**John Hopton for redOrbit.com – @Johnfinitum**

Four years ago, Vanderbilt Professor of Physics, Tom Weiler, and graduate fellow Chiu Man Ho, now at Michigan State University, published a theory proposing that the Large Hadron Collider (LHC) could be creating a peculiar kind of particle that’s capable of traveling ahead and back in time.

Time traveling particles? With the LHC being fired up again we needed to hear more, so we talked to Professor Weiler, hot off the heels of his recent appearance on *Through the Wormhole** *with Morgan Freeman.

**Here’s his take (in italics) on the theory behind the time-traveling particles:**

*In our 3+1 space-time dimensions, the only ways found to time-travel and to remain consistent with Einstein’s General Relativity, require a form of matter never seen, matter with negative energy.*

*So my postdoc at the time, Chiu Man Ho, and I, asked if this unfortunate result might be evaded in a theory with extra dimensions, as is the case in a credible model called “string theory”.*

*Since gravity is postulated to exist everywhere that there is space, gravity waves or quantized gravity particles called gravitons should exist in these extra dimensions. Some string models allow certain particles, the so-called “gauge singlets”, which are postulated particles having no electric, weak, or strong charges, to also travel from our space-time into these extra dimensions. We chose a hypothetical relative of the newly discovered Higgs boson, the “Higgs singlet”, as our time-traveler. The choice was motivated by simplicity of the model, and the reality of the Higgs.*

*There are different versions of time travel. We looked for the version that produces “closed timelike curves”, CTCs.*

*These are paths that return a time-traveler, here the particle, to its starting point with no time appearing to have elapsed according to the observer, although time has elapsed on the particles own clock. In a CTC, any positive time of travel is negated by an equal amount of negative time of travel, as seen by the observer.*

**Returning to the starting point**

*We enabled the return to the starting point in a simple way: we assumed that the extra dimensions were compactified, meaning each dimension is closed upon itself, as with a circle.*

*Extra dimensions have never been observed, so we know that if they exist at all, their compactification radii are very tiny.*

*The compactification radius has to be large enough to contain the particle’s quantum-mechanical wave function, which, for our purposes, translates into a minimum compactification radius of 10^{-19} meters if particles produced at the LHC are to travel in the extra dimension. Being compactified and very small, these extra dimensions are clearly different than our large, clunky dimensions, and so may well have properties different from our known dimensions.*

*We were free to assume that the geometry of these extra dimensions mixed new space with our conventional time in such a way as to allow some particles to appear to move backwards in our conventional time (the math describing this process was first constructed for our standard dimensions over sixty years ago, by two Europeans, Goedel and van Stockum). We showed that a fairly simple description of the compactified geometry was consistent with Einstein’s equations extrapolated to higher dimensional space, and that the extra-dimensional space was void of all physics pathologies like negative energies.*

*We also showed that a particle may traverse the extra dimension many times, to arrive back at its starting point in our spacetime, BEFORE it left. In other words, that the cause-effect relation could be broken. For example, a time-traveling particle could decay into a flash of standard particles BEFORE the production of the time-traveling particle was apparent at the LHC.*

*In the words of my German colleague, Heinrich Paes, the particle would have no need to “remember” its origin; it could be said that now the particle “pre-membered” its origin!*

*If backwards time-traveling particles are to be a reality, then passing information, e.g. using the particle as a kind of Morse code, becomes possible. Then arises the issue that passing information to an earlier time may lead to psychological paradoxes. But Nature may be more imaginative than human psychology on this issue.*

**In conclusion**

*To summarize, we had to assume:*

*(i) the existence of compactified extra dimensions,*

*(ii) the existence of Higgs singlet particles (which would be made at the LHC in a mixture with the Higgs particle), and*

*(iii) non-flat spacetime in the extra dimensions mixing coordinate time with the new space-dimension(s) (actually, one extra dimension sufficed).*

*The odds of each assumption being true is perhaps small, the product much smaller, but that doesn’t matter – all that matters is the possibly whimsical nature of Nature. She appears to have given us one Universe. It may be simple as William of Ockham would have it, or it may be less simple as many of us would like it to be.*

**In Part II, we find out what it would mean for humanity if the theory turned out to be correct (including the possibility of sending messages through time).**

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