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Chapter 21: Problem 10

The cosmological principle says that a. the universe is expanding. b. the universe began in the Big Bang. c. the rules that govern the universe are the same everywhere. d. the early universe was 1,000 times hotter than the characteristic temperature of the CMB.

Short Answer

Expert verified
Option c.

Step by step solution

01

Understand the Cosmological Principle

The cosmological principle suggests that the universe is homogeneous and isotropic on large scales. This implies that the general properties and physical laws are consistent throughout the universe.
02

Analyze Each Option

Compare the stated options to the definition of the cosmological principle:a. Expansion of the universe: This describes a characteristic of the universe but not the cosmological principle directly.b. Big Bang: This talks about the origin of the universe, not its uniformity or isotropy.c. Same rules everywhere: This directly states the essence of the cosmological principle.d. Early universe temperature: This provides specific details about conditions in the early universe, not about its large-scale properties.
03

Select the Correct Option

From the analysis, option c clearly aligns with the concept of the cosmological principle as it states that the rules governing the universe are identical everywhere.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

headline of the respective core concept
The cosmological principle is a cornerstone in our understanding of the universe. It fundamentally suggests that on a large scale, the universe is both homogeneous and isotropic. These terms, though scientific, carry simple meanings that are crucial to comprehend to fully grasp the cosmological principle.
Homogeneous Universe
In cosmology, saying the universe is homogeneous means that it looks the same no matter where you are within it. Imagine looking at a vast desert; no matter where you stand, if all you see is endless sand dunes stretching to the horizon, then that desert is pretty homogeneous. This is how cosmologists view the universe when observing it on an extremely large scale.
The idea of homogeneity implies:
  • Uniform Distribution: Matter and energy are spread out evenly when considering the universe as a whole.
  • No preferred location: There isn’t any special center or edge; it’s balanced, much like the water in a still pond.
On a smaller scale, like looking at galaxies or star systems, the universe isn’t homogeneous due to the varying density of stars, planets, and galaxies. But when zooming out to a vast scale, like billions of light-years, the pattern appears uniform.
Isotropic Universe
The concept of an isotropic universe means that no matter which direction you look, the universe appears the same. Think of standing in the middle of a football field spun around; you would see the same scene all around you. This symmetry in all directions is what we mean by isotropy.
Key points about isotropy include:
  • Directional uniformity: Observations and properties of the universe are consistent in all directions.
  • Cosmic Microwave Background Radiation (CMB): The CMB is a perfect example, appearing almost the same no matter where or in which direction it is observed.
While small patches of the universe might show some anomalies, cosmologists consider the overall large-scale structure to exhibit this isotropic nature.
Physical Laws
The rules governing the universe sometimes referred to as physical laws, remain constant no matter where you go in the universe. This is crucial for the cosmological principle because it implies that the same physics apply everywhere, making our universe predictable and uniform to a great extent.
Important aspects about universal physical laws:
  • Consistency: The laws of physics, such as gravity and electromagnetism, are the same throughout the cosmos.
  • Predictability: Scientists can make predictions about cosmic phenomena based on these laws because they don’t change with location.
Imagine the chaos if the rules of the game changed from place to place; this consistency is what allows astronomers to study distant galaxies and draw meaningful conclusions based on known principles established here on Earth.

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Most popular questions from this chapter

What do astronomers mean when they say that the universe is isotropic? a. More distant parts of the universe look just like nearby parts. b. Intergalactic gas has the same density everywhere in the universe. c. The laws of physics apply everywhere in the universe. d. The universe looks the same in every direction.

The simplest way to estimate the age of the universe is from a. using the slope of Hubble's law. b. the age of Moon rocks. c. models of stellar evolution. d. measurements of the abundances of elements.

Does the expansion of the universe make the Sun bigger? What about the Milky Way? Why or why not?

Assume that the most distant galaxies have a redshift \(z=10\) The average density of normal matter in the universe today is \(4 \times 10^{-28} \mathrm{kg} / \mathrm{m}^{3} .\) What was its density when light was leaving those distant galaxies? (Hint: Keep in mind that volume is proportional to the cube of the scale factor.)

Science's greatest strength is the self-correcting nature of scientific inquiry: minds can be changed in the face of new data, as described in the Process of Science Figure. Consider a modern paradigm of science such as the Big Bang, climate change, or the power source of stars. In a short paragraph, describe your current viewpoint, and give a piece of evidence that would make you change your mind if it were true. For example, Einstein believed the universe was static. Measurements of the movement of galaxies caused him to change his mind.
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