Bitcoin Unlimited’s Placebo Controls
Placebo controls surround us everyday. The thermostat in your office? Probably a fake. The elevator close button? It does nothing. The button to cross the sidewalk in a major city? Wired to nothing. But every day, people push these buttons or turn these knobs, thinking it has some effect on them. Why? Because people like to feel like they’re in control, even if they aren’t. Bitcoin Unlimited offers the same kinds of Placebo Controls to its users — something that allows them to feel like they have control of the system, when in fact, they have none.
Bitcoin Unlimited uses two configurable parameters for users to give the illusion of defining a maximum block size. These parameters are the Default Accept Block Size, and Default Accept Block Depth. For users, both are utterly useless, other than to temporarily fork you onto a chain you won’t follow.
The Default Accept Block Size parameter is much like the Block Size Limit in Bitcoin — blocks larger than this are temporarily rejected. However, they can be accepted once they get to a certain depth. That depth is defined by the Accept Block Depth, which is set as 4 by default, but can be configured. This means that miners can effectively ignore your block limit as long as they eventually produce more than the Accept Block Depth. It’s the Maginot Line of defense against blocks you are unwilling to support — something that looks nice, seems like it might stop something, but in reality, is completely sidestepped.
You could set your Accept Block Depth number to something arbitrarily large, but all that will do is delay the inevitable. Miners will continue doing what they are going to do, because in the end, you’ll accept what they give you. Setting this number to anything other than zero will only temporarily fork you away from the network. It’s a parameter in fact worse than a placebo — temporarily giving you the illusion of doing something when in the end, it will be overruled.
So why all this complication for something that does nothing? The illusion of control; the illusion of a choice. Bitcoin Unlimited more simply is a system where miners are in complete control of block sizes. Once they control the block sizes, they can price you out of other forms of validation, such as validating inflation or even the validity of transactions. Miners have zero incentive to mine anything based on user preferences. In the end, they will do what they want. But the only way to pull off such a trick is to let people believe they have a choice in the matter.
You may enjoy pressing the sidewalk crossing button, but you are going to be waiting for a green light. Press the elevator’s door close button, and you’ll have to wait for the elevator to decide when the doors should shut. Change your office thermostat, because it’s probably not even wired up. And like the engineers who put these placebos in place, to give you the illusion of control, Bitcoin Unlimited presents you with meaningless options that are designed to pacify you while you hand over your ability to control the resources needed to fully validate blocks.