String Theory and Quantum Gravity
The video discusses the attempts to reconcile Albert Einstein’s theory of relativity with quantum physics. These two large physical theories discuss radically different types of physical systems, and attempts to apply them both often come into conflict.

The theory of relativity describes how gravity works, and is built around the notion of space-time. Quantum physics, on the other hand, works amazingly well on the smallest scales and with the smallest particles, but has curious behavior like quantum entanglement.

Fortunately, because they operate at such widely different scales, the conflicts of these two theories don’t cause problems for us in our day-to-day lives. In fact, it doesn’t even usually cause problems for physicists!

But sometimes scientists try to look at problems where the rules of both apply, such as trying to discover quantum entanglement in big systems, and that’s where the conflict between how the rules operate creates huge problems. The attempt to reconcile the two conflicting sets of rules occupied Albert Einstein for the last decades of his life, and motivated much of the work of the famed physicist Stephen Hawking. The goal was a “theory of everything,” or a theory of quantum gravity, that would reconcile them.

One promising approach, developed over the last quarter of the twentieth century, is called string theory. It predicts that the universe is composed of vibrating strings of energy which make up all particles. Unfortunately, there’s no clear way to test whether string theory is true, but theoretical physicists continue to develop models to see if they can find a way.

Andrew Zimmerman Jones is a science writer with a physics background who co-authored the book String Theory For Dummies, explaining string theory and the search for quantum gravity. You can see Andrew discuss it in this YouTube video, or you can hear about it directly from physicist Clifford Johnson.

The Origin and Fate of the Universe
When we look at the stars or into the distant reaches of space, the light we see takes time to reach us. That means that each time we look into the night sky, we are actually looking into the distant past of our universe. Astronomers and physicists have looked far into the past over the last century, and have used their understanding of the physical properties of the universe to learn much about the history and change of the universe over time. The field of physics that focuses on understanding the history and evolution of the universe on large scales is called cosmology.

CERN physicist Tom Whyntie explores this growing understanding of the history of our universe in this video. Much of our information about the history of the universe comes from research done by NASA, and this article explores the different eras of the universe that cosmologists have discovered.

Since the universe is expanding, though, what is it expanding into? This video from Sajan Saini discusses the possibilities of what could happen to our universe in the distant future.