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The Accelerating Universe

On this episode of Our Island Universe: You may already know that the universe is expanding, but did you know that it is accelerating?

Host: Shanil Virani, Director of the John C. Wells Planetarium Harrisonburg, VA.

Follow on Twitter as shanilv  

Transcript:

The dawn of the 20th century witnessed the discovery of the Expanding Universe, but by the end of it, the Universe we discovered it is weirder still: the Universe is not only expanding, it is accelerating! What causes it? Dark Energy. But that's just a clever way of saying we don't have a clue. Moreover, this thing that we have no clue about, makes up over two-thirds of the Universe! Let's step back and see how we got into this mess.

In the 1990s, astronomers using large ground-based telescopes as well as the Hubble Space Telescope located above the Earth's atmosphere, observed a particular kind of supernova that serves as a "standard candle" in astronomy. We have a good idea of how intrinsically powerful they are so by measuring how bright we see them across the Universe, it tells us how far away they are from us. Much the same that a dim headlight on a dark night tells you a car is farther away compared to a bright headlight up close where you can actually see the car the light is coming from! With this data, the expectation was that Hubble's Law - the farther away a galaxy, the faster its moving - would still apply. Nature had other ideas. Instead, these supernovae were farther away then expected from a straight line extrapolation of Hubble's Law. The conclusion was inescapable: the Universe was accelerating in its expansion!

This result has led to a field day in theoretical astrophysics over the last decade plus! The simplest explanation for dark energy is an energy associated with the vacuum of space. But this is still an idea that needs to be tested. Circa 2015, all we really know is that the Universe mostly consists of Dark Energy and Dark Matter. The stuff you, I, planets, and stars are made up of make up only ~4% of the Universe.