PHYSICAL_READ_BYTES_DELTA and PHYSICAL_READ_BYTES_TOTAL
The documentation explains it perfectly:


  The total value is the value of the statistics since instance
  startup. The delta value is the value of the statistics from the
  BEGIN_INTERVAL_TIME to the END_INTERVAL_TIME in the DBA_HIST_SNAPSHOT
  view.


So in this case, the PHYSICAL_READ_BYTES_TOTAL is the number of physical reads (in bytes) since the instance was started, and PHYSICAL_READ_BYTES_DELTA is the number of physical reads (in bytes) since the previous snapshot (SNAP_ID).