Modern ideas

A Brief History of Beginnings

Non mythological beginnings, that is Georges Lemaître and his primordial atom

Vatican Astronomer Alexander Friedman: Big Bang

Russian Mathematician He didn’t name the beginning ‘The Big Bang’

It wasn’t remotely big and it didn’t go BANG! A pejorative term given by Sir Frederick Hoyle

Einstein wasn’t comfortable with either theory, although he did verify the correctness of Friedman’s mathematics

N.B. We will have to think in very, v-e-r-y short times scales here!

The Evidence

Hubble’s Law Edwin Hubble found

that, the more distant the galaxy, the faster it was receding from us Ho is the slope of this

line Currently is thought to

be ~ 73

Ho is in units of km/sec/Mpc Ultimately units of time Gives us the age of the

Universe! 13.75 +/- 0.12 Gyr

The Rationale:

According to the Red Shift of distant galaxies, the Universe is expanding

If the Universe is expanding, we can run the clock backwards and find the starting point (whatever that means)

Important! Wrap your minds around this: By the beginning we don’t mean that all the

matter and energy exploded into an existing space.

We mean that all matter, energy, SPACE and TIME all began at this singular point.

Definitions

Homogeneous The same everywhere

at a certain scale

Isotropic The same in every

direction

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String-Theory

Stems from the transition from continuum Physics to quantum Physics at the turn of the 20th C

Starting in the ‘80’s the notion arose that strings were a better model for the basic constituents of matter

Strings were on the Planck length scale 10-35m Since we can’t see detail at that scale,

particles would naturally be the first approximation

First applied to describe strong interaction, but the theory generated gravitons, much to everyone’s surprise

And strings demanded 10 dimensions!

Feynman diagrams too convoluted to incorporate these extra dimensions

“Branes” are introduced to explain interactions

Dimensions

M-Theory

String theory required 9+1 dimensions

However, this produced 5 equally valid variations! Unacceptable!

A lesser known theory, Supergravity, postulated 10+1 dimensions

Merging the two ideas resolved the 5 variations

However, the addition of the 11thdimension caused the strings to weave into Membranes

Insane in the

(mem)Brane

A theory of the “trigger”

Multidimensional Universe or multiverse

Gravity is the weakest force because it stretches between branes and is diluted

Intersection of branes initiates a BB

So time didn’t have to begin with the BB

Other Dimensions

Flatland, a Romance in Many Dimensions Edwin Abbott

Abbott, 1885 A square and his

wife in Flatland

An introduction to greater dimensions

Lisa Randall

Astrophysicist at Harvard

Leading ‘Brane’ proponent

Warped Passages: Unraveling the Universe's Hidden Dimensions

See also David Deutsch, Hugh Everett…

How the Universe Got Its Spots

Jenna Levin and others propose a more topological description of cosmology than String Theory

An Aside About Theories…

Theories like Newton’s Law of Gravitation and Einstein’s General Theory of Relativity are testable and have been verified many, many times

Inflation is not yet testable because the energies are too high to be currently reproduced in the laboratory

Furthermore, direct evidence supporting inflation is not visible because it happened long before the Universe was transparent

Why Bother with Inflation?

It accounts for certain observed phenomena: Flatness Horizons No monopoles

Not a “deus ex machina” The Universe is currently inflating, after

all

Stelliferous Era From about 380,000 years A.B.B (after the Big

Bang) until now Galaxies at about 1 billion A.B.B

Average temp = 3K The era of stars, galaxies, and us

What we’ve talked about most of the semester! Top down vs. bottom up

Did massive clouds of gas form first, generating the stars (top down) or did stars form first, collecting into galaxies (bottom up)?

Probably a combination Where gas was dense enough, stars formed first Where gas was rarefied, dark galaxies formed, later

yielding stars Era will continue until the year 100 trillion A.B.BYoungest object ever imaged @

800MYr A.B.B

The First Stars

The Universe at 2 Gyr Old

Hubble Ultra Deep Field

1 million second exposure

Red shifts allow for dating and therefore 3D imaging

Looking back to 700 million years A.B.B.

The last image shows a red galaxy, the earliest object ever imaged

Then, 40 Years Ago

Current Mix of Cosmological Stuff

Vacuum and/or Dark Energy

Very low energy density If the whole Earth volume were V.E. it would be about 1

day’s worth of electricity for 1 person The Quintessence (f) is B-A-C-K!

If true, then constants evolve

And here we are today…

What will happen in the distant future?

Fate

Entropy vs Gravity (curvature)

Entropy: a thermodynamic law dictating the inevitable march to disorder Simple disorder, like breaking glass Thermodynamics disorder:

concentrations of energy, as in a star The ‘arrow’ of time

Gravity (curvature) pulls together (order), entropy corrupts (disorder) over time

Expansion

The Universe continues to expand

Expansion occurs partially due to L, the cosmological constant

Where matter is closely spaced, gravity (curvature) overwhelms L

Elsewhere L wins And ultimately L will

win!

The Future:

The most likely* outcome will be the open Universe AKA The Big R.I.P.

The actual density of the Universe is less than the critical density

The Universe will expand forever Three Foreseeable Epochs (after the

Stelliferous Era): The Time of Degeneracy The Time of Black Holes The Time of Photons

But first… A way to get a handle on these massive time

scales Remember from our first lectures, the idea of

powers of 10? 101 = 10 102 = 100 103 = 1000, etc

Let’s define a cosmic decade, 10t years 101 years is the first cosmic decade, 102 is the second,

and so on The decade is ‘t’ Like stairs where every next step is 10X the height of

the last We are in the 10th cosmic decade The Stelliferous Era will last to the 14th cosmic

decade

The Time of Degeneracy

Not about deplorable behavior: how matter behaves

From cosmic decade 14 to 37 How do we know?

From the mean half-life of a proton, 1037 years Once in a while, two White Dwarfs may

collide and produce a supernova If not, all WDs will shine away all their

energy The End of Structure

The Time of Black Holes

Cosmic Decade 37 to 100 How do we know?

Steven Hawking determine the rate of black hole evaporation, now know as Hawking radiation

Particle pair production near the event horizon

Due to the stretching of space-time One particle falls in, the other escapes Radiation follows blackbody curve

‘Cooling’ time can be calculated

The Time of Photons

Cosmic Decade 100 until ??? Very long wavelength photons Cold, dark Entropy wins Or does it?

Very difficult to make predictions 10100 years in the future

Could be that new complexity begins From other ‘branes’ Via processes we can’t imagine

THANK YOU FOR YOUR INDULGENCE!

But this will all happen after the final exam