A Meta-Law to Rule Them All:
Physicists Devise a “Theory of Everything”
“Constructor theory” unites in one framework how information is
processed in the classical and quantum realms
May 26, 2014 |By Zeeya Merali
Painted portrait of Claude Shannon, the "father of information theory".
Credit: Flickr/thierry ehrmann
“Once you have eliminated the impossible,” the fictional detective
Sherlock Holmes famously opined, “whatever remains, however
improbable, must be the truth.” That adage forms the foundational
principle of “constructor theory”—a candidate “theory of everything”
first sketched out by David Deutsch, a quantum physicist at the
University of Oxford, in 2012. His aim was to find a framework that could
encompass all physical theories by determining a set of overarching
“meta-laws” that describe what can happen in the universe and what is
forbidden. In a May 23 paper posted to the physics preprint server,
arXiv, constructor theory claims its first success toward that goal by
unifying the two separate theories that are currently used to describe
information processing in macroscopic, classical systems as well as in
subatomic, quantum objects. Computer scientists currently use a theory
developed by the American mathematician and cryptographer Claude
Shannon in the 1940s to describe how classical information can be
encoded and transmitted across noisy channels efficiently—what, for
instance, is the most data that can be streamed, in theory, down a fiberoptic cable without becoming irretrievably corrupted. At the same time,
physicists are striving to build quantum computers that could, in
principle, exploit peculiar aspects of the subatomic realm to perform
certain tasks at a far faster rate than today’s classical machines. But the
principles defined by Shannon’s theory cannot be applied to information
processing by quantum computers. In fact, Deutsch notes, physicists
have no clear definition for what “quantum information” even is or how
it relates to classical information. “If we want to make progress in
finding new algorithms for quantum computers, we need to understand
what quantum information actually is!” he says. “So far, the algorithms
that have been discovered for quantum computers have been surprises
that were discovered by blundering about because we have no
underlying theory to guide us.”
In 2012 Deutsch outlined constructor
theory, which, he believes, could provide the underlying foundation for
a grand unification of all theories in both the classical and quantum
domains. This latest paper is a first step toward that larger goal—a
demonstration of how classical and quantum information can be used to
unify two physical theories. According to constructor theory, the most
fundamental components of reality are entities—“constructors”—that
perform particular tasks, accompanied by a set of laws that define which
tasks are actually possible for a constructor to carry out. For instance, a
kettle with a power supply can serve as a constructor that can perform
the task of heating water. “The language of constructor theory gives a
natural way to describe the most fundamental principles that must be
obeyed by all subsidiary theories, like conservation of energy,” explains
Chiara Marletto, a quantum physicist also at Oxford, who co-authored
the new paper. “You simply say that the task of creating energy from
nothing is impossible.”
Dean Rickles, a philosopher of physics at the
University of Sydney who was not involved in the development of the
theory, is intrigued by its potential to unify nature’s laws. “It’s a very
curious new take on the notion of a theory of everything,” he says. “In
principle, everything possible in our universe could be written down in a
big book consisting of nothing but tasks [and in] this big book will also be
encoded all of the laws of physics.”
To develop their description of
information, Deutsch and Marletto homed in on one key task that is
possible in classical systems but impossible in quantum systems: the
ability to make a copy. Since the 1980s physicists have known that it is
impossible to make an identical copy of an unknown quantum state. In
their new paper Deutsch and Marletto define a classical information
medium as one in which states can all be precisely copied. They then
work out which tasks must be possible in such a system to remain in line
with Shannon’s theory.
The collaborators then go on to define the
concept of a “superinformation” medium that encodes messages that
specify particular physical states—in this case, one in which copying is
impossible. They discovered that a special subset of their
superinformation media display the properties associated with quantum
information processing. “We found that with this one constraint in place
telling you what you cannot do in a superinformation medium—the task
of copying—you end up discovering the weird new informationprocessing power that is a property of quantum systems,” Marletto
says.
The team showed that with this restriction on copying in place a
number of other properties begin to emerge: Measuring the state of a
superinformation medium will inevitably disturb it—a feature commonly
associated with quantum systems. But because it is forbidden to make
an exact copy of certain sets of states in a superinformation medium this
forces some uncertainty into the outcome of the measurement.
The
team has also shown that entanglement—the spooky property that
binds quantum objects together so that they act in tandem, no matter
how far apart they are—also arises naturally, once this constraint on
copying is in place. According to Marletto, the crucial property of a
system containing two entangled states is that the information stored in
the combined system is more than the information that can be gleaned
just by examining each member of the pair individually. The quantum
whole is more than the sum of its parts.
In their paper Deutsch and
Marletto demonstrate that information can be encoded in two
superinformation media in such a way that it is impossible to retrieve it
by measuring the single subsystems separately—that is, entanglement is
inevitable. Similarly, in a classical medium, entanglement is impossible.
“The appealing thing about this formalism is the way that common
features of quantum mechanics fall out,” says Patrick Hayden, a
quantum physicist at Stanford University, adding: “I have real respect for
the creative thinking behind constructor theory and its ambitions.” He
notes, however, that there are competing attempts by other researchers
to develop a deeper understanding of quantum mechanics, including
ideas based on copying, and as yet it is too early to say which, if any, will
prove to be the best description.
Rickles agrees that it will take time
for physicists to verify that the theory—which has not yet passed
through peer review—is truly successful at uniting classical and quantum
information theory. But if affirmed, it would give a boost to Deutsch’s
goal to help in the hunt for the long-sought theory of quantum gravity,
uniting the currently incompatible quantum theory and general
relativity. “This is the first time in the history of science that it’s known
that our deepest theories are wrong, so it’s obvious that we need a
deeper theory,” Deutsch says.
Rickles believes that constructor theory
has the potential to prescribe meta-laws that general relativity and
quantum theory must obey. “The meta-laws are more stable creatures,
they survive scientific revolutions,” he says. “Having such principles in
hand gives us a better grasp of the nature of reality. I’d say that’s a
pretty good advantage.”
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jtdwyer
May 26, 2014, 9:57 AM
At first reading, this appears to be just more imaginary information as it
pertains to physical systems...
What medium - what information - what physical processes transcribe
information into physical systems and encode information from physical
systems?
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dracma
May 26, 2014, 12:13 PM
Rickles agrees that it will take time for physicists to verify that the
theory—which has not yet passed through peer review—is truly
successful at uniting classical and quantum information theory. But if
affirmed, it would give a boost to Deutsch’s goal to help in the hunt for
the long-sought theory of quantum gravity, uniting the currently
incompatible quantum theory and general relativity.
If so why not a Nobel Award for this fundamental research?
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jtdwyer
May 26, 2014, 8:54 PM
I reiterate - utter nonsense! Information is in the mind of the observer.
In physical systems, information produces no physical effects - there are
no physical processes that produce physical effects based on
information. Information in physics is merely an artifact of the
observation of physical properties. Without observers no information
exists as a discrete physical element. As always, I must disclose that I am
not a qualified physicist - merely a retired information systems analyst.
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yessmaam jtdwyer
May 26, 2014, 11:30 PM
just like classifications, categories, and the very laws 'we' state...
they are all products of human observations based on a very few years
of data especially on a galactic time scale....
and I don't think that being a physicist or not a physicist has anything to
do with a valid point or observation...
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crbazevedo jtdwyer
May 27, 2014, 12:54 AM
"there are no physical processes that produce physical effects based on
information"
Well, it just did it. The information contained in the SciAm article has
been physically processed by your neuronal cells and prompted you to
type the above comment by physically pushing buttons on your
keyboard. It turned out that the pixels represented in my laptop monitor
were enconded into photons with very specific polarizations that were in
turn captured by my retina neurons and, guess what, the electrical
stimuli transmitted from the retina to my brain were again processed
and prompt me to physically push my keyboard buttons in reply to the
(mis)information conveyed in your comment.
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jtdwyer crbazevedo
May 27, 2014, 3:06 AM
No, no - it was my intellectual processes that caused me to interpret the
information represented and produce my comment. If the information
had been represented in Spanish I'd have made no comment
whatsoever.
What abstract information is used to physically produce gravitational
interactions throughout the universe? What processes retrieve and
interpret that supposed encoded information to produce those physical
effects?
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crbazevedo jtdwyer
May 27, 2014, 8:14 AM
Are you then suggesting that ghosts exist? Because if your "intellectual
processes" are not physical processes, what are them?
The fact you are physically reacting to the information (=patterns of
symbolic language for which our cognition has evolved over millions of
years in order to recognize them, produce more of them, and react to
them) encoded in this article and interacting with me is enough evidence
that information IS physical and can naturally prompt observable
physical effects in the world around us.
You don't even need an "intellectual process" to decode it. Just picture
the way proteins are continuously produced in your body by intricate
machines known as ribossomes, in response to patterns of amino-acid
sequences encoded in RNA.
The tendency that complex systems have of producing persistent
patterns of matter organization that are physically copied and
transmitted across other physical entities and, ultimately, organisms, is
enough evidence that natural systems produce and process information
all the time.
And one can of course measure and quantify the amount of information
contained in a physical system by just studying its physical effects over
time. There's nothing abstract in this.
The abstraction only comes when applying mathematical models such as
those conveyed by Shannon to help us to understand what are the limits
of accurate information transmission and representation in terms of the
underlying probabilistic behavior of a physical system. Note that
probability theory is also too much of an abstraction in its own terms.
Now, with Deutsch's contribution, it seems that Shannon's classical
theory of information may be a natural consequence of physical
contraints regarding what kind of information processing operations are
possible within a given physical system. And that's indeed very exciting.
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jctyler
May 27, 2014, 9:26 AM
A theory of everything must apply to everything else it's not a theory of
everything.
But if it applies to everything it must also apply to language.
Also, if it applies to everything it must also apply to the simplest
lifeforms.
if it applies to even the simplest lifeform and to language, it must be
explainable in simple words.
When I read the above the very first thing I notice is, this is not a simple
text using a simple vocabulary to explain a simple theory; this is basically
a bunch of scientists who ignore for example Hawking's statement that
for a theory to be applicable to everything it must in essence be
understandable by all = simple.
Ergo, since the content, the style, even the text itself contradicts the
theory's claim, the theory is in essence invalid.
I've seen a better work. The funny bit about that paper is that it adheres
strictley to the theorem that a universally valid theory must be
explainable in simple words. But anything in simple words is
immediately disregarded by scientists because it lacks scientific
vocabulary. Arrogance is not the prerogative of the ignorant. Which
shows the limits of contemporary physicists' brainpower. A theory of
everything must apply to physics and biology and the economy and the
climate. What vocabulary are you then going to write it in? If you use
biology vocabulary, the climatologists and physicists are at a loss. if you
don't write it in physicists' terms these guys will immediately disregard
it.
So:
a) the theory described is NOT a theory of everything;
b) scientists are so tunnel-visioned, so limited to their field that they
disregard anything not written in their language and that therefore, if
one day a proper theory of everything is published, scientists won't
understand it (for a very long time) because they are too narrowminded.
So, this is no TOE, therefore no cigar.
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jtdwyer crbazevedo
May 27, 2014, 10:40 AM
Excited as you may be, pondering the possibilities, you did not address
my questions:
- What abstract information is used to physically produce gravitational
interactions throughout the universe?
- What processes retrieve and interpret that supposed encoded
information to produce those physical effects?
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mpc755
May 27, 2014, 1:11 PM
Dark matter has mass and fills what would otherwise be considered to
be empty space.
Particles of matter move through and displace the dark matter.
The matter the Milky Way consists of moves through and displaces the
dark matter. This is why the Milky Way's halo is lopsided.
'The Milky Way's dark matter halo appears to be lopsided'
http://arxiv.org/abs/0903.3802
"The emerging picture of the asymmetric dark matter halo is supported
by the \Lambda CDM halos formed in the cosmological N-body
simulation."
The Milky Way's dark matter halo is lopsided due to the matter in the
Milky Way moving through and displacing the dark matter.
The Milky Way's halo is the state of displacement of the dark matter.
The Milky Way's halo is curved spacetime.
A moving particle has an associated dark matter displacement wave. In a
double slit experiment the particle travels through a single slit and the
associated wave in the dark matter passes through both.
Dark matter displaced by the particles of matter which exist in it and
move through it relates general relativity and quantum mechanics.
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