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[Chicago Astronomer - Astro Joe]

New model 'permits time travel'

Researchers speculate that time travel can occur within a kind of feedback loop where backwards movement is possible, but only in a way that is "complementary" to the present.

In other words, you can pop back in time and have a look around, but you cannot do anything that will alter the present you left behind.

The new model, which uses the laws of quantum mechanics, gets rid of the famous paradox surrounding time travel.

Quantum behaviour is governed by probabilities. Before something has actually been observed, there are a number of possibilities regarding its state. But once its state has been measured those possibilities shrink to one - uncertainty is eliminated.

So, if you know the present, you cannot change it. If, for example, you know your father is alive today, the laws of the quantum universe state that there is no possibility of him being killed in the past.

It is as if, in some strange way, the present takes account of all the possible routes back into the past and, because your father is certainly alive, none of the routes back can possibly lead to his death.

"Quantum mechanics distinguishes between something that might happen and something that did happen," Professor Dan Greenberger, of the City University of New York, US, told the BBC News website.

"If we don't know your father is alive right now - if there is only a 90% chance that he is alive right now, then there is a chance that you can go back and kill him.

"But if you know he is alive, there is no chance you can kill him."

More here from the BBC: news.bbc.co.uk/2/hi/science/nature/4097258.stm

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Everytime I attempt to contemplate the time travel paradox...my brain hurts...

Dr. McCoy, give me that Hypospray!

[Maddad]

It's only a paradox becaue of a misunderstanding about the nature of time. If you go back in time, then everything you do changes what will be the next future. You will be part of that change, whether you kill your father before you were born or not. If you do, you would not suddenly vanish. The new version of you simply would not be born, thereby preventing your double from being created. You would still be there, without any paradox.

If you want to get a grip on what time is, there's a science fiction book written by James P. Hogan called "Thrice Upon a Time". It's old, maybe a quarter century, but it explores the meaning of time. The book's hard to find because it's been out of print. Hogan may have released it again recently though; I'm not sure. Amazon will have it, of course. Oh, and be prepared. It's one of Hogan's earliest works, written before he figured out how to get a story moving in the first half the book. Be patient.

Don't be put off becuase it's science fiction; Hogan's got tons of solid physics credentials behind him.

[Chicago Astronomer - Astro Joe]

Add dimensional physics to the pot, and the whole exploration of time travel expands exponentially.

I still think we are too young as a species to begin to comprehend time travel. It would be like a Roman with the fastest chariot finding a way to break the sound barrier.

In time tho, I think time travel will be possible.

[Maddad]

The classic objection though is where are the time travelers if time travel will be developed some day? You have to get cheesy with regulations prohibiting any past-timer from being told about it to allow the idea, and then you have to explain why nobody will ever break that law when every other law man has ever made has been broken.

[Chicago Astronomer - Astro Joe]

Mankind corrupts just about everthing he touches, so this would be no different.

Policing the timeline reminds of the special section of Starfleet that monitors time infractions by Captains of various vessels. They were fed up with Capt. Janeway always screwing with the timeline.

I think when that day does come when we are able to travel, it bids the end of humanity, as I said before...man's touch.

[Maddad]

You've still got the problem of explaining why not even one rogue trime traveler will ever break the rules.