The Hidden Reality: Parallel Universes and the Deep Laws of the Cosmos

by Brian Greene

Universes, Computers, and Mathematical Reality

The Simulated and the Ultimate Multiverses

To Create a Universe

The essential conclusion is that as an inflaton-filled region rapidly grows, the inflaton extracts energy from the gravitational field’s inexhaustible resources, resulting in the region’s energy rapidly growing too. And because the inflaton field supplies the energy that’s converted into ordinary matter, inflationary cosmology—unlike the big bang model—does not need to posit the raw material for generating planets, stars, and galaxies. Gravity is matter’s sugar daddy.

The Stuff of Thought

How do you know you’re not hooked into the Matrix?

Experience is dictated by brain processes, not by what activates those processes.

Simulated Universes

Are You Living in a Simulation?

Seeing Beyond a Simulation

The Library of Babel

Any multiverse that’s ever been or ever will be proposed is itself composed of possible universes, and will therefore be part of this mega-conglomerate, which I’ll call the Ultimate Multiverse. Within this framework, if you ask why our universe is governed by the laws our research reveals, the answer harks back to anthropics: there are other universes out there, all possible universes in fact, and we inhabit the one we do because it’s among those that support our form of life. In the other universes where we could live—of which there are many since, among other things, we can certainly survive sufficiently tiny changes to the various fundamental parameters of physics—there are people, much like us, asking the same question. And the same answer applies equally well to them. The point is that the attribute of existence affords a universe no special status, because in the Ultimate Multiverse all possible universes do exist. The question of why one set of laws describes a real universe—ours—while all others are sterile abstractions evaporates. There are no sterile laws. All sets of laws describe real universes.

Total nothingness, from our familiar vantage point of somethingness, entails the most profound loss. But because nothing also seems so vastly simpler than something—no laws at work, no matter at play, no space to inhabit, no time to unfurl—Leibniz’s question strikes many as right on the mark. Why isn’t there nothingness? Nothingness would have been decidedly elegant.

In the Ultimate Multiverse, a universe consisting of nothing does exist.

Nozick’s answer to Leibniz, then, is that in the Ultimate Multiverse there is no imbalance between something and nothing that calls out for explanation.

Multiverse Rationalization

Max Tegmark of the Massachusetts Institute of Technology, who has been a strong promoter of the Ultimate Multiverse (which he has called the Mathematical Universe Hypothesis), justifies this view through a related consideration. The deepest description of the universe should not require concepts whose meaning relies on human experience or interpretation. Reality transcends our existence and so shouldn’t, in any fundamental way, depend on ideas of our making. Tegmark’s view is that mathematics—thought of as collections of operations (like addition) that act on abstract sets of objects (like the integers), yielding various relations between them (like 1 + 2 = 3)—is precisely the language for expressing statements that shed human contagion. But what, then, could possibly distinguish a body of mathematics from the universe it depicts? Tegmark argues that the answer is nothing.

There’s no switch that turns math “on.” Mathematical existence is synonymous with physical existence.

Simulating Babel

The Roots of Reality

CHAPTER 11

The Limits of Inquiry

Multiverses and the Future

Table 11.1 Summary of Various Versions of Parallel Universes

PARALLEL UNIVERSE PROPOSAL: Quilted Multiverse

DESCRIPTION: Conditions in an infinite universe necessarily repeat across space, ...

PARALLEL UNIVERSE PROPOSAL: Inflation...

EXPLANATION: Eternal cosmological inflation yields an enormous network of bubble universes, of whi...

PARALLEL UNIVERSE PROPOSAL: Bran...

EXPLANATION: In string/M-theory’s braneworld scenario, our universe exists on one three-dimensional brane, which floats in a higher-dimensional expanse potentially popul...

PARALLEL UNIVERSE PROPOSAL: Cycli...

EXPLANATION: Collisions between braneworlds can manifest as big bang-like beginnings, yielding univer...

PARALLEL UNIVERSE PROPOSAL: Landsca...

EXPLANATION: By combing inflationary cosmology and string theory, the many different shapes for string theory’s extra dimensions give ri...

PARALLEL UNIVERSE PROPOSAL: Quant...

EXPLANATION: Quantum mechanics suggests that every possibility embodied in its probability waves is realized in one of a v...

PARALLEL UNIVERSE PROPOSAL: Holograph...

EXPLANATION: The holographic principle asserts that our universe is exactly mirrored by phenomena taking place on a distant bounding surface, a ...

PARALLEL UNIVERSE PROPOSAL: Simulat...

EXPLANATION: Technological leaps suggest that simulated universes may...

PARALLEL UNIVERSE PROPOSAL: Ultima...

EXPLANATION: The principle of fecundity asserts that every possible universe is a real universe, thereby obviating the question of why one possibility—ours—is special. These universe...

Is the Copernican Pattern Fundamental?

Perhaps future discoveries will cast a different light on the series of Copernican corrections. But from our current vantage point, the more we understand, the less central we appear.

Can Scientific Theories that Invoke a Multiverse Be Tested?

Can We Test the Multiverse Theories We’ve Encountered?

When scientific proposals are brought forward, they are not judged by hunches or gut feelings. Only one standard is relevant: a proposal’s ability to explain or predict experimental data and astronomical observations.

How Does a Multiverse Affect the Nature of Scientific Explanation?

Should We Believe Mathematics?

Nobel laureate Steven Weinberg once wrote, “Our mistake is not that we take our theories too seriously, but that we do not take them seriously enough. It is always hard to realize that these numbers and equations we play with at our desks have something to do with the real world.”