Portal Reloaded, the phenomenal time travel fan game based on Portal 2, now has a co-op mode that enhances the Valve puzzle game even further.

The NBC sci-fi series La Brea has blown its mystery box wide open in Season 2, revealing more of what caused that mysterious time travel sink hole and just how deep (sorry) the conspiracy might reach.

Physics Bizarre portal-like ‘ring wormholes’ could let you time travel. A ring wormhole is one that you could simply step through, like a portal through space – but new, more detailed models ...

They're on sale until March 6, so you've got loads of time. Paying almost nothing for Portal 2 makes Valve's excellent puzzler quite the deal, ... and a third green, time-travel portal as well.

The ship arrives at Krometh B, where an ancient time travel portal was first discovered by the Enterprise 120 years prior. ... Time travel happens pretty much all the time in the Star Trek universe.