Lee Corbin
2014-01-05 23:00:59 UTC
Here is an article about Aharonov's team, the group of physicists that are working on the Two-State Vector Formalism interpretation of QM (aka Time Symmetric Quantum Mechanics), the idea that a particle now is affected both by its past (obviously) and by its future.
http://discovermagazine.com/2010/apr/01-back-from-the-future#.UsewgvRUd8E
If youâve not seen the article, it talks about an experiment that the physicists did to test out their theoryâmore about âweak measurementsâ, supposed measurements that don't fully âcollapse the wave functionâ (snicker suppressed).
Here are the *salient* parts from the article, which, typically enough, begins with a long unnecessary blast of hot air that, thanks to me, you donât have to wade through.
"First the physicists would measure spin in a set of particles at 2 p.m. and again at 2:30 p.m. Then on another day they would repeat the two tests, but also measure a subset of the particles a third time, at 3 p.m. If the predictions of backward causality were correct, then for this last subset, the spin measurement conducted at 2:30 p.m. (the intermediate time) would be dramatically amplified. In other words, the spin measurements carried out at 2 p.m. and those carried out at 3 p.m. together would appear to cause an unexpected increase in the intensity of spins measured in between, at 2:30 p.m."
"The idea was that ripples of the measurements carried out in the future could beat back to the present and combine with effects from the past, like waves combining and peaking below a boat, setting it rocking on the rough sea. The smaller the subsample chosen for the last measurement, the more dramatic the effects at intermediate times should be, according to Aharonovâs math. It would be hard to account for such huge amplifications in conventional physics."
There is an obvious question, of course:
"Does this mean that when the intermediate step is carried out, the future is set and the experimenter has no choice but to perform the later, postselection measurement? It seems not. Even in instances where the final step is abandoned, Tollaksen has found, the intermediate weak measurement remains amplified, though now with no future cause to explain its magnitude at all."
"I put it to Tollaksen straight: This finding seems to make a mockery of everything we have discussed so far."
"Tollaksen is smiling; this is clearly an argument he has been through many times. The result of that single experiment may be the same, he explains, but remember, the power of weak measurements lies in their repetition. No single measurement can ever be taken alone to convey any meaning about the state of reality. Their inherent error is too large. 'Your pointer will still read an amplified result, but now you cannot interpret it as having been caused by anything other than noise or a blip in the apparatus,' he says."
"In other words, you can see the effects of the future on the past only after carrying out millions of repeat experiments and tallying up the results to produce a meaningful pattern. Focus on any single one of them and try to cheat it, and you are left with a very strange-looking resultâan amplification with no causeâbut its meaning vanishes. You simply have to put it down to a random error in your apparatus. You win back your free will in the sense that if you actually attempt to defy the future, you will find that it can never force you to carry out postselection experiments against your wishes. The math, Tollaksen says, backs him on this interpretation: The error range in single intermediate weak measurements that are not followed up by the required postÂselection will always be just enough to dismiss the bizarre result as a mistake."
"Here, finally, is the answer to Aharonovâs opening question: What does God gain by playing dice with the universe? Why must the quantum world always retain a degree of fuzziness when we try to look at it through the time slice of the present? That loophole is needed so that the future can exert an overall pull on the present, without ever being caught in the act of doing it in any particular instance."
"'The future can only affect the present if there is room to write its influence off as a mistake,' Aharonov says."
***
So the bottom line is that over many runs, the statistical result on the 2:30 pm measurement changes slightly if the 3:00 pm measurement is done. But the change on any particular particle, or even all of them, is so small that it could be written off as random noise.
This too suggests that thereâs hardly anything real here.
Anyone have any thoughts on this?
Thanks,
Lee
http://discovermagazine.com/2010/apr/01-back-from-the-future#.UsewgvRUd8E
If youâve not seen the article, it talks about an experiment that the physicists did to test out their theoryâmore about âweak measurementsâ, supposed measurements that don't fully âcollapse the wave functionâ (snicker suppressed).
Here are the *salient* parts from the article, which, typically enough, begins with a long unnecessary blast of hot air that, thanks to me, you donât have to wade through.
"First the physicists would measure spin in a set of particles at 2 p.m. and again at 2:30 p.m. Then on another day they would repeat the two tests, but also measure a subset of the particles a third time, at 3 p.m. If the predictions of backward causality were correct, then for this last subset, the spin measurement conducted at 2:30 p.m. (the intermediate time) would be dramatically amplified. In other words, the spin measurements carried out at 2 p.m. and those carried out at 3 p.m. together would appear to cause an unexpected increase in the intensity of spins measured in between, at 2:30 p.m."
"The idea was that ripples of the measurements carried out in the future could beat back to the present and combine with effects from the past, like waves combining and peaking below a boat, setting it rocking on the rough sea. The smaller the subsample chosen for the last measurement, the more dramatic the effects at intermediate times should be, according to Aharonovâs math. It would be hard to account for such huge amplifications in conventional physics."
There is an obvious question, of course:
"Does this mean that when the intermediate step is carried out, the future is set and the experimenter has no choice but to perform the later, postselection measurement? It seems not. Even in instances where the final step is abandoned, Tollaksen has found, the intermediate weak measurement remains amplified, though now with no future cause to explain its magnitude at all."
"I put it to Tollaksen straight: This finding seems to make a mockery of everything we have discussed so far."
"Tollaksen is smiling; this is clearly an argument he has been through many times. The result of that single experiment may be the same, he explains, but remember, the power of weak measurements lies in their repetition. No single measurement can ever be taken alone to convey any meaning about the state of reality. Their inherent error is too large. 'Your pointer will still read an amplified result, but now you cannot interpret it as having been caused by anything other than noise or a blip in the apparatus,' he says."
"In other words, you can see the effects of the future on the past only after carrying out millions of repeat experiments and tallying up the results to produce a meaningful pattern. Focus on any single one of them and try to cheat it, and you are left with a very strange-looking resultâan amplification with no causeâbut its meaning vanishes. You simply have to put it down to a random error in your apparatus. You win back your free will in the sense that if you actually attempt to defy the future, you will find that it can never force you to carry out postselection experiments against your wishes. The math, Tollaksen says, backs him on this interpretation: The error range in single intermediate weak measurements that are not followed up by the required postÂselection will always be just enough to dismiss the bizarre result as a mistake."
"Here, finally, is the answer to Aharonovâs opening question: What does God gain by playing dice with the universe? Why must the quantum world always retain a degree of fuzziness when we try to look at it through the time slice of the present? That loophole is needed so that the future can exert an overall pull on the present, without ever being caught in the act of doing it in any particular instance."
"'The future can only affect the present if there is room to write its influence off as a mistake,' Aharonov says."
***
So the bottom line is that over many runs, the statistical result on the 2:30 pm measurement changes slightly if the 3:00 pm measurement is done. But the change on any particular particle, or even all of them, is so small that it could be written off as random noise.
This too suggests that thereâs hardly anything real here.
Anyone have any thoughts on this?
Thanks,
Lee