Ch. 22: The Beginning of Time

True or false: Process of Science: Inflation can explain some general features of the Universe but it is not directly testable and cannot be considered a theory

False

The Big Bang theory is closely linked to Hubble's discovery that the universe is expanding, which seems to imply that there was a time in the past when the expansion first began. Nevertheless, the Big Bang theory did not gain widespread acceptance among scientists until the 1960s. Why wasn't expansion alone enough to convince scientists that the Big Bang really happened?

Although expansion seems to imply a Big Bang, no other specific predictions of the Big Bang theory were tested and confirmed until the 1960s In science, it is never enough just to say that some idea makes logical sense. Rather, a proposed model or hypothesis can become a theory only if it makes specific predictions that have been tested and verified. The Big Bang theory gained acceptance in the early 1960s because that was when one of its key predictions—the existence of the cosmic microwave background—was first tested and verified.

During the history of the universe, what important event occurred about 0.001 seconds after the Big Bang?

Most matter was annihilated by antimatter. Although most matter was annihilated, virtually all antimatter suffered this fate. That is why antimatter has been very rare in the universe ever since that time, which marked the end of what is known as the "particle era."

During the history of the universe, what important event occurred about 380,000 years after the Big Bang?

Light began to travel freely through the universe. This time when light could first travel freely marks the release of the cosmic microwave background, which we can still observe today

What happens when a particle of matter meets its corresponding antiparticle of antimatter?

The combined mass of the two particles is completely transformed into energy (photons).

What do we mean by inflation?

a sudden expansion of the universe after the strong force froze out from the GUT force

The Big Bang theory is supported by two major lines of evidence that alternative models have not successfully explained. What are they?

(1) The theory predicts the existence of and the specific characteristics of the observed cosmic microwave background (2) the theory correctly predicts the observed overall chemical composition of the primeval universe

_____________ was a dramatic expansion of the universe thought to have occurred when the universe was only a tiny fraction of a second old

Inflation

Shown following are several times in the history of the universe. Rank these times from left to right based on the peak wavelength in the spectrum of the cosmic microwave background, from shortest to longest 1. 500,000 years after the Big Bang 2. today 3. 100 million years after the Big Bang 4. 1 million years after the Big Bang 5. 1.5 billion years after the Big Bang

1. 500,000 years after the Big Bang 2. 1 million years after the Big Bang 3. 100 million years after the Big Bang 4. 1.5 billion years after the Big Bang 5. Today The cosmic microwave background is essentially the thermal radiation emitted by the universe as a whole, and the laws of thermal radiation tell us that hotter objects emit light with a shorter peak wavelength (higher energy). Because the universe cools with time (see Part A), we conclude that the peak wavelength of the cosmic microwave background must get longer as time passes

Today, most scientists accept the Big Bang theory because its predictions agree so well with observations. But a scientific theory can always be revised or discarded if future observations do not agree with its predictions. Consider the following hypothetical future observations. Which one(s) would be inconsistent with the Big Bang theory? 1. Over the next 10 years, the temperature of the cosmic microwave background falls to 1 K 2. Astronomers discover a nearby galaxy that has a helium abundance of 27%. 3.Astronomers discover distant protogalactic clouds with a helium abundance below 20%. 4. Astronomers find an error in previous measurements that means the temperature of the cosmic microwave background is actually 2.71 K rather than 2.73 K. 5. Careful studies of quasar spectra show that, 12 billion years ago, the temperature of the cosmic microwave background was slightly lower than it is today.

1. Over the next 10 years, the temperature of the cosmic microwave background falls to 1 K 3.Astronomers discover distant protogalactic clouds with a helium abundance below 20%. 5. Careful studies of quasar spectra show that, 12 billion years ago, the temperature of the cosmic microwave background was slightly lower than it is today. Any observation showing that the cosmic microwave background has heated up with time would contradict the Big Bang theory's prediction that it must cool as the universe expands. An observation of dramatic change in the background temperature over a mere decade would contradict the idea that the background is a characteristic of the universe itself. A helium abundance significantly below 25% would contradict the predicted abundance

There are several eras that are used to describe the history of the universe. Rank the eras in the order in which they occurred, from first to last

1. Planck era 2. GUT era 3. electroweak era 4. particle era 5. era of nucleosynthesis 6. era of nuclei 7. era of atoms 8. era of galaxies

Rank the eras from left to right based on the size of the observable universe during each one, from smallest to largest

1. Planck era 2. GUT era 3. electroweak era 4. particle era 5. era of nucleosynthesis 6. era of nuclei 7. era of atoms 8. era of galaxies.

Rank the eras of the history of the universe based on the temperature of the universe during each one, from coolest to hottest

1. era of galaxies 2. era of atoms 3. era of nuclei 4. era of nucleosynthesis 5. particle era 6. electroweak era 7. GUT era 8. Planck era

Shown following are several times in the history of the universe. Rank these times from left to right based on the average temperature of the universe at each time, from coolest to hottest 1. today 2. 500,000 years after the Big Bang 3. 100 million years after the Big Bang 4. 1.5 billion years after the Big Bang 5. 1 million years after the Big Bang

1. today 2. 1.5 billion years after the Big Bang 3. 100 million years after the Big Bang 4. 1 million years after the Big Bang 5. 500,000 years after the Big Bang The universe has been expanding since its birth in the Big Bang, and this expansion causes the universe as a whole to cool with time

Shown following are several times in the history of the universe. Imagine that you were able to watch a single photon that has been part of the cosmic microwave background since it first became present in the universe. Rank these times from left to right based on the wavelength this photon would have at each time, from shortest to longest 1. 500,000 years after the Big Bang 2. today 3. 1 million years after the Big Bang 4. 100 million years after the Big Bang 5. 1.5 billion years after the Big Bang

500,000 years after the Big Bang, 1 million years after the Big Bang, 100 million years after the Big Bang, 1.5 billion years after the Big Bang, today Individual photons stretch to longer (redder) wavelength as the universe expands; this is the phenomenon sometimes referred to as cosmological redshift

Why might inflation have occurred at the end of the GUT era?

An enormous amount of energy was released when the strong force froze out from the GUT force

When a particle of ordinary matter meets its precise opposite particle of antimatter, the result is ____________ with complete conversion of mass into energy.

Annhiliation

The ___________ is a single force that unifies the electromagnetic and weak forces

Electroweak force

Observations of the ___________ provide a way to test our theory of the Big Bang

Cosmic microwave background

True or false: Current measurements of the density of the universe support the prediction of the theory of inflation that the universe should be flat

False

True or false: The Big Bang predicts that one in four atoms in the universe is helium

False

True or false: The theory that inflation occurred in the early universe is incompatible with the theory of relativity

False

A _________ predicts that the strong, weak, and electromagnetic forces should become indistinguishable at high temperatures

Grand unified theory

What happens to gas as it freely expands?

It gets less dense and cools

Which of the following statements about the cosmic background radiation is not true?

It is the result of a mixture of radiation from many independent sources, such as stars and galaxies

Which statement about the cosmic microwave background is NOT true?

It is the result of a mixture of radiation from many independent sources, such as stars and galaxies

Classify each statement below as an observation or as an inference based on the current Big Bang model. (Note that the helium abundance is defined as the mass of helium relative to the mass of hydrogen.) 1. Photons of the cosmic microwave background have traveled through space for almost 14 billion years. 2. The cosmic microwave background is radiation left over from the big bang. 3. Large-scale structures look about the same in all directions. 4. The temperature of the cosmic microwave background varies slightly with direction. 5. The cosmic microwave background temperature is 2.73 K. 6. The helium abundance is at least 25% in every galaxy studied so far. 7. Fusion during the universe's first five minutes produced 75% hydrogen and 25% helium. 8. Large-scale structure grew around density variations present in the early universe

Observation: 3. Large-scale structures look about the same in all directions. 4. The temperature of the cosmic microwave background varies slightly with direction. 5. The cosmic microwave background temperature is 2.73 K. 6. The helium abundance is at least 25% in every galaxy studied so far. Inference: 1. Photons of the cosmic microwave background have traveled through space for almost 14 billion years. 2. The cosmic microwave background is radiation left over from the big bang. 7. Fusion during the universe's first five minutes produced 75% hydrogen and 25% helium. 8. Large-scale structure grew around density variations present in the early universe. Observations are things we actually see and measure with our eyes, telescopes, or instruments. Inferences are proposed explanations or conclusions from models that are built with those observations in mind

____________ forces us to think about why the sky is dark at night

Olbers paradox

Which of the following statements can NOT be tested by science today?

Prior to the Planck time, our universe emerged from another universe

Which of the following important events occurred earliest in the history of the universe?

Space-time rapidly expanded during a brief period of inflation. Inflation is thought to have occurred when the universe was only a tiny fraction of a second old.

The universe is getting cooler with time

The universe is getting cooler with time

Why can't current theories describe what happened during the Planck era?

We do not yet have a theory that links quantum mechanics and general relativity

What do we mean by inflation?

a sudden and extremely rapid expansion of the universe that occurred in a tiny fraction of a second during the universe's first second of existence

Although we can divide the history of the universe into many distinct "eras," sometimes it's useful just to have a broad perspective on what events occurred in the very early universe and what events occurred later. (within the first 5 mins or sometime after the first 5 mins). Match the events that occurred either before or after the first five minutes in the history of the universe to the appropriate time period

Within the first 5 minutes: - Inflation occurred - Anti-electrons (positrons) as common as electrons - Temperature fell to 10^15 K - Strong force and electroweak force first became distinct Sometime after the first 5 minutes: - Stars formed - Galaxies formed - Carbon nuclei formed by fusion - Photons of cosmic microwave background released

Essentially all the hydrogen nuclei that will ever exist in our universe were created _________.

by the time the universe was about 3 minutes old Hydrogen nuclei are protons, and protons were formed during the particle era. During the next three minutes, many of these protons fused and then broke back apart, but by the end of that period these reactions stopped. Essentially all the hydrogen that will ever exist was therefore present in the universe when the universe was just 3 minutes old. Subsequent fusion in stars has consumed some of this hydrogen, but it has not made any more

Compared to when the cosmic microwave background was first released, the radiation of the cosmic microwave background today is __________.

fainter and has most of its photons at longer wavelengths The universe is expanding and cooling with time, causing the cosmic microwave photons to stretch to longer wavelengths.

In the past, the temperature of the universe was _____

hotter than it is today

What is postulated to have caused a sudden inflation of the early universe?

the "freezing out" of the strong force from the GUT force

Helium originates from...?

the Big Bang with a small contribution from stellar nucleosynthesis

Which of the following observations cannot be explained by the Big Bang theory unless we assume that an episode of inflation occurred?

the fact that the temperature of the cosmic microwave background is almost the same everywhere

Consider this statement from Part A: "Photons of the cosmic microwave background have traveled through space for almost 14 billion years." This statement follows from our model of the Big Bang, because the Big Bang model is based on the idea that __________.

the universe began very hot and dense and has been cooling as it expands The Big Bang model holds that the universe began extremely hot and dense and has been cooling ever since. Photons could first travel freely when the universe was about 380,000 years old and had a temperature of about 3,000 K. These photons are what we see today—almost 14 billion years later—as the cosmic microwave background

One of the inferred statements from Part A is that "Large-scale structure grew around density variations present in the early universe." Observational evidence that such density variations really existed comes from the fact that the cosmic microwave background exhibits __________.

tiny temperature variations in different directions The tiny variations in temperature correspond to variations in density. These variations served as "seeds" for the later formation of large-scale structure; without such seeds, gravity could not have created such large structures in only 14 billion years.

How many forces operated in the universe during the GUT era?

two, gravity and the GUT force

A "GUT" (grand unified theory) refers to theories that _________.

unify the strong force with the electromagnetic and weak nuclear forces