Time can run backwards at quantum levels?

Introversion · Jun 9, 2015

I believe this phenomenon is also called "quantum post selection"? A team's devised a way to experimentally demonstrate it.

http://secondnexus.com/technology-a...-backward-and-the-future-can-affect-the-past/

What they found is weirder than anything seen to date: Every time the two grates were in place, the helium atom passed through, on many paths in many forms, just like a wave. But whenever the second grate was not present, the atom invariably passed through the first grate like a particle. The fascinating part was, the second grate’s very existence in the path was random. And what’s more, it hadn’t happened yet.

In other words, it was as if the helium particle “knew” whether there would be a second grate at the time it passed through the first. The possible future presence of that second grate appeared to be determining the past state of the atom as it passed through grate #1. Whether it continued as a particle or changed into a wave depended on something that might happen in the future.

But how could a future event–the insertion of the second grate–determine the past state of the helium atom? Time would have to run backward, or something would have to know in advance that the second grate was going to be in place.

(The linked-to site appears to be struggling under load (George Takei linked to them on FaceBook) so don't be surprised if you get 503 errors or the like.)

jjdebenedictis · Jun 13, 2015

A couple of days late, but that's really interesting!

Dennis E. Taylor · Jun 14, 2015

jjdebenedictis said:
A couple of days late, but that's really interesting!

Or are you a couple of days early? .... :roll:

shakeysix · Jun 14, 2015

I wish I were schooled in this stuff. --s6

jjdebenedictis · Jun 14, 2015

I was having trouble understanding their explanation of Wheeler's "delayed choice" thought experiment, so I did a bit more reading.

The point here seems to be that this only implies a paradox if you believe that a quantum particle is either a particle or a wave, not both at the same time.

It's a bit of a pet peeve of mine that people tend to play up the spooky aspects of the double-slit experiment (and by extension, this experiment) just to capture the imagination of the public. "Observation" always means you hit the quantum particle with another quantum particle; it's not a benign thing. Of course you change the thing you're measuring when you smack it with another thing that's comparable in size.

It seems to me that all this experiment has done is confirmed that a quantum particle does NOT choose to be a particle sometimes and a wave at other times. It is always a wave-particle duality, even when you temporarily make it behave more like one than the other. Thus, you always get results in keeping with it intrinsically being a duality, not temporarily a particle, then a wave.

Dennis E. Taylor · Jun 14, 2015

Another problem is the word "Observation." It's an unfortunate bit of anthropomorphism that implies some intelligence or consciousness has to be there in order for the quantum state to collapse. In fact, all you need is for the result to affect something else (conscious, living, or not) and that's your "observer". Of course, then the whole package including the observer is in an indeterminate state in relation to the wider world. Add an observer to collapse that state...

Introversion · Jun 14, 2015

A pox on you, fickle reality, for raising my hopes for backwards time! :rant:

King Neptune · Jun 15, 2015

jjdebenedictis said:
I was having trouble understanding their explanation of Wheeler's "delayed choice" thought experiment, so I did a bit more reading.

The point here seems to be that this only implies a paradox if you believe that a quantum particle is either a particle or a wave, not both at the same time.

It's a bit of a pet peeve of mine that people tend to play up the spooky aspects of the double-slit experiment (and by extension, this experiment) just to capture the imagination of the public. "Observation" always means you hit the quantum particle with another quantum particle; it's not a benign thing. Of course you change the thing you're measuring when you smack it with another thing that's comparable in size.

It seems to me that all this experiment has done is confirmed that a quantum particle does NOT choose to be a particle sometimes and a wave at other times. It is always a wave-particle duality, even when you temporarily make it behave more like one than the other. Thus, you always get results in keeping with it intrinsically being a duality, not temporarily a particle, then a wave.

I agree, and there are further implications.

Maxx · Jun 25, 2015

jjdebenedictis said:
I was having trouble understanding their explanation of Wheeler's "delayed choice" thought experiment, so I did a bit more reading.

I didn't read up on any of this, BUT I've always been intrigued by Wheeler's strange proto-S-matrix thinking in 1937 when he suggested that a positron was just an electron going backwards in time. While not true, it did lead to some of Feynman's insights and diagrams and ultimately those have proved very useful (though for field theory -- which was not really what Feynman wanted, I guess).

Time can run backwards at quantum levels?

Introversion

Pie aren't squared, pie are round!

jjdebenedictis

is watching you via her avatar

Dennis E. Taylor

Get it off! It burns!

shakeysix

blue eyed floozy

jjdebenedictis

is watching you via her avatar

Dennis E. Taylor

Get it off! It burns!

Introversion

Pie aren't squared, pie are round!

King Neptune

Maxx

Got the hang of it, here