# The Naked Scientists Forum

### Author Topic: Universe's Shape, Size and.. Something Illogical?  (Read 1660 times)

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##### Universe's Shape, Size and.. Something Illogical?
« on: 11/01/2016 16:48:12 »
Hi,

There is something I don't understand about the Big Bang theory but before that I want to make sure we're all on the same logic here, if you to the x direction from determined point zero, relative to point zero your position changes over time, in other words the distance between point zero and you increases over time in the x dimension. So far so good right we all agree here? Now we can consider curved space where going enough forward will eventually bring you backwards but that's irrelevant, unless if our observation are not accurate.

Now for the question I had, the way I understand the Big Bang is this:
There is a zero dimensional existence (or pre existence whatever)
Something happened at that zero dimensional existence
Suddenly three sapital dimensions and one time dimension spawned ( our 4d universe )
But those three dimensions where very small and everything had enough time to communicate with each other which is why the microwave background radiation is so equal
Then the universe inflated and now it's infinite and flat according to observations

You see the problem there? First how can anything that is three dimensional and not curved be bounded by any particular size? Your answer might be that it's not that space started somewhere and then expanded outwards rather it was that space simultaneously spawned everywhere and we're just expanding since, if that's the case how could anything had enough time to communicate with the other side? You see I'm have a problem understanding how to connect the fact that the universe is infinite, flat, had any particular size and evenly spread out microwave background radiation

If the universe is not infinite then how can it be flat, at the edge of the universe three sapital dimensions and time seizes to exist? If the universe is infinite and flat how could have it had any particular size in the past? How could the microwave background spread evenly throughout the universe so fast?
« Last Edit: 11/01/2016 16:49:54 by Spaskiba »

#### evan_au

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##### Re: Universe's Shape, Size and.. Something Illogical?
« Reply #1 on: 11/01/2016 19:25:18 »
I'm have a problem understanding how to connect the fact that the universe is infinite, flat,  had any particular size...
This may be confusing some concepts:
• finite (ie does not go on forever) and bounded (ie has a distinct boundary).
• flat (ie obeys Euclidean geometry) and curved (ie does not obey Euclidean geometry, if you measured it accurately enough, on large enough scales)
A 2-dimensional analogy may be the surface of the Earth, which has a finite area, but has no distinct boundary, so if you continue in one direction, you eventually reach your starting point. It is curved on the local scale (hills and valleys) and on the global scale, but you would have trouble proving this with parallel lines drawn on a sheet of paper.

A hint of this is contained in the dismissive
Quote
consider curved space where going enough forward will eventually bring you backwards but that's irrelevant
We can't measure the universe well enough, or see past the Big Bang to determine if we would arrive back at our current location, if we left at some time in the past.

The discovery of Dark Energy suggests that if we left now with an ion drive spaceship, we would not arrive back at our starting point, because the universe would have expanded faster than we could travel.

All our measures suggest that while space is curved on the scale of solar systems & galaxies, it is flat on larger scales. But perhaps we are not measuring on a large enough scale?

#### dhjdhj

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##### Re: Universe's Shape, Size and.. Something Illogical?
« Reply #2 on: 11/01/2016 21:46:03 »
What if our universe is just one of many and space is a three dimensional entity into which our universe is born, will grow (expand) and ultimately die when all energy ceases to emit from stars. Would everything then collapse back into a black hole or holes and re-emerge to create another universe in the same volume. This would of course mean that the universe was bounded, but it would float or exist in an unbounded space curved or otherwise. Is it possible to establish whether the expansion is by the universe getting bigger? as if each galaxy is on a kind of grid where the grid is expanding or is it expanding by everything moving radially away from some point somewhere. Do our observations tell us? If we had a balloon filled with gas and in this gas were smaller balloons floating. There would two ways there could be relative expansion between the internal balloons ( I am assuming the internal balloon has a hard skin so does not expand in itself). One is if the external pressure is reduced the encompassing balloon would expand taking the internal ones with it, or energy could be applied to the internal balloons moving them towards the outer skin of the outer balloon. Now an ant (a very intelligent ant) sitting on one of the internal balloons would have no way of knowing which it is. Do we not have the same situation? We are assuming that dark energy and dark matter are driving accelerated expansion, but could not space itself be expanding?

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##### Re: Universe's Shape, Size and.. Something Illogical?
« Reply #3 on: 12/01/2016 02:04:04 »
I'm have a problem understanding how to connect the fact that the universe is infinite, flat,  had any particular size...
This may be confusing some concepts:
• finite (ie does not go on forever) and bounded (ie has a distinct boundary).
• flat (ie obeys Euclidean geometry) and curved (ie does not obey Euclidean geometry, if you measured it accurately enough, on large enough scales)
A 2-dimensional analogy may be the surface of the Earth, which has a finite area, but has no distinct boundary, so if you continue in one direction, you eventually reach your starting point. It is curved on the local scale (hills and valleys) and on the global scale, but you would have trouble proving this with parallel lines drawn on a sheet of paper.

A hint of this is contained in the dismissive
Quote
consider curved space where going enough forward will eventually bring you backwards but that's irrelevant
We can't measure the universe well enough, or see past the Big Bang to determine if we would arrive back at our current location, if we left at some time in the past.

The discovery of Dark Energy suggests that if we left now with an ion drive spaceship, we would not arrive back at our starting point, because the universe would have expanded faster than we could travel.

All our measures suggest that while space is curved on the scale of solar systems & galaxies, it is flat on larger scales. But perhaps we are not measuring on a large enough scale?

Ok aside from correcting me, thanks btw, how could have the universe had a finite size in the past?

#### Ethos_

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##### Re: Universe's Shape, Size and.. Something Illogical?
« Reply #4 on: 12/01/2016 03:56:57 »

Ok aside from correcting me, thanks btw, how could have the universe had a finite size in the past?
I personally believe that "our universe" was just a finite local event which occurred within an infinite spatial expanse. I can't prove that hypothesis so don't ask me to so. My position is very much like so many other opinions on this subject, the information we need lies somewhere beyond the big bang and out of reach. We are left with only speculation.

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##### Re: Universe's Shape, Size and.. Something Illogical?
« Reply #5 on: 12/01/2016 14:30:27 »

Ok aside from correcting me, thanks btw, how could have the universe had a finite size in the past?
I personally believe that "our universe" was just a finite local event which occurred within an infinite spatial expanse. I can't prove that hypothesis so don't ask me to so. My position is very much like so many other opinions on this subject, the information we need lies somewhere beyond the big bang and out of reach. We are left with only speculation.

As much as I like theories and ideas, I like them only where we're stuck, right now we still didn't resolve the problem of which is it, a finite universe that was bounded by the end of dimensions (whatever that means) or was it a universe unbounded dimensions that came into existence but then how did the microwave background radiation became so evenly spread?

#### Ethos_

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##### Re: Universe's Shape, Size and.. Something Illogical?
« Reply #6 on: 12/01/2016 23:20:04 »

As much as I like theories and ideas, I like them only where we're stuck, right now we still didn't resolve the problem
Evidently, you haven't understood my hypothesis. Our universe came from a finite big bang and therefore will remain finite itself. However, when I refer to "our universe", I'm not speaking about the "Infinite Cosmos" within which our universe resides. While our universe is indeed finite, the Cosmos is not, it is infinite. But because the space outside "our personal universe" is unobservable from our place within it, we can never view what lies beyond. The speed of light and the expansion of "our universe" prevents observation from ever being possible.
« Last Edit: 13/01/2016 23:09:24 by Ethos_ »

#### evan_au

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##### Re: Universe's Shape, Size and.. Something Illogical?
« Reply #7 on: 13/01/2016 08:14:21 »
how could have the universe had a finite size in the past?
It is commonly thought that the universe after the Big Bang had a finite mass, and a finite size, giving a finite (but very high) density, and a finite (but very hot) temperature. This has now expanded so that it still has a finite mass (roughly the same as it started with), and a finite size (very much larger than when it started), producing a finite (but very low) density, and a finite (but fairly low) average temperature.

As alluded to in the OP, Guth's theory about rapid inflation allows for the very uniform CMBR across the sky.

It is possible that we may not be able to see the entirety of our universe, as the expansion of the universe may have taken some parts of it beyond where light can reach our telescopes.

If there are other universes (a "multiverse"), it is not clear whether we could see any of them, either.

So we are just left with a finite observable universe, which derived from a presumed finite initial universe.
http://en.wikipedia.org/wiki/Observable_universe

#### Alohascope

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##### Re: Universe's Shape, Size and.. Something Illogical?
« Reply #8 on: 15/01/2016 21:56:50 »
This is relatively 'odl' news in cosmological developments, but measurements indicate Cosmic Microwave Background is just heat from dust, not rapid expansion.

CMB was initially an excuse to explain why observations did not match theory .. 'oh, the universe is bigger than we thought, there must have been a period of intense expansion.'

My link is not allowed, so search 'cosmic inflation signal just dust.'

#### alysdexia

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##### Re: Universe's Shape, Size and.. Something Illogical?
« Reply #9 on: 17/01/2016 17:43:03 »
I don't necessarily believe in inflation, which the Guth equation shows was hıperbolic exponential growth rather than only exponential growth as Wikipedia prose says, but that smoothness is a result of local conservation laws.

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##### Re: Universe's Shape, Size and.. Something Illogical?
« Reply #9 on: 17/01/2016 17:43:03 »