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INTRO:
What is a quantum laser micrometer? Very simply, a micrometer is a device to measure the width of a very small object. Usually, small widths are measured mechanically or electronically. With a laser quantum micrometer, nano-distances can be measured with a greater accuracy than can be measured by other means, and you can make one cheaply at home!
In this simple but detailed instructable I’m going to show you how to reconstruct my spin on the famous “double slit” experiment at home to illustrate some freaky quantum mechanical effects and how they work, find the width of a human hair, have stuff be in two spots at once, and “erase” information from the universe, showing that sometimes stuff acts like it is in two spots at the same time, but changes back to being at one spot once you interact with it. After completing this instructable, you will hopefully have a more complete understanding of quantum mechanics, what it means, why it is relevant, and how to creatively use it.
What people do not realize is that it is possible to reconstruct the very experiment that sparked the field of quantum physics right at home using only household materials. After one chemistry lecture in which one of my professors was explaining quantum mechanics, I bet one friend that I could perform the “double slit experiment” using only a human hair, a laser pointer, a string, a measuring tape, along with tape and some other common materials. What resulted from this is a new device that can be used to measure nano-distances right at home at a cost of around only a few dollars: the quantum laser micrometer (or Nestor's micrometer if you are feeling like giving an honorable mention).
Quantum Physics is a relatively new field of physics. Just as Sir Isaac Newton’s theories explained the actions of the very large, quantum mechanics focuses on the mysterious world of the very small, and has made several startling claims. Quantum Physics was founded on the notion that matter behaves like particles (solid) when it is a part of a large object because it has a larger influence on its environment, but behaves more like a wave (in many possible places at once, like a cloud or a “wave of potentials” that radiates outward) when it is smaller and interacts less with its environment. In fact, the notion of particles themselves is not as "solid" as one might initially think, but can be thought of distributions of energy (such as light) at discrete quantities ("quanta"). This is initially a difficult concept to grasp, but essentially the wave/particle duality means that matter (stuff) is in no one definite spot at once until the universe records its presence there by interacting with it (such as when it bumps into something or light hits it); thus smaller particles are more likely to behave more “wavelike” and larger pieces or matter behave more “solid.” I’ll talk about this more later.
What is a quantum laser micrometer? Very simply, a micrometer is a device to measure the width of a very small object. Usually, small widths are measured mechanically or electronically. With a laser quantum micrometer, nano-distances can be measured with a greater accuracy than can be measured by other means, and you can make one cheaply at home!
In this simple but detailed instructable I’m going to show you how to reconstruct my spin on the famous “double slit” experiment at home to illustrate some freaky quantum mechanical effects and how they work, find the width of a human hair, have stuff be in two spots at once, and “erase” information from the universe, showing that sometimes stuff acts like it is in two spots at the same time, but changes back to being at one spot once you interact with it. After completing this instructable, you will hopefully have a more complete understanding of quantum mechanics, what it means, why it is relevant, and how to creatively use it.
What people do not realize is that it is possible to reconstruct the very experiment that sparked the field of quantum physics right at home using only household materials. After one chemistry lecture in which one of my professors was explaining quantum mechanics, I bet one friend that I could perform the “double slit experiment” using only a human hair, a laser pointer, a string, a measuring tape, along with tape and some other common materials. What resulted from this is a new device that can be used to measure nano-distances right at home at a cost of around only a few dollars: the quantum laser micrometer (or Nestor's micrometer if you are feeling like giving an honorable mention).
Quantum Physics is a relatively new field of physics. Just as Sir Isaac Newton’s theories explained the actions of the very large, quantum mechanics focuses on the mysterious world of the very small, and has made several startling claims. Quantum Physics was founded on the notion that matter behaves like particles (solid) when it is a part of a large object because it has a larger influence on its environment, but behaves more like a wave (in many possible places at once, like a cloud or a “wave of potentials” that radiates outward) when it is smaller and interacts less with its environment. In fact, the notion of particles themselves is not as "solid" as one might initially think, but can be thought of distributions of energy (such as light) at discrete quantities ("quanta"). This is initially a difficult concept to grasp, but essentially the wave/particle duality means that matter (stuff) is in no one definite spot at once until the universe records its presence there by interacting with it (such as when it bumps into something or light hits it); thus smaller particles are more likely to behave more “wavelike” and larger pieces or matter behave more “solid.” I’ll talk about this more later.
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Signing UpStep 1Understanding the Experiment
Okay I don’t want to scare any of you away. This experiment is actually really simple, but the concepts behind it are somewhat confusing at first (it is quantum physics after all). Basically we know that matter behaves “solid” like a single point if it’s a really big glob of it, but the smaller the glob gets the more it behaves like a “wave.” Normally when people think “wave” they think of ocean waves or sound waves. When the word “wave” is used here, it means simply that like ripples in a pond, if a wavelike particle were moving, where it would be at any given time after it started moving would be anywhere and everywhere along a “ripple” that radiates outward from the source where it began moving. The picture above shows what I mean. That’s one of the “spooky” quantum effects we will illustrate.
Since we know that matter (things) should only be in one place at once, not two, the instant that one of the ripples hits another object, thus “interacting” with the universe, the wavelike behavior of the blob of matter disappears and begins to act like it’s in one spot (“solid”) again. So in other words if the ripple bumps into something or we try to see the blob acting like it’s in many spots at the same time the blob says to itself “oh no! They’re catching on to me… I’m going to act like I’m in one spot again.”
Even though stuff acts like this, we can still catch it behaving like it’s in many spots at the same time and acting like a wave. The “double slit” experiment is how we do this. If we pass blobs of stuff through two slits and it creates a pattern of two bands of hits on the back of the wall we know that it’s acting like a solid particle. If it makes a pattern with many bands of hits on the back of the wall we know that it’s acting wavelike.
Since we know that matter (things) should only be in one place at once, not two, the instant that one of the ripples hits another object, thus “interacting” with the universe, the wavelike behavior of the blob of matter disappears and begins to act like it’s in one spot (“solid”) again. So in other words if the ripple bumps into something or we try to see the blob acting like it’s in many spots at the same time the blob says to itself “oh no! They’re catching on to me… I’m going to act like I’m in one spot again.”
Even though stuff acts like this, we can still catch it behaving like it’s in many spots at the same time and acting like a wave. The “double slit” experiment is how we do this. If we pass blobs of stuff through two slits and it creates a pattern of two bands of hits on the back of the wall we know that it’s acting like a solid particle. If it makes a pattern with many bands of hits on the back of the wall we know that it’s acting wavelike.
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It was a good choice for a demonstration to elucidate your explaination as it is a very intuitive and accessible set of behaviors - while quantum mechanical explainations are often very abstract. This 'ible provides an accessible perspective on QM.
While I agree with kelseymh & xellers that you did not "demonstrate" in the sense that "demonstrate"="provide evidence", I do not think that was your intention. I think you meant to give a "demo" that could be referenced during your explaination. It was a fun demo and I think other readings will make more sense now.
Good 'ible!
A better analogy would be trying to drive your truck up a steep hill that ends in a vertical cliff face. No matter how fast your truck goes, it will NOT be able to drive up that cliff. Speed becomes irrelevant once the cliff is vertical.
Light in glass goes slightly slower than it does in air (and different wavelengths are slowed differently, which is why you see rainbow effects on prisms) BUT due to relativity, it all works out OK.
Speed of light remains a constant.
For example, you could get on a spaceship travelling at 0.99 speed of light and turn on a torch shining forward. You haven't just exceeded the speed of light. From the point of view (frame of reference) of not being on your spaceship, your torch shines at the speed of light and from your point of view it shines at the speed of light too...
Sounds crazy? Yes it is. But trust me, it works. Since Einstein figured it all out there hasn't been a serious disagreement with the theory.
Going back to your example about 2 trucks. One truck is always stronger because it can apear to bend the laws of physics to make sure it is stronger.
And remember, if you've already done 3 impossible things this morning, why not join me for lunch at the restaurant at the end of the universe.
Malus' law gives the intensity of light transmitted through a polarizer based on the angle between the initial direction of polarization of a light wave and the direction of the polarizer. When the angle is 90 degrees, cos theta is zero, so no light is transmitted. However, if we add third polarizer and split the 90 degree angle into two 45 degree angles, then cos theta is nonzero, so some light is transmitted through each step. Think of it in terms of vector projections. If you try to project a vector in an orthogonal direction, then it becomes a zero vector. However, if you project it twice in non-orthogonal directions such that the final direction you project in is orthogonal to the original vector, then you won't end up with a zero vector.
I'm not trying to be mean, just constructive! I think you could still mention this experiment in your instructable, so long as you explain it correctly.
Xellers
You're using an undimmed laser pointer. That means that the entire experiment can be analyzed purely classically, using simple wave optics. Huygen's did it, and got the right answer, more than 350 years ago.
If you really want to do something quantum mechanical, then you need to reduce your laser power until you get one photon at a time going through your device. Then you need a way to accumulate hits from those photons in order to build up the interference pattern.
As it is, you're just blowing smoke.
This is a fundamental principle of scientific pedagogy. You need to understand that if you are going to design or create scientific demonstrations.
If you are aming a demonstration at "everyone," then you need to use a process which is easily recognized as being non-classical, so that only a quantum mechanical explanation can describe what is being shown.
The purpose behind this instructable is to demonstrate some of the ramifications of quantum mechanics, and how to use them creatively to do something new. In fact.
Your experiment does not directly demonstrate anything quantum mechanical, unless you assume quantum mechanics to begin with (which is a trivial logical fallacy).
The interference pattern does not have to be the result of quantum behaviour. It can be calculated exactly using simple, classical wave mechanics. Christian Huygens did so in his 1678 work Treatise on Light. When you have a source which output large numbers of photons, the light behaves perfectly classically, and does not need any quantum mechanics to be analyzed. This is itself a mystery (the quantum-classicial transition), but it is irrelevant to the outcome of the experiment.
You can do exactly the same experiment you have described without recourse to a laser, and get exactly the same result: use a simple white-light source (sunlight, a candle, an incandescent light bulb), put it through a prism, and then put that through a pinhole to pick off one specific color (wavelength). Using that as your light source, you can generate the same interference pattern.
As I wrote above, if you really want to demonstrate something quantum mechanical, which cannot be explained classically, then you need to put one photon at a time through the experiment, record the individual hit positions, and show that the interference pattern develops over time from those individual hits. Please read the two I'bles I cited to see how you can set up such an experiment.
If you want to demonstrate QM, then you need to choose a phenomenon which cannot be explained with simple classical physics. The photoelectric effect (the frequency threshold is independent of intensity) is a good example. Self-interfererence with single particles is another.
The double-slit experiment, on its own, is not a demonstration of quantum mechanics. I can build and demonstrate the double-slit experiment with water waves or with sound waves. The same setup with light shows the same effect. This proves that light is a wave phenomenon (that is, good old Maxwell's EM). It doesn't say anything about the particulate nature of light.
If you want to claim (which is all you're doing in this I'ble) that light is quantum mechanical, then you have to assume the conclusion in order to interpret the double-slit experiment that way. That is a logical fallacy, and a pedagogical failure.
No doubt it is true, but this experiment would work whether it were true or not. Nor does it prove that photons are quantum particles.
Or maybe I should just go back to making wooden desklamps...