is the universe just a simulation?

are we…real?
but what does "real" mean? …

Physicists May Have Evidence Universe Is A Computer Simulation

November 10, 2012
Michael Rundle
Huffington Post, UK

Physicists say they may have evidence that the universe is a computer simulation.

How? They made a computer simulation of the universe. And it looks sort of like us.

A long-proposed thought experiment, put forward by both philosophers and popular culture, points out that any civilisation of sufficient size and intelligence would eventually create a simulation universe if such a thing were possible.

And since there would therefore be many more simulations (within simulations, within simulations) than real universes, it is therefore more likely than not that our world is artificial.

Now a team of researchers at the University of Bonn in Germany led by Silas Beane say they have evidence this may be true.

In a paper named 'Constraints on the Universe as a Numerical Simulation', they point out that current simulations of the universe – which do exist, but which are extremely weak and small – naturally put limits on physical laws.

Technology Review explains that "the problem with all simulations is that the laws of physics, which appear continuous, have to be superimposed onto a discrete three dimensional lattice which advances in steps of time."

What that basically means is that by just being a simulation, the computer would put limits on, for instance, the energy that particles can have within the program.

These limits would be experienced by those living within the sim – and as it turns out, something which looks just like these limits do in fact exist.

For instance, something known as the Greisen-Zatsepin-Kuzmin, or GZK cut off, is an apparent boundary of the energy that cosmic ray particles can have. This is caused by interaction with cosmic background radiation. But Beane and co's paper argues that the pattern of this rule mirrors what you might expect from a computer simulation.

Naturally, at this point the science becomes pretty tricky to wade through – and we would advise you read the paper itself to try and get the full detail of the idea.

But the basic impression is an intriguing one.

Like a prisoner in a pitch-black cell, we may never be able to see the 'walls' of our prison — but through physics we may be able to reach out and touch them.

Do we live in a computer simulation? UW researchers say idea can be tested

December 10, 2012
Vince Stricherz
News and Information
University of Washington
Seattle, Washington, USA

A decade ago, a British philosopher put forth the notion that the universe we live in might in fact be a computer simulation run by our descendants. While that seems far-fetched, perhaps even incomprehensible, a team of physicists at the University of Washington has come up with a potential test to see if the idea holds water.

The concept that current humanity could possibly be living in a computer simulation comes from a 2003 paper published in Philosophical Quarterly by Nick Bostrom, a philosophy professor at the University of Oxford. In the paper, he argued that at least one of three possibilities is true:
– The human species is likely to go extinct before reaching a “posthuman” stage.
– Any posthuman civilization is very unlikely to run a significant number of simulations of its evolutionary history.
– We are almost certainly living in a computer simulation.

He also held that “the belief that there is a significant chance that we will one day become posthumans who run ancestor simulations is false, unless we are currently living in a simulation.”

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 the UW team has suggested tests that can be performed now, or in the near future, that are sensitive to constraints imposed on future simulations by limited resources.

Currently, supercomputers using a technique called lattice quantum chromodynamics 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, 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 lattice quantum chromodynamics 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 Silas Beane of the University of New Hampshire, who collaborated while at the UW’s Institute for Nuclear Theory, and Zohreh Davoudi, a UW physics graduate student, suggest that the signature could show up as a limitation in the energy of cosmic rays.

In a paper they have posted on arXiv, an online archive for preprints of scientific papers in a number of fields, including physics, 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, 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.

Martin Savage

The conical (red) surface shows the relationship between energy and momentum in special relativity, a fundamental theory concerning space and time developed by Albert Einstein, and is the expected result if our universe is not a simulation. The flat (blue) surface illustrates the relationship between energy and momentum that would be expected if the universe is a simulation with an underlying cubic lattice

MORE INFORMATION:

The Measurement That Would Reveal The Universe As A Computer Simulation
If the cosmos is a numerical simulation, there ought to be clues in the spectrum of high energy cosmic rays, say theorists

From MIT Technology Review
October 10, 2012

One of modern physics’ most cherished ideas is quantum chromodynamics, the theory that describes the strong nuclear force, how it binds quarks and gluons into protons and neutrons, how these form nuclei that themselves interact. This is the universe at its most fundamental.

So an interesting pursuit is to simulate quantum chromodynamics on a computer to see what kind of complexity arises. The promise is that simulating physics on such a fundamental level is more or less equivalent to simulating the universe itself.

There are one or two challenges of course. The physics is mind-bogglingly complex and operates on a vanishingly small scale. So even using the world’s most powerful supercomputers, physicists have only managed to simulate tiny corners of the cosmos just a few femtometers across. (A femtometer is 10^-15 metres.)

That may not sound like much but the significant point is that the simulation is essentially indistinguishable from the real thing (at least as far as we understand it).

It’s not hard to imagine that Moore’s Law-type progress will allow physicists to simulate significantly larger regions of space. A region just a few micrometres across could encapsulate the entire workings of a human cell.

Again, the behaviour of this human cell would be indistinguishable from the real thing.

It’s this kind of thinking that forces physicists to consider the possibility that our entire cosmos could be running on a vastly powerful computer. If so, is there any way we could ever know?

Today, we get an answer of sorts from Silas Beane, at the University of Bonn in Germany, and a few pals. They say there is a way to see evidence that we are being simulated, at least in certain scenarios.

First, some background. The problem with all simulations is that the laws of physics, which appear continuous, have to be superimposed onto a discrete three dimensional lattice which advances in steps of time.

The question that Beane and co ask is whether the lattice spacing imposes any kind of limitation on the physical processes we see in the universe. They examine, in particular, high energy processes, which probe smaller regions of space as they get more energetic

What they find is interesting. They say that the lattice spacing imposes a fundamental limit on the energy that particles can have. That’s because nothing can exist that is smaller than the lattice itself.

So if our cosmos is merely a simulation, there ought to be a cut off in the spectrum of high energy particles.

It turns out there is exactly this kind of cut off in the energy of cosmic ray particles, a limit known as the Greisen–Zatsepin–Kuzmin or GZK cut off.

This cut-off has been well studied and comes about because high energy particles interact with the cosmic microwave background and so lose energy as they travel long distances.

But Beane and co calculate that the lattice spacing imposes some additional features on the spectrum. “The most striking feature…is that the angular distribution of the highest energy components would exhibit cubic symmetry in the rest frame of the lattice, deviating significantly from isotropy,” they say.

In other words, the cosmic rays would travel preferentially along the axes of the lattice, so we wouldn’t see them equally in all directions.

That’s a measurement we could do now with current technology. Finding the effect would be equivalent to being able to to ‘see’ the orientation of lattice on which our universe is simulated.

That’s cool, mind-blowing even. But the calculations by Beane and co are not without some important caveats. One problem is that the computer lattice may be constructed in an entirely different way to the one envisaged by these guys.

Another is that this effect is only measurable if the lattice cut off is the same as the GZK cut off. This occurs when the lattice spacing is about 10^-12 femtometers. If the spacing is significantly smaller than that, we’ll see nothing.

Nevertheless, it’s surely worth looking for, if only to rule out the possibility that we’re part of a simulation of this particular kind but secretly in the hope that we’ll find good evidence of our robotic overlords once and for all.

Ref: arxiv.org/abs/1210.1847: Constraints on the Universe as a Numerical Simulation
http://arxiv.org/pdf/1210.1847v2.pdf
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FURTHER READING suggested by TLA:

Probably the best website on everything related to quantum physics, relativity et al. created by Andrew Thomas (who, by the way, holds a doctorate in physics from the UK.) The webpage in the URL discusses this topic very well and quite comprehensive:

http://www.ipod.org.uk/reality/reality_universe_computer.asp

A fun game on cell automaton, the so-called "game of life":

http://www.bitstorm.org/gameoflife/

Again, the original scientific article mentioned in the above pieces:

http://arxiv.org/pdf/1210.1847v2.pdf