Lava lamp with green paraffin floating in clear liquid. On silver conical base. Made by Mathmos in Poole, Dorset.
Lava lamp by the the original manufactorer Mathmos, which has produced them since 1963. This particular one is likely from around 2010, and was often seen in the background during interviews conducted in Stephen Hawking's office.
Lava lamps are common scientific toys, as well as symbols of the playful 1960s-70s generation that Stephen Hawking was part of. Scientifically, they evoke thermodynamic processes of phase transitions and chaos. Lava lamps for example feature in the George book series by Stephen and Lucy Hawking, used to describe geological processes.
Distributed around Stephen Hawking's Office are a selection of items with layers of scientific significance easily missed by the untrained eye. These are toys and gifts that have the closest connection to Stephen's theoretical work: research he was particularly proud of, and which also provided an easy way to illustrate difficult aspects of his theories to visitors.