In most people’s minds, there is only one Holy Grail – the cup from the Last Supper. What would happen if it were found? Would grail hunters go through withdrawels after losing their reason for living? Or would something else move up on the Grail List from #2 to Holy Grail? If there is such a list, what’s at #2? What’s YOUR #2? Some might choose time travel and the powers both going backward and forward on the continuum might give. Well, if that’s your #2, you may have to start thinking about your #3. A college student may have just proven the physical feasibility of time travel. Where is he now? Past or future? Checking what grade he will get on the paper or going back to make some changes?
“Classical dynamics says if you know the state of a system at a particular time, this can tell us the entire history of the system. This has a wide range of applications, from allowing us to send rockets to other planets and modelling how fluids flow. For example, if I know the current position and velocity of an object falling under the force of gravity, I can calculate where it will be at any time. However, Einstein’s theory of general relativity predicts the existence of time loops or time travel – where an event can be both in the past and future of itself – theoretically turning the study of dynamics on its head.”
Germain Tobar, a senior honor student pursuing a Bachelor of Advanced Science degree at the University of Queensland, chose time travel as his theme and his quest. In fact, in the press release announcing his new paper in the journal Classical and Quantum Gravity, Tobar refers to a unified theory that could reconcile both traditional dynamics and Einstein’s Theory of Relativity as “the holy grail of physics.” And, according to the paper and Monty Python, he’s found his grail.
“Say you travelled in time, in an attempt to stop COVID-19’s patient zero from being exposed to the virus. However if you stopped that individual from becoming infected – that would eliminate the motivation for you to go back and stop the pandemic in the first place. This is a paradox – an inconsistency that often leads people to think that time travel cannot occur in our universe. Some physicists say it is possible, but logically it’s hard to accept because that would affect our freedom to make any arbitrary action. It would mean you can time travel, but you cannot do anything that would cause a paradox to occur.”
UQ physicist Dr Fabio Costa, who supervised Tobar’s research, present a current real-life example of the paradox that stops time travel in the present – the freedom of choice. Throwing in Ray Bradbury’s “butterfly effect” and the fear of the consequences of altering the past with a single seemingly random act strengthens the paradox. Tobar claims he’s found the hole in that argument big enough to drive a time machine through.
“Previous research has proposed a framework for deterministic, reversible, dynamics compatible with non-trivial time travel, where observers in distinct regions of spacetime can perform arbitrary local operations with no contradiction arising. However, only scenarios with up to three regions have been fully characterised, revealing only one type of process where the observers can verify to both be in the past and future of each other. Here we extend this characterisation to an arbitrary number of regions and find that there exist several inequivalent processes that can only arise due to non-trivial time travel. This supports the view that complex dynamics is possible in the presence of CTCs, compatible with free choice of local operations and free of inconsistencies.”
In simpler terms, by expanding the number of random events that could lead to a certain consequence, Tobar shows that eliminating one would merely cause the rest to recalibrate and lead to the same present outcome anyway. At the time the time traveler stepped on that one butterfly, another of the billions in existence at that moment flew in to take its place and the continuum quickly got back on its inevitable path. Or, to use Costa’s COVID-19 ‘patient zero’ example …
“In the coronavirus patient zero example, you might try and stop patient zero from becoming infected, but in doing so you would catch the virus and become patient zero, or someone else would. No matter what you did, the salient events would just recalibrate around you. This would mean that – no matter your actions – the pandemic would occur, giving your younger self the motivation to go back and stop it. Try as you might to create a paradox, the events will always adjust themselves, to avoid any inconsistency. The range of mathematical processes we discovered show that time travel with free will is logically possible in our universe without any paradox.”
In other words, the sheer magnitude of the number of events going on at a single moment in time stops the paradox, not time travel, dead in its tracks. So, having proven he won’t kill his own grandfather by traveling back in time, where is Germain Tobar now? Somewhere in the Jurassic Age stomping on prehistoric butterflies? Two weeks ago altering his path across campus so he bumps into the coed of his dreams?
“Our results are derived in an abstract framework, that does not depend on the details of the dynamics or of the space-time geometry. Further studies will be necessary to find genuine physical scenarios realising the acausal processes we have discovered.”
“Further studies will be necessary.” He’s pursuing the holy grail of all research physicists – grant money for more research.
Don’t step on that butterfly just yet.