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

Science starts with curiosity ...something that is born in all of us

The starting point is to find patterns in the natural world

Seeing the Universe

Visible light is a half-tone range where EM spectrum is full piano

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1011

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

A Factor of Ten Billion

The second factor is efficiency of detecting photons

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.

For a gain of nearly 100% efficiency over 1% or so, or a factor of 100

WHAT IS THE LAST FACTOR OF 1000?

The Copernican Revolution

The history of astronomy displaces us from cosmic importance

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

DEDUCTIONDeduction 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

DEDUCTIONInduction 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

Science Limitations

Uncertainty, imprecision, and error arise three different ways:

CONCEPTUAL

MACROSCOPIC

MICROSCOPIC

Making a false premise, confusing correlation with causation, inferring a pattern where none is present

There is no such thing as perfect data. Every data set is limited and every instrument has limitations

Heisenberg’s uncertainty principle sets a fundamental limit to precision for measurement of particle position and velocity, or energy and time

Evidence is:

• based on data

• reproducible

• quantitative

• not subjective

• never perfect

Science is Evidence

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!!!

• 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!

Good Science

: a model which survives repeated testingTheory

For 99.999999999999999999999999999% of the universe, including all stars and all galaxies, the evidence is indirect.

Distance Units

1 pc

1 Mpc

10 Gpc

Typical distance between stars is 1 pc = 3.36 light years = 6 trilllion km, or 6,000,000,000,000 km.

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.

Us

Milky Way

Earth

THE UNIVERSE AND US

Solar System

Universe Multiverse?

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

• 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

And at this scale, light is reduced to very slow walking speed. There’s no way information in the universe can travel any faster

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

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

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

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.

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

Nearby “Now”

“Long Ago” Galaxies

LOOKBACK TIME

“Recent” Stars

“Ancient” Universe

Scattered in a universe 46 billion light years across

Galaxies

The Milky Way is typical with 400 billion stars

Stars

Almost all the simple elements hydrogen and helium

Atoms

1080

A hundred million photons for every particle

Photons

1088

Mediocrity

We therefore live on an:

• Average planet around

• An average star in an

• Average galaxy in a• Very large universe

Copernicus

Science is Seeing

A Timeline

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!

No Arrow of Time

Arrow of Time

Black Holes

TIME SENSE

Single Atoms

Sentient Life

Lots of Atoms

Speed of Light

Size

Time

The Universe

The early universe expanded much faster than the speed of light, so there are objects and large regions of space we have never seen.

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.

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.

Hubble Expansion

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

• 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.

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

Photons in this 2D space have their wavelengths stretched or redshifted by the expansion as they travel

Nature of the Expansion

Galaxies are held together by gravity and do not expand, so imagine coins glued to the balloon

Dark matter binds galaxies and dark energy drives cosmic acceleration.

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.

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

Unity

Science is Seeing

Ouroboros

A sand grain of diameter 0.5mm weighs about 3 grams. The sand is SiO2, molecules 60 times hydrogen mass.

1019 atoms

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.

1028 atoms

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.

One solar mass is 2 x 1030 kg. Which is an enormous factor larger than a hydrogen atom 2 x 10-27 kg. Earth is 330,000 times less massive.

1057 atoms

The typical galaxy contains 1012 stars

The whole universe contains 1011 galaxies

1069 atoms 1080 atoms

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

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.

Why are astronomer so confidentthat dark matter really exists?

Because the law of gravity haspassed so many tests, and if weput dark matter into computersimulations, we evolve structurethat looks just like the universe.

So far, we can only rule items out:

Stars: (normal matter) census of stars does not allow it

MACHOs: (sub-stars & planets) gravitational lensing rules it out

Black holes: (dark, collapsed stars) no sign of preceding supernovae

Dust: (dust up to rocks) re-radiation in infrared not seen

Which leaves: weakly interacting particles, supersymmetric extension to standard model

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.

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

Objects

Atoms

Universe

TOP DOWN

Dark Matter

Molecules

String Theory

String theory postulates dynamic 1-dimensional entities that are only noticeable on scales of 10-43 meters, 33 orders of magnitude smaller than atoms!

In string theory, the smoothness and the emptiness of space are illusions. If we could imagine ourselves at the incredibly tiny Planck scale, 10-43 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...

Atoms

Strings

BOTTOM UP

Bosons

Quarks

Leptons

Electrons

Four Forces

Strength: 10-38 10-19 0.0073 1

Range: Long Subatomic Long Subatomic

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”

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

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)

Light is an electromagnetic

wave

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.

Light is a Particle

If you pass white light through a prism, it separates into its component colors

ROY G B I V

spectrum

long wavelengths

short wavelengths

• Emission• Absorption• Transmission• Reflection or Scattering

Terminology: • Transparent: transmits light• Opaque: blocks (absorbs) light

Everything we know about the universe is a result of these effects

Light Interacts with Matter

• Electrons in every atom have distinct energy levels

• Each chemical element, ion or molecule, has a unique set of energy levels

Atomic Energy Levels

Distinct energy levels lead to distinct emission or absorption lines

Hydrogen Energy Levels

Emission: atom loses energy

Absorption: atom gains energy

• 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.

Chemical Fingerprints

Continuous Spectrum

Hot/Dense Energy Source prism

Emission Line Spectrum

prismHot low density cloud of Gas

Absorption Line SpectrumCooler low density cloud of Gas

Hot/Dense Energy Source prism

Types of Spectra

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

COOLER HOTTER

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

E = mc2

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

small numberbig number huge number

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

What is Dark

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

Re

dsh

ift c

z (k

m/s

)

Riess et al. (1998)Perlmutter et al. (1999)

Constant or faster in past (expected)

Slower in past (big surprise!)

Riess, Press, & Kirshner (1996)

30,000

300,000

3,000100 1,000 10,000

Distance (Mpc)

Farther in the past

Expansion History of the Universe

Einstein’s Theory: General

Relativity

Riess et al. 1998Perlmutter et al. 1999

Accelerating

Decelerating

No Big

Bang

0

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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

Riess et al. 2004Tonry et al. 20038 HST SN Ia z > 1

Dark energy is much moremysterious than even darkmatter. It’s existence restson the unexpectedly faintdistant supernovae, and afew less direct arguments.The direct detection of darkenergy is very challenging.

Physics provides no assistance. The vacuum of space could have energyin quantum theory, but it would be 1080 times larger than is observed!

Dark energy is a repulsive force that counter gravity. It does not changeits strength with time (Einstein’s gravitational constant “blunder”)

The density of dark energy and dark matter are roughly equal, this is theonly time in the history of the universe that is true: is this a coincidence?

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

Hierarchies in Astronomy

Mergers of black holes… …and galaxies

TIME

A hierarchy of self-reproducing universes in the big bang

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

Matter is subject to gravity, which gives structure on many scales

Radiation does not interact with itself and has no form or structure

Superforce

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

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

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

Cosmological

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

Quantum fluctuations are a mechanism for multiple realizations of the universe

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

More than just this… 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

String Theory Landscape String Theory Landscape

Perhaps 10 different vacua Perhaps 10 different vacua

500500

de Sitter expansion in these vacua create quantum fluctuations and provide the initial conditions for inflation. String theory provides context for the “multiverse”

Knowing1 Space

2

Time3

Matter

4

Energy

5Structure

6

Life 7

Meaning 8

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?

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?

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.

Anthropic Principle

• 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.

Conditions for Life

• Gravitational 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

Fundamental Forces

• 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.

Coincidences

• Gravitational 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

Fine-Tuning of Forces

0 X

• 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

Cosmological Fine-Tuning

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….

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

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.

Multiverse Redux

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.

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”

The odds of double six are always 1 in 36, so the supposition above doesn’t explain it

A double six will occur eventually in a long sequence of throws, sequential or parallel

This is the “inverse gamblers” fallacy

Applying Logic

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?

Quantum creation and string theory give the context for the multiverse ensemble

Fine-tuning might be due to happenstance, providence, or self-selection in a multiverse

And how to assign likelihood or probability on an infinite set of hypothetical universes?

But these theories are not yet well-tested and other universes are unobservable

Epistemology

• 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.

Sentience and

mortality define the

human condition

Sentience and

mortality define the

human condition