Big Bang

Currently, the Big Bang model is accepted by most cosmologists, because the evidence is so substantial that it suggests that this theory is correct.

Below is a brief summary of the discoveries that gradually led to the development of this theory.

Anyway, keep in mind that this is what we think happened; there is still a long way to go, before we have definitive answers to essential questions such as the origin of the Universe and of life.

Importance of the light that comes from the stars

In 1666, Isaac Newton was certain that light was made up of many colors.

In February 1672, he presented a communication to the Royal Society in which he provided experimental evidence that white light was a mixture of rays of different colors.

These different rays are detected when a ray of light passes through a glass prism.

Colors
White light entering a glass prism, exits the prism with rays of  various colors. Credit: Wikipedia.

Long after, in 1859, Gustav Kirchhoff showed that hot bodies emit light composed of different colors depending on their chemical composition.

Spectrum
Different lines spectrum. Credit: web “path2space.com/spectra/”

Kirchhoff demostrated that a hot solid object, surrounded by a faint gas at lower temperatures, produces light in a continuous spectrum with gaps at discrete wavelengths whose positions depend on the chemical composition of the surrounding gas.

From these discoveries, an important branch of astronomical science began to develop: spectroscopy, the study of the spectra of light emitted by hot bodies.

Spectrum
Study of the Sun’s spectrum. Credit: web “path2space.com/spectra/

The study of the spectrum of colors of the light emitted by a star, makes it possible to know what are the materials that compose it.

From these observations it was deduced that all stars have the same chemical elements already known on Earth

Importance of the Doppler effect

In 1842, Christian Doppler, discovered the variation of the wavelength of any type of wave emitted or received by a moving object.

Doppler explained this effect in a monograph entitled “On the color of light in binary stars and other stars.”

Since then it has been explained why the pitch of a sound emitted by a source approaching the observer is higher than when the source is moving away.

Doppler Efffect
Doppler effect vector illustration. Credit: web “dreamstime.com”

Hippolyte Fizeau independently discovered the same phenomenon in the case of electromagnetic waves in 1848.

In the case of the visible spectrum of electromagnetic radiation, if the object moves away, its light shifts at longer wavelengths, towards red.

If the object gets closer, its light has a shorter wavelength, shifting towards the blue.

This deviation towards red or blue is very slight even at high speeds, such as the relative speeds between stars or between galaxies, and cannot be captured by the human eye; just measure it using precision instruments such as spectrometers.

Study of the Andromeda Nebula

By 1887, considerable progress had been made in obtaining photographs.

Isaac Roberts obtained the first photographs of the Andromeda Nebula, showing for the first time the basic features of its spiral structure.

Andromeda
Photograph of the Andromeda Galaxy. Credit: NASA.

At the beginning of the 20th century, astronomers vigorously debated whether the nebulae observed in the sky were part of our Milky Way or if they were outside it and belonged to other galaxy.

Most believed that the Milky Way was the only galaxy in the universe, made up of stars and nebulae.

In 1912, the Lowell Observatory astrophysicist Slipher measured the radial velocity of the “Andromeda Nebula” and found that it had a velocity that was the fastest ever recorded: about 300 km per second.

Hubble was able to distinguish stars in the Andromeda Nebula and was able to estimate their distance from Earth, which he calculated at 800,000 light years, eight times farther than the most remote stars known.

From the Doppler effect, Edwin Hubble began the study of the Big Bang theory.

NGC 6872
Spiral galaxy NGC 6872.  Credit: NASA

In 1924, Edwin Hubble pointed out that our galaxy is not the only one in the Universe, but that there are thousands of galaxies and that the Universe is expanding.

In 1929, Hubble published an analysis of the radial velocity of nebulae whose distance he had calculated; it was their speeds relative to Earth.

He claimed that the vast majority showed redshifts in their spectra.

This phenomenon could only be explained by assuming that these nebulae were moving away.

Even more surprising was the discovery that there was a direct relationship between the distance of a nebula and its speed of rebound.

Hubble
Studio Portrait of Edwin Hubble in 1931. Credit: Wikipedia. Photographer: Johan Hagemeyer.

Hubble concluded that the only consistent explanation was that, pulling apart a local group of nearby galaxies, all the extragalactic nebulae were receding; and that the farther away they were, the faster they moved away.

The expansion of the universe

In the 1940s, many physicists and astrophysicists had verified the truth of the distance of the stars and galaxies and, therefore, of the expansion of the universe.

This meant that, according to the laws of physics, the world was getting cold.

From there to deduce that previously, the world was warmer and more compressed, there was only one step.

Applying mathematical formulas, it was reached that there was an original moment in which the entire Universe was reduced to a minimum space and subjected to enormous temperatures.

It was concluded that there was a time when “it” began to expand at great speeds.

Verification of the Big Bang Theory

The predictions of the Big Bang theory have been able to be verified throughout the second half of the 20th century and at the beginning of the 21st century.

The prodigious advances in the technique in the last 50 years have made it possible to observe and measure, with increasing precision,

  • the distance of galaxies,
  • the fossil radiation of photons,
  • the distribution of quasars in space,
  • the number of families elementary particles.

    Big Bang
    A graphical representation of the expansion of the universe from the Big Bang to the present day. Credit: web “en.wikipedia.org/wiki/”

In this image, the inflationary epoch is represented as the dramatic expansion of the metric seen on the left.

This visualization can be confusing because it appears as if the universe is expanding into a pre-existing empty space over time.

All this has corroborated the validity of this theory, until now.

It is conceivable that the force of universal gravity causes the expansion of the universe to occur at a decreasing speed.

And that there will come a time when all the galaxies will begin to come together.

But the “latest news” is that this speed of expansion is increasing.

Galaxies
In the Universe there are billions of galaxies. Credit: web “cosmosmagazine.com”

Not everything is explained with the Big Bang Theory.

The mathematics underlying this theory are inadequate and powerless to explain what happens at the borders of time and space.

  • What was there before time zero?
  • What temperature was there at time zero?
  • What was space before the Big Bang?
  • How long before the Big Bang?

Scientifically it is impossible to define a zero time, at which time the temperature would reach an infinite value and the space would reach a zero volume.

That is simply the limit of our knowledge

If the Big Bang theory is correct, currently all the stellar matter should be distributed on the surface of an immense sphere that is becoming more extensive every second.

Inside this universal sphere, nothing would remain but the radiation produced by the stars.

Hawking
Stephen Hawking English theoretical physicist. Credit: web “britannica.com/biography/Stephen-Hawking”

In 2007, the prestigious scientist Stephen Hawking said that, according to calculations, if the expansion speed, 1 second after the Big Bang had been less than one part in 100,000 trillion, the universe would have collapsed on itself before now, due to the pull of gravity.

But if the expansion speed, 1 second after the Big Bang had been greater by one part in 100,000 trillion, the universe, exceeding the force of gravity, would have expanded so much that it would now be practically empty.