The size of the universe and seeing back in time


#1

On one hand we see that the universe is about 13,7 billion years old and about 150 billion light years across. So when we look at the far reaches (the edges) of the universe we are seeing back in time.

On the other hand, the universe started as a small point and expanded from there. So why is it that the farther we look out in any direction, we don’t see a smaller, more condensed universe since we are actually looking back in time when things had less time to expand into what they are today?

This is one of those questions that only a layman would ask, I’m pretty sure! I think I’m just not understanding some fundamental thing that others do, so help me wrap my brain around this!


(Larry Bunce) #2

My understanding of how the universe expanded from an original point to its present size can be visualized as an inflating balloon. The original point at the time of the Big Bang is always at the surface of the balloon, and we are somewhere inside the balloon. The oldest part of the universe that we can see is the farthest away we can see in any direction. The reason we can see objects more than 13.7 billion light-years away is because they were much closer to us when their light began heading in our direction.

The Big Bang was hypothesized in the 1930s, based on Hubble’s observations of redshifts in more distant objects. The farther away an object was, the more its redshift, indicating it was moving away from us faster. Projecting this motion backwards in time, astronomers calculated that the universe would have started out as a point about 14 billion years ago. This idea was rejected by most scientists until the 1960s, when radio telescopes detected a background radiation coming from all directions in space, representing exactly the initial temperature that had been predicted by the Big Bang theory.


#3

Thanks for responding. I’m also familiar with the balloon analogy, but that visualization is exactly my question.

If the beginning is on the outer, larger surface of the balloon (and thus farther back in time), and if things expand outward from a small, condensed singularity, why isn’t the balloon analogy exactly the opposite? Wouldn’t the farther back in time we look be physically smaller (closer to the singularity), not physically larger (as in the edges of the balloon)?


(Phil) #4

I find the rising raisin bread model to be helpful in visualizing the universe also, being in 3 dimensions . If the raisins all started from a central point and expanded, the raisins all are equally at the center of the big bang, and once expanded, the ones on the other side of the pan or in the middle of the pan are no more condensed than the ones near the edge. All have equal claim to being at the origin of the big bang.


(Larry Bunce) #5

The start of the universe is a very strange world. At the moment of the Big Bang, the universe had no size at all. The outside of that point, still with no size, is all that there was. With the expansion of space, the ever increasing outside of the universe, corresponding to the outside of the balloon, still contained matter from the initial Big Bang. Everything in the universe today had its start with the Big Bang, but the outside of our current universe still has matter from the earliest time when matter formed. I don’t remember offhand how long after the Big Bang it was when things cooled off enough that subatomic particles could form atoms.


(Jay Johnson) #6

Just the thought that the light we see from distant objects has traveled to us from the distant past blows my mind! If we could somehow see the same objects as they appear at this exact moment (if light could arrive instantaneously, rather than having to travel vast distances to reach us), I wonder how things would change?

Speaking of the Big Bang, here is an interesting article from phys.org No Big Bang? Quantum equation predicts universe has no beginning

I have no idea how this theory has been received by the scientific community. It is interesting to speculate how this would impact theology if it supplanted the Big Bang and became the new cosmological paradigm.


(Larry Bunce) #7

Thank you for the link the article on quantum theory and the Big Bang. I looked around at some other articles on the web, and found one that said that these new equations don’t really eliminate the Big Bang. The new equations only eliminate the singularity, which is the point where all of our laws of physics break down. I also saw a transcript of a lecture by Stephen Hawking where he talks about another theory that the initial point of the Big Bang was like the North Pole-- it may be a starting point, but it is indistinguishable from other places on earth., or in the cosmos in this case

The world of higher math leads to many conclusions that seem like science fiction to ordinary people.


(Jay Johnson) #8

I’m very ordinary in that regard!


(system) #9

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