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Information is physical
1961· Idea
ProvenTested many times; part of working physics.
The idea that information is not abstract: every bit is stored in some physical thing, and handling it obeys the laws of physics.
See it on the Science map →How it works
In 1961 IBM physicist Rolf Landauer showed that erasing one bit of information must release a tiny, fixed minimum of heat. So information has an energy cost, like any physical stuff. Wiping a memory clean is not free; it pushes disorder (entropy) out into the surroundings. Landauer summed it up later in a 1991 paper titled "Information is physical." The idea also settled Maxwell's demon, an 1867 puzzle about a tiny being that seemed to beat the second law.
Why it matters
It turned information into something physics can count and conserve. That is why losing information in a black hole became a crisis, and why physicists now ask whether information is the most basic ingredient.
Think of it like
A ledger entry is not free-floating: it is ink on paper or charge on a chip. Shredding the records still costs energy and leaves waste behind.
How we know
Charles Bennett used it in 1982 to resolve Maxwell's demon. In 2012 Bérut and colleagues (Nature) erased a single bit stored in a trapped glass bead and measured heat approaching Landauer's minimum.
Still a mystery
Whether information is merely carried by matter, or is somehow more basic than matter, is unsettled and partly philosophy.
Connections (5)
▸Entropy: disorder always grows is really missing information, linking to Information is physicalProven
The relationship
Entropy measures how many microscopic arrangements fit what we see in bulk. That is the same as how much information we lack about the exact arrangement. Treating entropy as missing information means information must obey thermodynamics too: erasing a bit raises the entropy of the surroundings, which is exactly Landauer's rule that information is physical.
How the link was found
Ludwig Boltzmann's 1870s entropy formula and Claude Shannon's 1948 information formula turned out to match. Leo Szilard (1929) and Rolf Landauer (1961) connected them to heat, and Charles Bennett (1982) used the link to defeat Maxwell's demon.
Why it's proven
The math is exact. In 2012 Bérut and colleagues measured the heat from erasing one bit, approaching Landauer's minimum. Earlier, in 2010, Toyabe and colleagues converted information into usable work in a lab.
Open questions and mysteries
Whether entropy is purely about our knowledge or an objective property of the world is still argued by philosophers of physics.
▸Information is physical makes losing it a crisis in The black-hole information paradoxOpen question
The relationship
If information were just an abstract description, losing it inside a black hole might not matter. But information is physical, and quantum theory requires that it is never truly destroyed, only scrambled. So Hawking's claim that evaporating black holes erase information threatened a core law of physics, not a bookkeeping detail.
How the link was found
Stephen Hawking argued in 1976 that black holes destroy information. Gerard 't Hooft and Leonard Susskind led the pushback through the 1980s-90s, treating information conservation as non-negotiable.
Is it proven?
Information conservation, called unitarity, holds in every quantum experiment ever done. Landauer's principle, measured in 2012, confirms information carries physical cost. Black holes themselves have not been tested.
Open questions and mysteries
Exactly how information escapes an evaporating black hole, and in what form, is still being worked out.
▸Information is physical leads to "It from bit"Philosophy
The relationship
Landauer showed that information always lives in physical stuff. Wheeler flipped the direction: maybe physical stuff ultimately comes from information. The first claim is measured physics; the second is a philosophical extension that treats bits, not particles, as the basic ingredient.
How the link was found
John Wheeler made the leap in 1989, drawing on Shannon's information theory, Landauer's work and quantum measurement.
Is it proven?
The first direction is proven by experiments such as the 2012 measurement of Landauer's limit. The reverse direction is unproven philosophy.
Open questions and mysteries
Can bits exist without something to be bits of? That chicken-and-egg question has no settled answer.
▸Information theory (Shannon) gave the "bit" to Information is physicalProven
The relationship
Shannon gave a precise measure of information, the bit, and a formula for its uncertainty that matched thermodynamic entropy. With information quantified, physicists could ask what processing it costs. Landauer answered: erasing one bit must release a minimum amount of heat, tying the bit to energy.
How the link was found
Claude Shannon at Bell Labs in 1948; John Tukey coined the word "bit," which Shannon popularized. Rolf Landauer at IBM made the physical link in 1961.
Why it's proven
Landauer's limit was measured in 2012 by Bérut and colleagues. Shannon's theory underlies every working communication system.
Open questions and mysteries
Whether Shannon's information and physical entropy are truly identical or just share a formula is still discussed.
▸Jacob Bekenstein tied black holes to Information is physicalWell supported
The relationship
Bekenstein argued that a black hole must have entropy, proportional to its horizon area, or else throwing hot gas into one would destroy entropy and break thermodynamics. Entropy here means hidden information. So information has a physical home and a maximum density, a concrete case of information being physical.
How the link was found
Jacob Bekenstein, as John Wheeler's graduate student at Princeton, in 1972-73. He later proposed the Bekenstein bound (1981) on information in any region.
Is it proven?
Stephen Hawking, initially skeptical, confirmed it in 1974 by showing black holes radiate with a temperature. Hawking radiation has not been observed directly.
Open questions and mysteries
What microscopic states make up black-hole entropy in our universe is unknown, though string theory counted them for special cases in 1996.