Here\u2019s what you\u2019ll learn when you read this story:<\/p>\n
Scientists have taken one more step down the very long road to time travel.<\/p>\n
A new paper combines the Alcubierre \u201cwarp\u201d drive with the idea of \u201ccontrolled closed timelike curves.\u201d<\/p>\n
Though far out, research like this helps push physics forward through open-minded exploration.<\/p>\n
Two physicists from the University of Queensland in Australia recently laid out a model<\/a> for studying hypothetical time travel<\/a>. Their work expands on what\u2019s called the Alcubierre spacetime, first published by physicist Miguel Alcubierre over 30 years ago. Time travel is very hypothetical, with a few paths that scientists explore mostly for fun and to push the boundaries of physics research in interesting directions. In that spirit, the Australian physicists have tweaked the Alcubierre theory to take one more step into the beyonds of time travel.<\/p>\n Alcubierre is invoked more often as a possible (and, again, very hypothetical) path to travel at \u201cwarp speed,\u201d or faster than the speed of light<\/a>. In our known universe, it isn\u2019t possible to travel faster than light speed, because the physics of our particular spacetime just don\u2019t allow it. To skirt this fact, the Alcubierre drive involves making a bubble of sorts that moves spacetime itself from the front to the back of the spacecraft. It\u2019s kind of like the spaceship is sitting on your dining room table while you pull the tablecloth of spacetime out from under it.<\/p>\n In their introduction, the scientists explain that they also use Austro-Hungarian mathematician Kurt G\u00f6del\u2019s idea of a spacetime allowing for \u201cclosed timelike curves\u201d (CTCs) in their argument. G\u00f6del published his idea in 1949<\/a> as part of a special solution to an enduring set of equations by Albert Einstein<\/a>. In 1994, Alcubierre himself said that his \u201cAlcubierre bubble\u201d might be constrained so that it, too, can have CTCs.<\/p>\n \u201cThis seems intuitive, as protocols that allow for superluminal travel can generally be used to create a time machine<\/a> with a slight modification,\u201d the scientists wrote. Now, intuition doesn\u2019t always lead to scientific results, but in the three decades since Alcubierre\u2019s presentation of his warp drive idea, others have found that you could time travel using two Alcubierre bubbles or by capitalizing on a special case of rotating spacetime. (\u2018Could\u2019 is doing some heavy lifting here\u2014this is pure science, not a blueprint.)<\/p>\n So, what\u2019s the latest step forward in this corner of theoretical physics<\/a>? Quantum information legend Tim C. Ralph joined forces with Ph.D. candidate Achintya Sajeendran to publish a paper in the peer-reviewed journal<\/a> APS Physical Review D. In their paper, they stabilize one measurement of an Alcubierre spacetime by anchoring it to coordinates in the bubble, turning the CTCs into complex shapes called geodesic circles.<\/p>\n Dubbing these \u201cclosed timelike geodesics\u201d (CTGs), Ralph and Sajeendran explain in the paper: \u201cSuch a CTG would be ideal for studying situations in which a particle interacts with its past or future self<\/a>, such as the billiard ball problem, and may generally serve as a useful playground for investigating classical and quantum models of time travel.\u201d<\/p>\n In other words, this is a specially controlled case of a specially controlled case, and by limiting the variables even further than before, scientists may be able to shake loose new insights into the mind-boggling questions<\/a> that come up when thinking about time travel, Alcubierre bubbles, or anything else that veers off the beaten path of classical physics.<\/p>\n And wait, what\u2019s the \u201cbilliard ball problem?\u201d It\u2019s a great illustration of exactly how mind-boggling time travel theories<\/a> can be. In pocket spacetimes (pun intended) with closed timelike curves, one billiard ball may not have one predictable path. What if one lands in a wormhole<\/a>, scientists wondered in 1990, where it might generate two outcomes instead of one predictable outcome? What if, they wondered in 2017, the billiard ball could collide with its own past self<\/a>?<\/p>\n