Today @CERN endorsed an ambitious vision for the future of particle physics - a 100km super-collider to study the fundamental ingredients of our universe in unprecedented detail.

Is this a good investment? Here's a long thread on why, scientifically, I think it is:

We are at a crucial juncture in our exploration of nature at the fundamental level. The LHC's greatest achievement so far is the discovery of the Higgs boson, a quantised wobble in the Higgs field. The Higgs is unlike anything we've ever seen before...

This isn't hype, particle physicists aren't just making a big fuss about the latest particle. The Higgs is the simplest particle we have ever discovered; it has no spin, no charge. Its only property is its mass and this is what makes it so theoretically perplexing.

What we know about quantum field theory tells us that the Higgs as we find it should not exist. Quantum fluctuations at very short distances ought to blow the Higgs field to zero or way up the scale of quantum gravity (aka the Planck Scale at 10^19 GeV).

This would be REALLY BAD because fundamental particles get their masses from the Higgs. If the Higgs field were zero or at the Planck Scale there would be no atoms, and therefore, no us.

However, in our universe the Higgs field has a value of 246 GeV, which is neither 0 nor 10^19 GeV. This situation is akin to dropping a pencil on a table and it landing tip down and standing up. It makes no sense!

Confronted with such a weird situation it is natural to assume that there must be something else going on - maybe a super-thin wire suspended from the ceiling or a tiny clamp is keeping the pencil upright? Zoom in close enough and we should see what's responsible.

Likewise, if we zoom in on the Higgs we'd expect to see something new that's responsible for keeping it stable. There are various ideas - supersymmetry, extra dimensions or the idea that the Higgs is made of smaller things. However, so far the LHC hasn't seen any of them.

This has started to shake the foundations of fundamental physics. In fact, it challenges the approach that's proven so successful for centuries; the idea that as we zoom in on matter we discover new, deeper layers that explain the layers above.

The LHC is suggesting that this process might be coming to an end. That we can't explain the Higgs by zooming in closer. However, the LHC isn't powerful enough to settle the argument. By the time it shuts down in the mid 2030s we will still only have a fairly fuzzy picture...

The 100km collider would let us zoom in on the Higgs and study it in exquisite detail. If it still looks like a fundamental particle under this super-powerful microscope and we don't see any other new particles, we would know for damn sure that we're missing something BIG.

This would be a huge shake to the foundations of physics and would force us to rethink the fundamentals of the subject. The LHC is only hinting in this direction. To settle this we need the next collider.

Critics have said 'you promised we'd find new particles at the LHC so we didn't find any, and there's no reason to expect any at a bigger collider'. This is wrong in detail, but also fundamentally misunderstands what particle physics is about.

Despite being built into the name of the subject, particle physics isn't about finding new particles, some new bumps on a plot and catching a plane to Stockholm. It's about understanding the laws of nature at the most fundamental level.

The Higgs is challenging our understanding of these fundamental laws. We need to know one way or another whether it really is alone and fundamental, because if it is it will force a major rethink of our historic approach to understanding nature.

There are loads of other great arguments besides this - the nature of dark matter, the origin of matter in the universe, and the basic fact that exploratory experiments often throw up things we never imagined or expected.

But for me, understanding the Higgs is a strong enough argument on its own. We are guaranteed to learn something new about the fundamental laws of nature with this new machine.

You might just ask, why not just ask theorists to assume the Higgs is solitary and fundamental and get them to rethink their ideas. Well, as leading-theorist Nima Arkani-Hamed said to me recently, "You need experiment to turn to turn your entire fucking world upside down."