# Quantum Physics - Questions about Photon Test **URL:** \ **Category:** Factual Questions\ **Created:** [August 8, 2001, 5:49pm UTC](https://boards.straightdope.com/t/quantum-physics-questions-about-photon-test/75475 "2001-08-08T17:49:07Z")\ **Posts on this page:** 12\ **Page:** 2
**Author:** ![bonzer](https://avatars.discourse-cdn.com/v4/letter/b/45deac/32.png) [@bonzer](https://boards.straightdope.com/u/bonzer)\ **Post date:** [August 10, 2001, 7:35am UTC](https://boards.straightdope.com/t/quantum-physics-questions-about-photon-test/75475/21 "2001-08-10T07:35:02Z")
> [@](#): > > > [@](#): > > > > bonzer wroteOffhand, I don’t know exactly what Ring is quoting as (1967) > > It’s one of the most famous science quotations of all time. Try any of the following – there must be a hundred of them. My phrasing was a tad unclear: while I recognised the quotation, I couldn’t (and can’t) make sense of the reference. Offhand, I couldn’t remember whether it was from _Character_ or _Lectures_ and I had no idea what the hell (1967 a) might be - it’s too late to be either of them. > [@](#): > > > [@](#): > > > > The big metaphysical advantage of multiple universes is that a measurement by us doesn’t alter the totality of all universes > > Each measurement creates an entirely new universe. I carefully said the _totality_ of all universes. In the many-worlds interpretation there’s a single state vector that describes this totality. It evolves, but this state vector is _exactly_ the same after a measurement as before one. If a superposition ``` Eigenstate 1 + Eigenstate 2 ``` forms and we make a suitable measurement, it is the case that from “our viewpoint” we wind up in just one of these states. The _overall_ state is however still very much ``` Eigenstate 1 + Eigenstate 2. ``` With “someone else” thinking they’re in the other state, of course. That the state vector is independent of the details of what measurements are made and when is the great formal attraction of the interpretation. This is why quantum gravity people tend to like it: it allows you to talk about (even calculate) state vectors without worrying about what a “measurement” means in such a context. > [@](#): > > Every measurement creates another us in the new universe. From the point of view of us, here, now, the process _is_ that of following a single path through a forking tree. From a less parochial viewpoint, it doesn’t create a new us, it bifurcates the existing one into a superposition. For all that, I personally don’t find the idea appealing ---
**Author:** ![ducttapelovesme](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@ducttapelovesme](https://boards.straightdope.com/u/ducttapelovesme)\ **Post date:** [August 11, 2001, 3:52am UTC](https://boards.straightdope.com/t/quantum-physics-questions-about-photon-test/75475/22 "2001-08-11T03:52:35Z")
One thing I never understood is how there could be two outcomes for one situation. If two particles are going to collide, isn’t the outcome determined by their speed and direction? I don’t know if this is too big of a leap then, but isn’t everything at some level the outcome of particals reacting together? Even our own brain are made up of chemical reactions. Our decisions are based upon past choices, and I supposed randomness in our thoughts are triggered by whatever happens to be floating around at that moment. That make any sense to anyone? ---
**Author:** ![SPOOFE](https://avatars.discourse-cdn.com/v4/letter/s/c5a1d2/32.png) [@SPOOFE](https://boards.straightdope.com/u/SPOOFE)\ **Post date:** [August 11, 2001, 9:21am UTC](https://boards.straightdope.com/t/quantum-physics-questions-about-photon-test/75475/23 "2001-08-11T09:21:15Z")
> [@](#): > > One thing I never understood is how there could be two outcomes for one situation. Well, there are two (or more) _potential_ outcomes for one situation. “Potential” is the key word to remember. The Many Worlds theory is based on the idea that, even if you choose Door #1, somewhere, another version of you (You 2.0?) chose Door #2. The Photon Test simply indicates (assuming the MW theory to be accurate) that there is overlap between the universes… that they are connected somehow. But it could also indicate something else entirely. ---
**Author:** ![Pleonast](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pleonast/32/1183_2.png) [@Pleonast](https://boards.straightdope.com/u/Pleonast)\ **Post date:** [August 11, 2001, 11:58am UTC](https://boards.straightdope.com/t/quantum-physics-questions-about-photon-test/75475/24 "2001-08-11T11:58:05Z")
> [@](#): > > Quite frankly, CurtC, I have a hard time swallowing the whole consciousness interferes with the experiment thing. > [@](#): > > Where can I find this? Or is there a doper generous enough to attempt an explanation here? The only places I’ve heard of this consciousness hypothesis of quantum mechanics is in two philosophy courses. My physics courses and books (and I have a PhD in physics) never mention this. Here is my understanding. The Copenhagen interpretation (i.e., usually considered the standard) divides a quantum experiment into two parts: the quantum system, and a classical measuring device. The quantum system exists in a superposition of eigenstates until the measuring device forces it to collapse to one eigenstate. (Eigenstates are wavefunctions coresponding to particular measurement results.) Typically the physicist has no problem separating the two parts of the experiment. For example, the electron is the quantum system, and the slits and screen are the classical measuring devices. But the philosopher, of course, wants to how the physicists knew to divide where he did. The physicist says “because it simplifies the problem and predicts the what I observe”. The philosopher is not satisfied. Some philosophers go on to posit that the actual dividing line is consciousness (i.e., only consciousness can make a measurement). Personally, I have a “universal decoherence” interpretation. A measurement is made by a system that is large enough to decohere the quantum system. (Decoherence is the process by which a quantum state “degrades” because of interactions with the surrounding environment.) The universe at large is making measurements on quantum systems. I’m not certain of the philosophical implictions of this interpretation, but it has the advantage of being somewhat straight-forward to calculation from the equations. ---
**Author:** ![ducttapelovesme](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@ducttapelovesme](https://boards.straightdope.com/u/ducttapelovesme)\ **Post date:** [August 11, 2001, 5:02pm UTC](https://boards.straightdope.com/t/quantum-physics-questions-about-photon-test/75475/25 "2001-08-11T17:02:19Z")
I understand the concept of potential outcomes, ie you flip a coin, and there is a potiential to be heads or tails. However, wasn’t there only one true outcome? The final way it landed was determined by almost an infinite amout of factors like the force of the person who fliped it, air resistance, etc. all the forces acting upon it. If you knew all the factors, you could , in theory, calculate the outcome? ---
**Author:** ![Dr.Lao](https://avatars.discourse-cdn.com/v4/letter/d/2bfe46/32.png) [@Dr.Lao](https://boards.straightdope.com/u/Dr.Lao)\ **Post date:** [August 11, 2001, 6:17pm UTC](https://boards.straightdope.com/t/quantum-physics-questions-about-photon-test/75475/26 "2001-08-11T18:17:58Z")
> [@](#): > > \*Originally posted by ducttapelovesme \* > **If you knew all the factors, you could , in theory, calculate the outcome?** It appears that even in theory, if you knew every parameter to the highest possible percision, it is not possible to determine the outcome of certain events. According to QM, subatomic events with more than one outcome are truely random. The probabilities of each outcome can be calculated, but the result cannot be determined with certainty beforehand. ---
**Author:** ![JasonFin](https://avatars.discourse-cdn.com/v4/letter/j/4af34b/32.png) [@JasonFin](https://boards.straightdope.com/u/JasonFin)\ **Post date:** [August 13, 2001, 3:26am UTC](https://boards.straightdope.com/t/quantum-physics-questions-about-photon-test/75475/27 "2001-08-13T03:26:42Z")
In understanding the appeal of the Many-Worlds Interpretation, it is important to note that quantum theory, under the MWI, is both a _deterministic_ theory and a _local_ theory. That is, there are no random factors altering the evolution of the universal state vector, and there are no faster-than-light interactions or influences. Einstein might have liked this interpretation had it been around during his lifetime, as it addresses some of his well-known philosophical disagreements with quantum mechanics (at the cost of introducing some potential for new ones, I’ll admit). A nice FAQ about the MWI can be found [here](http://kuoi.asui.uidaho.edu/~kamikaze/documents/many-worlds-faq.html) . ---
**Author:** ![douglips](https://avatars.discourse-cdn.com/v4/letter/d/e68b1a/32.png) [@douglips](https://boards.straightdope.com/u/douglips)\ **Post date:** [August 13, 2001, 4:31am UTC](https://boards.straightdope.com/t/quantum-physics-questions-about-photon-test/75475/28 "2001-08-13T04:31:31Z")
Thanks, **Pleonast** , your views correspond with mine pretty well. I mean, can’t the damn cat tell when it dies for itself? ---
**Author:** ![Slip\_Mahoney](https://avatars.discourse-cdn.com/v4/letter/s/e47774/32.png) [@Slip\_Mahoney](https://boards.straightdope.com/u/Slip_Mahoney)\ **Post date:** [August 13, 2001, 5:49am UTC](https://boards.straightdope.com/t/quantum-physics-questions-about-photon-test/75475/29 "2001-08-13T05:49:40Z")
Here’s another Feynman quote: “Nobody understands Quantum Physics. You just get used to it.” And Everett’s Many Worlds Interpretation, although completely untestable, is elegant and has a great deal of explanatory power. I’ve always liked it, which probably means that it’s wrong. ---
**Author:** ![DPWhite](https://avatars.discourse-cdn.com/v4/letter/d/d26b3c/32.png) [@DPWhite](https://boards.straightdope.com/u/DPWhite)\ **Post date:** [August 13, 2001, 6:28am UTC](https://boards.straightdope.com/t/quantum-physics-questions-about-photon-test/75475/30 "2001-08-13T06:28:34Z")
And nobody knows the why of it, and if anyone tells you they do, they are full of poop, and its a pretty good indication that they don’t even know the what. ---
**Author:** ![JS\_Princeton](https://avatars.discourse-cdn.com/v4/letter/j/57b2e6/32.png) [@JS\_Princeton](https://boards.straightdope.com/u/JS_Princeton)\ **Post date:** [August 13, 2001, 6:52am UTC](https://boards.straightdope.com/t/quantum-physics-questions-about-photon-test/75475/31 "2001-08-13T06:52:29Z")
Just wanted to point out that “many worlds” interpretation of reality is a lot older than quantum mechanics. It’s actually the age-old question of free-will vs. predestination come to haunt us again. Fact of the matter is, it doesn’t really concern most experimental scientists except when they get drunk or play parlour logic games. It is, to some extent, unknowable. That’s the whole problem with probabilities in general… they don’t tell you anything deterministically, but go out and flip that coin one hundred times and you will get an answer. ---
**Author:** ![Philster](https://avatars.discourse-cdn.com/v4/letter/p/13edae/32.png) [@Philster](https://boards.straightdope.com/u/Philster)\ **Post date:** [August 13, 2001, 2:30pm UTC](https://boards.straightdope.com/t/quantum-physics-questions-about-photon-test/75475/32 "2001-08-13T14:30:52Z")
I would say that having consciousness affect the outcome of anything is a strong argument for some type of pre-destiny. However, isn’t their a bit of unpredictability and randomness that would counter that arguement? Anyway, it seems that things happen with probability at the atomic level, but that lends itself to a degree of unpredictabilty. So, the randomness prevents total predictability at the atomic level, but the level of probability ensures a stability of the atomic world. [Previous page](https://boards.straightdope.com/t/quantum-physics-questions-about-photon-test/75475.md?page=1)