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At the End of the 19At the End of the 19thth Century, a certain Century, a certain scientific smugness was in the airscientific smugness was in the air

Munich physics professor Philipp von Jolly Munich physics professor Philipp von Jolly advised his student Max Planck against advised his student Max Planck against going into physics:going into physics: “…“…in this field, almost everything is already in this field, almost everything is already

discovered, and all that remains is to fill a few discovered, and all that remains is to fill a few holes.”holes.”

Lord Kelvin,1900:Lord Kelvin,1900: ““There is nothing new to be discovered in There is nothing new to be discovered in

physics now. All that remains is more and physics now. All that remains is more and more precise measurement.”more precise measurement.”

Albert Michelson, America’s Albert Michelson, America’s first Nobel Prize winner:first Nobel Prize winner: ““The more important The more important

fundamental laws and facts fundamental laws and facts of physical science have all of physical science have all been discovered, and these been discovered, and these are now so firmly established are now so firmly established that the possibility of their that the possibility of their ever being supplanted in ever being supplanted in consequence of new consequence of new discoveries is exceedingly discoveries is exceedingly remote . . . Our future remote . . . Our future discoveries must be looked discoveries must be looked for in the sixth place of for in the sixth place of decimals.”decimals.”

In 1899, the head of the United States In 1899, the head of the United States Patent Office, Charles Duell, allegedly Patent Office, Charles Duell, allegedly argued to close the Patent Office because argued to close the Patent Office because "everything that could have been invented, "everything that could have been invented, has been invented.“has been invented.“ This could be apocryphal, but it illustrates the This could be apocryphal, but it illustrates the

moodmood A recurrent themeA recurrent theme

Resurfaced at the end of the 20Resurfaced at the end of the 20 thth century century Hubris, hubris, hubrisHubris, hubris, hubris

"Flight by machines heavier than air is impractical and insignificant, if not utterly impossible." -- Simon Newcomb, Director, U.S. Naval Observatory, 1902

CloudsClouds

There were a few unresolved issues, howeverThere were a few unresolved issues, however 1900: Lord Kelvin gave a lecture to the Royal 1900: Lord Kelvin gave a lecture to the Royal

Institution of Great Britain titled “Nineteenth-Institution of Great Britain titled “Nineteenth-Century Clouds over the Dynamical Theory of Century Clouds over the Dynamical Theory of Heat and Light”Heat and Light”

He was talking about the null result of the He was talking about the null result of the Michelson-Morley experiment and the problems Michelson-Morley experiment and the problems of blackbody radiationof blackbody radiation Where was the ether?Where was the ether? Why are there discrete spectral lines?Why are there discrete spectral lines? Also, what the heck is Brownian Motion?Also, what the heck is Brownian Motion?

The Luminiferous AetherThe Luminiferous Aether Proposed by Aristotle Proposed by Aristotle

and again almost 2000 and again almost 2000 years later by years later by DescartesDescartes

1881: Albert 1881: Albert Michaelson, along with Michaelson, along with Edward Morley, set out Edward Morley, set out to find itto find it

The idea is this: if light The idea is this: if light is a wave, then it must is a wave, then it must travel through a travel through a medium, like water medium, like water waveswaves

Therefore waves will Therefore waves will be different going with be different going with the “current” than the “current” than across itacross it

It’s still here!

Null ResultNull Result

Michaelson and Morley found no evidence Michaelson and Morley found no evidence of any aetherof any aether

Then how could light be a wave?Then how could light be a wave? Recap:Recap:

• 1670: Huygens; light is a wave1670: Huygens; light is a wave• 1699: Newton; light is a stream of particles1699: Newton; light is a stream of particles• 1801: Thomas Young; light is a wave1801: Thomas Young; light is a wave

So now what?So now what?

And then there’s Discrete SpectraAnd then there’s Discrete Spectra

If light comes from If light comes from accelerated electrons accelerated electrons and light carries away and light carries away energy from the energy from the electrons, why electrons, why doesn’t all matter doesn’t all matter collapse as energy is collapse as energy is lost?lost?

Resolutions circa 1910Resolutions circa 1910 Energy isn’t continuous but comes in discrete Energy isn’t continuous but comes in discrete

packets called packets called quantaquanta The death of The death of continuum continuum physics and the birth of physics and the birth of

quantumquantum physics physics Max Planck (a converted continuist); his “kludge” from Max Planck (a converted continuist); his “kludge” from

the Spectra PPT was a major instigatorthe Spectra PPT was a major instigator Light is neither a particle nor a wave but has the Light is neither a particle nor a wave but has the

qualities of bothqualities of both And therefore requires no aether to propagateAnd therefore requires no aether to propagate Demonstrated by Einstein and later by ComptonDemonstrated by Einstein and later by Compton

Both denied ‘common sense’Both denied ‘common sense’ Both required new ways of thinkingBoth required new ways of thinking

Einstein vs NewtonEinstein vs Newton

Newton’s UniverseNewton’s Universe

Objects attract each other Objects attract each other with a force proportional with a force proportional to their masses and to their masses and inversely proportional to inversely proportional to the square of the distance the square of the distance between thembetween them

There is an absolute state There is an absolute state of restof rest

““Law” for almost 200 Law” for almost 200 years, but with a cause years, but with a cause for gravityfor gravity

Albert Einstein (1879-1955)Albert Einstein (1879-1955)

Life/CareerLife/Career AchievementsAchievements Important Important

PublicationsPublications 1905 papers1905 papers 1915 papers1915 papers 1921 Nobel Prize1921 Nobel Prize 1935 EPR1935 EPR

Einstein’s UniverseEinstein’s Universe General Theory of General Theory of

Relativity, 1915Relativity, 1915 Mass curves spaceMass curves space *There is not absolute *There is not absolute

state of reststate of rest i.e. there is no perfect i.e. there is no perfect

place from which to view place from which to view the Universethe Universe

*All motion is relative, *All motion is relative, but the speed of light is but the speed of light is fixed for everyonefixed for everyone

BTW, Einstein explained BTW, Einstein explained Brownian Motion in a 1905 Brownian Motion in a 1905 paperpaper

*Special Theory of Relativity, 1905

William Wallace CampbellWilliam Wallace Campbell

Director of Lick Observatory 1900-1930Director of Lick Observatory 1900-1930 Pioneer of the astronomical Pioneer of the astronomical

spectroscopy; catalogued radial speeds spectroscopy; catalogued radial speeds of stars.of stars.

Tried to confirm Einstein’s theory with Tried to confirm Einstein’s theory with eclipse viewed in Kieveclipse viewed in Kiev

Clouds!Clouds! Tries again in 1918 in WATries again in 1918 in WA

Bad gear, no confirmationBad gear, no confirmation

Goes to London to report negative Goes to London to report negative resultresult

Sir Arthur EddingtonSir Arthur Eddington An English pacifist during WWIAn English pacifist during WWI

Felt kinship with German Felt kinship with German pacifist Einsteinpacifist Einstein

Wanted to show science was Wanted to show science was above politicsabove politics

Also, first to propose a fusion-like Also, first to propose a fusion-like process for the Sun’s energyprocess for the Sun’s energy

Journeyed to island of Principe Journeyed to island of Principe off Africa for the best view of off Africa for the best view of 1919 eclipse1919 eclipse

Results nebulous, but Results nebulous, but Eddington wires London with Eddington wires London with confirmationconfirmation

ConfirmedConfirmed

1922, WWC goes to Australia for eclipse 1922, WWC goes to Australia for eclipse viewing, confirms GT with 92 starsviewing, confirms GT with 92 stars

Modern TestingModern Testing

Cassini Spacecraft Cassini Spacecraft sends back radio sends back radio signals from Saturnsignals from Saturn

The curvature of The curvature of spacetime near the spacetime near the Sun is testedSun is tested

Einstein is correct!Einstein is correct!

Gravitational LensingGravitational Lensing

MicrolensingMicrolensing

Used for:Used for: Additional Additional

magnification of magnification of distant objectsdistant objects

Evidence of dark, Evidence of dark, intervening objectsintervening objects

Space-time Space-time curvature datacurvature data

In other words:In other words:

““Mass tells space how to bend and space Mass tells space how to bend and space tells matter how to move” tells matter how to move”

GR predicts many things that were GR predicts many things that were heretical at the timeheretical at the time Stars, under certain conditions, can shrink to Stars, under certain conditions, can shrink to

nothing with infinite densitynothing with infinite density It is unlikely that the Universe is staticIt is unlikely that the Universe is static

1914-1918: WWI1914-1918: WWI Karl Schwarzschild (1873-Karl Schwarzschild (1873-

1916)1916) Child prodigyChild prodigy

Published a paper on orbits at Published a paper on orbits at age 16age 16

His son Martin also became a His son Martin also became a famous Astrophysicistfamous Astrophysicist

Member of Prussian Academy Member of Prussian Academy of Sciences up until the war of Sciences up until the war

Joined the German army at Joined the German army at age 41age 41

Submitted papers while serving Submitted papers while serving in Russiain Russia

1915: found a solution to GR that allowed stars to 1915: found a solution to GR that allowed stars to collapse into zero volume and infinite densitycollapse into zero volume and infinite density

Later named “Black Holes” by John WheelerLater named “Black Holes” by John Wheeler KS was not the first mathematician to conceive of such thingsKS was not the first mathematician to conceive of such things

Einstein verified the solution but didn’t like the Einstein verified the solution but didn’t like the consequencesconsequences

Massive StarsMassive Stars If a giant star at the end If a giant star at the end

of its giant phase has > of its giant phase has > 1.4 M1.4 Msunsun, it will collapse , it will collapse suddenly and then suddenly and then violently explode as its violently explode as its materials rebound off a materials rebound off a superdense coresuperdense core

There is about 1 SN There is about 1 SN every century in our every century in our galaxy, 1 every second in galaxy, 1 every second in the Universethe Universe

In a few weeks they emit In a few weeks they emit more energy than the more energy than the Sun does in a centurySun does in a century

However, if the giant However, if the giant star has > 3 Mstar has > 3 Msunsun at at the end of its giant the end of its giant phase, the explosion phase, the explosion stalls due to the stalls due to the overwhelming gravity, overwhelming gravity, and the star continues and the star continues to collapse to an to collapse to an infinitely tiny point, or infinitely tiny point, or singularitysingularity

Space is so tightly Space is so tightly curved around it that curved around it that nothing can escapenothing can escape

To sum up GR (a little):To sum up GR (a little):

But he realized that his equations wouldn’t But he realized that his equations wouldn’t permit this stabilitypermit this stability Remember Poisson’s equation?Remember Poisson’s equation? It says that the condition of no acceleration (e.g. no It says that the condition of no acceleration (e.g. no

gravitational force) can only exist in an empty gravitational force) can only exist in an empty UniverseUniverse

Introduced a cosmological constant, Introduced a cosmological constant, (lambda), (lambda), into GR to counteract any acceleration that into GR to counteract any acceleration that would change his static modelwould change his static model

The Steady State ModelThe Steady State Model

One assumption that underlay the One assumption that underlay the discussion of the shape of the cosmos discussion of the shape of the cosmos was that the Universe was eternal and was that the Universe was eternal and unchangingunchanging

SSM formally posed in 1948, but its SSM formally posed in 1948, but its demise was already present in GRdemise was already present in GR

The idea was hard to bury, despite being a The idea was hard to bury, despite being a source of paradoxsource of paradox

Kepler’s *Paradox Kepler’s *Paradox (AKA Olber’s Paradox)(AKA Olber’s Paradox)

If the Universe is eternal If the Universe is eternal and infinite, why is the and infinite, why is the sky dark at night?sky dark at night?

In Kepler’s words: “If [this] In Kepler’s words: “If [this] is true, and if they are is true, and if they are suns having the same suns having the same nature as our sun, why do nature as our sun, why do not these suns not these suns collectively outdistance collectively outdistance our sun in brilliance?”our sun in brilliance?”

*Ryden’s Law of Misonomy – Olber actually saw no paradox, stating that the universe soaks up a little light from every star

Not So SteadyNot So Steady

1692: Newton receives a letter from theologian 1692: Newton receives a letter from theologian Richard BentleyRichard Bentley Asks Newton how would the Universe change with Asks Newton how would the Universe change with

time if all matter was initially distributed perfectly time if all matter was initially distributed perfectly symmetricallysymmetrically

Newton replies that it would be static Newton replies that it would be static But perfect symmetry is as likely as “an infinite But perfect symmetry is as likely as “an infinite

number of needles standing on their tips on a mirror”number of needles standing on their tips on a mirror” Bentley replies that isn’t that the same likelihood Bentley replies that isn’t that the same likelihood

as an infinite number of fixed stars?as an infinite number of fixed stars?

Learning to Love Learning to Love

Einstein himself held that the Universe Einstein himself held that the Universe was static and homogeneous with was static and homogeneous with spherical geometryspherical geometry Remember, in 1915 when he produced GR, 5 Remember, in 1915 when he produced GR, 5

years before The Great Debate, the scope of years before The Great Debate, the scope of the Universe was not knownthe Universe was not known

He therefore looked at He therefore looked at onlyonly stars in the MW stars in the MW and saw that there was no obvious expansion and saw that there was no obvious expansion or contractionor contraction

*With a nod to Dr. Barbara Ryden

Alexander Friedman 1888-1925Alexander Friedman 1888-1925 Russian Russian

Mathematician and Mathematician and CosmologistCosmologist

Like Schwarzschild Like Schwarzschild found a solution to found a solution to GRGR

His 1922 solution His 1922 solution showed that GR showed that GR predicted an predicted an expanding Universeexpanding Universe

1929 Hubble data 1929 Hubble data confirmed thisconfirmed this

Edwin Hubble’s work, circa 1925Edwin Hubble’s work, circa 1925

His observations helped settle the Great DebateHis observations helped settle the Great Debate But they also posed a new question:But they also posed a new question:

Why is practically everything in the Universe moving Why is practically everything in the Universe moving away from us?away from us?

Bigger and BiggerBigger and Bigger

Hubble’s data Hubble’s data suggests that the suggests that the Universe is Universe is expandingexpanding

Not only that, more Not only that, more distant objects are distant objects are moving away fastermoving away faster

Hubble determined Hubble determined these distances these distances and velocities using and velocities using red shiftred shift

BlunderBlunder With Hubble’s discovery Einstein removed With Hubble’s discovery Einstein removed and and

called the constant his “greatest blunder”called the constant his “greatest blunder” ““Much later, when I was discussing cosmological Much later, when I was discussing cosmological

problems with Einstein, he remarked that the problems with Einstein, he remarked that the introduction of the cosmological term was the biggest introduction of the cosmological term was the biggest blunder of his life”. -- blunder of his life”. -- George Gamow, My World Line, 1970George Gamow, My World Line, 1970

Ironically, he was Ironically, he was rightright: : is back in is back in modern cosmologymodern cosmology

• If only he had stuck by his guns!If only he had stuck by his guns!

Georges Lemaître 1894-1966Georges Lemaître 1894-1966

Belgian Roman Belgian Roman Catholic Priest and (!) Catholic Priest and (!) CosmologistCosmologist

1927 submitted a 1927 submitted a paper that paper that independently arrived independently arrived at Friedman’s solutionat Friedman’s solution Primordial atomPrimordial atom

Einstein read both Einstein read both and, at the time, and, at the time, dismissed themdismissed them

Expansion of the UniverseExpansion of the Universe

A tricky ideaA tricky idea What is What is notnot happening: happening:

• Objects are getting biggerObjects are getting bigger• The space in atoms is increasingThe space in atoms is increasing

Proper motion is not part of the expansionProper motion is not part of the expansion Expansion means that Expansion means that spacespace is stretching, is stretching,

like polka dots on the surface of an like polka dots on the surface of an inflating balloon with conditionsinflating balloon with conditions

Regardless of how, Hubble showed, and Regardless of how, Hubble showed, and Einstein agreed, that the Universe was Einstein agreed, that the Universe was indeed expandingindeed expanding

This implies:This implies: The Universe is not staticThe Universe is not static The Universe is not infinitely oldThe Universe is not infinitely old The Universe had a beginningThe Universe had a beginning

However, at first, Hubble’s equation was However, at first, Hubble’s equation was good but his measurements were off, good but his measurements were off, causing the Universe to be too young at 2 causing the Universe to be too young at 2 Gyr.Gyr.

And this explains it all, right? And this explains it all, right?

Called the Robertson-Walker metric (AKA FLRW)Called the Robertson-Walker metric (AKA FLRW) Shows how space and time scale with expansionShows how space and time scale with expansion For the curious:For the curious:

Distance: sDistance: s Cosmological scale factor: aCosmological scale factor: a Time: tTime: t Curvature: kCurvature: k Radial distance: rRadial distance: r Azimuth angle Azimuth angle Altitude angle: Altitude angle:

In a way, it’s like measuring distances on the surface of the EarthIn a way, it’s like measuring distances on the surface of the Earth

It’s not that It’s not that everything in everything in the Universe is the Universe is expanding in a expanding in a big box, it’s that big box, it’s that the box itself is the box itself is expandingexpanding

How it expands How it expands is the subject of is the subject of CosmologyCosmology

The so-called The so-called Big Bang is Big Bang is just a part of just a part of the subjectthe subject

(details to (details to follow later)follow later)

Still there were doubtersStill there were doubters Sir Frederick Hoyle

1915-2001 Respected

Astrophysicist Postulated stellar

nucleosynthesis

Proponent of Steady State Theory

Dismissed Friedman’s idea of a “Big Bang”

Cited 2 Gyr cosmos

SSMSSM

Hoyle and his camp agreed that the Universe Hoyle and his camp agreed that the Universe was expandingwas expanding

But to avoid a “beginning” he had the Universe But to avoid a “beginning” he had the Universe constantly creating matter between the galaxiesconstantly creating matter between the galaxies

Karl Jansky 1905-1950Karl Jansky 1905-1950 1931: discovered radio waves 1931: discovered radio waves

emanating from the Milky Wayemanating from the Milky Way A clue!A clue!

George GamowGeorge Gamow With colleagues *Ralph Alpher and

Robert Hermann pictured the early Universe as a nuclear oven in which light elements were cooked, backing up the Big Bang theory

They posed that the earliest temperatures would be staggeringly high ~ 100 billion K

During the late 1940s and early 1950s they made predictions that the cosmos would have cooled like a blackbody radiator to a temperature ranging from 5K to 50K

Evident as microwave radiation• Hoyle actually backed them up on this

while maintaining his SSM!

*GG’s grad student, the mathematician of the group

Hot objects (T > 0K) emits a spread of “heat’ Hot objects (T > 0K) emits a spread of “heat’ radiationradiation

Peak occurs ~ 1mmPeak occurs ~ 1mm

Blackbody RadiationBlackbody Radiation

CMBCMB

Cosmic Microwave BackgroundCosmic Microwave Background First observed in 1940 by Andrew McKellar First observed in 1940 by Andrew McKellar Cyanogen excitation (0 -> 1) corresponds to 2.4KCyanogen excitation (0 -> 1) corresponds to 2.4K These data were not recognized for what they were at These data were not recognized for what they were at

the time, or even in an important paper in 1950the time, or even in an important paper in 1950

HissssssssssssHissssssssssss 1965: Arno Penzias and Robert 1965: Arno Penzias and Robert

Wilson, worked for Bell Labs in NJWilson, worked for Bell Labs in NJ Used an ultra-sensitive microwave Used an ultra-sensitive microwave

receiving system to study radio receiving system to study radio emissions from the Milky Wayemissions from the Milky Way

Found an unexpected background Found an unexpected background of radio noiseof radio noise

They consulted with Princeton They consulted with Princeton physicist Robert H. Dicke who had physicist Robert H. Dicke who had predicted that if the Big Bang predicted that if the Big Bang theory was correct, a background theory was correct, a background radiation at 3-degree Kelvin would radiation at 3-degree Kelvin would exist exist

This and better Hubble This and better Hubble measurements in 1949 verified measurements in 1949 verified BBBB

Wilson explaining the noise

Cr.mpg

Another ViewAnother View Wilkinson Microwave Wilkinson Microwave

Anisotropy ProbeAnisotropy Probe Colleague of Robert DickeColleague of Robert Dicke

The red regions are where The red regions are where CMB photons, losing energy CMB photons, losing energy as they climb out of a as they climb out of a gravitational potential, are gravitational potential, are red-shifted red-shifted

And the reverse, of courseAnd the reverse, of course 1967 calculations by Sachs 1967 calculations by Sachs

and Wolfe predicted this at and Wolfe predicted this at structures ~1structures ~1oo of arc of arc

More on that in another pptMore on that in another ppt

The Future depends on The Future depends on