There's nothing that unites humanity more than the awe we feel when we look up at the stars and admire the beauty of our amazing Universe. With NASA's budget rising to over $22 billion in 2020, and the space industry nearing the trillion-dollar mark, it is surprising that most of us don't know much about how the universe was formed, what it's made of, and how we even got here.
Enter the Universe Expansion Calculator — a simple tool that helps you find all these answers in a fun and interactive way. Create your own universe, see how each component affects its fate... all while learning the scientific reason behind why our universe is the way it is.
Did you know that without dark energy, our universe would be much smaller? It might even collapse back into a single point and sort of "reincarnate" itself as a second Big Bang, creating a new universe. Is this enough to pique your interest? Come in and answer your questions about the universe!
What is the universe? / How to describe the universe with maths
The universe is everything. It is made of many different components, such as stars, light, x-rays, planets, gas clouds, and black holes — which makes it difficult to model mathematically.
Astronomers have found ways to divide the constituents of the universe into four major groups:
- Matter (Ωm);
- Radiation (Ωr);
- Dark energy (ΩΛ); and
- Spatial curvature (Ωk).
Additionally, there is another parameter that measures the expansion rate of the universe: the Hubble constant (H0).
Each component of the universe affects its evolution in a different manner, described by Friedmann's equations — a set of formulas that explain most of the phenomena we see in the universe. They allow us to observe the effects of each component separately and get a better picture of what their role is in the evolution of the universe.
Hubble constant (H0)
When astronomers first saw all the galaxies around us, they discovered that all of them seemed to be moving away from us. In fact, the speed at which they "run away" from us is proportional to the distance between us and them. The only possible explanation for this is that the whole universe is expanding, like a piece of fabric getting stretched. The first one to notice this was Edwin Hubble (and also George Lemaître). The key to this discovery was the evidence of the Doppler effect in the data from far galaxies.
This expansion of the universe was thought to be constant (now we know that its expansion is accelerated), and the value of this constant speed was, understandably, named after Dr. Hubble. Measuring it by looking at distant galaxies yields a value of 73.4 km/s per Mpc. If you look at the remnants of the Big Bang, Hubble's constant is 67.7 km/s per Mpc.
We know the discrepancy is not due to experimental error, so what gives? There must be a hole in our knowledge of the universe that we must fix! In this calculator, we use 67.7 km/s per Mpc by default but you can set it to 73.4 km/s per Mpc to see what this difference means for the evolution of the universe.
Effects of Dark Energy (ΩΛ)
Dark energy is more complicated to understand than the other components. Not even cosmologists know what it really is, and it only has an effect when considering very large scales.
Dark energy, identified in cosmology by the Greek letter Lambda (Λ), is responsible for the accelerated expansion of the universe we experience in our reality. Dark energy makes space expand exponentially, so its effects will only become noticeable after billions of years.
On the other hand, nothing prevents dark energy from making space compress exponentially. One can easily imagine such a scenario: ΩΛ would be negative and the universe would contract and collapse into a single point.
Effects of Matter (Ωm)
Matter is a more understandable component of the universe. Sort of. It is composed of two major types: (cold) dark matter and regular (or baryonic) matter. We still don't really know what dark matter is, but we know that it represents about 90% of all matter in the universe. Fortunately, all matter behaves mostly the same.
Its effect on the evolution of the universe is almost the opposite to that of dark energy. A universe composed of mostly matter would expand very rapidly at the beginning and will slow down as years pass.
Effects of Radiation (Ωr)
Similar to matter, radiation is another concept that we use in our everyday life. Think UV radiation, gamma rays, infrared... In short: light. On top of light (photons), neutrinos are also considered to be radiation for our purposes since they have the same effects.
The way photons and neutrinos interact with the expansion of the universe is qualitatively similar to how matter does it. Radiation makes the universe expand faster than matter does, at least at the beginning.
Curvature density (Ωk) and the shape of the universe
There is one last parameter we must talk about: the curvature density (Ωk). If Ωk > 0, we have a closed universe that tends to collapse again onto itself. For Ωk < 0, we have an open universe that tends to expand forever. And for Ωk = 0, we have a flat universe with no spatial tendency to expand or contract.
In this calculator, the curvature is derived automatically from the other three components, since the total density of the universe must satisfy Ωm + Ωr + ΩΛ + Ωk = 1.
We have to remember that this is only a simplistic explanation, and the actual outcome of any given universe will depend on the values of each of the four parameters. However, all this knowledge should be enough for you to be able to play around with the calculator and get a grasp on the impact that each parameter has on the evolution of the universe.
From the Big Bang until now — and the possible deaths of our universe
From the birth of the universe (the Big Bang) until now, our universe has been expanding for about 13.8 billion years. What happens next depends entirely on the balance of its components:
- Big Freeze (Heat Death): if dark energy dominates, the universe expands forever, getting colder and emptier — the most likely fate of our own universe.
- Big Crunch: if there is enough matter (a closed universe) or if dark energy is negative, gravity wins, the expansion reverses, and everything collapses back into a single point.
How to build your own universe
- Choose the Hubble constant H0 (67.7 for CMB / Planck, or 73.4 for local measurements).
- Set the matter density Ωm, the radiation density Ωr, and the dark energy density ΩΛ.
- Pick your preferred measurement system: Metric (km) or American (miles).
- Click Calculate to see the shape, age, expansion behaviour, and ultimate fate of your universe.
- Try the example buttons (Our Universe, Matter Only, No Dark Energy, Big Crunch) to explore different scenarios.