The physics of observers

Physicists believe that around 82% of all the matter in the Universe is invisible dark matter. But if it's invisible how do they know it's there?

Cosmology has an ambitious goal: to understand the Universe in its entirety. Find out more here.

Since he Universe is all there is, there's nothing for it to expand into. So what does "expansion" mean?

Some of the Universe's most important secrets are hidden in the shape of a beautiful undulating curve: the power spectrum of the cosmic microwave spectrum. This article explains how.

Find out all you need to know about the cosmic microwave background in this comprehensive overview.

To understand the why the cosmic microwave background tells us so much about the Universe, you first need to understand what created it: sound waves travelling through the early Universe.

The cosmic microwave background is the earliest light we can see in the Universe. So important is this baby picture of the Universe, it's been involved in two Nobel Prizes. Why?

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Imagine if your body weight depended on the colour of your underwear. Strangely, something quite similar happens when you make measurements in quantum mechanics. Discover more about contextuality in this video interview with Jeremy Butterfield, philosopher of physics.
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Quantum mechanics suggests that observers can influence the outcomes of measurements. If that's the case, then do these observers need to be conscious? Does consciousness play a special role in physics at all?

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Modern theories suggest that the Universe really is unimaginably large — perhaps it's infinite, but even if it's not, it's so large it may as well be. But does this sheer scale affect how we reason about cosmology? In this video interview, we talk to David Wallace to find out more.