The Spookiness Of Quantum Mechanics

It's been 75 years since Albert Einstein decried the "spooky action at a distance" of quantum entanglement. Tom Siegfried, editor-in-chief of Science News, explains how quantum mechanics is being put to use, even though scientists still don't quite understand how it works.

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IRA FLATOW, host:

This is SCIENCE FRIDAY from NPR. I'm Ira Flatow.

The most famous feline in physics, Schrodinger's cat, turns 75 this year -happy birthday. The imaginary cat was devised by physicist Erwin Schrodinger to describe the hard-to-grasp ideas of quantum physics. And one of the weirdest of the concepts is that of quantum entanglement. Yeah, it's so strange that even Einstein called it spooky action at a distance.

And basically, it means that two particles can somehow instantly communicate with each other even though they may be very far apart, and far apart is the opposite ends of the universe, as an example.

Let's say two particles can be either black or white, but they can't be both at the same color at the same time. So if you see one particle and it's black, you know that the other one must be white. But if your white one turns black and your black one turns white, they just have to switch colors. One knows about switching the color and changing into the other color instantly.

And this relationship exists even if the particles are separated, as I say, by huge distances. So somehow, they can communicate with each other. How can that be? Well, so far there's no good explanation for that, but that hasn't stopped researchers from trying to put quantum mechanics to work. And they know how weird the world of quantum mechanics is.

For example, a very famous physicist, John Wheeler, has said, if you're not completely confused by quantum mechanics, you don't understand it, if you're not confused. Richard Feynman said it's safe to say that nobody understands quantum mechanics. It works great, but if they tell you why they know how it works, they're lying to you, he basically said.

Here's somebody who's not lying to us who's going to talk about it because quantum mechanics is the topic and the focus of Science News, editor-in-chief of Science News, Tom Siegfried, is with us, and that's the upcoming issue dedicated to this spooky topic of quantum mechanics. And you can read more about it at sciencenews.org. Welcome, Tom.

Mr. TOM SIEGFRIED (Editor-in-Chief, Science News): Thank you, Ira.

FLATOW: Do you find this as interesting and spooky as everyone else does, I'm sure?

Mr. SIEGFRIED: It's - or more interesting and spookier.

FLATOW: And why such a fascination with this? Why did you devoted, basically, almost the whole issue to this topic?

Mr. SIEGFRIED: Well, I mean, two reasons. One, of course, it's the 75th anniversary of this famous paper by Schrodinger, in which he introduced the cat that was half alive and half dead at the same time, and also named this concept that bothered Einstein of entanglement, this mysterious connection between distant particles that you mentioned.

But that alone, the anniversary alone, wouldn't have warranted this much space. What warranted the space was the amount of active research that's going on in this field, making lots of new discoveries about it and finding out practical ways to use it.

FLATOW: Mm-hmm. Let's talk about quantum entanglement, what you say, and as I said before what Einstein called spooky action at a distance. I mean, this is so spooky that we know that it happens but we have no idea why it happens?

Mr. SIEGFRIED: Well, there's no way to explain or draw a picture or make a story that explains how it happens. It's just part of quantum mechanics. It's something that quantum mechanics says has to happen. And like with so much with quantum mechanics, it's just weird. There's no explanation if you restrict your explanations to things that the human brain can grasp as a simple cause and effect explanation, like the old classical physics used to do. We just don't have those kind of explanations anymore.

FLATOW: Yeah. And simply stated, it's have - if you entangle two particles, what do they do?

Mr. SIEGFRIED: Well, it's as though two particles separated from birth somehow know what to do when something happens to the other one. The confusing thing is if these particles fly off, say with - and you're going to measure how they're spinning, they don't have a definite answer to that question until you measure it. So even though they don't start out with any property, when one of them gets the property by a measurement, the other one suddenly has it as well, no matter how far apart they are. And that is, I think, spooky.

FLATOW: Wow. Certainly. But because it works so well, does - it allows us to make things? I mean, if you don't know why it works, how can you make anything practical out of it?

Mr. SIEGFRIED: Well, it allows you to do things because combined with - the entanglement combined with this other property that the cat illustrates, which they call superposition - being in two places at once or doing two things at once - that enables a whole new kind of information to use in computing.

Obviously, they call it quantum information, but it's the difference between a ordinary bit in a computer that can be zero or one, or a quantum bit, or a qubit, is both zero and one at the same time. So you get enough of those together that, you know, vastly increases the computation power you have because each bit has infinitely more information than an ordinary computer bit.

FLATOW: So we can actually use them to make computers to store information. Can we use them to communicate with each other, I mean, us, using this entanglement principle?

Mr. SIEGFRIED: Yes. You can use the principle for - in a variety of ways. For one thing, for communicating - what it's best for is communicating with utter secrecy. You can create a code using these entangled quantum particles that no eavesdropper could break because if an eavesdropper tried, they would be making measurements in disturbing the quantum particles and you could detect that. So that's a practical application that is already - can be done, that is already done. People have demonstrated that over great distances through optical fibers and things, and that sort of thing is already a practical application of the quantum weirdness.

FLATOW: You really think that people have made unbreakable codes using...

Mr. SIEGFRIED: Oh yeah. Yeah. No. It can be done now. It's probably a lot more expensive that you would need to do for most of the things that you would want to keep secret. But as computing power increases, the codes they use today ultimately could be broken. And if you want a code that absolutely cannot be broken, you need a quantum code.

The - and ironically, the way that today's codes might be broken someday is through more powerful quantum computers because they can crack the hard math problems that are at the core of keeping today's code secret.

FLATOW: Maybe you can explain in lay terms for me something I have trouble explaining to people and to myself about quantum entanglement, is it appears -because you can have these entangled particles so far away, further than, let's say, light can travel in a second...

Mr. SIEGFRIED: Right.

FLATOW: ...how they know instantly in less than a second, instantly, what one is doing about what one - the state of one knowing about the other? It seems like it's, you know, it's disobeying the laws of the speed of light.

Mr. SIEGFRIED: That's, yeah, that's why - that's what makes people worried about it. But there is no way to actually send information that the other person can use faster than the speed of light. It's - we know what the other person will find out, but we would still have to call them on the phone or send email to tell them what we found out. And by that time, they would've already found out. So they really can't get information in advance.

But there is - the explanation - I'll give you one explanation that Murray Gell-Mann, who was a famous physicist for - or he still is - famous physicist for discovering the concept of quarks, and his collaborator, Jim Hartle, view it this way: If quantum mechanics permits different possible realities, like the cat that's both alive and dead, that just might mean that there are different possible realities out there and there are different chains of events. And we're in one of those chains of events and the other possibilities go off in other chains of events. And the only requirement is that each chain is consistent within itself.

So when one particle far off gets measured and it's a quantum coin and it turns up heads, you know the other one far away is tails because you were in - that's the consistent chains of events that you're in. And in another consistent chain of events, the first coin is tails and the other coin is heads. There's no magical communication between them. It's more you finding out which chain of events you live in. And, of course, that - response to that is often, that is still very, very weird.

FLATOW: It's very weird. Will any experiments - let's say at the Large Hadron Collider - help to un-weird some of this stuff?

Mr. SIEGFRIED: I don't - there may be some indirect results that you get from things that are found at the Large Hadron Collider, but most of the experiments that test these sort of things are done with, you know, lasers in labs or sending the laser beams and entangled particle beams over optical fiber, or through space. Someday, there's plans to have an experiment where you shoot lasers from the space station to labs on earth and try to test entanglement that way. And over those even greater distances, that would be an interesting experiment to see.

But the other interesting experiments, though, would be - of course, when people build bigger and better quantum computers in the laboratory that can do more and more elaborate computations using quantum physics to see if these ideas really play out when you scale them up.

FLATOW: Let's see if we can get a quick call in - Colin in Marietta, Ohio. Hi, Colin.

COLIN (Caller): Hi, thank you for having me on. I wanted to just interject and lay out a movie that I've seen that really puts an easy explanation on quantum mechanics and quantum physics. And I wanted to know if you guys have seen it. It's "What the Bleep Do We Know?"

It came out several years ago, but it had scientists, and seemed to really put quantum mechanics and the idea of quantum entanglement and spooky action at a distance very, very simple and very actually - you know, was a great movie. I just wanted to know if you guys have seen it, and how factual the points that they had in the movie were.

FLATOW: All right, Colin. Thanks for calling.

COLIN: Thank you.

Mr. SIEGFRIED: Yes, I've seen it, and all I can really say is I discussed it with a number of the leading quantum physics researchers and the consensus is that the factualness of that movie was not very high on the scale. They took some of the weird ideas and extrapolated them in ways that are not ways that practicing quantum physicists would find very sound. So, I mean, it was very interesting, but it did not really illuminate the science.

FLATOW: Well, you have some of these new age people who believe that since -they use quantum physics to say since anything is possible, why can't I be in two places at once, right?

Mr. SIEGFRIED: Well, it is open to those kinds of interpretations. And at one level, it is weird enough to say there are some strange things out in the world that we don't understand. But the people who know quantum physics the best will also tell you that it does not give you a license to speculate wildly about all kinds of things without limits.

The Heisenberg Uncertainty Principle, for example - it's the core of quantum mechanics - doesn't mean that everything is uncertain, because Heisenberg's principle is really very certain. So it's easy to get carried away and extend it to things where it doesn't really apply. But I think keeping it within the realm of physics is still very much weird and fun enough.

FLATOW: Well, I suggest to all of you to go out and get the special issue of this magazine, 'cause it's got great new stuff in it. The Science News magazine, that special issue about quantum mechanics, and you can go to their website at sciencenews.org and then check out more of Tom Siegfried and all his great writers over there. Thanks, Tom.

Mr. SIEGFRIED: Glad to be here, Ira.

FLATOW: For taking time to be with us. Tom Siegfried, who is editor-in-chief of Science News. And as I say, go over to the website at sciencenews.org.

We're gonna take a break and come up and talk about - if your hair doesn't hurt already from talking about spooky action at a distance, we're gonna talk about the science of consciousness. How do we decipher that? Tonio Damasio is here to talk about it. So stay with us. We'll be right back after this break.

I'm Ira Flatow. This is SCIENCE FRIDAY from NPR.

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