1. On Knowing

2. Science starts with curiosity ...something that is born in all of us
The starting point is to find patterns in the natural world

3. Seeing the Universe
Visible light is a half-tone range where EM spectrum is full piano

4. Sensitivity Improvement over the Eye
Improving on the Eye
2012
1011
1010
Photographic & electronic detection
108
Telescopes alone
Electronic
Sensitivity Improvement over the Eye
106
Photography
Hubble Space Telescope
104
102
Short’s 21.5”
Rosse’s 72”
Mount Wilson 100”
Mount Palomar 200”
Soviet 6-m
Herschell’s 48”
Huygens
eyepiece
Slow f ratios
Galileo
1600
1700
1800
1900
2000
Year of Observation

5. A Factor of Ten Billion The largest telescope can see 1011 times
(100 billion x) fainter than the naked eye
WHERE DOES THIS GAIN COME FROM?
The first factor is light gathering power
A gain of 10m over 1cm (or 0.01m) squared, a factor of 106

6. The second factor is efficiency of detecting photons
For a gain of nearly 100% efficiency over 1% or so, or a factor of 100
WHAT IS THE LAST FACTOR OF 1000?
The eye must “read out” every 1/10 of a second, like a movie camera, to give the illusion of motion. On the other hand, a CCD can integrate for hours before the image is read out.

7. The Copernican Revolution
The history of astronomy displaces us from cosmic importance

8. X 10 Accuracy For most exploratory calculations
Estimation
Scientists often use estimation or order of magnitude calculations in their work. Often it is not possible, or necessary, to derive very accurate numbers. This is particularly true in astronomy where the objects under consideration are usually very faint and very far away.
X 10 Accuracy For most exploratory
calculations
X 2 Accuracy For most numbers in
cosmology
10% Accuracy For the best-measured
parameters

9. DEDUCTION
Deduction combines statements or premises and combines them to reach a conclusion.
The conclusion is valid only if the premises are justified and the logical construction is correct.
Deduction preserves truth but doesn’t always expand knowledge.
i.e. symbolic logic, arithmetic, algebra
2 + 2 = 4

10. DEDUCTION
Induction involves a generalization from a limited amount of data to a broad conclusion.
Induction cannot yield certainty, but backed by a lot of data, gives reliable conclusions.
Induction can expand knowledge so is a basic tool of science.
i.e. data is always finite so theories are always subject to verification.
INDUCTION

11. Science Limitations
Uncertainty, imprecision, and error arise three different ways:
Making a false premise, confusing correlation with causation, inferring a pattern where none is present
CONCEPTUAL
MACROSCOPIC
There is no such thing as perfect data. Every data set is limited and every instrument has limitations
MICROSCOPIC
Heisenberg’s uncertainty principle sets a fundamental limit to precision for measurement of particle position and velocity, or energy and time

12. Science is Evidence Evidence is: based on data reproducible
quantitative
not subjective
never perfect

13. The Importance of Evidence
There is no science without evidence
All assertions must be supported by data
Every claim in science is subject to verification
Science is data-driven, so progress is made by:
1. Gathering more data
2. Repeating the experiment
3. Someone else repeating the experiment
GOOD!
BETTER!!
BEST!!!

15. Theory Good Science : a model which survives repeated testing
Science seeks robust explanations for observed phenomena that rely solely on natural causes.
Science progresses by creating and testing models of nature that explain the observations as simply as possible.
Occam’s Razor (there may be more than one explanation for any particular data set)
A scientific model must make testable predictions that may force us to revise or abandon the model.
Plus, the role of luck and persistence: Science is a very human enterprise!
Theory
: a model which survives repeated testing

16. For % of the universe, including all stars and all galaxies, the evidence is indirect.

17. On Space

18. Distance Units
Typical distance between stars is 1 pc = 3.36 light years = 6 trilllion km, or 6,000,000,000,000 km.
1 pc
1 Mpc
Typical distance between galaxies is 1 Mpc = 106 pc or 3 million light years. It’s an incredible 1019 km.
The size of the observable universe is about 10 Gpc = 1010 pc, or 30 billion light years. That distance is an unimaginable 1023 km.
10 Gpc

19. THE UNIVERSE AND US Us
Earth
Solar System
Milky Way
Universe
Multiverse?

20. A Scale Model
Set the Earth to the size of a walnut, or a 1:10,000,000 scale model =
The Moon is a pea at arm’s length
The Sun is a 3 m ball 100 m away
Neptune is another pea 2 km away
The nearest star is 50,000 km away

21. And at this scale, light is reduced to very slow walking speed
And at this scale, light is reduced to very slow walking speed. There’s no way information in the universe can travel any faster
The Moon is a seconds walk away
The Sun is 8 minutes walk away
10 hours to walk the Solar System
A year to walk to the nearest stars

22. Reduce the scale by a factor of 100,000,000
The Solar System is a grain of sand
The distance between stars is 10 m
The Milky Way is the size of India
The MW has 100,000,000,000 stars

23. Now reduce by another factor of 100,000,000
The Milky Way is the size of a plate
The nearest galaxy is 10 m away
The universe is the size of India
Billions of galaxies within this space

24. How Empty is Space?
A one-inch cube of the air you’re breathing holds 1020 atoms in it
The average density of the universe is 1022 times lower, about 1 atom per cubic meter

25. Distant Light = Old Light
Lookback Time
If the speed of light were infinite, light from everywhere in the universe would reach us at exactly the same time and we would see the entire universe as it is now.
But it is not, so we see distant regions as they were in the past.
Distant Light = Old Light

26. How can we know what the universe was like in the past?
Light travels at a finite speed (300,000 km/s).
Thus, we see objects as they were in the past:
The farther away we look in distance,
the further back we also look in time.
Destination
Light travel time
Moon
1 second
Sun
8 minutes
Sirius
8 years
Andromeda (M31)
2.5 million years
Point out how fast the speed of light is: could circle Earth 8 times in one second….
Also note that the speed of light is always the same…

27. LOOKBACK TIME
Nearby “Now”
“Recent” Stars
“Long Ago” Galaxies
“Ancient” Universe

28. Scattered in a universe 46 billion light years across
Galaxies
100 billion
galaxies
Scattered in a universe 46 billion light years across

29. The Milky Way is typical with 400 billion stars

30. Almost all the simple elements hydrogen and helium
Atoms
1080
Atoms
Almost all the simple elements hydrogen and helium

31. A hundred million photons for every particle
1088
A hundred million photons for every particle

32. We therefore live on an: Average planet around An average star in an
Mediocrity
We therefore live on an:
Average planet around
An average star in an
Average galaxy in a
Very large universe
Copernicus

33. On Time

34. A Timeline
Science is Seeing

35. How do our lifetimes compare to the age of the universe?
The Cosmic Calendar: a scale on which we compress the 13.7 billion year history of the universe into 1 year.
This is a time scale model that used a scale factor of 14,000,000,000:1.
Our lives would scale similarly, so 80 years goes down by a factor of 14 billion too.
In the scale model, a human life lasts about 2 tenths of a second!
Our favorite way to present the scale of time: a modified version of Carl Sagan’s Cosmic Calendar. Worth noting:
Since we are compressing the 14 billion-year history of the universe into one calendar year, 1 month represents about 1.2 billion real years, 1 day represents about 40 million years; 1 second represents about 440 years.
the universe already 2/3 of the way through its history before our solar system even formed.
dinosaurs arose the day after Christmas, died yesterday.
All of (recorded) human history is in the last 30 seconds.
You and I were born about 0.05 seconds before midnight, Dec. 31.

36. TIME SENSE
Black Holes
Arrow of Time
Sentient Life
Lots of Atoms
Single Atoms
No Arrow of Time

37. The early universe expanded much faster than the speed of light, so there are objects and large regions of space we have never seen.
Size
The Universe
Speed of Light
Time
This violates no law of physics since the cosmic expansion is governed by general relativity, which sets no limit on the speed of expanding space.

38. Hubble Expansion
Galaxy spectra show redshifts, where all the spectral features shift to longer wavelengths. The amount of the shift increases with growing distance: more distant galaxies are moving away faster.
This linear relation was discovered by Edwin Hubble back in 1929.

39. The redshift is not a Doppler shift; it is due to the expansion of space itself. Photons are stretched.

40. Galaxies are all moving away from each other, so every galaxy sees the same Hubble expansion, i.e there is no center.
The cosmic expansion is the unfolding of all space since the big bang,
i.e. there is no edge.
We are limited in our view by the time it takes distant light to reach us,
i.e. the universe has an edge in time not space.

41. Nature of the Expansion
Space really does expand, like the material of the balloon. The balloon surface area is finite but unbounded. The universe is close to flat so imagine a large balloon with little curvature
Galaxies are held together by gravity and do not expand, so imagine coins glued to the balloon
Photons in this 2D space have their wavelengths stretched or redshifted by the expansion as they travel

42. Dark matter binds galaxies and dark energy drives cosmic acceleration.

43. Nature of the Expansion
Early expansion is rapid, driven by radiation. It slows as dark matter begins to dominate and more recently has begun to accelerate due to dark energy.

44. On Matter

45. Unity
Life occurs in
a range of scales that extends from galaxies to the atomic nucleus, as symbolized by the ancient symbol of the ouroboros, the snake that eats its tail

46. Ouroboros
Science is Seeing

47. A sand grain of diameter 0. 5mm weighs about 3 grams
A sand grain of diameter 0.5mm weighs about 3 grams. The sand is SiO2, molecules 60 times hydrogen mass.
How Many?
1019 atoms

48. A normal monk, one who does not like “momos” too much, weighs about 50 kg. Monks are made of water, H2O, molecules 17 times hydrogen mass.
NOTE: EVERYTHING THAT HAS MASS EXPERIENCES THE GRAVITY FORCE, INCLUDING ATOMS. HOWEVER, THE BEHAVIOR OF ALL SMALL OBJECTS, SUCH AS MONKS AND MOUNTAINS, IS GOVERNED BY THE FAR STRONGER ELECTRIC FORCE BETWEEN ATOMS. FOR ANY OBJECT WITH MORE THAN ABOUT 1045 ATOMS, OR A SIZE ABOUT 100 KILOMETERS, GRAVITY BECOMES THE DOMINANT. SO GRAVTY DRIVES THE BEHAVIOR OF PLANETS, STARS, GALAXIES, AND THE UNIVERSE.
How Many?
1028 atoms

49. One solar mass is 2 x 1030 kg. Which is an enormous factor larger than a hydrogen atom 2 x kg. Earth is 330,000 times less massive.
How Many?
1057 atoms

50. How Many? 1069 atoms 1080 atoms The typical galaxy contains 1012 stars
The whole universe contains 1011 galaxies
How Many?
1069 atoms
1080 atoms

51. What is Dark Matter?
THE SHORT ANSWER IS: WE DON’T KNOW. BUT SEVERAL LINES OF EVIDENCE INDICATE 10X MORE INVISIBLE THAN VISIBLE MATTER
The rotation speed of galaxies does not decline with radius, violating Kepler’s law unless without a halo of unseen matter

52. Light from distant galaxies is bent by an intervening cluster to form little arcs. The amount of bending indicates a lot of unseen matter in the cluster.
Light from all distant galaxies is very slightly distorted and bent as it travels through the “sea” of dark matter. With the best images, these distortions of 0.1% in shape can be seen.

53. X X X X Why are astronomer so confident
that dark matter really exists?
Because the law of gravity has
passed so many tests, and if we
put dark matter into computer
simulations, we evolve structure
that looks just like the universe.
So far, we can only rule items out:
Stars: (normal matter) census of stars does not allow it X
MACHOs: (sub-stars & planets) gravitational lensing rules it out X
Black holes: (dark, collapsed stars) no sign of preceding supernovae X
Dust: (dust up to rocks) re-radiation in infrared not seen X
Which leaves: weakly interacting particles, supersymmetric extension to standard model

54. Experiments in the 1960’s and 1970’s showed that, just as atoms are not simple and fundamental, so protons and neutrons are made of much smaller particles that were named quarks.

55. This scheme has multiple generations of particles and their anti-particles, so it is not very elegant or simple. This has led physicists to suppose that there may be an even deeper level of sub-atomic structure

56. TOP DOWN
Dark Matter
Objects
Atoms
Molecules
Universe

57. String Theory
String theory postulates dynamic 1-dimensional entities that are only noticeable on scales of meters, 33 orders of magnitude smaller than atoms!

58. In string theory, the smoothness and the emptiness of space are illusions. If we could imagine ourselves at the incredibly tiny Planck scale, meters, we would see a chaotic version of space-time. At every point, the six hidden dimensions that are not apparent in the everyday world would be manifested...

59. BOTTOM UP
Atoms
Quarks
Electrons
Bosons
Leptons
Strings

60. Four Forces Strength: 10-38 10-19 0.0073 1
Range: Long Subatomic Long Subatomic

61. The forces are associated with particular families of particles
The forces are associated with particular families of particles. But just as these particles are secondary manifestations of strings, the individual forces are manifestations of a single underlying “superforce”

62. On Energy

63. Energy is a very broad concept
Energy is a very broad concept. It is anything that can make matter move or change
Energy changes forms constantly but is not created or destroyed: this is a law of physics
Use this figure to define the nucleus; protons, neutrons, electrons; scale of atom and “electron cloud.”

64. Energy can be kinetic, the overall motion of an object
Energy can be radiant, light or other electromagnetic waves
Energy can be potential, stored in a number of ways
Chemical bonds
Electric fields
Magnetic fields
Gravity fields
Elastic (materials)

65. Light is an electromagnetic wave
Use this slide to define wavelength, frequency, speed of light.

66. Light is a Particle
Photons: they are “pieces” of light, each with a precise wavelength, frequency, and energy. Think of photons as tiny bullets, localized in space
Photon energy is proportional to frequency of the wave
Within the visible spectrum, blue light has higher energy than red light
Within the electromagnetic spectrum, X-rays have the highest energy, followed by UV, visible light, IR, and radio
Remember: Light is just one form of electromagnetic wave of energy, the kind we can detect with our eyes.

67. Our first key idea is that visible light is only a small part of the complete spectrum of light. You may wish to spend some time explaining the various things shown in this figure… You may also want to repeat this slide at various points to summarize other ideas.

68. If you pass white light through a prism, it separates into its component colors
long wavelengths
ROY G B I V
short wavelengths
spectrum

69. Light Interacts with Matter
Emission
Absorption
Transmission
Reflection or Scattering
Everything we know about the universe is a result of these effects
Briefly explain the 4 major interaction processes.
Terminology:
Transparent: transmits light
Opaque: blocks (absorbs) light

70. Atomic Energy Levels
Electrons in every atom have distinct energy levels
Each chemical element, ion or molecule, has a unique set of energy levels
This slide represents the first introduction to quantized energy levels.

71. Distinct energy levels lead to distinct emission or absorption lines
Hydrogen Energy Levels
Emission: atom loses energy
Absorption: atom gains energy

72. Chemical Fingerprints
Atoms, ions, and molecules have unique spectral “fingerprints”
We identify chemicals in a gas by their spectral fingerprints
With additional physics, we can figure out abundances of the chemicals, and often temperature, pressure, and much more.

73. Types of Spectra Hot/Dense Energy Source Continuous Spectrum
prism
Continuous Spectrum
prism
Hot low density cloud of Gas
Emission Line Spectrum
Hot/Dense Energy Source
prism
Cooler low density cloud of Gas
Absorption Line Spectrum

74. Anywhere in the universe, atoms and molecules are always in constant, microscopic motion
Temperature is a measure of the average kinetic energy of the particles in a substance
Students sometimes get confused when we’ve said there are 3 basic types of energy (kinetic, potential, radiative) and then start talking about subtypes, so be sure they understand that we are now dealing with subcategories.
COOLER
HOTTER

75. All the atoms and molecules in the universe are in constant (invisible) microscopic motion or vibration:
Thermal energy
As a result, every substance emits a smooth spectrum of radiation, mostly at invisible infrared wavelengths:
Thermal radiation

77. Mass-Energy
Another way to think about this is that the energy that holds the helium nucleus together has a tiny amount of equivalent mass, and that energy gets released going by fusion from hydrogen to helium
E = mc2
big number
small number
huge number

78. When 0.7% of the mass of a hydrogen atom is converted to radiant energy it is a huge amount relative to the mass involved
The mass-energy in the ink in the dot at the end of a sentence in a book could power a typical family home for an entire year

79. What is Dark Energy?
THE SHORT ANSWER IS: WE DON’T KNOW. BUT ONE OBSERVATION OF DISTANT SUPERNOVAE POINTED TO A COSMIC ACCELERATION

80. Expansion History of the Universe
30,000
300,000
3,000
100
1,000
10,000
Constant or faster in past (expected)
Redshift cz (km/s)
Riess, Press,
& Kirshner (1996)
Slower in past (big surprise!)
Farther in the past
Riess et al. (1998)
Perlmutter et al. (1999)
Distance (Mpc)

81. Einstein’s Theory: General Relativity3
Riess et al. 1998
Perlmutter et al. 1999
No Big Bang 2
Strength of cosmological constant, L
Riess et al. 2004
Tonry et al. 2003
8 HST SN Ia z > 1
If the acceleration is caused by Einstein’s cosmological constant, HST data on 8 SN Ia have increased our cosmology knowledge by a factor of 7 1
Accelerating
I also had a chance to recalculate constraints in the omega_M,omega_l space
The new constraints are about 5 times more precise than the ones either team published in 1998
There is a lot more we can do with this data and more like it in the future to understand the nature of dark energy x
Decelerating
Closed
Open 1 2
Strength of matter

82. Dark energy is much more mysterious than even dark
matter. It’s existence rests
on the unexpectedly faint
distant supernovae, and a
few less direct arguments.
The direct detection of dark
energy is very challenging.
Dark energy is a repulsive force that counter gravity. It does not change
its strength with time (Einstein’s gravitational constant “blunder”)
Physics provides no assistance. The vacuum of space could have energy
in quantum theory, but it would be 1080 times larger than is observed!
The density of dark energy and dark matter are roughly equal, this is the
only time in the history of the universe that is true: is this a coincidence?

83. On Structure

84. Hierarchies are the relationships between things, when few items are composed of many. This is represented as a tree or as a network.

85. Hierarchies in Astronomy
TIME
Mergers of black holes… …and galaxies

86. A hierarchy of self-reproducing universes in the big bang

87. Sometimes the structures in physics and biology are strikingly similar, and can be described by similar mathematical forms

88. Matter is subject to gravity, which gives structure on many scales
Radiation does not interact with itself and has no form or structure

89. Superforce

90. First instant after the big bang event
Most of the history of the universe
The underlying unity suggested by string theory and the unification of forces is only realized in the big bang itself

91. A few dimensionless parameters govern the behavior of the universe:
Matter Density
Energy Density
Fine Structure Constant
Entropy per Baryon
Dielectric Constant
Number of Space Dimensions
A few pure number occur over and over through mathematics

92. The 92 stable elements in the periodic table lead to almost infinite complexity. Life uses only about 20.

93. Cosmological
The universe was initially very smooth; over time complex structures grew by the action of gravity

94. Quantum fluctuations are a mechanism for multiple realizations of the universe
…leading to the concept of the “multiverse”

95. More than just this… LEVEL 1: regions we can not see in big bang model
LEVEL 2: many bubbles of space-time, unobservable by us, different properties
LEVEL 3: indeterminacy, and quantum variation
LEVEL 4: mathematical forms, multi-dimensional space-times, 10 preferred

96. String Theory Landscape
500
Perhaps 10 different vacua
de Sitter expansion in these vacua create quantum fluctuations and provide the
initial conditions for inflation. String theory provides context for the “multiverse”

97. On Meaning

98. Knowing Meaning Space Life Time Structure Matter Energy 1 8 2 7 3 6 45
Structure
Matter
Energy

99. ? ? ? ? ?
As creatures who occupy a tiny portion of time and space we have learned much about our universe. But many important questions are still answered.
WHAT IS TIME?
WHAT IS SPACE?
WHAT IS MATTER?
WHAT CAUSED THE BIG BANG?
IS THE UNIVERSE UNIQUE?
ARE WE ALONE?

100. In the universe with ten thousand billion billion stars, and a likely myriad of life forms, we’re special in some ways yet we are not in a cosmic sense. This leads to another big question:
WHY ARE WE HERE?

101. Anthropic Principle
Brandon Carter presented the “anthropic principle” in 1973 in Poland during the 500th birthday of Nicklaus Copernicus. The idea seems to subvert the sense that we are not special, by elevating the role of intelligent observers in the universe to central importance.
The weak form of the anthropic principle states that we can only observe a universe with properties such that intelligent observers exist. This is self-evident and little more than a tautology.
The strong form of the anthropic principle states that the universe has to be the way it is because intelligent observers exist. This is much more audacious because it implies a special role for life.

102. Conditions for Life
Stars of the right type for sustaining life supportable planets only can occur during a certain range of ages for the universe
stars of the right type only can form for a narrow range of values of the gravitational constant
Living cells consists of light and heavy elements (hydrogen, carbon, oxygen, and metals such as iron, copper, etc.)
To make both the light and heavy elements in the correct proportions, the strengths of the various fundamental forces must lie within a very narrow range of values
But does this place too specific a requirement on life? Perhaps life just needs disequilibrium chemistry and an energy source, not necessarily carbon and a star.

103. Fundamental Forces Gravitational force Electromagnetic force
Attractive force between all objects with mass
Weakest, long range
Electromagnetic force
Attractive and repulsive
Long range, 1039 times stronger than gravity
Nuclear Weak force
Cause neutrons to decay into protons
Range <10-17 m, 1028 times stronger than gravity
Nuclear Strong force
Holds the nucleus together
Range <10-15 m, 1041 times stronger than gravity

104. Coincidences
Some physical coincidences are noteworthy and so beg for an explanation. All the seemingly arbitrary, unrelated constants in physics have one strange thing in common – they have just the values that would create a universe capable of sustaining life. In other words, our universe could have quite different values of the fundamental forces and it would be physically sensible, but it would contain no carbon-based life forms.

105. Fine-Tuning of Forces Gravitational force Electromagnetic force
A bit stronger, and stars have rapid, unstable lives
A bit weaker, no supernovae, so no heavy elements
Electromagnetic force
A bit stronger, no shared electrons, no chemistry
A bit weaker, atoms cannot hold their electrons
Nuclear Weak force
A bit stronger, neutrons all decay, no heavy elements
A bit weaker, all hydrogen converted to inert helium
Nuclear Strong force
A bit stronger, nuclear reactions too efficient, H to Fe
A bit weaker, electrical repulsion splits apart nuclei

106. Cosmological Fine-Tuning
The following incredibly precise tweaking of the Universe is known as the flatness-oldness problem
The critical density is the matter density just required to eventually overcome the expansion of the big bang
If X is critical density, what is the actual density?
It could have any value, but the matter density has a huge impact on the evolution of the universe
Only a value relatively close to the critical value leads to an old and flat universe X

107. OPEN
FLAT
CLOSED
If the density is much below critical, early expansion is too rapid for stars and galaxies to form, so no life
If the density is much above critical, the universe will recollapse quickly, with not enough time for stellar evolution to create carbon, and once again, no life
The matter density is only ¼ critical; the other major component affecting the expansion is dark energy, which leads to another issue related to fine-tuning….

108. Anthropic Principle Multiverse Redux
Our universe emerged from a quantum space-time foam at the Planck epoch. Other universes may have been spawned this way, with physical properties that are randomly different.
Most of the past, present and future universes in the multiverse would be inhospitable to life. Ours is just a mediocre member of the ensemble.
Anthropic Principle

109. Applying Logic
Is there really a logical basis for anthropic arguments about life?
1. We shouldn’t be surprised to see features of the universe that are compatible with our existence
2. We should be surprised not to see features of the universe that are incompatible with our existence
1 is true, but 2 does not follow from it
This universe has special features, like a double six thrown with dice. The multiverse hypothesis is akin to speculating that there are many possible outcomes, ours is “double six”
A double six will occur eventually in a long sequence of throws, sequential or parallel
This is the “inverse gamblers” fallacy
The odds of double six are always 1 in 36, so the supposition above doesn’t explain it

110. Scientific Method? Epistemology
Let’s look at the strange conceptual journey we have just followed
We can only observe a universe that is capable of creating observers like us
Some features of the universe are very finely-tuned around the existence of life
But is this an unduly anthropocentric view of life based on stars and carbon?
Fine-tuning might be due to happenstance, providence, or self-selection in a multiverse
Quantum creation and string theory give the context for the multiverse ensemble
But these theories are not yet well-tested and other universes are unobservable
And how to assign likelihood or probability on an infinite set of hypothetical universes?
Scientific Method?

111. Sentience and mortality define the human condition
The physical parameters of nature and the universe are tuned to values that allow carbon-based life.
The big bang allows for other universes and other realities but most of these might be devoid of life.
The universe is “built for life” in a profound way, but this begs the question of the definition again.
Is it self-selection, coincidence, or evidence of design?
We share a planet with other sentient life forms, and it’s very likely there is sentience elsewhere.
Our power carries moral responsibility and obligation.