How do we know that the universe is expanding?

– (Middle Studio/Strange World)

The intensity of light emitted by supernovae – the explosion of stars with more than 10 times the mass of the Sun – outside our galaxy is evidence of this expansion. First, astronomers calculate the amount of light the phenomenon should produce. Then they compare the value with the effective luminosity that reached Earth.

Generally, the observed light is less intense than expected, which proves that that supernova (and, consequently, the galaxy it is part of) is moving away from us. But does not stop there. Together with data obtained since 1929, when astronomer Edwin Hubble discovered that the Universe is expanding, it is noted that the speed of this displacement has increased. The force responsible is “dark energy”: one of the great recent enigmas in astronomy.

eye upgrade

Used since the 17th century, optical telescopes extended man’s view of space, but they only worked for visible light. Electromagnetic radiation emitted by stars outside this range, such as X-rays and infrared, was only captured by telescopes invented in the 20th century. Hubble took advantage of this to push the boundaries of astronomy.

making waves

By analyzing the light from galaxies, Hubble noticed that the wavelength of each one varied. This behavior of electromagnetic waves, called the cosmological Doppler effect, had already been proven in other types of waves, such as sound: the wavelength of a moving source decreases when approaching a reference frame, and increases when moving away from it.

universal shuttle

As in the visible electromagnetic spectrum the wavelength increases from violet to red, when the light of a galaxy is observed more reddish than it should be, it is moving away from Earth. Most galaxies move like this. But when the light tends towards blue, it indicates that it is approaching, as is the case with Andromeda.

recognized value

With these results, Hubble created the basis for the Big Bang theory, established in 1946, and nailed Hubble’s Law: the speed of a galaxy relative to another is proportional to the distance between them. He died in 1953, and was honored by having the first space telescope named after him, put into orbit in 1990.

CONSULTANCY Thiago Pereira, professor of physics at UEL, Elcio Abdalla, theoretical physicist at the Institute of Physics at USP, Ronaldo Marin, physicist at the Institute of Arts at Unicamp, and Júlio César Borin, a physicist graduated from UEL

SOURCES documentaries Black Hole: Who Came First? It is Galaxies – Ours, The Othersfrom Univesp TV; What Explains the Existence of the Black Hole?, from Globo Ciência; websites physics.uel.br/astrophysics It is chandra.harvard.edu; book The 4 Percent Universe: Dark Matter, Dark Energy, and the Race to Discover the Rest of Reality, by Richard Panek; articles “The Origin of Universe»by João Evangelista Steiner, and “Quantum Theory of Gravitation: Strings and M Theory”, by Élcio Abdalla