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Chapter 22: Problem 17

Describe the observational evidence suggesting that Einstein's cosmological constant (a repulsive force) may be needed to explain the historical expansion of the universe. Explain how Einstein was "right for the wrong reason."

Short Answer

Expert verified
Evidence of the universe's accelerating expansion suggests that Einstein's cosmological constant is needed for a different reason than he initially proposed.

Step by step solution

01

Observing the Expansion of the Universe

Scientific observations indicate that galaxies are moving away from each other, suggesting the universe is expanding. Edwin Hubble's observations in the 1920s showed a direct relationship between a galaxy's distance from us and its velocity, commonly referred to as Hubble's Law.
02

Understanding the Cosmological Constant

Initially, Einstein introduced the cosmological constant \( \Lambda \) as a repulsive force to achieve a static universe, a common belief at that time. This constant acted against gravity to prevent the universe from collapsing.
03

Discovery of the Accelerating Universe

In the late 20th century, astronomers discovered that the universe's expansion is accelerating, not just continuing. This was a surprising outcome and suggested that a repulsive force, similar to Einstein's cosmological constant, might be at work.
04

Einstein's Mistake

Einstein originally thought the cosmological constant was a mistake after Hubble's discovery of an expanding universe. However, the recent discovery of the accelerating expansion implies that such a repulsive force indeed exists but is needed for a different reason than Einstein's initial belief.
05

Einstein's Correct Conclusion for Wrong Reason

Einstein was 'right for the wrong reason' because he introduced a concept that later proved necessary. Though he intended to explain a static universe, it turns out the cosmological constant explains the accelerating universe.

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Key Concepts

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

Universe Expansion
The concept of the universe expanding means that galaxies are moving away from each other over time. This idea first gained traction through observations made by Edwin Hubble in the 1920s. Hubble noticed a pattern where galaxies farther from us appeared to move away faster. This observation is essential because it suggests that the universe itself is stretching.
Hubble's discovery provided the first clear evidence that the universe is expanding rather than static.
Repulsive Force
Einstein's cosmological constant, symbolized by \( \Lambda \), was introduced as a form of repulsive force. Einstein initially proposed it to counterbalance gravity and achieve a static universe, which was the prevailing thought of the time. The cosmological constant was essentially a 'fudge factor' added to his equations to prevent universal collapse.
However, Einstein abandoned this idea after learning that the universe is expanding. Surprisingly, the concept of a repulsive force became relevant again with the discovery of an accelerating universe.
Hubble's Law
Hubble's Law describes the relationship between the distance of a galaxy and its velocity moving away from us. Mathematically, it is expressed as \( v = H_0 d \), where \( v \) is the galaxy's velocity, \( H_0 \) is Hubble's constant, and \( d \) is the distance. This law was groundbreaking because it provided a method to measure the expansion of the universe.
Hubble's work laid the foundation for understanding cosmic expansion and ultimately hinted at the need for a force to drive this expansion.
Accelerating Universe
In the late 20th century, astronomers discovered that the universe isn't just expanding; it's accelerating. By observing distant supernovae, scientists found that galaxies' velocities were increasing over time. This discovery was surprising because it indicated an unknown force countering gravitational attraction.
The accelerating universe suggests that there is an additional force, akin to Einstein's cosmological constant, driving galaxies apart faster than previously thought.
Einstein's Mistake
After Hubble's revelation of the expanding universe, Einstein called the cosmological constant his 'biggest blunder.' He had initially introduced it to support the idea of a static universe. However, the discovery that the universe's expansion is accelerating has shown that a repulsive force is indeed necessary.
As a result, Einstein was correct in proposing such a force, but for the wrong reason. While he intended to stabilize the universe, the cosmological constant now helps explain the accelerating expansion.

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Most popular questions from this chapter

During the period of inflation, the universe may have briefly expanded at \(10^{30}\) (a million trillion trillion) or more times the speed of light. Why did this ultra-rapid expansion not violate Einstein's special theory of relativity, which says that neither matter nor communication can travel faster than the speed of light?

Current understanding indicates that the universe (choose all that apply) a. is closed. b. is flat. c. is open. d. is inflating. e. has accelerating expansion.

Clips and full episodes from a four-part series of the television show \(N O V A\) called "The Fabric of the cosmos" can be accessed on PBS's website (http://pbs.org/wgbh/nova/physics/ fabric-of-cosmos.html). Watch at least one of the episodes. Are the arguments made in these programs compelling? Is the science explained in a way that makes sense to a general audience?

If astronomers ignored any cosmological constant (or dark energy, the future of the universe could be determined solely from a. the mass of the universe. b. the volume of the universe. c. the amount of light in the universe. d. the density of the universe.

Suppose you measure the angles of a triangle and find that they add to 185 degrees. From this you can determine that the space the triangle occupies is a. flat. b. positively curved. c. negatively curved. d. filled with dark matter.
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