What is quantum foam?

© 2025 Kieron Conway - All rights reserved.

In modern physics, we know that empty space isn’t really empty. Even in a perfect vacuum, tiny bursts of energy are constantly being created and disappearing. These are called quantum fluctuations, and they give space a kind of fizzy, restless background.

Many scientists use the nickname “quantum foam” to describe this ever-changing activity.

If you recall, there is energy at every point in the vacuum of space and Heisenberg's uncertainty principle allows quantum fluctuations to occur by borrowing from this inherent energy. This borrowed energy has to be paid back in a time period governed by the the relationship;

ΔE x ΔT < ħ/2

Where ΔE is the amount of energy borrowed, ΔT is the time period over which the energy is borrowed and ħ is Planck's constant, that you met in Part 1 associated with the quantum of energy.

We talk about virtual particles coming into existence, which are a mathematical representation of the many complex reactions that can occur. We never see these virtual particles as the corresponding excitations are very low-level and come and go at random over very short durations, governed by the above equation.

Has Quantum Foam Been Detected?

We can’t see quantum foam directly, but one experiment shows its effects very clearly: the Casimir effect, predicted in 1948 by Dutch physicist Hendrik Casimir.

He imagined placing two uncharged metal plates extremely close together, only a tiny fraction of a millimetre apart. When this is done in real experiments, the plates mysteriously push themselves together. A tiny force is exerted by quantum foam pushing the plates together.

Why does this happen?

It all comes down to the strange behaviour of the vacuum:

1. Outside the plates, quantum fluctuations of all wavelengths, both long and short, are free to exist.

2. Between the plates, the space is so narrow that long-wavelength fluctuations can’t fit, only the short ones are created where the wavelengths are shorter than the gap between the plates.

3. This creates an imbalance. There’s more fluctuating energy outside the plates, where all wavelengths can be generated, than between them and that difference produces a small but measurable inward push.

   
   

This imbalance is depicted in the diagram at the start of the article.

How strong is this force?

It's Surprisingly strong! If the plates are separated by about the width of 100 atoms, the pressure between them can reach roughly one atmosphere, which is about the same pressure that the air exerts on you at sea level.

That’s astonishing for a force coming from what we normally call “empty” space and the experiment with the two plates has been successfully conducted in a vacuum chamber, indicating that it's nothing to do with the atoms of the air, in case that's what you might be thinking.

Are there other phenomena that show quantum foam exists?

In 1947, Willis Lamb and Robert Retherford discovered a tiny difference in the electron orbital of hydrogen that had not been predicted by earlier theories. The minute difference in energies of 2S and 2P orbitals is due to the interaction between the electron and photon quantum-fluctuations of the electromagnetic field.

Interaction between electrons and virtual photons also explains why electrons readily drop from excited energy levels to lower levels. In classical physics, the electron should remain in its excited state indefinitely. In quantum theory, interaction between the electron and virtual photons provides the necessary “nudge” for the transition to occur.

So does quantum foam exist?

Experiments like the Casimir effect and detailed measurements of atomic orbital energies, show that the quantum fields of the vacuum are full of energetic activity as opposed to complete inactivity. While scientists use the term “quantum foam” in different ways, the essential idea is the same: the vacuum of space itself is alive with tiny fluctuations and we can measure their effects, even if we can't see the cause.

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