Calculate lookback distance based on cosmological redshift (z)
Determines lookback distance by integrating the Friedmann equation for a ΛCDM flat universe.
In 1929, Edwin Hubble discovered a startling fact: the further away a galaxy is, the faster it appears to be moving away from us. This relationship is the foundation of modern cosmology. By measuring the Redshift ($z$) of a galaxy's light, we can estimate how many billions of light-years away it is.
Measuring distance in an expanding universe is tricky. This calculator specifically finds the Lookback Distance (or light-travel distance). This represents how far the light traveled to reach us. However, because the universe kept expanding while the light was in flight, the galaxy is actually much further away now than it was when it emitted the light!
When this calculator tells you a galaxy is 10 billion light-years away, it means you are seeing that galaxy as it looked 10 billion years ago. You are seeing the "ghost" of the galaxy's past. The higher the redshift, the deeper into the past you are peering, eventually reaching the era of the very first stars and galaxies.
The math behind this conversion isn't a simple straight line. It depends on the balance of Matter (which slows expansion down) and Dark Energy (which speeds it up). This tool uses the parameters from the ΛCDM model, which suggests our universe is "Flat" and dominated by an invisible energy that is pushing everything apart at an accelerating rate.