If humans are still around in say 2220, what would a telescope have to be able to do to see the edge of the universe (This is also with caveat of FTL being possible)

  • $\begingroup$ Welcome to the site! What kind of FTL travel is possible, and just how fast is it? $\endgroup$ – Zxyrra Feb 2 '20 at 20:42
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    $\begingroup$ Seeing the edge of the universe is a bit like seeing the edge of a sphere. $\endgroup$ – Starfish Prime Feb 2 '20 at 21:00
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    $\begingroup$ What is the "edge of the universe"? $\endgroup$ – AlexP Feb 2 '20 at 21:16
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    $\begingroup$ I agree with @Zxyrra this isn't offtopic. By the 23rd century technical improvements in radio & optical telescopes will bring the limits of the observable universe in view. Very plausible. This is a distance of 90 billion light years. If FTL telescopy is possible, this could be extended further. A bigger observable universe. SW speeds are approximately one million c. So an observable universe with radius 90 million billion light years. Big improvement needed. $\endgroup$ – a4android Feb 3 '20 at 0:50
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    $\begingroup$ I think this question is on topic. But I'm going to vote to put it on hold until the author can answer some questions about the nature of FTL. Then it can -- in my opinion -- be reopened. $\endgroup$ – SRM Feb 3 '20 at 2:27

It depends on the shape of the universe

The observable universe is a sphere with a radius of about 46.508 billion light years. Our radius of observation is limited by the fact that light takes a really, really long time to reach us, so we can only see to a certain distance past which light hasn't had time to get here. A non-travelling telescope couldn't see any faster than light because optics are light-based; even if spaceships can defy the universal speed limit, the information reaching a telescope can't.

Hypothetically, you could send out FTL probes or ping FTL radar signals out across space. Assuming the observer is stationary but FTL travel exists, you could cross cosmological distances at arbitrary speeds in order to broaden your viewing horizon. In that way, the observable universe would get much larger.

Here's the problem: even if you gather information faster than light, the universe might not have an end you can reach - it depends on its shape. This is a really complex idea and my explanation won't do the actual science justice, but for sake of answering this question, there are two possibilities for the universe.

  • Scenario A: The universe is infinite. You can keep going in any direction and you will continue to encounter brand new space, forever. If you leave the Earth from the North pole and go "North" through space, you'll never find the Earth again. This means the universe is unmappable.
  • Scenario B: The universe is finite. If you take off in a random direction in space, you'll end up back where you started. If you leave the Earth from the North pole at infinite speed, you'll cover a finite distance and eventually arrive at the South pole. This means the universe can be mapped.

In summary:

The observable universe can be simplified as "the region of space that we can see light from at the present time." A telescope constrained to light can never see past this limit, but humans could see past the observable universe in an FTL world by sending probes or signals there.

However, if the universe is infinite, humans can never see all of it. If the universe is finite, humans can't really see all of it, but they can map it.

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    $\begingroup$ Scenario C: The universe is finite. You fall off the edge. It’s turtles all the way down. $\endgroup$ – Joe Bloggs Feb 2 '20 at 21:16
  • $\begingroup$ The universe may be finite (i.e having a finite mass), but boundless. $\endgroup$ – Alexander Feb 2 '20 at 21:55
  • $\begingroup$ @Alexander How does that differ from Scenario B? $\endgroup$ – Zxyrra Feb 2 '20 at 22:21
  • $\begingroup$ @Zxyrra You would at some point leave any matter behind, mapping only empty space. $\endgroup$ – Trish Feb 2 '20 at 22:48
  • $\begingroup$ @Trish At first that's what I thought Alexander meant, but that runs contrary to our understanding that the universe is isotrophic (roughly the same in all directions). It wouldn't make sense for the big bang to have deposited all of its matter in one location yet expanded everywhere; the two seem linked. In other words, the universe isn't supposed to have a center - which one island of matter would be. I think Scenario B still foots the bill as finite but without an edge, like the Earth. $\endgroup$ – Zxyrra Feb 2 '20 at 22:50
  1. Place telescope on FTL ship.

  2. Outrun the lightspeed expansion of the Big Bang. Some directions will get you there quicker than others. It might not matter.

  3. Once you see nothing ahead of ship, you can assume you have passed the front of the expanding universe.

  4. Turn around. Look at the edge coming towards you. Check box:"seen the edge of the universe". Record what you see because you are going to have to go back to Earth now if anyone else is going to see it.

  5. Go back to earth. Wonder if you outrunning the universe in your FTL actually increased the universe size because of your action.


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