Lecture: Heliocentric Theory: Narrator: Listen to part of a discussion in a history of science class. The class is discussing the heliocentric theory. Male Student: What I found really difficult to understand is why the heliocentric theory, um, why wasn't like believed by everybody right away? Professor: Well, one thing that's hard to do is to sort of see things from the perspective of someone who's hearing that theory for the first time. I mean today we tend to assume that the moment the heliocentric theory was laid out, the idea that the Sun, not the Earth, was the center of the solar system, that you know, you'd have to be in denial, not to accept it. But it really wasn't that easy. Male Student: But the idea that the Earth wasn't the center of the universe ... that has been tossed around for like centuries, right? I mean, lots of people would have the idea. Professor: Yes, that's true, going all the way back to the Ancient Greeks. But in Europe, when Galileo championed it in the 17th century, during part of his discoveries using a telescope, there still was some major resistance to it. Male Student: But I still don't understand why, I mean, isn't it obvious? Professor: Well, despite Galileo's ingenious arguments in support of the heliocentric theory, there was still a lot of reasons why people of that period couldn't buy into it. Remember, we are talking about four hundred years ago, so ah, let's think about a few of those reasons, Ok? So, first of all, they could work out that if the Earth was going around the Sun, then it had to be traveling at many thousands of kilometers per hour. And that was just beyond anything anyone could understand. You know, they could understand riding a horse or walking, maybe they could get up to 30, 32 kilometers per hour. But tens of thousands of kilometers per hour? That was just crazy. So, to many people, whatever is going on, it couldn't be that. Female Student: Um ... So people didn't believe the heliocentric theory because it was so hard to believe? Professor: Exactly. But, there were more scientific kinds of reactions as well. Because, look, if you have ever been on a carousel or you are on a ride at an amusement park and you are on something that is going round round and round, two things, alright? One, you know you are moving, there is no doubt. And the other thing is, you know that unless you hold on tight, you are gonna go flying out because of centrifugal force, right? Female Student: So, if I understand you for the average person 400 hundred years ago there was no evidence that we are moving at higher speed, right? Since everything was securely on the ground and no one was flying off into space? Professor: Yes. And in particular. And this was one specific difficulty for people in the period, even if they thought that there was some sort of force that maybe kept you and me and buildings and things on the surface of the Earth. Their theory about the nature of the atmosphere was that nothing was holding it down. So if, if you can understand that way of thinking, then clearly, if the Earth, was moving at a great speed, we should've lost all our atmosphere a long time ago. You know, it would be like, trailing away behind us. And so, I want to try a little sort of experiment, because, I, I think that what we will find is that some of us have ideas about motion that actually fit with anti-heliocentrism. Male Student: Anti-heliocentrism? No way. It's the 21st century. Professor: Well, then let's see. So, picture the following. You are at the equator, moving at 1600 kilometers per hour. Ok? And you drop something, small and light, like a matchstick for example. Where is it going to land? Male Student: That's easy. It will be long gone. The matchstick is so light that it will fly right out of my hand and end up away behind me somewhere. Professor: Ah, actually, that matchstick you dropped, it'll land right at your feet. Male Student: What? Professor: Well, let's think about it. If I got to consider that the Earth's rotating at 1600 kilometer per hour at the equator, and you, me, the air, and that matchstick will all moving together at the same speed, even though it doesn't seem or look or feel like we are moving. So class, clearly, even today, we actually have some inclination to think that if the Earth were moving around at a great speed, we all would see signs of it. Perhaps now you are less inclined to dismiss those who once found heliocentrism so hard to believe. Ok, let's move on.