Can future events affect the past?

[Jmeagle]

In a new experiment done,an Australian team of physicists have said they have said they had a particle in the future affect the past.
https://cosmosmagazine.com/physical-sciences/time-travel-and-single-atom

 

[phinds]

In a new experiment done,an Australian team of physicists have said they have said they had a particle in the future affect the past.

This forum requires specific citations in order to discuss an experiment.

 

[Jmeagle]

Sorry,just posted a link.

 

[phinds]

I'm out of my depth trying to explain that one but it sounds very interesting. That link is not included in the list of specifically acceptable sources for this forum and I have no idea if it's ok, but the experiment seems legit so I think it should be. We have many members who will be able to shed more light on it, I'm sure.

 

[Jmeagle]

So the team sent a particle back in time or prove retrocausality?

 

[phinds]

So the team sent a particle back in time or prove retrocausality?

No, that is not what it says. Did you read the link?

 

[e.bar.goum]

This is the recent implementation of the Wheeler's delayed choice experiment with cold atoms that has been talked about quite a lot in this forum. The paper: http://www.nature.com/nphys/journal/vaop/ncurrent/full/nphys3343.html

General reading. https://en.wikipedia.org/wiki/Wheeler's_delayed_choice_experiment

 

[Jmeagle]

Its says they affected the past from the future.im a bit confused.or am I misreading the article.

 

[StevieTNZ]

The past you refer to was undetermined (the system was in a superposition of acting as a wave and a particle at the same time). So a decision in the future caused the system to behave as a particle or wave.

I think however that explanation is very vague and up to interpretation. May I suggest 'Quantum Enigma' page 153:

The "delayed-choice experiment" suggested by quantum cosmologist John Wheeler, ..., comes closest to testing the backward-in-time aspect of quantum theory. It confirmed the prediction of quantum theory that an observation creates the relevant history."

to clarify what I mean.

 

[Jmeagle]

So an event in the future did not affect an event in the present or past in reality?

 

[Drakkith]

So an event in the future did not affect an event in the present or past in reality?

I don't think there's a 100% agreed upon answer to your question.

 

[Jmeagle]

Im a bit confused,what did the experiment prove?

 

[ShayanJ]

Im a bit confused,what did the experiment prove?

How much QM do you know?
I don't think you can get an answer, if you don't know enough about QM.(Which it seems to me is the case.)

 

[Jmeagle]

I Don't know really anything about QM I am just curious.

 

[ShayanJ]

I Don't know really anything about QM I am just curious.

I want to bring into your attention what StevieTNZ quoted a few posts ago:

The "delayed-choice experiment" suggested by quantum cosmologist John Wheeler, ..., comes closest to testing the backward-in-time aspect of quantum theory. It confirmed the prediction of quantum theory that an observation creates the relevant history."

This is what happened. This is what the experiment immediately implies and we shouldn't think further than this. This is a typical situation in QM.

Let me see if I can give you an analogy. Imagine I tell you that I want to take you somewhere, an island or a desert. For going to the island, we should use a boat. For the desert, we should use a car.
I don't tell you which one we're going to do. Then I close your eyes and do all things necessary to make sure you can't know we're on a boat or in a car. But after reaching there, I open your eyes and you see you're in an island and you immediately find out you were on a boat all along the way. This isn't strange because your history was there, you just didn't know it.
But this experiment is different. There was no specific history to the atom, but after the measurement, the relevant history is created. Its not a popular view to interpret it as "future affecting past". In fact I myself don't like "future affecting the past", its just over-thinking it.

 

[Jmeagle]

So retrocausality or time travel to the past is still impossible?

 

[ShayanJ]

So retrocausality or time travel to the past is still impossible?

I can't speak that generally. But about this experiment, yes, it doesn't mean you can affect the past or travel back in time.

 

[Drakkith]

This sounds similar to the idea of using quantum entanglement for FTL communication. I assume the problems inherent in that area are also applicable here.

 

[ShayanJ]

This sounds similar to the idea of using quantum entanglement for FTL communication. I assume the problems inherent in that area are also applicable here.

Actually I was thinking the same thing!

 

[bhobba]

So retrocausality or time travel to the past is still impossible?

Its a subtle issue and we have interpretations where it does:
https://en.wikipedia.org/wiki/Transactional_interpretation

Generally you can't send information into the past - that would violate causality.

But there are all sorts of notions about with parallel universes and what not that if true allow such problems to be circumvented.

It also needs to be said that experiment is just a variation of the delayed choice experiment and what's going on is no mystery:
http://quantum.phys.cmu.edu/CQT/chaps/cqt20.pdf

Thanks
Bill

 

[Jmeagle]

Ok,so its wrong to say the future can affect the past or present?because if that were to happen causality would be violated.

 

[Jmeagle]

So the experiment is nothing new?

 

[e.bar.goum]

So the experiment is nothing new?

It was a thought experiment when it was initially proposed in 1978. It has been previously done with single photons. (Jacques, V. et al. Experimental realization of Wheeler’s delayed-choice gedanken experiment. Science 315, 966–968 (2007).) This is the first time it has been done with single atoms.

I think the most popular interpretation of the experiment isn't retrocausality, but that it's better to abandon the idea that objects behave definitely as particles or definitely as waves.

Any explanation of what goes on in a specific individual observation of one photon has to take into account the whole experimental apparatus of the complete quantum state consisting of both photons, and it can only make sense after all information concerning complementary variables has been recorded. Our results demonstrate that the viewpoint that the system photon behaves either definitely as a wave or definitely as a particle would require faster-than-light communication. Because this would be in strong tension with the special theory of relativity, we believe that such a viewpoint should be given up entirely

http://www.pnas.org/content/110/4/1221

 

[Jmeagle]

Ok so no back to the future type deal,even for particles or atoms.

 

[e.bar.goum]

Ok so no back to the future type deal,even for particles or atoms.

It depends on your interpretation of the experiment. It's all a bit subtle.

 

[Jmeagle]

What about events in the future?can they affect the present or past or what that require faster than light methods?

 

[Jmeagle]

Which interpretation is the widely considered as the favorite?

 

[StevieTNZ]

I really think it is in your best interests to study a bit more about QM, rather than all these questions which in my mind have been addressed and we are simply getting a reiteration of the same question in different forms.

 

[bhobba]

Ok,so its wrong to say the future can affect the past or present?because if that were to happen causality would be violated.

No. Its an issue if information can be sent into the past. And even if you could there are some way out ideas that if true would mean its not an issue.

Thanks
Bill

 

[bhobba]

Which interpretation is the widely considered as the favorite?

Probably good old Copenhagen:
http://motls.blogspot.com.au/2011/05/copenhagen-interpretation-of-quantum.html

Thanks
Bill

 

[Jmeagle]

So you are saying the future can affect the past as long as no information is sent?

 

[bhobba]

So you are saying the future can affect the past as long as no information is sent?

It's possible - we have interpretations of QM where such is the case.

Thanks
Bill

 

[Jmeagle]

Is there an interpretation where there is nothing retrocausal?

 

[Jmeagle]

Can particles affect the past without violating causality?

 

[bhobba]

Is there an interpretation where there is nothing retrocausal?

Indeed there is - nearly all are including Copenhagen.

Thanks
Bill