The Great Speedup: Accelerated Expansion of the Universe Quiz

The correct answer is B because if the expansion were constant or slowing down, distant supernovae would be closer and brighter. Finding them to be fainter than predicted implies they are further away, meaning the expansion rate must have increased over the billions of years the light traveled to reach us.

This statement is true because gravity acts to pull matter together and slow down expansion, whereas dark energy acts on the vacuum of space to push it apart. The discovery of acceleration proves that on a global scale, the repulsive effect of dark energy is currently stronger than the attractive pull of gravity.

The term standard candles is the correct answer because it refers to astronomical objects with a known intrinsic brightness. By comparing this fixed brightness to how dim the object looks from Earth, scientists can calculate an exact distance, which is necessary to track the history of the universe's expansion rate.

Options A, B, and C are correct because the afterglow of the Big Bang, the recession of galaxies, and the chemical ratio of hydrogen to helium are the three pillars of the model. While water on planets is interesting, it does not provide evidence for the origin or expansion rate of the entire universe.

The correct choice is B because the cosmological constant represents energy inherent to space itself. This energy provides the outward pressure required to drive the accelerated expansion of the universe. It does not measure stellar heat or calculate the specific mass of dark matter particles.

Option B is correct because redshift is a direct result of the stretching of space. As the expansion of the universe speeds up, the light waves traveling through that space are stretched to a greater degree, causing a larger shift toward the red end of the spectrum for more distant objects.

This is true because the rate of expansion increases with distance. Eventually, the space between us and a distant galaxy will be expanding faster than the speed of light. At that point, the light from that galaxy can never reach us, making it invisible and placing it beyond the observable limit.

Options A and B are correct because they describe scenarios where expansion continues forever. The Big Freeze involves the universe becoming too cold for star formation, while the Big Rip involves expansion becoming so violent that it tears atoms apart. The Big Crunch only occurs if expansion stops and reverses.

Dominance is the correct term because for the first few billion years of the universe, matter was dense enough for gravity to slow expansion. As space grew and matter spread out, the constant energy of the vacuum became the stronger force, causing the transition from a slowing expansion to an accelerating one.

The correct answer is B because the Hubble constant is the unit of measurement for the recession velocity of galaxies per unit of distance. While it has changed over billions of years, its current value helps scientists determine the expansion rate and the overall age of the cosmos.

Option B is correct because the Big Bang model originally assumed gravity would slow expansion. The discovery of acceleration forced scientists to integrate dark energy into the model to explain why the expansion is speeding up, thereby refining our understanding of the universe's total energy composition.

This is true because detailed maps of the microwave background allow scientists to calculate the total matter and energy density of the universe. When these values are combined with supernova data, they confirm that dark energy makes up 70 percent of the universe, which is required for acceleration to occur.

Options A and B are correct because all matter exerts a gravitational pull that acts to slow down expansion. In the early universe, matter was packed closely together, so its gravity was the dominant force. Dark energy only became dominant later as the universe expanded and matter density decreased.

The correct answer is B because knowing the expansion rate changed from slowing down to speeding up allows scientists to "rewind" the clock more accurately. This refined expansion history aligns with the age of the oldest star clusters, providing a consistent timeline for the history of the cosmos.

Brighter is the correct answer because if the expansion were decelerating, those distant objects would not be as far away as they are now. Being closer would make them appear brighter. The fact that they are fainer than that "slowdown" prediction is the evidence that the expansion is actually accelerating.

Option B is correct because dark energy is considered a property of space itself. Unlike matter, which becomes less dense as space grows, the energy of the vacuum stays the same per cubic centimeter. This means as more space is created, the total amount of dark energy in the universe increases.

This is false because the acceleration is a global property of the fabric of the universe. It is observed in every direction we look in deep space. While gravity keeps our local group of galaxies together, the vast voids between all distant galaxy clusters are expanding at an increasing rate everywhere.

Options B and D are correct because spectra allow us to see how much light has been stretched (redshift). This tells us how fast a galaxy is receding. By combining this speed with the distance from supernovae, we can see how the expansion rate has changed over time.

The correct choice is B because matter only provides gravity, which is an attractive force. In a universe containing only matter, there would be no repulsive force to cause acceleration. The expansion would simply coast or gradually decelerate as the gravitational pull of all galaxies worked to slow it down.

Cosmological is the correct answer because this type of redshift is caused by the expansion of the fabric of space itself while the light is in transit. This is distinct from the Doppler effect, which is caused by the local motion of objects through space, and is the key to measuring the universe's expansion.