5/1/2017 Evidence for the Big Bang Theory: Background Radiation, Red­Shift and Expansion ­ Video & Lesson Transcript | Study.com

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Evidence for the Big Bang Theory: Background Radiation, Red-Shift andExpansion

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Discover what evidence exists to support the Big Bang theory of the birth of the universe. Learn how cosmicbackground radiation, the red shift of light and the ongoing expansion of the universe led scientists to believethat the universe was started with the Big Bang.

The Big Bang TheoryBillions of years ago - more than 14 billion years - there was nothing: no matter, no energy, nospace. Scientists needed a way to explain how everything began, where it came from, whathappened. Although there are several diዬerent theories about the origins of the universe, the BigBang theory is the prevalent one because no other model is as good at explaining everything in theuniverse. The Big Bang theory isn't perfect, but it's the best we've got.

Contrary to popular belief, the Big Bang was not an explosion

Scientists believe our universe comes from a singularity. Scientists don't actually know where thissingularity came from or exactly what it is, but they do know that a singularity is an inዔnitely small,hot area of inዔnite pressure and density. These singularities defy our known laws of physicsbecause they didn't appear in space. Rather, space began inside them. Before the singularity,nothing existed. There was no space, no time, no matter, no energy.

One of the misconceptions about the Big Bang is that it was an explosion, like with ዔre and soundand, well, kind of like a bomb. It wasn't. Instead, it was probably more like a balloon being blown up- a really tiny balloon. A balloon starts small and expands outward at roughly the same speed allaround. Our universe is that balloon.

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5/1/2017 Evidence for the Big Bang Theory: Background Radiation, Red­Shift and Expansion ­ Video & Lesson Transcript | Study.com

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When scientists ዔrst propose a hypothesis to explain a phenomenon, they expect to ዔnd certainevidence to support it and turn their hypothesis into a theory. There are several main pieces ofevidence that support the Big Bang theory. One is the fact that the universe is expanding, provenwith something called red shift. The second is something called cosmic microwave backgroundradiation. The third is the abundance of diዬerent elements in the universe.

Universe Expansion and Red Shift

The red-shift of light is evidence that the universe is expanding

The evidence that the universe is expanding comes with something called the red shift of light.Light travels to Earth from other galaxies. As the light from that galaxy gets closer to Earth, thedistance between Earth and the galaxy increases, which causes the wavelength of that light to getlonger.

This is similar to the Doppler eዬect of sound waves, which also happens with light waves. I'm sureyou've heard it for yourself in real life: as an ambulance approaches you, the siren pitch seems toincrease, and as it moves away from you, the siren pitch decreases. This is due to how the soundwaves increase or decrease depending on the movement of the object emitting the waves relativeto the person hearing them. As the ambulance approaches you, the sound waves get closertogether and shorter, which results in a higher pitch. As the ambulance moves away from you, thesound waves stretch out and get longer, which results in a lower pitch. If everything in the universeis moving apart from everything else, then those light waves should move further apart and getlonger. Longer wavelengths of visible light are red, and that is why it is called the red shift.

This red shift of light gives scientists information on the speed and direction that a star is moving.This in turn tells scientists that stars are not only moving away from us, but they are also movingaway from each other.

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Edwin Hubble studied galaxies in the 1920s and proved that everything in the universe is expanding

In the 1920s, Edwin Hubble used the 100-inch Hooker telescope in Southern California to study theAndromeda Galaxy. He took pictures of faint galaxies and studied them. Eventually, he was able tocalculate the velocity for the galaxy and show that everything is moving away from everything elseand thus expanding. If that's true, then scientists ዔgured that the universe was previously muchsmaller than it is now. All of this evidence was the ዔrst observational support for the Big Bangtheory that Georges Lemaitre ዔrst proposed in 1927.

If the universe is currently growing, then the universe was smaller in the past. There must havebeen some point in time when the universe was half its current size. Then there must have been atime when it was half that size. Think about this: if the universe has grown to currently be a size 1,sometime in the past it was a size 1/2, and before that 1/4, and before that 1/8, 1/16, 1/32, 1/64,etc. If you keep doing the fractions, you will get down to an inዔnitesimally small size and,eventually, nothing. (Yes, I know you can't really get down to nothing, but as I mentioned, thesingularity from which the universe comes deዔes the laws of physics.)

Cosmic Background RadiationThe next piece of evidence that supports the Big Bang theory is the ዔnding of cosmic microwavebackground radiation (CMB). With a normal telescope, all you can see in between stars is darkness,but if you have a very sensitive radio telescope, you can see more. Cosmic microwavebackground radiation (CMB) is the faint background radiation that astronomers pick up withsensitive radio telescopes.

When the universe was ዔrst born, it was foggy, not clear the way it is now. The fog was from thehot hydrogen plasma that formed after the Big Bang. As the universe expanded, it cooled, stableatoms formed, and the fog dissipated. The CMB is the remnant from that initial fog. It is theafterglow scientists expected to ዔnd if the Big Bang started the universe, and they did ዔnd thisevidence to support their theory.

This background radiation was discovered by accident. In 1965, two astronomers, Arno Penzias andRobert Wilson, were trying to detect microwaves from outer space for a diዬerent project. Whatthey detected instead was background radiation that scientists now believe is left over from thebeginning of the universe.

Elements in the Universe

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5/1/2017 Evidence for the Big Bang Theory: Background Radiation, Red­Shift and Expansion ­ Video & Lesson Transcript | Study.com

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Elements in the Universe

The abundance of elements in the universe supports the Big Bang theory

The last major ዔnding that supports the Big Bang theory is the abundance of elements in theuniverse. The elements in the universe were created in one of two ways. The lighter elements, suchas helium and hydrogen, were produced in the ዔrst few moments of the Big Bang. The heavierelements, such as iron, silicon and magnesium, formed in the interiors of stars much later on in theuniverse's timeline. If the Big Bang theory is true, then scientists expected from their calculations toዔnd certain amounts of each heavy element in the universe. Observations have shown almostexactly the amounts that are predicted, which supports the theory.

Lesson SummaryThe Big Bang theory has many pieces of supporting evidence, but there are three main ones. Theevidence that the universe is expanding is shown with the red shift of light, the ዔnding of cosmicbackground radiation that is left over from the initial heat of the Big Bang and the amount andtypes of elements in the universe that are almost exactly the amounts predicted by the theory.Three main pieces of evidence for the Big Bang theory are the red shift of light, cosmic backgroundradiation and types of elements.

Learning OutcomesAfter watching this lesson, you should be ready to:

Deዔne singularity and describe the Big Bang theory

Summarize how red shift, cosmic background radiation and the abundance of elements in the universe allprovide evidence for the Big Bang theory

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