We will never be able to go back in time simply because time does not exist. For those who didn't know this, "time" is just an abstract form of measurements used to stay updated on what events could have happened during "9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom." as wikipedia puts it!

Thyme, not to be mixed up with Time, does however exist! The cake may be a lie, herbs are not!

Teleportation however... that could work as long as we have a device that hands out electrons, neutrons and protons into atoms perfectly according to schematics made by another device that reads every atom in your body! But ofcourse creating such a device is going to be more expensive than anything ever built before, and the time consumed just creating the plans for the device will probably take centuries! I say we leave this to some aliens with more time on their hands and get on with our lives.

Timetravel - Busted!
Teleportation - Plauseble but not likely to happen anytime soon!
(Gotta love Mythbusters!)