# Presentation: 146995

## Irreversible Time and the Big Bang

- Henri Bergson Conference at UC Berkeley

- April 8, 2005

## The Main Point

- The expansion of the early universe, that followed the Big Bang, played a major part in creating the “arrow of time.”

- Henri Bergson Conference at UC Berkeley

- April 8, 2005

## The Arrow of Time

- We instinctively know that this movie is wrong!

- Henri Bergson Conference at UC Berkeley

- April 8, 2005

## Statistical Mechanics

- However, if we zoom in on the individual atoms in the flower, we will find nothing wrong with their behavior.
- The individual atoms behave (almost) exactly the way we expect them to, according to the laws of physics!
- – They are not the reason for the arrow of time.

- So why does the movie seem strange?
- It is just that to grow back into a bud, the motion of the atoms in the flower will have to be correlated in a precise way. This is highly improbable.

- Henri Bergson Conference at UC Berkeley

- April 8, 2005

## Irreversible Processes

- 	We observe “irreversible processes” – processes that follow the arrow of time – in systems that are not in thermodynamic equilibrium.

- Let’s see what is “thermodynamic equilibrium.”

- Henri Bergson Conference at UC Berkeley

- April 8, 2005

## Thermodynamic Equilibrium

- 	Over time, an isolated system with a large number of interacting particles reaches thermodynamic equilibrium:
- Uniform density; (usually)
- Homogeneous composition; (usually)
- Uniform temperature;

- Why are we not in equilibrium?

- Theoretical problem:

- Henri Bergson Conference at UC Berkeley

- April 8, 2005

## Large Scale Structure

- In fact, this problem is
- much bigger ...

- Credit: S. Beckwith & the HUDF Working Group (STScI), HST, ESA, NASA
- Taken from http://antwrp.gsfc.nasa.gov/apod/ap040309.html

- Hubble Ultra Deep Field

- Our Universe now
- looks like this:

- Henri Bergson Conference at UC Berkeley

- April 8, 2005

## History of the Universe

- How did the universe get to be like this,
- with matter clumped in galaxies and
- almost nothing in between?

- What did our universe look like in the past?

- Henri Bergson Conference at UC Berkeley

- April 8, 2005

## Structure Formation

- Credit: F. Summers (Princeton), D. Cox, R. Patterson, E. Wesselak,
- and B. Sanders (NCSA), L. Carpenter (Pixar), GC3, Cosmic Voyage, Smithsonian
- http://antwrp.gsfc.nasa.gov/apod/ap970614.html

- Computer simulation demonstrating how structure could form by gravitational attraction in the early universe.

- Still not homogeneous!

- Henri Bergson Conference at UC Berkeley

- April 8, 2005

## And even earlier ...

- Credit: WMAP Science Team, NASA
- http://antwrp.gsfc.nasa.gov/apod/ap040711.html

- The early universe at a temperature of about 10,000°C
- We see by sensing light that is emitted from objects. Similarly, we can “see” the early universe by detecting the radiation that it emitted.
- Inferred from the Cosmic Microwave Background.
- Lighter regions are about  0.01% hotter than the average.

- Still, not quite homogeneous!

- Henri Bergson Conference at UC Berkeley

- April 8, 2005

## Initial Fluctuations

- This is one of the most active areas of research nowadays.
- We believe that a completely satisfactory answer will require a successful merger of gravity with quantum mechanics and particle physics – a grand unified theory!

- How did these 0.01% density fluctuations form?
- We cannot “see” anything earlier than the CMB.
- But we have several promising theoretical ideas.

- Henri Bergson Conference at UC Berkeley

- April 8, 2005

## Big Bang Theory

- The Big-Bang theory combines formulas of:
- General relativity,
- Particle and Nuclear Physics,
- Quantum Mechanics,
- Statistical theory and Thermodynamics.

- The universe is expanding!

- Henri Bergson Conference at UC Berkeley

- April 8, 2005

## Expansion of the Universe

- The expansion sets an arrow of time.
- It also allows the early universe to evade reaching an equilibrium.
- By a complicated process – a leading theory holds – the expansion played a major role in forming those initial 0.01% fluctuations.
- (The theory of “inflation.”)

- Henri Bergson Conference at UC Berkeley

- April 8, 2005

## Summary

- Irreversibility of time, departure from thermal equilibrium, and the lack of homogeneity in the universe are all related to each other.
- They are largely a consequence of the expansion of the early universe, following the big bang.
- However, to fully understand the early universe requires a complete theory of high energy physics
- – a grand unified theory.

- The search continues ...

- Henri Bergson Conference at UC Berkeley

- April 8, 2005

## Fin

- Henri Bergson Conference at UC Berkeley

- April 8, 2005