NewsNews

Why 2.726 K?

Why isotropic?

Large Hadron Collider27 km long loop at a depth of 50-150 mSmashes 7 Tev protons together, moving at99.999999% the speed of light! First collisions scheduled for August 2008

Fundamental Forces & ParticlesFundamental Forces & Particles

Particles are classified in terms of:Mass

ChargeSpin

Bosons have integral spin, and are force carrier particles

Fermions have odd 1/2 integral spin

Proton

Neutron

Unified Field TheoryUnified Field Theory

1970s: Electromagnetic & Weak Forces are 2 aspects of the same force, now called the electroweak force.

Present: Are all forces different manifestations of the same “unified” force? String theory: perhaps particles & forces are vibrations of “string- like” structures in 10 or more dimensions.

QuestionsQuestions

Why 2.726 K?

Why isotropic?

Is there a Higgs field which endows particles with mass?

If so the LHC will detect a Higgs boson.

Is there a theory that unifies the strong, electro-weak, and gravity? This may be a string theory, where particles arise as excitations of a string. In string theory the universe has more than 4 dimensions - maybe 10 or 26. But the other dimensions are small or thin.

The LHC will produce microscopic black holes!

Perhaps it will detect extra-dimensions

QuestionsQuestions

Why 2.726 K?

Why isotropic?

Is there a Higgs field which endows particles with mass?

If so the LHC will detect a Higgs boson.

Is there a theory that unifies the strong, electro-weak, and gravity? This may be a string theory, where particles arise as excitations of a string. In string theory the universe has more than 4 dimensions - maybe 10 or 26. But the other dimensions are small or thin.

The LHC will produce microscopic black holes!

Perhaps it will detect extra-dimensions Lisa Randall

The history of the Galaxy got a little muddled, for a number of The history of the Galaxy got a little muddled, for a number of reasons: partly because those who are trying to keep track of it reasons: partly because those who are trying to keep track of it have got a little muddled, but also because some very muddling have got a little muddled, but also because some very muddling things have been happening anyway. things have been happening anyway.

From “Mostly Harmless”, by Douglas AdamsFrom “Mostly Harmless”, by Douglas Adams

There is a theory which states that if ever anybody discovers There is a theory which states that if ever anybody discovers exactly what the Universe is for and why it is here, it will exactly what the Universe is for and why it is here, it will instantly disappear and be replaced by something even more instantly disappear and be replaced by something even more bizarre and inexplicable. There is another theory which states that bizarre and inexplicable. There is another theory which states that this has already happened. this has already happened.

Douglas AdamsDouglas Adams

X-ray image of Cygnus X-1 from NASA’s Marshall Flight Center.

COSMOLOGY

The Large-Scale Structure of The Large-Scale Structure of the Universe is Dominated by the Universe is Dominated by

GalaxiesGalaxiesA Spiral Galaxy

An Elliptical Galaxy

The Milky WayThe Milky Way

The Milky Way is a spiral The Milky Way is a spiral galaxy and appears as a bright galaxy and appears as a bright band in the night sky.band in the night sky.

It contains ~100 billion (10It contains ~100 billion (101111) ) stars.stars.

There are ~100 billion galaxies There are ~100 billion galaxies in the universe.in the universe.

Image of galaxy NGC 4256 with a white dwarf supernova

Olbers’s Paradox: Olbers’s Paradox: Why is the sky dark at Why is the sky dark at

night?night? If the universe were infinite and the If the universe were infinite and the

density of galaxies was the same density of galaxies was the same everywhere in the universe, then everywhere in the universe, then there should be a star in every single there should be a star in every single direction: the sky should be bright at direction: the sky should be bright at night, but it is not.night, but it is not.

ResolutionResolution

Distant stars are dim, so we receive little Distant stars are dim, so we receive little light from them.light from them. Wrong.Wrong. Though we receive less light from Though we receive less light from

distant stars there are also more distant stars distant stars there are also more distant stars and this makes up for the dimming with and this makes up for the dimming with distance.distance.

There’s invisible dust between us and the There’s invisible dust between us and the distant starsdistant stars Wrong.Wrong. The dust would eventually heat up The dust would eventually heat up

and emit its own radiation. We don’t see this.and emit its own radiation. We don’t see this.

Resolution: Resolution: The universe is not The universe is not

infinite!infinite!

The universe has a finite age and size.The universe has a finite age and size. Right.Right. These two concepts are closely related. These two concepts are closely related.

When we look to great distances in the When we look to great distances in the universe we are looking far back in time. If we universe we are looking far back in time. If we look to distances so great that we are seeing look to distances so great that we are seeing times before the formation of stars, then the times before the formation of stars, then the sky in that direction is dark.sky in that direction is dark.

The force of gravity is The force of gravity is always attractive. Why always attractive. Why

then doesn’t the universe then doesn’t the universe collapse under it’s own collapse under it’s own

gravitational attraction?gravitational attraction?

Is the Universe Stable?Is the Universe Stable? The force of gravity is always attractive. The force of gravity is always attractive.

Why then doesn’t the universe collapse Why then doesn’t the universe collapse under it’s own gravitational attraction?under it’s own gravitational attraction?

Newton said it was an act of God (Give Newton said it was an act of God (Give him credit though, no one else realized him credit though, no one else realized that there was a problem).that there was a problem).

Einstein realized the same problem Einstein realized the same problem occurred with his theory of gravity and, in occurred with his theory of gravity and, in what he called the biggest blunder of his what he called the biggest blunder of his life, fudged the equations so that the life, fudged the equations so that the universe would be stable.universe would be stable.

AnswerAnswer

Despite these deep-seated prejudices Despite these deep-seated prejudices from mankind’s two greatest from mankind’s two greatest luminaries, the answer is simple: the luminaries, the answer is simple: the universe is not stable, it is expanding.universe is not stable, it is expanding.

Doppler ShiftsDoppler ShiftsA stationary (with respect to an observer) light source emits radiation with a wavelength (the green wave). If that same source is moving towards the observer, the waves get compressed and the wavelength is less than (the blue wave). If the source is moving away from the observer, the waves are stretched out and the wavelength is greater than (the red wave).

Light from approaching objects is called blue shifted and light from receding objects is called red shifted, because blue and are on the short-wavelength and long-wavelength ends of the visible spectrum. The light is not necessarily blue or red.

We can identify blue or red shifts by examining the characteristic spectral lines of the elements. In the spectrum above the entire pattern of spectral lines is shifted to either the blue or red. By identifying the spectral lines*, we know what the un-shifted wavelengths should be.

* These absorptions are formed from hydrogen transitions out of the 1st excited state.

Hubble, Hubble, Galaxies and Galaxies and Red ShiftsRed Shifts

Images of galaxies & their spectra. The distance of the galaxies from Earth in millions of light years (Mly) is listed under the images and the velocity deduced from the Doppler shift appears under the spectra. The bright bands above and below the spectra are used for calibration. The two dark bands in central stripe are used to measure the Doppler shift, the size of which is indicated by the red arrow.

The more distant galaxies show larger Doppler shifts.

63 Mly

990 Mly

1440 Mly

2740 Mly

3960 Mly

In 1925, Hubble accumulated radial velocities for 40 galaxies.

Wait: how did he measure galactic Wait: how did he measure galactic distancesdistances

Need bright objects of known luminosity.

White dwarf supernova emit 10 billion times the light of the Sun

Relationship Between Distance & Relationship Between Distance & VelocityVelocity

Mpc stands for Mega Parsec. 1 Mpc = 3.3 million light years. 1 ly = 9.46x1015 m

The slope of the line is called Hubble’s Constant: H = V/D ~ 70 km/s/Mpc

Hubble’s Law Suggests that Hubble’s Law Suggests that Galaxies were once much Galaxies were once much

closer togethercloser togetherImagine that all the galaxies were once much closer together and had a spread of velocities – some were moving fast and some slow. After a period of time (billions of years) the fast moving galaxies would be very far away, but the slow moving galaxies not so far away. The faster a galaxy was moving, the further away it would be. This is just what Hubble measured. Thus, it seems that galaxies were once much closer together.

Notice that, no matter where you are, everything seems to be moving away.

Balloons and Raisin Balloons and Raisin BreadBread

As the bread rises the distance between raisins increases in a more or less uniform manner. It would look the same no matter what raisin you were sitting on. Think of the raisins as galaxies.

A better analogy is the expanding balloon. As the balloon expands the dots on the balloon get further apart; however, there is no center to the surface of the balloon and the expansion would look the same no matter where you were.

General Relativity & the Big General Relativity & the Big BangBang

The most beautiful thing that we can experience is the mysterious. It is the source of all true art and science.

- Albert Einstein

Space is curvedSpace is curved

Forget forces. Planets travel in orbits, following the curvature of space.

Ubiquitous Radio NoiseUbiquitous Radio Noise

In 1964, Arno Penzias and Robert Wilson adapted a radio dish previously used for communication satellites, to observe radio emissions from a distant supernova. They hoped to map radio emissions of the Milky Way.

Chance favors only the mind that is prepared - Louis Pasteur

Scientific MethodScientific Method

They were startled to find that no matter where they pointed the antenna, they measured the same low-level radio signal. So they tested the old horn to make sure it was not defective. They also cleaned the antenna of a “thin white dielectric film” left by pigeons.

They concluded that the signals were real and a property of the universe.

Chance favors only the mind that is prepared - Louis Pasteur

Cosmic Background Cosmic Background RadiationRadiation

Unknown to Penzias and Wilson, a Russian Astrophysicist, George Gamov, had predicted the existence of these radio signals as a consequence of something we now call the Big Bang.

COBE MeasurementsCOBE Measurements

Data & prediction of emission from a 2.726 K body.

Why microwave radiation? Why microwave radiation?

Why 2.726 K?

Why isotropic?

Explanation 1Explanation 1

Gas gets hot when it is compressed and cool when it expands. The same is true for the Universe.

The early Universe was a mixture of matter and radiation. Shortly after the Big Bang, the universe was tightly compressed, and thus extremely hot. Its radiation was typical of that for warm bodies (i.e. it obeyed Wein’s law). As the universe expanded both the matter and radiation cooled. In fact, the radiation cooled from unimaginably high temperatures to 2.726 K, the temperature of the universe today.

Explanation 2Explanation 2

We get the same answer by considering that when we look very far away we are seeing diffuse radiation from the hot big bang. However, this radiation comes from great distances (10-20 billion light years) and has been Doppler shifted to very long wavelengths. In fact, it has been Doppler shifted all the way from gamma rays to radio waves; the radio waves discovered by Penzias and Wilson.

Evidence for the Big BangEvidence for the Big Bang

The universe is expanding at a rapid rate and The universe is expanding at a rapid rate and seems to have been doing so since its creation.seems to have been doing so since its creation.

The Cosmic Background Radiation can be The Cosmic Background Radiation can be explained as the afterglow of the Big Bang.explained as the afterglow of the Big Bang.

The cosmic abundances of hydrogen, The cosmic abundances of hydrogen, deuterium, and helium are consistent with deuterium, and helium are consistent with expectations based on synthesis by nuclear expectations based on synthesis by nuclear reactions in the Big Bang.reactions in the Big Bang.

How old is the Universe?How old is the Universe?

Consider Hubble’s Consider Hubble’s FindingFinding

The slope of the line is called Hubble’s Constant: H = V/D ~ 70 km/s/Mpc The Universe appears to be expanding at a constant rate: V = H x D

The beginning of the Universe

The Age of the UniverseThe Age of the UniverseIf the universe expands at a constant rate:

V = H x D

From measurements of D & V: H ~70 km / sec / Mpc

Over the age of the universe, T, galaxies have traveled a distance D with at a velocity V:

D = V x TOr:

T = D / V

Therefore:

T = D / (H x D) = 1 / HOr:

T = 14 x 109 yrs for H=70 km/s Mpc

1 pc = 3.26 lyr = 3.1x1013 km1 Mpc = 3.1x1019 km

H = 70 km/s / 3.1x1019 kmH = 2.26 x 10-18 sec-1

H = 7.13 x 10-11 yr-1

14 Billion years old !

The Big Bang solves the problem of the stability of the universe: the force of gravity does, in fact, pull the universe together; however, it is not collapsing because it is still flying apart at high speeds.

This raises the question, will the universe continue to fly apart or is gravity strong enough to stop the expansion and pull all the pieces back together in a Big Crunch?

Put another way, is the escape velocity of the universe greater or lesser than the rate at which it is expanding?

The collision of 2 galaxies.

Fate of the UniverseFate of the Universe1) The amount of luminous matter in the universe appears to be

too small to stop its expansion. This might imply that the universe would continue expanding forever, except that there seems to be a “dark matter” in the Universe. If there is enough dark matter, the universe could be “closed,” i.e. it may someday stop expanding and start contracting.

2) Careful studies of the velocities of galaxies should be able to reveal if the rate of expansion is slowing down. However, the latest studies found a big surprise: the rate of expansion is increasing! If true, the universe will probably expand forever, but the results are only a few years old and deserve more careful scrutiny before firm conclusions are adopted.

Rotational speeds of stars in our GalaxyRotational speeds of stars in our Galaxy

Evidence for Dark MatterEvidence for Dark Matter

Stars far from the galactic center obey Kepler’s 3rd law, but they indicate the presence of far more mass in the galaxy than expected based on visible light, hence the term “dark matter.”

Is the Expansion Is the Expansion Speeding Up?Speeding Up?

V = H * DH = Hubble “constant”, V= velocity, D=distance

ConvertiConverting one ng one particle particle

into into anotheranother

How was nature How was nature different in the different in the

past?past?

SummarySummary

The solution to Olbers’s paradox is that the night sky is dark The solution to Olbers’s paradox is that the night sky is dark because the universe is a finite age.because the universe is a finite age.

The universe is expanding from a primordial creation event The universe is expanding from a primordial creation event 10-20 billion years ago. 10-20 billion years ago.

The universe is filled with thermal radiation at a temperature The universe is filled with thermal radiation at a temperature of 3 K that is the modern residue of the primordial fireball.of 3 K that is the modern residue of the primordial fireball.

There is far more mass in the universe than can be seen. The There is far more mass in the universe than can be seen. The nature of this “dark matter” is unknown.nature of this “dark matter” is unknown.

We’re not sure if the universe will keep expanding forever or We’re not sure if the universe will keep expanding forever or if gravity will cause it to contract to a Big Crunch. The latest if gravity will cause it to contract to a Big Crunch. The latest evidence favors expansion forever.evidence favors expansion forever.