New Model Solves Grandfather Paradox

goldfishy writes "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 theory, you could go back in time and meet your infant father but you could not kill him." From the article: "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."

Comments

Summary

[823723423]

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

That's great!

[cytoman]

This means that you cannot be killed when you go back in time, nor can you kill or destroy anything! That's just perfect!!

Go back in time and be able to observe, only... no ability to interact with anyone either... it should be kinda like ghosts... we go back in time and observe and be like ghosts in the sense that we cannot interact and change anything that has already happened but only observe!

Imagine the possibilities of history classes of the future... maybe there are already a lot of ghosts watching us right now... the future students studying history!!

Re:That's great!

[Lemmy Caution]

Here's an interesting twist: I can change the past in a way that changes the future, if I do so in a way that I don't know now. I could, for example, buy some shares of a stock that I know will rise a hundred-fold in value, but make sure that I don't get the money until after the moment I depart current time. Since I don't know that I don't have an envelope worth millions of dollars hidden, with a mechanism that will inform me of it, say, a week after my time-travel tip, it does not contradict what is known about the present that I become a millionaire a week from now.

No no no!

[jerald_hams]

"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."

That's not clear at all. If I went back in time and killed the baby George W Bush, it's like he would disappear in the middle of a speech. Rather the entire course of history branching from that moment would be changed, so that in the "present" no one would ever know GW had existed.

-Alex

Re:How?

[The Good Reverend]

How can that even be remotely possible? Anything and EVERYTHING (no matter how small or big of an event it is) will change SOMETHING in the future.

Sci-fi writers have had two main theories for a long time. Either you can go back in time and change things, or you can go back in time and "fulfill" the past you expireinced. Just because you have an influence on the past doesn't mean your influence didn't shape time into the way you remembered it.

Anyone who thinks any differently needs to go back to school.

Yes, because I'm sure these quantum physicists haven't spent any time in school...

what is _wrong_ with this reporter?!

[Blymie]

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.

So let me get this straight, BBC reporter. Your proof that time can't be changed, is simply that you don't remember it happening?

There are just so many flaws in that reasoning. ;)

First, time changes could be happening everywhere, but perhaps you have not witnessed one. Wait! How about this? How about time changing, and altering your memory at the same time?

What's the matter with you? Do you believe that it is impossible for something to occur, without you being aware of it?

Is this a God complex?

What unmitigated self-importance, BBC reporter!

Now sure, I know this reporter was likely trying to parse some marlaky that they were told, but this has to be the worst use of logic I have seen.

Re:Verifying the Theory

[Malicious]

Um Doc... how about we test on a monkey first?

Lame!

[khasim]

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.

Ummm, if you prevented their births, they wouldn't exist to "fade into the ether".

It could be happening all the time and you wouldn't be aware of it (by definition).

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.

Sounds like bad fiction to me.

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.

Sounds like the techno-babble "justification" in the bad fiction.

So, if you know the present, you cannot change it.

And the easiest way to not change it is for time travel to be impossible.

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.

If, for example, you knew a picture would be taken, you could reflect light from your body and appear in that picture, thereby altering the future.

So, travelling back in time, you cannot reflect light, and, by the same token, you cannot absorbe light.

And it just moves up from there for all other physical effects. Nothing touched, no air breathed, no light disturbed, nothing.

So, how would you even know you were in the past?

Re:You insensitive clod!

[The Only Druid]

No, his name is Philip J. Fry. Farnsworth is the last name of his nephew, the professor, many generations removed.

Re:What about parallel and multi-universes?

[fimbulvetr]

I don't like that. Let's say I travel back in time to two days before today and I land in wet cement, leaving foot prints. However, the day before I left (Which would be the day after I arrive), the cement layer came to work in the morning and saw no foot prints. Doesn't that prevent me from traveling back, because history records show the cement was smooth?

Or...Does it allow me to 'land' back in time *only* where my landing does not affect anything in the future. Where would that be? Wouldn't my biological struture have influence on just about any environment?

Re:You insensitive clod!

[EvilTwinSkippy]

The next time someone talks about the difficulties of multiple inheritence, they may not be talking about OOP.