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byron178
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does this experiment violate any type of causality?
xts said:Causality? How?
It rather violates our intuitive demand of realism - shows that it really makes no sense to think about photons (and other quantum objects) as existing while they travel or as traveling along some paths. It shows that our attempts to catch the photon on its run are fundamentally void and hopeless.
If I am told something like that, my quick-response-sub-conscious-neurons-specialized-on-criticism immediately respond with two questions:byron178 said:I ask this because i was told it violates strong causality.
xts said:If I am told something like that, my quick-response-sub-conscious-neurons-specialized-on-criticism immediately respond with two questions:
1. what do you mean by 'strong causality'?
2. could you explain the machanism of violation you claim?
Then, the answer usually is: 'err... I was told so, it was convincing, but I don't remember the reasoning...'
So do some follow-up, and ask him for more elaborate answer: how it violates?byron178 said:I ask this because i contacted John G.Cramer and he said that wheeler's delayed choice experiment violates a type of causality.
xts said:Sure, Faster Than Light communication would violate causality.
FTL means that you may start experiment in one of two modes (called 0 and 1) up to your choice, and your assistant in remote part of the lab will know what was your choice in a time shorter than distance between you and him (divided by c).
xts said:But who says that Wheeler's experiment demonstrates FTL communication? No such communication may be constructed using Wheeler's machine.
xts said:There are no 'hypothetical non-relativistic axes' If you insist to think about such, then "communication FTL" loses its meaning and you must consider rather "communication backward in time".
xts said:Try again to describe the experiment without using QM terms. We are tossing ordinary coin this time.
xts said:When the wave function collapses 'below-the-table', it instantaneously collapses above the table.
I see you've fallen into a pitfall of understanding 'collapse' as something really happening in a nature.
xts said:You are sitting above the table. How may you check if the collapse happened or not?
xts said:So do some follow-up, and ask him for more elaborate answer: how it violates?
I'll be happy to see his answer! Forward it to me!
Here you have an implicit assumption, that there exists such physical reality, as "path of photon". Could you propose any empirical test of its existence? Or maybe I should ask for a bit more: are you able to track or map the photon's path? No, you can't. Quantum Mechanics prohibits to track photons. But you believe photons must travel along some path! All rabbits, mammooths, men and even stupid fizzy women always travels along paths. Photons must do that as well. You can't imagine how it may happen, that photon started at some point A, got detected at other point B, but its path make no sense. Thus - the path must exist, even if it is fundamentally impossible for photon to leave single footprint on its way. Bees don't leave footprints, but they fly over defined paths, so maybe photons are more like bees than like rabbits?byron178 said:In such experiments, the "cause" is a measurement performed
in the present, and its "effect" is the path of a photon in the past
That's the point!present influences the past, but not in a way that allows one to send messages to the past.
xts said:Here you have an implicit assumption, that there exists such physical reality, as "path of photon". Could you propose any empirical test of its existence? Or maybe I should ask for a bit more: are you able to track or map the photon's path? No, you can't. Quantum Mechanics prohibits to track photons. But you believe photons must travel along some path! All rabbits, mammooths, men and even stupid fizzy women always travels along paths. Photons must do that as well. You can't imagine how it may happen, that photon started at some point A, got detected at other point B, but its path make no sense. Thus - the path must exist, even if it is fundamentally impossible that photon left single footprint on its way. Bees don't leave footprints, but they fly over defined paths, so maybe photons are more like bees than like rabbits?
What, if the intuition of 'path of photon' just makes no sense? What is then affected by Wheeler's measurement?
That's the point!
Dragon in my garrage! (I hope you know this metaphore, if not: http://www.godlessgeeks.com/LINKS/Dragon.htm)
He is there, he was there yesterday and my todays action affect his past. But, of course, he is invisible and there is no way to check that empirically. But I have perfect intelectual arguments, that my present affects dragon's yesterday path...
OK. I'll be less ironic and more explicit...byron178 said:so the present can influence the past?
xts said:OK. I'll be less ironic and more explicit...
It depends on your definition of the word 'influence'.
If the 'influence' means 'may produce any empirically detectable effect' - physicist's anwer is: 'no'
If the 'influence' means 'there are effects, but they are restricted to undetectable beings (daemons, photon paths, invisible dragons, ghost of your grandma...)' - physicist's answer is: 'go with this question to a priest or shaman'
xts said:After time travel your presence would be detectable there, thus you could bring some information backward in time, thus it is impossible.
But, of course, your may penetrate past as an invisible and undetectable ghost. Just don't clang chains! That's not allowed.
We (I hope you too) live in countries respecting freedom of thought and speech. It is safe.byron178 said:so its safe to say they wheelers delayed choice allows influence to the past?
xts said:We (I hope you too) live in countries respecting freedom of thought and speech. It is safe.
Once again: you may define the word 'influence' such or such. Up to your philosophical taste.
If you are a mystic and you like to speak about 'undetectable influence' - say so.
If you are empiricist and you restrict meaning of 'influence' to 'detectable influence' - you can't say so.
If you want to be honest - make clear to the audience which meaning you use.
ok, to me a violation of causality is an influence that can affect the past in reality,i hope you see the confussion here.also is there a view in which the present does not affect the past?xts said:So now you just changed your philosophic-lexical question from 'what influence means' to 'what physical reality means'.
If your ontological taste restricts 'reality' to something detectable, answer is again 'no'
If you accept that photon paths, invisible dragons, or your grandma's ghost are physically real - feel happy with answer: 'wheelers delayed choice allow influence the past in physical reality'
I see, and I am happy you've finally accepted common-sense defnition of reality as something detectable.byron178 said:ok, to me a violation of causality is an influence that can affect the past in reality,i hope you see the confussion here.
Oooch? Are there people who do not believe in ghosts, invisible dragons and photon paths? Yes. They are. Not many, but there are some.also is there a view in which the present does not affect the past?
xts said:I see, and I am happy you've finally accepted common-sense defnition of reality as something detectable.
I also hope you see that Wheeler experiment does not influence past physical reality (in a meaning you've just accepted) and thus doesn't violate causality.
Oooch? Are there people who do not believe in ghosts, invisible dragons and photon paths? Yes. They are. Not many, but there are some.
#16? I said so?byron178 said:im confused because in post #16 you said that the present can influence the past.
xts said:#16? I said so?
I was sure it is me who need some sleep (2AM) to think clearly... Goodnight then!
byron178 said:so its safe to say they wheelers delayed choice allows influence to the past? i ask this because you said that he was right in saying that the present can influence the past.
mathal said:Wheeler proposed delayed time experiments to demonstrate that actions in a 'present' could alter the outcome of an experiment where photons (or any other quantum object) began their path before the alteration occured. Experiments have demonstrated over and over again that he was correct.
To make this clear.
0.Wheeler did accept that actions in the present can alter the past. He went to the extreme of referring to measurements in the present altering a photons history to the 'present' from it's inception billions of years ago, to make that point.
the experiments - precis
1. a photon begins it's path.
2. the path of one of the possibilities of the photon is altered.
3. a measurement of each photon's path is noted.
The statistical results of such experiments (and that is necessarily all you'll ever get-statistical non specific data) is in agreement with the conditions if the experiment had been set up ahead of time ,as if the entire experiment was like when the photon's path was altered.
There is only one model, the De Broglie-Bohm theory, that can offer an explanation that is not either acausal or time-reversed.
perhaps there is another model? (i.e.do you know of one or is De Broglie-Bohm what you aver to?)
Personally I prefer a block universe acausal model.
mathal
mathal said:There is only one model, the De Broglie-Bohm theory, that can offer an explanation that is not either acausal or time-reversed.
xts said:You missed one word. You should say There is only one realistic model...
'Realistic' :== 'assuming objective existence of intuitive, but nondetectable entities like "photon paths" '
Or maybe you meant that using the word 'acausal'...?
Anyway - since EPR/Bell I definitely prefer and advocate non-realistic models than shy time-reversed causalities , Bohmian pilots, and similar constructs.
Wheeler's Delayed Choice Experiment is a thought experiment proposed by physicist John Archibald Wheeler to investigate the nature of quantum mechanics. It involves a choice of whether to measure the path of a particle after it has already passed through a double-slit apparatus, or to not measure the path at all.
The purpose of this experiment is to explore the concept of wave-particle duality and the role of observation in determining the behavior of particles at the quantum level. It also raises questions about the nature of reality and the role of consciousness in the physical world.
In the experiment, a single particle is sent through a double-slit apparatus, which can either be set up to measure the path of the particle or not. If the path is measured, the particle behaves like a particle and creates a pattern on the detector screen. If the path is not measured, the particle behaves like a wave and creates an interference pattern. The choice to measure or not is made after the particle has already passed through the apparatus.
The experiment suggests that the behavior of particles at the quantum level is influenced by the act of observation or measurement. This challenges our understanding of causality and raises questions about the true nature of reality. It also has implications for the development of quantum technologies such as quantum computers.
Yes, the experiment has been performed in various forms in real laboratories. In 1984, a team of physicists led by Alain Aspect conducted an experiment using polarized photons and confirmed the predictions of quantum mechanics. More recently, in 2015, a team at the Australian National University successfully performed the experiment using helium atoms. However, the implications of the experiment are still a topic of debate and further research is needed to fully understand its implications.