Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
What was before the Big Bang, and howmight we be able to tell?
Cosmology of the Very Early Universe
Robert BrandenbergerMcGill University
Physics Matters Lecture, September 7, 2017
1 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
Outline
1 What is Cosmology?
2 FrameworkSpace-TimeStandard Big Bang Cosmology
3 Inflationary Cosmology
4 String Cosmology
5 Conclusions
2 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
Plan
1 What is Cosmology?
2 FrameworkSpace-TimeStandard Big Bang Cosmology
3 Inflationary Cosmology
4 String Cosmology
5 Conclusions
3 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
Goals of Early Universe Cosmology
1. Understand origin and early evolution of the universe.
What is the “Big Bang"?Was there a “Big Bang"?What was before the “Big Bang"?
2. Explain observed large-scale structure.
4 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
Goals of Early Universe Cosmology
1. Understand origin and early evolution of the universe.
What is the “Big Bang"?Was there a “Big Bang"?What was before the “Big Bang"?
2. Explain observed large-scale structure.
4 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
Goals of Early Universe Cosmology
1. Understand origin and early evolution of the universe.
What is the “Big Bang"?Was there a “Big Bang"?What was before the “Big Bang"?
2. Explain observed large-scale structure.
4 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
Optical Telescopes: Gemini Telescope
5 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
Galaxies: Building Blocks of the Cosmology
6 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
Large-Scale Structure
From: talk by O. Lahav
7 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
Microwave Telescopes on the Earth: ACTTelescope
8 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
Microwave Telescopes on the Earth: SPTTelescope
9 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
Microwave Telescopes in Space: WMAPTelescope
10 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
Isotropic CMB Background
11 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
Anisotropies in the Cosmic MicrowaveBackground (CMB)
Credit: NASA/WMAP Science Team12 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
Quantification of the CMB data
Credit: NASA/WMAP Science Team
13 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
Goals of Early Universe Cosmology
1. Understand origin and early evolution of the universe.
What is the “Big Bang"?Was there a “Big Bang"?What was before the “Big Bang"?
2. Explain observed large-scale structure.
Patterns in the distribution of galaxies on large scales.Anisotropies in CMB maps.
3. Make predictions for future observations.
14 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
Goals of Early Universe Cosmology
1. Understand origin and early evolution of the universe.
What is the “Big Bang"?Was there a “Big Bang"?What was before the “Big Bang"?
2. Explain observed large-scale structure.
Patterns in the distribution of galaxies on large scales.Anisotropies in CMB maps.
3. Make predictions for future observations.
14 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
Plan
1 What is Cosmology?
2 FrameworkSpace-TimeStandard Big Bang Cosmology
3 Inflationary Cosmology
4 String Cosmology
5 Conclusions
15 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
Framework
The Universe is:
Space-timeMatter which lives in space-time.
To describe the Universe:
Space-time described by Einstein’s theory of GeneralRelativity.Matter as described by Physics.More specifically: matter described on large scales byclassical physics, on small scales by quantummechanics and on even smaller scales by superstringtheory ?
16 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
Framework
The Universe is:
Space-timeMatter which lives in space-time.
To describe the Universe:
Space-time described by Einstein’s theory of GeneralRelativity.Matter as described by Physics.More specifically: matter described on large scales byclassical physics, on small scales by quantummechanics and on even smaller scales by superstringtheory ?
16 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
Framework
The Universe is:
Space-timeMatter which lives in space-time.
To describe the Universe:
Space-time described by Einstein’s theory of GeneralRelativity.Matter as described by Physics.More specifically: matter described on large scales byclassical physics, on small scales by quantummechanics and on even smaller scales by superstringtheory ?
16 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
Framework
The Universe is:
Space-timeMatter which lives in space-time.
To describe the Universe:
Space-time described by Einstein’s theory of GeneralRelativity.Matter as described by Physics.More specifically: matter described on large scales byclassical physics, on small scales by quantummechanics and on even smaller scales by superstringtheory ?
16 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
Framework
The Universe is:
Space-timeMatter which lives in space-time.
To describe the Universe:
Space-time described by Einstein’s theory of GeneralRelativity.Matter as described by Physics.More specifically: matter described on large scales byclassical physics, on small scales by quantummechanics and on even smaller scales by superstringtheory ?
16 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
Framework
The Universe is:
Space-timeMatter which lives in space-time.
To describe the Universe:
Space-time described by Einstein’s theory of GeneralRelativity.Matter as described by Physics.More specifically: matter described on large scales byclassical physics, on small scales by quantummechanics and on even smaller scales by superstringtheory ?
16 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
Framework
The Universe is:
Space-timeMatter which lives in space-time.
To describe the Universe:
Space-time described by Einstein’s theory of GeneralRelativity.Matter as described by Physics.More specifically: matter described on large scales byclassical physics, on small scales by quantummechanics and on even smaller scales by superstringtheory ?
16 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
Space-Time as Described by General Relativity
Space-time dynamical (no longer absolute like inNewtonian theory)Matter curves space-time.
17 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
Space-Time as Described by General Relativity
Space-time dynamical (no longer absolute like inNewtonian theory)Matter curves space-time.
17 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
Mass curves Space-Time
18 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
Space-Time as Described by General Relativity
Space-time dynamical (no longer absolute like inNewtonian theory)Matter curves space-time: Space-time is dynamical.Note: Newton’s gravitational force is a consequence ofthe curvature of space.Einstein Equivalence Principle determines the motionof matter in curved space-time.Space with a homogeneous distribution of mattercannot be static - it must expand (or contract).
19 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
Space-Time as Described by General Relativity
Space-time dynamical (no longer absolute like inNewtonian theory)Matter curves space-time: Space-time is dynamical.Note: Newton’s gravitational force is a consequence ofthe curvature of space.Einstein Equivalence Principle determines the motionof matter in curved space-time.Space with a homogeneous distribution of mattercannot be static - it must expand (or contract).
19 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
Space-Time as Described by General Relativity
Space-time dynamical (no longer absolute like inNewtonian theory)Matter curves space-time: Space-time is dynamical.Note: Newton’s gravitational force is a consequence ofthe curvature of space.Einstein Equivalence Principle determines the motionof matter in curved space-time.Space with a homogeneous distribution of mattercannot be static - it must expand (or contract).
19 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
Space-Time as Described by General Relativity
Space-time dynamical (no longer absolute like inNewtonian theory)Matter curves space-time: Space-time is dynamical.Note: Newton’s gravitational force is a consequence ofthe curvature of space.Einstein Equivalence Principle determines the motionof matter in curved space-time.Space with a homogeneous distribution of mattercannot be static - it must expand (or contract).
19 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
The Expanding Universe
20 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
Evidence for the Expansion of Space
The Hubble diagram for type Ia supernovae.
Kirshner R P PNAS 2004;101:8-13
©2004 by National Academy of Sciences 21 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
Standard Big Bang Cosmology
Standard Big Bang Cosmology (SBB): the old paradigm ofcosmology (ca. 1960).
The SBB is based on:
Cosmological principle: universe homogeneous andisotropic on large scales.General Relativity governing dynamics of space-time.Classical matter as source in the Einstein equations.Classical matter: cold (pressure-less) matter(describing the galaxies) + radiation(describing theCMB).
22 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
Standard Big Bang Cosmology
Standard Big Bang Cosmology (SBB): the old paradigm ofcosmology (ca. 1960).
The SBB is based on:
Cosmological principle: universe homogeneous andisotropic on large scales.General Relativity governing dynamics of space-time.Classical matter as source in the Einstein equations.Classical matter: cold (pressure-less) matter(describing the galaxies) + radiation(describing theCMB).
22 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
Standard Big Bang Cosmology
Standard Big Bang Cosmology (SBB): the old paradigm ofcosmology (ca. 1960).
The SBB is based on:
Cosmological principle: universe homogeneous andisotropic on large scales.General Relativity governing dynamics of space-time.Classical matter as source in the Einstein equations.Classical matter: cold (pressure-less) matter(describing the galaxies) + radiation(describing theCMB).
22 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
Standard Big Bang Cosmology
Standard Big Bang Cosmology (SBB): the old paradigm ofcosmology (ca. 1960).
The SBB is based on:
Cosmological principle: universe homogeneous andisotropic on large scales.General Relativity governing dynamics of space-time.Classical matter as source in the Einstein equations.Classical matter: cold (pressure-less) matter(describing the galaxies) + radiation(describing theCMB).
22 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
Standard Big Bang Cosmology
Standard Big Bang Cosmology (SBB): the old paradigm ofcosmology (ca. 1960).
The SBB is based on:
Cosmological principle: universe homogeneous andisotropic on large scales.General Relativity governing dynamics of space-time.Classical matter as source in the Einstein equations.Classical matter: cold (pressure-less) matter(describing the galaxies) + radiation(describing theCMB).
22 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
Standard Big Bang Cosmology (ctd.)
The universe is expanding now.In the past it was hotter and more dense.Thus, it was expanding faster in the past.At a finite time in the past the temperature was infinite .A finite box of space had zero size at that time.This is the Big Bang!
What is the Big Bang? What was before the Big Bang?
To be taken seriously a theory must have made successfulobservational predictions.
23 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
Standard Big Bang Cosmology (ctd.)
The universe is expanding now.In the past it was hotter and more dense.Thus, it was expanding faster in the past.At a finite time in the past the temperature was infinite .A finite box of space had zero size at that time.This is the Big Bang!
What is the Big Bang? What was before the Big Bang?
To be taken seriously a theory must have made successfulobservational predictions.
23 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
Standard Big Bang Cosmology (ctd.)
The universe is expanding now.In the past it was hotter and more dense.Thus, it was expanding faster in the past.At a finite time in the past the temperature was infinite .A finite box of space had zero size at that time.This is the Big Bang!
What is the Big Bang? What was before the Big Bang?
To be taken seriously a theory must have made successfulobservational predictions.
23 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
Standard Big Bang Cosmology (ctd.)
The universe is expanding now.In the past it was hotter and more dense.Thus, it was expanding faster in the past.At a finite time in the past the temperature was infinite .A finite box of space had zero size at that time.This is the Big Bang!
What is the Big Bang? What was before the Big Bang?
To be taken seriously a theory must have made successfulobservational predictions.
23 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
Standard Big Bang Cosmology (ctd.)
The universe is expanding now.In the past it was hotter and more dense.Thus, it was expanding faster in the past.At a finite time in the past the temperature was infinite .A finite box of space had zero size at that time.This is the Big Bang!
What is the Big Bang? What was before the Big Bang?
To be taken seriously a theory must have made successfulobservational predictions.
23 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
Standard Big Bang Cosmology (ctd.)
The universe is expanding now.In the past it was hotter and more dense.Thus, it was expanding faster in the past.At a finite time in the past the temperature was infinite .A finite box of space had zero size at that time.This is the Big Bang!
What is the Big Bang? What was before the Big Bang?
To be taken seriously a theory must have made successfulobservational predictions.
23 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
Standard Big Bang Cosmology (ctd.)
The universe is expanding now.In the past it was hotter and more dense.Thus, it was expanding faster in the past.At a finite time in the past the temperature was infinite .A finite box of space had zero size at that time.This is the Big Bang!
What is the Big Bang? What was before the Big Bang?
To be taken seriously a theory must have made successfulobservational predictions.
23 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
Standard Big Bang Cosmology (ctd.)
The universe is expanding now.In the past it was hotter and more dense.Thus, it was expanding faster in the past.At a finite time in the past the temperature was infinite .A finite box of space had zero size at that time.This is the Big Bang!
What is the Big Bang? What was before the Big Bang?
To be taken seriously a theory must have made successfulobservational predictions.
23 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
Standard Big Bang Cosmology (ctd.)
The universe is expanding now.In the past it was hotter and more dense.Thus, it was expanding faster in the past.At a finite time in the past the temperature was infinite .A finite box of space had zero size at that time.This is the Big Bang!
What is the Big Bang? What was before the Big Bang?
To be taken seriously a theory must have made successfulobservational predictions.
23 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
Standard Big Bang Cosmology (ctd.)
Universe begins as a homogeneous and very hotfireball.Initially radiation dominates: hot plasma.Space expands and matter cools.After about 30,000 years cold matter starts to dominate.After about 300,000 years atoms (hydrogen) forms anduniverse becomes transparent to lightNow the age of the universe is about 13 billion years.
Prediction: Existence and black body nature of the CosmicMicrowave Background.
24 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
Standard Big Bang Cosmology (ctd.)
Universe begins as a homogeneous and very hotfireball.Initially radiation dominates: hot plasma.Space expands and matter cools.After about 30,000 years cold matter starts to dominate.After about 300,000 years atoms (hydrogen) forms anduniverse becomes transparent to lightNow the age of the universe is about 13 billion years.
Prediction: Existence and black body nature of the CosmicMicrowave Background.
24 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
Standard Big Bang Cosmology (ctd.)
Universe begins as a homogeneous and very hotfireball.Initially radiation dominates: hot plasma.Space expands and matter cools.After about 30,000 years cold matter starts to dominate.After about 300,000 years atoms (hydrogen) forms anduniverse becomes transparent to lightNow the age of the universe is about 13 billion years.
Prediction: Existence and black body nature of the CosmicMicrowave Background.
24 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
Standard Big Bang Cosmology (ctd.)
Universe begins as a homogeneous and very hotfireball.Initially radiation dominates: hot plasma.Space expands and matter cools.After about 30,000 years cold matter starts to dominate.After about 300,000 years atoms (hydrogen) forms anduniverse becomes transparent to lightNow the age of the universe is about 13 billion years.
Prediction: Existence and black body nature of the CosmicMicrowave Background.
24 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
Standard Big Bang Cosmology (ctd.)
Universe begins as a homogeneous and very hotfireball.Initially radiation dominates: hot plasma.Space expands and matter cools.After about 30,000 years cold matter starts to dominate.After about 300,000 years atoms (hydrogen) forms anduniverse becomes transparent to lightNow the age of the universe is about 13 billion years.
Prediction: Existence and black body nature of the CosmicMicrowave Background.
24 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
Standard Big Bang Cosmology (ctd.)
Universe begins as a homogeneous and very hotfireball.Initially radiation dominates: hot plasma.Space expands and matter cools.After about 30,000 years cold matter starts to dominate.After about 300,000 years atoms (hydrogen) forms anduniverse becomes transparent to lightNow the age of the universe is about 13 billion years.
Prediction: Existence and black body nature of the CosmicMicrowave Background.
24 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
Standard Big Bang Cosmology (ctd.)
Universe begins as a homogeneous and very hotfireball.Initially radiation dominates: hot plasma.Space expands and matter cools.After about 30,000 years cold matter starts to dominate.After about 300,000 years atoms (hydrogen) forms anduniverse becomes transparent to lightNow the age of the universe is about 13 billion years.
Prediction: Existence and black body nature of the CosmicMicrowave Background.
24 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
Credit: NASA/WMAP Science Team
25 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
Spectrometer
26 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
Successes of the SBB Model
Key success: Existence and black body nature of the CMB.
27 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
Unanswered Questions
What is the Big Bang?What was before the Big Bang?
28 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
Isotropic CMB Background
29 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
Conceptual Problems of the SBB Model
No explanation for the homogeneity, spatial flatness andlarge size and entropy of the universe.Horizon problem of the SBB:
30 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
Conceptual Problems of the SBB Model II
No explanation of the observed inhomogeneities in thedistribution of matter and anisotropies in the CosmicMicrowave Background possible!
31 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
What to do?
With a little help from a friend , the particle physicist:
At very high temperatures close to the Big Bangclassical physics breaks down - and quantummechanics and particle physics give the rightdescription of matter.→ Standard Big Bang theory breaks down.In the very early universe matter is a plasma ofelementary particles.All described in terms of quantum fields.Quantum field (scalar fields) can lead to a differentexpansion rate of space namely inflationary expansion.
32 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
What to do?
With a little help from a friend , the particle physicist:
At very high temperatures close to the Big Bangclassical physics breaks down - and quantummechanics and particle physics give the rightdescription of matter.→ Standard Big Bang theory breaks down.In the very early universe matter is a plasma ofelementary particles.All described in terms of quantum fields.Quantum field (scalar fields) can lead to a differentexpansion rate of space namely inflationary expansion.
32 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
What to do?
With a little help from a friend , the particle physicist:
At very high temperatures close to the Big Bangclassical physics breaks down - and quantummechanics and particle physics give the rightdescription of matter.→ Standard Big Bang theory breaks down.In the very early universe matter is a plasma ofelementary particles.All described in terms of quantum fields.Quantum field (scalar fields) can lead to a differentexpansion rate of space namely inflationary expansion.
32 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
What to do?
With a little help from a friend , the particle physicist:
At very high temperatures close to the Big Bangclassical physics breaks down - and quantummechanics and particle physics give the rightdescription of matter.→ Standard Big Bang theory breaks down.In the very early universe matter is a plasma ofelementary particles.All described in terms of quantum fields.Quantum field (scalar fields) can lead to a differentexpansion rate of space namely inflationary expansion.
32 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
What to do?
With a little help from a friend , the particle physicist:
At very high temperatures close to the Big Bangclassical physics breaks down - and quantummechanics and particle physics give the rightdescription of matter.→ Standard Big Bang theory breaks down.In the very early universe matter is a plasma ofelementary particles.All described in terms of quantum fields.Quantum field (scalar fields) can lead to a differentexpansion rate of space namely inflationary expansion.
32 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
What to do?
With a little help from a friend , the particle physicist:
At very high temperatures close to the Big Bangclassical physics breaks down - and quantummechanics and particle physics give the rightdescription of matter.→ Standard Big Bang theory breaks down.In the very early universe matter is a plasma ofelementary particles.All described in terms of quantum fields.Quantum field (scalar fields) can lead to a differentexpansion rate of space namely inflationary expansion.
32 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
What to do?
With a little help from a friend , the particle physicist:
At very high temperatures close to the Big Bangclassical physics breaks down - and quantummechanics and particle physics give the rightdescription of matter.→ Standard Big Bang theory breaks down.In the very early universe matter is a plasma ofelementary particles.All described in terms of quantum fields.Quantum field (scalar fields) can lead to a differentexpansion rate of space namely inflationary expansion.
32 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
Plan
1 What is Cosmology?
2 FrameworkSpace-TimeStandard Big Bang Cosmology
3 Inflationary Cosmology
4 String Cosmology
5 Conclusions
33 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
Time line of inflationary cosmology
ti : inflation beginstR: inflation ends, reheating
34 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
Successes of Inflationary Cosmology
The Inflationary Universe Scenario is the current paradigmof early universe cosmology (1980).
Successes:
Solves horizon problemSolves flatness problemSolves size/entropy problemProvides a causal mechanism of generating primordialcosmological perturbations (Chibisov & Mukhanov,1981).
35 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
Successes of Inflationary Cosmology
The Inflationary Universe Scenario is the current paradigmof early universe cosmology (1980).
Successes:
Solves horizon problemSolves flatness problemSolves size/entropy problemProvides a causal mechanism of generating primordialcosmological perturbations (Chibisov & Mukhanov,1981).
35 / 70
Early Universe
R. Branden-berger
Cosmology
FrameworkSpace-Time
Std. Cosmology
Inflation
String gas
Conclusions
Successes of Inflationary Cosmology
The Inflationary Universe Scenario is the current paradigmof early universe cosmology (1980).
Successes:
Solves horizon problemSolves flatness problemSolves size/entropy problemProvides a causal mechanism of generating primordialcosmological perturbations (Chibisov & Mukhanov,1981).
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Credit: NASA/WMAP Science Team
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How to Obtain Inflation?
Assume: Space-time described by General RelativityPhase with exponential expansion of space requiresmatter with negative pressureCheap way to obtain this: assume the existence of aslowly rolling scalar field ϕ
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How to Obtain Inflation?
Assume: Space-time described by General RelativityPhase with exponential expansion of space requiresmatter with negative pressureCheap way to obtain this: assume the existence of aslowly rolling scalar field ϕ
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How to Obtain Inflation?
Assume: Space-time described by General RelativityPhase with exponential expansion of space requiresmatter with negative pressureCheap way to obtain this: assume the existence of aslowly rolling scalar field ϕ
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Toy Model of a Scalar Field
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Review of Inflationary Cosmology II
Space-time sketch of inflationary cosmology:
Note:H = a
acurve labelled by k : wavelength of a fluctuation
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Successes of Inflation
inflation renders the universe large, homogeneous andspatially flatclassical matter redshifts → matter vacuum remainsquantum vacuum fluctuations: seeds for the observedstructure [Chibisov & Mukhanov, 1981]
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Status of the Big Bang in InflationaryCosmology
The inflationary phase had a beginning.There was a Big Bang before the period of inflation.
Unanswered questions:
What is the Big Bang?What was before the Big Bang?
Note: quantum field theory is not applicable very close tothe singularity.
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Status of the Big Bang in InflationaryCosmology
The inflationary phase had a beginning.There was a Big Bang before the period of inflation.
Unanswered questions:
What is the Big Bang?What was before the Big Bang?
Note: quantum field theory is not applicable very close tothe singularity.
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Status of the Big Bang in InflationaryCosmology
The inflationary phase had a beginning.There was a Big Bang before the period of inflation.
Unanswered questions:
What is the Big Bang?What was before the Big Bang?
Note: quantum field theory is not applicable very close tothe singularity.
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Challenges for the Current Paradigm
In spite of the phenomenological successes, theinflationary scenario suffers from several conceptualproblems.In light of these problems we need to look for input fromnew fundamental physics to construct a new theorywhich will overcome these problems.Question: Can Superstring theory lead to a new andimproved paradigm?Question: Can this new paradigm be tested incosmological observations?Question: Was there a Big Bang ?
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Challenges for the Current Paradigm
In spite of the phenomenological successes, theinflationary scenario suffers from several conceptualproblems.In light of these problems we need to look for input fromnew fundamental physics to construct a new theorywhich will overcome these problems.Question: Can Superstring theory lead to a new andimproved paradigm?Question: Can this new paradigm be tested incosmological observations?Question: Was there a Big Bang ?
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Challenges for the Current Paradigm
In spite of the phenomenological successes, theinflationary scenario suffers from several conceptualproblems.In light of these problems we need to look for input fromnew fundamental physics to construct a new theorywhich will overcome these problems.Question: Can Superstring theory lead to a new andimproved paradigm?Question: Can this new paradigm be tested incosmological observations?Question: Was there a Big Bang ?
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Challenges for the Current Paradigm
In spite of the phenomenological successes, theinflationary scenario suffers from several conceptualproblems.In light of these problems we need to look for input fromnew fundamental physics to construct a new theorywhich will overcome these problems.Question: Can Superstring theory lead to a new andimproved paradigm?Question: Can this new paradigm be tested incosmological observations?Question: Was there a Big Bang ?
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Conceptual Problems of InflationaryCosmology
What is the scalar field?Why does it have the special conditions to obtaininflation?Trans-Planckian problemSingularity problemApplicability of General Relativity
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Trans-Planckian Problem
Success of inflation: At early times scales are insidethe Hubble radius → causal generation mechanism ispossible.Problem: If time period of inflation is slightly more thanthe minimal length it must have, then the wavelength issmaller than the Planck length at the beginning ofinflation→ new physics MUST enter into the calculation of thefluctuations.
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Singularity Problem
Standard cosmology: Penrose-Hawking theorems →initial singularity → incompleteness of the theory.Inflationary cosmology: In scalar field-driveninflationary models the initial singularity persists [Bordeand Vilenkin]→ incompleteness of the theory.
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Singularity Problem
Standard cosmology: Penrose-Hawking theorems →initial singularity → incompleteness of the theory.Inflationary cosmology: In scalar field-driveninflationary models the initial singularity persists [Bordeand Vilenkin]→ incompleteness of the theory.
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Applicability of GR
Einstein’s theory breaks down at extremely highdensities.In models of inflation, the energy scale of at whichinflation takes place is close to the limiting scale for thevalidity of Einstein’s theory.We cannot trust the predictions made using GR.
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Zones of Ignorance
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Message I
The current cosmological paradigm has seriousconceptual problems.We need a new paradigm of very early universecosmology.With a little help from a friend - the string theorist!New cosmological model motivated by superstringtheory: String Gas Cosmology (SGC) [R.B. and C.Vafa, 1989].New structure formation scenario emerges from SGC[A. Nayeri, R.B. and C. Vafa, 2006].
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Message I
The current cosmological paradigm has seriousconceptual problems.We need a new paradigm of very early universecosmology.With a little help from a friend - the string theorist!New cosmological model motivated by superstringtheory: String Gas Cosmology (SGC) [R.B. and C.Vafa, 1989].New structure formation scenario emerges from SGC[A. Nayeri, R.B. and C. Vafa, 2006].
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Message I
The current cosmological paradigm has seriousconceptual problems.We need a new paradigm of very early universecosmology.With a little help from a friend - the string theorist!New cosmological model motivated by superstringtheory: String Gas Cosmology (SGC) [R.B. and C.Vafa, 1989].New structure formation scenario emerges from SGC[A. Nayeri, R.B. and C. Vafa, 2006].
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Message I
The current cosmological paradigm has seriousconceptual problems.We need a new paradigm of very early universecosmology.With a little help from a friend - the string theorist!New cosmological model motivated by superstringtheory: String Gas Cosmology (SGC) [R.B. and C.Vafa, 1989].New structure formation scenario emerges from SGC[A. Nayeri, R.B. and C. Vafa, 2006].
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Message II
String Gas Cosmology makes testable predictions forcosmological observations
Blue tilt in the spectrum of gravitational waves [R.B., A.Nayeri, S. Patil and C. Vafa, 2006]
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Message II
String Gas Cosmology makes testable predictions forcosmological observations
Blue tilt in the spectrum of gravitational waves [R.B., A.Nayeri, S. Patil and C. Vafa, 2006]
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Plan
1 What is Cosmology?
2 FrameworkSpace-TimeStandard Big Bang Cosmology
3 Inflationary Cosmology
4 String Cosmology
5 Conclusions
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What is String Theory?
String theory is a quantum theory of all forces of natureincluding gravity.String theory unifies all forces of nature.Basic objects: elementary strings. Compared toelementary point particles.String theory is mathematically consistent only in 10space-time dimensions.Thus, string theory predicts extra spatial dimensions.
Note: string theory is “in development".
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What is String Theory?
String theory is a quantum theory of all forces of natureincluding gravity.String theory unifies all forces of nature.Basic objects: elementary strings. Compared toelementary point particles.String theory is mathematically consistent only in 10space-time dimensions.Thus, string theory predicts extra spatial dimensions.
Note: string theory is “in development".
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What is String Theory?
String theory is a quantum theory of all forces of natureincluding gravity.String theory unifies all forces of nature.Basic objects: elementary strings. Compared toelementary point particles.String theory is mathematically consistent only in 10space-time dimensions.Thus, string theory predicts extra spatial dimensions.
Note: string theory is “in development".
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Conclusions
What is String Theory?
String theory is a quantum theory of all forces of natureincluding gravity.String theory unifies all forces of nature.Basic objects: elementary strings. Compared toelementary point particles.String theory is mathematically consistent only in 10space-time dimensions.Thus, string theory predicts extra spatial dimensions.
Note: string theory is “in development".
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What is String Theory?
String theory is a quantum theory of all forces of natureincluding gravity.String theory unifies all forces of nature.Basic objects: elementary strings. Compared toelementary point particles.String theory is mathematically consistent only in 10space-time dimensions.Thus, string theory predicts extra spatial dimensions.
Note: string theory is “in development".
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What is String Theory?
String theory is a quantum theory of all forces of natureincluding gravity.String theory unifies all forces of nature.Basic objects: elementary strings. Compared toelementary point particles.String theory is mathematically consistent only in 10space-time dimensions.Thus, string theory predicts extra spatial dimensions.
Note: string theory is “in development".
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PrinciplesR.B. and C. Vafa, Nucl. Phys. B316:391 (1989)
Idea: make use of the new symmetries and new degrees offreedom which string theory provides to construct a newtheory of the very early universe.Assumption: Matter is a gas of fundamental stringsAssumption: Space is compact, e.g. a torus.Key points:
New degrees of freedom: string oscillatory modes.Leads to a maximal temperature for a gas of strings,the Hagedorn temperature.New degrees of freedom: string winding modes.Leads to a new symmetry: physics at large R isequivalent to physics at small R.
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PrinciplesR.B. and C. Vafa, Nucl. Phys. B316:391 (1989)
Idea: make use of the new symmetries and new degrees offreedom which string theory provides to construct a newtheory of the very early universe.Assumption: Matter is a gas of fundamental stringsAssumption: Space is compact, e.g. a torus.Key points:
New degrees of freedom: string oscillatory modes.Leads to a maximal temperature for a gas of strings,the Hagedorn temperature.New degrees of freedom: string winding modes.Leads to a new symmetry: physics at large R isequivalent to physics at small R.
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PrinciplesR.B. and C. Vafa, Nucl. Phys. B316:391 (1989)
Idea: make use of the new symmetries and new degrees offreedom which string theory provides to construct a newtheory of the very early universe.Assumption: Matter is a gas of fundamental stringsAssumption: Space is compact, e.g. a torus.Key points:
New degrees of freedom: string oscillatory modes.Leads to a maximal temperature for a gas of strings,the Hagedorn temperature.New degrees of freedom: string winding modes.Leads to a new symmetry: physics at large R isequivalent to physics at small R.
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“Large" is Equivalent to “Small" in String Theory
T-Duality Symmetry
Momentum modes are light if space is large: En = n/RWinding modes are light if space is small: Em = mRLlarge space is equivalent to small spaceSymmetry: R → 1/R (n,m) → (m,n)Mass spectrum of string states unchanged
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“Large" is Equivalent to “Small" in String Theory
T-Duality Symmetry
Momentum modes are light if space is large: En = n/RWinding modes are light if space is small: Em = mRLlarge space is equivalent to small spaceSymmetry: R → 1/R (n,m) → (m,n)Mass spectrum of string states unchanged
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“Large" is Equivalent to “Small" in String Theory
T-Duality Symmetry
Momentum modes are light if space is large: En = n/RWinding modes are light if space is small: Em = mRLlarge space is equivalent to small spaceSymmetry: R → 1/R (n,m) → (m,n)Mass spectrum of string states unchanged
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Temperature in String CosmologyR.B. and C. Vafa, Nucl. Phys. B316:391 (1989)
Temperature of a box of strings in thermal equilibrium.
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Temperature in Standard and InflationaryCosmology
Temperature of a box of particles in thermal equilibrium.
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String Gas CosmologyR.B. and C. Vafa, Nucl. Phys. B316:391 (1989)
We will thus consider the following background dynamics forthe scale factor a(t):
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Dimensionality of Space in SGC
Begin with all 9 spatial dimensions small, initialtemperature close to TH → winding modes about allspatial sections are excited.Expansion of any one spatial dimension requires theannihilation of the winding modes in that dimension.
Decay only possible in three large spatial dimensions.→ dynamical explanation of why there are exactly threelarge spatial dimensions.
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Dimensionality of Space in SGC
Begin with all 9 spatial dimensions small, initialtemperature close to TH → winding modes about allspatial sections are excited.Expansion of any one spatial dimension requires theannihilation of the winding modes in that dimension.
Decay only possible in three large spatial dimensions.→ dynamical explanation of why there are exactly threelarge spatial dimensions.
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Structure formation in inflationary cosmology
N.B. Perturbations originate as quantum vacuumfluctuations.
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Background for string gas cosmology
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Structure formation in string gas cosmologyA. Nayeri, R.B. and C. Vafa, Phys. Rev. Lett. 97:021302 (2006)
N.B. Perturbations originate as thermal string gasfluctuations.
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Power spectrum of cosmological fluctuations
Key features:
scale-invariant like for inflationslight red tilt like for inflation
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Anisotropies in the Cosmic MicrowaveBackground (CMB)
Credit: NASA/WMAP Science Team63 / 70
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Quantification of the CMB data
Credit: NASA/WMAP Science Team
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Spectrum of Gravitational Waves
Key features:
scale-invariant (like for inflation)slight blue tilt (unlike for inflation)
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BICEP-2 Results
0 50 100 150 200 250 300−0.01
0
0.01
0.02
0.03
0.04
0.05
Multipole
l(l+
1)C
lBB/2
π [µ
K2 ]
B2xB2B2xB1cB2xKeck (preliminary)
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Status of the “Big Bang" in String GasCosmology
The universe was very, very hot and dense 13 billionyears ago.In this sense there was a hot “primordial" fireball.But: there was no Big Bang Singularity.There was no beginning of time.
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Status of the “Big Bang" in String GasCosmology
The universe was very, very hot and dense 13 billionyears ago.In this sense there was a hot “primordial" fireball.But: there was no Big Bang Singularity.There was no beginning of time.
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Plan
1 What is Cosmology?
2 FrameworkSpace-TimeStandard Big Bang Cosmology
3 Inflationary Cosmology
4 String Cosmology
5 Conclusions
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Conclusions
Cosmology is a vibrant field with lots of observationaldata.Paradigms of early universe cosmology have beendeveloped.Paradigm 1: Standard Big Bang Model.Paradigm 2: Inflationary Universe scenario - currentparadigm.In both Paradigms 1 and 2 there was a Big Bangsingularity.Paradigms 1 and 2 have conceptual problems →motivates the search for an improved paradigm.Superstring theory may provide a new paradigm.Superstring cosmology may resolve the Big Bangsingularity.It is possible to observationally probe string cosmology.
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Conclusions
Cosmology is a vibrant field with lots of observationaldata.Paradigms of early universe cosmology have beendeveloped.Paradigm 1: Standard Big Bang Model.Paradigm 2: Inflationary Universe scenario - currentparadigm.In both Paradigms 1 and 2 there was a Big Bangsingularity.Paradigms 1 and 2 have conceptual problems →motivates the search for an improved paradigm.Superstring theory may provide a new paradigm.Superstring cosmology may resolve the Big Bangsingularity.It is possible to observationally probe string cosmology.
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Conclusions
Cosmology is a vibrant field with lots of observationaldata.Paradigms of early universe cosmology have beendeveloped.Paradigm 1: Standard Big Bang Model.Paradigm 2: Inflationary Universe scenario - currentparadigm.In both Paradigms 1 and 2 there was a Big Bangsingularity.Paradigms 1 and 2 have conceptual problems →motivates the search for an improved paradigm.Superstring theory may provide a new paradigm.Superstring cosmology may resolve the Big Bangsingularity.It is possible to observationally probe string cosmology.
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Conclusions
Cosmology is a vibrant field with lots of observationaldata.Paradigms of early universe cosmology have beendeveloped.Paradigm 1: Standard Big Bang Model.Paradigm 2: Inflationary Universe scenario - currentparadigm.In both Paradigms 1 and 2 there was a Big Bangsingularity.Paradigms 1 and 2 have conceptual problems →motivates the search for an improved paradigm.Superstring theory may provide a new paradigm.Superstring cosmology may resolve the Big Bangsingularity.It is possible to observationally probe string cosmology.
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Status of the “Big Bang"
We know that going back in time 13 billion years therewas a very hot early phase, a primordial fireball.If this is what you mean by “Big Bang": then there WASa “Big Bang".We do not know if there was a “Big Bang singularity", abeginning of time.Our current paradigms of early universe cosmologypredict a beginning of time.But only if we extrapolate the models beyond wherethey can be used.Superstring theory may lead to a cosmology without abeginning of time.If this is true then there may not have been a “BigBang" (singularity).
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