Yet another mysterious anomaly in space physics that threatened Albert Einstein’s so-far bulletproof General Theory of Relativity has failed to penetrate its Kevlar armour.

But its success means the continued survival of a theory that hasn’t been proven to exist.

The universe has been expanding since the Big Bang more than 13 billion years ago, but about five billion years ago the rate of expansion started speeding up – and no one knows why.

The predominant theory is dark energy – an invisible, repulsive force that only interacts with normal energy via gravity, but remains hypothetical. Along with dark matter – which is needed to explain how galaxies work – these mysterious forces seem to account for 95 percent of the energy in the universe, which we can’t actually see.

Its rival theory is that the strength of gravity has been changing – which would run counter to Einstein’s equations, which have held up pretty well since he formulated them more than a century ago.

But new observations of galaxies billions of light-years away – and therefore billions of years in the past – suggest gravity’s been the same this whole time.

Astronomers analysed millions of galaxies, and found their shapes all conformed to General Relativity, Universe Today reported this week.

“There is still room to challenge Einstein’s theory of gravity, as measurements get more and more precise,” study co-author Agnès Ferté of NASA’s Jet Propulsion Laboratory said in a statement.

It’s already known Einstein’s equations break down when confronted with extreme situations, like black holes, so will one day likely need to be replaced. Upcoming missions such as the European Space Agency’s Euclid and NASA’s Nancy Grace Roman Space Telescope will look back 8 and 11 billion years respectively, perhaps uncovering what’s really been going on.