New model 'permits time travel'

[RuffRat]

If you went back in time and met your teenage parents, you could not split them up and prevent your birth - even if you wanted to, a new quantum model has stated.

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.

Paradox explained

Although the laws of physics seem to permit temporal gymnastics, the concept is laden with uncomfortable contradictions.

The main headache stems from the idea that if you went back in time you could, theoretically, do something to change the present; and that possibility messes up the whole theory of time travel.

Clearly, the present never is changed by mischievous time-travellers: people don't suddenly fade into the ether because a rerun of events has prevented their births - that much is obvious.


You go back to kill your father, but you'd arrive after he'd left the room, you wouldn't find him, or you'd change your mind
Professor Dan Greenberger, City University, New York
So either time travel is not possible, or something is actually acting to prevent any backward movement from changing the present.

For most of us, the former option might seem most likely, but Einstein's general theory of relativity leads some physicists to suspect the latter.

According to Einstein, space-time can curve back on itself, theoretically allowing travellers to double back and meet younger versions of themselves.

And now a team of physicists from the US and Austria says this situation can only be the case if there are physical constraints acting to protect the present from changes in the past.

Weird laws

The researchers say these constraints exist because of the weird laws of quantum mechanics even though, traditionally, they don't account for a backwards movement in time.

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."

In other words, even if you take a trip back in time with the specific intention of killing your father, so long as you know he is happily sitting in his chair when you leave him in the present, you can be sure that something will prevent you from murdering him in the past. It is as if it has already happened.

"You go back to kill your father, but you'd arrive after he'd left the room, you wouldn't find him, or you'd change your mind," said Professor Greenberger.

"You wouldn't be able to kill him because the very fact that he is alive today is going to conspire against you so that you'll never end up taking that path leads you to killing him."

Greenberger and colleague Karl Svozil introduce their quantum mechanical model of time travel on the ArXiv e-print service.

Source - http://news.bbc.co.uk/2/hi/science/nature/4097258.stm

[DiAmOnD RaStA]

That's deep. lol

Some people may think thats shitty cuz the only reason why they would ever want to time travel would be to change their own lives, or something that has happened.

I guess my dream where i buy weed, smoke it, go back in time, smoke it again, go back in time, smoke it again then go back to the future is a NO GO then heh? hahaha

[RuffRat]

^ ha ha that would be tight, just find the dankest weed and keep smoking it

[Foreman]

1st

Originally Posted by RuffRat

"You go back to kill your father, but you'd arrive after he'd left the room, you wouldn't find him, or you'd change your mind," said Professor Greenberger.

"You wouldn't be able to kill him because the very fact that he is alive today is going to conspire against you so that you'll never end up taking that path leads you to killing him."
http://news.bbc.co.uk/2/hi/science/nature/4097258.stm

how do they know this?

i dont like a ny of it because it blows the whole back to the future theory out of the water

[adamBC]

but in back to the future, he never changed anything, he just made out with his mom.



and he invented a new style of rock.

[KoRnOnTheKob]

nice. If time travel were possible, i would travel back to the time when weed was legal, and buy like 5 pounds of it. It would be cheep because of inflation, so then i would come back to present time and sell/use it!

[popsson]

another sign of the apacolypse

[Foreman]

Originally Posted by adamBC

but in back to the future, he never changed anything, he just made out with his mom.



and he invented a new style of rock.

actually before he went back his family was all fucked up, and biff's and asshole. after he gets back his family's all normal,and biff's their bitch!

oh yea and if i could go back i'd go and kill harry j anslinger

[plumface_2002]

thats nuts, i have always been so intruged by time travel, too bad that it most likely wont ever happen in my lifetime, even though though it would be fucking sweet.

[RuffRat]

yeah and when it does happen, the public wont be aloud to use it

[IGotTheCottons]

Originally Posted by KoRnOnTheKob

nice. If time travel were possible, i would travel back to the time when weed was legal, and buy like 5 pounds of it. It would be cheep because of inflation, so then i would come back to present time and sell/use it!

Hell yeah dude... You could get papers stating when it was purchased, and they couldn't throw your ass in jail, 'cause you bought it when it was legal, lmao. Gotta love ex post facto... Or however it's spelled, lol.

[negligent]

shit even i could of told u that u cant go back in time n change shit. like preventing ur birth, if you split ur parents up so they didnt have u that means u never existed to begin with to go back in time, haha no big secret there, any kind of change in the past has potential to change the future, whether it be somethin little or somethin huge

[JeraldoRonaldo]

Hey, did you ever think that time travel was already invented? Like, some guy invented it, went back, and had sex with his mom, so his mom didn't have sex with his dad, so he never got born, so he never invented time travel.



Or they know it because they can travel time, they just won't tell us.

[popsson]

yea. what if we are living in the past and some of the people we see are from the future.

[popsson]

i thought the past was all in your mind, i dont think you can go back in time.

i think video cameras are the closest we are gonna get to time travel.