The Shrinking Theory

A Useful Reframing of the Expanding Universe

While I know the universe is expanding, I prefer a helpful reframing: that the Universe is a fixed size and all matter within it is “shrinking.”

I prefer this reframing because it makes certain abstract ideas about our universe easier to visualize. Things like a fourth spatial dimension. And universes within universes. And what our universe is expanding into.

Stepping Back: What is a reference frame?

Freely skip this section if you already understand reference frames.

We use reference frames to establish new foundational contexts. The most common example: if you are moving (say, in a car), you can assert you are stationary and the world around you is moving (see image below).

Left: I am stationary, Right: I am in motion.

Sometimes changing reference frames feels intuitively wrong. Other times the switch comes naturally. For example, intellectually, I know the rotation of the Earth causes the Sun to rise and set. But, day to day, I think of Earth as firmly grounded and the Sun as the object in motion 🌅.

The Useful Reframing

So how do we apply reference frames and reframing to the expanding universe? Today you imagine the universe as a quite huge inflating thing. Now imagine a small, fixed-size universe you can hold in your hand, all matter within it shrinking relative to you.

This feels contradictory because all the physicists on all the planets in the fixed-size Universe observe red-shifted galaxies and proclaim their Universe expanding. How can it rest in your hand and not change size? A simple reference frame correction (i.e. reframing) resolves the faux paradox: all the matter within the sphere “shrinks” relative to us 🌼.

Visualizing the Resolution

Freely skip this section if you can visualize the previous section.

First assume that all observers are correct: [1] you observe a fixed size sphere on your hand and [2] those living in the fixed-size universe observe an expanding universe.

Now imagine an expanding universe with only two galaxies, as seen in Part 1 (A → B) of the sequence below. Now imagine the outside observer backing away from the expanded Universe, as seen in Part 2 (B → C).

Part 1: Universe Expanding, Part 2: Observer backing away

Now consider a second sequence, identical to the first but without state B.

Same as above with state B omitted.

Holding onto our visual, this sequence shows either [1] an expanding universe from the perspective of someone backing away (at the perfect pace) or [2] a fixed size expanding universe whose matter “shrinks” relative to us, analogous to a car that “shrinks” as it drives away.

Applying the Idea

So what is the use of imagining the universe at fixed size? It provides us a tool for visualizing—directly visualizing, not by metaphor—what 4th-dimensional space looks like.

Back in 2009, Radiolab put out a short called “DIY Universe,” that featured a conversation with Brian Greene talking about synthetic Universes. Back then, the media was abuzz with fears that the Large Hadron Collider could destroy the world by setting off another Big Bang, a universe within our universe. Greene and others were quite unconcerned with this, saying:

This Universe that you create would, in essence, create its own space. It wouldn’t encroach on your space by expanding into your domain…It would expand by creating new space, space that hadn’t existed before.

The reframing helps us visualize:

• 4th dimensional space: Imagine a fixed size sphere in your hand. The space within the fixed size sphere grows, like the expanding galaxy in the example above. This “extra space” that opens up is the 4th spatial dimension. When I hold a universe in the palm of my hand and watch the galaxies and atoms within it shrink, I am observing them recede into the 4th spatial dimension. They only appear shrinking because they are moving ever farther away.
• Universes within universes: Holding a universe in my hand means I can support universes within universes. The universe I hold in my hand can house people that hold universes in their hands, and so on.
• What our universe is expanding into: Rather than say it expands, we can say its size is fixed and that the matter within it “shrinks” relative to an outside observer, thus not “encroaching on” what lies beyond.

James Thompson works at Facebook on issues of global import. Previously worked at Palantir. Studied at Stanford. NSF Fellow. Married with 1 cat.