Think of a very busy, three lane superhighway. Workmen shut down one lane so potholes can be repaired, and oncoming traffic has to slow down and squeeze into two lanes temporarily. Immediately, a traffic jam forms, because cars arrive at the jam faster than they can pass through and leave out the other side. After the potholes are filled, the road crew finishes and reopens the lane, but the traffic jam remains for a while. You don’t even need workmen and potholes; maybe a motorist pulled onto the shoulder to fix a flat and the people slowing down to rubberneck precipitated the jam.

Approaching drivers, have to slow down because the cars ahead of them have done so. But when they get to the constructon zone, they may see no reason why the jam formed at that spot. There is nothing there!

To a bird flying above, the cars all seem to pile up at one end of the jam, and it takes them time to before they can get through and speed up again; for no apparent reason! The “jam” isn’t a thing, its an event. Think of it as a verb, not a noun.

From a plane miles above the earth, the individual cars can’t be seen, but the jam is clearly visible, in fact, it seems to move backwards along the highway, opposite the direction of traffic.

To a hitchiker walking through the jam, the cars all seem to be slowing down for no reason all. It all depends on your point of view.

The universe is like that traffic jam, but much more complicated, and happening in eleven dimensions. Maybe more, maybe less, depending on how YOU decide to do the math. But its all particles (the cars) and waves (the jam).