Force Fields:

Whenever waves travel via a vacuum, they manifest as force fields (in the situation of EM waves) or as undulations in space-time (i.e., gravitational waves). It took scientists a long time to believe the fact that waves can propagate without any obvious medium to carry them.

Both gravitational and EM waves are transverse disturbances. The magnetic and electrical force fields in visible light, radio waves, IR, UV, x-rays, or gamma rays pulsate at right angles to each other and at right angles to the direction of propagation. This takes place in 3-dimensions; therefore it can be visualized in the "mind's eye." Gravitational waves are more esoteric; they cause space-time to oscillate in 4-dimensions. When anyone claims to be able to visualize 4-dimensional wave oscillation directly, you are necessary in suspecting that they are either crazy or joking. Nonetheless, they can be defined quite simply with mathematics.