Time travel experiment demonstrates how to avoid the grandfather paradox

[The Straight Story]

Among the many intriguing concepts in Einstein’s relativity theories is the idea of closed timelike curves (CTCs), which are paths in spacetime that return to their starting points. As such, CTCs offer the possibility of traveling back in time. But, as many science fiction films have addressed, time travel is full of potential paradoxes. Perhaps the most notable of these is the grandfather paradox, in which a time traveler goes back in time and kills her grandfather, preventing her own birth.

In a new study, a team of researchers has proposed a new theory of CTCs that can resolve the grandfather paradox, and they also perform an experiment showing how such a scheme works. The researchers, led by Seth Lloyd from MIT, along with scientists from the Scuola Normale Superiore in Pisa, Italy; the University of Pavia in Pavia, Italy; the Tokyo Institute of Technology; and the University of Toronto, have published their study in a recent issue of Physical Review Letters. The concepts in the study are similar to an earlier study by some of the same authors that was posted at arXiv.org last year.

“Einstein's theory of general relativity supports closed timelike curves,” Lloyd told PhysOrg.com. “For decades researchers have argued over how to treat such objects quantum mechanically. We believe that our theory is the correct theory of such objects. Moreover, our theory shows how time travel might be accomplished even in the absence of general relativistic closed timelike curves.”

In the new theory, CTCs are required to behave like ideal quantum channels of the sort involved in teleportation. In this theory, self-consistent CTCs (those that don’t result in paradoxes) are postselected, and are called “P-CTCs.” As the scientists explain, this theory differs from the widely accepted quantum theory of CTCs proposed by physicist David Deutsch, in which a time traveler maintains self-consistency by traveling back into a different past than the one she remembers. In the P-CTC formulation, time travelers must travel to the past they remember.

http://www.physorg.com/news/2011-03-grandfather-paradox.html

[Very_Boring_Name]

1. It's like Captain Janeway says

I swore I'd never let myself get caught in one of these Godforsaken paradoxes. The past is the future, the future is the past, it all gives me a headache.

[poverlay]

2. Thanks for the Janeway reference. I totally miss Voyager. Such a great ship. I'll never forget

"Year of Hell", one of the coolest sci fi episodes ever made!

[Hugabear]

3. Or, if you subscribe to the multiverse theory, altering the past simply creates a new timeline

Say you were to go back in time and kill Hitler. According to multiverse theory, you would simply create a new timeline in which Hitler was assassinated, but the original timeline would also stay intact. There would be two coexisting timelines. In actuality, there could be an infinite number of parallel universes coexisting, with some virtually identical to each other except with minute differences at the quantum level. So therefore going back in time would simply create a new parallel universe.

[starroute]

10. But that's exactly what this new theory rejects

From the linked article: "As the scientists explain, this theory differs from the widely accepted quantum theory of CTCs proposed by physicist David Deutsch, in which a time traveler maintains self-consistency by traveling back into a different past than the one she remembers. In the P-CTC formulation, time travelers must travel to the past they remember."

[Merlot]

12. Or, you could just watch "Groundhog Day"

[DavidDvorkin]

4. Pfft. We sf novelists have come up with numerous solutions to this problem.

For example.

Okay, so we control the plots, which makes it easier. And we can skip the math. That does simplify things.

[pokerfan]

5. Pair o' docs what pair o' docs?

Primer timeline: http://neuwanstein.freeweb.hu/primer_timeline.html

[DavidDvorkin]

9. I had to make a timeline for my time travel novel

because I was getting confused.

Maybe I should put it online, too.

[Zax2me]

6. what a cool story

thanks!

[The Doctor.]

7. A new timeline is created at the point of arrival for the traveler.

It's really just that simple.

[WatsonT]

8. Futurama already figured this out

although it gets a little weird.

http://en.wikipedia.org/wiki/Roswell_That_Ends_Well

[Leopolds Ghost]

11. "Chew on THAT, causality!!"

[Initech]

13. "Oh like we need a lesson in changing history from Mr. I'm My Own Grampa!"

:rofl:

[Paradoxical]

14. Does this break causality?