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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.

Step 1: Understanding 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.
Your instructable is a wonderful demonstration of Quantum theory for the laymen, everything that I have read concerning the double slit experiment says exactly what you stated concerning quantum mechanics and the explanation of its effect. It seems kelsymh doesn't get enough recognition where he supposedly teaches at and wants 15 minutes of instructable fame by schooling someone on a basic demonstration. I appreciate your post and think that people (ie kelsymh) who have the OCD necessity to criticize shouldn't waste everyone's bandwidth with their own insecurities because they can't get tenure. Thanks for the instructable.
Where I was working previously, we used 650nm lasers, diffused, reflecting off a moving mirror shard and back to a camera to measure distance traveled by our nano indentation devices. When an interference line moved across a reticule on the computer screen it was measured by pixel hue to determine the start of a line. It was very accurate and was used to calibrate the device for travel. The machines are used for indentation into materials to measure hardness, modulus, etc. using a calibrated diamond (three sided pyramid) tip which was really best seen under a microscope. Calibrating the tip involved indentations into a silica wafer and adjusting parameters until it read the silica properly. The machines are used in various places, especially in the microchip industry. We developed a way of using the device to scan the surface of a sample and make a 3D picture of the surface, such as a microchip circuit.
I found *this post* to be a very interesting description of a practical application of the phenomenon in this instructable. I love learning about the application of observations to solve a problem or perform a task.
Need to correct you on that last sentence; the wavelength is a function of color, not intensity. I like your instructable. Bring us more of your ideas - <a href="http://castironenamelcookware.org">enameled cast iron cookware</a>
Thanks for this explaination &amp; acompanying demonstration. <br><br> 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.<br><br>While I agree with kelseymh &amp; xellers that you did not &quot;demonstrate&quot; in the sense that &quot;demonstrate&quot;=&quot;provide evidence&quot;, I do not think that was your intention. I think you meant to give a &quot;demo&quot; that could be referenced during your explaination. It was a fun demo and I think other readings will make more sense now.<br><br>Good 'ible!
what will happen if i will use a 1000mw laser for this?
About Light Speed being the ultimate speed limit that we assume at this time for now. Does not seem to be correct just like assuming one truck is stronger or faster than the other when you hook them together with a chain. And they both give it all they got and most of the time one will always be better or faster or stronger. After saying that, then imagine that you try the same experiment with Light and a Black Hole. As we know that the speed of Light does not overcome the suction or vacum speed of the Black Hole. So in my book the Black Hole is the winner of this contest of speed. Although I have never heard of any calculations of the speed that a Black Hole Travels while consuming everything in its path. But it's a bit faster than Light Speed. Just my opinion. But hopefully in the near future we will find a way around these speed limits and jump right to it.
The gravitational pull of a black hole doesn't have a &quot;speed&quot;. Gravity is curved space. <br><br>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.
Hmm, there is weird stuff that goes on near the event horizon, like time dilation. Also, the black hole doesn't move much, only the light/matter going into it does. So, the light going in is still moving at the speed of light, even if that seems to be a higher speed of light than the speed of light in normal space. <br><br>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.<br>Speed of light remains a constant.<br><br>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...<br>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.<br>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.<br><br>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.
Maybe the Two trucks was a wrong example. But at the event horizon someone would shine a light back away from the Black Hole, yes you would be able to see the light eventually. But once the light crossed the event horizon the vacuum of the Black Hole would start taking over the light to the point that even at Light Speed the light can not escape the Black Hole. So that would show a clear example that the speed of the vacuum of a Black Hole would be pulling so hard and fast that the speed of light can not travel fast enough to over power the speed of the vacum. Even at the point of view anywhere with end the event horizon it still cant escape the speed of the vacuum. So we are not talking about the vacuum being just fast enough to over power the speed of light but a considerable amount faster. And I would like to join you for lunch at the end of the universe but my ship is not up to speed yet. And lunch would probably get mighty cold by the time it gets me there. But the next time your headed that way and have the room I would go with you.
Need to correct you on that last sentence; the wavelength is a function of color, not intensity. I like your instructable. Bring us more of your ideas!
Wavelength and color are related but all that I am saying is that with increased intensity, the signal is stronger and it is easier to measure accurately
see the images
Very nice looks really neat
The experiment described here is a good demonstration of ordinary, classical diffraction. It involves ordinary, classical interference of light waves, and the effect can also be demonstrated with actual ripples in a tank of water. Some hands-on science museums contain exhibits which do just that (there's a good setup at the EcoTarium in central MA, for example). I think the best way to improve this instructible would be to remove the (incorrect) explanation based on quantum mechanics. The explanation here might really confuse someone who is trying to learn about the actual Young's double-slit experiment, or wave-particle duality, or the uncertainty principle, or the quantum eraser experiment. Wikipedia has good articles on each of those topics, none of which are relevant to the experiment described here.
Please see the discussion I had earlier about this
Your number 'n': is this the number of bright spots from the center of the laser 's wall point to the outer spot in one direction only, or is it the TOTAL number of bright spots in BOTH directions from where the laser is centered on the wall? <br>
N is NOT in both directions
Good read. Good science. Lots to way bright minds. Thanks guys
It's a lovely demonstration, but you don't need to throw around any of your quantum mechanical mumbo jumbo to explain it. <br><br>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.<br><br>If you really want to do something quantum mechanical, then you need to reduce your laser power until you get <a href="https://www.instructables.com/id/Observing-single-photons/">one photon at a time</a> going through your device. Then you need a way to <a href="https://www.instructables.com/id/Double-slit-Interference-Experiment/">accumulate hits</a> from those photons in order to build up the interference pattern.<br><br>As it is, you're just blowing smoke.
The interference pattern is a direct result of the quantum behavior of photons, and while years ago the behavior of light could be modeled, it was not understood until the last 50 years. In fact, lasers themselves have not been around that long.<br><br>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.
I'm sorry. I am a professional experimetal particle physicist (B.S. UCLA 1988, Ph.D. Caltech 1996, currently on research staff at the SLAC National Accelerator Laboratory). I do this, and teach it, for a living.<br><br>Your experiment does not directly demonstrate anything quantum mechanical, unless you <i>assume</i> quantum mechanics to begin with (which is a trivial logical fallacy).<br><br>The interference pattern does not <i>have to be</i> the result of quantum behaviour. It can be calculated <i>exactly</i> using simple, classical wave mechanics. Christian Huygens did so in his 1678 work <i>Treatise on Light</i>. When you have a source which output large numbers of photons, the light behaves perfectly classically, and does not need <i>any</i> quantum mechanics to be analyzed. This is itself a mystery (the quantum-classicial transition), but it is irrelevant to the outcome of the experiment.<br><br>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.<br><br>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.
The interference pattern arises whether or not you produce one photon at a time or not, and so do the effects. The &quot;classical&quot; wave behavior of light is a result of the particle/wave duality of photons. This experiment relies directly on quantum mechanical principles and is a good way to demonstrate them. For example, it is the Heisenberg Uncertainty Principle that allows for greater accuracy of measurement with shorter wavelength (position). You can produce a beam of particles (photons) via a prism and through filtering but I really don't see the point of this? For the sake of simplicity a laser pointer can be used as a beam source to reproduce the Double Slit Experiment. Also, I understand that you went to Caltech and everything, and I am myself an engineer from UCB, but all I'm doing here is giving an instructable for beginners to understand and demonstrate some quantum-mechanical phenomenon. The wavelength of light, for example, determines the number of bands on the interference pattern, just like the de-broglie wavelength of electrons determines the interference pattern produced by an electron beam. Photons can be regarded as quantum particles and their wavelike behavior can be measured because they are, just like electrons or any other particle.
Don't teach your grandmother to suck eggs. If you're a Berkeley engineer, then presumably you know something about teaching, and about explaining complicated issues.<br><br>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.<br><br>The double-slit experiment, on its own, is <b>not</b> 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.<br><br>If you want to <i>claim</i> (which is all you're doing in this I'ble) that light is quantum mechanical, then you have to <b>assume the conclusion</b> in order to interpret the double-slit experiment that way. That is a logical fallacy, and a pedagogical failure.
Photons can be interpreted as quantum particles and more readily available than electrons or other particles to the household hobbyist, so thus I used them, relying on quantum mechanical principles to explain the classical behavior. Its all self-consistent. Physically, this experiment makes sense classically and in qm. I dont see how using photons is any less &quot;legit&quot; than electrons or whatever else. Also, firing one quantum at a time is sort of entertaining, but unnecessary and more difficult, as three pattern will be the same, all it does is show that photons also fall under the wave/particle relationship, but we already know that because we are using them as quantum particles (as explained in the instructable). There is no fallacy, everything is self-consistent. Photons are quantum particles, we dont need to demonstrate it for it to be true (unless you feel that we need to also break down the laser pointer into its components and also demonstrate that a battery produces volts before allowing the assumption that it powers the laser). Personally, it seems sort of unnecessary
Here is where you make the assumption that kelsymh was talking about: &quot;Photons are quantum particles, we dont need to demonstrate it for it to be true&quot;<br><br>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.<br><br>Or maybe I should just go back to making wooden desklamps...
If photons were not quantum particles a coherent beam would not display wavelike behavior. The purpose is not to show explicitly that photons are quantum particles, but rather that since they are they behave this way, and thus can be creatively used in the way detailed in the instructable.
The thing is that 'photon' is a loaded word in this context. The idea that light is made up of photons is <em>part of</em> the quantum mechanical theory of light, so if you were trying to demonstrate or prove quantum mechanics, you can't start by assuming people agree that light is made up of photons.<br> <br> The philosophical question is how did this:<br> <br> http://en.wikipedia.org/wiki/Corpuscular_theory_of_light<br> <br> then this:<br> <br> http://en.wikipedia.org/wiki/Christiaan_Huygens#Wave_theory<br> <br> turn into this:<br> <br> http://en.wikipedia.org/wiki/Quantum_mechanics<br> <br> I.e. what happened in the 1920s to convince people that they needed a new theory to explain how light behaved.
This is a misunderstood premise. The purpose of this instructable is not to convince people that photons are quantum particles.
Fair enough - I was just thinking about how you and kelseymh ended up talking at cross purposes. Like I said in my other reply, you're starting from what we know now and saying 'look isn't it cool what we can do with this', whereas he's talking about how scientific theories evolve and how science is taught.<br> <br> I like all the philosophical stuff about how do we decide whether a theory is worth adopting, so I was just reflecting on that really.
I think I'm going to trust the high-engergy physicist on this one, bud.
I think you and kelseymh have different things in mind. You've posted a neat instructable about how to measure a human hair using laser light, and thrown in some stuff about quantum mechanics as part of your description. I.e. you're starting from what we know now and using it to do something (measure a hair). He's talking about a more philosophical point around what you have to do to demonstrate that a new theory is worth adopting.
My grandmother is dead
You seem to agree that photons are particulate and quantum particles, yet are refuting any treatment of them as such. This experiment/demonstration can be understood classically and in qm. The universe is self-consistent. For example, is Hawking Radiation a ramification of information theory or particle physics? It's both because the universe is self-consistent.
I think where your hangup is is that you do not feel that this demonstration falls under the realm of &quot;quantum mechanics&quot; because I am using photons as the quantum particles (though a quantum particle is a quantum particle no matter what it is), and that since historically they have been understood to be waves anyways that it should instead fall into the realm of &quot;optics&quot; or &quot;classic physics&quot; or whatever else. Historically, the properties of light could not be fully understood. It is only after the avent of quantum mechanics that it could really be *explained. It is a quantum-mechanical phenomenon that we observe in this demonstration, abd even though photons have no mass they are regarded as having a relativistic mass (see author's notes). Keep in mind that this demonstration is aimed towards everyone, not just physicists, so it is designed to be simple.
No. My hangup is that you're trying to use a classical phenomenon to &quot;demonstrate&quot; quantum mechanics. That means that it <i>doesn't</i> actually demonstrate quantum mechanics, since an ostensibly &quot;simpler&quot; (i.e., classical) explanation can describe the phenomenon.<br><br>This is a fundamental principle of scientific pedagogy. You need to understand that if you are going to design or create scientific demonstrations.<br><br> If you are aming a demonstration at &quot;everyone,&quot; then you need to use a process which is easily recognized as being <b>non-classical</b>, so that <i>only</i> a quantum mechanical explanation can describe what is being shown.
Very cool experiment! Is there a chance you could add more photos of the test apparatus and setup? Perhaps a few examples of equations so people doing the experiment know they're on the right track?
Yeah ill add more soon- if your calculated hair width falls within the range 0.00001m and 0.0002m you are most likely doing it right. From my experience, alot of cheapy red pointers don't work very well, mainly because they are dim, don't usually have an accurate wavelength, and don't produce many bands.
The &quot;quantum eraser&quot; experiment you describe makes for a pretty interesting demonstration (my chemistry teacher confuses students every year by showing them that the third polarizer can allow light to pass though), but the reason for this is purely classical:<br><br>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.<br><br>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.<br><br>Xellers
*particle* (typo)
It's like this: Hawking Radiation can be understood to be a ramification of a number of theories, and many could claim &quot;this isnt information theory, its possible physics&quot; etc. It doesnt work like that, its a ramification of both. The universe is self-consistent so it can be understood to be a ramification of both.
It is true that this can be explained classically, but it can also be understood to be a ramification of Heisenberg's Uncertainty Principle. The universe is self-consistent, so thus both reasons are correct, otherwise either reasoning would be violated and both are true.
I think that a few are misunderstanding the premise and purpose here, so in light of what I have already said, I dont know that i'm really going to change some people's minds, especially since the atmosphere has quickly changed from a discussion to condescending and sarcastic commentary. I have provided a detailed description in the instructable as to how this relates directly to quantum mechanics, though classic mechanics is certainly also involved. Waves can be understood classically, but seeing a photon as a particle/wave is a conclusion based on quantum mechanics, and much of the phenomenon can be understood with greater accuracy with an understanding of the underlying quantum mechanical principles involved (explained clearly in the instructable). Again, remember I'm catering to everyone, not just people with an advanced background in physics or math, so I made it very basic and easy to follow (do you really think a breakdown of wave functions and trying to use advanced calculus would make for many views?). If you do not see the correlation between quantum mechanics and this demonstration, I really dont think I can help you any further.

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