USAAAO 2021, I кръг — Задача 6
USAAAO 2021 - First Round · 30 януари 2021 г.
PHYSICAL AND ASTRONOMICAL CONSTANTS
| c | Speed of light in vacuum | |
| e | Elementary charge | |
| m | Neutron rest mass | |
| m | Proton rest mass | |
| m | Electron rest mass | |
| m | Helium-4 rest mass | |
| h | Planck’s constant | |
| H | Hubble’s constant | 70 (km/s)/Mpc |
| k | Boltzmann’s constant | |
| b | Wien’s constant | |
| G | Gravitational constant | |
| Stefan-Boltzmann constant | ||
| c | First Radiation Constant | |
| c | Second Radiation Constant | |
| N | Avogadro constant | |
| R | Gas constant | |
| a | Bohr radius | |
| Bohr magneton | ||
| M | Solar mass | |
| R | Solar radius | |
| L | Solar luminosity | |
| T | Solar temperature | 5770 K |
| M | Earth mass | |
| R | Mean Earth radius | |
| I | Earth moment of Inertia | |
| R☾ | Mean Moon radius | |
| M♃ | Mean Jupiter mass | |
| R♃ | Mean Jupiter radius | |
| a♃ | Mean orbital radius of Jupiter | 5.2 AU |
| a☾ | Mean semimajor axis Moon orbit | |
| 1 light year | ||
| 1 AU | Astronomical Unit | |
| 1 pc | Parsec | |
| 1 year | ||
| 1 sidereal day | 86164 s | |
| 1 erg | ||
| 1 bar |
ENERGY CONVERSION : 1 joule (J) = electronvolts (eV)
Условие
Which of the following is a problem of the conventional Big Bang theory that is resolved by the theory of inflation?
(a) Under the conventional Big Bang theory, it is extremely unlikely for our universe to be flat or nearly flat today, contrary to observation.
(b) Under the conventional Big Bang theory, it is impossible for the Cosmic Microwave Background to have come into thermal equilibrium by the time of recombination, despite its observed uniform temperature.
(c) The conventional Big Bang theory predicts a huge abundance of magnetic monopoles, while no magnetic monopoles have ever been discovered.
(d) All of the above
Отговори
- D
Решение
Each of (a), (b), and (c) are correct. Answer choice (a) is known as the flatness problem. As the universe expands, any deviation from flatness will grow quickly with time, according to the Friedmann equation. Thus, in order to have the flat () universe that we observe today, the early universe must have been extremely flat (down to 18 decimal places at second), which is a bizarrely fine-tuned initial condition. Inflation would rapidly flatten the universe, resolving this problem. Answer choice (b) is known as the horizon problem. The Cosmic Microwave Background is observed today to be very uniform in all directions, implying that the universe was in thermal equilibrium at recombination (when CMB radiation was released). However, the conventional Big Bang theory predicts the horizon distance was much smaller than the surface of last scattering (i.e. that light would not have had enough time to travel between opposite points of the CMB), so such a thermal equilibrium should be impossible. Inflation resolves this, since it is possible for the universe to be in thermal equilibrium before inflation. Then, the rapid expansion from inflation would create a universe uniform in temperature regardless of the horizon distance at recombination. Answer choice (c) is the magnetic monopole problem. Grand Unified Theories predict the existence of magnetic monopoles in the very early universe (perhaps 1 in every cubic horizon distance). Not only has no one discovered any magnetic monopoles, the conventional Big Bang theory actually predicts an abundance of magnetic monopoles so large that the density parameter would exceed ! If the magnetic monopoles formed before inflation, however, the density of magnetic monopoles would drop exponentially, making them impossible to detect today. These three answer choices are the three primary problems of the conventional Big Bang theory, leading to the cosmologists to supplement it with the theory of inflation.
Answer: D
Оригинал в Архива: usaaao2021_exam1.pdf · официални решения: usaaao2021_exam1_solutions.pdf