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The double slit experiment What do I need to know?

by Proxymei
Tags: quantum physics
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Jan15-13, 06:50 PM
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I'd like to know a few things:

Are there different explanations of this experiment, and if so – which are the most common?
What are the different implications and how much do we understand about it today?

I don't know much about quantum physics, but I'd like to learn and since I'm jumping right into it, I really need these questions answered.

My goal is to understand the different possibilities and implications of the experiment.

Thank you in advance.
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Jan15-13, 07:42 PM
Drakkith's Avatar
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What do you mean by a "different explanation"? There should only be one correct explanation.
Jan16-13, 06:56 AM
P: 2
Quote Quote by Drakkith View Post
What do you mean by a "different explanation"? There should only be one correct explanation.
Good, so you answered my first question. What is the explanation then? And what are other possible implications of, say, particles being in a superposition? For example, I heard that a superposititon could imply two different occurrences in different universes -- that we may live in a multiverse. (I'm less interested in how probable these ideas are, so I appreciate any input).


Jan16-13, 09:59 AM
P: 5,632
The double slit experiment What do I need to know?

proxy...welcome to physics forums...

Likely you'll learn more and get better answers if you do some background reading....
then ask some specific questions about specifics you don't understand...The implications
of such findings from double slit type experiments covers most of scientific knowledge...from the tiniest Plank scale to cosmological horizons.

Wikipedia has a very good explanation of the basic 'double slit experiment'....and some
interpretations towards the end of the article....also check out 'quantum superposition'

If you haven't already, be sure to read out the 'delayed choice' and 'quantum erasure' experiments...those are truly mind-blowing.

It is worthwhile noting that one of the fundamental equations of quantum theory is the Schrodinger equation. That is a linear representation [formula] describing how quantum systems evolve over time....Do you remember all the trigonometric identities from High school?? like Sin2X = 2SinXcosX.......well in a linear system, all those add up....each is a solution and so is the total....they vary in amplitude and phase....
So which wave represents a particle, a local excitation? They each do!!

That wavefunction is thought to be the most complete description of a physical system. And there are limitations that come with such descriptions in quantum discrete or 'quantum' size parcels.....which appear to have minimum size [Planck Length] and other minimum values. In general, quantum mechanics does not permit particles to inhabit a space smaller than their wavelengths…

Carlo Rovelli puts it this way:

Roughly speaking, we learn from GR that spacetime is a dynamical field and we learn from QM that all dynamical field are quantized. A quantum field has a granular structure, and a probabilistic dynamics, that allows quantum superposition of different states.
So in the double slit experiment, there is ambiguity about what the next particle will do....where it will appear. Not only that, how we observe each particle also effects its behavior!! Even after it passes!! [see quantum erasure and delayed choice explanations].
Jan16-13, 10:05 AM
P: 5,632
Regarding superposition, I found a quote I really like...did not record the source:

'virtual particles' a theoretical particles present in all vacuum energy open space in our universe....

..There is not a definite line differentiating virtual particles from real particles the equations of physics just describe particles (which includes both equally). The amplitude that a virtual particle exists interferes with the amplitude for its non-existence; whereas for a real particle the cases of existence and non-existence cease to be coherent with each other and do not interfere any more. In the quantum field theory view, "real particles" are viewed as being detectable excitations of underlying quantum fields...
What links this to double slit type experiments is the wavelike description of particles, that is, the mathematical formalism.
Jan16-13, 05:48 PM
P: 317
Quote Quote by Drakkith View Post
What do you mean by a "different explanation"? There should only be one correct explanation.
Don't differnet interprations offer different explanations?

I'm thinking of MWI (Many Worlds) vs say Copenhagen. Wouldn't these physically interpret the double slit experiment in a completely different manner?

Yeah, the math will predict the same thing in both interpretations, but that's only one level of the problem here.
Jan21-13, 01:22 AM
P: 16
I thought I might post a question on the subject. When I read about this experiment I often see that we can deduce from it that observation makes reality collapse into what we observe. That the very action of observation does this. But by this they mean observation as in measuring right? With detectors and such. Sometimes it sounds like the very presence, at the very moment of the experiment, of a human beings living eyes would influence the results. I hope I get my question across :)
Jan21-13, 12:43 PM
P: 5,632
we can deduce from it that observation makes reality collapse into what we observe.
they do mean measuring yes.

But it is not 'reality' that collapses.....You probably mean the "collapse of the wave function" which is a description of quantum system over time. usually via the Schrodinger [wave] equation....although I'll bet there are others by now.
edit: in fact it just occurred to me that the matrix mechanics of Heisenberg are exactly equivalent to the wave mechanics of Schrodinger...

Check this out for more:

and also "The Nature of Collapse"...within.

I'm not expert, but my understanding is that different people mean different things by 'collapse of the wave function'. And there is not universal agreement about exactly what the wave function actually it physical or statistical?

In the statistical interpretation, the function psi [the wave] does not give more than the statistics of positions…or momenta…the state psi corresponds to a probability distribution. The wave function psi is defined in configuration space not ordinary space. The conclusions (measurements) of quantum theory are statistical in nature and depend upon the nature of the measurement (observation).

That's what's happening in the double slit experiment: different measurements, even the 'same' measurements at different times, produces 'different' results.
Jan21-13, 12:55 PM
P: 5,632
by the way, search these forums for 'double slit experiment' and you'' turn up a LOT of discussions on the subject...some go on for months!
Jan22-13, 01:56 AM
P: 16
Thank you Naty1, very guiding! :)

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