Wednesday, July 30, 2014

Seeing the effects of relativity with the naked eye

Our natural tendency is to think that to see the effects of Einstein's special theory of relativity you have to be travelling at some significant fraction of the speed of light. However, this is not the case. In solid state physics I am aware of three concrete phenomena that are purely due to relativistic effects.

1. Gold metal is the colour "gold".
According to Wikipedia, "non-relativistic gold would be white. The relativistic effects are raising the 5d orbital and lowering the 6s orbital.[11]"

2. Mercury is a liquid at room temperature.
This is nicely discussed in a recent blog post by Henry Rzepa concerning a recent paper that shows that relativistic effects shift the melting temperature by about 100 K.

3. Magnetic anisotropy and hysteresis in ferromagnets.
This results from spin-orbit coupling which is a consequence of relativity.


  1. I was told once that 'tin pest' occurring at close to room temperature is because of relativistic effects (there is a competition between diamond and 'beta-tin' structures). See possibly this paper.

    So if you believe a probably incorrect interpretation of history, (the inadequacy of) relativistic effects were involved in Napoleon's failure to conquer Russia.

  2. Great post Ross!

    Gold and Mercury are probably the best examples, but everything in their neighborhood also possess different chemical and physical properties due to relativistic effects. Lanthanide contraction being an example, but Thallium, Lead and Bismuth have different oxidation states than the other elements in their groups, which alter their structural forms for instance. In this row and the above we find the elements most commonly associated with topological insulators, where spin-orbit is pretty much relevant.

    Unfortunately beyond that the elements are all radioactive, so not quite as much data on their properties. Nevertheless just wanted to emphasize your point, a lot of physical and chemical properties depend on relativistic effects, sometimes beyond perturbation theory, majorly when heavy elements are present