According to quantum theory, the building blocks of matter – like electrons, nuclei and the molecules they form – can be portrayed either as waves or particles. Misconceptions feeding the idea of the empty atom can be dismantled by carefully interpreting quantum theory, which describes the physics of molecules, atoms and subatomic particles. To be fair, you will also find a reasonable share of articles debunking the idea. Google ‘atoms empty space’, and you will find tens of essays, blog posts and YouTube videos concluding that atoms are 99.9 per cent empty space. Of the 180 voters, 43 per cent answered that they mostly agreed, and 27 per cent fully agreed. While preparing this essay, I ran a poll on Twitter asking whether people agreed with Sagan’s quote above. Today, as a professional theoretical chemist, I know that Sagan’s statements failed to recognise some fundamental features of atoms and molecules. I still remember how deeply these words spoke to me when I heard them as a kid in the early 1980s. After wondering how small the nuclei are compared with the atom, Sagan concluded that ost of the mass of an atom is in its nucleus the electrons are by comparison just clouds of moving fluff. It is unclear who created this myth, but it is sure that Carl Sagan, in his classic TV series Cosmos (1980), was crucial in popularising it. The empty atom picture is likely the most repeated mistake in popular science. Atomic nuclei in a molecule are not tiny dots, and there are no empty spaces within the atom. How often have you seen such a scene or read something equivalent to it in popular science? I am sure plenty, if you are fans of this genre like me. The narrator lectures that the nucleus of an atom is tens of thousands of times smaller than the atom itself, and poetically concludes that we are made from emptiness. An initially imperceptible tiny dot grows smoothly, revealing the atomic nucleus. ![]() The camera focuses on a single atom within the strand, dives into a frenetic cloud of rocketing particles, crosses it, and leaves us in oppressive darkness. In short: the uncertainty principle describes a trade-off between two complementary properties, such as speed and position.The camera zooms in on the person’s arm to reveal the cells, then a cell nucleus. Conversely, if we wanted to know the exact position of one peak of a wave, we would have to monitor just one small section of the wave and would lose information about its speed. The location is spread out among the peaks and troughs. The more peaks and troughs that pass by, the more accurately we would know the speed of a wave-but the less we would be able to say about its position. To measure its speed, we would monitor the passage of multiple peaks and troughs. To understand the general idea behind the uncertainty principle, think of a ripple in a pond. ![]() Quantum objects are special because they all exhibit wave-like properties by the very nature of quantum theory. Though the Heisenberg uncertainty principle is famously known in quantum physics, a similar uncertainty principle also applies to problems in pure math and classical physics-basically, any object with wave-like properties will be affected by this principle. ![]() In other words, if we could shrink a tortoise down to the size of an electron, we would only be able to precisely calculate its speed or its location, not both at the same time. ![]() Formulated by the German physicist and Nobel laureate Werner Heisenberg in 1927, the uncertainty principle states that we cannot know both the position and speed of a particle, such as a photon or electron, with perfect accuracy the more we nail down the particle's position, the less we know about its speed and vice versa.
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