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TopHat Overview
TopHat in Antarctica

What is TopHat?

TopHat and Understanding the "Big Bang"

TopHat is an instrument that has been designed to collect data on the CMBR. Its mission is to study light in the microwave and infrared wavelengths.

The TopHat experiment includes a spinning telescope and a detector system. It will map a 48 degree diameter disk of the sky above the Southern Polar Cap. To accomplish this, the telescope will simply spin at a constant rate about its vertical axis. As the Earth rotates, the entire polar cap will be observed each day.

TopHat on the Balloon
TopHat Wireframe
A scale drawing of TopHat on top of the balloon together with a blow-up image of the top package. A wireframe drawing of the top of the TopHat test package, showing the mirrors, the dewar and the rotation stage. Click here for an animated view. (594K) (47K)
TopHat Dewar
A cutaway view of the indigo dewar.

The detector system uses bolometers. These heat sensing detectors are very sensitive and are ideal for making these measurements. This is because the CMBR is a form of heat in the sky. Using them, TopHat will be able to make observations of cosmic microwave background anisotropy of unprecedented sensitivity.

The TopHat balloon flight from McMurdo Station, Antarctica will last approximately 2 weeks.

TopHat and Understanding the "Big Bang"

The ability to understand the origin and evolution of our universe is the driving force behind the TopHat project. We can gain valuable insights into the characteristics of our universe by making measurements of the Cosmic Microwave Background Radiation (CMBR).

The Big Bang is the generally accepted theory as to how the Universe began. The idea is that the universe started out very hot and very small. As time went on, the universe expanded and cooled off. Eventually, it was large enough and cool enough for helium and hydrogen (the lightest elements) to form. This happened between 150,000 and 300,000 years after the Big Bang. It took yet another billion years or so for the first stars and galaxies to form - and nearly another 10 billion years for our sun and the Earth to form. All this time the universe has continued to expand and cool off. In fact, we can measure this expansion in the stars and galaxies around us today!

The Cosmic Microwave Background Radiation was produced at the same time the first hydrogen were produced. Since at the time the universe was very hot (over 3,000 degrees Celsius!) the universe "glowed" - just like a fireplace glows and keeps us warm. The CMBR is the leftover radiation from that glow.

TopHat measures the brightness of the CMBR in different parts of the sky. This tells us which areas of the universe were extra hot and which areas were extra cold when the hydrogen and helium were produced. It turns out that many characteristics of the universe can be inferred from the distribution of these hot and cold spots on the sky. In fact, with TopHat's measurements we can explore some very fundamental questions, including:

How fast is our universe expanding?

Will it expand forever? Or will it eventually start contracting?

What's making our universe expand?

How much of our universe is made up of the same materials that we're made of?

You can learn more about the properties of our universe and the CMBR at the following web sites:

Good for beginners:

A bit more advanced: