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Dark energy is supposed to pull galaxies apart, their gravity not sufficient to escape or even slow the expansion of space. Notable scientists like Dr. Kaku all seem to agree that this results in heat death, wherein everything eventually is receding from everything else so rapidly that it has dropped off of our horizon. As a consequence, distant stars disappear until an observer will detect no light from anywhere. Without light or other effects of locality, structured matter cannot sustain its heat, hence the term heat death.

However, something seems awfully wrong with this story, even worse than its implication that all life is frozen to extinction permanently. If an object is receding from us and that object has mass, relativity tells us that the object cannot appear to travel faster than light. Massive objects, as they approach light speed in any frame of reference including ours, are to gain mass such that accelerating them will require more and more energy, asymptotically forbidding them from reaching c. Our observational horizon effectively expands at exactly c, so how is it possible to leave it?

Is this problem related to the image we should observe in perpetuity of something that falls into a black hole? I.e. the mass itself is long gone, but an external observer sees them falling indefinitely. If this is the case, what is the difference between our future dilemma and falling into a black hole, such that an image of a star will not remain in our view?

Finally, is there a way to measure how much normal matter has left our horizon due to dark energy already? If not, then we have apparently lost the information that would otherwise be available in their ever-redshifting image, so does entropy paradoxically fall as well?

sqykly
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  • If an object is receding from us and that object has mass, relativity tells us that the object cannot appear to travel faster than light - true for objects and anything that has mass. However, space-time itself can expand faster than the speed of light – Dhruv Saxena Feb 16 '17 at 22:07
  • Then what does it look like as it approaches the horizon? We watch a thing accelerating, we have a data point that gets redder and redder then... poof? It dettaches from our spacetime bubble? If it does, what's the difference between that and getting eaten by black hole? Either way, we see objects being partitioned into their own spacetime, so is it the same type of horizon? How would we know if, say, 75% of the universe was already behind the edge? – sqykly Feb 17 '17 at 01:19
  • The point beyond which no light from a distant world would ever reach us is called Cosmological Horizon. And Event Horizon is the horizon around a black hole. I'd be punching above my weight to delve further without corrupting the technical nuances. However, for any light source beyond these horizons, one major difference is: in case of Cosmological Horizon the light cannot overcome the distance - whereas, in the latter case, it can't overcome the curvature - of space-time. – Dhruv Saxena Feb 17 '17 at 03:17
  • I watched a moderately vigorous and very credible lecture on youtube (will link) involving tensor networks modelling spacetime at the event horizon, which mentioned that space is being created inside the hole's horizon faster than c. They were exploring wormhole travel, creating 2 black holes with entangled particles and concluding that it would be a wormhole, Alice and Bob can meet in the middle of it, but they still can't ever travel via wormhole since they can never leave due to spacetime falling into the hole at greater than c. That's why I am going on about this. – sqykly Feb 17 '17 at 04:01
  • Specifically, I am conjecturing that spacetime in cosmological scale appears to have a conjugate geometry to a black hole. Another credible conference lecture (will link) specifically about black holes (featuring the guy that wrote the book you read about them in uni) suggested that spinning black holes may have an inner horizon as well, and I submit to your judgment that our observable universe is contained in one of them. Hawking radiation then accounts for dark energy (evaporation = loss of visible matter to the external spacetime) and antimatter in cosmic rays. – sqykly Feb 17 '17 at 04:20
  • I encountered a video and remembered this conversation. So, thought it might be of interest to you: https://www.youtube.com/watch?v=Fb9ivmAi6rM. It's just an extension of comments above but in a much greater detail and perhaps with more sophistication. And no, I wasn't implying that we're contained in a Black Hole or an Event Horizon. We're however "limited" by a Cosmological Horizon. Even though there may still be a very similar universe beyond it, we won't ever be able to reach there, nor would anything from there be able to reach us (including light). – Dhruv Saxena Mar 22 '17 at 16:06
  • Your link uses the videos I referred to (Susskind and the guy that invented the laser - sorry man, I suck at names and proper nouns) as sources. I guess I am not the first person to notice this, no surprise. Your link has a guy who described a mathematical accounting of the mass of the universe involving the Schroedinger equation - a link I am unequipped to follow without seeing it written out. Can I get a link to this accounting in completion? – sqykly Mar 23 '17 at 19:03
  • And if you watch nearly any of Lenny Susskind's lectures post-2015 you will see the point I am talking about. If stuff outside our cosmo horizon exists and our cosmo horizon is expanding toward them but cannot keep pace with expansion, I don't see the difference between a point in his expanding wormhole and a point outside the system in a quantitatively different spacetime. The tensor geometry is certainly identical. – sqykly Mar 23 '17 at 19:13
  • I hadn't noticed that he actually said Schrodinger Equation! Although the existence of black holes does have its own Quantum Mechanical implications, I was unable to find an exact co-relation between size/mass of a black hole and the Schrodinger Equation as such, despite there being some loose and indirect links (such as Schrodinger Newton Equation). However, evaluating that doesn't seem to be as easy as the narrator says :). – Dhruv Saxena Mar 25 '17 at 01:25
  • So, I'm now pretty much inclined to think that perhaps Schwarzschild radius was the intended reference, which certainly is a more direct relation between the mass and the radius (size) of a black hole. Therefore, out of curiosity, I ran a Wolfram Alpha test: in the mass field, you input Universe and it gives out the Event Horizon radius. – Dhruv Saxena Mar 25 '17 at 01:26
  • I had a feeling that the result would prove that the universe is bigger than the higher limit of the radius that it would need to be for it to be a black hole. I was stumped to find that, the radius of the Observable Universe (which is actually only a subset of the Whole Universe) is, in fact, smaller than the radius of a hypothetical black hole if it were to contain all the mass of our universe! Mathematically, this means, our Observable Universe with its current mass and size, could as well exist as one unimaginably large Black Hole. I admit, this was indeed a very baffling find! – Dhruv Saxena Mar 25 '17 at 01:27
  • However, the mathematical possibility alone shouldn't amount to disregarding the other essential physical properties of a black hole. This is where, I think, following few Q&As would come into play: http://physics.stackexchange.com/q/1901/139130 and http://physics.stackexchange.com/q/166620/139130. Particularly, this answer spells out why everything contained in a black hole has to be a singularity; thereby we can't be living inside one. – Dhruv Saxena Mar 25 '17 at 01:28
  • For any observer, in-falling towards a Black Hole, the singularity would be in the future, whereas for us, the Big Bang's initial singularity was in a distant past. In a black hole, you fall towards the singularity from all possible directions. Whereas, from our observations, the universe is expanding in any direction we look. For the other topic of Metric Expansion of space, maybe this lecture, and two more that follow, might be of some interest. – Dhruv Saxena Mar 25 '17 at 01:28

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