We all know about black holes, those cosmic devourers from whose gravitational pull nothing, not even light, can escape. They are a point of fascination in both science and sciences fiction so common that the phrase “like a black hole” has become a part of our vernacular. But while you’ve probably heard about black holes you’re likely not all that familiar with their astronomical twin: the mythical white hole. In this month’s Mind Blown section I take a look at a natural phenomenon so mind bending to this point it has only been theorized about.
So what exactly is a white hole? Originally proposed by Russian astrophysicist Igor Novikov in 1964 a white hole is a theoretical area of space time that cannot be entered but emits matter and light. Effectively operating as the opposite of a Black hole in the general theory of Relativity. Simple right? Not so much.
According to our currently held laws of thermodynamics entropy in the universe can only increase or remain constant. Operating by those rules white holes cannot exist because their presence would decrease the amount of entropy in the universe which is theoretically impossible to do.
As a result of this impossibility theoretical physicists have put forth a number of work-arounds which connect the existence of white holes to the existence of black holes which have already been proven to be real.
Here is where things start to get interesting. Unfortunately it’s also where they tend to go off the rails a bit. For a long time a white hole’s primary use in astrophysics is to help complete Einstein’s field equations and establish the possible existence of an Einstein-Rosen Bridge. While solutions to these equations could be found they were also considered by many astrophysicists to be unrealistic. That is until Stephen Hawking proved that black holes disappear over time.
Pause for a second because I know that we just made a jump there. What does the fact that black holes disappearing over time have to do with whether or not white holes can exist? Well we know (or at least we think we do) that matter can neither be created nor destroyed. So long as black holes were believed to be cosmic constants they did not violate this principle, the matter that crossed their event horizon could simply exist there for the rest of eternity like goods in a cosmic safe. But if a black hole ceases to exist than either the matter it has captured in its gravity must either have been destroyed or expelled. Either one of those options fundamentally alters the way that we understand the universe.
White holes then would provide a solution for this problem. In one theory an Einstein-Rosen Bridge links a black hole in our universe to a white hole in another universe essentially dumping the matter that it absorbs there. Another theory that uses loop quantum gravity as a basis puts forward that instead of a black hole achieving infinite density there is actually a snap back point when the “loops” that make up our reality can no longer be broken down, forming a white hole. In this theory the whole life span from collapsing star to black hole to white hole would only take a few thousandths of a second but due to the effects the black hole’s gravitational distortions on our perception of time it could appear to last for eons.
Finally there is the theory supported by Hawking himself that each black hole is also a white hole sharing the same event horizon. The white hole exists infinitely in the past as the black hole exists infinitely in the future. This would be due to theories to time and gravity that stretch our understanding of the forward flow of time. (Which we will get into next time!)
To this point all of this is theory as no quantifiable evidence has been found that supports the existence of white holes and their possible existence remains a contentious point amongst theoretical physicists. But the possibility that they might? It’s enough to blow your mind.