Transcript THE BIG BANG - Dublin City Schools

What is the Big Bang Theory?
• Not the TV show..
• It is a theory of what happened 14 (13.7) BILLION years ago. It tells us how the
universe began!
• Singularity: The theory is that one single finite speck (much much smaller than a
pin head) with extremely high density and temperature instantly started
expanding and inflating. (like the surface of an inflated balloon)
• The big bang is not an explosion of matter…
it created space and matter and time…
Expansion of the universe!
• An astronomer noticed that there are more galaxies going away from us than
approaching us
• Astronomers know that a galaxy is approaching or receding by looking at the
spectrum of its light.
• If the spectrum is shifted toward a shorter wavelength (BLUESHIFT) then the
galaxy must be approaching
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like a fire truck siren approaching you (shorter sound wavelength).
• If the spectrum is shifted toward a longer wavelength (REDSHIFT) then the
galaxy must be receding.
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Like a fire truck siren that has passed you (longer sound wavelength)
He observed more galaxies whose spectrum was redshifted than those whose spectrum was
blueshifted
Hubble
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Edwin Hubble discovered that farther galaxies are going away from us at higher
speeds.
more distant galaxies had higher redshifts (light takes millions or even billions of
years to reach us from a distant galaxy)
This means we are seeing an image from millions or billions of years ago.
He noticed that the light, when it was emitted, would have shorter wavelengths.
But, he observed longer wavelengths…this is because….expansion of space over
the years that the light was traveling to us!
This redshift appeared to have a larger displacement for faint, presumably further,
galaxies. Hence, Hubble’s Law- the farther a galaxy, the faster it is receding from
Earth.
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This graph shows different
galaxies. Their distance
apart (x) and the velocity at
which they are spreading
(y).
Going backwards…the
smaller the distance, the
smaller the velocity.
This continues until all
matter is compacted into a
completely shrunk volume
of the universe that is
incredibly dense.
THIS is the moment of the
big bang. (zero distance
and zero velocity)
Dating
• In order to figure out how old our universe is, scientists examine the oldest
things found in the universe.
• They use radioactive dating of uranium isotopes!
• we know that the oldest isotopes were created (through nuclear reactions in
supernovae) about 10 billion years ago.
• We now know that the oldest stars in our Galaxy are about 12 billion years
old.
• These ages are consistent with the age (13.7 billion) estimated from the
observed expansion of the universe
Hydrogen and Helium Abundance
in the Universe
• The most basic fundamental element is hydrogen. This was the first element to
form after the big bang.
• Helium is created by nuclear fusion! Fusion of the nuclei of two hydrogen
isotopes (deuterium) produces helium.
• Since this only occurs at EXTREMELY
hot temperatures, it was theorized to
have occurred during the big bang
with the extreme temperatures.
Continued…
• Stars and hydrogen bombs are the only things we know of that make helium
in the present universe.
• As we already know…H-bombs and stars combine hydrogen nuclei (protons)
into helium nuclei through nuclear fusion, releasing great amounts of
energy!
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Astronomers calculate that the night sky should be much brighter if all the
helium we now observe had come from stars burning…
• Some, if not most, of the helium must have existed before star formation
• This abundance of helium is another piece of evidence that proves the big
bang theory
• studies of other galaxies have confirmed that the majority of the observed
helium did exist before any star formation.
• Astronomers in the 1970s realized that no known process in the present
universe could have produced deuterium (Remember, deuterium is an
isotope of hydrogen with one extra neutron ). This is because any deuterium
created in stars will immediately convert to helium due to the high
temperatures.
• Scientists found that the some material between stars contain a trace of
deuterium. Since stars could not have produced the deuterium, it must have
been created either very early in the formation of the galaxy or even before!
Cosmic Background Radiation (microwave radiation)
• there is a very low energy and very uniform radiation that we see filling the
Universe (the afterglow of the big bang)
• essentially a perfect blackbody spectrum obtained by NASA's Cosmic
Background Explorer (COBE) satellite. (absorbs all electromagnetic
radiation and emits it…so we can see where radiation is! Look at the pic
below)
• This radiation is the strongest evidence for the validity of the big bang
• the radiation was originally produced in the big bang, but is now redshifted
to longer wavelengths because we are seeing radiation from 14 billion years
ago!
The End