Most astronomers and theoretical physicists believe that there's a black hole at the centre of our galaxy. There seem to be plenty more scattered around the observable universe. Although no-one's ever seen one directly, they can be inferred from the way they bend light, a process called gravitational lensing.
And they're not voids. Far from it. They are incredibly dense accumulations of matter formed when stars larger than a certain mass run out of the fuel (fusionof hydrogen to helium) which counteracts the force of gravity. When the convection currents stop, gravity pulls the star in on itself and it becomes ever more dense. Everything that's sucked in stays there. Eventually the gravity at the surface is so strong, that nothing, not even light, can escape, because the escape velocity is greater than the speed of light. So the black hole appears black.
They do, however, emit radiation - a product of the energy released as matter is destroyed (ie converted to energy) as it falls in.
If you were near a black hole, you'd eventually be sucked in, but the gravity gradient is so steep that your feet would be shredded before your head: 'spaghettified', as Stephen Hawking put it.
Whether they would permit time travel or whether they are gateways to other universes has not been demonstrated, but Einstein's equations show that, on the edge of a black hole, time stands still (General Theory of Relativity).
The holes in your socks could qualify if they're heavy enough, but they'd just be mini black holes with a mass equivalent to that of Mt Everest.
