What's the Ultimate Question‏

Our Mathematical Universe

Max Tegmark

Part One: Zooming Out

1 What is Reality

• What's the Ultimate Question

For as long as our humans ancestors

have walked the Earth,

they've undoubtedly wondered

what reality is all about,

pondering deep existential questions.

Where did everything came from?

How will it all end?

How big is it all?

These questions are so captivating

that virtually all human cultures

across the globe have grappled with them

and passed on answers 

from generation to generation,

in the form of elaborate creation myths,

legends and religious doctrines.

---

• Is our Universe infinitely old?

Yes: Hinduism, Buddhism,

No: Ahmadiyya, Apache, Aztec, Babylonian,

Bahai, Christianity, Egyptian, Greek, Hopi,

Islam, Judaism, Maya, Norse, Rastafarian,

Sumerian, Zoroastrian.

• Will our Universe last forever?

Yes: Buddhism, Greek, Hinduism, Norse, Zoroastrian.

No: Ahmadiyya, Apache, Aztec, Babylonian,

Bahai, Christianity, Egyptian, Hopi,

Islam, Judaism, Maya, Rastafarian,

Sumerian.

• Are there other universes?

Yes: Hinduism

No: Ahmadiyya, Apache, Aztec, Babylonian,

Bahai, Buddist, Christianity, Egyptian, Greek, Hopi, Islam, Judaism, Maya, Norse, Rastafarian, Sumerian, Zoroastrian.

• If something created our Universe,

then what was it?

God/gods: Apache, Aztec, Babylonian,

Christianity, Hopi, Islam, Judaism,

Maya, Sumerian, Zoroastrian.

Egg: Egyptian, Finnish, Greek,

Hinduism, Taoism.

Elements:  Mesopotamiam, 

Egyptian (water), Norse (fire/ice).

Many cosmological questions

that we'll tackle in this book

have fascinated thinkers

throughout the ages,

but no global consensus has emerged.

The classification above

is based on a 2011 presentation

by MIT student David Hernández

for my cosmological class.

Because such simplistic taxonomies

are strictly impossible,

they should be taken  with a grain of salt:

many religions have multiple branches

and interpretations, and some fall

into multiple categories.

For example, Hinduism contains aspects 

of all three creation options shown:

according to one legend, 

both the creation god Brahma

and our Universe emerged

from an egg, which in turn

may have originated from water.

_____________

Other big questions 

tackled by ancient cultures

are at least as radical.

What is real?

Is there more to reality than meets the eye?

Yes! Was Plato's answer over two millenia ago.

In his famous cave analogy,

he likened us to people 

who'd lived their entire lives

shackled in a cave,

facing a blank wall,

watching the shadows

cast by things

passing behind them,

and eventually coming

to mistakenly believe

that these shadows

were the full reality.

Plato argued that

what we humans call

our everyday reality

is similarly just 

a limited and distorted 

representation

of the true reality,

and that we must 

free oursrelves

from our mental shackles

to begin comprehending it.

If my life as a physicist

has taught me anything at all,

it's that Plato was right:

modern physics 

has made abundantly clear

that the ultimate nature of reality

isn't what it seems.

But if reality isn't 

what we thought it was,

then what is it?

What's the relation between 

the internal reality of our mind 

and the external reality?

What's everything ultimately made of?

How does it all work?  Why?

Is there a meaning to it all,

and if so, what?

As Douglas Adams put it

in his science fiction spoof

The Hitchhiker's Guide to the Galaxy:

«What's the answer to the ultimate question

of life, the universe, and everything?»

Thinkers throughout the ages

have offered a fascinating spectrum

of responses to the question

«What is reality?»

-either attempting to answer it

or attempting to dismiss it.

Here are some examples

(this list makes no claims to be complete,

and not alternatives are mutually exclusive).

This book (and indeed my scientific career)

is my personal attempt to tackle this question.

Part of the reason 

that thinkers have offered 

such a broad spectrum of answers

is clearly that they've chosen 

to interpret the question in different ways, 

so I owe you an explanation of how 

I interpret it and how I approach it.

The word reality can have 

many different connotations.

I use it to mean 

the ultimate nature of 

the outside physical world

that we're part of,

and I'm fascinated

by the quest 

to understand it better.

So what's my approach?

One evening back in high school,

I started reading Agatha Christie's

detective novel Death on the Nile.

Although I was painfully aware

that my alarm clock would go off

at seven a.m., I couldn't for the life of me

put it down until the mystery 

had been solved, around four a.m.

I've been inexorably drawn

to detective stories ever since I was a kid,

and when I was around twelve,

I started a detective club

with my classmates Andreas Bette,

Matthias Bothner and Ola Hansson.

We never captured criminals,

but the idea of solving mysteries

captured my imagination.

To me, the question «What is reality?»

represents the ultimate detective story,

and I consider myself incredibly fortunate

to be able to spend so much of my time pursuing it.

In the chapters ahead, 

I'll tell you about other occasions

when my curiosity has kept me up

in the wee hours of the morning,

totally unable to stop reading

until the mystery was resolved.

Except that I wasn't reading a book,

but what my hand was writing,

and what I was writing

was a trail of mathematical equations

that I knew would ultimately

lead me to an answer.

___________

Some Responses to «What is Reality?»

• The question has a meaningful answer.

- Elementary particles in motion

- Earth, wind, fire, air and quintessence

- Atoms in motion

- Elementary particles in motion

- Strings in motion

- Quantum fields in curved spacetime

- M-theory (substitute your favorite capital letter…)

- A divine creation

- A social construct

- A neurophysiological construct

- A dream

- Information

- A simulation (à la The Matrix)

- A mathematical structure

- The Level IV Multiverse

• The question lacks a meaningful answer.

- There is a reality, but we humans 

   can't fully know it: we have no access 

   to what Immanuel Kant called «das Ding an sich.» 

   The thing in itself. (La cosa en sí. )

- Reality is fundamentally unknowable.

- Not only don't we know it,

   but we couldn't express it if we did.

- Science is nothing but a story (postmodern 

  answer by Jacques Derrida and others).

- Reality is all in our head (constructivist answer).

- Reality doesn't exist (solipsism).

__________________

I'm a physicist, 

and I'm taking a physics approach

to the mysteries of reality.

To me, this means starting

with great questions such as

«How big is our Universe?»

and «What's everything made of?»

and treating them exactly

like detective mysteries:

combining clever observations

and reasoning and persistently

following each clue wherever it leads.