Itty Bitty Bang

 Another question this week from Papou: Since a Black Hole can continuously acquire mass (except those cases wherein it loses matter per S. Hawking), does it follow that those Black Hole’s Event Horizon is also continuously getting larger. If that were not the case and the Event Horizon continuously reduced its boundary, does it not follow that Black Hole would become a point mass followed by a Big Bang. If that were the case, then it would be irrational that there was only one Big Bang and we are the product of that singular Big Bang. It is more likely, then, that there may have been other Big Bangs and there are other Universes out in Space. Is there anywhere in space where the Red Shift is not consistent with our Big Bang; which would then imply that there may have been multiple Big Bangs.

I think you get my drift ..... basically I am saying:   “Can a Black Hole become a Big Bang? What is the latest Red Shift evidence?

There are a couple different issues at play here, so let's address them one by one. First off, the event horizon of a black hole: A black hole is a region of space where matter has become so dense, light cannot escape its gravitational pull. The size of that space, called the Schwartzschild radius, is proportional to the amount of mass inside it:

where G is the gravitational constant, M is the mass, and c is the speed of light. You can actually find this yourself by looking for when the escape velocity is equal to c. This radius is sometimes called the event horizon, since in Special Relativity, events are described as points in space and time that are observed through light. If light cannot escape the black hole, we cannot observe events within it.

That brings us to the next part of the question: What happens to a black hole over time? As the equation above states, the event horizon radius is directly proportional to the mass within it, so if it loses mass due to Hawking radiation, or gains mass due to objects falling it, the radius can shrink or grow, but for fixed mass, the event horizon should stay fixed. For small black holes, Hawking radiation can eventually reduce the mass to zero, which is believed to result in the black hole evaporating. As the black hole shrinks, it will cross between the theories of General Relativity, and Quantum Mechanics. In their current forms, these theories are incompatible, but it's believed the evaporating black hole would release a burst of gamma rays as it vanished.

Still, there is a connection between event horizons and big bangs: In 2013, a group of scientists proposed that our universe could exist as the event horizon of a black hole in 4 spacial dimensions. In our 3 spatial dimensions, an event horizon is the surface of a sphere, which is 2D. A 4 dimensional black hole though would result in a 3D event horizon. Of course, that implies the possibility of a 2D universe on the event horizons of our universe.

Finally, the connection to red shift: The universe is expanding at every point, which means every point is moving away from every other point. I often find it helpful to imagine a big rubber sheet being stretched outward; any two points drawn on the sheet will get farther apart. As light moves through the universe, its wavelength gets stretched too, making it "redder", i.e. lower frequency. If you point a radio telescope at an empty part of the sky, as Arno Penzias and Robert Wilson did in 1965, you'll find a constant signal in the microwave band of light, called the Cosmic Microwave Background (CMB). This light is distributed in the blackbody spectrum, the range of photons emitted by objects of a given temperature. That temperature is from 380,000 years after the Big Bang, when things had cooled enough for protons and electrons to combine into hydrogen, about 3000 Kelvin. Over the billions of years that light has travelled, it's been red shifted down to around 2.725 Kelvin, in the microwave range.

If you look at a picture of the CMB, you may notice that it's not entirely uniform:

NASA

These anisotropies are mainly due to gravity pulling particles into clumps, which cool differently. Some have suggested the CMB also contains evidence of "bruises" from collisions between our universe and others existing in a larger multiverse. However, no such collisions have been detected so far.

Thanks for another great question, Papou!