还原论和演生论： 两种宇宙观 (Emergence and reductionism: two world views)(2012-11-12 08:25:01)
长程量子纠缠 (long-range entanglement)
给出光和电子的统一起源 (gives rise to an unified origin of light and electrons)
People have been wondering about the origin of light, electrons, and gravity
for very long time.
physics in last 100 years.
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.
understanding of photons and electrons and to understand unique 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 does not make sense.
For example, due to the particle-wave duality in quantum theory,
solid correspond to a kind of particle called phonon.
particle-like as any other elementary particles.
closely, we do not see smaller parts that form a phonon.
that form the entire solid.
phonons are simply collective motions of those atoms.
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.
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.
collection of qubits is called a lattice spin systems.
use such a condensed matter terminology and view space itself as a qubit or a
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.
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!
entangled states are the long sought-after ether -- a medium that supports a
wave that satisfies the Maxwell equation.
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
We may try to use such a point view of long-rang entanglements to
understand many fundamental issues in theoretical physics.
that long-range entanglements 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 of view. But the
entanglements may have some very fundamental implications to particle physics
It has been 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 electromagnetic interaction) 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 condensed state.
- 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.
Seven wonders in our universe:
(2) Identical particles.
(3) Gauge interactions.
(4) Fermi statistics.
(5) Chiral fermions.
(6) Lorentz invariance.