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《黑客帝国》<Matrix> 里有两个世界：真实的物质世界，虚拟的信息世界（在计算机里）。真实的物质世界是由基本粒子组成的。 虚拟的信息世界是由bits组成的。（我个人观点）其实真实的物质世界不太真实，虚拟的信息世界更真实。物质世界和信息世界根本就是一个世界。更确切的说，我们的世界是一个量子信息世界。空间=含有许多许多qubits的集合。基本粒子=qubits的运动激发。也就是说，世间万物（物质世界）是由qubits的激发组成的。

*我们生活在一个量子计算机里*

"Matrix" is a story of two worlds: A real material world and a virtual information world (inside computers). The real material world is formed by elementary particles. The virtual information world is formed by bits. (My point of view) in fact, the real material world is not real, the virtual information world is more real. The material world and the information world is actually the same world.

To be more precise, our world is a quantum information world:

Space = a collection of many many qubits.

Vacuum = the ground state of the qubits.

Elementary particles = collective excitations of the qubits.

In other words, all matter are formed by the excitations of the qubits.

*We live inside a quantum qubit world*

上面的描述十分通俗，但也很贴切。更学术更准确的论述：

People have been wondering about the origin of light, electrons, and gravity

for very long time. Such a curiosity has driven the development particle

physics in last 100 years. In another field --modern condensed matter

physics, physicists have been trying to find new types of matter, so that they

can use the new materials to make new devices. It turns out that these two

seemly unrelated fields have a deep connection.

In early days of particle physics, our approach has been dominated by the

reductionist approach: to gain a deeper understanding of something,

we simply need to divide the thing into small parts. Thus to gain a deeper

understanding of photons and electrons and to understand the strange properties of

photons and electrons, we need to find a smaller parts of photons and

electrons. The different properties of a photon and an electron

may be due to their different internal structures.

However, this line of thinking may be fundamentally flawed. They are based on

the reductionist belief that the space is empty and that things placed in the

empty space are divisible. However, there are many examples from condensed

matter physics indicating that sometimes this line of thinking doesnot make sense.

For example, due to the particle-wave duality in quantumtheory, sound waves in a

solid correspond to a kind of particle called phonon. Phonons are as much

particle-like as any other elementary particles. But if we look at phonons

closely, we do not see smaller parts that form a phonon. We see the atoms

that form the entire solid. The phonons are not formed by those atoms, the

phonons are simply collective motions of those atoms. We see that phonons

cannot be understood by dividing them into smaller parts and the reductionist

approach does not work.

This leads us to wonder that are we misguided by the reductionist principle

all those years? It should occur to us that photons, electrons, gravitons,

etc, may not have smaller parts. Looking for the smaller parts of photons,

electrons, and gravitons to gain a deeper understanding of those elementary

particles may not be a right approach.

Motivated by those considerations, here I will advocate a different view of

the elementary particles based on the principle of emergence. In this

approach, we view the empty space as a dynamical medium formed by quantum

degrees of freedom If there is no degrees of freedom, there will be no space.

The simplest local degrees of freedom in quantum theory are qubits. So in this

approach, space = a collection of qubits. In condensed matter physics, a

collection of qubits is called a lattice spin systems. Here, we will

use such a condensed matter terminology and view space itself as a qubit system or a

spin system. The deformations of this medium (ie the rearrangements or the

collective motions of qubits/spins) are waves, which in quantum theory correspond

to various particles. Thus in the emergence approach, we may understand the

origin of various particles by understanding the origin of various waves.

The different orders of bosons/spins lead to different kinds of waves which in

turn lead to different types of particles.

In the field of condensed matter physics, we find recently that a new class of

quantum states of qubits -- long-range entangled states -- can exist. Amazingly,

the collective wave-like excitations in some of those highly entangled quantum

states can satisfy the Maxwell equation and Dirac equation, despite the original

qubit system has no gauge fields and no Grassman fields! So, those long-range

entangled states are the long sought-after ether -- a medium that supports a

wave that satisfies the Maxwell equation. This suggests

that we can view our vacuum as a long-range entangled state and view the

elementary particles as the excitations in such a long-range entangled state.

Such a point of view may provides an unification and an origin for all

elementary particles.

We may try to use such a point view of long-rang entanglement to

understand many fundamental issues in theoretical physics. It seems possible

that long-range entanglement can unify many fundamental mysteries/wonders,

which will totally change our view of universe. People have been studying

entanglements from quantum computing and quantum matter points ofview. But the

entanglement may have some very fundamental implications to particle physics

as well.

We have shown that light and electrons can indeed have a unified origin

from qubits that form the entire space, provided that those space-forming

qubits are in a particular long-range-entangled state -- string-net liquid state.

So, such an emergence picture based on long-range entanglements can explain

the origin of gauge interaction (such as the electromagneticinteraction) and

Fermi statistics, and unify these two seemingly totally unrelated phenomena:

Q:

**Where do light and fermions come from?**A: Light and fermions come from the qubits that form the space.

Q:

**Why do light and fermions exist?**A: Light and fermions exist because the space-forming qubits form a string-net condensedstate.

Q:

**What are light and fermions?**A: Light waves are collective motions of strings and fermions are ends of open strings in the string-net condensed state.

The basic picture is:

Space = a collection of qubits. No qubits no space. There is nothing between the qubits.

Vaccum = ground state of qubits (ie a particular pattern of entanglement of qubits)

Motion of qubits (ie deformation of the pattern of entanglement) = waves

For right ground state (or for a right pattern of entanglement), the wave happen to satisfy Maxwell equtions, and correspond to the eletromagnetic wave. To form the right pattern of entanglement, the qubits first form string-net and string-nets then form a quantum liquid. The wave that satisfies Maxwell equtions is the string densoty wave.

The quanta of the eletromagnetic wave are photons

The electrons are ends of strings.

If light and electrons can be unified by qubits that form our space, then, can we unify everything under qubits, even all the eight wonders in our universe?

**Eight wonders in our universe:**

(1) Locality.

(2) Identical particles.

(3) Gauge interactions.

(4) Fermi statistics.

(5) Chiral fermions.

(6) Small mass of fermions. (Much less than Planck mass)

(7) Lorentz invariance.

(8) Gravity.

So far, we can unify seven out of eight wonders (1 -- 7) by qubits organized into string-nets.

The traditional physics theory of our world (the U(1)xSU(2)xSU(3) standard model) is based on the above 8 strange and random "wonders". We just put this 8 fact into our theory by hand and do not ask where they come from. If we assume the space is the ether made of qubits, then we can unify the seven random assumptions into one very simple and reasonable assumption.

**Qubits unify everything**

This line of thinking is an **unification of matter, interaction, and information**!

In fact, quantum theory already unifies matter and information.

This is because, acoording to quantum theory and relativity theory

**Changing information (qubits) -> energy -> mass -> matter.**

To understand the above relations, we note that

- Frequency ~ a property of information

- Energy/mass ~ a property of matter

In quantum theory

Changing information -> Frequency

Frequency x Planck constant = Energy

In relativity

Energy/c^2 = mass.

So Frequency ~ Energy ~ mass.

But can simple qubits (quantum information) really produce/unify the following

fascinating and mysterious properties of universe:

(1) all interactions are gauge interaction (electromagnetism, strong/weak interation).

(2) matter are formed by fermions (electrons, quarks, etc.). Who ordered Fermi statistics in our universe?

(3) angular momentum of fermions are fractionalized (spin-1/2)

The answer is yes! **Information can really unifies ****matter and interaction. ****Information and ****matter are really the same.**

道生一，一生二，二生三，三生万物 --> 信息与物质的统一

We see that, in the string-net approach to elementary particles, the qubits are the ultimate things that build up our world. Such an emergence approach has a falsifiable prediction: The U(1)xSU(2)xSU(3) standard model is incomplete. The correct theory must contain an extra discrete gauge theory which leads to new cosmic strings. [see http://arxiv.org/abs/1210.1281 Topological order: from long-range entangled quantum matter to an unification of light and electrons （section IV D)]

Refs:

1. arXiv:hep-th/0109120 *Origin of Light *Xiao-Gang Wen

An origin and unification of light and electrons from qubits was proposed.

2. arXiv:hep-th/0302201 *Quantum order from string-net condensations and origin of light and massless fermions* Xiao-Gang Wen

An origin and unification of photons/gluons and leptons/quarks from qubits was proposed. But the SU(2) gluons couple to left-hand and right-hind fermions equally, while in our world the SU(2) gluons couple to left-hand and right-hind fermions differently.

3. http://dao.mit.edu/~wen/talks/LightStory.htm

A simple introduction to origin of light from qubits

4. arXiv:hep-th/0507118 *Quantum ether: photons and electrons from a rotor model *Michael Levin, Xiao-Gang Wen

An origin and unification of light and electrons from qubits in more details.

5. The universe is a quantum computer Seth Lloyd

The universe is a quantum computer is simply another way to say (抓眼球的表达) quantum theory describes our world.

**Spirits flying in a mysterious void. Magnetic waist, electric head, sparkles fill the dark sky. Vibrating strings radiate rainbow light. Spreading nets weave into colorful fabric. Neither nonbeing nor being, nonbeing gives birth to being. Both illusive and real, illusive becomes real.Transforming and regenerating not due to divine power. Mother of all matter and root of universe.**

2005 summer by Xue Wanqin

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