Physicists in South Africa ran the math on collapsing neutron stars and landed somewhere odd. Researchers from Durban University of Technology and the University of KwaZulu-Natal found that inside these extreme environments, time appears to run backward. You can’t actually go see this happen, but the numbers are solid and intriguing enough to be worth talking about.
The paper appeared in the European Physical Journal C and focuses on the arrow of time and the everyday observation that time only moves forward. This direction comes from entropy, the steady drift of things from order toward mess. A dropped glass that shatters never puts itself back together, nor does warmth leak out of a room and pool back up on its own. In every case, the movement is strictly forward.
Feed a collapsing neutron star into the equations, though, and the drift flips. The team watched the relevant measures decrease steadily as the collapse deepened, which is the mathematical equivalent of entropy shrinking instead of growing.
Think of toothpaste miraculously sliding back into the tube. Physicists usually invoke that example to illustrate what’s impossible under the normal arrow of time, but inside a collapsing neutron star, the numbers show something strikingly similar.
Why would gravity pull a stunt like that? It’s because two flavors of entropy are at war. The everyday version spreads stuff out and breaks it down, while the gravitational version does the reverse and gathers matter into tighter and tighter clumps. Whichever one dominates depends on how intense the gravity is, and a neutron star sits at the far end of that scale.
The weird physics of cosmic remnants
A neutron star is genuinely one of the strangest objects in the universe. It’s what’s left of a massive dead star’s core, compressed into a sphere so dense that a walk across its surface would take a couple of hours, yet packing more mass than the Sun.
In many respects, they behave more like black holes than ordinary stars. The moment one starts collapsing, physicists tag its energy state as “unstable,” and that’s the version the team incorporated into their model spacetime before running the numbers.
The findings take on greater significance when linked to the Big Bang. Although the infant universe was loaded with entropy, here we sit, still near the early end of the arrow, with tons of headroom for disorder to keep piling up.
Bridging this apparent contradiction has troubled cosmologists for a long time. One escape hatch is the possibility that certain regions or processes have been quietly winding the clock backward this whole time, keeping the ledger or cosmic balance, if you will, intact.
Nobody on the team is claiming they’ve nailed the cosmic arrow-of-time puzzle. They frame the work as a stepping stone, one more configuration in the long grind of figuring out how various gravities and curvatures behave. Each result hands something to the next, which is a forward motion all its own.
Sources: Springer, Popular Mechanics