3 ms·

> Rather it's that the rate of expansion of the universe is accelerating, so that we're moving away from parts of it faster than its light can cover the distanc

by Twisol 4y ago

> Rather it's that the rate of expansion of the universe is accelerating, so that we're moving away from parts of it faster than its light can cover the distance to us. From my understanding, it's not that we're moving away from parts of the universe, but that the distance between us is growing so fast that light sent from one part will find that after traveling toward us for some amount of time, the remaining distance to travel is actually more than than when it started. One way for the distance between two objects to increase is indeed for those objects to literally be moving in opposite directions through space. But the expansion of the universe itself causes the distance between two otherwise-stationary points to nonetheless increase. Put differently, it's the cosmic yardstick that's shrinking, not the entities that must necessarily be moving. (This is also why two points can be "moving apart" faster than light speed, the cosmic speed limit.)

shagie 4y ago
That rate is "only" approximately 68 kilometers per second per megaparsec. 68 kps isn't that fast (it's about the same speed as the Helios 2 solar probe) and a mega parsec is big distance (3.2M light years). Its that there's a lot of megaparsecs between here and there and the sum of all of those 68 kps is more than the speed of light. The relevant Kurzgesagt : TRUE Limits Of Humanity – The Final Border We Will Never Cross - https://youtu.be/uzkD5SeuwzM https://youtu.be/uzkD5SeuwzM
- Twisol 4y ago
  Yes, true -- the distance between two points doesn't grow linearly, but rather proportionally to itself :D
- sfifs 4y ago
  So such an expansion phenomenon should affect everything uniformly right? Are we (people /animals) then getting "bigger"? Over time innthe extreme will it cause problems in signal transmission in our own nervous systems (since apparently we have a problem seeing light beyond the observable limit)
  - kgwgk 4y ago
    You don’t get larger - just like you don’t dissolve in water and wind doesn’t spread parts of you all over the land. There are interactions of matter keeping you together.
  - shagie 4y ago
    With the current rate of expansion, no. We're still bound together more tightly than the rate. This extends all the way out to a fair distance (galactic distance). If the rate does get to the point where it is noticeable the "galaxies can't hold together" you get into the Big Rip end of the universe situation.
  - deleted 4y ago
    [deleted]
  - Twisol 4y ago
    Gravitational attraction still dominates on even fairly large scales, and chemical bonds absolutely dominate over anything expansion could possibly do -- it would contribute an incredibly light force opposing any bonds. So no, we (and our galaxy) are in no danger of being inflated from the inside by space itself.
    - sfifs 4y ago
      Thanks for the explanation!
  - xenadu02 4y ago
    The strong nuclear force, electromagnetic force, and even gravity are strong enough to overwhelm the expansion within individual galaxies and even local groups of galaxies. In other words the expansion of spacetime very very very slightly tries to shift the atoms of your body apart but we can't even detect it because ordinary forces like chemical (electromagnetic) bonds are exponentially stronger - enough to pull things back where they should be. Actually in the current epoch I'm not sure if the expansion is strong enough to shift an electron by 0.01% of its own width let alone move an atom. Space is really really big so that tiny amount of expansion adds up over long distances.
chrisweekly 4y ago
You have it right. My cosmology teacher at UVA a couple decades ago used the analogy of points marked on the surface of a balloon that's being inflated. (maybe more intuitive than other shortcuts to understanding?)
SkyMarshal 4y ago
> but that the distance between us is growing so fast that light sent from one part will find that after traveling toward us for some amount of time, the remaining distance to travel is actually more than than when it started. Good clarification, that's what I meant, I guess I didn't say it accurately. I don't actually think of us as moving, but more like the scale of the entire universe is increasing while the ability to traverse it - light speed - remains a constant.

by Twisol 4y ago

shagie 4y ago

That rate is "only" approximately 68 kilometers per second per megaparsec. 68 kps isn't that fast (it's about the same speed as the Helios 2 solar probe) and a mega parsec is big distance (3.2M light years). Its that there's a lot of megaparsecs between here and there and the sum of all of those 68 kps is more than the speed of light. The relevant Kurzgesagt : TRUE Limits Of Humanity – The Final Border We Will Never Cross - https://youtu.be/uzkD5SeuwzM https://youtu.be/uzkD5SeuwzM

Twisol 4y ago
Yes, true -- the distance between two points doesn't grow linearly, but rather proportionally to itself :D
sfifs 4y ago
So such an expansion phenomenon should affect everything uniformly right? Are we (people /animals) then getting "bigger"? Over time innthe extreme will it cause problems in signal transmission in our own nervous systems (since apparently we have a problem seeing light beyond the observable limit)
- kgwgk 4y ago
  You don’t get larger - just like you don’t dissolve in water and wind doesn’t spread parts of you all over the land. There are interactions of matter keeping you together.
- shagie 4y ago
  With the current rate of expansion, no. We're still bound together more tightly than the rate. This extends all the way out to a fair distance (galactic distance). If the rate does get to the point where it is noticeable the "galaxies can't hold together" you get into the Big Rip end of the universe situation.
- deleted 4y ago
  [deleted]
- Twisol 4y ago
  Gravitational attraction still dominates on even fairly large scales, and chemical bonds absolutely dominate over anything expansion could possibly do -- it would contribute an incredibly light force opposing any bonds. So no, we (and our galaxy) are in no danger of being inflated from the inside by space itself.
  - sfifs 4y ago
    Thanks for the explanation!
- xenadu02 4y ago
  The strong nuclear force, electromagnetic force, and even gravity are strong enough to overwhelm the expansion within individual galaxies and even local groups of galaxies. In other words the expansion of spacetime very very very slightly tries to shift the atoms of your body apart but we can't even detect it because ordinary forces like chemical (electromagnetic) bonds are exponentially stronger - enough to pull things back where they should be. Actually in the current epoch I'm not sure if the expansion is strong enough to shift an electron by 0.01% of its own width let alone move an atom. Space is really really big so that tiny amount of expansion adds up over long distances.

chrisweekly 4y ago

You have it right. My cosmology teacher at UVA a couple decades ago used the analogy of points marked on the surface of a balloon that's being inflated. (maybe more intuitive than other shortcuts to understanding?)

SkyMarshal 4y ago

> but that the distance between us is growing so fast that light sent from one part will find that after traveling toward us for some amount of time, the remaining distance to travel is actually more than than when it started. Good clarification, that's what I meant, I guess I didn't say it accurately. I don't actually think of us as moving, but more like the scale of the entire universe is increasing while the ability to traverse it - light speed - remains a constant.