Even something as simple as a single atom exhibits quantum uncertainty. If you ask the question, “where is any particular electron at a moment in time?” you can only know the answer to a certain precision, never to arbitrary accuracy. (Credit: agsandrew / Adobe Stock and remotevfx / Adobe Stock)

Ask Ethan: Where does quantum uncertainty come from?

No matter how good our measurement devices get, certain quantum properties always possess an inherent uncertainty. Can we figure out why?

Ethan Siegel
9 min readSep 23, 2022

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Perhaps the most bizarre property we’ve discovered about the Universe is that our physical reality doesn’t seem to be governed by purely deterministic laws. Instead, at a fundamental, quantum level, the laws of physics are only probabilistic: you can compute the likelihood of the possible experimental outcomes that will occur, but only by measuring the quantity in question can you truly determine what your particular system is doing at that instant in time. Furthermore, the very act of measuring/observing certain quantities leads to an increased uncertainty in certain related properties: what physicists call conjugate variables.

While many have put forth the idea that this uncertainty and indeterminism might only be apparent, and could be due to some unseen “hidden” variables that truly are deterministic, we have yet to find a mechanism that allows us to successfully predict any quantum outcomes. But could the quantum fields inherent to space be the ultimate culprit? That’s this week’s question from Paul Marinaccio, who wants to know:

“I’ve been wondering for a long time: does…

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Ethan Siegel

The Universe is: Expanding, cooling, and dark. It starts with a bang! #Cosmology Science writer, astrophysicist, science communicator & NASA columnist.