The Science of Creation The Big Bang Evidence The Science of Creation

Goals What is the evidence for the Big Bang? What predictions does the Big Bang theory make? What observations can we make? How good of a theory is the Big Bang?

How do scientists estimate the age of the universe? They take the distance to a nearby galaxy and divide it by its speed of recession (time = distance/velocity). They take the distance to a very distant galaxy and divide it by its speed of recession (time = distance/velocity). They take the distances to all galaxies and divide them by their speed of recession (time = distance/velocity). Answer: C

What does it mean to say that our universe is expanding? Galaxies are moving apart through space. Space itself is expanding. Everything is expanding, including galaxies, star clusters, and star systems. Answer: B

Olbers’ Paradox Why is it dark at night? In an infinite and unchanging universe: Every line of sight should end at the surface of a star. Either: Universe has edge. Universe has a beginning.

Concept Test Olbers’ paradox asks why the night sky is dark, when every line of sight must eventually fall on a star. Which of the following reasons would best explain the darkness at night? It is because the universe is: Infinite and mostly empty. Clumpy, so not every sightline intercepts a star. Expanding, so distant stars are red-shifted. Young, so there are only stars to a finite distance. None of the above.

Cosmological Principle Isotropy – The view from here is the same in all directions. (observation) Homogeneity – We live in an average place the same as any other. (statistics) This is the cosmological principle. Implies: Universe has no edge! Universe has no center!

What observed feature of the universe motivated scientists to propose the big bang theory? There is lots of debris in space, as would be expected from an explosion. The universe is expanding, and the expansion must trace back to a specific point and time of origin in the past. Everything has a beginning, middle, and end. Answer: B

Scientific Evidence A scientific model must do two things: Explain what is seen. Predict what will happen accurately. Or, predict what can be seen before one thinks to look.

What does the big bang theory predict can be seen today if there really was a big bang? Radiation from the big bang might be detected. It was gamma rays 14 billion years ago, but today it is cooler and would look like weak microwaves coming from all of space. The Big Bang produced three elements, which might be seen in the oldest stars: 75% hydrogen, 25% helium, 1 part in a billion lithium. The universe must be finite in mass and dimension. all of the above A and B Answer: E

At the beginning of the universe, the temperature was billions of degrees. the density was enormously high. matter could turn into energy and vice versa. all of the above A and B Answer: D

Cosmic Microwave Background The Big Bang: Massive amount of energy. Very high temperature  thermal radiation As Universe expands: Temperature cools  thermal radiation gets redder. or Cosmological redshift  same thing.

Origin of the CMB Once cool enough for atoms, radiation could move freely through space.

The Temperature of Space After 500,000 yrs: T=3000K lpeak a 1/T lpeak = near infrared. The Universe was red. After 16 billion yrs: Universe 1000x bigger. lpeak = 1000x longer. lpeak = microwaves (radio). T = 3K!

Where do you look? Recall Lookback time. Universe is a time machine. Look beyond the youngest galaxies. Look everywhere.

What We See

Cosmic Microwaves Big Bang theory predicted cosmic microwave background. In 1965: discovery of radio waves (microwaves) from sky. Prediction confirmed.

COBE Early 1990s: NASA Cosmic Background Explorer Measure the intensity of radiation at many wavelengths. 3K thermal emission! lpeak = (3 x 10-3 m/K) / 3 K = 0.001m = 1mm

COBE cont. Also measure the (temperature) intensity and wavelength in various directions. Look for fluctuations out of which galaxies came. V = 600 km/s

Large Scale Structure WMAP

Concept Test The cosmic background radiation is visible in every direction because: We are at the center of the universe. It is just now passing by us at the speed of light. It pervades all space. It has reflected in every direction over the age of the universe. All of the above.

Evidence of Eras Can’t see what happened before origin of CMB. Can estimate given change of temperature and density with time. Look for Proof. CMB (Age of Nuclei) Ratio of H/He and Li (Age of Nucleosynthesis) Weak Bosons (Electroweak Era)

Which of the two main predictions of the big bang theory turned out to be true? Radiation has been found coming from all of space, just as predicted. The oldest stars are made of hydrogen, helium, and lithium, in the proportions predicted. both A and B neither A nor B Answer: C

A Good Theory? The Big Bang is a very successful theory. Makes predictions: CMB. Hydrogen, Helium, Lithium abundances. Formation of structure. Expansion of Universe. Are other Creation theories: Scientific? Successful?

What do we see when we look beyond the cosmological horizon? Galaxies that are just about to form. Galaxies that are about to enter the universe. White dwarfs that are about to go supernova. The beginning of the universe. We cannot look beyond the cosmological horizon because we cannot look back to a time before the universe began. Answer: E

Homework #22 For Friday: Come prepared to discuss your observing projects with your groups. What have you seen? What did you think you’d see? How do they compare?