ROBERT SIEGEL, HOST:

Time, according to a couple of studies, is the most commonly used noun in the English language. I learned that from reading Alan Burdick's new book, "Why Time Flies," a study of time that he calls a mostly scientific investigation. Alan Burdick, thanks for joining us today.

ALAN BURDICK: My pleasure. Thanks for having me.

SIEGEL: And this inquiry into the nature of time is, you should explain, mostly scientific because it's also philosophical and it's also a lot about watching your twin sons grow up.

BURDICK: Yeah, that's right. It - you know, something had to happen in this book, and what happened was a lot of time passing and watching my kids get older.

SIEGEL: You examine time in a very granular way, getting down to the shortest possible time spans we can imagine. But you're also talking about long spans of time and are trying to - you're trying to hold on to the times of dealing with your twin boys. Same thing - we're talking about time in both cases?

BURDICK: Yeah. You know, really one of the first things that I learned about time - I mean, I would go around to scientists and ask them - what is time exactly? And they would all turn it around on me and say, well, what do you mean by time? The point being that what we call time is actually a lot of different experiences. It's understanding what the time of day is, but it's also understanding the difference between before and after.

So watching my kids grow, I realized it was very much an experience of me educating them about what time is. Not just, you know, how do you tell time, but what does it mean to wait? What does it mean to hurry up? These are all experiences that we learn, that we exchange with each other and kind of convey as a culture to the next generation.

SIEGEL: One question that sums up much of what you write about is what is the meaning of now? Now that I've finished posing that question, it's already in the past. Your answer is about to depart the future and join it in the past. So after all of your investigations, what is the present? What is now?

BURDICK: If you were to ask St. Augustine, Augustine would say that there is only now. There's no past, present and future. There's only your current awareness of the past, which is your memory. And there's only your current awareness of the future, which is expectation. And there's only your current awareness of the present, which is your attention. Everything is present for him.

SIEGEL: Now, once we think we have a grip on what the present is, we then encounter some experimental work in psychology that's been done that challenges our very ideas. And there's experiment that I'd like you to describe. I found this fascinating. The subjects of the experiment struck a computer keypad to produce a flash in a box on a screen. And at some point, they experienced the illusion that the flash preceded their keystroke, that the cause actually came after the effect. Describe that.

BURDICK: You know, your brain - our brains do a lot of work to kind of hide what you might call reality from us. So, you know, every time you type, for instance, on a computer keyboard there's actually about a 35-millisecond delay between you pressing a key on the keypad and that letter appearing on the screen. But as far as your brain is concerned, it happens instantaneously. There's no gap. It's actually been shown that your brain can sustain about a tenth-of-a-second delay between your action and its consequence.

SIEGEL: You still think it's instantaneous.

BURDICK: You still think it's instantaneous. David Eagleman, a neuroscientist who's now at Stanford, rigged up this experiment where he had a mouse and you could move this mouse around to various spots on the screen. You'd click the mouse and it would move to the next spot. And what he did is he sort of trained you to expect a 100-millisecond delay between your click and the thing moving. And after a while, you just didn't notice it. And then he removed the 100-millisecond delay. And the weird thing is once that delay is removed, your brain is so expecting a 100-millisecond delay that it seems as though the cursor has moved before you've clicked the mouse.

SIEGEL: In effect, during that earlier clicking our brain is calibrating to make that feel like now, like instantaneous.

BURDICK: That's exactly right, yeah. And your brain is doing this calibrating all the time. And it can be fooled. And when I did it, I have to say it was funny and really eerie.

SIEGEL: I mean, clearly you write this book - this is a narrative, and your personal experience is interwoven with what you're learning about the study of time. Clearly, at some point, time became a - is obsession too weak or strong a word to use for you, or a preoccupation?

BURDICK: A preoccupation. It was a bit like peering into the bottom of existence. I mean, man, it got really existential (laughter) for a while. You can't really talk about the perception of time and the perception of now without addressing somehow consciousness. My ability to perceive a present is very wrapped up in my ability to perceive a self. And yeah, you know, I spent, like, 10 years peering into that well, and came out of it and felt like I had a long white beard and flying cars were flying through the sky.

SIEGEL: Alan Burdick. Thanks a lot for talking with us about time and about your book, "Why Time Flies."

BURDICK: Thanks for having me. Transcript provided by NPR, Copyright NPR.