What is a quantum state? How can two particles share the same state? What is entanglement, and does it really allow for faster-than-light communication? I discuss these questions and more in today’s Ask a Spaceman!
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EPISODE TRANSCRIPTION (AUTO-GENERATED)
Stay tuned at the end of the episode for a special announcement. Spoiler alert, I wrote a book. PMSider.com/book for more info. Anyway, have you ever encountered mystery boxes, blind bags, baseball cards, Pokemon cards? Do Pokemon even have cards?
I have no idea. Kinder Surprise eggs. Like, anything where and I know kids are, like, crazy obsessed with this kind of stuff. I was as a kid and as an adult, it's 100% baffling, but here we are, where it's some sort of prize in a box. You buy it, you pay a couple bucks, you get the thing, and you don't know exactly what is in the box or in the bag or in the pack or the whatever.
You don't know what it's gonna what you're gonna get, but on printed on the bag or the box or the pack is a list of what you might get. The entire collection, here's everything available, and you're gonna get one of these once you open it up. But you don't know what you're gonna get. Some of the items will have, rarities associated with them. Like, oh, oh, this one is super rare.
One in a million chance that you'll actually grab this one. Some are really common, like, basically every single one has has this particular item. You know that only one kind of item is inside of your mystery box, your box, your blind bag, your baseball card pack, your whatever. But you don't know which you're gonna get. It'll be revealed once you open it up.
But you know that there's only one kind actually in there. It exists. It's there. You can you can hear it if you rattle the box around, but you don't know which one you're gonna get. That's a blind box, a blind bag, a mystery box, whatever we're all familiar with.
Instead, let me give you a quantum blind box. A quantum mystery box. Inside of it is not a toy or a card or an action figure. It's a fundamental particle, like an electron, with some property that you want to measure. Maybe you want to measure its speed or its position or its span.
It doesn't matter. There's something about this electron that you want to measure. The first of many mind blowing sentences in this episode, the first step into the world of quantum weirdness that we're gonna explore, is that in this quantum mystery box, all possible results exist simultaneously. I'll say it again. My notes even are telling me right now say it again, so I'll do it.
All possible results exist simultaneously. This can apply to position, to speed, to spin. Whatever property you wanna measure, all possible results exist at the same time until you actually go to perform the measurement. I need to define all possible results. If you read the back of that mystery box and it tells you that some items are common, some are rare, some are super duper triple rare, Congratulations.
You've just read something in mathematics we call probability distribution. It's a mathematical equation. Feel free to drop that jargon term in anywhere you want in casual conversation. It's a math equation that describes the results that you could get when you open up the box. It's it's your chances for getting any particular item.
That probability distribution, that math equation has become vitally, vitally important for what we're about to explore. And, of course, I'm talking about, today, entanglement. Tons of great questions coming in via multiple channels about entanglement. We have at Infirmus on Twitter, at p gravinese on Twitter, Derek m, email, John r Facebook, Omega Chess Facebook, Messimiliano s Facebook, Chris s on Facebook, Michael e, email, Martin n on Facebook, at Infirmus. Again, on Twitter with the second question, Elizabeth c on email at bravo one zero two, Twitter.
Joe r on email, James w on email, at josh petri on Twitter, kayla m on email, david a on email, and at petrodude underscore on Twitter. All asking questions about this very, very intriguing thing called quantum entanglement. If you have your own questions, hit me up on askaspaceman dot com, askaspaceman at g mail dot com, Twitter, Facebook. My name is at paulmatt sutter. I take questions any way you can send them to me.
So we've got a quantum blind box, a quantum mystery box where all results simultaneously exist until we make the measurement and that's critically important to quantum mechanics. As a side note, have you heard the story of the dead cat? This is a thought ex I know I know this episode went in a very weird direction very quickly, but bear with me here. The thought this is a thought experiment cooked up by Erwin Schrodinger, and he'll be a star of a future episode. Don't worry.
But feel free to ask. You might have heard of this thought experiment. And the thought experiment is you put a cat in a box, there's a radioactive material in there that has a perfect fifty fifty chance of decaying and killing the cat. So the thought experiment goes, if this is a quantum mystery box with a cat inside of it, that the cat is both dead and alive until you open up the box and you actually observe either a dead cat or a dead cat. But until you make that observation, until you make that measurement, the cat simultaneously exists in both states.
That's ridiculous. That's stupid. No one would believe it. Of course the cat is dead or alive. You just haven't figured it out yet because you haven't opened up the box.
It doesn't exist in both states. The cat is not a quantum system. A lot of people use this thought experiment to show the weirdness of quantum situations and quantum situations are incredibly weird, but a cat in a box is not a quantum system. Erwin Schrodinger was using this thought experiment to show how ridiculous it is to apply quantum thinking into non quantum situations. Just because the quantum world is weird, doesn't mean everything in the normal macroscopic world is up for grabs.
That's just a side note about quantum states and measurements and observations. We are talking about quantum systems here that we have prepared very carefully. They're usually subatomic that are dealing with very specific scenarios. It's gonna get weird, but it doesn't mean that your normal everyday life is weird. It might be.
I don't know your personal, you know, situation. It might be very very weird, but generically quantum rules do not apply to the macroscopic world. So we have a quantum mystery box. This quantum mystery box where there's an electron or a particle with some property that you want to measure is called a quantum state. You have a particle and you want to know something about it.
In order to know something about it you have to observe it and make a measurement. Duh. The quantum state tells you what you might observe when you actually go to take a peek of the particle. So the probability distribution, the listing on the side of the box about things that are common and rare and super rare, that is the quantum state associated with the particle. Until then, and this is quantum mechanics in a nutshell, in the best nutshell I can provide right now, the quantum state is the thing that matters.
It limits your ability to know the properties of the particle and to make predictions. Here's another half baked mixed bag of a metaphor. You know roulette? You know, the spinny ball thing and then it lands on a colored square with a number and one person some people win and some people lose. Imagine instead of having to develop a theory of physics that just involves the roulette ball, you have to work with the entire roulette wheel simultaneously.
Every possible result must be treated in your mathematical equations in order to make predictions. This limits what you can know about the future of an event because you don't know where the ball is gonna land in the roulette wheel, so you have to consider all possible options simultaneously. Another example, instead of a single card like, jack of spades, you have to work with the entire deck simultaneously. You have to be prepared for any card that might come out of that deck in your mathematics, and this limits what we can know about the universe. Instead of knowing the exact position and speed and spin and entire state of a particle, Instead, we have the quantum state of the particle which is a list of what the particle could do when we go to look.
There is a whole other entire discussion on the reality of the quantum state, what it means to make an observation, what happens in the transition between the quantum state and the final result. Happy to discuss that all. Go ahead and ask. Just not now. I'm gonna sidestep all of that so I can focus on the issue of entanglement.
So here are some honorable mentions of concepts not appearing in today's episode. The wave function, decoherence, Copenhagen interpretation, Bell's theorem, de Broglie wavelength, Heisenberg uncertainty principle, and there's a bunch more juicy juicy topics for another day my children, another day. Why am I skipping all that juicy stuff? Because we're about to double down on the quantum weirdness and that's enough. That's it.
That's already a double bacon cheeseburger anymore and we're going straight to the morgue. So we gotta keep it we gotta keep it small bites. We gotta keep our portions under control. Everything I've been talking about so far has been about a single particle with a single quantum state. Here's this one particle with the property that you want to measure and you have a list of what you might measure when you go to open up that box.
Here's a question I'm about to answer. Is it possible to have two particles share a quantum state. And what does that even mean? First answer is yes. Second answer is that's the rest of the episode.
I hope we're getting comfortable with this idea of a quantum state associated with a particle, the list of things you might know about a particle as soon as you get around to measuring it. Until then, it's just a list. It's just a mystery box. It's just a blind bag. It's just a baseball card packet.
That quantum state is vitally important. Is the heart of quantum mechanics? What does it mean for two particles to share a quantum state? It means that the list of things you might know, what's written on the back of the box, describes both particles at the same time. It's a combo.
It's a twofer. It's a buy one get one. When two particles share a quantum state, you can only know about them simultaneously in combination. The two of them together, you don't get to understand just one. As soon as you understand one, you understand the other.
They are connected. To dig into this to dig into this, it is a jargon pit of doom. So I'm gonna switch gears and this is a very tricky topic, very slippery. So I'm gonna switch gears to perhaps the cheesiest metaphor I've ever presented in the history of Ask a Spaceman. I'm going to subscribe to a Cheese of the Month Club.
You know, you sign up, you pay some money, you get a cheese delivered to you every single month in a nice little gift box. Maybe there's a little write up, some history of the cheese, biography of the cow, it came from in the cheese maker, you know, the whole deal. This is a very strange cheese of the month club. They don't tell you what kind of cheese you're gonna get. It's a random cheese.
It's just a a blank box and they don't tell you what cheese you're gonna get, but they do give you a list of possible cheeses in the chances of getting that cheese. So maybe printed on the side of the box or on the website, you have a 10% get chance of getting Roccifer, 20% chance of a Comte, 15% of a Monterey Jack, 5% Asiago, etcetera, etcetera. Now this isn't any ordinary random cheese of the month club. It's a quantum Cheese of the Month Club. So this list gets elevated.
It gets promoted to be a quantum state. That means, as ridiculous as the whole cat thing was with Schrodinger, we're gonna adopt the language now so he can make some headway, That when I get that blank box, the quantum state is printed on the side, the chances of observing a particular cheese when I open up the box, all cheeses exist simultaneously inside the box. When I open it, one cheese will be discovered. But it's not until I actually open it and make the observation, my eyes gaze upon it, do I actually reveal what cheese the quantum state has randomly chosen for me. The act of me opening the box makes the selection from the quantum state and reveals the cheese.
Not that there's already a cheese in there that some factory worker or a robot or a handpicked artisan cheese picker put in there and I just don't know it. No. The act of me opening the box makes the selection. There is no way to know what kind of cheese I'm going to get until I open the box. That is the essential core of Quantum Mechanics.
You don't know what you're gonna get and there is no way to know what you're gonna get until you open the box. Now I'm going to simplify this Cheese of the Month Club. There are only two cheeses available. This month, special, only two cheeses. And for the purposes of this illustration, I'm gonna pick two great American cheeses.
I'm gonna go with Colby and Pepper Jack. Feel free to substitute any two cheeses from your own locality, but that's why I'm going with Colby and Pepper Jack. Each cheese has a perfect fiftyfifty chance of being in the box or more accurately, I have a fiftyfifty chance of observing either cheese when I open it. 50% chance Colby, 50% Pepper Jack. Now I'm going to buy two subscriptions to the Cheese of the Month Club because I particularly enjoy cheese.
And I want to set up a special state. Because this is a quantum Cheese of the Month Club, when I buy two subscriptions I get two boxes. You know, there's one cheese in one box, one cheese in the other box. These boxes share a quantum state, And we can list the possible combinations when I open up both boxes. I open up one box, open up the other.
What can I get? I can get two Pepperjacks. I can get two Colbys. I can get one Pepper Jack and one Colby or I can flip it around and the first box will be Colby and the other will be Pepper Jack. Those are my four possibilities, right, of revealing the cheeses inside these two boxes.
And I have a common quantum state that describes the contents of these two boxes. This is entanglement. When two or more particles or boxes of cheese share a quantum state where a single mathematical equation in a single list describes both boxes at the same time. I can't consider each box separately. A single mystery box opens up to both.
So what's the big deal? Why is that weird? Notice that I never said how far apart these particles were. These two boxes of cheese, let that sink in. The two boxes of cheese can share a quantum state if they're right next to each other, or on opposite sides of the room, or the world, or the universe.
The distance doesn't matter for the quantum state. The quantum state is just a list of what you might find in the box. It doesn't care how far apart these boxes are. Now we'll make it really spooky. Let's say we prepare our two boxes, or the the the cheese of the month club prepares the two boxes so there's a very very limited quantum state.
Either you'll get Pepper Jack and Colby or Colby and Pepper Jack. I've set it up so that two Pepper Jacks or two Colbys are forbidden to occur. Happy to talk about how we can actually set that up without cheese and with actual particles in another episode. Feel free to ask. But this is what I get.
I got two boxes sitting in front of me. I know that only one can contain a Pepper Jack and the other must contain a Colby, but I don't know which yet until I open it up. Now I pull these boxes apart, way apart. I keep one and I give it to you. Wherever you live, I'm feeling especially generous.
I open up the box. I make an observation. What do I see? A Patreon ad? What the heck?
That's not in the quantum state. Patreon.com/pmsutter is how you support the show. It is your contributions every single month that keep this show going. I'm eternally grateful, no matter the quantum state, for your contributions. That's patreon.com/pmsutter.
What do I actually see? I open up one box. I just open it up. Tada. Make my measurement.
Maybe it's a Colby. Maybe it's a Pepperjack. Jack. Fifty fifty chance. Let's say it's a Colby.
Alright. I pick Colby. Open up the box. I see a Colby cheese. Okay.
Whatever. Big deal. Here's the big deal. If I see a Colby, what do I instantly instantly know about the cheese in your mystery cheese of the month club box? I know it's a pepper jack.
I know that if you opened your box what kind of cheese you're going to get. I know your prize. I know your surprise. I know it. These two cheeses are connected.
They share a quantum state. As soon as you know about one, you know about the other. They're entangled. They're correlated. I've set up this special scenario.
Obviously, more realistic and complicated scenarios exist. This is for illustration, which should be obvious by the fact that I'm using cheese for the metaphor. I've opened up one box and it reveals the contents of the other box without having to look. I don't need to open up your cheese box to know that you have a pepper jack. And the reverse is also true.
If I found pepper jack in my box I know immediately that your box has Colby. How was I able to affect your cheese without ever touching it? Which taken out of context is perhaps the weirdest sentence I've ever uttered on this show. Is there some hidden back channel of communication that entangled cheeses use to coordinate their efforts. So, like like, as soon as I open up my box, you know, and it's Colby who says, hey.
Hey. I'm Colby. And so, hey. Over you in the entangle box, make sure you're pepper jack. In the peb in the elder, she's like, okay.
Got it. I'm gonna be pepper jack. Or maybe the boxes carry with them extra information everywhere they go so that when they get entangled, when when they're set up at the at the cheese of the month club factory, they swap notes and they go their separate ways and then they wait around for a measurement. So they say, okay. Okay.
Okay. When when they open up the box, I'll be a Colby and you be a Pepper Jack. Cool? Cool. Okay.
So really, the whole point of quantum mechanics is lost where I've been saying in quantum mechanics you don't know. There's absolutely no way to know what is in the box before you open it. Maybe there is. Maybe there's some hidden information there that quantum mechanics just doesn't reveal. If there is a mac channel, if there's a way for these two cheese boxes to talk to each other, it's faster than the speed of light.
Because we've tested this, the timing of opening boxes just right given their distance, and as far as we can tell, it is instantaneous. That as soon as one cheese is revealed, the other cheese instantly flips to what it needs to be. Instantly. If there is the other possibility of extra hidden information, then that means quantum mechanics is at best incomplete and at worst wrong because quantum mechanics insists that it's all probabilities all the time until you make the measurement, that there is no hidden information, there is no backdoor, there is not some secret code that reveals the pure state of the universe. It's all quantum.
It's all quantum states. It's all probabilities. We're just really ignorant. The biggest proponent of this second idea called hidden variables was none other none other than Albert Einstein himself. Interestingly enough, I find this so curious.
Einstein was one of the key players in the early development of quantum mechanics. If you'd like to learn how, you know what to do. And he throughout the decades, he continued to have an insightful role, but he was never excited by it. He always argued that it was incomplete. Famous saying, he said God does not play dice, that there is deeper information, quantum mechanics is too service level, everyone's missing the point.
And in 1935, he, with a couple collaborators, wrote a paper outlining this exact issue when it comes to entanglement. The two collaborators are Podolsky and Rosen, who and they in this paper, they they followed a similar line of thinking, obviously not involving cheeses and actually somewhat more complex scenario where they pointed out how quantum mechanics either seems to either violate causality, because these particles or cheeses can communicate faster than light or there were hidden variables. Here's the thing about Einstein when it comes to quantum mechanics. He was wrong. Dead wrong.
As far as we can tell, he was wrong. Einstein never liked it, always thought always argued that we were on the wrong path in developing quantum mechanics, but evidence is evidence and data are data. Nature doesn't really care what even our smartest people have to say. She'll do what she wants. If you're wrong, you're wrong even if you're Einstein.
We've been able to set up experiments, and again, I'm happy to go into this, that test if there is any hidden information. There's no sign of it. There is no sign of any hidden information, hidden variables, backhand extra knowledge that was there the whole time that we were just too ignorant to dig out. It was never there, never detected. But then we're left with this problem.
Are you are we seriously saying that these two cheeses or particles communicate faster than light? Isn't the going faster than the speed of light kind of forbidden and isn't that kind of important and a big deal? How do these cheeses coordinate so that if I pick Colby, you automatically get Pepper Jack, and if I get Pepper Jack, you automatically get Colby? How do they do it? Here's the resolution and where the migraines seriously come in.
There is no communication. There is no signal. There is no walkie talkie, cigarette winks, or hand gestures. There is no communication between the cheeses. But how can one particle and so this, by the way, this is how faster than light communication is not violated because there is no communication occurring.
But how can one particle or cheese know what the other is doing if there is no communication? I haven't solved anything. All I've just I've just rejected is saying, no. There's no communication. But how does this actually play out?
Let's look carefully at the situation. I open up my mystery cheese box. I find a Colby. I know instantly that you'll get a pepper jack, but I don't tell you. Let's say I don't tell you.
I'm just not gonna tell you. I'm gonna keep it to myself. Then you, at some point in the future I don't care. I've ignored you. I've I've gone off to eat my Colby.
At some point in the future, you open up your mystery box, and, of course, you find a pepperjack because there is no other choice for you. But ask yourself, self, did I find a pepperjack because Paul opened his mystery box first and found a Colby, forcing my box to become a pepper jack? Or because Paul hasn't called me or texted me or emailed me, was I the first one to open up the boxes? And I just randomly got a pepper jack. I had a fiftyfifty shot of getting pepper jack, and I just randomly got it, and I'm the one that settled the quantum state.
I'm the one that resolved it, and I forced Paul's cheese to be a Colby. Each individual local measurement appears to be completely and normally following the rules of quantum mechanics. When I open my box, I've got fifty fifty shot of getting Colby or Pepper Jack. When you open up your box, you have a fifty fifty shot of getting Colby or Pepper Jack. We don't know in that moment of opening the box and revealing the cheese if it's the result of the random chance because you were the first one to disentangle this state or because the other one opened first and you were forced into this cheese state.
Later, after we compare those, finally I get on the phone with you, finally I text like, hey, by the way, what kind of cheese did you get and when did you open up your cheese box? We find that our results were connected. And that comparison of notes can only happen along traditional, boring, slower than light channels, radio signals, maybe we meet up for coffee, or, you know, cheese and crackers. This is the difference, and quantum mechanics reveals this difference to them, something we never really thought about before, the difference between locality and causality. Quantum mechanics appears to violate locality.
One entangled particle can immediately affect another particle as far away as that particle is. It could be on the other side of the universe. And as long as our two cheeses are entangled, they can affect each other state. But causality, the sharing of information, is still preserved and limited to the speed of light. Dealing with violations of locality is one of the most mind bending things in an already mind bending field known as quantum mechanics, but it's something that appears we have to live with.
Entanglement breaks locality, but not causality. The sharing of information is still limited by the speed of light. So here's what I like to say to sum up entanglement. The act of entanglement happens instantaneously, but the revelation of entanglement doesn't. Confused?
Good. Now you are in the proper state of mind to appreciate quantum mechanics. And you can send your favorite cheeses to Paul Sutter, PO box three three two two, Columbus, Ohio four three two one o. I'd like to thank my top Patreon contributors this month, Robert r, Justin g, Kevin o, Justin r, Chris c, and Helga b, for all your generous contributions and all the amazing contributions of everyone else you guys are keeping this show going. That's patreon.com/pmsutter.
And you can keep sending me questions. It's hashtag ask a space man. My handle on all social media channels is at at paulmattsutter. You can also catch me on youtube.com / paulmattsutter. You can email askaspaceman@gmail.com.
And the special announcement is that I have a book. I wrote it last year. It was an adventure to say the least. It's a really, really fun book. It's called Your Place in the Understanding Our Big Messy Existence.
It's the story of cosmology of the universe, of our understanding of the universe, and how we have reacted to that in a healthy dose of how the universe works. It will be out November 2018, published by Prometheus Books. It'll be in Barnes and Noble, Amazon, Books a Million, every all the major distributors, indie bound, it'll be out there. You can preorder the book right now. Go to pmsudder.com/book.
There's a link. Sorry. I don't have any, like, discounts or anything cool like that, but you can preorder the book to lock it in. I'm gonna be doing lots of events. I'll talk more about the book later, but I wanted to give you, faithful podcast Ask a Spaceman listeners, a special preview.
That's pmsutter.com/book. If the publisher lets me, I'm gonna read aloud some selections from the book right here on the podcast, but I have to check on that. Also, go to astrotours.co for all sorts of amazing adventures in 2018. We're going to Iceland with Egan Siegel. We're going Ireland with Dean Riggis.
We're going to Costa Rica with Fraser Cain. We're going to Colorado with Sarah El Shafee. We're going to Arizona with Pamela Gay. We're we're doing lots of adventures, and you should find out about them. I will see you next time for more complete knowledge of time and space.