Interdimensional stasis field

Ordinary matter common to our Universe cannot pass through the underspatial boundary in any shape or form naturally; the only way to make the transit is to be confined in an artificial interdimensional stasis field - a type of a special localized space-time bubble. Development of devices capable of generating these fields was crucial in the development of FTL interdimensional travel.

The Gateway Device was capable of producing such fields at a large enough scale to allow starship sized objects to pass through into the dimension beyond. Once the field was formed, a capacitor running on the starship's own power was used to maintain the integrity of the field for the duration of the interdimensional transit. If the field would fail, the starship would be annihilated instantly, as it was not compatible with the physical reality of the Portal Dimension.

Later, the Plasmasphere Drive was developed, capable of producing these fields without the need of a stationary gateway.