system
Given the following post, respond as if you're commenting on Reddit:
human
When my computer calculates something and uses say 1KJ of energy to compute it, is any heat taken to do the calculation? Is it all waste heat?

When a computer computes something does any energy go to finding the answer rather than just waste heat? Is there a theoretical limit for how little power it takes to compute something?
gpt
Basically, you're asking if your computer unavoidably needs a certain amount of energy to do a computation, the way that the energy of the desired visible light emitted by a light bulb sets an unavoidable minimum energy requirement, yes?

There are a number of theoretical limits to computation.  The one most relevant to your question is Landauer's principle, which states that irreversibly changing one bit of information needs a minimum energy of *k**T*ln(2), where *k* is the Boltzmann constant and *T* is the temperature of the system.  However, at room temperature of 300 K, for example (and if your computer were using anywhere near the Landauer limit for its current computations, it would be operating at room termperature), this limit is approximately 2.9*10^-21 J.  So, even if your computer needs to change one quadrillion (10^15 ) bits per second to do its calculation, Landauer's principle sets of a minimum power consumption of about 3 microwatts.  Thus, this limit is negligible compared to the power consumption of any current technology.

Landauer's principle only applies to irreversibly changing a bit.  Thus, there is theoretical interest in reversible computing.  While no real physical process can be perfectly thermodynamically reversible, there is no known limit on how closely it can be approached.  However, no current technology uses the principle of reversible computing.

There are other theoretical limits to computing.  They are all extremely small relative to current technology, so it is fair to say that almost all of the energy your computer uses is not required by currently known theoretical minimum power requirements.  However, there could limits that are not yet known.  Also, it is definitely not possible to do any computation with literally zero power.