Even if these radio signals were from aliens, the physical speed limit of the universe is the speed of light, some scientists say if it were possible to travel faster then people would move forward through time. The only credible theory of being able to return back to their time would be if the traveler created a wormhole on the way forward, so going backwards through a wormhole faster than the speed of light could reverse the time travel. It's not credible because inside a wormhole the strings are unstable to a point matter would be broken, crushed and stretched... so the travelers wouldn't complete the journey in one piece. If the radio signals are from aliens they would be unlikely to be still around after 150 billion years as well. What makes this story strange is the universe is 13.8 billion years old, so it's strange how the signals took 150 billion years to arrive. If there is any life out there, it's likely too far away to make any noticeable difference to us.