6 ms·

Your intuition that there is an limited observable distance because is correct. But because of the expansion, that limit is bigger than "speed_of_light * age o

Your intuition that there is an limited observable distance because is correct. But because of the expansion, that limit is bigger than "speed_of_light * age of universe" . I don't know enough General Relativity to give a solid explanation. But here is a rough over-simplification: Imagine you've spent the last 5 seconds blowing up a balloon, but there is an ant walking on that balloon, starting from a marked spot. In the 1st second, the ant moved 10mm. But in the next four seconds you blew up the balloon, so that 10mm of rubber is now 70mm long. The total distance from the ant's starting mark to her end-point can now be well over than 70mm, even though she only walks at less than 10mm/second. As the ant, so the photon.

laurencei 7y ago
Yep - I kind of understand that. Thanks.
sytelus 7y ago
I'm bit confused. Regardless of expansion, these objects are right now > 13.8B ly away. So the light from them still needs that much time to get here. If light from them has arrived sooner, we would see less redshift and perceive them as a closer. No?
- undreren 7y ago
  The light we see is from when the galaxy was closer. As the light left the galaxy and travelled towards us, the universe expanded "between" the photons and the galaxy.
  - piva00 7y ago
    And how do we know that now the galaxy is much further away? Just by the red shift of the light emitted over time?
    - undreren 7y ago
      As far as I understand, yes. The red shift of the light can be measured, which tells us for how long the light has traveled.
undreren 7y ago
The ant and balloon analogy is really good from an intuition stand point. Great explanation! Well done :)
- brutt 7y ago
  Except for fact than in balloon analogy, ant is moving in a direction by balloon surface, while in our case our "balloon" is perfectly still in all directions. Imagine that balloon is not inflated at all, but ant magically moves 70mm instead of 10mm. How this is possible??? I can accept, that our part of Laniakea is expanding, but not whole Universe.
  - fragmede 7y ago
    What'll really blow your mind is that it's expanding faster, not slower.
    - deftnerd 7y ago
      It kind of makes sense to me with some further caveats to the analogy. If you think of the ant as a 2 dimensional creature living on a two dimensional surface of the balloon, the expansion is occurring in 3 dimensional space. The two-dimensional ant has no way to observe the space north or south (above and below, to us) its plane of existence. Now, imagine that the balloon is in a vacuum. It had a burst of air (the big bang) for a moment to get it started but it's not the further addition of air that's driving the expansion, it's the desire to equalize pressure between the exterior vacuum and the interior matter. With that in mind, push everything up a dimension. We're 3 dimensional creatures living in a 3 dimensional universe. That 3 dimensional universe exists as a plane in 4 dimensional space. The 4 dimensional balloon (that our universe is surrounding) is continuing to expand into the "nothingness" on the ana plane of the 4th dimensional universe because of the "pressure" imbalance on the kata plane of the 4th dimensional universe. (In 4th dimensional spatial terms, ana and kata indicates directions on the w axis, similar to up/down on the x axis, left/right on the y axis, and north/south on the z axis) At least, that's how I see it in my head, but I'm an odd ball who has never had a problem intuitively visualizing 4th spatial dimension objects and how they might interact with 3rd dimensional space. As for the increased speed of the expansion... actually, I hadn't thought about that. Does it indicate that equilibrium will never be found? The balloon analogy might be a useful tool, but our universe isn't made of rubber so it might have the capability of being able to expand infinitely without breaking and without its "nature" constraining the expansion speed. Anyway, if this is a reasonable analogy, the "nothingness" in the ana direction isn't as interesting to me as what might comprise the "pressure" that's in the kata direction that's causing the expansion. It's nothing we'd ever be able to observe or sample since it's outside of our plane of existence, but it's awfully fun to speculate about the composition and nature of it.
techas 7y ago
If space works as a balloon then the growth happens in all the volume of the universe (not just on the “boundary”). Is that how it works? Doesn’t that imply that we are getting “bigger”?
- ggggtez 7y ago
  No. Just because space is expanding doesn't change the electromagnetic forces holding you together.
  - ivoras 7y ago
    But just thinking of the electromagnetic forces in terms of what is required from them to keep matter together in the context of that same matter effectively expanding faster than the speed of light is... at best weird.
    - Filligree 7y ago
      The speed of expansion depends on the size of the object. Human-scale things aren't expanding at the speed of light; you need to get to larger-than-galaxy-cluster scales for that to happen. (In fact space inside galaxies isn't expanding at all, only space between galaxies. But I digress.)
    - noselasd 7y ago
      It's not faster than light at the scale where there's matter in the universe. Across a planet or solar system it's not measurable. It's when you measure between one side of the observable universe to the oposite side that the expansion speeds get crazy.
- ivoras 7y ago
  (I am not a physicist) As far as I understand the current theory (i.e. our best guess), the 4 fundamental forces are somehow countering the expansion so that, even as everything in the universe expands, including e.g. every single atom, the forces are even stronger and are pulling stuff together. I think this just opens more questions than it resolves, and would really like to hear a better explanation.
brutt 7y ago
Where is the waves? 13.8B years is too short to make Universe smooth again after such epic event. It's like to see green grass again just 1 second after nuke blast: mathematical formulas will need lot of magic constants for this to explain.
- madaxe_again 7y ago
  The universe isn’t smooth. The CMB is not uniform, and at a very large scale the universe is composed of attractors and voids, which stem from the anisotropy of the early universe.
  - brutt 7y ago
    For me, CMB is just light of distant stars with z=1100. Universe is composed of attractors and voids at any scale. Anyway, I see no shockwave of any kind in CMB. Where it is? Such massive explosion, with energy of 1E53 atomic bombs and no shockwave at all just miliseconds (in scale of Universe) after the Bing Bang. How this is possible?
    - yorwba 7y ago
      What do you expect that shockwave to look like? Circles expanding from the center of the explosion?
      - brutt 7y ago
        Yep. Something like that: https://www.youtube.com/watch?v=EmdBFoQtVvU https://www.youtube.com/watch?v=EmdBFoQtVvU .
    - zentiggr 7y ago
      Look into the inflationary portion of the BB timeline, and also add in the fact that those shockwaves have had the same 13.8B years to expand and dissipate. The CMB variations _are_ the remnants of that initial period, attenuated after all this time.
    - 7y ago
dwild 7y ago
> In the 1st second, the ant moved 10mm. But in the next four seconds you blew up the balloon, so that 10mm of rubber is now 70mm long. The total distance from the ant's starting mark to her end-point can now be well over than 70mm, even though she only walks at less than 10mm/second. Thus the expansion isn't caused by the movement of the photon but from something else? Then what caused that movement in the first place? And what cause the expansion?
- ecnahc515 7y ago
  If I understand correctly, the theory is that spacetime itself was created by the big bang. As-in, space, and time itself didn't exist prior to the big bang.
- sqreept 7y ago
  And and expansion is a lengthening of something within a frame of reference. What is the frame of reference?
  - devnulloverflow 7y ago
    The visible galaxies. That is we see red-shifts when we observe distant objects. And comparing that to other distance estimates, we see that far away things are more red-shifted. As if they are moving away from us. When we build cosmological models to explain this, we could choose reference coordinates for time and space in different ways. But if we choose to define time and distance in the usual way then we get a picture in which the distances between all galaxies is increasing with time.
- namirez 7y ago
  You're right; the expansion of the universe is not related to photons. It's caused by the pressure of dark energy. There are some hypotheses but no one knows for sure what dark energy is.

laurencei 7y ago

Yep - I kind of understand that. Thanks.

sytelus 7y ago

I'm bit confused. Regardless of expansion, these objects are right now > 13.8B ly away. So the light from them still needs that much time to get here. If light from them has arrived sooner, we would see less redshift and perceive them as a closer. No?

undreren 7y ago
The light we see is from when the galaxy was closer. As the light left the galaxy and travelled towards us, the universe expanded "between" the photons and the galaxy.
- piva00 7y ago
  And how do we know that now the galaxy is much further away? Just by the red shift of the light emitted over time?
  - undreren 7y ago
    As far as I understand, yes. The red shift of the light can be measured, which tells us for how long the light has traveled.

undreren 7y ago

The ant and balloon analogy is really good from an intuition stand point. Great explanation! Well done :)

brutt 7y ago
Except for fact than in balloon analogy, ant is moving in a direction by balloon surface, while in our case our "balloon" is perfectly still in all directions. Imagine that balloon is not inflated at all, but ant magically moves 70mm instead of 10mm. How this is possible??? I can accept, that our part of Laniakea is expanding, but not whole Universe.
- fragmede 7y ago
  What'll really blow your mind is that it's expanding faster, not slower.
  - deftnerd 7y ago
    It kind of makes sense to me with some further caveats to the analogy. If you think of the ant as a 2 dimensional creature living on a two dimensional surface of the balloon, the expansion is occurring in 3 dimensional space. The two-dimensional ant has no way to observe the space north or south (above and below, to us) its plane of existence. Now, imagine that the balloon is in a vacuum. It had a burst of air (the big bang) for a moment to get it started but it's not the further addition of air that's driving the expansion, it's the desire to equalize pressure between the exterior vacuum and the interior matter. With that in mind, push everything up a dimension. We're 3 dimensional creatures living in a 3 dimensional universe. That 3 dimensional universe exists as a plane in 4 dimensional space. The 4 dimensional balloon (that our universe is surrounding) is continuing to expand into the "nothingness" on the ana plane of the 4th dimensional universe because of the "pressure" imbalance on the kata plane of the 4th dimensional universe. (In 4th dimensional spatial terms, ana and kata indicates directions on the w axis, similar to up/down on the x axis, left/right on the y axis, and north/south on the z axis) At least, that's how I see it in my head, but I'm an odd ball who has never had a problem intuitively visualizing 4th spatial dimension objects and how they might interact with 3rd dimensional space. As for the increased speed of the expansion... actually, I hadn't thought about that. Does it indicate that equilibrium will never be found? The balloon analogy might be a useful tool, but our universe isn't made of rubber so it might have the capability of being able to expand infinitely without breaking and without its "nature" constraining the expansion speed. Anyway, if this is a reasonable analogy, the "nothingness" in the ana direction isn't as interesting to me as what might comprise the "pressure" that's in the kata direction that's causing the expansion. It's nothing we'd ever be able to observe or sample since it's outside of our plane of existence, but it's awfully fun to speculate about the composition and nature of it.

techas 7y ago

If space works as a balloon then the growth happens in all the volume of the universe (not just on the “boundary”). Is that how it works? Doesn’t that imply that we are getting “bigger”?

ggggtez 7y ago
No. Just because space is expanding doesn't change the electromagnetic forces holding you together.
- ivoras 7y ago
  But just thinking of the electromagnetic forces in terms of what is required from them to keep matter together in the context of that same matter effectively expanding faster than the speed of light is... at best weird.
  - Filligree 7y ago
    The speed of expansion depends on the size of the object. Human-scale things aren't expanding at the speed of light; you need to get to larger-than-galaxy-cluster scales for that to happen. (In fact space inside galaxies isn't expanding at all, only space between galaxies. But I digress.)
  - noselasd 7y ago
    It's not faster than light at the scale where there's matter in the universe. Across a planet or solar system it's not measurable. It's when you measure between one side of the observable universe to the oposite side that the expansion speeds get crazy.
ivoras 7y ago
(I am not a physicist) As far as I understand the current theory (i.e. our best guess), the 4 fundamental forces are somehow countering the expansion so that, even as everything in the universe expands, including e.g. every single atom, the forces are even stronger and are pulling stuff together. I think this just opens more questions than it resolves, and would really like to hear a better explanation.

brutt 7y ago

Where is the waves? 13.8B years is too short to make Universe smooth again after such epic event. It's like to see green grass again just 1 second after nuke blast: mathematical formulas will need lot of magic constants for this to explain.

madaxe_again 7y ago
The universe isn’t smooth. The CMB is not uniform, and at a very large scale the universe is composed of attractors and voids, which stem from the anisotropy of the early universe.
- brutt 7y ago
  For me, CMB is just light of distant stars with z=1100. Universe is composed of attractors and voids at any scale. Anyway, I see no shockwave of any kind in CMB. Where it is? Such massive explosion, with energy of 1E53 atomic bombs and no shockwave at all just miliseconds (in scale of Universe) after the Bing Bang. How this is possible?
  - yorwba 7y ago
    What do you expect that shockwave to look like? Circles expanding from the center of the explosion?
    - brutt 7y ago
      Yep. Something like that: https://www.youtube.com/watch?v=EmdBFoQtVvU https://www.youtube.com/watch?v=EmdBFoQtVvU .
  - zentiggr 7y ago
    Look into the inflationary portion of the BB timeline, and also add in the fact that those shockwaves have had the same 13.8B years to expand and dissipate. The CMB variations _are_ the remnants of that initial period, attenuated after all this time.
  - 7y ago

dwild 7y ago

> In the 1st second, the ant moved 10mm. But in the next four seconds you blew up the balloon, so that 10mm of rubber is now 70mm long. The total distance from the ant's starting mark to her end-point can now be well over than 70mm, even though she only walks at less than 10mm/second. Thus the expansion isn't caused by the movement of the photon but from something else? Then what caused that movement in the first place? And what cause the expansion?

ecnahc515 7y ago
If I understand correctly, the theory is that spacetime itself was created by the big bang. As-in, space, and time itself didn't exist prior to the big bang.
sqreept 7y ago
And and expansion is a lengthening of something within a frame of reference. What is the frame of reference?
- devnulloverflow 7y ago
  The visible galaxies. That is we see red-shifts when we observe distant objects. And comparing that to other distance estimates, we see that far away things are more red-shifted. As if they are moving away from us. When we build cosmological models to explain this, we could choose reference coordinates for time and space in different ways. But if we choose to define time and distance in the usual way then we get a picture in which the distances between all galaxies is increasing with time.
namirez 7y ago
You're right; the expansion of the universe is not related to photons. It's caused by the pressure of dark energy. There are some hypotheses but no one knows for sure what dark energy is.