3
$\begingroup$

Is there a physical limit to how far we can go? I am thinking there could be based on the following:

1: There are parts of the universe expanding faster than the speed of light that we will never be able to get to (without faster than light travel)

2: There are a finite number of galaxies between here and the distance where 1 takes place.

3: If we travel even at the speed of light, it seems we would at some point pass that finite number of galaxies, and would not be able to reach the next one!

Does this mean there is a limit to how far we can go, and furthermore, we will experience the “big rip”?

Improve this question
$\endgroup$
3
  • $\begingroup$ Interestingly, the Bible hints at the possibility of a big rip: [Psa 102:25-26 NLT] 25 Long ago you laid the foundation of the earth and made the heavens with your hands. 26 They will perish, but you remain forever; they will wear out like old clothing. You will change them like a garment and discard them. $\endgroup$
    – Jonathan
    Dec 22, 2017 at 1:13
  • 3
    $\begingroup$ Why don't you post this as an answer, so we can vote on it? $\endgroup$
    – Mick
    Dec 22, 2017 at 1:30
  • $\begingroup$ I was thinking, this does not necessarily imply the big rip. Eventually in the very distant future, even neighboring galaxies should reach that "critical" distance, and we could at that point never make it to the next galaxy. $\endgroup$
    – Jonathan
    Jan 7, 2018 at 23:09

1 Answer 1

Reset to default
10
$\begingroup$

Your 3 points are spot on. There is a finite number of galaxies we could theoretically reach for the reasons you say. The further away the distant galaxy the greater the expansion of space between us and that galaxy and beyond a certain distance, galaxies can't be reached, even by the speed of light. We can see galaxies that we couldn't possibly travel to.

Does this mean there is a limit to how far we can go, and furthermore, we will experience the “big rip”?

No. It only means that some galaxies that we can see, we could never travel to. There's no limit to how FAR we can go but there's still a finite number of galaxies that we could reach with close to the speed of light travel.

This article, using the current size estimate for the observable universe of 46 billion light years in radius, says that 14.5 billion light years distance is the limit that we could theoretically reach, about 3% of the observable universe or about 3 billion galaxies.

enter image description here

As for the big rip. Nobody knows if that's an accurate prediction. It's a possible outcome, but we don't know enough about dark energy to say if the big rip will happen or not. Nobody knows.

And it's a pretty psalm, but I don't see the prediction of dark energy in it. Only that it says the Universe will age, but life is eternal - which is a nice thought.

Improve this answer
$\endgroup$
2
  • $\begingroup$ It would seem that at some point, we will have reached the last galaxy we can reach since there is a finite number, or is there something wrong with my logic? I agree we can keep going distance wise, but it seems following this logic, at some point, we wouldn't be able to reach the next galaxy (and most likely wouldn't be able to go back to a "previous" galaxy if we turned around at that point). $\endgroup$
    – Jonathan
    Jan 2, 2018 at 21:33
  • 2
    $\begingroup$ Minor detail that I will keep correcting until everybody in the world knows: The article you quote bases its conclusion on a false, but very common, assumption, namely that the theoretical limit for sending a signal to (or receiving a signal from) a galaxy is where the recession velocity reaches the speed of light, which is ~14.5 Glyr. This is the edge of the "Hubble sphere", but in fact the limit is a bit larger, namely 16.5 Glyr, the so-called (cosmic) event horizon. Hence the reachable part of the Universe is not 3%, but an amazing 4.5%! Apart from that, your answer is excellent, so +1 :) $\endgroup$
    – pela
    Aug 12, 2019 at 7:40

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .