2023年4月19日 贵州师范大学セミナー.

1. ©Aman Chokshi
Hayato Shimabukuro（云南⼤学、SWIFAR）
Cosmic Histories and human perspectives:
A journey through time and space
＠贵州师范⼤学（2023/4/20）

2. •Born in Okinawa(冲绳)
•Ph.D from
Nagoya university（名古屋⼤学）(2016)
•Postdoc at
Paris observatory(2016-2018)
About me
•Postdoc at
Tsinghua University(2018-2019)

3. •Born in Okinawa(冲绳)
•Ph.D from
Nagoya university（名古屋⼤学）(2016)
•Postdoc at
Paris observatory(2016-2018)
About me
•Postdoc at
Tsinghua University(2018-2019)
•Yunnan university（2019-）

4. How has the view of the universe updated?

5. The origin of astronomy
•Astronomy is one of the oldest natural sciences. The old people in recorded history made
observations of the night sky
•Babylonians（如巴⽐伦）, Greeks（希腊）, Indians（印度）, Egyptians（埃及）,
Chinese（中国） etc…
•Astronomy in Babylonia. The original stone plate describes
astronomy, and history in B.C. 652- A.D 61 (2500 years ago !)
•It was important for old people to know the motion of stars and the sun for agriculture(农业)
•In this stone plate, there is a description of
aurora.

6. Ancient Chinese astronomy
后汉书
客星＝超新星（Supernova）: Explosion of giant star
The supernova appeared suddenly in the sky and then
slowly fade-away

7. Ancient Greek
Geocentric universe (地⼼宇宙)
Suggestion
Aristotle(亚⾥⼠多德)
(BC384-322)
The Earth lay at the center of the universe and all other bodies moved around it.

8. The universe is simpler!
Copernicus(哥⽩尼)
(1473-1543)
Copernican revolution
At 16th century, a major change has occurred in human’s view of the universe by
Copernicus.
Heliocentric model (⽇⼼模型，太阳中⼼模型)
The earth is not located at center of the universe. The
sun is located in the center and others planets orbit the
sun.

9. Tycho Brahe
(1546-1601)

10. Tycho Brahe
(1546-1601)
•Brahe had measured the motion of the sun, moon, planets and stars
for 29 years and he collected much data on the motion of the planet,
sun and moon.

11. Johannes Kepler
(1571-1630)
Tycho Brahe
(1546-1601)
•Brahe had measured the motion of the sun, moon, planets and stars
for 29 years and he collected much data on the motion of the planet,
sun and moon.
•Kepler found laws that can explain Brahe’s
data(Kepler’s law)

12. Galileo Galilei
(1564-1642)
Johannes Kepler
(1571-1630)
Tycho Brahe
(1546-1601)
•Brahe had measured the motion of the sun, moon, planets and stars
for 29 years and he collected much data on the motion of the planet,
sun and moon.
•Kepler found laws that can explain Brahe’s
data(Kepler’s law)
•Galileo’s observation
supports the idea of
Copernicus.

13. Galileo Galilei
(1564-1642)
Johannes Kepler
(1571-1630)
Tycho Brahe
(1546-1601)
•Brahe had measured the motion of the sun, moon, planets and stars
for 29 years and he collected much data on the motion of the planet,
sun and moon.
•Kepler found laws that can explain Brahe’s
data(Kepler’s law)
•Galileo’s observation
supports the idea of
Copernicus.
Our understanding of the universe
is had been gradually updated!

14. Isaac Newton
(1642-1727)
F =
GM1M2
r2
•Newton gave an explanation why Kepler’s law holds by developing
mechanics and his law of gravity.
m
d2
x
dt2
= F
Equation of motion Newton’s gravity
Modern physics was born to understand the universe!!
As you know, modern physics has
developed our daily life (e.g. PC,
smartphone, AI…)

15. Isaac Newton
(1642-1727)
F =
GM1M2
r2
•Newton gave an explanation why Kepler’s law holds by developing
mechanics and his law of gravity.
m
d2
x
dt2
= F
Equation of motion Newton’s gravity
We can say, “Our trial to understand the
universe has not only enrich our mind, but
also developed our life !”
“What is the astronomy useful for?”

16. Is Newton theory perfect?
Newton explained the motion of planets. So, that’s all? Did we understand gravity?
No! This is just beginning of the modern physics.
Newton’s theory has continued for 250 years! But, in 1905, Einstein suggested a new theory of
gravity, called theory of general relativity (⼴义相对论)
250 years
Albert Einstein

17. Einstein gravity
•In Newton's theory, he did not explain what gravity is. He just explained the how we calculate
the gravity.
Rμν −
1
2
gμνR + Λgμν =
8πG
c4
Tμν
Einstein equation
•However, Einstein explained “Gravity is a distortion of space-time(引⼒是时空的扭曲).”
时空的扭曲
物质（能量）
If there exists material (energy), it distorts space-time and then
gravity arises.

18. Basic knowledge of modern cosmology

19. Expansion of the universe
•General relativity theoretically predicts
“expanding universe (膨胀宇宙)”
In 1929, Hubble discovered that galaxies are moving away from earth at speeds proportion to
their distance.
V = Hr
The velocity of galaxy
How long distance galaxy is
away from us
•This is due to expansion of the universe.
Our universe is expanding !!
(
·
a
a)
2
+
kc2
a2
−
c2
Λ
3
=
8πG
3c2
ρ
Friedmann equation
Hubble constant

20. Q
.
If the universe is expanding, wouldn't the universe be smaller when we go back in time?
A
.
Yes, the early universe is smaller, hotter, and denser!
Light elements such as hydrogen, deuterium, helium, and lithium formed in the hot,
dense early universe (Big Bang nucleosynthesis). The Big Bang is not the explosion of
the universe, but the creation of elements in a hot, dense universe
Bigbang nucleosynthesis

21. p
h
o
t
o
n
s
pnD
First, deuterium (D) is synthesized from protons and neutrons.
However, deuterium is easy to be decayed and is destroyed by
photons (γ).
The first 3 minutes
p + n ⟷ D + γ

22. pnD
When the temperature of the universe reaches below
0.1MeV (about 3 minutes after the birth of the universe),
photons no longer have the energy to destroy deuterium,
and a sufficient amount of deuterium is produced.
The first 3 minutes
p
h
o
t
o
n
s
p + n ⟶ D + γ

23. H
e
D
Helium-4 is then synthesized in a series of two-body reactions.
D
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D + D ! 3
He + n
3
He + D ! 4
He + p
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D + D ! 4
He +
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D + D ! 3
H + p
3
H + D ! 4
He + n
Other paths to produce helium-4
The first 3 minutes
p
h
o
t
o
n
s

24. Bigbang nucleosynthesis
•Bigbang theory predicts the abundance of light elements. In particular, the abundance
of helium-4 is important.
0.25%

25. •When we look up at the sky and measure the temperature of the CMB, it is uniformly isotropic.
•The universe is filled with photons that are a remnant of the Big Bang. These photons are
called cosmic microwave background radiation (CMB).
Cosmic microwave background (CMB)
TCMB = 2.73[K]

26. •However, very small temperature fluctuations are embedded in the CMB
Cosmic microwave background (CMB)

27. •However, very small temperature fluctuations are embedded in the CMB
T
T
⇠ 10 5
Cosmic microwave background (CMB)

28. •However, very small temperature fluctuations are embedded in the CMB
T
T
⇠ 10 5
Cosmic microwave background (CMB)
•The fluctuations of CMB temperatures provide us fruitful cosmological information.

29. •To evaluate the CMB fluctuations, we describe them by power spectrum
•We can find measured CMB power spectrum can be explained by theory very well!
Cosmic microwave background (CMB)

30. •To evaluate the CMB fluctuations, we describe them by power spectrum
•We can find measured CMB power spectrum can be explained by theory very well!
Cosmic microwave background (CMB)
The age of the universe is 138亿岁

31. How has is universe evolved??

32. Current universe
©JWST

33. Current universe
Stars, galaxies, bright universe
©JWST

34. Past universe

35. Past universe
No stars, galaxies, dark universe

36. Past universe
No stars, galaxies, dark universe
How did the universe evolve from dark ages to present universe?

37. •We often use “redshift(红移)” to express distant or past（过去） universe.
Redshift
Redshift
Due to the expansion of the universe, the wavelength of the distant or past universe extends.
z =
0
0
Original wavelength
Extended wavelength
z=0: present universe
z=0.1: 1.4 Gyr ago
z=1: 7.8 Gyr ago
z=10: 13.2 Gyr ago
z=20: 13.7 Gyr ago
G:Giga, 10亿年

38. Present
Past
https://universe-review.ca/
Epoch of
Reionization
Dark ages
Dark Ages・・・No luminous object exists.
Epoch of Reionization(EoR)・・・UV photons by luminous objects ionize
neutral hydrogen in the Intergalactic medium(IGM) ( ).
z ∼ 6 − 15
Cosmic Dawn・・・First stars and galaxies form( ).
z ∼ 20 − 30
The history of the universe

39. Present
Past
https://universe-review.ca/
Epoch of
Reionization
Dark ages
Dark Ages・・・No luminous object exists.
Epoch of Reionization(EoR)・・・UV photons by luminous objects ionize
neutral hydrogen in the Intergalactic medium(IGM) ( ).
z ∼ 6 − 15
Cosmic Dawn・・・First stars and galaxies form( ).
z ∼ 20 − 30
The history of the universe
Not observed yet!!

40. （C)Kenji Hasegawa（Nagoya University）
Credit: M. Alvarez, R. Kae

41. （C)Kenji Hasegawa（Nagoya University）
Credit: M. Alvarez, R. Kae

42. 21cm line emission
Proton Electron
21cm line emission(1.4GHz)
(Neutral) hydrogen atom is a good tracer for IGM through the dark ages to EoR.
singlet
Triplet
21cm radiation: neutral hydrogen atom emits 21cm line emission due to hyperfine structure.
Transition
Tb =
TS T
1 + z
(1 exp(⌧⌫))
⇠ 27xH(1 + m)
✓
H
dvr/dr + H
◆ ✓
1
T
TS
◆ ✓
1 + z
10
0.15
⌦mh2
◆1/2 ✓
⌦bh2
0.023
◆
[mK]
Brightness temperature
Red : cosmology Blue : astrophysics

43. 21cm line emission
Proton Electron
21cm line emission(1.4GHz)
(Neutral) hydrogen atom is a good tracer for IGM through the dark ages to EoR.
singlet
Triplet
21cm radiation: neutral hydrogen atom emits 21cm line emission due to hyperfine structure.
Transition
Tb =
TS T
1 + z
(1 exp(⌧⌫))
⇠ 27xH(1 + m)
✓
H
dvr/dr + H
◆ ✓
1
T
TS
◆ ✓
1 + z
10
0.15
⌦mh2
◆1/2 ✓
⌦bh2
0.023
◆
[mK]
Brightness temperature
Red : cosmology Blue : astrophysics

44. 21cm line emission
We can map the distribution of HI in the IGM with 21cm line.
Liu & Shaw (2020)
To describe 21cm signal statistically…
Redshift

45. 21cm line emission
We can map the distribution of HI in the IGM with 21cm line.
Liu & Shaw (2020)
21cm global signal: Sky-averaged 21cm line
signal
To describe 21cm signal statistically…
Redshift

46. EDGES (Bouman et al 2018)
Too deep trough
Too flat
Did we detect global signal?

47. EDGES (Bouman et al 2018)
Too deep trough
Too flat
SARAS3 did not detect signal
（Singh + 2022, Nature astronomy）
Did we detect global signal?

48. EDGES (Bouman et al 2018)
Too deep trough
Too flat
SARAS3 did not detect signal
（Singh + 2022, Nature astronomy）
Under the debate! Need exotic physics? mis-
calibration? unknown systematics?
Did we detect global signal?

49. We can map the distribution of HI in the IGM with 21cm line.
Redshift
To describe 21cm signal statistically…
Liu & Shaw (2020)
21cm line emission

50. We can map the distribution of HI in the IGM with 21cm line.
21cm line power spectrum
h Tb(k) Tb(k
0
)i = (2⇡)3
(k + k
0
)P21
Redshift
To describe 21cm signal statistically…
Liu & Shaw (2020)
21cm line emission

51. Current radio interferometers
MWA LOFAR HERA
GMRT
•Some ongoing telescopes have started the observation
targeting detecting 21cm power spectrum.
But, we have not detected the 21cm power
spectrum yet!!

52. Current upper limits on 21cm PS
Current 21cm experiments put upper limit of the 21cm line power spectrum 2-3 order
of magnitude higher than theoretical expectation.
Challenges: ionosphere, RFI, foreground, etc
Shimabukuro et al 2022b
34

53. •In 2027, a more powerful radio telescope called SKA will start observation.

54. FARSIDE
Lunar Crater Telescope
“We choose to go to the moon”
-J.F. Kennedy(1962)
Go to the moon・・・
鸿蒙计划
•Is radio astronomy in the 2030s and 2040s the era of 'Lunar Radio
Astronomy' using lunar telescopes and lunar orbiting satellites?
•On the Moon, the effects of the ionosphere and artificial radio, which
are disturbing for low-frequency radio observations, can be
suppressed.
An exciting era will come soon!! We need young
power!

55. Summary
• Our view of the universe has been updated for these 2000 years
• Expanding universe, big bang theory, and CMB are essential to
modern cosmology
• Dark Ages and EoR have veiled epochs in the history of the
universe.
• The 21cm line is a very powerful tool to investigate Dark Ages
and EoR
• Exciting projects are coming soon!!