Expanding Universe 2D: Scale Factor & Hubble's Law |…

What is the Expanding Universe?

The expanding universe refers to the observation that galaxies are moving away from each other, with distances between them increasing over time. This phenomenon was first discovered by Edwin Hubble in 1929 and has since been a cornerstone of modern cosmology.

In this simulation, we model this expansion using a scale factor, which represents how much space itself is stretching at any given moment.

Scale Factor & Its Role

The scale factor, denoted as 'a(t)', is a measure of the overall size of the universe relative to some reference point. It varies with time and indicates how much space has expanded since the Big Bang.

For instance, if the current scale factor is 1 (at present), then at an earlier time when the scale factor was 0.5, distances between galaxies were half what they are now.

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Hubble's Law: Connecting Distance and Velocity

Hubble’s law states that the recession velocity of a galaxy is proportional to its distance from us. Mathematically, this can be expressed as v = H0 * d, where 'v' is the recession velocity, 'd' is the distance, and 'H0' is the Hubble constant.

In our simulation, adjusting the Hubble constant allows you to see how different values affect the rate at which galaxies move away from each other.

Measuring Expansion with Click-to-Measure Tools

The interactive tools in this simulation allow you to click on any two galaxies and measure both their distance apart and their recession velocity. These measurements help illustrate Hubble’s law directly.

By playing with the sliders for time since the Big Bang, you can observe how these distances and velocities change over cosmic history.

Frequently asked questions

What does a scale factor of 0 mean in this simulation?

A scale factor of 0 indicates that all galaxies were infinitely close together at the Big Bang, which is the starting point of our model. This corresponds to the initial singularity in the standard Big Bang theory.

How does changing the Hubble constant affect the simulation?

Changing the Hubble constant alters the rate at which galaxies move away from each other, demonstrating how different values can lead to different expansion rates of the universe.

Can this 2D model accurately represent the 3D universe?

While the 2D model simplifies the complexity of a 3D universe, it captures essential features like the expanding nature and the relationship between distance and velocity. It provides an intuitive understanding of cosmological concepts.

What does it mean if galaxies are moving away faster than light?

In the context of the expanding universe, galaxies are not actually moving through space at speeds greater than light. Instead, the space between them is stretching, causing distances to increase rapidly and leading to the appearance that they are moving apart faster than light.

Try it live

Everything above runs in your browser — open Expanding Universe 2D: Scale Factor & Hubble's Law and change the parameters while it is running. Nothing is installed, nothing is uploaded, the whole model lives in one tab.

▶ Open Expanding Universe 2D: Scale Factor & Hubble's Law simulation