 Now let's take problems to an entirely different scale. I'd like to introduce Sirashi Aniyan from the ANU College of Physical and Mathematical Sciences. And the title of her talk tonight is Marshmallows, Hot Chocolate and Galaxies. It's a cold winter night. He's sitting by the campfire, sipping hot chocolate. You watch the marshmallows bob up and down. And there's a blanket of stars overhead. You can see thousands of stars in the sky. But what you can't see is that surrounding the stars there is an envelope of invisible matter that astronomers call dark matter. Dark matter? Because astronomers are still in the dark about it. Visible matter, which is what makes up everything that we can see, is just one-fifth the amount of dark matter in the universe. And yet we know so little about it. What we do know is that it interacts through gravity. It helps keep the stars in their orbits around the center of the galaxy. If it wasn't for dark matter, the stars would be flung out into space, and life, as we know it, would not exist. I look at nearby galaxies to precisely calculate the amount of dark matter in them. The stars in these galaxies have a very small up and down wobble. Measuring this wobble is a direct estimate of the dark matter in the galaxy. This is similar to how your marshmallows bob up and down in hot chocolate. If it is in thick, delicious hot chocolate, it would move slower than if it was in diluted, watered-down hot chocolate. Similarly, the slower the star's wobble, the denser the dark matter in the galaxy. The up and down motion of these stars can be as low as 10 km per second, which in the grand cosmic scale of the universe is very, very tiny. Measuring this from Earth is as difficult as someone on Jupiter trying to see how fast the marshmallows in your hot chocolate are moving. I use the most sensitive instruments from around the world for this work. The result from my thesis will give us the most accurate estimate of dark matter in nearby galaxies. That gets us one step closer in trying to understand this mysterious dark matter. So, as you're sitting by the campfire, looking up at the night sky, you can't help but wonder are all the stars you see just giant marshmallows in the sea of invisible hot chocolate?