Free Republic
Browse · Search
News/Activism
Topics · Post Article

Skip to comments.

New model 'permits time travel'
BBC ^ | 6/17/05 | Julianna Kettlewell

Posted on 06/17/2005 12:06:22 PM PDT by LibWhacker

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.

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."


TOPICS: News/Current Events
KEYWORDS: mechanics; model; paradox; quantum; stringtheory; theory; time; timetravel; travel
Navigation: use the links below to view more comments.
first previous 1-20 ... 101-120121-140141-160161-178 last
To: Crawdad

If they can, they've already done it.


161 posted on 06/20/2005 8:23:16 AM PDT by <1/1,000,000th%
[ Post Reply | Private Reply | To 142 | View Replies]

To: AdmSmith; bvw; callisto; ckilmer; dandelion; FairOpinion; ganeshpuri89; gobucks; KevinDavis; ...
This topic is from June 2005.

· String Theory ping list · join · view topics · view or post blog messages · bookmark · post new topic ·

162 posted on 02/14/2007 10:03:32 PM PST by SunkenCiv (I last updated my profile on Wednesday, February 14, 2007. https://secure.freerepublic.com/donate/)
[ Post Reply | Private Reply | To 1 | View Replies]

To: SunkenCiv

TIME Travel? How absurd ... if we've lived from today to tomorrow, we've experienced time travel ... getting back to something already traveled? Well, that's the essence, isn't it!


163 posted on 02/14/2007 10:11:23 PM PST by MHGinTN (If you've had life support. Promote life support for others.)
[ Post Reply | Private Reply | To 162 | View Replies]

To: <1/1,000,000th%

WOW, you're right. Im doing that right now, right now, right now, right now, right now, right now, right now,
right now, right now, right now, right now, right now......

HELP ME!!!!!!!!


164 posted on 02/14/2007 10:18:09 PM PST by Kickass Conservative (Nightmare on Pennsylvania Avenue - Hitlery Clinton, Commie In Chief.)
[ Post Reply | Private Reply | To 6 | View Replies]

To: LibWhacker
My grandfather, who lived to be eighty-three, always said he would never go back and change a thing. I think he believed that all actions run consecutively and that if you change A, you can't have B. And if that was true, he wouldn't be sitting there in his recliner at a ripe old age saying "I'd never change a thing."
165 posted on 02/14/2007 10:18:11 PM PST by Pan_Yans Wife
[ Post Reply | Private Reply | To 1 | View Replies]

To: LibWhacker
Interesting. My explanation for the paradox is that while we may be able to travel to the past, we may not be able to interact with it's environment.

The article's theory is probably the better explanation, however.

166 posted on 02/14/2007 10:26:39 PM PST by TAdams8591 (Guilianni is a Liberal who cannot beat Hillary!)
[ Post Reply | Private Reply | To 1 | View Replies]

To: LibWhacker

could I travel back in time to save a life? like Vince Foster's


167 posted on 02/14/2007 10:30:24 PM PST by isom35
[ Post Reply | Private Reply | To 1 | View Replies]

To: LibWhacker

bump for later


168 posted on 02/14/2007 10:33:17 PM PST by Centurion2000 (If you're not being shot at, it's not a high stress job.)
[ Post Reply | Private Reply | To 1 | View Replies]

To: MHGinTN

It's useless if it doesn't involve looking into the future to grab the lotto numbers.


169 posted on 02/14/2007 10:39:30 PM PST by SunkenCiv (I last updated my profile on Wednesday, February 14, 2007. https://secure.freerepublic.com/donate/)
[ Post Reply | Private Reply | To 163 | View Replies]

To: SunkenCiv

Depends, eh? Grab the lotto numbers, collect millions, die eventually... what have you personally gained? If there is something about you that is not bound by spacetime as you seem to understand it, what have you actually gained if you reject the Lord of Salvation for your selfish directives?


170 posted on 02/14/2007 10:57:04 PM PST by MHGinTN (If you've had life support. Promote life support for others.)
[ Post Reply | Private Reply | To 169 | View Replies]

To: Mr. Jeeves
How else do you explain Billy Ray Cyrus? ;)

You haven't been paying attention, pal.

Billy Ray Cyrus is alive, well, and although he isn't selling millions of CDs, his daughter is.

Miley Cyrus is the star of the Disney Channel series Hannah Montana (about a Tennessee girl's big break singing in Hollywood), Billy Ray plays her father, and the soundtrack to the show hit #1 on Billboard's Album chart and has sold over two million thusfar -- more than -- among other artists with 2006 releases -- the Dixie Chicks.

171 posted on 02/14/2007 11:07:34 PM PST by L.N. Smithee (“In Hollywood it’s easier to come out as gay than as conservative...” - Joel Surnow, Creator of "24")
[ Post Reply | Private Reply | To 14 | View Replies]

To: LibWhacker
If you went back in time and met your teenage parents, you could not split them up and prevent your birth

OK, I buy that - but how about if I met Al Gore Sr and Pauline LaFon and split them up? Or Hugh Rodham and Dorothy Howell? Or Virginia Cassidy and whatever horny bum was around at the time? Would that have worked? Life would be different!

172 posted on 02/14/2007 11:14:35 PM PST by SFConservative
[ Post Reply | Private Reply | To 1 | View Replies]

To: timer

Oldie but goodie bump


173 posted on 02/14/2007 11:34:58 PM PST by investigateworld (Abortion stops a beating heart)
[ Post Reply | Private Reply | To 1 | View Replies]

To: LibWhacker
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.

Okay. Have to stop there. It is not obvious at all. If mischievous time-travellers changed anything, nobody would ever know.

174 posted on 02/15/2007 12:52:34 AM PST by Lancey Howard
[ Post Reply | Private Reply | To 1 | View Replies]

To: LibWhacker

Larry Niven wrote a short story, "Rotating Cylinders and the Possibility of Global Causality Violation". Any civilization that gets close to building a time machine suffers a natural catastrophe that prevents completion.


175 posted on 02/15/2007 1:20:06 AM PST by Gideon7
[ Post Reply | Private Reply | To 1 | View Replies]

To: LibWhacker

These guys are from the PT Barnum school of flimflammery. There is no such thing as "time" in and of itself, it's KINETIC ENERGY at some rate(t=dKE). Can you think of a "time" event that is NOT a Kinetic Energy event going on at some rate? $1000 in small, unmarked bills in a brown paper bag to the first person to do the demonstration.

Really, you have to laugh at these four flushers. Picture one of them at the high stakes poker table in vegas. Stud poker, 3 players left. Our FOUR FLUSHER is #3 and has 4 spades showing, which wins the hand against the other 2, IF he has a spade in the hole. There is $300,000 in the pot.

So, instead of showing his hole card he goes into this long alternate universe spiel about probabilities, and claims 1/4 of the pot($75,000)because that's the 25% probability that his hole card is a SPADE.

Now, what is the probability that his tied up/living body will be dumped in a hole(as a HOLE card)out in the desert, using a SPADE?


176 posted on 02/15/2007 2:15:11 AM PST by timer (n/0=n=nx0)
[ Post Reply | Private Reply | To 1 | View Replies]

To: LibWhacker

We cannot know whether the present has been changed by something happening in time travel because if something is changed then everything is changed including all memories.


177 posted on 02/15/2007 2:20:24 AM PST by arthurus (Better to fight them over THERE than over HERE)
[ Post Reply | Private Reply | To 1 | View Replies]

To: LibWhacker

Einstein's Relativity always allowed time travel. What is weird, among many weird paradoxical results from solutions is that if the astronaut returned to his starting point not only would his clock read different, but it would be running at a different rate.


178 posted on 02/15/2007 9:31:14 AM PST by RightWhale (300 miles north of Big Wild Life)
[ Post Reply | Private Reply | To 1 | View Replies]


Navigation: use the links below to view more comments.
first previous 1-20 ... 101-120121-140141-160161-178 last

Disclaimer: Opinions posted on Free Republic are those of the individual posters and do not necessarily represent the opinion of Free Republic or its management. All materials posted herein are protected by copyright law and the exemption for fair use of copyrighted works.

Free Republic
Browse · Search
News/Activism
Topics · Post Article

FreeRepublic, LLC, PO BOX 9771, FRESNO, CA 93794
FreeRepublic.com is powered by software copyright 2000-2008 John Robinson