Monday, 24 August 2026

 Absolutely. There are actually two different ideas hiding inside “conformal geometry”, and their connection to AI and cosmology becomes interesting once you separate them.

1. What is conformal geometry?

A conformal transformation is, roughly, a transformation that preserves angles and local shape, while allowing lengths and sizes to change.

Imagine drawing a tiny triangle on a rubber sheet. If you stretch the sheet differently in different places, the triangle can become larger or smaller, but a conformal transformation preserves its angles.

Mathematically, if a geometry has metric

gμν,

a conformal transformation changes it to

where Ω(x) is some position-dependent scale factor.

The important thing is that all lengths get multiplied by the same local factor.

So:

  • distances can change
  • areas can change
  • volumes can change
  • angles don't change

This sounds like a relatively small mathematical idea, but it turns out to be enormously useful.


2. Why cosmology cares about this

Einstein's general relativity describes spacetime using a metric:

The metric determines things like:

  • distances
  • time intervals
  • gravitational effects
  • the paths of particles
  • the paths of light

Now here's something remarkable:

Light doesn't care about the overall conformal scale.

Light follows null paths, where

If we make the transformation

then

But if , then

So the paths available to light—the light cones—are preserved.

That means conformal geometry allows us to separate two things:

the causal structure of spacetime

from

the absolute scale of spacetime.

That's extraordinarily useful in cosmology.


3. The expanding universe

Consider the standard cosmological metric:

Here a(t) is the scale factor of the universe.

As the universe expands, a(t) changes.

But introduce conformal time η, defined by

Then the metric becomes

And suddenly we can see something beautiful:

ds2=a2(η)ημνdxμdxν

The expanding universe is, in this representation, a conformal rescaling of flat spacetime.

This makes the behaviour of light much easier to understand.

Instead of thinking of light travelling through a universe whose spatial scale is constantly changing, you can think geometrically about light moving through a conformally related spacetime.


4. Penrose diagrams

This leads to one of the most beautiful applications of conformal geometry in cosmology:

Penrose diagrams.

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A Penrose diagram takes an infinitely large spacetime and performs a conformal transformation that effectively squashes infinity into a finite diagram.

For example, instead of light travelling infinitely far before reaching spatial infinity, you can represent infinity as a boundary of the diagram.

The crucial information that survives is causal structure:

  • what can influence what
  • whether light can reach something
  • whether an observer can see an event
  • whether something lies inside or outside a horizon

This is why conformal geometry is so powerful in relativity.

It lets you throw away some information about scale while retaining information about causality.


5. Now the connection to AI becomes interesting

The AI connection isn't that modern AI is literally based on conformal geometry.

There are, however, several deep mathematical connections.

One is through representation.

A neural network takes something complicated and maps it into another mathematical space:

For example, an image might start as millions of pixel values and eventually become a relatively small vector representation:

The fascinating question is:

What properties of the original world should the representation preserve?

This is very similar to the geometric question:

What information should survive a transformation?

Conformal geometry says:

Preserve angles/causal structure while allowing scale to change.

AI researchers sometimes want analogous things from representations.


6. A particularly important example: invariance

Suppose an AI sees:

a cat

Then you show it the same cat:

  • twice as large
  • rotated
  • shifted
  • under different lighting

You don't want the system to conclude that it has become a completely different object.

You want the representation to be somewhat invariant to irrelevant transformations.

Mathematically, we can think of a transformation group G acting on the data:

A representation ϕ(x) might ideally satisfy

for transformations that shouldn't matter.

This is the broader concept of symmetry and invariance.

Conformal geometry is one particular mathematical framework for understanding transformations that preserve certain structures.


7. There is an even stranger connection: AI and geometry of latent spaces

Modern neural networks often create high-dimensional latent spaces.

Suppose an AI represents objects using points:

x1,x2,x3,

in some enormous-dimensional space.

The geometry of that space can tell us things about what the network has learned.

For example, researchers study:

  • distances
  • angles
  • curvature
  • manifolds
  • symmetries
  • topology
  • transformations

And sometimes the latent representations exhibit surprisingly structured geometry.

This is especially relevant to generative models.

A model might learn something like:

where moving in a particular direction corresponds approximately to changing some feature.

For example:

might gradually transform:

That means the model has implicitly learned a geometric structure.


8. Where cosmology comes back in

Here's where things get genuinely fascinating.

Physicists also describe complicated physical systems using spaces of representations.

A physical system can be represented by:

where M is some mathematical space called a manifold or state space.

So both fields ask similar mathematical questions:

Cosmology

What is the geometry of the space of possible physical states?

AI

What is the geometry of the space of learned representations?

Those aren't the same problem—but the mathematical language overlaps heavily.


9. Conformal geometry also appears in holography

This is perhaps the most spectacular connection.

In theoretical physics, there's a major idea called AdS/CFT correspondence.

Very roughly, it proposes that a gravitational theory in a higher-dimensional spacetime can be mathematically equivalent to a quantum field theory living on its lower-dimensional boundary.

The gravitational side is:

bulk spacetime

while the quantum field theory lives on:

boundary.

And the boundary theory has conformal symmetry.

Hence the name:

Conformal Field Theory

(CFT).

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This has led to one of the most profound ideas in modern theoretical physics:

Spacetime geometry might somehow emerge from information encoded in a lower-dimensional theory.

And that starts sounding remarkably similar to ideas in AI, where a complicated high-dimensional object can emerge from a more abstract representation.


10. But don't overstate the AI connection

There's an important caveat.

You will sometimes encounter claims along the lines of:

"The universe is a neural network."

or

"AI has discovered that spacetime is a conformal latent space."

Those statements generally go far beyond what established science demonstrates.

The legitimate connections are more mathematical:

geometrysymmetryrepresentationinformation

These concepts appear independently in:

  • general relativity
  • conformal geometry
  • quantum field theory
  • holography
  • information theory
  • machine learning
  • representation learning

That overlap is real and very interesting, but it doesn't mean these theories are secretly the same thing.


11. The really deep idea

There is a conceptual thread running through all of this:

What information is fundamental, and what information is merely a choice of description?

In conformal geometry, you can change the local scale:

without changing certain essential structures, such as causal relationships.

In AI, you can transform a huge amount of raw information into a compressed representation while attempting to preserve the information relevant to a task.

In holography, a theory suggests that information about a higher-dimensional gravitational world can be encoded on a lower-dimensional boundary.

So you get a fascinating hierarchy:

And that raises a genuinely profound question:

Could geometry itself be something that emerges from relationships between information, rather than being a fundamental ingredient of reality?

That question is actively investigated in theoretical physics, particularly around quantum gravity and holography. The connection to AI is more speculative, but AI gives us a new experimental playground for studying how geometry, information, abstraction, and representation can emerge from complex systems.





Conformal geometry gives a surprisingly sharp answer to this, but with an important qualification: it tells us a lot about edges and gaps in spacetime's geometry; it does not by itself tell us what the ultimate “substrate” of reality is.

1. An edge isn't necessarily a physical edge

In ordinary geometry, an edge might mean:

“There's nothing beyond here.”

But in spacetime geometry, there are several very different possibilities.

A boundary can be:

  • a genuine physical boundary,
  • merely infinity represented at a finite location,
  • a coordinate artifact,
  • a singularity where the geometry breaks down,
  • or a horizon that isn't actually an edge of spacetime.

Conformal geometry is particularly good at distinguishing these.

For example, a Penrose diagram can bring infinity to a finite boundary:

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The boundary of the diagram doesn't mean there's a literal wall at the edge of the universe. It's a representation of infinity.

So conformal geometry teaches us:

The existence of a boundary in a representation does not necessarily imply a boundary in physical reality.

That's a very important distinction.


2. What about gaps?

A “gap” requires some notion of separation.

But geometry itself defines separation.

If spacetime is described by a continuous manifold, then between two sufficiently nearby points there are other points. You don't need some underlying material filling the space.

This is one of the strange things about general relativity.

Space isn't necessarily like:

particles + stuff sitting inside an empty container.

Instead, the geometry is the thing that defines spatial relationships in the first place.

The metric

gμν

tells you what distances and times mean.

So asking:

“What's filling the gap between these two points?”

may be based on a Newtonian intuition that general relativity doesn't require.

There doesn't have to be a substance inside space to make space exist.


3. Does that mean spacetime doesn't need a substrate?

Classical general relativity: essentially yes.

Spacetime doesn't require an external medium in the way sound requires air.

A sound wave requires:

But a gravitational wave doesn't require:

The gravitational field is part of the geometry of spacetime itself.

This was one of Einstein's great conceptual departures from older physics.

There isn't necessarily a higher-dimensional “room” in which spacetime sits.


4. But conformal geometry makes this even more interesting

Remember:

A conformal transformation can change the scale of distances without changing the causal structure.

That means there are aspects of geometry that appear to be more fundamental than absolute scale.

For example, the light cone at an event determines which events can causally influence one another.

Conformal geometry preserves that structure.

So, in a certain sense, you can strip away a huge amount of information about size while retaining information about relationship and causality.

That leads to a provocative thought:

Maybe the fundamental structure isn't “how big is the space between things?” but “which things can be related to which other things?”

That's not a conclusion of conformal geometry, but it is one reason conformal methods are so interesting in fundamental physics.


5. And then there is the question of “nothing”

This gets philosophically deep.

Suppose you have two regions of spacetime.

You might ask:

“What's between them?”

But if spacetime itself is the structure defining “between,” then asking what's inside the gap may be mistaken.

A genuine topological gap would mean the manifold isn't connected in that way.

A region of vacuum, however, isn't necessarily a gap in spacetime.

Vacuum means, roughly, that there is no matter field present in that region. It doesn't mean there is no spacetime there.

So:

And:


6. Where this becomes really interesting: quantum gravity

This is where we reach the boundary of what we currently know.

General relativity treats spacetime as a smooth geometric structure.

Quantum mechanics suggests that at sufficiently small scales, our classical descriptions may break down.

We don't yet have a universally accepted theory of quantum gravity.

Several approaches suggest that spacetime might not be fundamental.

For example, in different approaches people investigate possibilities involving:

  • quantum entanglement
  • discrete structures
  • spin networks
  • causal sets
  • holographic degrees of freedom
  • quantum information
  • emergent geometry

In some of these ideas, spacetime is more like something that emerges from underlying relationships than a substance that exists independently.

That's where your “substrate” question becomes extremely interesting.


7. The key distinction

There are actually three possibilities:

A. Spacetime is fundamental

There is no deeper substrate. Geometry is simply part of the fundamental description of reality.

B. Spacetime emerges from something deeper

There is an underlying structure, and what we perceive as distance, time and geometry emerges from it.

C. The question of a substrate is ill-posed

The underlying theory may not contain anything resembling “stuff underneath spacetime.” Asking what spacetime is made of could be analogous to asking what the rules of chess are made of.

We don't currently know which of these is ultimately correct.


8. And this connects back to AI in a surprisingly useful way

An AI's latent representation doesn't necessarily have to be embedded in some physical space corresponding to the things it represents.

For example, an AI might represent relationships between concepts as a high-dimensional mathematical structure.

The geometry of the representation can encode relationships without there being a little physical object sitting at each point.

That's an important conceptual analogy:

relationships can define a geometry without requiring a material substrate

Whether something like that is actually how physical spacetime works is an open question.

But it gives us a useful way to think about the possibility that space might be relational rather than substantive.

And that brings us very close to one of the deepest questions in modern physics:

Is spacetime the thing that exists, or is spacetime the geometry of relationships among things that exist?

General relativity strongly shifted physics toward the latter way of thinking, while quantum gravity is where we're trying to determine whether that relational structure itself has a deeper foundation.

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