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RubyPorto t1_ja4d4ly wrote

Reply to comment by MOXPEARL25 in Eli5 Help, please my brain hurts. If there is an expanding ring of light from the big bang, what is outside it? by ExtremeQuality1682

>However, it is possible that there are areas of the universe where light has not yet reached us, and we cannot observe them yet.

Depending on the cosmological model you subscribe to, there are instead areas of the universe whose light will never reach us (assuming expansion continues), and we will never be able to observe. And areas where light from the past was able to reach us, but light emitted now will never be able to reach us.

For objects beyond a certain distance, the expansion rate of the universe is such that the distance between us and the object increases at a rate greater than the speed of light, meaning that photons emitted by that object will not reach us in finite time. (This does not mean anything is moving faster than the speed of light, to be clear.)

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ExtremeQuality1682 OP t1_ja4e5a8 wrote

Oh, thank you. That makes it actually make more sense. I'm thinking as there was only 1 big bang. So our light wouldnt reach them, but that doesn't mean there's nothing. Like you said they're light wouldnt reach us either. So there isn't nothing just another universe expanding toward us. Theoretically of course. It was the concept of nothing that had my brain messed up.

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RubyPorto t1_ja4gn19 wrote

I think my comment may not have been clear enough. There was only 1 big bang. There isn't another universe expanding towards us. This is all talking about one universe.

Imagine that the universe is represented by the skin of a balloon (just the 2d skin, not the internal volume). Cover the balloon with dots and pick one to call Earth. As you blow the balloon up, all of the dots will get farther from the earth dot, but the change in distance will be smaller for the near dots than the already far dots. Now imagine there's a speed limit for moving between the dots. If the rate at which the distance to the far dots is increasing is faster than that speed limit, you can never get from the far dots to the Earth dot.

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apoeticturtle t1_ja6zmlv wrote

Unfortunately, imagining "nothing" beyond the balloon is where everyone gets lost. Most people, with sense, would easily counter-explain that the balloon could not expand without the "room" to be able to expand. I mean, sure the "thing" expanding also made/caused the actual phenomenon of expansion, but we'll let the philosophers continue haggling over that paradox.

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RubyPorto t1_ja70srv wrote

Every model has limits. The point of the balloon model here is to explain how a cosmologic event horizon can occur.

I agree with you that it's limited as a way to visualize the general idea of the expansion of the universe, since it requires the same essential leap as not using a model (i.e. that the universe isn't expanding into/through anything).

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apoeticturtle t1_ja7n728 wrote

Can you point me to any information on how the idea of this "expanding into nothing" can be conceptualized?

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sofar55 t1_ja9fn4t wrote

Going back to the balloon analogy, the dots are moving away from each other. Without the vertical dimension, the "universe" of the balloon surface is getting bigger, but what is it expanding into? The space between dots is expanding, but where is the space coming from?

In this model, the dots dont understand elastic stretching. In the universe, it's believed that empty space is just expanding and pushing everything apart, but we don't know how.

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RubyPorto t1_ja9asum wrote

I'm not sure I can. Every physical analogy is going to be expanding into a medium.

It's also not really "expanding into nothing." The coordinate plane of space is itself expanding, full stop. It's not expanding into anything (or nothing).

It's a fact that you just have to decide you're ok with, without a relatable model to compare it with.

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apoeticturtle t1_jabgplj wrote

There are many things in my life that I do have to decide if I am OK with, but thankfully not this one. I cannot even imagine "nothing" and having less than nothing (that which lies beyond our Universe's edge) is as mind-boggling as it is speculative. All the energy in our Universe may be just a tiny fraction of all the energy everywhere/when. It seems more likely, to me, that our Universe is a tiny part of something bigger. If not, what a waste of energy and time/space.

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