Try measuring it! You'll quickly see that the latency of addressing n bytes of memory is definitely not O(1).
See eg "The Myth of RAM": https://www.ilikebigbits.com/2014_04_21_myth_of_ram_1.html
See eg "The Myth of RAM": https://www.ilikebigbits.com/2014_04_21_myth_of_ram_1.html
8^(1/3) is 2
So according to OP (and you by agreement), upgrading my machine from 4GB of RAM to 32GB should double my RAM access time. Obviously, and demonstrably, nothing of the sort occurs!