Okay, welcome back. So when we deal with astronomy, when we get started with astronomy, one of the most difficult things is to deal with the enormous size scales and time scales involved with astronomy. It's really easy in astronomy just to have everything be really, really big, and really, really old. But that's really, not that helpful when we're trying to be specific and trying to understand different evolutionary processes that may operate on very different, though very long, time scales. So, for example, the age of the earth is 4.5 billion years, right? and the dinosaurs were wiped out about 65 million years ago. How do you hold those two numbers in your hand and make sense of them, right? the way that scientists do this is through something called scientific notation, that's how we deal with large numbers. So the age of the Earth is 4,500,000,000 years old, but that gets written as 4.5 times ten to the nine years. There's the first part of the number, the 4.5, which tells you where you are in your order of magnitude. But the important part is the order of magnitude, and that's the ten to the nine. It's the exponent on the ten. So we're talking about nine Powers of ten, essentially, for the age of the Earth. Now all of that may have not made much sense to you, so let's try and use something that is familiar to all of us, in order to understand the scientific notation, and let's use money, right. Because we all understand the power of money, and we all know how much money we have in our bank accounts and in our hand and what it feels like. So what we're going to do is we're going to think about dollars. We're goonna run through a set of examples thinking about dollars and thinking about those dollars in terms of order of magnitude. So lets start off with lets say you have a dollar. We all know what a dollar is. And what can a $1 buy right? Well basically these days a $1 will buy you a snickers bar. Okay. So $1 gets you a snickers bar and you know if you like snickers bars that's great but your not going to be able to go much further than that. So how about one order of magnitude more? Let's jump up one order of magnitude, $10 and what will that buy you? Well essentially $10 will get you a you know,kind of bad compilation CD of 70s hits or a really great one perhaps of Bob Marley depending on you know, which store you go to. But that's what $10, when you jump one order of magnitude, we go from a Snickers bar to a CD. And what about the next order of magnitude? That would be going up to 10 to the two, 10 raised to the two power of dollars, $100, and what will it, that get you? Well, that'll get you dinner at a nice restaurant, you know? Not the fanciest restaurant, but a pretty fancy restaurant, $100 should get you there. So in two orders of magnitude, we've gone from a Snickers bar, which isn't going to do much for you, to, you know, a nice restaurant. Okay. How about three orders of magnitude, $1000? Well, $1000 will get you a plane ticket, you know, to some place nice. Perhaps to, you know, a nice vacation, okay. So $1000, three orders of magnitude takes us from the Snickers bar to the ride on a jet plane. One more order of order of magnitude, and that will take us up to a luxury car. Now of course you're not going to be able to get a luxury car for $10,000, but maybe for $60 or $70 or $80,000. Again, this is what we mean by order of magnitude. you might be able to at least, you know, get, get started on the luxury car. Okay, so that is four orders of magnitude from the Snickers bar to driving around in, you know, a nice Sports coupe. How about five orders of magnitude. Well, five orders of magnitude will take you to you know, being able to get that nice apartment perhaps that you could use while you're driving around your sports coupe. So, you know, $1000 got you a plane ticket to a nice place, could be Paris. $10 to the 4, ten, tens of thousands of dollars gets you a sports coupe to drive around in Paris and hundreds of thousands of dollars will maybe get you an apartment in Paris. Okay? So just five orders of magnitude, that's really what you have to think about. Just five orders of magnitude took us from a Snickers bar to a, an expensive apartment in a nice city. Okay, and that is the important thing to see, is just five orders of magnitude what the difference, the physical difference in our experience would be, in having that much money. Now in astronomy, we may easily jump up 15, 20 orders of magnitude in both size and time scale, in going from one kind of physical process to another. So getting a handle on orders of magnitude would be a really essential thing for being able to understand the rest of the class. Okay.
