redshift

History

The Doppler effect for sound was described by Christian Doppler in 1842. Astronomer Vesto Slipher began measuring shifts of lines in the spectra of nebulae back in the 1910s. But the decisive step was made by Edwin Hubble in 1929, discovering the proportionality of redshift to the distance of galaxies.

How it works

Atoms emit light at specific wavelengths — like fingerprints. When a galaxy recedes, the wave crests arrive less frequently, and the entire spectrum shifts toward longer wavelengths — to the red. From the amount of shift, the recession velocity is calculated. It's like a comb with sparse teeth: if the source moves, the 'teeth' of the spectrum become even sparser.

History

The Doppler effect for sound was described by Christian Doppler in 1842. Astronomer Vesto Slipher began measuring shifts of lines in the spectra of nebulae back in the 1910s. But the decisive step was made by Edwin Hubble in 1929, discovering the proportionality of redshift to the distance of galaxies.

How it works

Atoms emit light at specific wavelengths — like fingerprints. When a galaxy recedes, the wave crests arrive less frequently, and the entire spectrum shifts toward longer wavelengths — to the red. From the amount of shift, the recession velocity is calculated. It's like a comb with sparse teeth: if the source moves, the 'teeth' of the spectrum become even sparser.

History

The idea of an expanding Universe arose from Friedmann's equations (1922) and Georges Lemaître's observations (1927), but gained wide acceptance after Edwin Hubble's work (1929) showing a linear relationship between redshift and distance. Lemaître was the first to interpret this as an expansion of space. Later, measurements of type Ia supernovae in 1998 led to the discovery of accelerated expansion (dark energy).

How it works

Redshift is measured spectroscopically: lines of known elements (e.g., hydrogen) are shifted by a factor (1+z). The Hubble law v = H₀ d relates recession velocity and distance. For large z, the relationship becomes nonlinear and is determined by the cosmological model. Peculiar velocities of galaxies make an additional, often negligible contribution. There is also gravitational redshift, predicted by General Relativity: photons lose energy when escaping a gravitational well. Redshift measurements rely on the Doppler effect and Hubble's law.

Open problems & fun facts

The nature of dark energy causing accelerated expansion remains a mystery.; The exact value of the Hubble constant H₀ — discrepancy between local measurements and cosmic microwave background data (Hubble tension).; Possible evolution of redshift over time due to unknown interactions between dark matter and energy.

💡 The highest recorded redshift for galaxy GN-z11 is z≈11, its light has been traveling to us for over 13 billion years, from an era when the Universe was only 400 million years old.