History of the Universe

If the universe was 1 year old...

Science/religion – either/or? How do we predict the conditions of the early universe? What are the different eras in the early universe? What key lines of evidence support the Big Bang model? What is the cosmic microwave background? Our goals for learning:

Why are we here? How did we get here? Questions of purpose can’t be answered by science Questions of mechanics can be answered by science

The Big Bang Were you THEEEEERE??? How can we possibly know what happened? Three lines of evidence: – Galaxies moving away from each other – Types/amounts of elements present in the universe – Observe light from Big Bang

Evidence for the Big Bang: Galaxies are moving apart Our own Milky Way Galaxy is just one of countless galaxies of stars that fill the observable universe. If anything, we might expect all these galaxies, including our own, to be falling towards each other, attracted by their mutual gravity. But in 1929, the astronomer Edwin Hubble made the unexpected discovery that distant galaxies are moving away from Earth. In fact, the more distant the galaxy, the faster away from us it is moving. Since the galaxies are moving apart, they must have been much closer together in the past. Based on the speeds and directions of the galaxies' motions, astronomers conclude that all the galaxies would have originated from the same spot about 14 billion years ago. Red shift: Observing Movement video; videovideo; video

Evidence for the Big Bang: Elements present in the universe In the 1940's, the physicist George Gamow and his colleagues realized that the early universe must have been extremely hot as well as dense. Scientists were just beginning to understand that under great heat and density, chemical elements can be transformed from one into the other. Gamow and his colleagues calculated that for a hot, dense, and expanding universe about one-quarter of the simplest chemical element - hydrogen - would have been "cooked" into the element helium. Astronomers have measured the proportion of hydrogen and helium scattered through our universe, and it matches the prediction perfectly. This was strong evidence that the early universe was hot as well as dense.

Evidence for the Big Bang: Leftover Light According to the Big Bang model, the Big Bang took place everywhere in space (not just at a point). For thousands of years after the Big Bang, all of space was filled with matter so hot that it glowed - much like the pottery oven at right. This afterglow of the Big Bang should still fill the universe today. In fact, a steady stream of this light is continuously arriving at Earth, from distant regions of space, having traveled for billions of years to get here. The light is no longer visible with the unaided eye – having dimmed and reddened as the universe expanded and cooled – but it is detectable with special instruments. In 1964, the radio astronomers Arno Penzias and Robert Wilson became the first to discover this afterglow of the Big Bang. Then in 1991, NASA's COBE spacecraft captured the first image of this ancient light coming from all directions in the sky, confirming the Big Bang scenario. The achievement has been hailed as one of the greatest triumphs of scientific exploration.

Cosmic Microwave Background The Universe is immersed in a sea of radiation. This is the same radiation which was unleashed at the end of the Era of Nuclei. 380,000 years after the Big Bang, the Universe had cooled enough for free electrons to become bound into atoms of H & He without electrons to scatter them, photons were able to travel unhindered throughout the Universe the Universe became transparent Its existence first predicted by George Gamov in 1940s The temperature of the Universe was 3,000 K at this time.

Cosmic Microwave Background Video here The spectral distribution of this radiation was the same as radiation from a 3,000 K object. like the surface of a red giant Since then, the Universe’s size has expanded 1,000 times. cosmological redshift has turned this radiation into microwaves. So the temperature of the background is 1000 times lower Gamov predicted that we should have a 3 K background At this temperature, most radiation comes in the wavelength of microwave  the cosmic microwave background

Fig. 19-6, p.394

Discovery of the Cosmic Microwave Background Penzias and Wilson with their horn Shaped antenna at Bell Lab 1964 – 1965: – Arno Penzias and Robert Wilson using the 20-foot radio antenna at Bell Lab for their research – Discovery of faint, uniform, persistent “noise” at 3K. – Meanwhile, Princeton team led by Robert Dicke was building a radio telescope to detect the big-band afterglow predicted by Gamov – The discovery of CMB won Penzias and Wilson the 1978 Nobel Prize

Two Key Predictions of the CMB The CMB is thermal – “black body radiation” The CMB is highly uniform (< ) difference from one spot to another

Cosmic Microwave Background… …was mapped by the COsmic Background Explorer (COBE) in 1990s Thermal radiation of / K While very smooth and uniform across the sky… COBE did find slight temperature variations from place to place on the level of a few parts in 100,000.