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PostPosted: Thu Jan 29, 2015 8:17 am
 


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The Quantum Experiment That Simulates A Time Machine

Physicists have simulated a photon interacting with an older version of itself in an experiment that could help reconcile quantum mechanics and relativity

One of the curiosities of general relativity is that it seems to allow time travel. Various physicists have discovered solutions to Einstein’s field equations that contain loops that return to the same point in space and time. Physicists call them closed time-like curves.

At first glance, these kinds of time machines seem to lead to all kinds of problems, such as the grandfather paradox. This is where somebody travels back in time and kills their grandfather meaning they could never have been born and so could not have gone back to kill the grandfather.

That’s just bizarre so physicists have attempted to find ways to prevent these paradoxes. In the early 90s, for example, cosmologists showed that a billiard ball entering a wormhole that leads to a closed time-like curve must always meet its older self coming out of the wormhole. What’s more, the resulting collision always prevents the ball entering the wormhole in the first place. In other words, the billiard ball would simply bounce off the entrance to a closed time-like curve.

So much for classical objects and time travel. But what would happen if a quantum particle entered a closed time-like curve? In the early 90s, the physicist David Deutsch showed that not only is this possible but that it can only happen in a way that does not allow superluminal signalling. So quantum mechanics plays havoc with causality but in a way that is consistent with relativity and so prevents grandfather-type paradoxes.

Deutsch’s result has extraordinary implications. It implies that closed time-like curves can be used to solve NP-complete problems in polynomial time and to violate Heisenberg’s uncertainty principle.

Image

As far as we can tell, nobody has ever created a Deutsch closed time-like curve. So it’s easy to imagine that until we do, we will never know whether Deutsch’s predictions are true. But today Martin Ringbauer and a few pals at the University of Queensland in Australia say that it’s not necessary to create a closed time -like curve to test how it behaves.

Instead, these guys have created a quantum system that reproduces the behaviour of a photon passing through a closed time-like curve and interacting with its older self. In other words, these guys have built a time machine simulator.


https://medium.com/the-physics-arxiv-bl ... 5a7cc9bd11


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PostPosted: Thu Jan 29, 2015 8:58 am
 


Pfft. I already knew that.


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PostPosted: Thu Jan 29, 2015 9:03 am
 


We did that experiment back in January 2015.


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PostPosted: Thu Jan 29, 2015 9:09 am
 


DrCaleb wrote:
We did that experiment back in January 2015.


Exactly, my older self told me all about it. Pretty goood reading though, thanks.. My personal theory is that interactions through closed time-like loops can, and maybe even do, happen. However they would spin off their own unniverse. So in the one where you kill your grandfather time proceeds along it's curve then loops back like a number nine (travelling back in time) to where you kill your grandfather (where the lines in the "9" intersect. And then the circle of the "9" just plays itself out over and over again. The universe is stuck in a time circle and time never moves forward again. Which serves you right for shooting your grandfather. What a mean thing to do.

9

Of course, I'm a believer in the many-worlds interpretation of quantum dynamics, so this seems the logical solution for me.


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PostPosted: Thu Jan 29, 2015 9:33 am
 


DrCaleb wrote:
We did that experiment back in January 2015.


You beat me to it by a significant margin. I hadn't managed this until March 14, 2017.


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PostPosted: Thu Jan 29, 2015 10:08 am
 


So loop-quantum gravity decisively beats string theory once and for all? Good. :mrgreen:

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PostPosted: Thu Jan 29, 2015 10:09 am
 


Zipperfish wrote:
DrCaleb wrote:
We did that experiment back in January 2015.


Exactly, my older self told me all about it. Pretty goood reading though, thanks.. My personal theory is that interactions through closed time-like loops can, and maybe even do, happen. However they would spin off their own unniverse. So in the one where you kill your grandfather time proceeds along it's curve then loops back like a number nine (travelling back in time) to where you kill your grandfather (where the lines in the "9" intersect. And then the circle of the "9" just plays itself out over and over again. The universe is stuck in a time circle and time never moves forward again. Which serves you right for shooting your grandfather. What a mean thing to do.

9

Of course, I'm a believer in the many-worlds interpretation of quantum dynamics, so this seems the logical solution for me.


Actually! . . . I think they proved mathematically that a billiard ball entering a closed time loop wormhole will always meet itself exiting the wormhole and get knocked away and prevented from entering the wormhole. In which case, it never entered the wormhole. 8O


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PostPosted: Thu Jan 29, 2015 10:19 am
 


DrCaleb wrote:
Zipperfish wrote:
DrCaleb wrote:
We did that experiment back in January 2015.


Exactly, my older self told me all about it. Pretty goood reading though, thanks.. My personal theory is that interactions through closed time-like loops can, and maybe even do, happen. However they would spin off their own unniverse. So in the one where you kill your grandfather time proceeds along it's curve then loops back like a number nine (travelling back in time) to where you kill your grandfather (where the lines in the "9" intersect. And then the circle of the "9" just plays itself out over and over again. The universe is stuck in a time circle and time never moves forward again. Which serves you right for shooting your grandfather. What a mean thing to do.

9

Of course, I'm a believer in the many-worlds interpretation of quantum dynamics, so this seems the logical solution for me.


Actually! . . . I think they proved mathematically that a billiard ball entering a closed time loop wormhole will always meet itself exiting the wormhole and get knocked away and prevented from entering the wormhole. In which case, it never entered the wormhole. 8O





In order to get knocked away, doesn't it have to meet itself and thus have entered the wormhole at some point? I mean where does the ball exiting the wormhole come from? And what time elapsed does the ball coming out of the hole experience vs the one being inserted in the hole? (this is starting to sound kinky)

the op also says that the loop returns to the same point in space/time. If it's the exact same point, how can the ball meet the older version of itself?


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PostPosted: Thu Jan 29, 2015 10:42 am
 


This theory is as clear as a bell after sucking on an LSD laced sugar cube.


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PostPosted: Thu Jan 29, 2015 10:45 am
 


Sometimes I quantum leap in my sleep. 8)


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PostPosted: Thu Jan 29, 2015 11:07 am
 


andyt wrote:
DrCaleb wrote:
Zipperfish wrote:
Exactly, my older self told me all about it. Pretty goood reading though, thanks.. My personal theory is that interactions through closed time-like loops can, and maybe even do, happen. However they would spin off their own unniverse. So in the one where you kill your grandfather time proceeds along it's curve then loops back like a number nine (travelling back in time) to where you kill your grandfather (where the lines in the "9" intersect. And then the circle of the "9" just plays itself out over and over again. The universe is stuck in a time circle and time never moves forward again. Which serves you right for shooting your grandfather. What a mean thing to do.

9

Of course, I'm a believer in the many-worlds interpretation of quantum dynamics, so this seems the logical solution for me.


Actually! . . . I think they proved mathematically that a billiard ball entering a closed time loop wormhole will always meet itself exiting the wormhole and get knocked away and prevented from entering the wormhole. In which case, it never entered the wormhole. 8O


In order to get knocked away, doesn't it have to meet itself and thus have entered the wormhole at some point? I mean where does the ball exiting the wormhole come from? And what time elapsed does the ball coming out of the hole experience vs the one being inserted in the hole? (this is starting to sound kinky)

the op also says that the loop returns to the same point in space/time. If it's the exact same point, how can the ball meet the older version of itself?


That's the nature of a wormhole through spacetime. The entrance and exit can be at the same point in time, so an object entering the wormhole can exit it at the same time as it enters, causing it to never enter the hole to begin with. Paradox!

That's why the 'grandfather' paradox is thought to be impossible. You can't go back in time and kill your grandfather, because you exist and therefore didn't (or won't) go back in time and kill him. That, or going back in time happens in an alternative universe where killing your grandfather doesn't prevent you from being born in this Universe.


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PostPosted: Thu Jan 29, 2015 3:20 pm
 


I wonder what quantum sex is like? [huh]


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PostPosted: Thu Jan 29, 2015 3:32 pm
 


I understood about 20-30% of this.


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PostPosted: Thu Jan 29, 2015 3:40 pm
 


Here's my shitty attempt to weigh into something way out of my league (par for the course for my whole membership here):

So we can't send an object back in time because the previous object basically closes the loop... But they are working on manipulating the past object? I wonder if they'll be able to figure out methods with which to alter past objects without "travelling" a current object back in time, causing the present object to start exhibiting that altered past?

This is why I stick to politics. You do not need to be very bright for politics.


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PostPosted: Thu Jan 29, 2015 4:06 pm
 


Public_Domain wrote:
You do not need to be very bright for politics.


Evident by every single successful politician of ANY background.


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