Transcript: What Popularizers of Quantum Mechanics Don’t Want You to Know by Ron Garret


Ron Garret

Ron Garret presents The Quantum Conspiracy: What Popularizers of QM Don’t Want You to Know at Google TechTalks Conference (Transcript). This event took place on January 6, 2011.

Google TechTalks — The Quantum Conspiracy: What Popularizers of QM Don’t Want You to Know – Slides


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Arthur Gleckler: Hi everyone. I’m Arthur Gleckler and I’m happy to introduce Dr. Ron Garret here, who’s going to be speaking about quantum mechanics today. He’s a former Googler from the very early days of the company, around 2000. He was the lead engineer on the first release of AdWords and the original author of the Google Translation console. He also wrote the first billing system that Google used. Also, for many years, he worked at the NASA Jet Propulsion Lab in Pasadena, specializing in AI and robotics. I’m hoping to convince him to come back and talk about his experiences, debugging spacecraft 250 million miles from the earth. Here’s Ron.

Ron Garret – Software engineer turned entrepreneur

Thanks. So I’m told that my abstract caused a little bit of a kerfuffle, so let me start out with a couple of disclaimers upfront to kind of manage expectations. The title of the talk was intended to be tongue-in-cheek. There is no actual conspiracy, at least, as far as I know but there is a fairly big disconnect between what you read about quantum mechanics in the popular press and what the actual underlying truth is, and that’s what this talk is about.

I am not a physicist. Do we have any actual physicists in the crowd? Oh, boy, okay. You can make sure you keep me honest. I’m a software engineer. I came upon this about actually 20 years ago when I read an article in Scientific American and I thought, “This can’t possibly be right.” And it took me 10 years to finally find a physicist at Caltech who could explain to me why in fact it wasn’t right and at that point, everything just kind of clicked and quantum mechanics made a lot more sense to me than it did before. And that’s what this talk is about.

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It’s about a different way to think about QM that hasn’t gotten very much attention and dispels this idea that quantum mechanics is sort of intractably weird. Somebody has said to me once that quantum mechanics obeys the law of conservation of weirdness. And to a certain extent, that is true. There is a certain amount of — quantum mechanics extracts a toll on your intuition and some of that will never go away. But I don’t think that quantum mechanics needs to be fundamentally any more incomprehensible than, say, relativity which most technical people seem to have no trouble wrapping their brains around nowadays.

So with that sort of expectation management out of the way, I want to start out by inviting you to think about the question: What does it mean to ‘measure’ something? So, imagine that we’re sitting here doing some experiment. We have some system — let me grab a pointer — that we want to measure some property of it, so we have some sensor here like a camera. And it gathers some data and we feed it to a computer, and that data shall pop up from the screen, and we look at that with our eyes, and we form some mental image in our head, and how do we know that this mental image that we form in our head actually corresponds to underlying physical reality?

Well, one indication that we have of this is that we can do experiments more than once and observe that we get consistent results. So, for example, what color is this? Green, yes. So we can observe through our common everyday experience that the results of measurements are consistent across space and time. And, I mean, this is really a very reliable aspect of our universe, but it’s actually a very deep mystery why this is so.

And Einstein famously said that, “The most incomprehensible thing about the universe is that it is comprehensible.” We can actually do experiments and get results that are consistent across space and time and we don’t really know why that — any inherent reason, why that should be the case.

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Now, there is one very plausible sounding explanation of why this is the case, and that is that the results of these measurements are actually an accurate reflection of some underlying metaphysical reality. That reality, that there really is a universe out there and when we measure it, we’re getting back actual information about that underlying physical reality. And that is the reason why these measurements are consistent because reality sees to it that that’s the case. Well, it turns out that we can demonstrate that that’s not true.

I’m about to lead you down a rabbit hole but my purpose in leading you down this rabbit hole is to do it in such a way that you can find your way back out again. So I’m going to do it very carefully, step by step, and tell you in advance where we’re going. I’m going to start out by reviewing the usual QM story. What you will read if you go to a popular account of quantum mechanics that you read, you know, pick up at Amazon or a bookstore or read about it in Wired or whatever.

I’ll then show you how that story can’t possibly be true, because if that story were true, it would lead to a violation of relativity, in particular, it would lead to faster-than-light communication. And it doesn’t do this in the usual way that most people think that it leads to faster-than-light communication, it does it in a more subtle way that really hasn’t gotten a lot of attention. So you physicists in the room, bear with me.

Then, I’m going to walk you through some of the actual underlying mathematics of quantum mechanics, in a way that is accessible to anyone who knows – can do basic algebra and knows what algorithm is.

And finally, tell a new story based on our understanding of what the underlying mathematics actually says about what’s really going on and hopefully we’ll achieve enlightenment at the end of that.

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Two-Slit Experiment

So, is there anybody here who has not heard of the two-slit experiment? All right, good. I will just blast through this very quickly. So, this is — you have a laser that shines through two-slits, and you get an interference pattern that shows that light is a wave and can interfere with itself like any other wave.

And there are two strange things about this. If you look at the results of this experiment with very low intensity light, what you find is, and this isn’t showing up very well, but this top image here shows just some dots scattered randomly. And then dots get denser and denser and denser until down here at the bottom you have a dense enough pattern of dots that you can start to see this interference pattern start to emerge. And this is an actual photograph of laser light going through a single slit and going through two slits. And you can see this interference pattern here, this is an actual photograph of the same experiment, this particular one happened to be done with electrons but the underlying physics is the same.

And the thing to notice here is that the total amount of light that you get in this pattern when there are two slits is brighter than the overall amount of light that you get with one slit, which is what you would expect. But that there are some places here where you have these dark bands that were bright up here when you only had one slit. And this is the interesting part that you want to kind of focus your attention on because what this means is that there’s a spot here where light was shining and then you open up an extra path for light to get to the screen and that spot goes dark. And that is the manifestation of interference.

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