Traditionally, observers play no special role in physics. Like bird watchers in a perfect hide, we observe the outcome of experiments, or gaze at the stars through our telescopes, taking no part in the action. Modern physics, however, tells a different story. It suggests that the very act of observation can influence what is being observed and challenges our classical understanding of observation in other ways too.

In this project, brought to you in collaboration with FQXi, we'll explore the role of observers in physics. With the help of leading experts, we will bring you articles, videos and podcasts that probe current understanding and cutting edge research into this strange and fascinating topic. And we even take a detour into the role of observation in mathematics. Enjoy!

**The limits of observation ** — Physics is all about observation, but how much can we actually see? These articles explore some of the limits of observation — be they natural, scientific, political, or down to quantum jelly.

**Watch and learn? ** — Quantum mechanics suggests that the very act of observation can change what is being observed. The very vastness of the cosmos means we need to understand our place in it before we can draw conclusions about it. How can this be? This series of articles and videos introduces basic questions about the role of the observers in physics.

**Context is everything ** — Imagine your weight depended on the colour of your underwear! Something quite similar may be happening when you are measuring things in quantum physics. Find out more about this so-called *quantum contextuality* in this series of articles and videos.

**The cosmic microwave background ** — Few observations have given as profound an insight into the workings of our Universe as the detection of the cosmic microwave background. This faint glow confirms that the Universe started in a Big Bang, tells us what it is made of, what shape it is, what its future is likely to be, and more. The CMB provides a great example of the interplay between observation and theory in physics. Find out more with this collection of articles.

**Can maths exists if you can't see it? ** — Unlike physicists, mathematicians don't need to "see" something to be certain it exists. Many mathematical proofs show that a mathematical object exists by logical necessity, without actually constructing it. Are these proofs really as valid as constructive proofs? And what happens if you try and avoid them? Find out with this collection of articles.

This project is a collaboration between *Plus* and FQXi, an organisation that supports and disseminates research on questions at the foundations of physics and cosmology.
The FQXi community website does for physics and cosmology what *Plus* does for maths:
provide the public with a deeper understanding of known and future discoveries in these areas, and their potential implications for our worldview.