Ages 8–12 · about 6 minutes

Can You Get Energy From Nothing?

If empty space is full of energy, can we plug into it?

Do this first · Try this at home

Keep an energy ledger

Start with your hands. The reading makes far more sense afterwards.

You need: Paper and a pencil; no real device

Tick each step as you do it

Draw four boxes labelled starting store, useful output, warmth leaving and remaining store.
Record ten units in the first box. In the other boxes record seven, two and one respectively.
Check that the last three numbers total ten. Work out how much must enter to restore the remaining store to ten.

0 of 3 steps done

What should I notice?

Notice: Seven plus two plus one equals ten. Restoring the store from one to ten needs nine more units. These invented numbers show bookkeeping, not a measured device.

Now read on to find out why it happens.

The big idea

Count stored energy and every transfer in and out, including the energy needed to start again.

ground state: A system's lowest-energy state for a fixed arrangement.
photon: One packet of light energy, including invisible microwave light.
ledger: A record of energy stored, entering and leaving.
cycle: A process that returns the whole system to its starting state.

A lamp transfers energy into light and warmth. A battery can supply energy it already stores. To understand any device, count that stored energy as well as everything entering and leaving it.

A child in pyjamas and a striped cat look at a small sealed box glowing at its seams on a kitchen table, next to a lamp shining with no cord. — An imagined energy box beside a lamp. The glow is an illustration, not a measurement or a diagram of the experiment below.

Follow every transfer

Starting energy + energy entering = ending energy + energy leaving.

This ledger says that energy changes form or moves somewhere else. Warmth leaving a device counts, even when you wanted only light. Count each transfer once. A battery that ends with less energy has helped pay for the output.

The quantum vacuum is a field's ground state for a fixed arrangement. Its fluctuations have physical effects. That does not make it a battery you can simply drain without changing anything else.

Light from a changing boundary

In 2011, Christopher Wilson and colleagues reported microwave photons from a superconducting circuit. Microwaves are light our eyes cannot see; a photon is one packet of its energy.

They used a device called a SQUID to change how the circuit reflected electromagnetic waves. A rapidly changing magnetic signal drove this electrical boundary. No metal mirror needed to race back and forth.

The team measured radiation and correlations between pairs of frequencies, supporting the dynamical Casimir effect. The drive supplies energy to this process. The result is not a lamp powered without an input.

Include the return journey

Casimir's calculation predicts attraction between ideal parallel conducting plates. Their interaction energy changes with their separation, so approaching plates can do work.

Separating them again requires work. In an ideal reversible return over the same path, that cost matches the work gained; losses add costs. A complete cycle restores the whole starting state, not just the position of a switch.

Check the claim

For a proposed energy device, include its drive, cooling, surroundings and changing stores in the account. Which missing entry could make output look larger than the input you counted?

Sources: NASA Glenn, First Law: Conservation of Energy; Wilson and colleagues, dynamical Casimir experiment (2011), 10.1038/nature10561; Casimir, attraction between perfectly conducting plates (1948).