Despite this, many attempts have been made to construct such machines, continuing into modern times.
Modern designers and proponents often use other terms, such as "over unity", to describe their inventions.
On the other hand, if the conservation laws are invalid, then the foundations of physics would need to change.
Scientific investigations as to whether the laws of physics are invariant over time use telescopes to examine the universe in the distant past to discover, to the limits of our measurements, whether ancient stars were identical to stars today.
Although scientists have established them to be impossible under the laws of physics, perpetual motion continues to capture the imagination of inventors.