An introduction to modern astronomy's most important questions. The four sections of the course are Planets and Life in The Universe; The Life of Stars; Galaxies and Their Environments; The History of The Universe.

Loading...

From the course by University of Rochester

Confronting The Big Questions: Highlights of Modern Astronomy

244 ratings

An introduction to modern astronomy's most important questions. The four sections of the course are Planets and Life in The Universe; The Life of Stars; Galaxies and Their Environments; The History of The Universe.

From the lesson

Are we alone in the Universe?

Planets and Life in The Universe - Exoplanets searches, exoplanet census, astrobiology

- Adam FrankProfessor

Physics and Astronomy

Welcome back everyone.

Â So, in our last little discussion we talked

Â about just the basic idea of orders of magnitude.

Â And we've used five orders of magnitude in dollars to

Â understand how big a jump there was from a snickers

Â bar, which was one dollar, to a, a possibly a

Â nice apartment in Paris for hundreds of thousands of dollars.

Â And that was just five orders of magnitude.

Â Let's now apply that idea to astronomy, to

Â understand how we can move through different size scales

Â in the universe.

Â So let's start with our size scale

Â and we're going to be measuring things in meters.

Â Now again, remember that when we talk about orders of magnitude, what

Â we're talking about is you know, the general size of, of quantities.

Â So for example, I'm about two meters tall.

Â I'm a little bit shorter than two meters tall.

Â Like to be two meters tall, didn't quite work out that way.

Â But, I'm about two meters tall.

Â However, in terms of order of magnitude, I am ten to the zero meters, right.

Â That's about one meter.

Â I'm, you know, in terms of order of magnitude, I'm about one meter tall, okay.

Â So that's the size scale of a human, and

Â we'll use that as our reference frame for moving forward.

Â Now, the next large-scale, or, you know, important structure in

Â the universe, after us, and perhaps we shouldn't even use ourselves.

Â But you know were going to, we have to have

Â a reference so we'll use ourselves to begin with.

Â And the next step up in structure in the universe are planets.

Â And planets

Â as we have seen range in you know from our discovery range in

Â size scale from 10 to the 6 to 10 to the 7 meters.

Â So the difference in size scale between me and a

Â planet is larger, the jump in orders of magnitude is

Â larger than the jump from a snickers bar to you

Â know the really nice hotel or the nice apartment in Paris.

Â So that's just on the first leap in terms of size scale.

Â The next structure that we have to deal with in astronomy

Â are stars, and stars have size scales between say 10

Â to the eight and 10 to the 12 meters in scale.

Â So there are you know, dwarf stars and there are giant stars.

Â So, after stars, the next structure that we're interested in are

Â planetary systems, the collection of planets that are orbiting around stars.

Â So like our solar system, but we've also found other planetary

Â systems, and the typical size scales there are on the order

Â of 10 to the 13 meters, so that's a factor of 10

Â to a factor of 100 or even 1,000 larger than the stars themselves.

Â The next size scale we're interested in are galaxies, and

Â galaxies are vast collections of stars that exist in, they're

Â gravitationally bound, and the typical size scale for a galaxy

Â is on the order of, say, 10 to the 19 meters.

Â Now, notice what a jump there was between the previous size

Â scale, which was a solar system, and a galaxy.

Â And so what we're really seeing there is

Â approximately nine orders of magnitude from the coherent size

Â of a solar system to the collection of

Â solar systems or stars that go into a galaxy.

Â So there can, there's this enormous range of, of, of size scales that we're

Â dealing with in astronomy, and we haven't even gotten to the top in some sense.

Â The next size scale that we're interested in are galaxy clusters.

Â These are groups of galaxies.

Â And typical size scales there are a 1,000 times or more the size of the galaxies.

Â So 10 to the 22 meters.

Â And then finally we have the clusters, this, the super

Â clusters of galaxies which are clusters of clusters of galaxies.

Â And there the size scales are 10 to the 24 meters,

Â so even a thousand times, hundred times, or a thousand times more.

Â So, then we go all the way up to the size of the universe itself.

Â Now we can talk about the observable universe,

Â which is the, the sort of, bubble of

Â light that encompasses the universe that we can see.

Â But the thing that's important to understand is there

Â is most likely a lot more universe beyond even that.

Â So in some sense, well, according to

Â our best understanding, is that the universe right

Â now, our understanding tells us that the universe

Â is, in fact, infinite, on the largest scales.

Â Okay, so now we've done the large scales.

Â Now let's turn things around and go to the small scales.

Â So, we now want to travel downward. Again, I'm a human being.

Â You are a human being.

Â We're both approximately one meter in size, and on

Â the order of magnitude, 10 to the 0th meters.

Â So, what about if we go downward? Well, think about a grain of dust.

Â A grain of dust is something we all have some experience with because we sweep.

Â Lots of them up every time we sweep our floors, and typical

Â size scale for a grain of dust is about a millionth of

Â a meter, 10 to the minus six.

Â So there are six orders of magnitude that you have to go

Â through from your basic size to the size of a dust grain.

Â And those dust grains are made up of atoms, and what are the size of an atom?

Â Well, typical size of an atom is going to be about 10

Â to the minus 9th of a meter, a billionth of a meter.

Â Okay.

Â So, now we see nine orders of magnitude between

Â your size and the size of your basic constituents.

Â Your atomic constituents.

Â So, of course, we know that atoms

Â are themselves built of even smaller particles.

Â Things like neutrons and protons that make up the nucleus.

Â And there's actually a whole zoo of sub

Â atomic particles and the typical sub atomic particle.

Â Size scale in terms of how we as when we

Â throw things at it, when things tend to bounce back.

Â Typical size scales are on the order of 10 to the minus 15 of a meter.

Â So that is a full six orders of magnitude from the atomic size scale.

Â So, another millionth

Â or a million times smaller.

Â So what we see is there's about 39 orders of magnitude from the

Â smallest known structures in the universe to

Â the largest known structures in the universe.

Â And how far down can we go?

Â Well, that's really an interesting question.

Â We know that at some point when you go

Â far enough down even space-time itself should break up

Â into some kind of foamy structure, and we'll talk

Â about that later on towards the end of the class.

Â but as you can see, there is this amazing,

Â psychotic range of size scales, both on the smallest

Â and on the largest scales that compose our universe.

Â And, you know, we're sort of sitting somewhere perhaps in the middle of

Â it, and it's really remarkable that creatures like us, who, you

Â know, evolved from you know, small cells billions of years ago.

Â Have come to the point where our ability to understand both the

Â largest and the smallest scales together. Okay?

Â Coursera provides universal access to the worldâ€™s best education,
partnering with top universities and organizations to offer courses online.