Understanding Our Universe
3rd Edition
ISBN: 9780393614428
Author: PALEN, Stacy, Kay, Laura, Blumenthal, George (george Ray)
Publisher: W.w. Norton & Company,
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Chapter 16, Problem 18QAP
To determine
The significance of flatness problem.
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What will happen if the density of the universe is less than the critical density?
1. The current (critical) density of our universe is pe = 10-26kg/m³. Assume the universe is
filled with cubes with equal size that each contain one person of m = 100kg. What would
the length of the side of such a cube have to be in order to give the correct critical density?
How many hydrogen atoms would you need in a box of 1 m³ to reach the critical density?
The matter we know, which consists mostly of hydrogen, constitutes only 4.8% of the current
critical energy density of our universe. So how many hydrogen atoms are actually in a box
of 1 m3 in our universe? Deep space is very empty and a much better vacuum than we can
obtain on earth in a laboratory.
The present number density of electrons in the Universe is the same as that of protons, about 0.2 m-3. Consider a time long before the formation of the microwave background, when the scale factor was x times smaller than its present value. What was the number density of electrons then?
Value: x = 12×106
Chapter 16 Solutions
Understanding Our Universe
Ch. 16.1 - Prob. 16.1CYUCh. 16.2 - Prob. 16.2CYUCh. 16.3 - Prob. 16.3CYUCh. 16.4 - Prob. 16.4CYUCh. 16.5 - Prob. 16.5CYUCh. 16.6 - Prob. 16.6CYUCh. 16 - Prob. 1QAPCh. 16 - Prob. 2QAPCh. 16 - Prob. 3QAPCh. 16 - Prob. 4QAP
Ch. 16 - Prob. 5QAPCh. 16 - Prob. 6QAPCh. 16 - Prob. 7QAPCh. 16 - Prob. 8QAPCh. 16 - Prob. 9QAPCh. 16 - Prob. 10QAPCh. 16 - Prob. 11QAPCh. 16 - Prob. 12QAPCh. 16 - Prob. 13QAPCh. 16 - Prob. 14QAPCh. 16 - Prob. 15QAPCh. 16 - Prob. 16QAPCh. 16 - Prob. 17QAPCh. 16 - Prob. 18QAPCh. 16 - Prob. 19QAPCh. 16 - Prob. 20QAPCh. 16 - Prob. 21QAPCh. 16 - Prob. 22QAPCh. 16 - Prob. 24QAPCh. 16 - Prob. 25QAPCh. 16 - Prob. 26QAPCh. 16 - Prob. 27QAPCh. 16 - Prob. 28QAPCh. 16 - Prob. 29QAPCh. 16 - Prob. 30QAPCh. 16 - Prob. 31QAPCh. 16 - Prob. 32QAPCh. 16 - Prob. 33QAPCh. 16 - Prob. 34QAPCh. 16 - Prob. 35QAPCh. 16 - Prob. 36QAPCh. 16 - Prob. 37QAPCh. 16 - Prob. 38QAPCh. 16 - Prob. 39QAPCh. 16 - Prob. 40QAPCh. 16 - Prob. 41QAPCh. 16 - Prob. 42QAPCh. 16 - Prob. 43QAPCh. 16 - Prob. 44QAPCh. 16 - Prob. 45QAP
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Need a deep-dive on the concept behind this application? Look no further. Learn more about this topic, physics and related others by exploring similar questions and additional content below.Similar questions
- Galaxies are found in the “walls” of huge voids; very few galaxies are found in the voids themselves. The text says that the structure of filaments and voids has been present in the universe since shortly after the expansion began 13.8 billion years ago. In science, we always have to check to see whether some conclusion is contradicted by any other information we have. In this case, we can ask whether the voids would have filled up with galaxies in roughly 14 billion years. Observations show that in addition to the motion associated with the expansion of the universe, the galaxies in the walls of the voids are moving in random directions at typical speeds of 300 km/s. At least some of them will be moving into the voids. How far into the void will a galaxy move in 14 billion years? Is it a reasonable hypothesis that the voids have existed for 14 billion years?arrow_forwardIn which model universe does the average density of the Universe equal the critical density?arrow_forwardWhat is the difference between hot dark matter and cold dark matter? How does this difference affect cosmology?arrow_forward
- Cosmological redshift caused by the expansion of space itself is not quite the same as the redshift caused by the physical motion of a light source away from an observer (that principle is more commonly known by its name, the hint: two words}).arrow_forwardAccording to the cosmological principle, our place in the universe does not appear to be particularly special compared to any other and it allows us to make predictions about the development of other galaxies and the evolution of the universe. The principle relies on Hubble's results that the universe appears to be the same in all directions (aka it is Question Blank 1 of 2) {hint: one word} and that any large region of space at a given distance from us appears like any other large region of space at a similar distance from us (aka it is Question Blank 2 of 2) {hint: one word}arrow_forwardThe Analysis of the Big Bang Theory.arrow_forward
- I'm doing a debate about Kalam cosmological. I need to have an example of something out of nothing (Or maybe we can't prove the cause)? Can you help give 5 modern physics example?arrow_forwardThe cosmic microwave background consists of: huge clouds of dark matter interspersed with equally huge clouds of H and He enormous cold voids separating warmer filaments of young protostas and protogalaxies denser areas of slightly warmer Hydrogen mixed with slightly less dense areas of slightly cooler Helium an enormous number of photons, particles of light that emerged after the Big Bang atoms of H and He, dark matter, and an immense amount of energy MacBook Air DII DD 30 D00 000 F7 F8 F9 F4 F5 F6 & 4 8 R Yarrow_forwardThe background radiation has an average temperature of 2.7 K, using Wien’s Law, the current background radiation in the microwave region, the peak wavelength is 1mm. In the past, when the cosmic background radiation had a peak wavelength of 51.1 µm, calculate the relative size of the universe compared to the current size of the universe, that is, the universe was how much smaller by a factor of what? Round to TWO places past the decimalarrow_forward
- Why do Weinberg and other scientists seriously consider the possibility that the Standard Model is just a tentative explanation for the composition of the universe?arrow_forwardWhere did all the antimatter go?arrow_forwardAssume a flat FRW universe, dominated by radiation throughout its history. Calculate the physical, cosmological horizon size at t=t_0 The initial conditions for the scale factor are a=a_0 at t=t0(today). Which asnwer is correct; a)R_H=2a_0ct_0 b) R_H = 3a_0ct_0 c)R_H = ct_0 d) R_H=2ct_0arrow_forward
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