# Time after time

Worried that the Large Hadron Collider is going to cause the universe to collapse? Well, a very weird paper suggests that it may shut itself down through the magic of time travel:

So what did the article say? Well, it started out with a reasonable enough point. One of the basic assumptions of classical physics is that time flows in one direction and that when describing a physical system one needs to know the equations of motion and the initial conditions in order to predict the future behavior of a classical system.

However, quantum mechanics changes this a bit. Classical mechanics can be formulated in such a way that one sets up an "action" integral. The solution to the physical system can be expressed as the path that minimizes the action integral. It turns out that in quantum mechanics one needs to not simply take one path--but take the sum over all possible paths. For example, if you want to work out how a photon gets from a lightbulb to your eye, you need to take into account not just its straight-line trajectory, but contributions of all possible paths it could have taken, including paths where the photon bounces round the room. It's a bit strange, but it seems to work and 60 years+ of detailed experiments have confirmed this description over and over again to remarkable quantitative precision.

The authors of this paper claim to show that other terms can be added to the quantum mechanical action that are consistent with current theory and experiment. However, some of these possible terms include conditions in the future that need to be taken into account and summed over. That is to say, what happens in the future could (according to this paper) affect what happens in the present.

Why the LHC? The authors argue that these sorts of time-violating interactions could be associated with whatever new particles we create at the LHC. For example, the production of a large number of Higgs particles in the future could have a backwards-in-time causal effect on the machine that produced them, stopping the machine from ever running. As possible "evidence" for such a backwards-in-time effect, the authors cite the now-canceled Superconducting Super Collider (SSC)--a particle accelerator that was meant to hunt the Higgs and was partially constructed in Texas before Congress pulled the plug on the project. As the authors write in their paper: "Such a cancellation after a huge investment is already in itself an unusual event that should not happen too often. We might take this event as experimental evidence for our model in which an accelerator with the luminosity and beam energy of the SSC will not be built."

It's as though the Higgs plays the role of the time traveler who goes back to the past and murders his grandfather, thus preventing his own birth.

This sounds like those convenient devices in time travel novels that keep a piece of mud on your shoe from subtly disrupting the future and causing it to cease to exist. Also, I don't know enough physics to guess whether this is a hoax. But it's amusing, anyway.