This article includes pictures of what the traffic managers see on their screens and how the information gets there. Unfortunately, ghost jams are generally caused by human idiot drivers:

But often we have only ourselves to blame: staying in the middle lane rather than keeping to the left whenever possible, getting too close to the car in front and subsequently having to brake, or simply changing lanes. When we overtake, for example – perhaps to get past the person in the middle lane – we create a space in the lane we’ve left. When that happens often enough, we create a phantom jam – a congestion from nowhere that will radiate exponentially backwards and take significantly longer to dissipate than it took to develop in the first place

via The dark science of the traffic jam: Ever wondered why you’re stuck in one when there’s no jam? | Mail Online.