Earth in the Universe · The Universe and the Solar System
The Origin of the Universe
One night during Noche de las Estrellas, at the Luis Enrique Erro Planetarium, Ximena looks at a star and asks: "How old is that light?" Starlight takes years, centuries, or millions of years to reach your eyes: looking at the sky means looking at the past. And if we look far enough, how far back in time can we go?
The Big Bang Model
When measuring the light from distant galaxies, astronomers noticed something strange: almost all of them are moving away from us, and the farthest ones are moving away faster. Why do galaxies move apart from one another instead of moving randomly?
Practice★☆☆Not started
Explain what the Big Bang theory consists of and state approximately how long ago the origin of the Universe occurred.
Explain what the Big Bang theory consists of and state approximately how long ago the origin of the Universe occurred.
A useful analogy: draw dots on a balloon and inflate it. Each dot moves away from all the others, and from any dot it looks like the others are moving away from it. None of them is the center.
Practice★★☆Not started
Hubble observed that the light from distant galaxies shifts towards the red. Explain what redshift is and what conclusion about the Universe can be deduced from this…
Hubble observed that the light from distant galaxies shifts towards the red. Explain what redshift is and what conclusion about the Universe can be deduced from this observation.
If you draw dots on a balloon and inflate it, all the dots move away from each other. Use this analogy to explain why the fact that galaxies are moving away from us does…
If you draw dots on a balloon and inflate it, all the dots move away from each other. Use this analogy to explain why the fact that galaxies are moving away from us does not mean that we are at the center of the universe.
The universe contains stars, which are grouped into galaxies (ours is the Milky Way); between the stars there are nebulae, huge clouds of gas and dust where new stars are born. Galaxies form clusters separated by immense voids.
Everything we see (stars, planets, gas, you) is ordinary matter, but it is only a small part of the total. A recent advance in astronomy is that most of the universe cannot be seen:
Component
Approximately
Ordinary matter
5 %
Dark matter
27 %
Dark energy
68 %
Dark matter does not give off light, but its gravity shows up in how galaxies rotate. Dark energy is linked to the fact that the expansion of the universe is accelerating. We still do not know what they are.
How We Explore the Cosmos: Electromagnetic Waves
Stars and galaxies are too far away to visit. What reaches us is light, and visible light is only one part of the electromagnetic spectrum: radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays. Each type reveals different things.
Optical telescopes: collect visible light (the National Astronomical Observatory at San Pedro Mártir, Baja California).
Radio and millimeter-wave telescopes: collect radio waves and millimeter waves, like the Large Millimeter Telescope at Sierra Negra, Puebla.
Infrared telescopes: see the dust and the stars being born inside nebulae.
The data are processed by computer: detectors record how much radiation arrives, and the computer converts it into images with assigned colors. In addition, when light is split into a spectrum, redshift can be detected and we can tell what an object is made of.
Formation of Stars and Chemical Elements
As the universe cooled, gravity gathered hydrogen and helium into denser and denser clouds. When the center of a cloud heats up and is compressed enough, nuclear fusion begins and a star is born. Stars, gas, and dust held together by gravity form a galaxy.
The Solar System formed about 4,600 million years ago from a nebula already enriched with those elements. First, a cloud of gas and dust collapsed under its own gravity. Most of the mass gathered at the center and the Sun was born. The rest of the material, spinning, flattened into a protoplanetary disk, where dust grains gradually stuck together and formed the planets.
Practice★★☆Not started
Describe the main stages of the formation of the Solar System from a nebula: collapse of the cloud of gas and dust, formation of the Sun at the center, and the…
Describe the main stages of the formation of the Solar System from a nebula: collapse of the cloud of gas and dust, formation of the Sun at the center, and the protoplanetary disk.
Science communicator Carl Sagan popularized the phrase "we are made of starstuff." Analyze the origin of the atoms in your body based on these data: hydrogen represents…
Science communicator Carl Sagan popularized the phrase "we are made of starstuff." Analyze the origin of the atoms in your body based on these data: hydrogen represents about $62\,\%$ of the total atoms, oxygen $24\,\%$, carbon $12\,\%$, and iron $0.001\,\%$ (essential in hemoglobin to transport oxygen).
a) Justify why carbon, oxygen, and iron had to form inside or during the death of earlier stars and not during the Big Bang.
b) Deduce why it was impossible for rocky planets with life like ours to exist around first-generation stars (Population III, formed shortly after the Big Bang consisting solely of hydrogen and helium).
The cosmic background radiation was emitted when the universe was about 380,000 years old. Before that it was a hot, opaque fog of charged particles; as it cooled, neutral atoms formed and light could travel freely. That light, stretched by expansion over 13,800 million years, now arrives as microwaves. It is detected with antennas and radio telescopes.
Practice★☆☆Not started
Name two lines of evidence supporting the Big Bang theory and briefly explain each one.
Name two lines of evidence supporting the Big Bang theory and briefly explain each one.
13,800 million years is hard to imagine. One way to picture it is to compress it into a one-year "cosmic calendar": the Big Bang is January 1 at 00:00 and the present is December 31 at 24:00. To place an event, calculate what fraction of history has passed up to it.
Practice★☆☆Not started
Look at the timeline of the Universe (not to scale): the letters A, B, C and D mark four events — Big Bang, formation of the Sun, formation of the Earth, and appearance…
Look at the timeline of the Universe (not to scale): the letters A, B, C and D mark four events — Big Bang, formation of the Sun, formation of the Earth, and appearance of life — without indicating which is which. Identify which event corresponds to each letter, order them from oldest to most recent, and state approximately how long ago each one occurred.
In the "cosmic calendar," the $13\,800$ million years of the universe are condensed into a single year of 365 days (January 1st at 00:00 h is the Big Bang and December…
In the "cosmic calendar," the $13\,800$ million years of the universe are condensed into a single year of 365 days (January 1st at 00:00 h is the Big Bang and December 31st at 24:00 h is the present moment).
a) Calculate approximately on what date (month and day) the Earth formed ($4\,600$ million years ago) and at approximately what date and time the human genus (Homo, about $2.8$ million years ago) appeared. Show your calculations.
b) In light of these results, refute the anthropocentric argument that the universe exists with the main purpose of harboring the human species, comparing the fraction of time occupied by our existence with that of the cosmos.
Back to the beginning: looking far away is looking into the past. The oldest light we can observe is the cosmic microwave background radiation, which shows us the universe when it was only 380,000 years old.
Summary
Let's practice! 3 medium exercises in this section