Gold doesn't change in value; everything else changes in relation to it.
Gold's value is determined by and is constantly changed by supply and demand.
The second part of this sentence is true, however. For some reason the goldbugs fail to realize that these changes in relation to gold could be in the adverse direction.
If you treat gold as a currency, then treat it like all currencies. There are times when it rises in purchasing power, and times when it falls. It's not a one-way ticket.