The Big Bang event is a physical theory that describes how the universe expanded from an initial state of high density and temperature.[1] Various cosmological models of the Big Bang explain the evolution of the observable universe from the earliest known periods through its subsequent large-scale form.[2][3][4] These models offer a comprehensive explanation for a broad range of observed phenomena, including the abundance of light elements, the cosmic microwave background (CMB) radiation, and large-scale structure. The overall uniformity of the Universe, known as the flatness problem, is explained through cosmic inflation: a sudden and very rapid expansion of space during the earliest moments. However, physics currently lacks a widely accepted theory of quantum gravity that can successfully model the earliest conditions of the Big Bang.
Crucially, these models are compatible with the Hubble–Lemaître law—the observation that the farther away a galaxy is, the faster it is moving away from Earth. Extrapolating this cosmic expansion backwards in time using the known laws of physics, the models describe an increasingly concentrated cosmos preceded by a singularity in which space and time lose meaning (typically named "the Big Bang singularity").[5] In 1964 the CMB was discovered, which convinced many cosmologists that the competing steady-state model of cosmic evolution was falsified,[6] since the Big Bang models predict a uniform background radiation caused by high temperatures and densities in the distant past. A wide range of empirical evidence strongly favors the Big Bang event, which is now essentially universally accepted.[7] Detailed measurements of the expansion rate of the universe place the Big Bang singularity at an estimated 13.787±0.020 billion years ago, which is considered the age of the universe.[8]
There remain aspects of the observed universe that are not yet adequately explained by the Big Bang models. After its initial expansion, the universe cooled sufficiently to allow the formation of subatomic particles, and later atoms. The unequal abundances of matter and antimatter that allowed this to occur is an unexplained effect known as baryon asymmetry. These primordial elements—mostly hydrogen, with some helium and lithium—later coalesced through gravity, forming early stars and galaxies. Astronomers observe the gravitational effects of an unknown dark matter surrounding galaxies. Most of the gravitational potential in the universe seems to be in this form, and the Big Bang models and various observations indicate that this excess gravitational potential is not created by baryonic matter, such as normal atoms. Measurements of the redshifts of supernovae indicate that the expansion of the universe is accelerating, an observation attributed to an unexplained phenomenon known as dark energy.
2. • In science, a theory is an explanation of a big idea
for which there is a lot of scientific evidence.
• A scientific theory can be supported by new
evidence. New evidence might modify or disprove
a scientific theory. A scientific theory can never be
proven like a scientific law (we can never be 100%
certain).
• The Big Bang Theory explains how our universe
was formed based on all the scientific evidence.
3. The Big Bang occurred
about 14 billion years ago.
All the matter of the entire
universe was in a small,
extremely hot mass that
expanded quickly
outwards under
tremendous pressure.
This “beginning” is called
time zero. What
happened before this is
not known.
4. • All known matter, dark matter, and energy
was formed in the Big Bang.
7. Expanding Universe
Evidence to Support the Big Bang
Theory
Astronomer Edwin
Hubble observed
that distant
galaxies were
moving away from
our Milky Way
galaxy.
How did he know
this, and what did it
mean?
8. Redshift and Blueshift of light from stars
and galaxies
Light and sound
travel as waves.
Red light has
longer
wavelengths
than blue light.
9. When an object is
moving, the
waves (sound or
light) will be either
compressed or
stretched. This is
called the Doppler
Shift.
When an object is moving towards the earth, the
light from objects will be compressed and shifted
towards blue light (shorter wavelengths). This is a
blueshift.
10. When an object is moving away from the earth, the
light from objects will be stretched and shifted
towards red light (longer wavelengths). This is a
redshift.
11. The wavelengths of light coming from almost all
galaxies we can see is getting longer (redshifted).
This means they are moving away from our Milky
Way galaxy. If the galaxies are moving away from
each other, the universe must be expanding.
The farther away the galaxy is from us, the faster it
moves. This is called Hubble’s Law.
12. Expanding Universe
Raisin Bread Analogy
The farther away the galaxy is from us, the faster it
moves. This is called Hubble’s Law.
13. Cosmic Background Microwave Radiation
According to the Big Bang Theory, enormous
amounts of energy were given off from the initial
explosive event that sent radiation out in all
directions.
After billions of years of cooling of the universe,
and of the radiation from the Big Bang event
traveling through space, the entire universe is
still “glowing” like a piece of firewood continues
to glow after the fire is put out.
14. This radiation, particularly in the microwave
frequencies, can be detected today using radio
telescopes, telescopes that can detect
electromagnetic waves outside of the visible
range.
This radiation is called Cosmic Background
Microwave (CMB) Radiation.
15. Image of the Cosmic Microwave Background
(CMB) Radiation of the early universe – bright
spots correspond to higher temperatures
16. What is the Big Bang Theory?
13.7 billion years ago the universe formed
when an infinitely dense point suddenly
and rapidly expanded in a single moment.
Editor's Notes
All matter, all atoms in the universe were formed.
