entry is an empty block, and the network accepts it exactly as it accepts a full one.

The reason they exist is a race. The instant a block is found, pools want their machines working on the next one, so they push out a stripped template — no transactions, tiny payload, arrives immediately. Building the full template takes longer: select transactions from the mempool, re-check validity against the block that just landed, rebuild the Merkle tree, then push a much larger payload to thousands of machines. For one or two seconds, the fleet is hashing on an empty template. If a valid hash turns up in that window, the block ships empty.

Miners are not being lazy or hostile. The block subsidy dwarfs the fees in a normal block, so the expected cost of forfeiting fees on rare occasions is far smaller than the cost of pausing every fleet for two seconds after every block. Every large pool makes the same calculation, which is why the behaviour is universal.

It matters for users only in the negative: nothing happens to you. Pending transactions stay in the mempool and confirm in the next block. Issuance continues on schedule. Empty blocks were over ten percent of all blocks in Bitcoin's early years and are under one percent today, thanks to faster propagation such as compact blocks. That share is the number worth watching — a rising trend would signal propagation or software trouble, whereas a single empty block signals nothing at all.

IN A SENTENCE

"The miner got lucky two seconds too early, and paid for it in forfeited fees."