Business, Science & Tech

Scientific Measurement: Calculating the Incalculable

Neil deGrasse Tyson

Lesson time 8:05 min

Neil explores one of his favorite subjects: scientific measurement. He distinguishes precision from accuracy and offers examples to illuminate the approximations that are inherent in any measurement.

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Topics include: Precision and Accuracy


[MUSIC PLAYING] - Oh, of my favorite subjects to think about is measurement, something we so take for granted every day. There are measurements all the time that we're exposed to, that we're handed, that we do ourselves. What's a typical one? Oh, how tall are you? Oh, I'm 5' 8", you say. Well, I say, well, how do you know that? Well, I was just at the doctor's. I just had a checkup last week. OK, how did they measure your height? Well, I took off my shoes. And I stood on this little thing. And there's a little rod that comes up and bends down over the top of my head. OK, fine. And they made the reading. There it was. 5' 8". I might ask, was it 5' 8" and 1/2? No, it was right on 5' 8". OK, you're content with that answer. But it was a measurement. And every measurement ever made, and ever will be made, has uncertainties built into it. You may see that term in books called measurement error. But it's not an error in the sense that you made a mistake. That's why I stay away from the word in that context. It's a measurement uncertainty. No, I'm exactly 5' 8". Well, wait a minute. You said it was exactly on that line. That line has a thickness to it, doesn't it? Is that line a 16th of an inch thick? A 32nd of-- are you-- did your height come in at the bottom of that line? The middle of that line? The top of that line? Oh, no, it was exactly in the middle. Exactly in the middle? How do you even know that? You didn't have anything to measure it. So all measurement in life comes down to the approximation that you're comfortable with. I have never heard anybody report their height in 32nds of an inch or 16ths of an inch, never. That is not part of our common conversation-- conversational principles. We're OK to a half an inch. In fact, have you heard anyone-- my height is something and 1/4? No. We're good to a half inch. And we move on. That is not as precise as it could be. But for that purpose, we don't need to be more precise. This is true for anything you will measure. There is no precise answer. There's only the answer that you'll be happy with. [MUSIC PLAYING] Now, don't get confused between precision and accuracy. These are two different words, scientifically. Two different words. Precision is, how tight is the measurement that you're making? How tight is it? All right. Am I measuring your height to 1/64 of an inch? That would be high precision. That's precise, 1/64th. You could be more precise, but that's pretty good, given how most people measure height. Accuracy is, I don't care how tight your measurement is, is the measurement right at all? Let me give you another example of the precision of measurement. Do you know how long a second is? It lasts a second. Well, who-- where you getting that-- where you getting that from? Well, there's a community of people in the world who think about this and defined the second. By the way, it includes astrophysicists. We care about time deeply. OK. ...

About the Instructor

With a hit talk show and bestselling books, Neil deGrasse Tyson is one of the most popular figures in modern science. Now the influential astrophysicist teaches you how his mind works and how he connects with audiences. Learn to think like a skeptic, open your own mind through scientific literacy, distill data, and navigate bias to discover objective truths—and deliver your ideas in ways that engage, excite, and inspire.

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Neil deGrasse Tyson

Renowned astrophysicist Neil deGrasse Tyson teaches you how to find objective truths and shares his tools for communicating what you discover.

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