Space and Physicsphysics

Why Do Christmas Lights Get Tangled? Blame The Laws Of The Universe


Dr. Alfredo Carpineti

Senior Staff Writer & Space Correspondent

clockDec 20 2021, 10:57 UTC
Image Credit: Oleinik Iuliia/

What happens in our attics and our closets with the Christmas lights depends on the important laws of the cosmos. Image Credit: Oleinik Iuliia/

Aristotle claimed that (on Earth) nature abhors a vacuum, but now we know better: what Nature really hates is order, and do not think for one second that Mother Nature takes a break during the holidays. Even at Christmas, the laws of physics are there to derail our best-laid plans.  


Take, for example, Christmas lights. You put them away neatly last January, and when you unpack them in December what do you see? Knots! You might want to imagine there are Christmas goblins tying up the lights into a tangled mess. That scenario is much preferable to the truth – the second law of thermodynamics has struck again.  

That inescapable (or is it?) law of physics deals with a quantity known as entropy, the measure of the disorder of a system. In an isolated system, like our Universe, the entropy always increases. So, systems tend to move towards chaos. Things break down, we age, and Christmas lights – even when neatly packed – end up tangled together. However, the knotting is not a straightforward event ruled by chaos alone. Scientists have discovered some of the complex mathematics behind it. 

In particular, the theory of strings that get knotted when shaken about was investigated in a piece of research in the Proceedings of the National Academy of Sciences back in 2007. The paper, titled Spontaneous Knotting of an Agitated String, led the two authors, Dorian Raymer and Douglas Smith, to win the Ig Nobel Prize in Physics in 2008.  

The paper examined what happens when you put a string in a box and the box is rotated. They looked at strings of varying length, with boxes of different sizes rotating at different speeds and with different numbers of rotations. In the 3,415 trials they conducted, they found complex knots being formed in the string – sometimes even in just a few seconds. Key factors are a minimum length (46 centimeters/18.124 inches) and enough space to rattle about in the box. 


What is fascinating in the study is that mathematically, the motions were not governed by a process made of random steps. As we said, it was not just chaos, although randomness was still an important factor in the formation of knots. The peculiar behavior of strings in a box doesn't just concern mathematical investigations or Christmas lights getting tangled. It has implications in the knotting of genetic material within certain viruses, but also on the fact that the umbilical cord does not knot easily.  

So when you put away your lights, remember the profound connections to the deep, the chaotic, the complex, and the baffling laws that govern our universe.  

Space and Physicsphysics
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