Reverse causality in QM and the philosophical implications
Posted: 12 June 2011 02:18 AM   [ Ignore ]
Sr. Member
RankRankRankRankRankRankRankRankRankRank
Total Posts:  1905
Joined  2007-10-28

From this article in Discover

A series of quantum experiments shows that measurements performed in the future can influence the present. Does that mean the universe has a destiny—and the laws of physics pull us inexorably toward our prewritten fate?

Reverse causality:

Tollaksen’s idea certainly meets that criterion. And yet, as crazy as it sounds, this notion of reverse causality is gaining ground. A succession of quantum experiments confirm its predictions—showing, bafflingly, that measurements performed in the future can influence results that happened before those measurements were ever made.

Using weak measurement:

Searching for backward causality required looking at the impact of the final measurement and adding the time twist. In the Rochester experiment, after the laser beams left the mirrors, they passed through one of two gates, where they could be measured again—or not. If the experimenters chose not to carry out that final measurement, then the deflected angles measured in the intermediate phase were boringly tiny. But if they performed the final, postselection step, the results were dramatically different. When the physicists chose to record the laser light emerging from one of the gates, then the light traversing that route, alone, ended up with deflection angles amplified by a factor of more than 100 in the intermediate measurement step. Somehow the later decision appeared to affect the outcome of the weak, intermediate measurements, even though they were made at an earlier time.

And the philosophical implication for temporal flow and human free will?

“It is upsetting philosophically,” he concedes. “All these experiments change the way that I relate to time, the way I experience myself.” The results have led him to wrestle with the idea that the future is set. If the universe has a destiny that is already written, do we really have a free choice in our actions? Or are all our choices predetermined to fit the universe’s script, giving us only the illusion of free will?

In other words, what we will choose determines what we are now…........the future influence the present and the past somehow, not vice versa.  cheese

 Signature 

I am, therefore I think.

Profile
 
 
Posted: 12 June 2011 05:07 AM   [ Ignore ]   [ # 1 ]
Sr. Member
Avatar
RankRankRankRankRankRankRankRankRankRank
Total Posts:  6054
Joined  2009-02-26

Wow..!
That boggles the mind.

 Signature 

Art is the creation of that which evokes an emotional response, leading to thoughts of the noblest kind.
W4U

Profile
 
 
Posted: 12 June 2011 05:48 AM   [ Ignore ]   [ # 2 ]
Sr. Member
Avatar
RankRankRankRankRankRankRankRankRankRank
Total Posts:  4812
Joined  2007-10-05

Don’t be so quick to assume this means the future influences the past.

Andrew Jordan, who designed the Rochester laser amplification experiment with Howell, notes that there is even fundamental controversy over whether his results support Aharonov’s version of backward causality. No one disputes his team’s straightforward experimental results, but “there is much philosophical thought about what weak values really mean, what they physically correspond to—if they even really physically correspond to anything at all,” Jordan says. “My view is that we don’t have to interpret them as a consequence of the future’s influencing the present, but rather they show us that there is a lot about quantum mechanics that we still have to understand.”

 Signature 

“In the beginning, God created the universe. This has made many people very angry and has been widely regarded as a bad move.”
Douglas Adams, The Restaurant at the End of the Universe

Profile
 
 
Posted: 12 June 2011 06:55 AM   [ Ignore ]   [ # 3 ]
Administrator
Avatar
RankRankRankRankRankRankRankRankRankRank
Total Posts:  15370
Joined  2006-02-14

Rule #1 in science: the most extravagant interpretation of the data is the least likely.

 Signature 

Doug

-:- -:—:- -:—:- -:—:- -:—:- -:—:-

El sueño de la razón produce monstruos

Profile
 
 
Posted: 12 June 2011 12:55 PM   [ Ignore ]   [ # 4 ]
Sr. Member
Avatar
RankRankRankRankRankRankRankRankRankRank
Total Posts:  6054
Joined  2009-02-26
DarronS - 12 June 2011 05:48 AM

Don’t be so quick to assume this means the future influences the past.

Andrew Jordan, who designed the Rochester laser amplification experiment with Howell, notes that there is even fundamental controversy over whether his results support Aharonov’s version of backward causality. No one disputes his team’s straightforward experimental results, but “there is much philosophical thought about what weak values really mean, what they physically correspond to—if they even really physically correspond to anything at all,” Jordan says. “My view is that we don’t have to interpret them as a consequence of the future’s influencing the present, but rather they show us that there is a lot about quantum mechanics that we still have to understand.”

A couple of musings,

Seems that the “gate” experiment has similarities with the double slit experiment, where the experiment exposes the dual nature of the particle/wave function, except that we are not dealing with single photons, but with a concentrated beam of trillions of photons.

I had a visual of a lake behind a dam. As long as the dam is closed the lake is calm and static (perhaps a few little waves on the surface). If now we open the dam the water will try to rush through, but as it can not all pass at once, a turbulence is generated “in front” of the dam as well as “behind” the dam. But that does not show a backward causality from behind the dam (the future) to the front of the dam (the present). It is the dam (gate) which governs the state (turbulence) of the lake, both in front and behind.
The act of opening the dam is a forward causality (both ways).

 Signature 

Art is the creation of that which evokes an emotional response, leading to thoughts of the noblest kind.
W4U

Profile
 
 
Posted: 13 June 2011 02:52 PM   [ Ignore ]   [ # 5 ]
Sr. Member
Avatar
RankRankRankRankRankRankRankRankRankRank
Total Posts:  4812
Joined  2007-10-05

Excellent analogy W4U. I hope someone with the proper math and physics background will think of it and explain this QM effect along similar lines.

 Signature 

“In the beginning, God created the universe. This has made many people very angry and has been widely regarded as a bad move.”
Douglas Adams, The Restaurant at the End of the Universe

Profile
 
 
Posted: 13 June 2011 11:12 PM   [ Ignore ]   [ # 6 ]
Sr. Member
Avatar
RankRankRankRankRankRankRankRankRankRank
Total Posts:  6054
Joined  2009-02-26

Thank you Darron….... smile

 Signature 

Art is the creation of that which evokes an emotional response, leading to thoughts of the noblest kind.
W4U

Profile