Travelling back in time

[Ags]

Richard Feynman once theorized that positrons are simply electrons travelling backward in time, because they are simply electrons with all properties reversed.

Balls of wool spontaneously form knots, while shoelaces spontaneously come undone... So are shoelaces simply balls of wool travelling back in time? 

[Tiki]

49 minutes ago, Ags said:

 

Balls of wool spontaneously form knots, while shoelaces spontaneously come undone... So are shoelaces simply balls of wool travelling back in time? 

 

Perhaps this is something for string theorists to ponder.....

 

Arghhh!

[ollypenrice]

Did he say that they were electrons travelling backwards through time or that they were indistinguishable from electrons travelling backwards through time? I've always thought this to be one of the eeriest discoveries in physics, along with the entangled photons and the double slit experiment. All strike me as pointing at the inadequacy of our present theory of time, such as we have one. (In the double slit experiment, do photons know what one after the other means?)

Olly

[SilverAstro]

1 hour ago, ollypenrice said:

 the inadequacy of our present theory of time, such as we have one. (In the double slit experiment, do photons know what one after the other means?)

I take comfort in the Probability Density Function - they can be anywhere at any time depending how hard you look for them, probably.

It's that cat I feel sorry for, aint noone going to let it out yet ?

And dont forget the garden extension cables that one rolls up all neat and tidy, only to become dreadfully entangled by next time of opening the box Cause & effect outada window.

And the Xmas Lights phenomenon, mind you, with Father Xmas hurtling about faster than C ( well he has to to get it all done ?) it is no wonder they get entangled and at least one ( if lucky, but which) is nolonger woikin

 

[Ravenous]

17 hours ago, Ags said:

Balls of wool spontaneously form knots, while shoelaces spontaneously come undone... So are shoelaces simply balls of wool travelling back in time? 

Impossible - because a ball of wool running backwards through time is one very confused sheep! 

[Tiki]

6 hours ago, ollypenrice said:

Did he say that they were electrons travelling backwards through time or that they were indistinguishable from electrons travelling backwards through time?

Apparently not. It was all JA Wheeler's idea.

The idea is based on the world lines traced out across spacetime by every electron. Rather than have myriad such lines, Wheeler suggested that they could all be parts of one single line like a huge tangled knot, traced out by the one electron. Any given moment in time is represented by a slice across spacetime, and would meet the knotted line a great many times. Each such meeting point represents a real electron at that moment.

At those points, half the lines will be directed forward in time and half will have looped round and be directed backwards. Wheeler suggested that these backwards sections appeared as the antiparticle to the electron, the positron.

Many more electrons have been observed than positrons, and electrons are thought to comfortably outnumber them. According to Feynman he raised this issue with Wheeler, who speculated that the missing positrons might be hidden within protons.[1]

Feynman was struck by Wheeler's insight that antiparticles could be represented by reversed world lines, and credits this to Wheeler, saying in his Nobel speech:

“ I did not take the idea that all the electrons were the same one from [Wheeler] as seriously as I took the observation that positrons could simply be represented as electrons going from the future to the past in a back section of their world lines. That, I stole![1] ”

Feynman later proposed this interpretation of the positron as an electron moving backward in time in his 1949 paper "The Theory of Positrons".[2] Yoichiro Nambu later applied it to all production and annihilation of particle-antiparticle pairs, stating that "the eventual creation and annihilation of pairs that may occur now and then is no creation or annihilation, but only a change of direction of moving particles, from past to future, or from future to past.

 

Cut and pasted from here: https://en.wikipedia.org/wiki/One-electron_universe

[ollypenrice]

Thanks Tiki, that's a great post.

Olly

[Stub Mandrel]

7 hours ago, ollypenrice said:

Did he say that they were electrons travelling backwards through time or that they were indistinguishable from electrons travelling backwards through time? I've always thought this to be one of the eeriest discoveries in physics, along with the entangled photons and the double slit experiment. All strike me as pointing at the inadequacy of our present theory of time, such as we have one. (In the double slit experiment, do photons know what one after the other means?)

Olly

Close to what bugs me.

How do electrons interfere with each other when they go through one of a pair of slits one at a time?

I understand why but my brain struggles with the how.

[SilverAstro]

34 minutes ago, Tiki said:

Apparently not. It was all JA Wheeler's idea.

Cut and pasted from here: https://en.wikipedia.org/wiki/One-electron_universe

Curiouser and curiouser because this one

https://en.wikipedia.org/wiki/Positron#Theory

says " Feynman, and earlier Stueckelberg, proposed an interpretation of the positron as an electron moving backward in time,[7] reinterpreting the negative-energy solutions of the Dirac equation. Electrons moving backward in time would have a positive electric charge. Wheeler invoked this concept to explain the identical properties shared by all electrons, suggesting that "they are all the same electron" with a complex, self-intersecting worldline. "

Both sources describe Wheeler referring to "all electrons" which is curious and ill defined ? What other elecrons was he thinking about, did he mean the muon and tau (also leptons)   Nope ! Tau not discovered till '75 ! but the muon was known before.

What a tangled web, now who is this Stueckelberg guy ?!

I gave up back in the days of Abdus Salam and  Steven Weinberg chasing the Eightfold Way, later becoming SU(3), I decided I had a better chance of earning a crust in electronics&telecoms

[SilverAstro]

Well that put the mockers on my theory that shoelaces, given enough time, always became strings of licorice on the grounds that they had mass and thus could oscillate between the two states.

mahtmacoat

 

[Tiki]

From the horses mouth: JA Wheeler in his nineties . Video no.59 is the one about the positron.

 

[SilverAstro]

Mandy Rice Davies (there are other arrangements of the letters)

shame Feynman isnt still with us. I'm not taking sides, just quoting another source ! out of curiosity to see where it leads

There is no doubt that they were bouncing ideas off each other, classic case of who had the killer idea and who the best publicist ? Many such end up indeterminate !

I haven't had time to look up this Stueckelberg fella yet either, this housework does get in the way a bit

[SilverAstro]

1 hour ago, Stub Mandrel said:

 one of a pair of slits one at a time?

I dont think we know that do we? We can single them down to one being emitted and one arriving at the detector, but not which slit 'it' went through, because it doesnt just go through one of them

I didnt mention PDFs lightly earlier ! they have a lot to do with it

[George Jones]

From a modern text on quantum field theory, "Quantum Field Theory in a Nutshell", by Anthony Zee:

Quote

In closing this chapter let me ask you some rhetorical questions. Did I speak of an electron going backward in time? Did I mumble something about a sea of negative energy electrons? This metaphorical language, when used by brilliant minds, the likes of Dirac and Feynman, was evocative and inspirational, but unfortunately confused generations of physics students and physicists. The presentation given here is in the modern spirit, which seeks to avoid these potentially confusing metaphors.

 

[ollypenrice]

On 2/23/2018 at 18:33, George Jones said:

From a modern text on quantum field theory, "Quantum Field Theory in a Nutshell", by Anthony Zee:

 

It would be interesting for those non-physicists amongst us to hear a fuller critique of these metaphors. In many cases they are all we have but handling them with due care is important, of course.

Olly