Welcome back to The Light is a Liar, our slightly sweary, hopefully mind-expanding series about why the universe looks the way it does — and why most of that is a bloody optical illusion. Today we’re diving into what might seem like a simple question: how far is that galaxy, really?

How far is that Galaxy Really?

Imagine this: you’re looking up at the night sky. You see a red dot through your telescope. That dot is a galaxy. You ask, “How far is it?” The universe leans in, smirks, and says: “Define far.”

Let’s begin.

🔭 Redshift and Blueshift: What the Hell is Actually Happening?

When we say a galaxy is “redshifted,” we mean its light has been stretched. The wavelength has been shifted toward the red end of the electromagnetic spectrum. Here’s the official equation:

z = (λobs−λemit) / λemit

Where:

  • λobs is the wavelength we observe here on Earth,
  • λemit is what the galaxy originally emitted.

If z is positive: redshift. If it’s negative: blueshift.

But here’s the kicker: redshift doesn’t always mean the galaxy is moving away in the usual sense. There are three types of redshift:

  1. Doppler redshift — classic velocity-based stuff: car horn driving away, same idea.
  2. Gravitational redshift — light climbing out of a deep gravity well loses energy, stretches out.
  3. Cosmological redshift — space itself expands and stretches the light as it travels. This one is the bastard we’re focusing on.

Think of redshift like an interstellar game of Telephone. The original message was clear, but by the time it arrives — eons later, warped by a stretching medium — you’re just hoping the punchline still lands.

Also, worth noting: even within Doppler redshift, relativistic corrections apply at high velocities. A simple “redshift = moving away” intuition breaks down once objects approach a significant fraction of light speed. Add expansion, and the mess compounds.

🌏 The Universe Isn’t Exploding, It’s Expanding

Enter: Hubble’s Law.

In the 1920s, Edwin Hubble looked at distant galaxies and noticed that they all seemed to be redshifted. The farther away they were, the more redshifted they looked. He plotted their redshifts against distance (based on Cepheid variables), and boom: straight line. Thus:

v = H₀ * d

Where v is velocity (apparent), H₀ is Hubble’s constant, and d is distance.

This led to the idea that space itself is expanding, like raisins in an inflating loaf of bread. But here’s where most analogies fall flat:

Galaxies aren’t flying through space. Space is stretching between them.

It’s subtle, but important. If you think of galaxies as swimmers in a pool that’s inflating, they’re not swimming away from each other — the water itself is stretching, and they’re being passively pulled along.

📊 [Placeholder: Redshift-distance graph with ΛCDM curve]

One complication? Hubble’s “constant” isn’t so constant. Depending on which method you use — early-universe data from the Planck satellite, or late-universe data from supernovae and Cepheids — you get slightly different values. This is the infamous Hubble tension, and it hints that we might be missing something fundamental about cosmic expansion.

⏳ Cosmological Redshift vs. Doppler Redshift

Let’s take a photon — say, from a galaxy that spat it out 13 billion years ago.

If the universe were static, the photon would travel through space like a bullet through air. Doppler shift would tell us how fast the galaxy was moving when it fired. Done.

But in an expanding universe, the space that photon is moving through is stretching as the photon travels. That light is being redshifted not because the source is moving, but because the road itself is stretching beneath its metaphorical feet.

It’s like trying to run across a treadmill that’s getting longer as you go. You never quite catch up, and your footprints keep getting farther apart.

📊 [Placeholder: Light wave stretching diagram]

Here’s what’s wild: photons don’t lose energy because of friction or obstacles. They get redshifted purely because the metric of spacetime is changing.

This redshift is cumulative and nonlinear. That means the longer the light travels, the more it gets stretched. But it also means:

  • Redshift isn’t a direct measure of velocity.
  • And it sure as hell isn’t a direct measure of distance.

The further complication is that when we observe this redshift today, we’re integrating across the entire history of expansion the photon experienced. Which means interpreting redshift requires plugging it into a cosmological model — and hoping our model is accurate.

😯 JWST and the “Too-Old Galaxy” Problem

Now, cue the James Webb Space Telescope. JWST sees deeper into infrared and earlier in time than Hubble could dream of.

And what did it find? Galaxies at redshifts of z > 10, meaning they formed less than 400 million years after the Big Bang. Cool!

Except these galaxies were way too massive and way too developed. Spiral arms, mature stars, metal content. Things that shouldn’t exist that early under the ΛCDM (Lambda-Cold Dark Matter) model.

For example, GN-z11 and CEERS-93316 both appear at shockingly high redshifts, but show evidence of complex structure.

This sparked all kinds of freak-outs in the cosmology community. Are we wrong about how fast stars formed? Is our timeline buggered? Is ΛCDM broken?

Probably not totally broken, but definitely rattled. Some theories now propose:

  • Faster early star formation
  • Alternate feedback mechanisms
  • Tweaks to inflation or dark matter interactions

But the real point is: we’re seeing ancient light, stretched and distorted by 13+ billion years of expanding space, and trying to reverse-engineer a coherent story from it.

It’s like finding Roman ruins with a Starbucks in them.

This also ties into a growing interest in alternative models, including early dark energy and modifications to inflation. Most still preserve the core of ΛCDM, but it’s clear that redshift alone doesn’t tell the full story.

📉 Why Redshift Does NOT Mean “Farther”

Okay, back to the core lie.

You see a galaxy with a redshift of z = 1. You might think, “Oh, that’s twice as far as one with z = 0.5.”

Nope.

Redshift doesn’t scale linearly with distance. It depends on the entire expansion history of the universe.

There are multiple ways to measure “distance” in cosmology:

  1. Lookback Time — How long the light has been travelling. Kinda intuitive, but not the full picture.
  2. Light Travel Time — The naive “distance = speed * time” approach. Misleading, because the space the photon traverses is expanding.
  3. Proper Distance — The actual distance to the object right now, if you could freeze the universe and measure.
  4. Comoving Distance — Accounts for expansion, placing objects on a grid that stretches with space. Think of it as the GPS coordinate system of the cosmos.

📊 [Placeholder: Timeline with lookback time vs light travel time]

Here’s an example:

Galaxy A: z = 1

  • Light travel time: ~7.8 billion years
  • Proper distance now: ~10 billion light-years

Galaxy B: z = 6

  • Light travel time: ~12.7 billion years
  • Proper distance now: ~27 billion light-years (!)

Wait — how can it be 27 billion light-years away if the universe is only 13.8 billion years old?

Because space expanded while the photon was in flight.

So yes, the universe is bigger than the age of the universe would suggest.

Also, it’s worth noting that these distance measures are model-dependent. Change the cosmological parameters (dark energy density, matter density, curvature), and the computed distances shift.

🩸 Bonus Mindfuck: Shouldn’t Galaxies Be Expanding Too?

Here’s a cheeky question we raised in Part 1: if space is expanding, why don’t galaxies (and atoms, and you) expand with it?

Answer: they would, if expansion happened at all scales. But it doesn’t.

Gravity and atomic forces fight back.

Below a certain scale (think galaxy clusters), local forces dominate and hold things together. Space is stretching between galaxy clusters, but not inside them.

Still… is it really that simple? What if we’re embedded in a slow expansion we can’t detect because our rulers are expanding too?

If your ruler is growing at the same rate as the thing you’re measuring, you’d never know.

More on that thought experiment in a future post.

And in some alternative formulations of physics, such as conformal cyclic cosmology or scale-invariant gravity theories, the idea of expansion becomes more about the scaling of the whole system rather than absolute growth.

👀 TL;DR (Too Long, Distorted Reality)

  • Redshift is about stretched light, not just moving galaxies.
  • Cosmological redshift comes from the expansion of space itself.
  • Hubble’s Law is a good first approximation, but things get weirder at high redshift.
  • Distance isn’t one thing. There are many flavours of cosmic distance, and redshift doesn’t map directly to any of them.
  • JWST is showing us galaxies that challenge our neat little timelines.
  • The light lies. But it’s all we have.

🚀 Next Time: Loop Me Up, Scotty

In Part 3, we’ll ask: what if the universe loops back on itself? Like, literally. We’ll explore cosmic topology, 3-tori, light paths that wrap around like a Pac-Man map, and what that might mean for our perception of the cosmos.

You might already be seeing the same galaxy from multiple angles and not even know it. Just sayin’.

Stay curious. Stay skeptical. And remember:

The map is not the terrain. And the light is a goddamn liar.