Question 1

All dark matter in our Universe falls into the category of "hot dark matter".

Accepted Answer

This statement is false. There are two categories of dark matter: hot dark matter (particles that move at high speeds, like neutrinos) and cold dark matter (particles that move slowly or not at all, like WIMPs). It is currently uncertain which type of dark matter dominates in our Universe.

Question 2

Cosmologists cannot begin their history of the big bang at a time of exactly zero because it cannot be explained by current physics.

Accepted Answer

The singularity at the time of the big bang cannot be explained by current physics and therefore cosmologists cannot begin the history of the big bang at exactly zero.

Question 3

In the early universe, the electromagnetic and strong nuclear forces were joined together to make the electrostrong force.

Accepted Answer

In the early universe, the electromagnetic and weak nuclear forces were unified into the electroweak force, not the electromagnetic and strong nuclear forces.

Question 4

When matter and antimatter particles combine, the two particles annihilate each other and convert their mass into energy in the form of two gamma rays.

Accepted Answer

When matter and antimatter particles combine, they do indeed annihilate each other and convert their mass into energy in the form of gamma rays. This is known as particle-antiparticle annihilation.

Question 5

Tiny amounts of lithium and beryllium were formed in the big bang.

Accepted Answer

The answer of Tiny amounts of lithium and beryllium were...

Question 6

The cosmological principle states that any observer in any galaxy sees the same general properties for the Universe.

Accepted Answer

The cosmological principle is a fundamental assumption in cosmology that states that the Universe is homogeneous (the same at every point) and isotropic (the same in all directions) on large scales. This means that any observer, regardless of their location in the Universe, would see the same general properties such as the distribution of galaxies and the overall expansion of the Universe.

Question 7

After nuclear reactions in the big bang had ended, about 25% of the mass of the Universe was in the form of helium nuclei.

Accepted Answer

This statement is true, according to current scientific understanding.

Question 8

The Universe has____.

Accepted Answer

The Universe, according to current cosmological theories, is considered to be infinite and uniformly filled with matter on the largest scales, implying it has no edge and no center. This concept aligns with the principle of cosmological isotropy and homogeneity.

Question 9

Olber's paradox is explained by the fact that the Universe is neither static nor infinite in age.

Accepted Answer

Olber's paradox is resolved by the fact that the Universe is expanding and has a finite age, which means that not all light from all stars has had enough time to reach us yet. Additionally, the Universe's expansion causes the light from more distant stars to be redshifted and dimmed, further contributing to the darkness of the night sky.

Question 10

The Universe is isotropic, but not homogenous.

Accepted Answer

The Universe is considered both isotropic, meaning it looks the same in all directions, and homogeneous, meaning it has a uniform composition throughout, on large scales.

Question 11

The "big bang" was an explosion of material that created galaxies flying away from the center of the explosion.

Accepted Answer

The "big bang" was not an explosion in space but rather an expansion of space itself, where galaxies are not flying away from a central point but rather moving apart as the space between them expands.

Question 12

The expansion of the Universe is accelerating.

Accepted Answer

This is correct according to current observations and measurements of the universe's expansion rate. It is believed to be driven by a mysterious force called dark energy.

Question 13

The decoupling of the strong force from the electroweak force provided energy for a rapid inflation of the Universe.

Accepted Answer

The decoupling of the strong force from the electroweak force is believed to have provided the energy necessary for a short period of rapid inflation in the early Universe. This is a widely accepted theory in cosmology known as inflation.

Question 14

Normal matter is baryonic.

Accepted Answer

Normal matter is primarily composed of baryons, such as protons and neutrons.

Question 15

The proper interpretation of the Hubble law (which relates the redshift of a galaxy to its distance) is that as time goes on, galaxies are____.

Accepted Answer

The Hubble Law implies that galaxies are not moving through space away from a common center, but rather, the space between galaxies is expanding, causing them to move apart. This expansion of space itself is what leads to the observed redshifts of distant galaxies, consistent with the Big Bang model of the universe.

Question 16

The Hubble time is____.

Accepted Answer

The Hubble time is an estimate of the age of the Universe based on the Hubble constant, which is a measure of the expansion rate of the Universe. It represents the time it would take for all galaxies to have been at the same point in the past, assuming a constant rate of expansion.

Question 17

Dark energy accounts for about 70% of the critical density of the Universe.

Accepted Answer

Dark energy is estimated to make up about 70% of the total energy density of the universe.

Question 18

The cosmological redshifts of galaxies are Doppler shifts.

Accepted Answer

Cosmological redshifts arise due to the expansion of the universe and are not Doppler shifts caused by the motion of galaxies away from us. This can be observed from the fact that the redshift is proportional to the distance of the object from us, which is not the case for Doppler shifts.

Question 19

The big bang happened everywhere in the Universe at the same time.

Accepted Answer

The Big Bang is believed to have happened at a single point in space-time, and expanded rapidly in all directions, meaning it did happen everywhere in the universe at the same time.

Question 20

Olber's paradox states that the ____.

Accepted Answer

Olber's paradox states that if the Universe is infinite and uniformly filled with an infinite amount of stars, then every line of sight should eventually lead to a star, and the sky should be as bright as the surface of a star in all directions. However, this is not what is observed, as the sky is dark at night. This paradox led to the development of the Big Bang theory and the understanding that the Universe is not static and infinitely old, but instead has a finite age and is expanding.

Quiz 18: Modern Cosmology