Fundamentally, the Universe is made of information
Or at least, that’s the idea more and more theorists are pursuing as they search for better descriptions of the laws that govern our Universe. Could particles, energy, space and time, even the entire multiverse, really be just a bunch of bits?
Information has multiple meanings: facts and knowledge; a news message; language; one of two opposite states (yes-no, one-zero, on-off); quantum entangled states; the power to explain and possibly to cause.
"Nobody knows what information really is," says theoretical physicist Erik Verlinde of the University of Amsterdam in the Netherlands. "The only thing we're very good at is count it."
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Verlinde is part of a growing group of physicists who believe that the Universe is made of information. Late last year, he took a further step in a controversial theory, known as entropic gravity, in which he reformulates gravity as caused by the rearrangement of that information.
Think of an ocean wave crashing on the shore, says Seth Lloyd, an MIT professor specializing in quantum information. Every molecule of water — by its configuration, by its rotation, by its position relative to other water molecules — carries with it bits of information. And then whenever any two water molecules collide, they change by processing those bits of information. Combine countless molecules interacting with one another, and you have a wave.
It seems easy to erase information, like pages of text or strings of bits, by simply pressing a button on a keyboard. But according to a principle proposed in 1961 by physicist Rolf Landauer, the act of destroying information has a tangible physical impact. Deleting information is associated with an increase in entropy, resulting in the release of a certain amount of heat for each erased bit.
Entropy is used by physicists to describe the 'disorder' of a system. A bucket full of red Lego, for instance, has a high entropy. Assemble those same blocks into a Lego castle though, and you've slashed entropy.
While Landauer's principle has recently been verified for those cases that follow the laws of classical physics, the question remains whether it also applies to quantum mechanical systems. A new study published last year found clues that the principle does indeed hold in the quantum landscape, and provides a bridge between physics and information theory.
To verify Landauer’s principle, the authors of the study used a system of three qubits — the quantum version of the bits found in a typical computer — made from trifluoroiodoethylene, a molecule which has three fluorine atoms. The nuclei of these three fluorine atoms have a quantum property called 'spin', which can be clockwise or counterclockwise, serving the same purpose as a 0 or 1 for a standard bit.
Making measurements of quantum systems is tricky, because in a quantum world, every time you measure the system, the interaction changes it. Therefore, the researchers used the third qubit as a work-around to measure the heat generated by erasing information from one of the other qubits. Looking at the average of multiple measurements, the researchers found that heat was generated as expected from Landauer's principle.
"However," said Lucas Céleri of the Federal University of Goiás in Brazil, a leader of the research team, "I can tell you how to calculate the amount of information in a system, but not what it is. We have no way to define the nature of information".
Nevertheless, quantum information is becoming more and more important in modern physics. The qubit used in quantum information theory is a medium that is not limited to only zero or one, but can also be zero and one at the same time, a phenomenon known as superposition. Qubits also have a strange property called entanglement, which means that they can be connected to each other, regardless of their distance.
It's mysterious behaviors like this that give a quantum computer its revolutionary features. It can also be used to generate genuinely random numbers suitable for encryption keys. Quantum cryptography is already being used commercially for some bank transfers and other highly secure transmissions.
Quantum information may even play a decisive role in the Universe. As it can intertwine and stick together into chains of entangeled ones and zeros, quantum information remains connected in a ghostly way, even over dazzling cosmic distances. That masterful web of entangled information might well be what underlies the entire Universe.
Late physicist John Archibald Wheeler characterized the idea of information as the foundation of reality as "It from bit", — "it" referring to all the stuff of the Universe and "bit" meaning information. So is that what information is, the spin of an electron coding for a one or a zero?
"No," says professor Verlinde. "The idea is that the electron itself has also been rebuilt from quantum information. You shouldn't think of information as a thing. Rather, it's what all things emerge from".
Imagine trying to build the ultimate hard drive, one that holds the maximum amount of information allowed by physics. Why should physics place a limit on the information storage capacity of this hypothetical hard drive? From a purely classical perspective, there is no reason why you couldn't store an infinite amount of information. But when we add quantum mechanics to the mix, we introduce fundamental limits on the accuracy of our measurements. These limits cause entropy to max out at about 1069 bits per square meter.
If you tried to pack information more densely than that, your hard drive would collapse into a black hole. That’s not just a whimsical footnote. Black holes, it turns out, are the universe’s very best information repositories, although they don’t make very practical hard drives.
In the 1970s, physicists Stephen Hawking and Jacob Bekenstein discovered that there’s something odd about the way a black hole grows. When an object is consumed by a black hole, all information about that object appears to be lost forever. At the same time the event horizon, the limit beyond which you can no longer escape the overwhelming attraction of the black hole, widens a tiny bit.
For every bit of information that's thrown into a black hole, the surface of its horizon grows with a square Planck length, the smallest possible length in the cosmos according to physicists. This means that every bit that disappears into a black hole, can be found at the black hole's two dimensional surface. Altough 'unreadable' in any practical sense, the information isn't really lost.
This is bizarre, as you would expect the amount of information you can pack into any object, like a book or a hard drive, to grow with the three-dimensional volume of the object, not its surface area. It has led some theorists to view the Universe as a projection of information encoded on some distant cosmic boundary. Where this boundary lies and how the projection occurs are still open questions, but these theorists argue that our reality may be, in essence, a hologram, something known as the 'holographic principle'.
Physicist Stephen Wolfram, founder of mathematical search engine Wolfram Alpha, posits that simple rules govern the behavior of space and time and generate what we see in nature. Although simple rules may be more fundamental than mathematics, he says, we should still recognize the difference between models and reality. "We shouldn't imagine that the actual way that the Universe works is by the operation of similar programs running in each particle," says Wolfram.
It might be possible to imagine a universe barren of matter and energy. After all, specifying that our Universe is furnished with both tells something about it and distinguishes it from other possible universes. But it's very hard to even conceive of a universe without information.