Alex McColgan

How do we know it's missing if we've never seen it?

We certainly weren't around back then.

Thankfully, the early universe itself left us the answer.

Measurements of the cosmic microwave background have allowed cosmologists to calculate exactly how much baryonic and

non-baryonic matter was created as a result of the Big Bang, to an accuracy level of better than a few percent.

That gives us a precise budget for how many atoms should be in the universe today.

But just because it's made of stuff that's visible to us, doesn't mean it's easy to see.

When astronomers go out and count up all the stars, gas, dust and plasma we can see,

With the help of models and simulations, we only find about 60% of what should be there.

The rest has to exist for early universe physics to make sense, but unless we can find it, we can't prove that our models are right.

Maybe we've got it all wrong.

Thankfully, scientists haven't been that quick to give up, and instead turned their attention to working out where the missing mass may be lurking.

And they came up with an intriguing hypothesis.

Missing baryonic matter is not the only missing mass, and perhaps they're hiding together.

Finding out that 40% of all baryonic mass is missing must have been seriously annoying for astronomers.

Understanding the universe is much harder with such a fundamental gap in our knowledge.

So, why not fill those gaps?

This is easier said than done when you're on the hunt for missing matter, but if you're trying to learn more about other subjects in maths, science, and computing, then Brilliant, the sponsor of today's video, is the tool for you.

I really like Brilliant's interactive approach to filling in knowledge gaps.

Their online platform gives you interactive challenges to try because most gaps are easiest to fill through doing rather than just reading or memorization.