Edwin Hubble’s discovery that the universe is expanding changed not only the way we think of the universe, but also how we understand the passage of time. Bill Nye the Science Guy explains how Hubble’s finding created the foundation for other 20th century discoveries, e.g. that the universe is not only expanding, but expanding at an accelerating rate. The implication is that stars are moving apart from each other faster and faster, and that space itself is expanding. Where is it expanding into if there is no space already there? That’s one of the mysteries of modern physics, says Nye.

Marty Behsman: Bill. How are you doing? My name is Marty Behsman. I'm from Boston Massachusetts, New England. My question for you is do you believe that as space expands it starts moving at a faster and less controlled rate? I've always wondered this given our ancestors had such a closer view of time and space than we have now and it seems to have been moving pretty much faster away from us than as they had says a huge view of galaxies and what they originally mapped out. Thank you very much.

Bill Nye: Marty. Marty. Marty. So you're asking a great question. Keep in mind that in my grandfather's time it was believed by a great many people that the universe was static, that it just is the way it's always been. It's big, some extraordinarily huge size and it had always been that way. Then in my father's time relativity was discovered and furthermore the expanding universe was discovered. It was discovered nominally or largely credited to Edwin Hubble and that's what we named the space telescope after Hubble because he was looking at the stars, he was an astronomer studying various types of stars and he could identify different types of stars and then realized that all of them of a certain type were moving farther away at a very high speed. And you determine this through this famous expiration the red shift. He noticed that the stars were slightly redder than he would have expected. And this he attributed to their speed stretching the wavelength of light out. It's amazing. And this was around 1927, 1928/29. Hubble realized the universe was expanding and this was consistent with certain aspects of relativity of Einstein's postulations or theories.

All right, well then, in your lifetime Marty, people discovered that the universe is not only expanding – in fact after Hubble made the discovery everybody presumed or question or tried to figure out at what rate the universe would slow down. In other words everybody figured there's gravity, there's a big - if everything is expanding it expanded from a place. And keep in mind the big insight is not just that the matter that you and I are made of and the sun is made of that space itself is expanding. It's a hard idea. If you're not troubled by this idea you're odd, but that space itself is expanding. And furthermore, it was presumed that it would slow down, that gravity would make things slow down in their expansion and people were trying to figure out that rate. But what they discovered around the year 2000, Nobel Prize I think was awarded in 2004, what they discovered is the universe is accelerating.
And do you know why it's exhilarating? Nobody knows why Marty and this is the fascination. This is a source that just makes us all crazy in a good way. And so in this mix now it's been discovered that there is about five times as much matter or whatever it is that we can't see that has come to be called dark matter. And it's about five times as much of that as there is of the stuff that you and I are made of. And you know why? Nobody knows why, but it's gravitational influence is of great significance when you start to study the cosmos. So you Marty are living at a time where the next great discovery about the expansion of the universe, the nature of space and time is understood. You may be here when the next amazing world changing insight in astrophysics or physics or science is made. So when you go to vote Marty vote to support basic research because these discoveries are important to us. That's how we have nuclear power plants. It's how we have the Internet is understanding this physics of subatomic particles and how they relate to the physics of the cosmos, our place in space. And so who knows what the next great discovery will lead to, but it's worth pursuing because we all want to know where we came from. We want to know where we fit in the cosmos, our place in space. Cool question. Carry on!