Editing Schrödinger's cat (section)

===Role of consciousness===
{{Main|Consciousness causes collapse}}
In 1932, [[John von Neumann]] described in his book ''[[Mathematical Foundations of Quantum Mechanics]]'' a pattern where the radioactive source is observed by a device, which itself is observed by another device and so on. It makes no difference in the predictions of quantum theory where along this chain of causal effects the superposition collapses.<ref name="Tales of the Quantum">{{cite book |last1=Hobson |first1=Art |title=Tales of the Quantum: Understanding Physics' Most Fundamental Theory |date=2017 |publisher=Oxford University Press |location=New York, NY |isbn=9780190679637 |pages=200–202 |url=https://books.google.com/books?id=mGduDQAAQBAJ |access-date=April 8, 2022}}</ref> This potentially infinite chain could be broken if the last device is replaced by a conscious observer. This solved the problem because it was claimed that an individual's consciousness cannot be multiple.<ref>{{cite book |last1=Omnès |first1=Roland |title=Understanding Quantum Mechanics |date=1999 |publisher=Princeton University Press |location=Princeton, New Jersey |isbn=0-691-00435-8 |pages=60–62 |url=https://books.google.com/books?id=XET_DwAAQBAJ |access-date=April 8, 2022}}</ref> Eugene Wigner asserted that an observer is necessary for a collapse to one or the other (e.g., either a live cat or a dead cat) of the terms on the right-hand side of a [[wave function]]. Wigner discussed the interpretation in a thought experiment known as [[Wigner's friend]].<ref name="Surfing the Quantum World">{{cite book |last1=Levin |first1=Frank S. |title=Surfing the Quantum World |date=2017 |publisher=Oxford University Press |location=New York, NY |isbn=978-0-19-880827-5 |pages=229–232 |url=https://books.google.com/books?id=Y1w-DwAAQBAJ |access-date=April 8, 2022}}</ref>

Wigner supposed that a friend opened the box and observed the cat without telling anyone. From Wigner's conscious perspective, the friend is now part of the wave function and has seen a live cat and seen a dead cat. To a third person's conscious perspective, Wigner himself becomes part of the wave function once Wigner learns the outcome from the friend. This could be extended indefinitely.<ref name="Surfing the Quantum World"/>

A resolution of the paradox is that the triggering of the Geiger counter counts as a measurement of the state of the radioactive substance. Because a measurement has already occurred deciding the state of the cat, the subsequent observation by a human records only what has already occurred.<ref>{{cite book |last1=Puri |first1=Ravinder R. |title=Non-Relativistic Quantum Mechanics |date=2017 |publisher=Cambridge University Press |location=Cambridge, United Kingdom |isbn=978-1-107-16436-9 |page=146 |url=https://books.google.com/books?id=qDbSDgAAQBAJ |access-date=April 8, 2022}}</ref> Analysis of an actual experiment by [[Roger Carpenter]] and A. J. Anderson found that measurement alone (for example by a Geiger counter) is sufficient to collapse a quantum wave function before any human knows of the result.<ref name="Carpenter2006">{{cite journal | title = The death of Schrödinger's cat and of consciousness-based wave-function collapse | journal = [[Annales de la Fondation Louis de Broglie]] | year = 2006 | author = Carpenter RHS, Anderson AJ | volume = 31 | issue = 1 | pages = 45–52| url = http://www.ensmp.fr/aflb/AFLB-311/aflb311m387.pdf  | access-date = 2010-09-10 |archive-url = https://web.archive.org/web/20061130173850/http://www.ensmp.fr/aflb/AFLB-311/aflb311m387.pdf |archive-date = 2006-11-30}}</ref> The apparatus indicates one of two colors depending on the outcome. The human observer sees which color is indicated, but they don't consciously know which outcome the color represents. A second human, the one who set up the apparatus, is told of the color and becomes conscious of the outcome, and the box is opened to check if the outcome matches.<ref name="Tales of the Quantum"/> However, it is disputed whether merely observing the color counts as a conscious observation of the outcome.<ref name="Okon2006">{{cite journal | title = How to Back up or Refute Quantum Theories of Consciousness | journal = Mind and Matter | year = 2016 | author = Okón E, Sebastián MA | volume = 14 | issue = 1 | pages = 25–49}}</ref>