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The article has multiple copies of most of the material (2 cosmic, 3 or 4 interferometer). The first set has too much detail and the second set repeats it. These sections have almost no refs. It has no History section, no discussion of the relationship to Bohr/Einstein. Not enough of Wheeler's analysis is presented and not enough of the recent implementations.
The current article does start with the Cosmic version which I think is a good plan. I think it is easier to explain and, being more extreme, does not rely on readers having to accept as many claims about experimental technology.
The current article mostly describes the experiments as Wheeler proposed them. I plan to move that material to the History. Then the new Experimental section can discuss the modern experimental results.
Wheeler's versions are famous but there are others especially in the modern era. I think it would be better to highlight Wheeler's role in the History and iconic examples but use a more generic title. Johnjbarton (talk) 00:35, 26 October 2024 (UTC)[reply]
The material that claims that Wheeler himself made the "cosmic" version of the thought experiment is incorrect. I am currently trying to track down the source of this experiment. Actually, it should be called a thought experiment. I just went over Wheeler's "The 'Past' and the 'delayed-Choice' Double-Slit Experiment" that appeared in Mathematical Foundations of Quantumn Theory edited by A.R. Marlow. There is not even a suggestion of such an experiment in what Wheeler wrote there.
The earliest I've been able to trace it so far is The Quantum Challenge by Greenstein and Zajonc. However.at least in the second edition, it is offered in a "tempting to think that...." manner with a promise to clarify things in a later chapter, but the later chapter is intensely technical and appears to make no mention of this specific thought experiment.
good. I got the original diagram and have tidied it up and made it lots easier to understand. I will try to remember how to upload a copy to Wikipedia. I used to do that a lot, and then I got sick of edit wars, article "possession," and ego madness. P0M (talk) 05:53, 9 April 2025 (UTC)[reply]
John Archibald Wheeler thought it possible that a quantum experiment in the present could change what happened millions of years agoP0M (talk) 11:40, 9 April 2025 (UTC)[reply]
The link you provided was very helpful. It must have been prepared using good OCR or perhaps it was copied out manually.
Reading the text beneath the 3-panel illustration in the book, it seems pretty clear to me that tghe left panel is wrong. The triangular image should have been copied, mirrored horizontally and pasted in to make something looking like a kite. P0M (talk) 16:59, 21 April 2025 (UTC)[reply]
I'm not completely sure what your concern is. Wheeler's caption makes it clear that the galaxy was intended to be "intervening" as he drew it. (The caption about what Wheeler thought is not correct. Wheeler's entire point is that we cannot make claims about the path of the particle because the experiment cannot affect events billions of years ago). Johnjbarton (talk) 17:13, 21 April 2025 (UTC)[reply]
Is there some way I could get access to the illustration you have put into the article?
Everybody else seems to think that he meant that what we do in the lab today will effect events billions of years ago. I think that the conclusion that there is some kind of retro-causality going on is wrong. If what you say is true, then I have been right for the wrong reasons. Just to check, is the following discussion correctly copied and is it in agreement with what you have stated?
From I.13 LAW WITHOUT LAW by Wheeler p. 193
Proposed delayed-choice experiment extending over a cosmological reach of space and time. Left, quasar Q recorded at receptor as two quasars by reason of the gravitational lens action of the intervening galaxy G1. Middle, schematic design of receptor for delayed choice experiment: (a) filter to pass only wavelengths in a narrow interval corresponding to a long wave train suitable for interference experiments. (b) Lens to focus the two apparent sources onto the acceptor faces of two optic fibers. (c) delay loop in one of these fibers of such length, and of such rate of change of length with time, as to bring together the waves traveling the two very different routes with the same, or close to the same, phase. Right, the choice. Upper diagram, nothing is interposed in the path of the two waves at the crossing of the optic fibers. Wave 4a goes into counter I and 4b into counter II. Whichever of these photodetectors goes off, that— in a bad way of speaking— signals “by which route, a or b, the photon in question traveled from the quasar to the receptor.” Lower diagram, a half-silvered mirror ,½S, is interposed as indicated at the crossing of the two fibers. Let the decay loop be so adjusted that the two arriving waves have the same phase. Then there is never a count in I. All photons are recorded in II. This result, again in a misleading phraseology, says that "the photons in question came by both routes". However, at the time the choice was made whether to put in ½S, or leave it out, the photon in question had already been on its way for billions of years. It is not right to attribute to it a route. No elementary phenomenon is a phenomenon until it is a registered phenomenon.
There is no retrocausality in Wheeler's interpretation. The route of a "photon" cannot cause a result in the detector because the photon has no route, nor is there a "photon" on a route. The photon enroute from a quasar only exists in one's imagination, it has no physical reality. This is exactly what Wheeler was demonstrating with the article concept. We only learn about particle routes when we measure them; at that time we can either determine its route or verify that it could have taken two different routes, but not both.
This concept is extremely difficult for people and sometimes they make up stuff like retrocausal particle actions to make sense of it.
Wheeler was one of the great 20th century physics thinkers. He worked on many different problems. At one point he worked with Richard Feynman on Wheeler–Feynman absorber theory which uses time-symmetry and which some interpreters view as a retrocausal theory. Maybe that is where folks are getting mixed up, IDK.
? Sure. You posted a copy of one of Wheeler's figures above, marked up with red blue and yellow colors. The left column is what I redrew. Johnjbarton (talk) 15:13, 23 April 2025 (UTC)[reply]
Why did you move the galaxy? In the original, there is just a "G" inside the two path lines you've drawn, no? For light to go through a galaxy, as your drawing would have it, and then be diverted toward earth would seem to be a rare event. Such a trip should cause an entering beam of light to diffuse as far as I can see. P0M (talk) 17:33, 23 April 2025 (UTC)[reply]
I redrew Wheeler panel; I did not "move the galaxy". Your conjectures about gravitational lensing puzzling. Rare? Indeed. Diffuse? Of course. Beam of light? Not at all. We are talking about trillions upon trillions of photons moving through gravitational fields. The only aspect relevant to the article is the possibility that two paths exist from the quasar to the telescope. Whether one draws it symmetrically or asymmetrically does not matter for the article. Johnjbarton (talk) 18:00, 23 April 2025 (UTC)[reply]
Wheeler's double-slit apparatus.
I thought that illustration looked familiar. I made it. I think it is correct, but it has no evidentiary status on its own. P0M (talk) 05:08, 23 April 2025 (UTC)[reply]
Replace beam splitter by registering projected telescope images on a common detection screen.
Also my work.
Where is the original for
Wheeler's cosmic interferometer uses a distant quasar with two paths to equipment on Earth, one direct and one by gravitational lensing? I won't believe it if I can't see it. P0M (talk) 05:14, 23 April 2025 (UTC)[reply]
I think this article has changed since I got interested in the problem after being told by a well-known physicist that what we do today can rewrite millions of years of history.
Why did this line of inquiry even get started? It seems incredible to me that anybody would make the claim. The article now says, "The result is two images of the star, one direct and one bent. Wheeler proposed to measure the interference between these two paths." To me, that sounds like looking at two images one from one streetlight and one from a streetlight across the road, imaging them on pieces of paper, and then directing the two images onto nearly the same point on another piece of paper and expecting to get interference. P0M (talk) 04:26, 23 April 2025 (UTC)[reply]
I have downloaded "Delayed-choice gedanken experiments and their realizations." I find nothing there to justify your assertions. P0M (talk) 05:06, 23 April 2025 (UTC)[reply]
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Done Johnjbarton (talk) 00:51, 26 October 2024 (UTC)
