This XKCD cartoon places many predictions on the same timeline (click through for the full version—it's much too long to include here). This is what I mean by only one future: all predictions have to happen (or not) in the same future. If they're mutually inconsistent, then somebody's wrong.
More and more, I find myself applying this filter when I hear or read some breathless prediction of fantastic technological breakthroughs that are supposed to be just ahead. We have a lot of predictions floating around, and I'm pretty sure some of them are wrong.