約翰·惠勒（1911年7月9日——2008年4月13日），美國物理開拓時期的科學家，普林斯頓大學教授，從事原子核結構、粒子理論、廣義相對論及宇宙學等研究。他27歲就與丹麥的波耳發展出核分裂理論；後與學生理查·費曼（1965年諾貝爾物理獎得主）改寫電磁理論，並提出時光回溯移動的構想。惠勒的研究為20世紀下半葉物理學的發展勾勒出了方向。
唯一一個表述「意識決定物質」的物理學實驗：惠勒延遲實驗
在人間：本文將用當代最前沿物理學實驗，證明：我們當下的所思所想、所作所為，足以影響已經發生的事情。（對於常人，只要這件事情還沒有被你自己發現記憶）（接下來，如何去影響呢？這便是宇宙的核心秘密---唯心所現、唯識所變。）當代美國物理學家惠勒的延遲選擇實驗，不斷地被一次次實驗所證明。它帶來的結論是一切自然科學革命式的顛覆。至少，孩子們從小學到大學的物理課上，最後一章可以不停留在「相對論、量子力學」啦，就連霍金的時間簡史，也將成為物理學的記憶了~~~o(∩_∩)o...不過令人奇怪和遺憾的是，這個30年前的實驗，中國物理學家們似乎視而不見喔~~~ 還有那可憐的唯物主義，大哲學家、大思想家們，恐怕又要重新認識世界啦~~~ 真的想看看這些大物理學家，如果能夠認真研讀一下佛經，結果會是如何。只可惜他們邊地受生，與佛無緣，也是我們世界共同的業力啊~~~ 約翰·阿奇博爾德·惠勒（John Archibald Wheeler，1911年7月9日—2008年4月13日）美國著名的物理學家、物理學思想家和物理學教育家。1911年7月9日出生在美國的佛羅裡達州，惠勒生前是美國自然科學院院士和文理科學院院士，曾任美國物理學會主席。
關於時間，愛因斯坦創立相對論時也有一個著名的結論，「過去、現在、將來的區別，只是一種幻覺，不管人們怎麼堅持這種區別也沒有用」。不過，相對論強調的是我們對時間的幻覺，而量子力學的結論更加普遍，那就是一切實相都是幻覺。惠勒最有代表性的思想是1979年在紀念愛因斯坦100周年誕辰學術研討會上提出的延遲選擇實驗，據此，他給出了一個顛覆我們通常時間次序的結論：「我們此時此刻作出的決定，對於我們有足夠理由說，它對已經發生了的事件產生了不可逃避的影響。」此時的決定，影響了，甚至決定了光子的過去。最絕的是，這個思想實驗不但具有可操作性，而且可以在宇宙尺度上操作。藉此，惠勒反覆強調：「沒有一個基本量子現象是一個現象，直到它是一個被記錄（觀察）的現象」；「並沒有一個過去預先存在著，除非它被現在所記錄」。於是，惠勒把哥本哈根學派的整體論從空間拓展到了時間。
英文不好的童鞋可以跳過英文原文，
看後面的中文~
Wheeler's delayed choice experiment
Wheeler's delayed choice experiment is a thought experiment proposed by John Archibald Wheeler in 1978[1], and later confirmed. Wheeler proposed a variation of the famous double-slit experiment of quantum physics, one in which the method of detection can be changed after the photon passes the double slit, so as to delay the choice of whether to detect the path of the particle, or detect its interference with itself. Since the measurement itself seems to determine how the particle passes through the double slits, and thus its state as a wave or particle, Wheeler's thought experiment has been useful in trying to understand certain strange properties of quantum particles. An implementation of the experiment in 2007 showed that the act of observation ultimately decides whether the photon will behave as a particle or wave, verifying the unintuitive results of the thought experiment.
Introduction
Wheeler's experiment consisted of a standard double-slit experiment, except that the detector screen could be removed at the last moment, thereby directing light into two more remote telescopes, each one focused on one of the slits. This allowed a "delayed choice" of the observer, i.e. a choice made after the presumed photon would have cleared the midstream barrier containing two parallel slits. The two telescopes, behind the (removed) screen could presumably "see" a flash of light from one of the slits, and would detect by which path the photon traveled.
According to the results of the double slit experiment, if experimenters do something to learn which slit the photon goes through, they change the outcome of the experiment and the behavior of the photon. If the experimenters know which slit it goes through, the photon will behave as a particle. If they do not know which slit it goes through, the photon will behave as if it were a wave when it is given an opportunity to interfere with itself. The double-slit experiment is meant to observe phenomena that indicate whether light has a particle nature or a wave nature. The fundamental lesson of Wheeler's delayed choice experiment is that the result depends on whether the experiment is set up to detect waves or particles.
Implications of the experiment
The conventional double-slit experiment shows that determining which path a particle takes prevents the interference pattern from forming. To avoid the notion that the photon somehow "knows" when the "other" slit is open or closed (or is being watched), Wheeler suggested 'detecting' which slit the photon used only long after it passed through the slits. Wheeler asked what happens when a single photon, presumably already determined to get detected as part of a two-slit interference pattern, suddenly gets detected in a path coming from only one slit. Does the interference pattern then disappear ?
In terms of the traditional double-slit apparatus, the Wheeler delayed choice experiment is to put telescopes that are pointed directly at each of the two slits behind the removable detector wall. If the photon goes through telescope A it is argued that it must have come by way of slit A, and if it goes through telescope B it is argued that it must have come by way of slit B.
Wheeler planned a thought experiment in which two ways of observing an incoming photon could be used, and the decision of which one to use could be made after the photon had cleared the double-slit part of the apparatus. At that point a detection screen could either be raised or lowered. If the detection screen were to be put in place, Wheeler fully expected that the photon would interfere with itself and (if many more photons were permitted to follow it to the screen) would form part of a series of fringes due to interference. If, on the other hand, the detection screen were to be removed, then:
Sufficiently far beyond the region of the plate, the beams from upper and lower slits cease to overlap and become well separated. There place photodetectors. Let each have an opening such that it records with essentially 100 percent probability a quantum of energy arriving in its own beam, and with essentially zero probability a quantum arriving in the other beam.
In that case, he argues, "one of the two counters will go off and signal in which beam — and therefore from which slit — the photon has arrived."
Wheeler's astronomical experiment
In a response to the argument that at short distances interactions at the screen with slits in it might be compromised by "knowledge" of events that occur at the location of the detector screen, Wheeler is reported to have come up with a more elaborate thought experiment.[5] Wheeler suggests that one may imagine a more extraordinary scenario wherein the scale of the experiment is magnified to astronomical dimensions: a photon has originated from a star or even a distant galaxy, and its path is bent by an intervening galaxy, black hole, or other massive object, so that it could arrive at a detector on earth by either of two different paths.
Einstein Cross, an example of gravitational lensing
（愛恩斯坦的十字架，重力透鏡的一個例子）
The thought experiment assumes that the emitter of the photon is so positioned that the two paths are equal. If experimenters observe the single photon with a detector screen, e.g., a photographic plate or other imaging device (as in the original experiment), they should see it as part of an interference pattern (to be filled out by additional incoming photons), but if they instead use two telescopes focused to either side of the black hole they may expect to observe the photon only in one of them.
Some interpretations of Wheeler's thought experiment are premised on the belief that interference will indeed occur between the two images, and the crux of the experiment lies in determining whether identifying photons as coming from one referred image or the other will make a difference in experimental outcomes. Experimenters are already gathering light from one referred image (one pathway) by means of one telescope, and they can add light that has come by the other pathway by means of the other telescope.
If experimenters keep the two telescope images separate physically, then they ought not to expect any kind of interference fringes or other "spooky" behavior. And it is known that some photons must have reached earth via each pathway.
On the other hand, if experimenters project the images from the two telescopes onto the same spot on a detection screen and they move the images with respect to each other to change their phase relationship so that they can get cancellation in some areas and reinforcement in another area, they will then get an interference pattern, and will have demonstrated that this experiment is another version of the double-slit experiment.
There appears to be a problem, however. It may be claimed that one knows which photons have come by path A and which photons have come by path B, and that one has that knowledge because the photons have been physically fenced in by the tubes out of which the telescopes are constructed. However, once experimenters merge the two images on the detection screen, one can no longer know that a photon that lights up a certain spot on the detection screen has come through telescope A or through telescope B. So they have abandoned that information by mixing the two streams.
There is one more possibility, as indicated in a diagram above. If interference is actually thwarted, then photons should be found only at the position of the two primary maxima. Suppose that experimenters project the images onto two separate detection screens. That should give them a situation analogous to the one where they were viewing a distant light source with only one slit open. In the physics laboratory there are some diffraction effects due to light's having been put through a narrow opening, but not the broad band that is known as the interference fringe.
If interference between the images brought in via two telescopes does appear, experimenters ought to see dimmer images at the secondary, tertiary, etc. maxima predicted for interference effects. They should not expect to see the same range and clarity of secondary images (if any at all) with one telescope capped off. What occurs in this case is again a matter for empirical study to determine.
The idea behind some interpretations of the Wheeler experiment is that it might be possible to determine which side of a double-slit experiment a photon traveled through without destroying the interference pattern that occurs when the two versions of its probability wave interact on the detector screen of the typical double-slit experiment. Another view is that whether interference fringes are noted or not depends not on anything that happened between the distant star and earth. Instead, it depends entirely on what form the observation or the measurement of the photon or photons takes. Looking for a photon on one path or the other will produce the observation of one photon at a single point by a telescope aimed in a certain direction. Looking for an interference pattern by merging the beams coming through both paths will produce interference fringes.
Most recent experiment
In 2007, the first "clean" experimental test of Wheeler's ideas was performed in France by the team of Alain Aspect, Philippe Grangier, Jean-François Roch et al.
Earlier experiments
In 2000, Yoon-Ho Kim, et al., reported success in their delayed choice quantum eraser experiment, a variation that combines Wheeler's delayed choice experiment with a quantum eraser experiment, so that the choice to observe the photon or not observe the photon is done after it hits the detector.
Another Quantum eraser experiment was done in 2002 by S. P. Walborn, M. O. Terra Cunha, S. Padua, and C. H. Monken.
Future experiments
Researchers with access to radio telescopes originally designed for SETI research have pointed to the possibility, and have explicated the practical difficulties, of conducting the Wheeler experiment with actual stellar objects.
Bibliography
Vincent Jacques et al., Experimental Realization of Wheeler's Delayed-Choice Gedanken Experiment, Science Vol. 315. no. 5814, pp. 966 - 968 (2007). Preprint available at http://arxiv.org/abs/quant-ph/0610241v1
John Archibald Wheeler, "The 'Past' and the 'Delayed-Choice Double-Slit Experiment'," pp 9–48, in A.R. Marlow, editor, Mathematical Foundations of Quantum Theory, Academic Press (1978)
John Archibald Wheeler and Wojciech Hubert Zurek , Quantum Theory and Measurement (Princeton Series in Physics)
John D. Barrow, Paul C. W. Davies, and Jr, Charles L. Harperm Science and Ultimate Reality: Quantum Theory, Cosmology, and Complexity (Cambridge University Press) 2004
References
1.^ Mathematical Foundations of Quantum Theory, edited by A.R. Marlow, Academic Press, 1978
2.^ a b Cho, Adrian. After a Short Delay, Quantum Mechanics Becomes Even Weirder. ScienceNOW Daily News. 16 February 2007
3.^ Castelvecchi, Davide. Tight Deadline. Photons: Decide what to do – and do it yesterday. Science News online. May 23, 2008
4.^ John Archibald Wheeler, "The 'Past' and the 'Delayed-Choice' Double-Slit Experiment", in Mathematical Foundations of Quantum Theory, edited by A.R. Marlow, p. 13
5.^ Source for this experiment in Wheeler's own writing has not been traced yet. Dr. John Cramer indicates that Wheeler offered the idea in response to criticism of a proposed experiment on a smaller scale. (Personal communication.)
6.^ Jacques, Vincent; et al. (2007). "Experimental Realization of Wheeler's Delayed-Choice Gedanken Experiment". Science 315: 966–968. arXiv:quant-ph/0610241v1. Bibcode 2007Sci...315..966J. doi:10.1126/science.1136303. PMID 17303748.
7.^ Quantum Astronomy (IV): Cosmic-Scale Double-Slit Experiment [edit] External linksWheeler's Classic Delayed Choice Experiment by Ross Rhodes The Quantum Eraser by John G. Cramer -- extremely clear elucidation of this experiment and related subjects Demystifying the Delayed Choice Experiments
附錄：現在改變過去——惠勒延遲選擇實驗
雷射脈衝源（laser pulse source）發出光子，到達半鍍銀的反射鏡BS1（作用是使光子有一半可能穿過了反射鏡BS1到達全反射鏡M1，一半可能被反射鏡BS1反射到達全反射鏡M2），兩個全反射鏡M1和M2把這兩部分的光子又交匯在一起。在終點觀察光子飛來的方向，我們就可以確定光子究竟是沿著哪一條路徑飛來的。
如果在終點處也插入一塊半鍍銀的反射鏡BS2，通過調整BS1-M1-BS2和BS1-M2-BS2兩個路徑的光子的相位，可以使這兩部分光子到達BS2時發生反相干涉，從而使光子在水平方向或者在豎直方向上「互相抵消」，最後只在豎直方向或者水平方向上輸出。然而，真正讓你感到不可思議的是，即使雷射脈衝源（laser pulse source）每次只發出一個光子，經過足夠長的時間，你還是可以看到同樣的幹涉結果，這說明一個光子每次到達BS2時和自己發生了幹涉——按照量子力學的官方說法就是一個光子同時通過BS1-M1-BS2和BS1-M2-BS2兩條路逕到達BS2後和自己發生幹涉（詳見著名的雙縫幹涉實驗，雷射脈衝源每次只發出一個光子，經過足夠長的時間，你同樣會看到幹涉條紋）。
楊氏雙縫幹涉實驗的雷射衍射產生的相涉效應
電磁波譜
楊氏雙縫幹涉實驗的雷射演示虛擬課件
但是，如果在終點處不放置半鍍銀的反射鏡BS2，雷射脈衝源（laser pulse source）每次只發出一個光子，則通過在終點觀察光子飛來的方向，我們每次卻只能看到光子從一個路徑飛來，或者沿水平方向，或者沿豎直方向。這說明，如果我們不在終點處放置半鍍銀的反射鏡BS2，光子就沿著某一條路徑而來，反之，它就同時經過兩條路徑而來。也就是說，我們的選擇決定了光子的「選擇」。
現在的問題是，如果在光子已經通過了第一塊半鍍銀的反射鏡BS1，快到達終點（還沒到達）的時候，我們才把半鍍銀的反射鏡BS2放入終點處，結果會怎麼樣呢？一般地，我們會認為光子通過了第一塊半鍍銀的反射鏡BS1後已經選擇了怎麼走，按前面的結果就是光子只沿著某一條路徑而來，應該不會再發生幹涉現象。可惜，結果再次讓你感到驚訝，光子還是選擇了同時經過兩條路徑而來。無論雷射脈衝源（laser pulse source）每次只發出一個光子還是多個光子，結果都是一樣的。這就是著名的惠勒延遲選擇實驗（Wheeler's delayed choice experiment）（詳見量子力學發展大事記）。實驗結果表明，我們現在的選擇（觀測行為）改變了光子過去的「選擇」。也就是說，我們可以在事情已經發生之後再來決定它應該怎麼發生——無論是否事情的結果在邏輯上已經在一段時間以前被決定！
實際上，「任何一種基本量子現象只在其被記錄（觀測）之後才是一種現象」，量子力學的創始人之一玻爾說，「而在觀察發生之前，沒有任何物理量是客觀實在的」。也就是說，觀察創造了全部的實相。現在，惠勒延遲選擇實驗在此基礎上更進一步的說明，觀察不但創造了實相，而且還可以在事情發生之後再逆時間地創造實相。關於客觀實在絕對性的世界觀的徹底失敗，詳見自然界違背貝爾不等式的阿斯派克特實驗（大家可以關注我的其他日誌）。
值得一提的是，關於時間，愛因斯坦創立相對論時也有一個著名的結論，「過去、現在、將來的區別，只是一種幻覺，不管人們怎麼堅持這種區別也沒有用」。不過，相對論強調的是我們對時間的幻覺，而量子力學的結論更加普遍，那就是一切實相都是幻覺。
惠勒延遲選擇實驗（英語：Wheeler's delayed choice experiment）是物理學家約翰·惠勒提出的一個思想實驗，它屬於雙縫實驗的一種變形，該實驗很好地體現了量子力學與傳統實在觀間的巨大分歧。惠勒是1979年在普林斯頓大學紀念愛因斯坦誕辰100周年討論會上正式提出延遲選擇實驗的，該實驗源自愛因斯坦曾提出的分光實驗（與雙縫實驗有同樣的物理意義）。實驗是按如下方式進行的：從一光源發出一光子，讓其通過一半鍍銀鏡，光子被反射與透射的概率各為50%。之後，在反射或透射後光子的行進路徑上分別各放置一反射鏡A和B，使兩條路徑反射後在C處匯合。而C處則放有兩探測器，分別可以觀察A路徑或B路徑是否有光子。此時只有一個探測器能夠測得光子，即能確定光子走的是哪一路徑（A→C或B→C）。而如果在兩個探測器前再放置一個半鍍銀鏡，可以使光子自我幹涉。如適當調整光程差，可使得在某一方向（A或B）上幹涉光相消，此方向上的探測器將無法收到信號，另一方向上的探測器則必定會接收到信號。按量子力學理論，這說明光子同時經過了兩條路徑。事實上，我們可以在光子已經通過A或B後再決定是否放置第二塊半鍍銀鏡（此即實驗名稱「延遲選擇」的由來）。如不放置，則根據前一種情況，光子只通過一條路徑；如放置，則根據後一種情況，光子通過兩條路徑。也就是說，觀察者現在的行為可以決定過去發生的事，而這一結論是與傳統實在觀相違背的。哥本哈根學派對此的解釋是，我們不能將觀察儀器與觀察對象分開來討論，儘管實驗中的兩種情況只有最後部分不同，但這局部的變化使得整個物理過程發生了改變，這兩種情況其實是兩個完全不同的實驗。玻爾對此就曾說：「事實上，在粒子路徑上再加任何一件儀器，例如一個鏡子，都可能意味著一些新的幹涉效應，它們將本質地影響關於最後記錄結果的預言。」
我國科學家首次實現量子惠勒延遲選擇實驗
9月份的《自然-光子學》封面文章發表了中國科學家首次實現量子惠勒延遲選擇實驗，挑戰「光是什麼」的傳統界限，並首次實驗觀察光子的波粒疊加態。
4日，記者從中科大郭光燦院士領導的中科院量子信息重點實驗室獲悉，該實驗室李傳鋒研究組首次實現了量子惠勒延遲選擇實驗，製備出了光的波-粒疊加狀態，豐富了人們對傳統玻爾互補原理的理解，挑戰「光是什麼」的古老科學問題。
光是什麼？研究組成員認為，從最初牛頓的粒子說，到惠更斯的波動說，直至愛因斯坦的光量子說，一直眾說紛紜。現在對光的理解可歸結為玻爾的互補原理，即光具有波粒二象性，波動性和粒子性這兩種屬性即對立又互補，一個實驗中具體展示哪種屬性取決於實驗裝置。
此前有一種隱變量理論認為，光子有自由意志，實驗觀察結果可展現其粒子性或波動性。為了檢驗這種隱變量理論和量子力學誰是誰非，玻爾的學生惠勒於1978年提出了著名的延遲選擇實驗。
在經典的惠勒延遲選擇實驗中，光的波動性和粒子性不能夠同時展現出來。李傳鋒研究組設計出一種量子實驗裝置，巧妙地利用光子的偏振比特作為輔助，使測量裝置處於量子疊加態，能同時探測光子的波動性與粒子性，從而實現了量子的惠勒延遲選擇實驗。該實驗排除了光子有自由意志的假設，並首次觀測到波與粒子的疊加狀態，處於這種疊加態的光子，既不像粒子態那樣沒有幹涉條紋，也不像波動態那樣表現出正弦形幹涉條紋，而是呈現出鋸齒形條紋這樣一種「非波非粒，亦波亦粒」的表現形式。
英國著名量子物理學家阿迪索教授認為，「該實驗挑戰了互補原理設定的傳統界限，在一個實驗裝置中展示光子可以在波動和粒子兩種行為之間相干地振蕩」。《自然-物理》雜誌也在「研究高亮」欄目報導了該成果，稱它「重新定義了波粒二象性的概念」。
量子力學對唯物論的致命一擊：延遲選擇思想實驗
現代量子力學的發現說明物質很難以獨立存在於觀測之外。著名物理學家惠勒博士（John A. Wheeler，曾與波爾和愛因斯坦共同研究理論物理）提出的「延遲選擇思想實驗」（Delayed Choice Experiment）已經被證實。這個思想實驗說明一個粒子在空間中走過的路徑竟然會由最後的觀測來決定，按理說客觀存在的粒子走過的路徑在觀測之前已經是客觀存在、不可更改的。至今物理學界對此也沒有令人滿意的答案。惠勒博士晚年時說的一些話表明他對物質的客觀實在性也非常懷疑。
雷射脈衝源（laser pulse source）發出光子，到達半鍍銀的反射鏡BS1（作用是使光子有一半可能穿過了反射鏡BS1到達全反射鏡M1，一半可能被反射鏡BS1反射到達全反射鏡M2），兩個全反射鏡M1和M2把這兩部分的光子又交匯在一起。在終點觀察光子飛來的方向，我們就可以確定光子究竟是沿著哪一條路徑飛來的。
如果在終點處也插入一塊半鍍銀的反射鏡BS2，通過調整BS1-M1-BS2和BS1-M2-BS2兩個路徑的光子的相位，可以使這兩部分光子到達BS2時發生反相干涉，從而使光子在水平方向或者在豎直方向上「互相抵消」，最後只在豎直方向或者水平方向上輸出。然而，真正讓你感到不可思議的是，即使雷射脈衝源（laser pulse source）每次只發出一個光子，經過足夠長的時間，你還是可以看到同樣的幹涉結果，這說明一個光子每次到達BS2時和自己發生了幹涉——按照量子力學的官方說法就是一個光子同時通過BS1-M1-BS2和BS1-M2-BS2兩條路逕到達BS2後和自己發生幹涉（詳見著名的雙縫幹涉實驗，雷射脈衝源每次只發出一個光子，經過足夠長的時間，你同樣會看到幹涉條紋）。
但是，如果在終點處不放置半鍍銀的反射鏡BS2，雷射脈衝源（laser pulse source）每次只發出一個光子，則通過在終點觀察光子飛來的方向，我們每次卻只能看到光子從一個路徑飛來，或者沿水平方向，或者沿豎直方向。這說明，如果我們不在終點處放置半鍍銀的反射鏡BS2，光子就沿著某一條路徑而來，反之，它就同時經過兩條路徑而來。也就是說，我們的選擇決定了光子的「選擇」。
現在的問題是，如果在光子已經通過了第一塊半鍍銀的反射鏡BS1，快到達終點（還沒到達）的時候，我們才把半鍍銀的反射鏡BS2放入終點處，結果會怎麼樣呢？一般地，我們會認為光子通過了第一塊半鍍銀的反射鏡BS1後已經選擇了怎麼走，按前面的結果就是光子只沿著某一條路徑而來，應該不會再發生幹涉現象。可惜，結果再次讓你感到驚訝，光子還是選擇了同時經過兩條路徑而來。無論雷射脈衝源（laser pulse source）每次只發出一個光子還是多個光子，結果都是一樣的。這就是著名的惠勒延遲選擇實驗（Wheeler’s delayed choice experiment）（詳見量子力學發展大事記）。實驗結果表明，我們現在的選擇（觀測行為）改變了光子過去的「選擇」。也就是說，我們可以在事情已經發生之後再來決定它應該怎麼發生——無論是否事情的結果在邏輯上已經在一段時間以前被決定！
實際上，「任何一種基本量子現象只在其被記錄（觀測）之後才是一種現象」，量子力學的創始人之一玻爾說，「而在觀察發生之前，沒有任何物理量是客觀實在的」。也就是說，觀察創造了全部的實相。現在，惠勒延遲選擇實驗在此基礎上更進一步的說明，觀察不但創造了實相，而且還可以在事情發生之後再逆時間地創造實相。關於客觀實在絕對性的世界觀的徹底失敗，詳見自然界違背貝爾不等式的阿斯派克特實驗。
值得一提的是，關於時間，愛因斯坦創立相對論時也有一個著名的結論，「過去、現在、將來的區別，只是一種幻覺，不管人們怎麼堅持這種區別也沒有用」。不過，相對論強調的是我們對時間的幻覺，而量子力學的結論更加普遍，那就是一切實相都是幻覺。
雖然聽上去古怪，但這卻是哥本哈根派的一個正統推論！惠勒後來引玻爾的話說，「任何一種基本量子現象只在其被記錄之後才是一種現象」，我們是在光子上路之前還是途中來做出決定，這在量子實驗中是沒有區別的。歷史不是確定和實在的——除非它已經被記錄下來。更精確地說，光子在通過第一塊透鏡到我們插入第二塊透鏡這之間「到底」在哪裡，是個什麼，是一個無意義的問題，我們沒有權利去談論它，它不是一個「客觀真實」！惠勒用那幅著名的「龍圖」來說明這一點，龍的頭和尾巴（輸入輸出）都是確定的清晰的，但它的身體（路徑）卻是一團迷霧，沒有人可以說清。
在惠勒的構想提出5年後，馬裡蘭大學的卡洛爾?阿雷（Carroll O Alley）和其同事當真做了一個延遲實驗，其結果真的證明，我們何時選擇光子的「模式」，這對於實驗結果是無影響的（和玻爾預言的一樣，和愛因斯坦的相反！），與此同時慕尼黑大學的一個小組也作出了類似的結果。
這樣稀奇古怪的事情說明了什麼呢？
這說明，宇宙的歷史，可以在它實際發生後才被決定究竟是怎樣發生的！在薛丁格的貓實驗裡，如果我們也能設計某種延遲實驗，我們就能在實驗結束後再來決定貓是死是活！比如說，原子在1點鐘要麼衰變毒死貓，要麼就斷開裝置使貓存活。但如果有某個延遲裝置能夠讓我們在2點鐘來「延遲決定」原子衰變與否，我們就可以在2點鐘這個「未來」去實際決定貓在1點鐘的死活！
這樣一來，宇宙本身由一個有意識的觀測者創造出來也不是什麼不可能的事情。雖然宇宙的行為在道理上講已經演化了幾百億年，但某種「延遲」使得它直到被一個高級生物所觀察才成為確定。我們的觀測行為本身參予了宇宙的創造過程！這就是所謂的「參予性宇宙」模型（The Prticipatory Universe）。宇宙本身沒有一個確定的答案，而其中的生物參予了這個謎題答案的構建本身！
John Archibald Wheeler是那些認真考慮過量子力學的人之一。在研究了哥本哈根對雙縫實驗的解釋---強調觀察者知道的和觀察者何時知道---之後，惠勒認識到觀察者的選擇可能會控制那些到實驗中的變量。
「如果你說的是真的」惠勒說（事實上），「那麼我會在一件事情可能已經發生後再選擇知道一個特性」惠勒意識到在這種情況下，觀察者的選擇可能會決定實驗的結果---而無論是否實驗的結果在邏輯上已經在一段時間以前被決定。
「沒有意義」簡化主義者們說。「垃圾」唯物主義者們說。「完全荒謬」幼稚的現實主義者們說。「是的」數學家們說。惠勒的思想實驗和量子力學的預言被帶到了實驗室中，接受實踐的檢驗。一下就是所發生的。
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