How big is the Universe?

The Universe is astronomically large, says Neil deGrasse Tyson and as he explained to Graihagh Jackson, it might tell us why we haven't found any evidence of life elsewhere...

Graihagh - It’s the Naked Scientists here, with me Graihagh Jackson and today, are we alone in the universe? Why haven’t we found any evidence of life elsewhere? Well, half the problem is the the universe is a big place… but how big is big…

Neil - Astronomical. You know that’s our word - right? People have used that word to describe how big national debts have been or how large things are. But let me use it in the way it was intended, the way nature had always planned to use it - the universe is astronomically large - there’s no other way to say it.

Graihagh - Meet Neil deGrasse Tyson.

Neil - An astrophysicist and co- author of Welcome to the Universe, and as my day job I serve as Director of New York City's Hayden Planetarium, which is part of the American Museum of Natural History.

Graihagh - I suppose it’s kind of hard to wrap your head around, so how big is astronomical?

Neil - You raise an interesting philosophical point because when normally when we describe our life experiences, we compare them to other things that are of commensurate intensity, or size, or weight. You know you'd say "how big was that hailstone?" "Oh it was as big as a golf ball." So you would compare two things that already exist in your life experience. But since the size of the universe falls outside of our life experience, there’s no easy corresponding thing to say "the universe is so big. It’s as big as a…" See that’s the end of the sentence. There’s nothing you can add or bring to the cause. So the way we try to do this is you try to build up from things that are familiar - how big the universe is, and you rapidly enter realms that are inaccessible. But you have a thread, however thin, that takes you back to something that you do recognise and that you do understand. And so that’s how this basically works. I’ll give you an example: If you take a school room globe - a foot across maybe - and ask people "if this is the size of the Earth where would you put the Moon?" Like how far away is the Moon. People typically put it at most a metre away - okay. But, in fact, on that scale the Moon is ten metres away. Ten metres away from a globe that size. And how far away is Mars on that scale? Well, it is many kilometers away. And you start building and building and building. How big is the Sun compared to Earth? Well, if you hollowed out the Sun, you could pour more than a million Earths into the Sun and still have room left over. So, oh my God, the Sun is huge. And so this is the kind of exercise you go through and that gives us some hope of grasping the sheer scale and size of things.

Graihagh - But that's only our solar system. We're talking about the whole universe here. So talking about understanding the universe, there’s theories out there that suggest actually there may be many universes and, actually, we can only see a section of our universe. But, within our universe, how many galaxies are there, how many stars within those galaxies, planets?

Neil - So the observable universe contains approximately 100 billion galaxies, and a galaxy contains upward of a 100 billion stars. And planets, we have come to recognise, are quite common and when you put in some good estimates you get about 1.8 billion planets in the galaxy.

Graihagh - Not a small number then?

Neil - No, not a small number.

Graihagh - And we talk a lot about Drake's equation. This is trying to calculate how much life or intelligent life could be out there. You say 1.8 billion planets - what number of those could be what we would consider habitable?

Neil - Just because you're a planet doesn't mean there’s life on them. And, by the way, this conversation could go both ways. Well, you could say you're not going to have life on all of those planets. Well, actually some planets have moons, and the moons themselves could have life, as an example. There are estimates ranging anywhere from one, which is just us, to I would say several hundred. Some cases of a few thousand but if you’re going to be sort of middle of the road conservative, you’d say several hundred civilisations in the galaxy.

Graihagh - Where do you site on that spectrum youself? Are you a more conservative estimate or are you thinking there might be much more life out there?

Neil - I don't know that I’m actually on the spectrum. I’m a little bit off the spectrum. I have a slightly unorthodox view and it's: who is deciding that we humans are intelligent? Cause we're looking for other lifeforms like us, but who decided that we are intelligent? Well - we did, so we say we’re intelligent. And the other life forms on Earth - no, just us, just us! So I keep wondering, could there be lifeforms out there that are vastly more intelligent than we are on a level where they would not rate us as intelligent? Consider us not even interesting enough to put on their list of a civilisation worthy of their attention. I think about this all the time.

Graihagh - I mean, most people are wondering about what they’re going to have for lunch you know. Ok, so if we loosen our definition of intelligence to include…

Neil - All big brained mammals right? Mammals are a branch of life that only really took a foothold by luck because the dinosaurs went extinct by an asteroid, so they had bad luck. But that pried open ecosystems enabling early mammals to take footholds in places where they previously just would have been h’orderves for the terrible lizards that we call dinosaurs. So the asteroids are bad for dinosaurs - good or mammals. So we rise up and now we are basically some of the most intelligent creatures on Earth. Rats and mice, and chimps and humans, and dolphins and whales, and the domesticated animals - dogs and cats. So if that branch never took hold then mammals would have never risen to what we now see. And that was only 65 million years ago out of a 3.5 billion year history of life on Earth. So the contingency of the existence of our intelligence is something that is not clear would just duplicate in another planetary system, because it's not obvious that what you need to develop intelligence is as important for survival like other things like: can you run fast, do you have big teeth, can you hide, do you have camouflage. There are plenty of ways you can dominate your ecosystem and thrive that have nothing to do with what we think of as intelligence. So I don’t see why most planets that have life would just have plenty of life just happily coming along, susceptible to the forces of natural selection and evolution of course, but without intelligence every arising up. I think there'll be plenty of such places are doing just fine in the galaxy and across the universe. Now, if you do happen to develop intelligence, and you did it earlier ago than mammal intelligence developed on Earth, then maybe you've had a billion years to develop intelligence instead of our measly 65 million years from the branch of life called mammals. So, imagine a life form that’s been developing intelligence far longer than ours. We could end up looking like no greater than worms slithering in the street in the presence of their intellect. I think about that all the time.

Graihagh - I have one final question for you and that is - if you ever got the chance to meet an alien, an extraterrestrial, what would you say?

Neil - Here's what I would do. I would show the alien - I'd assume they could see - and I would show the alien our periodic table of elements. I would find out how they count; they’ve got to be able to count. Once we learn how to count, once we learn about the elements, then we can do some rudimentary mathematics. Do they have representation for the value of Pi? Pi is very important mathematically and it's practically important. How do they present Pi? Then I compare my representations, our representations, with them? So you build a vocabulary from things we have in common. I'm not teaching them English - that’s not happening. And then I would ask how you have solved these various problems? I would ask for help because for sure human civilisation in 2016 needs help. Now I'd hope that they’re benign and kind, because if we were they, we would come upon civilisation less advanced than we are and we would just round them up into reservations, or kill them, or enslave them. Like I said - put them in a zoo as research curiosities. So I would hope they don’t treat us the way I know we would treat them.