Time travel is a dream shared by pretty much all of us.

But the dearth of visitors from the future – and the dismal turnout at the famed time traveler party – is alarming for hopefuls.

Still, hypothetical time travel ideas abound, including traversable wormholes propped open by undiscovered exotic states of matter, and a rocket ship skirting billions of light-years around a spinning Universe to end up back in its past.