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Scale of the Universe

(scaleofuniverse.com)
249 points Leftium | 7 comments | 19 Apr 24 03:53 UTC | HN request time: 0.249s | source | bottom
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ralegh ◴[19 Apr 24 09:31 UTC] No.40084787[source]▶
For a second I thought we'd seen a lot of the universe, the HDF being 1/5th the radius away and on googling Earandel is 2/3rds the radius... of the known universe.

"According to the theory of cosmic inflation initially introduced by Alan Guth and D. Kazanas, if it is assumed that inflation began about 10−37 seconds after the Big Bang and that the pre-inflation size of the universe was approximately equal to the speed of light times its age, that would suggest that at present the entire universe's size is at least 1.5×1034 light-years—at least 3×10^23 times the radius of the observable universe."

So, if true, all those metrics of atoms, stars, planets in the known universe are multiplied by 10^23.

Even if intelligent life were rare enough to only appear once per knowable universe, there could be 10^23 different intelligent species - single planet to galaxy spanning empires - that would probably never meet another intelligent species (except those with the same ancestors).

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deepsun ◴[19 Apr 24 13:27 UTC] No.40086574[source]▶
The problem is in words "at present". There's no some global timeline to say "present". The time in far away places just didn't happen yet.

UPDATE: minor consideration -- time can flow at different speeds (e.g. gravitational wells). That's probably doesn't matter to our discussion, but just another argument against "at present".

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1. rspoerri ◴[19 Apr 24 14:04 UTC] No.40086977[source]▶
Just because you dont see it, doesnt mean it didnt happen. The light the sun emits will only be seen by us ~8min later, but it's still being emitted right now.
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2. deepsun ◴[19 Apr 24 15:25 UTC] No.40088001[source]▶
No, there's a mistake in the statement.

Counter-example -- what's happening _right now_ at a distance of 20 billion light-years from us?

Or another question -- what happened 1 hour _before_ the Big Bang?

Both questions are already invalid by themselves.

UPDATE: I should've tried to answer my questions to show what I mean:

1. At 20B ly from us there's no space nor time to talk about. Physicists talk in formulas, and I suspect if I knew how, I just wouldn't be able to come up with a formula to formulate my question.

2. "before" the Big Bang there was no time itself to say "before".

In other words, we can only reason about, or imagine, reason about things, within our light cones. Outside light cone questions become invalid to ask.

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3. petsfed ◴[19 Apr 24 16:16 UTC] No.40088643[source]▶
Sort of.

The concept of simultaneity is mind-bending when you really dig into it [0]. The upshot is that the hard problem of synchronizing distributed systems is a problem of fundamental physics, rather than simply the capabilities of any given developer. Its always nice to know that the reason you haven't met some specification given to you by a non-technical user representative is because meeting that specification violates the known laws of physics.

0. https://en.wikipedia.org/wiki/Relativity_of_simultaneity

4. foobarian ◴[19 Apr 24 17:29 UTC] No.40089624[source]▶
Can't we imagine a bag of clocks at the Big Bang origin that were synchronized and allowed to travel in all directions along with various sections of the ejecta, including one on Earth? One could imagine events that happen at the same clock reading as ours in all the different parts of the visible and non-visible universe.
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5. riotnrrd ◴[19 Apr 24 18:55 UTC] No.40090693{3}[source]▶
The effects of relativity cause that thought experiment to fall apart quickly. I build two clocks, and send one to alpha centauri and back in a spaceship. When the travelling clock gets back to Earth it will be showing a different time (because of time dilation during acceleration). What does "the same clock reading" mean then?
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6. deepsun ◴[20 Apr 24 16:09 UTC] No.40098377{3}[source]▶
It's totally possible that such clocks could then touch each other in one place, while both showing widely different readings. Which one is right then?

PS: by the way, Poincare proved that there's no way to synchronize clocks perfectly, only up to a some margin.

7. foobarian ◴[21 Apr 24 18:30 UTC] No.40108019{4}[source]▶
Yes of course they won't show the same time if you bring them back. But the point is to argue that it is possible for there to be a "right now," as defined by what the traveling clock shows, outside of our light cone.