Quantum Physics simplified, page 3

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reply posted on 23-2-2010 @ 10:00 AM by buddhasystem

Greetings,
well I have a PhD in physics and I did a lot of reading on double slit experiment and the likes when I was young. There quite a bit of literature on this subject. One accessible modern source is none other than Wikipedia:

en.wikipedia.org...

Wave properties of matter are indeed hard to conceptualize for human brain, which is trained to interact with a world that largely behaves according to classical mechanics.

Reason, as applied to the events of our ordinary macro experience, tells us that a particle must pass through one slit or the other. The experiment tells us that there must be at least two slits to produce an interference pattern, and that anything that locates the particle before it hits the screen will destroy the interference pattern. Recent experiments have tried to identify which of the two slits a particle is coming out of on its way to the detection screen. Doing so will also prevent interference.

reply posted on 23-2-2010 @ 11:34 AM by Nichiren

reply to post by buddhasystem

Thank you so much for stopping by. I appreciate it!

I have a few specific questions re the double slit experiment using electrons. Since I don't understand the experiment, they probably make no sense. So please be patient with me. I probably also use terminology that is not correct, please correct me, so I can learn. I'm not able to do any math re this problem. I'm a layman, but am very intrigued by this experiment

1) Is an interference pattern by definition always caused by at least 2 particles interacting?

2) How do you shoot one very small electron through two very small slits? Don't you need to aim the particle at exactly one slit to do that? If so, how can it possibly go through both?

3) If you only send one "unobserved" electron and then measure the impact on the screen, do you already get an interference pattern, albeit very faint, or is it just one dot? Does the interference pattern happen over an extended amount of time, given we shoot one particle at a time.

4) I keep hearing and reading (on ATS) that the human mind, the observer/consciousness, has a fundamental impact on the experiment when we "measure" which way the particle went. Some people write that "the mind" collapses the wave-function of the particle. Is that really true or just a myth? If the experiment were done by computer only, would the result change?

4b) Also, are we able to measure which way the particle went without disturbing the particle at all?

5) If we measure which way the electron went before it (them LOL) hits the slits we don't get an interference pattern. What happens if we measure it right AFTER it has already gone through the slits (exit poll). The particle must have already "made up" its mind before we measure it this way?

6) Lastly, if you shoot one electron through the slits and you get an interference pattern would that mean that one electron turned into two? Therefore violating Einstein's e=mc2. Where does the mass or energy for a second particle come from?

Thank you in advance!

Best,

N

reply posted on 24-2-2010 @ 01:54 PM by buddhasystem

Originally posted by Nichiren
1) Is an interference pattern by definition always caused by at least 2 particles interacting?

By at least two waves, not particles

2) How do you shoot one very small electron through two very small slits?

You can't really shoot one electron. You can lower the intensity of the source such that you know that the rate is probably low. Once the electron leaves the source, it's impossible to ascertain which slit it went through, w/o destroying the pattern.

3) If you only send one "unobserved" electron and then measure the impact on the screen, do you already get an interference pattern, albeit very faint, or is it just one dot?

One dot.

4) I keep hearing and reading (on ATS) that the human mind, the observer/consciousness, has a fundamental impact on the experiment when we "measure" which way the particle went. Some people write that "the mind" collapses the wave-function of the particle. Is that really true or just a myth?

I don't think it's the mind.

If the experiment were done by computer only, would the result change?

Brain is a computer, so the point is moot.

4b) Also, are we able to measure which way the particle went without disturbing the particle at all?

No.

5) If we measure which way the electron went before it (them LOL) hits the slits we don't get an interference pattern. What happens if we measure it right AFTER it has already gone through the slits (exit poll).

No difference in the end result...

6) Lastly, if you shoot one electron through the slits and you get an interference pattern would that mean that one electron turned into two?

See above. Absorption of the electron will be localized, so you can't get two.

reply posted on 24-2-2010 @ 05:13 PM by Nichiren

reply to post by buddhasystem

Thank you! I will need time to digest this. You have raised more questions LOL.

reply posted on 24-2-2010 @ 05:41 PM by masterp

I don't have a PHD, but here is my attempt:

An observer is simply a photon (or electron) emitted on purpose in order to see what's going on.

It doesn't make any difference if a human is near the emission or not.

reply posted on 24-2-2010 @ 05:43 PM by drew hempel

reply to post by LiQuiD_FuSioN

The problem with Susskind is he dismisses nonlinear quantum models even though nonlinear models are not wacko -- there's several academic books documenting their accuracy.

reply posted on 24-2-2010 @ 05:47 PM by masterp

reply to post by Nichiren

Easy: fire a photon (or electron) through a double slit, and see multiple parallel vertical stripes forming onto the board; that's because the photon (or electron) behaves like a wave.

Do the experiment again, but this time get a flashlight to see the emitted photons (or electrons); the result would be two parallel vertical stripes.

The reason for this is that the the photons of the flashlight interfere with the fired photon and the wave function of the fired photon collapses, making the photon a 'tiny little bullet'.

reply posted on 24-2-2010 @ 06:16 PM by buddhasystem

Originally posted by masterp
I don't have a PHD, but here is my attempt:

An observer is simply a photon (or electron) emitted on purpose in order to see what's going on.

It doesn't make any difference if a human is near the emission or not.

I agree with this assessment.

reply posted on 25-2-2010 @ 07:29 AM by LightFantastic

Originally posted by buddhasystem

Originally posted by Nichiren
1) Is an interference pattern by definition always caused by at least 2 particles interacting?

By at least two waves, not particles

A single photon at a time through the double slits will still create the interference pattern by interfering with itself. Or is that still classed as two waves?

[edit on 25/2/2010 by LightFantastic]

reply posted on 25-2-2010 @ 11:42 AM by Nichiren

reply to post by masterp

So in essence the whole "wave-particle paradox" is just a measuring problem? Why was Einstein so confused about it?

reply posted on 25-2-2010 @ 12:02 PM by buddhasystem

Originally posted by LightFantastic

Originally posted by buddhasystem

Originally posted by Nichiren
1) Is an interference pattern by definition always caused by at least 2 particles interacting?

By at least two waves, not particles

A single photon at a time through the double slits will still create the interference pattern by interfering with itself. Or is that still classed as two waves?

a) each slit effectively becomes a source, so in a way you already have two waves

b) a single photon will be still observed locally, i.e. will leave a dot or count in a specific place on the screen, and not a pattern.

reply posted on 26-2-2010 @ 08:09 AM by LightFantastic

Originally posted by buddhasystem

a) each slit effectively becomes a source, so in a way you already have two waves

b) a single photon will be still observed locally, i.e. will leave a dot or count in a specific place on the screen, and not a pattern.

b) What I meant is that a single photon will hit in the 'light' areas rather than the 'dark' as if you were using multiple photons. If you know what I mean.

reply posted on 26-2-2010 @ 09:05 AM by Maslo

The double slit experiment, altough strange, can be explained if we assume that the photon acts like a probability wave between interactions.

The real weirdness is for example the quantum eraser experiment, where the nature seemingly conspires to prevent us from knowing which path the photon took by changing an event in the past.. crazy suff..

strangepaths.com...

reply posted on 28-2-2010 @ 09:20 PM by garritynet

I saw something in this thread about not knowing both the location and the momentum of a particle at the same time. There is a simple reason for that.

Simply put; Its just how the math works out. Everything else is just them trying to put into words what the math is saying.

There is an equation that that works. It will give you a good estimate to either the location or the momentum of a partice/wave. Its the only one they have that appears to work although it has many forms for different uses. This equation has values for both location and for momentum. As you shrink one value, say location, to a value of 1 the other part of the equation, momentum, approaches infinity. Thats why. There is more but in the end thats what it all comes down to.

Very interesting read, and a much better answer, for the non-PHD.

www.bbc.co.uk...

Edit to add: Before anyone starts talking about "Making a better equation..." just read the link. It has to do with how they make their measurements in the first place. These are the measurements that they place in their equations. Find a better way to measure(which I would really appreciate by the way) and then we can all start working on a better equation.

Edit again to add: When I said "to a value of 1" I was thinking in terms of probability where the value of '1' is certainty. I think it is actually that one side approaches 0 and the other approaches infinity.

[edit on 28-2-2010 by garritynet]

reply posted on 28-2-2010 @ 09:28 PM by SpacePunk

reply to post by Nichiren

The problem is the observer. Any quantum particle when unobserved takes on all states, or no states. Observation causes the quantum wave form to collapse into a quantifiable observation. It's like the Schrodinger's cat thought experiment. The cat is both alive, dead, and everywhere in between until it is observed. The observation causes the quantum wave form in the box to collapse and reveal the state of the cat... something like that.

It just gets really, really spooky.

reply posted on 28-2-2010 @ 09:40 PM by garritynet

reply to post by SpacePunk

Not really.

Quantum means that there has to be a minimum amount of anything interacting with anything else for something to happen. Your waves don't interact with each other a little here and there. They interact in discrete amounts.

So a wave has to move a discrete amount, of whatever it is a wave of, for something to happen. That "discrete amount" is the particle function. When you measure and "collapse the wave function" what you are doing is measuring that discrete amount of the wave that is necessary for something to happen. You cause the wave to interact with another wave so that something will happen and then you measure that something. Since that something is the result of discrete interactions we describe those discrete interactions as particles.

The interaction is the observation, not our interpetation of the measurement of that interaction. That which the wave interacts with is the observer. Blast an electron with a photon and the photon is the observer and the discrete amount of energy transfered between the two is the particle function.

Basically when you hit the electron particle/wave with a photon particle/wave there can be a discrete interaction that we call two particles hitting each other. This energy transfer changes the next interaction of each particle/wave which we take note of as our measurement since we designed the interaction to take place inside sensors. We then observe our measurements but with a different usage of the word "observe".

Since all the particle/wave observations that happen along the way for us to measure said particle/waves are basically the same we ignore them and only refer to the tested observation between the two as the "interaction".

The observer is the other particle/wave.

The cat is not literal. Alive or dead does not mean wave or particle. It means here or there. We do not open the box. Opening the box is the photon hitting the electron.

[edit on 28-2-2010 by garritynet]

[edit on 1-3-2010 by garritynet]

reply posted on 7-3-2010 @ 08:57 PM by predator0187

Ok the two-slit experiment:

Each atom fired at the slits is described by wave-functions that evolves in time. This wave-function is probabilistic in nature and tells us only the likely location of the atom. It is important here to stress that while we cannot regard the tiny atom as having suddenly turned into a spread-out wave function, the wave function provides us with the only means of tracking the atom from the moment it is fired until the moment it hits a particular point on the screen.

When the wave function encounters the slits it is spread out, splits in two with each piece going through one of the slits. I am describing the way the mathematical entity is changing, and it is by solving the Schrodinger equation That we can tell what the wave function looks like at any given time. We can never be sure what is going on or if there is anything going on at all, since we would have to look to check, but as soon as we look we will alter the experiment.

Ok, the problem here is that you want me to explain how the atom goes through two slits by using concepts familiar to you from everyday experience, unfortunately this is not possible. Whether we like it or not, such behavior is a feature of the quantum world and we must accept it. It does happen, and although we want a rational explanation, none has been found yet.

If someone could explain this it would be a breakthrough in QM. Quantum is a very mysterious subject and I will finish with a quote from Bohr.

'Anyone who is not shocked by quantum theory has not understood it." -Niels Bohr

People will come in an say they know quantum but nobody really does, it is beyond our grasp at this point and time, and if someone claims differently ask them for their nobel prize.