PQ3. 연습문제 3(Practice Question 3)

[에드엑스 강좌] ANUx -ASTRO4x Cosmology (우주론)

제1부. (요약)공간과 시간(Space and Time)
제2부. (요약)우리 우주의 역학과 기하학(Geometry and Dynamics of our universe)
제3부. 인플레이션(Inflation)
    V3.1 세가지 수수께끼(Three Mystery)
    V3.2 단순성 과 대칭성(Simplicity and Symmetry)
    V3.3 인플레이션(Inflation)
    V3.4 수수께끼의 답 찾기(Solving the Mysteries)
    V3.5 인플레이션의 끝(End of Inflation)
    V3.5b 연대기(Timescales)
    V3.6 로렌스 크라우스와 인터뷰(Lawrence Krauss) #1
    V3.7 로렌스 크라우스와 인터뷰(Lawrence Krauss) #2
    V3.8 로렌스 크라우스와 인터뷰(Lawrence Krauss) #3

PQ3. 연습문제 3(Practice Question 3)

[PQ3.1]--------------------------------------------------
The universe appears to be very uniform on large scales. This is true in all directions out as far as we can see.

In the absence of Inflation, this is surprising. Why?

a) Because quantum mechanical fluctuations would produce randomness
b] Because we can observe parts of the universe that have never been in contact with each other.
c) Because the potential energy would be negative
d) Because the metric has a discontinuity
e) Because everything in modern astrophysics is surprising

Explanation

If two regions are identical, this is normally because they have been in contact at some point in the past. In the absence of inflation, regions we can see today on opposite sides of the sky have never been in contact with each other.

[PQ3.2]--------------------------------------------------
One of the main theoretical arguments for inflation theories is the idea of spontaneous symmetry breaking.

What part of the theory of inflation is necessary to cause symmetry to break spontaneously?

a) The rapid expansion
b) The high energy of the false vacuum
c) The speed-of-light expansion of true vacuum regions
d] The mexican hat diagram
e) The cool name

Explanation

The mexican hat diagram causes symmetry to break spontaneously by forcing the universe to make an arbitrary choice as its energy drops.

[PQ3.3]--------------------------------------------------

As you may remember from Section 2, the Friedmann equation is derived from energy conservation. The kinetic energy of a galaxy must change to balance out changes in its (negative) potential energy.

Consider the gravitational potential energy of a galaxy caused by a given spherical region of the universe. How would this gravitational potential energy depend on the contents of this spherical region?

Which of the following contents would lead to the most negative potential energy?

a) Matter
b) Radiation
c] False vacuum

Explanation

False vacuum (as postulated by Inflation) has by far the highest energy (and hence mass) density and so will lead to the the most negative potential energy. It will thus result in the largest postive kinetic energy of the galaxy.

[PQ3.4]--------------------------------------------------
If inflation took place, what would you expect a graph of a(t) against time to look like?

Inflation curve possibilities


Pick the curve from the above diagram that shows signs of inflation?
a) a
b) b
c) c
d) d
e] e

Explanation

Inflation makes the scale factor grow very fast for a period, so we need a curve that is nearly vertical for a short while. It has to be relatively flat before and afterwards.