When we were hearing this lecture, we got to see slides illustrating it. I don’t have the slides for you, but author David J. Williams found this website: http://www.atlasoftheuniverse.com/ which gives you similar images so you can follow along. (Click on the images to see larger versions of them and more information.)
Just a note–any lecture wanders a bit, so I just plunked the tangents down when they happened, in parentheses. In future, I might experiment with adding them as footnotes, or just putting them all at the end.
Astronomy deals with enormous distances and times that are so difficult to understand that even when you know the numbers and the principles, you have to keep checking yourself. Even the distances in the solar system are minute compared to the distances outside it.
One of the biggest misconceptions people have, as seen in shows like Star Trek, is that space is like an ocean, filled with ships that take a few weeks to go from one place to another. The ocean analogy might work for trips inside the solar system with advanced spaceships where it would take weeks to go from planet to planet, but it does not work outside the solar system.
So if you try to create analogies to figure out sizes, you can start by thinking of an experience most of us have. For instance, that of being in a medium-sized classroom that’s 16×16 and then moving out by factors of hundred.
A room, taken back by a factor of 100, you get to a mile by a mile, or maybe a college campus.
Another factor of a hundred gives us a big chunk of a standard-sized American state, 100×100.
Another factor of a hundred gives us the whole earth. It seems like a big place, but you can fly around it in a day. Its diameter is 12,756 km. (Scientists would stick with meters, even if readers don’t. So if your scientists talk in meters, that will seem more accurate, though some groups of scientists won’t use the metric system, which can lead to problems like one which actually happened, where a Mars probe was lost because one group of scientists used metric, and another, the English system.)
Another factor of a hundred gives us the moon and the earth, at 384,000 km. (Mike notes that people–Westerners?–like to think about numbers in units of ten.)
Another factor of a hundred is the distance of the earth orbiting the sun, 150,000,000km. If you define this distance as a unit, 1 astronomical unit, then we can get back to talking about even bigger numbers in quantities that people have a better chance of understanding. Don’t break down enormous distances as trillions of kilometers, think about solar-system-sized distances in astronomical units (AUs).
Another 100, then we get the whole solar system, at about 100AU.
Another 100 (10,000 AU), and we’re making a circle around our solar system, including space… and we haven’t yet run into more stuff. Instead, there’s mostly nothing outside our solar system, just a circle of space. Distances between stars are really big compared to the other measurements we’ve been using.
It takes another step of 100 (approx 17 light years) before we start to get stars: our solar neighborhood. Here, there’s a handful of stars. (A light year is the distance light travels per year. Astronomers find it really frustrating when people want light years to be converted into miles or kilometers, but the enormously huge numbers that result don’t really have a significant meaning to people. A light year is about 63,000 AU, or 10(13) km.) The near stars are a few light years away (Proxima Centauri at 4.2 light years); closer than that, there’s nothing. (Mike notes that if you are writing near-future work where the humans are colonizing near earth, then they’re going to be working with stars that we actually know about. There are resources for finding out about these stars, and he’ll provide us with names for those.)
At another 100, we reach the extended solar neighborhood (perhaps the solar suburbs), 1,700 light years across. There’s an enormous number of stars in this range. (Ian asks, “How far out do you have to go before the sun stops being a disk and becomes a point of light?” Mike asks, “With what tool?” Ian answers, “With the naked eye.” Mike asks, “Is there an atmosphere?” Ian doesn’t have an answer. Mike says he’ll calculate it out later.) (Mike says, “There’s one thing writers should know if they’re going to submit to Analog. Don’t submit stories with colonies in orbit around a star that has a common name. The stars in the sky, Betelgeuse, etc., almost certainly don’t have life as we know it around them because they’re super giants or young and hot and there hasn’t been time for life to involve. The brightest stars are dangerous; they may be born and die in millions–not billions–of years. But picking the right kind of stars for your story is stuff that will be easy to do, with a little knowledge.)
Another 100, and you get the Milky Way, with a diameter that’s hard to measure, but is something like 75,000-100,000 years. (When you look through space, you’re looking through time. The starlight we see is old, because it’s taken many years for the light to reach us. The stars we’re looking at aren’t doing what we’re seeing; they did that years ago, maybe hundreds of thousands of years ago. The actual star may be blown up by now. But the exciting thing about this is that when we look at very distant objects, we’re seeing what the universe looked like billions of years ago.)
Another 100 gets us to the local group of galaxies, several million light years. Interestingly, the galaxies are closer to each other (relatively, considering their size) than the solar systems are to each other.
Another factor of 100, and we get a big chunk of the universe. There’s a large scale structure, where we can see galaxies forming clusters. We think we understand why this happens now, but exploring that has been an active area of research for the past 20 years. One of the theories some astronomers have put forward is that if you look at the universe at large enough scales, it seems uniform and homogeneous, and this might be true–if you could look at a large enough scale–but even somewhat local, we’re still seeing formations and structures.
This is something on the order of 100 billion light years. We can’t go out by another 100 factor, because that’s outside the observable universe.
We think the universe is infinitely big, but we can only see back to the beginning of the universe. We need to wait for the universe to get older so that light from more distant areas can reach us.
We can see back to light coming from the microwave background radiation from when the universe was about 400,000 years old. We can’t see back further because the universe was hotter and denser and opaque. If you imagine stretching the sun, which is opaque, over the entire sky (and making it less hot), then that’s what the universe was like.
The rate of expansion in the universe has changed over the age of the universe; we think we understand why, though giant questions remain. Mike will discuss this later.
We figure out how far stars are from the earth by seeing how they move during the earth’s orbit (or appear to move), and then triangulating their position. A parsec is one parallax second, a parallax that is a one arc second shift in distance during the earth’s orbit, which is how it’s derived. It’s also 3.26 light years. In cosmology, they’ll use megaparsecs as a unit.
We think we understand the past, but we’re uncertain about what will happen in the future. We no longer think there will be a collapse and a crunch. Now we’re trying to decide whether the universe is going to expand so much that galaxies will be so distant from each other that you can’t see other galaxies, or whether atoms themselves will rip apart.
In the past, when cities weren’t as big and light pollution wasn’t as bad, people had a more natural connection with the sky. You may not be able to assume people have had experiences with the stars because of where they live.
So: when you’re trying to convey scale, remember that no one has a grasp on these distances, not even astronomers. They use math tricks and analogies to get an idea. The general public needs even more of that. So, when trying to relate things to readers, relate them to everyday experience whenever possible, if only to boggle with the truth. For instance, how long would it take you to walk to the moon if you could? Or the sun, or another star? Or how about at jet plane speeds?
To illustrate his points about education, Mike Brotherton brought in a couple of videos that parallel the content of his lecture today.
The first one, Powers of Ten, is an old-fashioned video with pingy music that shows the powers of ten traveling from human scale, to intergalactic void, and then back down to human scale, and even further down to a single proton. The video is on youtube here, though our teacher said the owners are vigilant about the copyright, so it might get pulled down. Some interesting quotes: “This lonely scene, the emptiness with dust specks of galaxies, is normal. It’s what most of space looks like. The richness of our neighborhood is what’s unusual.” Also: “Notice the rhythm alternating between activity and stillness as we pan out and pan back in to look at microscopic material. This is a pattern that remain steady through both journeys.)
The second one is the introduction to the movie Contact. Basically, it’s a Hollywood take on Powers of Ten. It’s less informative, but much more beautiful. I particularly liked the way that they used radio sound to show that as you move away from earth, you’d hear older and older radio waves, because the new ones haven’t had a chance to travel yet… unfortunately, it also contains errors. 1) For instance, my favorite thing, the radio, isn’t quite accurate. As you go out into space, you move back in time because the radio signals travel at the speed of light, but the movie doesn’t synch them correctly. Mike says he gives them artistic license on that because of the way the movie works; as the movie pans out further, the speed goes faster, and so what you’d actually hear if the movie did it right would be radio from the last few years for a login time, then the last century going by really fast. On the other hand, it’s nicely done, and it’s a good visual dump for establishing that radio travels at a speed, which is important later in the movie. 2) The asteroid belt they show looks much more dense in the film than it would really look. If you were out on an asteroid, really, an asteroid the size of Texas, you wouldn’t see another asteroid. This is a big misconception about how dense the belt is. 3) Some of the objects that the path goes through, because they’re cool looking, you couldn’t actually pull through in a smooth path. So this is not a real line of sight. The film actually shows what would be a weird jerky path, despite the smooth impression it gives.
This brings up the question, for Carrie Vaughn, about where you draw the line between exact accuracy and illustrating a concept. For instance, CONTACT isn’t totally accurate, but it illustrates the concept beautifully and is very engaging–and gives the audience an accurate impression of the overall, even though there’s an inaccurate impression of the minutiae. So is that okay? Well, Mike says he’d rather be accurate, but he acknowledges that being more accurate can make things less interesting. He says if you have to be inaccurate, you should at least be sure not to be misleading.
Kelly Barnhill suggests that education is done by metaphor. You start out learning that electrons travel linear paths, even though that’s not true, and then as you get older, you get more sophistication–atoms are probabilities.
Mike acknowledges that, but warns us that the educational metaphorical short-cuts can cause real problems. CONTACT is very effective, he acknowledges, and it’s one of his favorites and one of the most accurate science fiction films in decades… and it’s still got errors. For instance, when the main character gives the numbers for calculating the percentages of planets that would have alien life, she gets the math wrong by orders of magnitude.
Mike says that with books people are interested in getting things right–there’s time and space allotted to get things right. In movies, you have to get creators who care, or nothing will happen. Some creators care–Kubrick working with Clark on 2001. However, there are lots of other circumstances where the creators don’t care. They don’t think problems will bother the audience. And that speaks to an issue of general scientific literacy. If the audiences knew enough science to care, it would throw you out of the movie when you noticed an error. But enough people in the audience have to have scientific literacy before they care, and accurate movies would be one way to create that audience of people who care, so it’s a chicken and egg problem.
People are good at figuring out things about human behavior. So we notice when actors are very poor. But we aren’t experts at science, so when the universe on screen doesn’t conform to the real universe, we don’t notice.
James Cameron is a stickler for getting things right, so he ran into a scientist who told him that in Titanic where they can see the stars when the lights go out, you’ve got the wrong stars. You’ve got the southern hemisphere stars, not the northern hemisphere stars. Cameron dismissed him–but when he did a remastered edition, they called the scientist so they could fix it.
So sometimes, the question is getting the right people in the right position to exert influence–along with creators who care.