5 ms·

You would never reach your destination and at some point you would be stranded in dark space. This kurzgesagt video has some info on this topic.[1] [1] <https:

You would never reach your destination and at some point you would be stranded in dark space. This kurzgesagt video has some info on this topic.[1] [1] <https://www.youtube.com/watch?v=uzkD5SeuwzM https://www.youtube.com/watch?v=uzkD5SeuwzM>

stouset 5y ago
I don’t quite understand this. I think I’d maybe understand if space dilated to the point where you couldn’t quite hit that edge. Though now that I say it that “solution” seems to come with a whole bunch of problematic consequences. But “not getting to anything past the furthest thing we can see from earth today” seems fundamentally incompatible with the idea of reaching those farthest points in a reasonably bounded timeframe. There is stuff beyond the limits we can see, it’s just further than light has had a chance to travel so far (and may ever travel). My intuition is that as you approached those far objects, you’d observe them rapidly evolving forward in time until they reached their “present day” situation, able to see billions in light years in all directions with Earth right at the edge. But then what happens when you look at Earth? Surely you don’t see it’s billions of years old past. You’d have to see it at least as old as it was when you left. But something doesn’t seem quite right about that to me. Surely I’m missing something.
- est31 5y ago
  Space is expanding. Which means stuff is getting further away from each other. https://en.wikipedia.org/wiki/Expansion_of_the_universe https://en.wikipedia.org/wiki/Expansion_of_the_universe If you go far enough, stuff moves fast enough away from us than the speed of light. Thus, some places can't be reached from someone starting at our present location, ever, even though we might still see their light. That light is closer to us than the object that sent it out.
  - edf13 5y ago
    Can you (Or stuff) go faster than the speed of light?
    - marcyb5st 5y ago
      Not with our current understand of physics. Even reaching the speed of light takes infinite amount of energy for things with mass. This is because the faster you go the more massive you become. Furthermore, even before reaching the speed of light you will become a black hole as more energy is added. Things without mass, instead, can only travel at the speed of light (photons for instance). Finally, there is a quirk in the math that would allow for the appearance of faster than light travel. If you compress the spacetime in front of you and expand it behind you you could can move faster than light without turning into a black hole or needing infinite energy (Google Alcubierre drive for more information). It is only an appearance than faster than light travel because you would still move at sub-luminal speed in your bubble of "normal" space time, but the compression/expansion effect would drag you through space-time at faster than light speed. This, however, require so called "exotic matter", ie matter with negative energy density (this is not anti-matter, but matter that has a repulsive gravitational field) and it is probably only a quirk of the math and nothing more.
    - simiones 5y ago
      No, the "speed of light", c, is actually the speed of energy and matter. Everything is always moving at this speed in 4-dimensional space-time. If you are not moving in space, you are moving through "time" at this speed. Since this is just the speed things move at, it makes no sense to discuss moving faster or slower than this speed.
      - ccozan 5y ago
        Correct explanation!
    - eru 5y ago
      Well, if you take a really strong laser pointer and point it at the moon, than a flick of the wrist can make that point race faster along the moon's surface than the speed of light.
      - MaxikCZ 5y ago
        But its not really a point thats traveling faster than speed of light. The individual photons that makes the point travel always at the speed of light from your laser pointer to the moon. Its not point on the moon thats traveling, the travel is just ilusion because it looks like the point that was there a split second ago.
  - ajconway 5y ago
    So, when you reach the "edge" you were going for, you arrive at the point when everything has already moved past your horizon (including Earth), there isn't a single hydrogen atom around, so you're stuck in the darkness forever?
    - est31 5y ago
      Yeah from current understanding that's your fate. Everyone's fate actually, if you see gravitationally bound structures as one unit. You'd be alone waiting for the heat death. Therefore, I recommend decelerating to somewhere interesting during the time window which allows intergalactic travel.
  - drran 5y ago
    Expansion of the (visible) Universe is hypothesis, not a fact. Nobody pointed to an incredibly powerful energy source required to expand the whole visible Universe. A non-zero curvature of space is not confirmed also. We are able to see gravitational waves at this point. Where is a gravitational turbulence, created by the massive expansion? (Non-native speaker, but you got the idea).
  - stouset 5y ago
    Ah, I think I understand! Something 18bnly away from us today has a light bubble that includes objects outside our light cone. If you can get there in 45y, that doesn’t mean 45y has passed at that location. In fact if it’s 18bnly away, that means you’d arrive in 18bn years from their perspective. And not 18bn years from what you saw when you left, but 18bn years from when they saw you leave. By that time, space will have expanded enough that it’s no longer possible to see past.

stouset 5y ago

I don’t quite understand this. I think I’d maybe understand if space dilated to the point where you couldn’t quite hit that edge. Though now that I say it that “solution” seems to come with a whole bunch of problematic consequences. But “not getting to anything past the furthest thing we can see from earth today” seems fundamentally incompatible with the idea of reaching those farthest points in a reasonably bounded timeframe. There is stuff beyond the limits we can see, it’s just further than light has had a chance to travel so far (and may ever travel). My intuition is that as you approached those far objects, you’d observe them rapidly evolving forward in time until they reached their “present day” situation, able to see billions in light years in all directions with Earth right at the edge. But then what happens when you look at Earth? Surely you don’t see it’s billions of years old past. You’d have to see it at least as old as it was when you left. But something doesn’t seem quite right about that to me. Surely I’m missing something.

est31 5y ago
Space is expanding. Which means stuff is getting further away from each other. https://en.wikipedia.org/wiki/Expansion_of_the_universe https://en.wikipedia.org/wiki/Expansion_of_the_universe If you go far enough, stuff moves fast enough away from us than the speed of light. Thus, some places can't be reached from someone starting at our present location, ever, even though we might still see their light. That light is closer to us than the object that sent it out.
- edf13 5y ago
  Can you (Or stuff) go faster than the speed of light?
  - marcyb5st 5y ago
    Not with our current understand of physics. Even reaching the speed of light takes infinite amount of energy for things with mass. This is because the faster you go the more massive you become. Furthermore, even before reaching the speed of light you will become a black hole as more energy is added. Things without mass, instead, can only travel at the speed of light (photons for instance). Finally, there is a quirk in the math that would allow for the appearance of faster than light travel. If you compress the spacetime in front of you and expand it behind you you could can move faster than light without turning into a black hole or needing infinite energy (Google Alcubierre drive for more information). It is only an appearance than faster than light travel because you would still move at sub-luminal speed in your bubble of "normal" space time, but the compression/expansion effect would drag you through space-time at faster than light speed. This, however, require so called "exotic matter", ie matter with negative energy density (this is not anti-matter, but matter that has a repulsive gravitational field) and it is probably only a quirk of the math and nothing more.
  - simiones 5y ago
    No, the "speed of light", c, is actually the speed of energy and matter. Everything is always moving at this speed in 4-dimensional space-time. If you are not moving in space, you are moving through "time" at this speed. Since this is just the speed things move at, it makes no sense to discuss moving faster or slower than this speed.
    - ccozan 5y ago
      Correct explanation!
  - eru 5y ago
    Well, if you take a really strong laser pointer and point it at the moon, than a flick of the wrist can make that point race faster along the moon's surface than the speed of light.
    - MaxikCZ 5y ago
      But its not really a point thats traveling faster than speed of light. The individual photons that makes the point travel always at the speed of light from your laser pointer to the moon. Its not point on the moon thats traveling, the travel is just ilusion because it looks like the point that was there a split second ago.
- ajconway 5y ago
  So, when you reach the "edge" you were going for, you arrive at the point when everything has already moved past your horizon (including Earth), there isn't a single hydrogen atom around, so you're stuck in the darkness forever?
  - est31 5y ago
    Yeah from current understanding that's your fate. Everyone's fate actually, if you see gravitationally bound structures as one unit. You'd be alone waiting for the heat death. Therefore, I recommend decelerating to somewhere interesting during the time window which allows intergalactic travel.
- drran 5y ago
  Expansion of the (visible) Universe is hypothesis, not a fact. Nobody pointed to an incredibly powerful energy source required to expand the whole visible Universe. A non-zero curvature of space is not confirmed also. We are able to see gravitational waves at this point. Where is a gravitational turbulence, created by the massive expansion? (Non-native speaker, but you got the idea).
- stouset 5y ago
  Ah, I think I understand! Something 18bnly away from us today has a light bubble that includes objects outside our light cone. If you can get there in 45y, that doesn’t mean 45y has passed at that location. In fact if it’s 18bnly away, that means you’d arrive in 18bn years from their perspective. And not 18bn years from what you saw when you left, but 18bn years from when they saw you leave. By that time, space will have expanded enough that it’s no longer possible to see past.