Are we inside a black hole?
This is not exactly right, because the universe is expanding. You can't treat matter which is outside the cosmological horizon (if the concept is even meaningful, which I don't admit) as part of the matter which is gravitating, because it is not in causal or gravitational communication with matter here. The bounds you give are for matter sitting still.
The proper view is that the universe itself is an inside-out black hole, with a cosmological horizon that surrounds us. In this point of view, the matter inside the universe and the cosmological constant are, together, responsible for the shape of the enclosing horizon, or black hole.
But this is not a black hole, in that it isn't singular in the center, only (in certain energy models) singular in the past.
Hmm... The Schwarzschild radius prevents light from getting out of a black hole, but not from getting in, doesn't it? If so, then what matters is that the Schwarzschild radius is bigger than the observable universe, while the opposite proves nothing, no?
WIMPs link to the discover magazine article is interesting, but I noticed that one of the counterarguments is that the universe is expanding, not contracting. But, if we were inside a black hole, wouldn't expansion be exactly what we'd experience?
Consider this: if we're inside a black hole, then everything is moving towards the singularity. Things closer to the singularity are moving faster, and vice versa. This means that for us, everything else is moving away from us (because things closer to the singularity move faster, and we move faster than things further away from the singularity).
The expansion wouldn't be entirely uniform, and I may be wrong, but I seem to recall reading recent data that in fact implies that it isn't.
I am going to out myself as a big fan of the "living in a black hole" idea. I like how intuitively the "pull" of a singularity would explain everything moving forward in time, or even possibly be an explanation for "dark energy" aka acceleration of the apparent (from our point of view) expansion of the universe (since we are moving closer to the singularity).
No one yet pointed out that the currently established radius of the observable universe actually doesn't meet the Schwarzschild radius requirement to make it a black hole in itself. Not meant to be misleading but this was deliberate in my original post, as it is significantly close in magnitude and doesn't much change the essence of my question.
Here were my assumptions:
- Even by conservative estimates, the observable universe's radius is established at ~46 billion lightyears.
- An object of observable mass of 3 × 10^52 kg. would have to be contained within a Schwarzschild radius of ~10B ly
Now 10B ly is smaller than 46B ly.
However it's a substantial fraction, and a universe merely 10 times more massive, achieved by a cube-root extension of the 46B ly radius (assuming continued mean density into the additional volume required) to 99 B ly would already fall inside its new corresponding Schwarzschild radius of 100 B ly.
Even considering the non-Euclidean topology of space at these distances, 10x would not be far off from the actual factor required to meet the Schwarzschild criteria for a black hole.
The reason this question still intrigues me as relevant is that intuitively, I'd find it highly unlikely that the actual universe's size matches so closely to the observable universe's. Similar to the coincidence we're at the center of the universe.
One more wrinkle--and I'm almost ready to hear again about needing to keep within distances that are causaly(gravitationally) connected, where borders are defined by receding at light speed. No doubt this is merely a limitation of my understanding, but let's say I in Poland and you in Norway technically have different reaches of causality. Though our spheres largely overlap, our causally-connected/observable universes may not be 100% the same, and this effect is slightly more pronounced if you happen to be on the other end of the Great Wall. To me this further makes a well-defined event horizon at universe scales rather nebulous, suggesting black holes have possibly relative placement?