The animation below illustrates how gravitational waves are emitted by two neutron stars as they first orbit each other and then coalesce. Though gravitational waves were predicted to exist in 1916, actual proof of their existence wouldn't arrive until 1974, 20 years after Einstein's death.
Uroabdomen can result from various causes, but the most common is related to trauma. Damage to the kidney, ureter, bladder, or urethra may cause urine to leak into the abdomen. Some common forms of trauma that can result in a disruption of the urinary tract in cats include:
Proteinuria is leakage of protein from the blood into the urine. This page explains what protein is, how it gets into the urine and what doctors can do to deal with any problems caused by proteinuria. Protein is one of the three main types of chemical that make up our body (the others are fats and sugars).