Astronomy Quiz: Age Of The Universe
20 questions · exam conditions
0:00
Age Of The UniverseQuestion 1 of 20

The age of the universe is described as being estimated at a 'survey level,' implying it is based on large-scale observations. Which of the following measurements is the best example of a survey-level input to a cosmological age calculation?

The parallax measurement of the single star Proxima Centauri to help calibrate the cosmic distance ladder.
The all-sky map of temperature fluctuations in the Cosmic Microwave Background from the Planck satellite.
The laboratory measurement of the half-life of Thorium-232 for use in nucleocosmochronology.
The detailed spectroscopic analysis of the atmosphere of the single, ancient star HD 140283.
← Back to quizzes

Astronomy Quiz

Astronomy Quiz: Age Of The Universe

Practice Age Of The Universe in Astronomy with focused quiz questions that help you check what you know, review explanations, and build confidence with test-style prompts.

What this quiz covers

This quiz focuses on Age Of The Universe, giving you a quick way to practice the rules, question types, and explanations that matter most for Astronomy.

How to use this quiz

Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

All questions

Question 1

The age of the universe is described as being estimated at a 'survey level,' implying it is based on large-scale observations. Which of the following measurements is the best example of a survey-level input to a cosmological age calculation?

  1. The parallax measurement of the single star Proxima Centauri to help calibrate the cosmic distance ladder.
  2. The all-sky map of temperature fluctuations in the Cosmic Microwave Background from the Planck satellite. (correct answer)
  3. The laboratory measurement of the half-life of Thorium-232 for use in nucleocosmochronology.
  4. The detailed spectroscopic analysis of the atmosphere of the single, ancient star HD 140283.
Explanation: A 'survey-level' measurement involves collecting data from a large area of the sky or a large sample of objects to understand global or statistical properties. The all-sky map of the CMB is the quintessential example, as it provides a snapshot of the entire observable universe at one epoch. This data is used to constrain the cosmological parameters that determine the age. The other options are measurements of single, local objects or laboratory values (A, C, D), which are crucial inputs but are not themselves cosmological surveys.

Question 2

Imagine astronomers in a trillion years, after cosmic acceleration has pushed all other galaxy superclusters beyond their cosmic event horizon. Which statement best describes their likely conclusion about the universe's age, based on the evidence available to them?

  1. They would calculate a much older age for the universe, as the measured Hubble constant from remaining local galaxies would be extremely small.
  2. They would determine the correct age of ~1 trillion years by dating the oldest white dwarfs and red dwarfs in their own supercluster.
  3. They would likely conclude the universe is static and eternal, having no observational evidence of large-scale expansion or a hot, dense past. (correct answer)
  4. They would calculate the same age we do, because the Cosmic Microwave Background, though faint, would still be detectable with advanced technology.
Explanation: In this future scenario, all external galaxies would have redshifted out of sight, leaving only the gravitationally bound Local Group (or its remnant). There would be no Hubble expansion to observe. Furthermore, the Cosmic Microwave Background would be redshifted to such long wavelengths and low energies that it would be virtually undetectable, lost beneath the glow of local sources. Without evidence of expansion or a hot past (the CMB), future astronomers would likely conclude they live in a static, isolated 'island universe,' with no reason to suspect a Big Bang or a finite age.

Question 3

The cooling sequence of the oldest, faintest white dwarfs in a star cluster can be used to estimate the cluster's age, which in turn helps constrain the age of the universe. What is the fundamental principle of this method?

  1. It calibrates the Hubble constant by providing an independent distance to the cluster, which is then used in Hubble's law.
  2. It measures the rate at which white dwarfs accrete dark matter, a process that is assumed to have been constant over cosmic time.
  3. It provides a firm lower limit on the age of the universe, as the universe must be older than the age of the cluster plus the time it took for the first stars to form. (correct answer)
  4. It directly measures the age of the universe by finding the oldest white dwarf that has cooled to the exact temperature of the Cosmic Microwave Background.
Explanation: White dwarfs are the remnants of stars like the Sun. They are born hot and then cool and fade over billions of years at a predictable rate. By finding the faintest (and thus oldest and coolest) white dwarfs in a cluster, astronomers can determine the age of that cluster. Since the cluster exists within the universe, the universe must be at least as old as that cluster. Adding the time required for the first stars and clusters to form gives a robust lower bound on the total age of the universe. This method constrains the age; it does not calibrate H₀ (Choice A), involve dark matter accretion (Choice B), or rely on cooling to CMB temperature (Choice D).

Question 4

Two hypothetical flat universes have the same current Hubble constant (H₀). Universe A contains only matter (Ωₘ=1, Ω_Λ=0). Universe B contains both matter and dark energy, similar to our own (Ωₘ=0.3, Ω_Λ=0.7). How does the calculated age of Universe A (t_A) compare to the age of Universe B (t_B)?

  1. t_A < t_B, because the stronger gravitational deceleration in Universe A means it expanded more rapidly in the past to reach the same current state. (correct answer)
  2. t_A > t_B, because the absence of accelerating dark energy in Universe A results in a slower average expansion rate over its history.
  3. t_A = t_B, because the age is determined primarily by H₀, which is the same for both universes.
  4. The relationship cannot be determined without knowing the specific value of H₀.
Explanation: For a given current Hubble constant (H₀), the age of the universe depends on the history of its expansion. In a matter-only flat universe (Universe A), gravity consistently decelerates the expansion. This means the expansion rate was much higher in the past. The age is given by t_A = (2/3)H₀⁻¹. In a universe with dark energy (Universe B), the recent acceleration counteracts the earlier deceleration, making the average expansion rate over time closer to the current rate. Its age is t_B ≈ H₀⁻¹. Therefore, Universe A, with its stronger past expansion, reached its current state more quickly and is younger than Universe B. The common misconception is that age is always simply 1/H₀ (Choice C).

Question 5

There is a well-documented tension between the value of the Hubble constant (H₀) measured from the 'late' universe (e.g., using Cepheids and Type Ia supernovae) and the value inferred from the 'early' universe (the CMB). Late-universe measurements suggest H₀ ≈ 73 km/s/Mpc, while early-universe inferences yield H₀ ≈ 67 km/s/Mpc. If the late-universe value of 73 km/s/Mpc were correct and the standard ΛCDM model were used to calculate the age, how would this age compare to the canonical 13.8 billion-year age (derived using the early-universe value)?

  1. It would be significantly younger, because a faster current expansion rate implies less time has passed since the Big Bang. (correct answer)
  2. It would be significantly older, as a faster expansion rate allows more time for galaxies to reach their current positions.
  3. It would be nearly the same, as the age calculation is more sensitive to the matter density (Ωₘ) than to H₀.
  4. It would be indeterminate, as the standard ΛCDM model is fundamentally inconsistent with such a high value of H₀.
Explanation: The age of the universe is roughly proportional to the inverse of the Hubble constant (t₀ ≈ 1/H₀). A larger value for H₀ implies a faster rate of expansion. If the universe is expanding faster now, it must have taken less time to reach its current size, starting from the Big Bang. Therefore, using H₀ ≈ 73 km/s/Mpc would result in a calculated age that is significantly younger than the 13.8 billion-year age calculated using H₀ ≈ 67 km/s/Mpc. Choice B has the inverse logic. Choice C is incorrect as the age is very sensitive to H₀. While there is tension (Choice D), an age can still be calculated within the model framework for a given H₀.

Question 6

Cosmologists use the angular power spectrum of the Cosmic Microwave Background (CMB) to precisely determine the universe's age. The location of the first acoustic peak is primarily sensitive to the universe's geometry. How do other features, such as the relative heights and positions of subsequent peaks, contribute to the age determination?

  1. They directly measure the rate of cooling of the plasma at recombination, which sets a clock for how long the universe existed before that epoch.
  2. They provide a precise value for the Hubble constant (H₀) independent of other cosmological parameters, from which the age is calculated.
  3. They are used to measure the abundance of primordial elements like helium, which directly correlates with the universe's age.
  4. They constrain the densities of baryonic matter, dark matter, and dark energy, which are crucial inputs for the model of expansion history used to find the age. (correct answer)
Explanation: The age of the universe is calculated by integrating the Friedmann equation, which requires knowing the energy densities of the universe's components (matter, dark energy) and the current expansion rate (H₀). The detailed morphology of the CMB power spectrum (e.g., the ratio of odd to even peak heights, the damping tail) is sensitive to the physical densities of baryons (Ω_b h²) and cold dark matter (Ω_c h²). By fitting the full ΛCDM model to these features, cosmologists can constrain these densities and H₀ simultaneously, which then yields a precise age. The parameters are not independent (Choice B), and the spectrum doesn't directly measure cooling rates (Choice A) or helium abundance for this purpose (Choice C).

Question 7

The calculation of a single age for the universe from measurements of H₀ and density parameters relies critically on the Cosmological Principle. If the universe were found to be significantly anisotropic on large scales, how would this most directly undermine our current estimate of its age?

  1. The Cosmic Microwave Background would be completely uniform, removing our best tool for measuring cosmological parameters.
  2. The expansion rate (H) could be different in different directions, making a single 'age of the universe' a poorly defined concept. (correct answer)
  3. An anisotropic universe would imply a much higher matter density, leading to a systematically younger calculated age.
  4. The laws of radioactive decay would vary with direction, making stellar age estimates inconsistent and unreliable.
Explanation: The Cosmological Principle states that the universe is homogeneous and isotropic (the same in all locations and in all directions) on large scales. This allows us to describe the entire universe with a single scale factor and a single Hubble constant, H₀. If the universe were anisotropic, the expansion rate itself could be different in different directions. In that case, extrapolating back to a beginning would yield different timescales depending on which direction one looked, and a single, universal age would not be a valid concept. The CMB would show large-scale anisotropies, not be uniform (A). There is no necessary link between anisotropy and matter density (C) or the laws of physics themselves (D).

Question 8

Assuming the age of the universe is exactly 14.0 billion years and that it can be accurately approximated by the Hubble time (t_H = 1/H₀), what would be the corresponding value of the Hubble constant in km/s/Mpc? (Note: 1 year ≈ 3.16 × 10⁷ s; 1 Mpc ≈ 3.09 × 10¹⁹ km).

  1. 55 km/s/Mpc
  2. 62 km/s/Mpc
  3. 70 km/s/Mpc (correct answer)
  4. 78 km/s/Mpc
Explanation: First, convert the age from years to seconds: t = 14.0 × 10⁹ yr × (3.16 × 10⁷ s/yr) = 4.424 × 10¹⁷ s. Next, calculate H₀ in units of s⁻¹: H₀ = 1/t = 1 / (4.424 × 10¹⁷ s) ≈ 2.26 × 10⁻¹⁸ s⁻¹. Finally, convert the units from s⁻¹ to km/s/Mpc using the given conversion for megaparsecs: H₀ = (2.26 × 10⁻¹⁸ s⁻¹) × (3.09 × 10¹⁹ km/Mpc) ≈ 69.8 km/s/Mpc, which rounds to 70 km/s/Mpc. The other answers result from common calculation or unit conversion errors.

Question 9

The Hubble constant, H₀, is typically given in units of km/s/Mpc. To estimate the age of the universe using the Hubble time, t_H = 1/H₀, one must first perform a unit conversion. What is the conceptual significance of the distance units (km and Mpc) canceling out during this conversion?

  1. It demonstrates that the age of the universe is independent of the distances to any specific galaxies used in the measurement.
  2. It is a mathematical artifact with no deep physical meaning, simply required to obtain the correct final units of time.
  3. It proves that the speed of light is the ultimate speed limit for recessional velocities in the expanding universe.
  4. It reflects the scale-free nature of Hubble expansion; the time to double in size is the same for any two points, regardless of their initial separation. (correct answer)
Explanation: H₀ has units of (distance/time)/distance. When the distance units (km and Mpc, after one is converted to the other) cancel, H₀ is left with units of 1/time. The fact that the distance cancels out is a direct reflection of the uniform, scale-free nature of the expansion described by the Cosmological Principle. A galaxy 10 Mpc away recedes at some speed v, and a galaxy 20 Mpc away recedes at 2v. The time it takes for the distance between them to double is the same. Thus, the expansion timescale, 1/H₀, is a universal property, not dependent on which pair of observers you choose. This is a profound physical insight, not just a mathematical artifact (B).

Question 10

The Hubble constant, H₀, is typically given in units of km/s/Mpc. To estimate the age of the universe using the Hubble time, t_H = 1/H₀, one must first perform a unit conversion. What is the conceptual significance of the distance units (km and Mpc) canceling out during this conversion?

  1. It demonstrates that the age of the universe is independent of the distances to any specific galaxies used in the measurement.
  2. It is a mathematical artifact with no deep physical meaning, simply required to obtain the correct final units of time.
  3. It proves that the speed of light is the ultimate speed limit for recessional velocities in the expanding universe.
  4. It reflects the scale-free nature of Hubble expansion; the time to double in size is the same for any two points, regardless of their initial separation. (correct answer)
Explanation: H₀ has units of (distance/time)/distance. When the distance units (km and Mpc, after one is converted to the other) cancel, H₀ is left with units of 1/time. The fact that the distance cancels out is a direct reflection of the uniform, scale-free nature of the expansion described by the Cosmological Principle. A galaxy 10 Mpc away recedes at some speed v, and a galaxy 20 Mpc away recedes at 2v. The time it takes for the distance between them to double is the same. Thus, the expansion timescale, 1/H₀, is a universal property, not dependent on which pair of observers you choose. This is a profound physical insight, not just a mathematical artifact (B).

Question 11

Cosmologists use the angular power spectrum of the Cosmic Microwave Background (CMB) to precisely determine the universe's age. The location of the first acoustic peak is primarily sensitive to the universe's geometry. How do other features, such as the relative heights and positions of subsequent peaks, contribute to the age determination?

  1. They directly measure the rate of cooling of the plasma at recombination, which sets a clock for how long the universe existed before that epoch.
  2. They provide a precise value for the Hubble constant (H₀) independent of other cosmological parameters, from which the age is calculated.
  3. They are used to measure the abundance of primordial elements like helium, which directly correlates with the universe's age.
  4. They constrain the densities of baryonic matter, dark matter, and dark energy, which are crucial inputs for the model of expansion history used to find the age. (correct answer)
Explanation: The age of the universe is calculated by integrating the Friedmann equation, which requires knowing the energy densities of the universe's components (matter, dark energy) and the current expansion rate (H₀). The detailed morphology of the CMB power spectrum (e.g., the ratio of odd to even peak heights, the damping tail) is sensitive to the physical densities of baryons (Ω_b h²) and cold dark matter (Ω_c h²). By fitting the full ΛCDM model to these features, cosmologists can constrain these densities and H₀ simultaneously, which then yields a precise age. The parameters are not independent (Choice B), and the spectrum doesn't directly measure cooling rates (Choice A) or helium abundance for this purpose (Choice C).

Question 12

There is a well-documented tension between the value of the Hubble constant (H₀) measured from the 'late' universe (e.g., using Cepheids and Type Ia supernovae) and the value inferred from the 'early' universe (the CMB). Late-universe measurements suggest H₀ ≈ 73 km/s/Mpc, while early-universe inferences yield H₀ ≈ 67 km/s/Mpc. If the late-universe value of 73 km/s/Mpc were correct and the standard ΛCDM model were used to calculate the age, how would this age compare to the canonical 13.8 billion-year age (derived using the early-universe value)?

  1. It would be significantly younger, because a faster current expansion rate implies less time has passed since the Big Bang. (correct answer)
  2. It would be significantly older, as a faster expansion rate allows more time for galaxies to reach their current positions.
  3. It would be nearly the same, as the age calculation is more sensitive to the matter density (Ωₘ) than to H₀.
  4. It would be indeterminate, as the standard ΛCDM model is fundamentally inconsistent with such a high value of H₀.
Explanation: The age of the universe is roughly proportional to the inverse of the Hubble constant (t₀ ≈ 1/H₀). A larger value for H₀ implies a faster rate of expansion. If the universe is expanding faster now, it must have taken less time to reach its current size, starting from the Big Bang. Therefore, using H₀ ≈ 73 km/s/Mpc would result in a calculated age that is significantly younger than the 13.8 billion-year age calculated using H₀ ≈ 67 km/s/Mpc. Choice B has the inverse logic. Choice C is incorrect as the age is very sensitive to H₀. While there is tension (Choice D), an age can still be calculated within the model framework for a given H₀.

Question 13

The cooling sequence of the oldest, faintest white dwarfs in a star cluster can be used to estimate the cluster's age, which in turn helps constrain the age of the universe. What is the fundamental principle of this method?

  1. It calibrates the Hubble constant by providing an independent distance to the cluster, which is then used in Hubble's law.
  2. It measures the rate at which white dwarfs accrete dark matter, a process that is assumed to have been constant over cosmic time.
  3. It provides a firm lower limit on the age of the universe, as the universe must be older than the age of the cluster plus the time it took for the first stars to form. (correct answer)
  4. It directly measures the age of the universe by finding the oldest white dwarf that has cooled to the exact temperature of the Cosmic Microwave Background.
Explanation: White dwarfs are the remnants of stars like the Sun. They are born hot and then cool and fade over billions of years at a predictable rate. By finding the faintest (and thus oldest and coolest) white dwarfs in a cluster, astronomers can determine the age of that cluster. Since the cluster exists within the universe, the universe must be at least as old as that cluster. Adding the time required for the first stars and clusters to form gives a robust lower bound on the total age of the universe. This method constrains the age; it does not calibrate H₀ (Choice A), involve dark matter accretion (Choice B), or rely on cooling to CMB temperature (Choice D).

Question 14

An astronomer observes a quasar with a redshift corresponding to a lookback time of 13.1 billion years. The currently accepted age of the universe is 13.8 billion years. What is the most accurate conclusion that can be drawn from this observation?

  1. The universe must have been expanding at a nearly constant rate for the light to travel for 13.1 billion years.
  2. The quasar is approximately 13.1 billion years old today.
  3. The light from the quasar was emitted when the universe was approximately 0.7 billion years old. (correct answer)
  4. The age of the universe must be at least 26.9 billion years, the sum of its current age and the lookback time.
Explanation: Lookback time is the time it took for light emitted from a distant object to reach us. If the universe is 13.8 billion years old and the light has been traveling for 13.1 billion years, then the light must have been emitted 13.1 billion years ago. The age of the universe at that moment was its current age minus the lookback time: 13.8 Gyr - 13.1 Gyr = 0.7 Gyr (or 700 million years). Choice B is incorrect; 13.1 Gyr is when the light was emitted, not the quasar's age. The other choices represent common misconceptions about lookback time and cosmic age.

Question 15

The age of the universe is described as being estimated at a 'survey level,' implying it is based on large-scale observations. Which of the following measurements is the best example of a survey-level input to a cosmological age calculation?

  1. The parallax measurement of the single star Proxima Centauri to help calibrate the cosmic distance ladder.
  2. The all-sky map of temperature fluctuations in the Cosmic Microwave Background from the Planck satellite. (correct answer)
  3. The laboratory measurement of the half-life of Thorium-232 for use in nucleocosmochronology.
  4. The detailed spectroscopic analysis of the atmosphere of the single, ancient star HD 140283.
Explanation: A 'survey-level' measurement involves collecting data from a large area of the sky or a large sample of objects to understand global or statistical properties. The all-sky map of the CMB is the quintessential example, as it provides a snapshot of the entire observable universe at one epoch. This data is used to constrain the cosmological parameters that determine the age. The other options are measurements of single, local objects or laboratory values (A, C, D), which are crucial inputs but are not themselves cosmological surveys.

Question 16

The precise age of the universe derived from the ΛCDM model (≈13.8 Gyr) is the result of fitting a model with multiple parameters to cosmological data. Which set of parameters, when constrained by observations, provides the most direct path to calculating the age by solving the Friedmann equation?

  1. The baryon-to-photon ratio, the reionization redshift, and the spectral index of primordial fluctuations.
  2. The Hubble constant (H₀), the matter density parameter (Ωₘ), and the dark energy density parameter (Ω_Λ). (correct answer)
  3. The age of the oldest globular clusters, the distance to the Large Magellanic Cloud, and the peak luminosity of Type Ia supernovae.
  4. The current temperature of the CMB, the number of neutrino species, and the primordial helium abundance.
Explanation: The age of the universe is found by integrating the Friedmann equation, which describes how the scale factor of the universe evolves over time. The inputs to this equation that govern the expansion history are the current expansion rate (H₀) and the relative energy densities of the universe's components: matter (both baryonic and dark, Ωₘ) and dark energy (Ω_Λ). By constraining these three key parameters with data from the CMB, supernovae, etc., the expansion history can be calculated, and thus the time elapsed since the Big Bang can be determined. The items in choice C are observational data used to constrain the parameters in B, but they are not the model parameters themselves. The parameters in A and D are also part of the full ΛCDM model but are less direct in setting the overall expansion history and age.

Question 17

The calculation of a single age for the universe from measurements of H₀ and density parameters relies critically on the Cosmological Principle. If the universe were found to be significantly anisotropic on large scales, how would this most directly undermine our current estimate of its age?

  1. The Cosmic Microwave Background would be completely uniform, removing our best tool for measuring cosmological parameters.
  2. The expansion rate (H) could be different in different directions, making a single 'age of the universe' a poorly defined concept. (correct answer)
  3. An anisotropic universe would imply a much higher matter density, leading to a systematically younger calculated age.
  4. The laws of radioactive decay would vary with direction, making stellar age estimates inconsistent and unreliable.
Explanation: The Cosmological Principle states that the universe is homogeneous and isotropic (the same in all locations and in all directions) on large scales. This allows us to describe the entire universe with a single scale factor and a single Hubble constant, H₀. If the universe were anisotropic, the expansion rate itself could be different in different directions. In that case, extrapolating back to a beginning would yield different timescales depending on which direction one looked, and a single, universal age would not be a valid concept. The CMB would show large-scale anisotropies, not be uniform (A). There is no necessary link between anisotropy and matter density (C) or the laws of physics themselves (D).

Question 18

Suppose a new, highly reliable stellar dating technique reveals that the oldest globular clusters are 14.6 ± 0.3 billion years old. Current cosmological models based on Planck data estimate the age of the universe to be 13.8 billion years. What is the most significant implication of this hypothetical discrepancy?

  1. The amount of dark matter in the universe must be much higher than estimated, as its gravity would be needed to form clusters so early.
  2. The Hubble constant (H₀) would likely need to be revised to a lower value to reconcile the age of the universe with the age of its contents. (correct answer)
  3. The globular clusters must have formed from primordial matter before the first galaxies, violating hierarchical structure formation.
  4. The temperature of the Cosmic Microwave Background must have been significantly higher at recombination than is currently believed.
Explanation: The universe cannot be younger than the objects within it. This scenario creates an "age crisis." The calculated age of the universe is inversely proportional to the Hubble constant (t₀ ∝ 1/H₀). To increase the calculated age of the universe from 13.8 Gyr to be consistent with >14.6 Gyr, the value of H₀ used in the cosmological model would need to be smaller. Increasing dark matter (Choice A) for a fixed H₀ would actually decrease the universe's age. The formation mechanism of clusters (Choice C) doesn't solve the age paradox. The CMB temperature at recombination (Choice D) is tightly constrained by physics and is not a parameter that can be easily changed to resolve this discrepancy.

Question 19

Assuming the age of the universe is exactly 14.0 billion years and that it can be accurately approximated by the Hubble time (t_H = 1/H₀), what would be the corresponding value of the Hubble constant in km/s/Mpc? (Note: 1 year ≈ 3.16 × 10⁷ s; 1 Mpc ≈ 3.09 × 10¹⁹ km).

  1. 55 km/s/Mpc
  2. 62 km/s/Mpc
  3. 70 km/s/Mpc (correct answer)
  4. 78 km/s/Mpc
Explanation: First, convert the age from years to seconds: t = 14.0 × 10⁹ yr × (3.16 × 10⁷ s/yr) = 4.424 × 10¹⁷ s. Next, calculate H₀ in units of s⁻¹: H₀ = 1/t = 1 / (4.424 × 10¹⁷ s) ≈ 2.26 × 10⁻¹⁸ s⁻¹. Finally, convert the units from s⁻¹ to km/s/Mpc using the given conversion for megaparsecs: H₀ = (2.26 × 10⁻¹⁸ s⁻¹) × (3.09 × 10¹⁹ km/Mpc) ≈ 69.8 km/s/Mpc, which rounds to 70 km/s/Mpc. The other answers result from common calculation or unit conversion errors.

Question 20

Imagine that future observations reveal the density of dark energy (Ω_Λ) is actually 0.8 and the density of matter (Ωₘ) is 0.2, keeping the universe flat (Ω_total = 1) and the Hubble constant (H₀) fixed at its current measured value. How would the calculated age of this hypothetical universe compare to the standard age of 13.8 billion years (which assumes Ω_Λ ≈ 0.7)?

  1. It would be older, because more dark energy implies a longer period of acceleration, meaning the expansion was slower for a greater portion of past history. (correct answer)
  2. It would be younger, because a higher dark energy density causes a faster overall expansion throughout cosmic history.
  3. It would be unchanged, as the age is primarily determined by H₀, which is held constant in this scenario.
  4. It would be younger, because there is less matter (Ωₘ = 0.2) to gravitationally slow down the expansion.
Explanation: For a fixed current expansion rate (H₀), the age of the universe depends on the expansion history. Dark energy causes the expansion to accelerate. If there is more dark energy (Ω_Λ = 0.8 vs 0.7), the recent acceleration must have been stronger. To arrive at the same H₀ today, the expansion must have been slower in the past compared to the standard model. A slower past expansion means it would take more time to reach the present state. Therefore, the universe would be calculated to be older.