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A question pops in my head whenever I see news of signal detection from the early age of the universe. As the universe expands we can see further in the past s

by badosu 6y ago

A question pops in my head whenever I see news of signal detection from the early age of the universe. As the universe expands we can see further in the past since light has been traveling a longer distance. However, since time has passed to reach the stage where this distance is significant there's a limit to how far we can see, and this limit is continually pushed further as the universe expands (and accelerates expansion). Now, my question is, how is it possible that we can see so far in the past? Has the early expansion rate of the universe been much faster than what I assume that it's still possible to capture these signals, are we capturing signals spread and reflected over time, or is there some other explanation/wrong assumption?

wahern 6y ago
> Now, my question is, how is it possible that we can see so far in the past? I think you're overthinking it. Forget about expansion for a moment, or other weird effects. We can see 12 billion years into the past because the universe is far larger than 12 billion (or 24 billion) light years across--possibly infinite, possibly not, but nonetheless at least that large, and at least that large at the moment the signal was emitted. What we're seeing isn't a reflection, it's light that has been traveling 12 billion years in a straight line from point of origin. Because of expansion, the earth[1] and the emission source may have been closer than 12 billion light years, but they were still very far apart. The big bang doesn't mean the universe exploded from a point source, at least not in any intuitive sense of the phrase. The exact topology is still unknown, but assuming a flat, infinite universe, the universe was already flat and infinite when the signal was emitted. See https://en.wikipedia.org/wiki/Shape_of_the_universe https://en.wikipedia.org/wiki/Shape_of_the_universe [1] Disregarding that the earth and our solar system didn't yet exist.
waheoo 6y ago
The universe is bigger than the observable universe.
- badosu 6y ago
  Is that verified? That would be a reasonable explanation
  - williamdclt 6y ago
    I'm not any sort of competent in the matter, but AFAIK there's nothing that would suggest that the universe is not bigger than the observable universe
    - tsegratis 6y ago
      Do we see the same distance into the past in all directions? Then we're the center, or prob more likely, universe stretches immeasurably beyond
      - undersuit 6y ago
        We're in the center of the observable universe, unless light travels at different speeds in different parts of the universe.
      - Balgair 6y ago
        We are very unlikely to be in the center of the universe, and all evidence points to the universe having no center. The observable universe is centered around the observer, by definition. This article explains it better than I can in a HN comment block: https://www.livescience.com/62547-what-is-center-of-universe.html https://www.livescience.com/62547-what-is-center-of-universe...
        tsegratis 6y ago
        Thanks. Is red-shift average the same in all directions? If there were a big-bang, and we were at the edge, different parts would accelerate away from us at different speeds That would give a measurable center...?? Otherwise, I suppose universe is a sheet of elastic stretched everywhere equally -- I learnt stuff from the link, it suggests universe wraps like a balloon does in 2D, but with a higher dimension. So center is not visible. They conclude no center, but equally say no evidence for higher dimensions... Of course balloons have centers just need to express them in the right dimensions So I think they defeat their own argument?? (4D objects still have centers -- just expressed 4D) But anyway, was mainly trying to find if there is an infinity within reality; or just stupendous immeasurablility? -- That would be more crazy than being at the center, imho
praveen9920 6y ago
My guess is that these signals are ambient in nature, like microwave background radiation. Like the article mentions, it is assumed that they changed the wavelength over time but in theory they exists. Imagine it is something like ambient light of a room without a light source during the day
badosu 6y ago
I found a good article on this matter: https://arxiv.org/pdf/astro-ph/0310808v2.pdf https://arxiv.org/pdf/astro-ph/0310808v2.pdf

by badosu 6y ago

wahern 6y ago

> Now, my question is, how is it possible that we can see so far in the past? I think you're overthinking it. Forget about expansion for a moment, or other weird effects. We can see 12 billion years into the past because the universe is far larger than 12 billion (or 24 billion) light years across--possibly infinite, possibly not, but nonetheless at least that large, and at least that large at the moment the signal was emitted. What we're seeing isn't a reflection, it's light that has been traveling 12 billion years in a straight line from point of origin. Because of expansion, the earth[1] and the emission source may have been closer than 12 billion light years, but they were still very far apart. The big bang doesn't mean the universe exploded from a point source, at least not in any intuitive sense of the phrase. The exact topology is still unknown, but assuming a flat, infinite universe, the universe was already flat and infinite when the signal was emitted. See https://en.wikipedia.org/wiki/Shape_of_the_universe https://en.wikipedia.org/wiki/Shape_of_the_universe [1] Disregarding that the earth and our solar system didn't yet exist.

waheoo 6y ago

The universe is bigger than the observable universe.

badosu 6y ago
Is that verified? That would be a reasonable explanation
- williamdclt 6y ago
  I'm not any sort of competent in the matter, but AFAIK there's nothing that would suggest that the universe is not bigger than the observable universe
  - tsegratis 6y ago
    Do we see the same distance into the past in all directions? Then we're the center, or prob more likely, universe stretches immeasurably beyond
    - undersuit 6y ago
      We're in the center of the observable universe, unless light travels at different speeds in different parts of the universe.
    - Balgair 6y ago
      We are very unlikely to be in the center of the universe, and all evidence points to the universe having no center. The observable universe is centered around the observer, by definition. This article explains it better than I can in a HN comment block: https://www.livescience.com/62547-what-is-center-of-universe.html https://www.livescience.com/62547-what-is-center-of-universe...
      - tsegratis 6y ago
        Thanks. Is red-shift average the same in all directions? If there were a big-bang, and we were at the edge, different parts would accelerate away from us at different speeds That would give a measurable center...?? Otherwise, I suppose universe is a sheet of elastic stretched everywhere equally -- I learnt stuff from the link, it suggests universe wraps like a balloon does in 2D, but with a higher dimension. So center is not visible. They conclude no center, but equally say no evidence for higher dimensions... Of course balloons have centers just need to express them in the right dimensions So I think they defeat their own argument?? (4D objects still have centers -- just expressed 4D) But anyway, was mainly trying to find if there is an infinity within reality; or just stupendous immeasurablility? -- That would be more crazy than being at the center, imho

praveen9920 6y ago

My guess is that these signals are ambient in nature, like microwave background radiation. Like the article mentions, it is assumed that they changed the wavelength over time but in theory they exists. Imagine it is something like ambient light of a room without a light source during the day

badosu 6y ago

I found a good article on this matter: https://arxiv.org/pdf/astro-ph/0310808v2.pdf https://arxiv.org/pdf/astro-ph/0310808v2.pdf