Is Information Physical?

Information is not stored in empty air

Rolf Landauer’s central point is that information does not exist only as abstract symbols. Real computation uses physical degrees of freedom—charge, magnetization, light—and those devices obey physical law.

‘Information is physical’ means that writing, erasing, and transmitting information require physical implementation. It is not simply the claim that information and matter are identical.

• Rolf Landauer, Information is Physical (1991)

  Landauer’s account of physical constraints on computation and information processing.

Does every computation carry the same cost?

Landauer’s principle is often compressed into ‘all computation costs energy,’ but its sharper focus is logically irreversible operations, especially erasure. Combining several possible states into one creates a thermodynamic cost associated with lost information.

It does not say that every logical step must dissipate the same minimum energy. Reversible computation must be distinguished from erasure.

Physical information and the substance of the world

The physicality of storage and erasure is significant, but it does not prove that information is the substance of the universe. ‘Information is physically implemented’ and ‘physics arises from information’ point in different directions.

The first is an experimentally grounded principle of computation; the second is a broader ontological program. Keeping them separate is central to this chapter.

A difference that can be recorded

Information requires distinguishable states. To read reality as information, we should first ask what is distinguished, how it is stably recorded, and which physical laws permit its transformation.