"The future ain't what it used to be."

Time Balloons




I read about a theoretical time machine experiment by Yakir Aharonov
in which a massive balloon that can be instantaneously inflated or deflated can be used to travel through time somehow by altering the worldline of a person inside of it. The balloon can supposedly allow a person inside to travel either forward OR backward in time. Although I can see how such a device might be used to alter one?s time passage into the future by either speeding up or slowing down a person?s passage of time into the future, I don?t see how altering the gravitational density of such an object could allow one to travel backwards in time. Any help clarifying all this would be greatly appreciated. Thanks!