That time travel guy at UCONN

("Frame-dragging": The Earth, like anything with mass, warps spacetime around it. The math shows that it may also "drag" spacetime as it spins.)

Jumping forward in time is easy. We do it constantly. Every time you board a plane, drive on the highway, or move at any significant speed, time moves more slowly for you than for the rest of the world. At the speeds we can currently achieve, you gain only billionths of a second, and this has no practical effect whatsoever, but this is technically time travel as predicted by relativity. As the speed at which humans routinely travel increases over the next centuries, this effect will have to be taken into account. Eventually, as we begin to travel close to the speed of light, travellers will find that while hours have passed for them, years will have passed on earth. Take a light-speed ship out to the nearest star and back, and you'll return to a future earth. The real trick is travelling backwards in time:

I like Ron Mallett, I think he's a neat guy with a fascinating story, and his previous work on standard physics problems is solid. That said, his "laser time travel" device is cuckoo-bananas. The paper that lays out the physics behind his device is here.

Basically, Mallett has shown that by creating a circular high-energy laser, he can mimic the mass of a very large object. Awesome! We're all with him so far, but this is the point at which he leaves experimental physics and enters theoretical and speculative physics. From this spinning mass, he predicts, we might observe some amount of "frame-dragging". Now, frame-dragging is probably an observable effect, but we've not actually observed it yet.

(The math predicting frame-dragging has been around since 1918, but developing experiments to prove the theory took a bit longer to work out. Until last year, actually, when we began gathering data with "Gravity Probe-B". It's a pretty amazing satellite, launched in 2004 to detect the frame-dragging effects of the closest giant spinning object around, the Earth. The data is....complicated. The scientists doing the work think it will be at least 2010 before they've worked out exactly if / how the theory fits the reality.)

So okay, Mallett is on theoretically solid ground here. Whether he can replicate an effect with a desktop-sized device that we're barely sure is created by the whole earth is a different story.

Mallett then adds a theoretical property to a theoretical effect. With enough frame-dragging, he proposes, a "closed time-like curve" (CTC) could emerge, where space and time are so warped that "distance" (across space and time) becomes meaningless. Leaving aside for a moment the fact that space twisted around itself to that extent is not really a place you want to hang out (Mallett says just particles for now), and assuming he can work out all of the engineering problems that arise from channeling that much energy through some lenses and mirrors (no answers on this yet), the absolute best case scenario is that the particle would exit the loop just before it entered. That would be cool, but we won't be hunting T-Rexes anytime soon.

I gave him the benefit of the doubt several times there, and now I'm going to take it back. Mallett claims that the metric tensor he's worked out creates BOTH CTCs and an exit vector. Either I'm missing something big (totally possible), or Mallett's imagination has far outrun his math. Every solution I can think of just makes a death-trap, an inescapable loop that neither light nor particle can emerge from once entered. Essentially, a black hole. In order to bend a lightcone enough to make it fold back on itself (and therefore allow something to return to the place in time and space that it entered), you need A LOT of mass (or in this case, a VERY powerful laser mimicking a LOT of mass). This mass bends one edge of an object's lightcone around it, but it bends the other side too. So nothing could emerge without turning off the laser. But the device would have to be on to send a particle back in time. Theoretically, a particle should emerge the first time Mallett moves toward the "ON" switch. But then he'd have to be sure to turn the machine on anyway. Clearly, there are also some causality issues to be worked out.

In reading his paper, I couldn't help but notice that he solved the Einstein field equations with a metric based on an INFINITELY long cylinder of light. On one hand, this is genius (more on why at the end), on the other hand, it's a total cop-out. We've long known (since Frank Tipler in 1974) that an infinitely long cylinder of matter can produce relativistic effects that might make limited forms of time travel possible. This hasn't been particularly useful due to the...shall we say, difficulties, of building something infinite. This is the genius and the stupidity of Mallett's work. He's shown that light will behave the same way (genius), but ignored the irrelevence of the proof if it only works with infinite light (stupid). He has not addressed this issue, but has instead gone ahead with building a finite laser based on the theoretically sound properties of an infinite one.

Again, Mallett HAS done something genius here by applying the mass-energy equivalence rule of relativity to lasers. I can think of 10 amazing potential uses for this technology. Time travel, I'm afraid, will never be one of them.