The energy surface of a massless, non-interacting Wilson fermion. The continuum dispersion relation is shown as the red surface. (Credit: Silas R. Beane et al.)
The concept that we could possibly be living in a computer simulation has been suggested by science writers and others, and was formalized in a 2003 paper published in Philosophical Quarterly by Nick Bostrom, a philosophy professor at the University of Oxford.
With current limitations and trends in computing, it will be decades before researchers will be able to run even primitive simulations of the universe. But a University of Washington team has suggested tests that can be performed now, or in the near future, that could resolve the question.
Currently, supercomputers using a technique called lattice quantum chromodynamics (LQC), and starting from the fundamental physical laws that govern the universe, can simulate only a very small portion of the universe, on the scale of one 100-trillionth of a meter, a little larger than the nucleus of an atom, said Martin Savage, a UW physics professor.
Eventually though, more powerful simulations will be able to model on the scale of a molecule, then a cell and even a human being. But it will take many generations of growth in computing power to be able to simulate a large enough chunk of the universe to understand the constraints on physical processes that would indicate we are living in a computer model.
However, Savage said, there are signatures of resource constraints in present-day simulations that are likely to exist as well in simulations in the distant future, including the imprint of an underlying lattice if one is used to model the space-time continuum.
The supercomputers performing LQC calculations essentially divide space-time into a four-dimensional grid. That allows researchers to examine what is called the strong force, one of the four fundamental forces of nature and the one that binds subatomic particles called quarks and gluons together into neutrons and protons at the core of atoms.
“If you make the simulations big enough, something like our universe should emerge,” Savage said. Then it would be a matter of looking for a “signature” in our universe that has an analog in the current small-scale simulations.
Savage and colleagues suggest that the signature could show up as a limitation in the energy of cosmic rays.
In a paper they have posted on arXiv, they say that the highest-energy cosmic rays would not travel along the edges of the lattice in the model but would travel diagonally, and they would not interact equally in all directions as they otherwise would be expected to do.
“This is the first testable signature of such an idea,” Savage said.
If such a concept turned out to be reality, it would raise other possibilities as well. For example, co-author Zohreh Davoudi suggests that if our universe is a simulation, then those running it could be running other simulations as well, essentially creating other universes parallel to our own.
“Then the question is, ‘Can you communicate with those other universes if they are running on the same platform?’” she said.
There are, of course, many caveats to this extrapolation. Foremost among them is the assumption that exponential growth of computers will continue into the future. Related to this is the possible existence of the technological Singularity, which could alter the curve in unpredictable ways.
And, of course, human extinction would terminate the exponential growth — or its simulation.
Hybrid dual-quantum dot/superconducting resonator device (credit: K. D. Petersson et al./Nature)
A team led by Princeton‘s Associate Professor of Physics Jason Petta has developed a new method that could eventually allow engineers to build a working quantum computer consisting of millions of quantum bits (qubits).
Quantum computers take advantage of the strange behaviors of subatomic particles like electrons. By harnessing electrons as they spin, scientists could use the particles to form the basis for a new type of computing.
The problem, though, is that these incredibly tiny electrons are hard to control. So far, scientists have only been able to harness extremely small numbers of them.
“The whole game at this point in quantum computing is trying to build a larger system,” said Andrew Houck, an associate professor of electrical engineering at Princeton who is part of the research team.
A cage for trapping electrons
To transfer information Petta’s team used a stream of microwave photons to analyze a pair of electrons trapped in a tiny cage called a quantum dot. The “spin state” of the electrons — information about how they are spinning — serves as the qubit, a basic unit of information.
The microwave stream allows the scientists to read that information.
“We create a cavity with mirrors on both ends — but they don’t reflect visible light, they reflect microwave radiation,” Petta said. “Then we send microwaves in one end, and we look at the microwaves as they come out the other end. The microwaves are affected by the spin states of the electrons in the cavity, and we can read that change.”
In an ordinary sense, the distances involved are very small; the entire apparatus operates over a little more than a centimeter. But on the subatomic scale, they are vast. It is like coordinating the motion of a top spinning on the moon with another on the surface of the Earth.
“It’s the most amazing thing,” said Jake Taylor, a physicist at the National Institute of Standards and Technology, who worked on the project with the Princeton team. “You have a single electron almost completely changing the properties of an inch-long electrical system.”
One challenge facing scientists is that the spins of electrons, or any other quantum particles, are incredibly delicate. Any outside influences, whether a wisp of magnetism or glimpse of light, destabilizes the electrons’ spins and introduces errors.
Over the years, scientists have developed techniques to observe spin states without disturbing them. (This year’s Nobel Prize in physics honored two scientists, Serge Haroche and David Wineland, who first demonstrated the direct observation of quantum particles.) But analyzing small numbers of spins is not enough; millions will be required to make a real quantum processor.
Making quantum dots
To make the quantum dots, the team isolated a pair of electrons on a small section of material called a “semiconductor nanowire.” Basically, that means a wire that is so thin that it can hold electrons like soda bubbles in a straw. They then created small “cages” along the wire. The cages are set up so that electrons will settle into a particular cage depending on their energy level.
This is how the Princeton team reads the spin state: electrons of similar spin will repel, while those of different spins will attract. So the team manipulates the electrons to a certain energy level and then reads their position. If they are in the same cage, they are spinning differently; if they are in different cages, the spins are the same.
The second step is to place this quantum dot inside the microwave channel, allowing the team to transfer the information about the pair’s spin state — the qubit.
Petta said the next step is to increase the reliability of the setup for a single electron pair. After that, the team plans to add more quantum dots to create more qubits. Team members are cautiously optimistic. There appear to be no insurmountable problems at this point but, as with any system, increasing complexity could lead to unforeseen difficulties.
“The methods we are using here are scalable, and we would like to use them in a larger system,” Petta said. “But to make use of the scaling, it needs to work a little better. The first step is to make better mirrors for the microwave cavity.”
Support for the research was provided by the National Science Foundation, the Alfred P. Sloan Foundation, the Packard Foundation, the Army Research Office, and the Defense Advanced Research Projects Agency Quantum Entanglement Science and Technology Program.
Stephen William Hawking, (born 8 January 1942) is a British theoretical physicist. He is known for his contributions to the fields of cosmology and quantum gravity, especially in the context of black holes. He has also achieved success with works of popular science in which he discusses his own theories and cosmology in general; these include the runaway best seller A Brief History of Time, which stayed on the British Sunday Times bestsellers list for a record-breaking 237 weeks.
Hawking's key scientific works to date have included providing, with Roger Penrose, theorems regarding singularities in the framework of general relativity, and the theoretical prediction that black holes should emit radiation, which is today known as Hawking radiation (or sometimes as bekenstein-Hawking radiation). He is a world-renowned theoretical physicist whose scientific career spans over 40 years. His books and public appearances have made him an academic celebrity. He is an Honorary Fellow of the Royal Society of Arts, and a lifetime member of the Pontifical Academy of Science. On August 12, 2009, he was awarded the Presidential Medal of Freedom, the highest civilian award in the United States.
Hawking is the Lucasian Professor of Mathematics at the University of Cambridge (but intends to retire from this post in 2009), a Fellow of Gonville and Caius College, Cambridge and the distinguished research chair at Waterloo's Perimeter Institute for Theoretical Physics.
Hawking has a neuro muscular dystrophy that is related to amyotrophic lateral sclerosis (ALS), a condition that has progressed over the years and has left him almost completely paralysed.
Research fields
Hawking's principal fields of research are theoretical cosmology and quantum gravity.
In the late 1960s, he and his Cambridge friend and colleague, Roger Penrose, applied a new, complex mathematical model they had created from Albert Einstein's general theory of relativity. This led, in 1970, to Hawking proving the first of many singularity theorems; such theorems provide a set of sufficient conditions for the existence of a singularity in space-time. This work showed that, far from being mathematical curiosities which appear only in special cases, singularities are a fairly generic feature of general relativity.
He supplied a mathematical proof, along with Brandon Carter, Werner Israel and D. Robinson, of John Wheeler's "No-Hair Theorem" – namely, that any black hole is fully described by the three properties of mass, angular momentum, and electric charge.
Hawking also suggested that, upon analysis of gamma ray emissions, after the Big Bang, primordial mini black holes were formed. With Bardeen and Carter, he proposed the four laws of black hole mechanics, drawing an analogy with thermodynamics. In 1974, he calculated that black holes should thermally create and emit subatomic particles, known today as Hawking radiation, until they exhaust their energy and evaporate.
In collaboration with Jim Hartle, Hawking developed a model in which the universe had no boundary in space-time, replacing the initial singularity of the classical Big Bang models with a region akin to the North pole: One cannot travel north of the North Pole, as there is no boundary there. While originally the no-boundary proposal predicted a closed universe, discussions with Neil Turok led to the realisation that the no-boundary proposal is also consistent with a universe which is not closed.
Hawking's many other scientific investigations have included the study of quantum cosmology, cosmic inflation, helium production in anisotropic Big Bang universes, large N cosmology, the density matrix of the universe, topology and structure of the universe, baby universes, Yang-Mills instantons and the S matrix, anti de Sitter space, quantum entanglement and entropy, the nature of space and time, including the arrow of time, spacetime foam, string theory, supergravity, Euclidean quantum gravity, the gravitational Hamiltonian, Brans-Dicke and Hoyle-Narlikar theories of gravitation, gravitational radiation, and wormholes.
At a George Washington University lecture in honour of NASA's 50th anniversary, Prof. Hawking theorised on the existence of extraterrestrial life, "primitive life is very common and intelligent life is fairly rare."
From Wikipedia
The Computer
Communication system
I communicate with a computer system. I have always used IBM compatible computers, on my wheel chair. They run from batteries under the wheel chair, although an internal battery will keep the computer running for an hour if necessary. The screen is mounted on the arm of the wheel chair where I can see it, more recent systems have the whole computer in a box on this arm. The original systems were put together for me by David Mason, of Cambridge Adaptive Communications. This company manufacture and supply a variety of products to help people with communication problems express themselves. Recently, Intel engineers designed a new computer for me powered by a Pentium II processor, which I now use.
On the computer, I run a program called Equalizer™, written by a company called Words Plus inc. A cursor moves across the upper part of the screen. I can stop it by pressing a switch in my hand. This switch is my only interface with the computer. In this way I can select words, which are printed on the lower part of the screen. When I have built up a sentence, I can send it to a speech synthesizer. I use a separate synthesizer, made by Speech+. It is the best I have heard, though it gives me an accent that has been described variously as Scandinavian, American or Scottish. I also can use Windows 98 through an interface called EZ Keys, again made by Words Plus. I am able to control the mouse with the switch through cleverly selected process from a small box shown on the desktop. I can also write text using similar menu's to those in Equalizer.
I can save what I write to disk. I write papers using a formatting program called TEX. I can write equations in words, and the program translates them into symbols, and prints them out on paper in the appropriate type. I can also give lectures. I write the lecture beforehand, and save it on disk. I can then send it to the speech synthesiser, a sentence at a time. It works quite well, and I can try out the lecture, and polish it, before I give it.
Recent Improvements
Professor Hawking is determined that he is able to keep up with the recent improvements in computer and communication technology. Below are some of the recent improvements, which have been carried out on the system within the last 12 months.
In non-wireless areas, Intel manage a 3G account for us so that Professor Hawking is able to use the internet from anywhere in the world, via a PCMCIA 3G card.
The computer has been replaced about once per year; it is currently (Jan 2009) running on a Lenovo Thinkpad T60 and the next model will have an X61 at its heart.
Upgrade to Windows XP (in around 2001)
The computer is running on Windows XP. For many years it has been impossible to upgrade beyond Windows'98, because Professor Hawking's favourite speech software, Equalizer by Words-Plus, was made in 1986, and was designed to run only on DOS based operating systems. However, Intel has kindly funded the conversion of the software to XP. This involved Words-Plus re-writing the whole program for today’s operating system.
Power
Due to Professor Hawking's active lifestyle, it is impossible to power his chair computer via the mains as he is never in one place long enough to make this practical. Thus the laptop needs to be powered by the wheelchair batteries, which are similar to car batteries, in the back of the chair.
Keep talking
It is essential that Stephen is able to make use of a telephone. He is able to use Voice over IP, or connect his chair computer directly to a telephone socket. The process works by sending digital commands from his computer instructing the phone system to dial a number, answer the phone or hang up at the end of a call.
Who's got the remote?
Stephen has a universally programmable infra-red remote control attached directly to his computer system. This enables him to operate many of the electronic items in his home, such as televisions, video recorders and music centres. He also has a radio control device which enables him to open doors and operate lights throughout his home. He is now also able to operate doors within his workplace. With the opening of the newly built Centre for Mathematical Sciences, he will be able to get about the building virtually unassisted.
From official website of Professor Stephen William Hawking, by Nicki Ley and Graduate Assistant, Sam Blackburn.
