[QUOTE=prendrelemick;1002668]
Also, it has been known since the twenties that photons behave oddly when not observed and predictably when observed. Nobody knows why though./QUOTE]
How do we know they behave oddly if they are not being observed?
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[QUOTE=prendrelemick;1002668]
Also, it has been known since the twenties that photons behave oddly when not observed and predictably when observed. Nobody knows why though./QUOTE]
How do we know they behave oddly if they are not being observed?
^ The two slit experiment:
Shine a light through two slits onto a screen. you don't get two light bands on the screen, you get several. This is right and proper and predictable because light travels in waves that interfere and collide with each other as they emerge from the slits.
Now adjust your light so that it fires one Photon at a time (that means they can't collide with each other) The result is the same - several light bands on the screen. No one knows why!
So to try and see what is happening, place photon detectors along the route the photons travel. Strangely, they then behave as predicted, two bands of light on the screen. Remove the detectors and they revert back to their many banded odd behavior.
Of course this has spawned many imaginative theories as to what is going on. My favourite is that reality splits in two as the photon approaches the slits, creating a whole new alternative universe.
An interesting idea but would the alternative universe be similar to this one?Quote:
Originally Posted by prendrelemick
Very similar, the only difference being the photon went through the left slit in universe A and through the right slit in universe B.
You see there is an infinite number of universes and every time a "choice" is made by anything, from a particle to an Elephant, a new universe is created that breaks away from the universe where the alternative choice was taken.
Even stranger, there are highly educated professors who are paid lots of money to think this stuff up.
I'm beginning to see the logic in the government's cuts in education.Quote:
Originally Posted by prendrelemick
Is this just not confusing the particle/wave duality of photons? I think you're also making a mistake that the photon experiment isn't one photon at a time, but one photon wide.Quote:
Originally Posted by prendrelemick
I'm nobody's physicist, but I don't think you've presented the case as it's seen by physicists.
There's a lot more here and here.
Fascinating, but not really a hole in physics.
Nope. it was as I said. one particle at a time, so even if they were acting like a wave they could not interfere with each other.
here is a simple and annoying explanation of the effect I was describing. (with electrons)
http://www.youtube.com/watch?v=DfPeprQ7oGc
The point I was making is that the presence of an observer, or an attempt at measurement, or placing a detector is significant in quantum physics, and not only in this experiment. (It decoheres the probability wave or something)
You might want to look at this too, same annoying bloke on paired particles.
http://www.youtube.com/watch?v=Jh8uZ...eature=related
Do you have something other than a bloke on Youtube?Quote:
Originally Posted by prendrelemick
If there's some science behind his claims, it should be available elsewhere; there will be publications and peer reviews. My understanding - which I'll readily admit is lousy - is that he's wrong, but I could easily be barking up the wrong river.
The thing about individual electrons (or photons, it works in both cases) is mentioned in pretty much every layman's book about modern physics and its interesting implications. I must admit that my personal exposure came from (laymen's) science magazines which I can't recall the name of, science programs on TV (again, probably more than one), and best-selling popularizations. At the moment, I have Brian Greene's "Fabric of the Cosmos" somewhere, but it would take a while to dig it up to find exact page numbers, for example. Roger Penrose and others also describe it in other books for the layman.
Here's another *non-video* discussion. It's lengthy and detailed, but skipping up to the middle section called "The Double Slit Experiment Revisited" will bring you to the part about introducing an observation of the electrons in transit, and thus bringing an end to the interference pattern.
http://www4.ncsu.edu/unity/lockers/u...s/quantum.html
Apparently Feynman's famous lecture on this can be found in the Third volume of his Feynman Lectures On Physics (which Google Books only excerpts). Feynman's idea that the particles are passing through infinite paths is called Sum Over Histories. What it would actually *mean* regarding multiple universes is open to some debate--but I think the basic idea is that the wave travels *each possible path*, and all of the paths cancel each other out except for the one that we finally observe. That's how the math is meant to work, anyhow.
Stephen Hawking describes Feynman's idea about this like so:
Quote:
Feynman suggested that particles travel from one location to another along every possible path through spacetime. With each trajectory Feynman associated two numbers, one for the size – the amplitude – of a wave and one for its phase – whether it is a crest or a through. The probability of a particle going from A to B is found by adding the up the waves associated with every possible path that passes through A and B.
At about 8:40 on this youtube clip (yes, another youtube guy...), you can hear a Fermilab physicist come to the end of a lecture on this famous experiment (and how sending individual electrons produces the same interference pattern that we would get if the electrons were sent in larger numbers, etc.). He goes on to explain the effects of observing which slit the individually-sent electrons happen to actually pass through: in that case, the interference pattern does not appear, you just get two dots, one for each slit as Newtonian physics would predict (a resulting physics similar to what one gets with only one slit).
http://www.youtube.com/watch?v=UXvAl...ayer_embedded#
Here is Stephen Hawking going over the same ground in his book The Grand Design. (see page 81)
Quote:
Originally Posted by The Atheist
There are loads of sites on the interweb about this (see Bill's post above.) This is not some fringe loony Physics, this is fundemental Mainstream stuff. For 90 years scientists have been refining and redoing the experiment, they are still getting the same result, and are still unable to "see" what is happening, though theories abound.
I linked to Dr Quantum because he ignores the Maths (which is all Greek to me) and was a quick and easy explanation. He is the creation of Fred Alan Wolf (you can wiki him)a Theoretical Physicist, who is probably cleverer than me.
My main sources are, as with Billl, magazine articles and popular TV documentries.
Thanks!Quote:
Originally Posted by billl
Here is the nub of it all:
Which is the problem with wave/particle duality - you can't measure the wavelength of a particle and you can't measure the height or length of a wave with a particle locator.Quote:
When you fire your photon emitter, what actually comes out is a Y wave (ie a wavefunction). It is not random: it travels according to the perfectly predictable laws of wave propagation, moving out in all directions and interfering with itself and all that good stuff. According to the Copenhagen interpretation, the Y wave represents the probability of the photon being at any particular place. So at this stage, the question "Where is the photon?" does not have an answer—there is only a wave of probabilities traveling outward. ....
But when we put measuring devices in the slits, we collapse the wavefunction much earlier. We force the photon to choose which slit to go through: one probability becomes "definitely yes" and the other becomes "definitely no" in that instant. Thereafter, there is only one beam, and hence no interference and no interference pattern.
Yep - I should have checked a bit more deeply, but I'm on the right wavelength now!Quote:
Originally Posted by prendrelemick
I think the problem was my reading of your description of what's actually happening.
If you follow the Copenhagen interpretation above, the proton isn't being observed, but located, and to be located, it actually has to be somewhere.
Just think - thanks to CERN, our grandchildren will be learning this stuff at school in a couple of decades' time.
Yes Billl, a very interesting and informative paper. I should've looked harder before linking Dr Quantum. I should just say that Niels Bohr's probability wave, is not the only explanation, there are some weird and wonderful theories out there, like the multi-universe explanation and the idea of conciousness interacting with the physical
Are we ready to do paired particles yet?
When I was a kid I imagined that death was not a reality, but that you inhabited different aspects of yourselves in different universes as and when your body in one universe was killed. It must have been the eternalist in me after reading about the theory somewhere ...
Never mind them, I think we're venturing into infinite improbablity drive!Quote:
Originally Posted by prendrelemick
You're right on theories, and it's difficult to tell the difference between the crazy and the sane, because some of the facts seem more bizarre than the oddest theory. The paired particles are a case in point - it shouldn't happen, but it obviously does, so there might be a dark energy or ............. [/insert theory] cause.
I think the paired particles (as well as discussion of the various "interpretations" that there are for these various weird results) is a bit more difficult than this double-slit business. Maybe another thread, if someone wants to really give it a shot...?
The improbability drive would actually be more relevant to this thread (and I don't mean to be as snarky as I might seem).