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The Home Parallel Universe Test
Sam Sachdev writes "David Deutsch, a physcicist at Oxford, has designed a home test for parallel universes. Using a pin, a red laser pointer, a piece of paper, and a relatively dark room, he claims that the results from this experiment confirm the existence of parallel universes." Okay, so it may not really be proof of parallel universes, but it's a fun trick to try with a laser pointer nonetheless.
Yeah, here is a nice summary with pictures.
I'm not a quantum physicist, but I think I have a idea what this is about; the light waves just interfere differently with four slits. Since this Deutsch guy draws wildly different conclusions about the result, I guess he's either much stupider or much smarter than me. And since he's the university physicist and not me, I feel bad for him if it's the former.
You have understood nothing. The phenomenon is real and one of the strangest and most spooky things in physics. It shows that it it possible to get a particle (in this case a photon) to interfere with itself.
The only question is how you interpret it. The first interpretation, created by Einstein, Bohr and other dignitaries of the time, was the "Copenhagen Interpretation" which requires an "observer".
The "Many-worlds interpretation", first thought of in the late fifties gets rid of the need for a mystical observer by introducing parallell universes, where entangled particles can still interfere with each other.
This interpretation is championed by many of the leading physicists. For example Deutsch and Murray Gell-Mann.
I believe Feynman has a strange third interpretation involving particles travelling backwards in time, that cancel out the waves of forward travelling particles at specific points in space-time.
Opinions stated are mine and do not reflect those of the Illuminati
I hate to break it to you, but that's not a valid interpretation; a single photon can and does interfere with itself. Where you think of a particle, QM sees that a "photon" is a localized wave packet, represented by a probability wave that has useful values in a small volume (because it still looks like a particle) but exists everywhere. This probability wave can and does go through the different holes, and what you get out is effectively an interference of the photon with itself. This is the basic idea behind Feynman's "sum of all histories" (properly, the path integral formulation of QM) approach, that looks at all possible paths - in this case, all the holes.
In english, The photon is not a point, only when it hits something does it act like a point, as it only hits one point. A photon is a weird fuzzy thing that is mostly here, and partly here and over there, but a little bit everywhere else. It interferes with itself because it squeezed through both holes, and because it squished itself through both holes, it's shape (places where it mostly and partly was) changed, and so there are some places that it is more likely to hit, and some places that it can't hit.
Laws are horrible moral guides, moral guides make even worse laws.
Another point: regarding your link to the blog, I mention the following comment from Physics Forums: The blog did not indicate two things: (1) that there's no references to the Afshar experiment and (2) that it is having problems in the refereeing stage. In fact, unconfirmed reports have indicated that the Afshar experiment report that was uploaded to the e-print archive was removed, something that is unheard of for arXiv. Until peer review of this supposed invalidation, lack of skepticism is silly.
"Politicians and diapers must be changed often, and for the same reason."
Experiments have shown that subatomic particles act very funny when you try to describe or figure them out. Basically, these particles act like particles half the time, and like waves the other half of the time, but never both at the same time. Certain well known experiments (like the banding described in the article, which are due to wave interference of light particles) have shown that particles can somehow seem to act is if they are in multiple places at once, yet they cannot be observed in multiple places at once. This has led a lot of physicists to surmise that there are 'multiple parallel universes' where that exist simultaneously. The rationale is that since the inherent particles that make up our universe are in multiple states at the same time, these inherently MPD (multiple personality disorder) particles make up a sort of multi-verse that exists at the same time in different states, thereby creating different realities/parallel universes.
...and I will reiterate, IANAQP, but it seems to me that there is a lot of going from A, B, C to X, Y, Z with nothing in the middle with that notion. We cant observe the quantum weirdness at our human-sized perceivable universe, and to assume that this quantum weirdness can cause other realities where GWBush is in Mensa seems to be a far step of logic.
If there are any quantum experts out there, and see a problem with my reasoning, or just want to educate the ignorant masses (please leave out the math, its just boring), I urge you to help.
--J
Beer, now there's a temporary solution -- Homer Jay S.
IAAQP, and while I've not read this man's book, I'd be skeptical. Most physicists subscribe to the "Copenhagen" interpretation of quantum mechanics, which does not deal with parallel universes. The so-called "many-universe" theory has its followers but doesn't get much attention, for one reason: introducing the extra idea of multiple universes doesn't add anything to the descriptive power of the theory.
Before quantum theory was developed, most phenomena in nature were considered to be either particles or waves. This classification system broke down when particles were shown to diffract and waves were shown to be quantized. So nothing is really particle or wave, but everything has a particle or wave nature.
The canonical example is electron diffraction: shine a beam of electrons through two slits, and get an interference pattern on your photographic plate. Woo. Repeat with one electron at a time, recording each result.... and you still get an interference pattern. This presents a problem: each electron must have gone through both slits and interfered with itself. On the other hand, you can never measure the electron to be in two places at once, so we need to construct a third option. This is the idea of a superposition state: the electron is in a superposition of places (again, not actually "in" them); this superposition has wavelike properties and can interfere. When a measurement is made (by the photographic plate) the superposition "collapses" to one location.
This is where many-universe theory (to my understanding) comes in: how does the particle know which state to collapse to? Copenhagen Qm says it's random, but weighted by the superposition; i.e. quantum mechanics predicts probabilities only. Many-universe theory says that when that collapse occurs, the universe splits into a bunch of new ones, one for each outcome of the measurement. I've not yet read a good explanation (anyone have a link to one? I'd love to) of why measurement (that is, a phase-randomizing interaction with a larger system) should create a new universe.
Anyway, I hope this helps! If you are curious about QM, there's an inexpensive book by Isham that has really wonderful discussion (and even mentions many-universe). Feynman's book "QED" takes his path-integral approach and is a great layman's introduction; just don't try solving any problems with that method later (the math is rough).