In Kurzgesagt's video TRUE limits of Humanity is it stated that most of the universe will be forever unreachable because the universe is expanding faster than the speed of light. This is possible because dark energy makes the actual space expand. However, if that is possible, it seems that we might be able to find a way to shrink the universe itself, thus making them reachable again. Or do we already know that considering the current framework of physics, this is not possible, for example like time travel?

  • $\begingroup$ Related: physics.stackexchange.com/q/456973/123208 $\endgroup$
    – PM 2Ring
    May 14, 2021 at 13:12
  • $\begingroup$ Which way would you go? I've heard that for any direction that you look, you are seeing the early universe. $\endgroup$
    – R.W. Bird
    May 14, 2021 at 14:45
  • $\begingroup$ @R.W.Bird I'm not sure I understand your question, but what I've meant was somehow reverse the space expansion. I've seen analogy with dots on a stretchy sheet where if you pull from all directions the dots get far away from each other but not because they move but the underlying space stretches. Thus if we reverse the stretch everything would be closer again right? The universe how we see it might not exist, but that does not matter, we would simply pull closer whatever is there. $\endgroup$
    – eXPRESS
    May 15, 2021 at 8:12

1 Answer 1


We do not understand the origin of dark energy and dark matter. If we understand the nature of dark energy and dark matter and how to control them, maybe we can make it. At the same time, even if we understand every detail of dark matter and dark energy, we could not reach the unreachable part of the universe. So the unreachable part is 100% unreachable in the current framework of physics, but who knows in the future? Therefore, my best answer to your question is that the current framework of physics do not know much about the universe, and the Kurzgesagt's video is based on the current framework of physics. Many scholars like thousands of years ago believed that earth is the center of the universe...

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    $\begingroup$ ... and flat! And membership of the Flat Earth Society seems to be on the rise today. Sign o'the times? $\endgroup$
    – Gert
    May 14, 2021 at 13:43
  • $\begingroup$ @AboveThreshold Good point, but I think there is a difference between not understanding something (like dark matter) and understanding it in our way which does not have to be true (like time travel). The nuance which I probably did not express well in my question is does our current understanding prohibits the proposition or do we simply lack information/evidence to show the proof of work. My takeaway from your answer is that the latter is true here, which is why I think it might be too soon for us to call it "unreachable space" without an asterisk yet. $\endgroup$
    – eXPRESS
    May 15, 2021 at 8:19
  • $\begingroup$ @Gert But there is so much evidence on Youtube! And did you know "NASA" means "to deceive" in Hebrew? :D $\endgroup$
    – eXPRESS
    May 15, 2021 at 8:28
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    $\begingroup$ @eXPRESS If it's on UToob it MUST be true! Flat Earth here I come... $\endgroup$
    – Gert
    May 15, 2021 at 11:13

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