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?

  • $\begingroup$ 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 $\endgroup$ Feb 16, 2017 at 22:07
  • $\begingroup$ 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? $\endgroup$
    – sqykly
    Feb 17, 2017 at 1:19
  • $\begingroup$ 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. $\endgroup$ Feb 17, 2017 at 3:17
  • $\begingroup$ 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. $\endgroup$
    – sqykly
    Feb 17, 2017 at 4:01
  • $\begingroup$ 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. $\endgroup$
    – sqykly
    Feb 17, 2017 at 4:20


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