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STEVE INSKEEP, host:

Now that we're partway through this Thanksgiving weekend, you might be getting wistful. After all, it's only three days until Monday. But we do have a tip for you, a way to extract a little more pleasure from your holiday.

Here's NPR's Robert Krulwich.

ROBERT KRULWICH: If you're the kind of person who really loves vacations, you love them so much you want every single second to slow down because they're precious. Well, there is a way that you can actually slow down, for example, this Thanksgiving weekend. I mean this literally, consistent with the laws of physics and with Einstein, this according to physics professor Brian Greene.

Professor BRIAN GREENE (Physics): That is the point.

KRULWICH: This is true then.

Prof. GREENE: We're really talking about the laws themselves, what the laws of physics tell us.

KRULWICH: And what the laws of physics say is, to slow down this weekend, all you have to do - it's this simple - is: Go downstairs.

That is right. If you go down from your apartment, from your bedroom, from your office and you spend this entire four-day Thanksgiving weekend on, say, the street instead of upstairs, the street is just a little bit closer to the center of the earth. And the pull of gravity - the earth's gravity - is just a little stronger when you're down on the street.

Prof. GREENE: And gravity's strength, in particular, affects the passage of time.

KRULWICH: This is directly from Einstein.

Prof. GREENE: If you go near a very massive object, the nearer you go to it, the more time will slow down for you. So even here on earth, right now, if we're sitting on the surface of the earth, time is elapsing at a certain rate.

KRULWICH: Right.

Prof. GREENE: If I then go up, say, the Empire State Building, I go to the top of the Empire State Building, gravity's a little bit weaker up there because I'm further away from the earth up in the Empire State Building at the observation deck. Time for you on earth will tick away more slowly than it will be for me higher up on the Empire State Building.

KRULWICH: Really?

Prof. GREENE: Yes.

(Soundbite of street noise)

KRULWICH: So, let's see, I'm down here on 34th Street in New York City surrounded by people and by traffic. You are where, exactly?

Prof. GREENE: Way up here at the observation deck.

KRULWICH: Where?

Prof. GREENE: Eighty-sixth floor, Empire State Building.

KRULWICH: And up there where you are, because you are farther from the center of the earth, Albert Einstein says that time for you is ticking a little faster, while for me down here - I would notice this, but because I am closer to the center of the earth - time for me is ticking slower.

Prof. GREENE: Slower.

KRULWICH: I'm slower. Why am I slower down here?

Prof. GREENE: Well, gravity and gravity's strength in particular affects the passage of time. Just like motion affects the passage of time, the strength of gravity affects the passage of time as well. So if you...

KRULWICH: So the hug of the earth is a little bit fiercer on me than it is up there on you.

Prof. GREENE: Yes, exactly. And that means, according to general relativity, that time elapses more slowly for you than it does for me. In fact, we...

KRULWICH: Wait. Does that mean that Heidi up there in the Swiss Alps is going to age a little more quickly than people who live in the valley?

Prof. GREENE: Yes.

(Soundbite of music)

KRULWICH: So, therefore, if you want to slow down your Thanksgiving weekend and you, like Heidi, live up on the hill, what you do is you go down to the valley. If you live upstairs, you go down to the lobby or down to the basement or down to the subway or to the deepest cave you can find.

And then when you emerge four days later, compared to the people who spent the same weekend above you, because your time ticks slowly, you will have aged less.

How much less than you have I aged?

Prof. GREENE: Not much. Only...

KRULWICH: Give me the hard number.

Prof. GREENE: Well, it's roughly a hundred billionth of a second.

KRULWICH: So that's why you're so cranky and kind of - sort of - you just strike me as much older than you used to be before the weekend started.

Robert Krulwich, NPR News in New York.

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