# I got my quantum spin measured in an MRI

## Метаданные

- **Канал:** Looking Glass Universe
- **YouTube:** https://www.youtube.com/watch?v=ClZgYZCUqqc

## Содержание

### [0:00](https://www.youtube.com/watch?v=ClZgYZCUqqc) Segment 1 (00:00 - 05:00)

I'm about to do an MRI and have it measure the quantum spin of the protons in my body, except I don't understand how that's possible. When I was studying physics in university, they told us that no one understands quantum spin. So how come I could just walk into a hospital and have them measure the spin of all of my protons? And then use that to tell me how messed up my organs are. I'll tell you about my MRI results later. But first I really want you to see this. Oh. This is an MRI, and as you can see, an MRI is basically a massive magnet. This is the reason that they made me swear up and down that I wasn't wearing any metal jewellery or anything because the strongest MRIs that you can get at a hospital are about as strong as the magnets in the Large Hadron Collider, and there are research grade MRIs that are way stronger. So firstly, how is it even safe to put yourself inside such a massive magnet? Like for example, shouldn't we be worried about iron? There's iron in our blood and iron is attracted to magnets. Well, thankfully in our blood, the form iron is in hemoglobin isn't actually attracted to magnets. So we don't have to worry about iron being ripped out of us when we're in an MRI. But there is another important source of magnets in your body. And that's your protons to explain. Let me show you this experiment. I've got some normal copper wire here, and as you can see, this is not magnetic. If it were, you could use it to pick up these pins, but now I'm gonna attach it to a battery and you can see that this is gonna form a circuit because we'll get some tiny little littles box there. And suddenly it is a magnet. This is one of the most surprising things people ever discovered in physics because it shows that there's a link between magnets and charged particles. Here's why this wire loop is full of electrons, but at first, each of them is just sitting there. But when you put a battery on, it forces the charge particle to rotate around, and now suddenly this is a magnet. So the rule we discovered is whenever you have a positive or negatively charged particle rotating around, it's a magnet. But let's shrink this loop until the proton here is just spinning around. This should still be a magnet. So if a proton is a ball spinning on its axis, this rule would say that it must be magnetic. In the early 19 hundreds, they realized that protons are always magnetic, and same with electrons. So naturally they assumed that they must be spinning, and that is what's making them magnetic. This is where the term quantum spin was coined. But it turns out that this picture of spin is oversimplified and we will come back and correct that a bit later. So for now, let's just say that protons and electrons are spinning balls, and that's what makes them magnetic. But if all of the electrons and protons inside of me are magnetic, then how come I'm not a magnet overall? For electrons. The answer is that misery loves company. Electrons in your body tend to pair up in molecules where each member in the pair is spitting in opposite directions. So they're like magnets pointing in exactly the opposite direction to each other, so they cancel out and overall, your electrons aren't magnetic. But if we look at a proton, that's all alone in a H2O molecule. It's not paired. And there's many, many of these unpaired protons in your body. So why don't they make us magnetic? It's because each individual proton is facing a random direction. So for example, this proton cancels out that proton, and in the end, you're not magnetic. Overall, that changes inside an MRI though remember that in an MRI, you're lying inside a massive magnet where this is north and this is south. I've simulated this by putting some north facing magnets along this side and south facing ones on this side. So now let's see what one randomly oriented proton will do. When it's in the MRI. You can see how quickly it aligned itself to the field. So if each individual proton actually did align itself to the field like this, you would become a super strong magnet. But don't worry, not all your protons can align. There's loads of energy in your body that knocks around each proton that stops them aligning even though they want to. An estimate I've heard is that only a one in about a million protons can actually end up aligning to the field. So your magnetic inside of an MRI

### [5:00](https://www.youtube.com/watch?v=ClZgYZCUqqc&t=300s) Segment 2 (05:00 - 10:00)

but not that magnetic. And as soon as you're out of the MRI, all of that jostling is going to just randomize the direction of your protons. So they're not going to on net be aligned anymore. And so you're not gonna be magnetic as soon as you're out of the MRI. Well, that's reassuring that you don't walk out of an MRI with magnets sticking to you for the rest of your life. But let's think about a spinning proton when it's in the MRI. Again, when they spin like this, they're like magnets facing this way. So in the MRI, which way will a proton want to spin? Well, since the MRI magnet looks like this, the protons will want to have its north facing down. That means that if your proton is like this spinning top, then it's in its most relaxed state when it's allowed to just hang like this. And so this is how they start out in the MRI. But we can't just let the protons relax, right? The actual point of the MRI is that we give them a jolt and then we see how they react to that jolt. The idea is that if we give this jolt to all parts of your body at once, the protons in this part of your body are going to react differently than the protons in that part of your body, and that's because in this the proton might be surrounded by. Bone, but in this part it's surrounded by tissue and that makes both of them react a little bit differently. So telling the difference between how all of these protons react will let you map out what's happening in the whole body. But how is this jolt administered exactly? Well, after they slid me into the MRI borehole, suddenly everything started vibrating. And the sounds were so bizarre. There was this bit that was like pew, pew, DUUUSH, DUUUUSHH. It felt like being in an intergalactic space battle. It was like the wave. It was honestly so confusing, but it turns out that all that they were doing was shining radio frequency light on me, and I couldn't see that because radio frequency light is invisible to the human eye, but I could hear it because to make that light, you had to turn on and off some like very noisy coils quite quickly. And so apparently that's where the sounds were coming from. But honestly, at the time it was quite scary. But what's that light gonna do to my relaxed protons? Well, the light is at exactly the right frequency for those protons to absorb, and after that, they're in a high energy state. So as an example, let's look more closely at this spinning top. So it looks really fancy, but there's actually nothing to it. It's very similar to just like a regular spinning top. The only difference is that when I pull this string, it makes the middle bit rotate, so it's like the middle bit really that's rotating. Now, if the top isn't spinning and I start it in a high energy state, then it will just fall back down. But watch what happens when instead, I start it spinning and then put it into its high energy state. The why doesn't it just fall straight down? It's 'cause spinning objects are honestly so weird. And this particular phenomena is called lamore procession, and it is one of the hallmarks of spin. So if you watch this video, you can see how this object, instead of just dropping at some point, like you kind of expect it gracefully, spirals down. You might think that it fell here, but let's replay that really slowly. Look how it gradually loses height and eventually it's nearly vertical and it still hasn't fallen. If this table didn't get in the way here, it would've gracefully spiraled all the way down. So a spinning object like this will realign to its most relaxed state by slowly and gracefully circling around until eventually it's pointing downwards. And incredibly, this is what protons do as well. But the question that matters medically is how long will it take the proton to go from its excited state down to its relaxed state. Well, this all depends on the environment of the proton and how easily it can transfer energy from itself to that environment. So, for example, look at these two spinning tops. I've added some tape to one, to add friction and make it easier for it to lose energy more quickly. And as you can see, that one drops more quickly than the other one. That's because it was able to more effectively transfer its energy to the environment. And in a similar way, a proton that's surrounded by, let's say blood will take longer to relax

### [10:00](https://www.youtube.com/watch?v=ClZgYZCUqqc&t=600s) Segment 3 (10:00 - 13:00)

than one that's surrounded by fat. Because fat more readily absorbs the energy from the proton relaxation. Time is the time it takes for a proton to go back into its relaxed state. And since we know the relaxation times of the different environments in the body. If you are able to measure the average relaxation time for a particular part of the body, you would be able to tell what's there, but how do you actually measure the relaxation time? Well, it turns out that protons are actually emitting radio frequency light the whole time while they're spiraling down. And so if you are able to actually measure the radio frequency light coming from those protons, then you can just time how long that signal goes, and that's the relaxation time. And actually that's exactly what they did. They had this sheet that they put on top of me in the MRI and they called it a camera, and I guess it was a camera, just wasn't a camera in the regular frequency of light. It was a camera in the invisible radio frequency, and the images I got out was so incredibly helpful. I have a condition called endometriosis that causes these growths to pop up in my abdomen and they have this unfortunate side effect of, um, gluing together my organs, but I also have a fair bit of scar tissue from previous surgeries and it also can cause some adhesion. And so sometimes in some scans it can be a bit hard to tell those two apart. But not in an MRI because it turns out that scar tissue and, uh, endometriosis growths have quite different relaxation times, so they're very easy to tell apart. And MRIs don't just measure relaxation time either. There are all kinds of different ways that an MRI pokes and prods these protons to figure out exactly what their environment is. So it gives a super detailed picture of what's going on inside. Which is why I can't believe that all of this comes from quantum spin because here's the crazy thing, protons aren't actually spinning. I don't understand this because in every other way, protons act like they really are spinning charge balls. Like why do they do lamore procession? Lama procession is such a specific thing to spinning objects. So why does quantum mechanics decide to mimic that even though nothing is actually spinning? Honestly, I don't get it, but I am so grateful to the people who took this esoteric idea from the quantum world and used it to help patients like me. I mean, I went in for a completely routine MRI, and I really wasn't expecting to see anything because I thought we were kind of on top of it. But the MRI scan revealed that, you know, these growths had kind of aggressively started growing into some of my organs in a way that. Would've become irreversible pretty quickly. So yeah, I am very grateful that getting my K spin measured meant that they caught that in time. I.

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*Источник: https://ekstraktznaniy.ru/video/25479*