Time Travel

[Crookbond]

Excerpt from a recent article I just read (Do read the full article. It is interesting): Teleportation only works inside very carefully controlled quantum systems. For instance, quantum teleportation might work as an internal "wiring" element, within a quantum computer. But it won't work for physical objects. To beam up a person, you'd have to create a suitable -- but not easily conceivable -- entangled resource, a second "person." Then you would have to destroy the original self of the teleported living thing, Grangier said. "It's quite possible to teleport photons and ions, maybe many of them within a very carefully controlled quantum computer. But beyond that, the complexity of the resource and its vulnerability to decoherence make it completely impossible," he said. "For usual macroscopic objects, the complexity of the entangled resource becomes just incredible and unmanageable, and it will be instantaneously destroyed by decoherence." Source: How Quantum Teleportation Can Bring Us Secure Communications http://www.popsci.com/technology/article/2012-05/fyi-how-photon-teleportation-can-bring-us-secure-communications

So no time travel then.

[Vijay.Sharma]

Wormholes are the most plausible mathematical constructions to admit time travel under the framework we know of, and even then there are certain theorems assumed in their construction which prevent time travel in most scenarios. For time travel to be a reality we need: 1. New mathematics which allows the construction of objects allowing it because the most plausible construct, wormhole does not do a very good job. 2. There are certain restrictions in the construction which can restrict either forward of backward travel in time. For a realistic confirmation of time travel both directions should be allowed in the theory, which is even harder to do.

So basically what you are saying is that time travel is an implausibility given our current understanding of things. If our understanding of the way the universe works changes then we may discover it? The Star Wars (2009) movie presented an intriguing situation when Spock (Leonard Nimoy) tells the young captain Kirk that the fact that Kirk has met an old Spock meant that there would be a new "future". This brings us to the question - are there many pasts and many futures? If that is so then wouldn't time travel be an instance of us accessing one of those "parallel realities"? All said and done, we would still have held a 8-zip record with our padosis in all of them parallel realities

[Crannypete]

I went Pakistan in 2010 and when I got there it was 1985 Eerie

[Sachin=GOD]

Should Time Travel Be A Moral Imperative?

If time travel is possible, should society be ethically obligated to try and reverse some of history’s worst crimes against humanity? That’s the question I posed to MIT quantum mechanic Seth Lloyd, who was part of a 2010 team that used quantum teleportation to send a photon a few billionths of a second back in time in order to try and have it destroy its former self. Lloyd, who also holds a master’s in history and the philosophy of science, said the team’s effort was in part unsuccessful, but it doesn’t mean that time travel for ethical purposes would ultimately be impossible. “If you think you can go back to change something,” said Lloyd, “clearly you would be tempted to do this. The question is would it do any good?” Certainly, the alternate reality one “enters” (or creates) might be a better place; with no Holocaust, and no Armenian or Rwandan genocides, says Lloyd. But he says it’s still not clear that such events could, in fact, actually be prevented in our current reality. He doesn’t exclude the possibility that going back to right such wrongs might inadvertently set some other horrible chain of events into motion. “The universe is a chancy place,” said Lloyd. Of two different physical theories of time travel, only one allows for changing one’s past. In Type 1 time travel — the type highlighted in the “Back to the Future” films — all possible pasts and futures in some sense exist simultaneously, says Lloyd. So, that when you go back and change the past in order to enter a different future, your “old” future is in some sense still “there.” “From a theoretical physics standpoint,” said Lloyd, “Type 1 is certainly possible, but we still don’t have a very good theory of how it would work.” He notes that current physical theory favors Type 2 time travel scenario in which the past can’t be changed no matter how hard one tries. “Our theory of time travel is Type 2,” said Lloyd, “[which means] no matter how hard you try to mess with the past you can’t do it.” In a 2010 experiment, led by Aephraim Steinberg, a quantum physicist at the University of Toronto, the team confirmed this fact when they sent an elementary particle a few billionths of a second backwards in time. “When we aimed the photon gun at itself in the past,” said Lloyd, “at the last minute, a little quantum fluctuation [always] whisked the photon bullet out of the way.” But eventually both Type 1 and Type 2 time travel could see fruition. And if that happens, the ultimate question is whether the powers that be will choose to interfere with the space-time continuum? It’s a question that might best be answered with a question. If time travel is possible, why don’t we see evidence of our future selves visiting us in the present? Lloyd says that just as in “Back to the Future,” time travelers would likely do their utmost to blend in with the epoch they were visiting. Lloyd is the first to admit that our current understanding of “time” is pretty minimal. But to actually send people back to the past, he says, would require something like a rapidly-rotating black hole in order to manipulate the fundamental fabric of space and time in ways that he acknowledges can be “quite hard to do.” “Time travel is allowed by Einstein’s Theory of General Relativity,” said Lloyd, “but we don’t know how to implement the conditions to actually make it happen.” Lloyd jokingly notes that any attempts to create a “rapidly-rotating” miniature black hole in the lab would likely be promptly rebuffed by MIT’s workplace safety board. But at least he and colleagues are working on such “thought” experiments. “Everybody talks about time travel but nobody does anything about it,” he laments. The conventional theory of time is that it moves on a long string, says Lloyd. But in time travel, he says, time is more like a Mobius strip that twists back onto itself. Although the laws of physics seem to allow it, Lloyd says from a practical standpoint we don’t know how to create the requisite closed timelike curves to make this “Mobius twist” happen. However, as Lloyd points out, normally, if something is allowed by the laws of physics, then it’s mandatory. “But at the moment,” said Lloyd, “your best bet for time travel is to jump into a rapidly-rotating black hole and pray.”

http://www.forbes.com/sites/brucedorminey/2013/08/28/should-time-travel-be-a-moral-imperative/