The Universe has boundary?

RJBeery said:
It really forces us to consider, what IS space? Is it "something" beyond emptiness? If not, "what" does GR predict is curved in the presence of energy?
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Space and energy would seem to have a codependent existence, as energy occupies space, each of them necessarily three dimensional.

Empty space, if it could be, would have no energy, but is more like the nonexistence of energy; however, one cannot exist without the other. While nothingness is the absence of all things, space is the lack of something, and that something is energy. There’s a bit more to it, but this concerns ‘nothing’, which is not the subject here.
 
So, then, if the so-called vacuum fluctuates everywhere, then the cosmos, if not the universe, is boundless.
 
Pete said:
Spacetime is something real that has real properties, such as geometry.
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Now wait a minute, I know you don't claim to be an expert on this but any explanation should be consistent. If spacetime is considered "real", and you believe space has no boundaries, then did "something" extend infinitely in all spatial directions immediately following the BB?
Uni of Michigan said:
This occurance was not a conventional explosion but rather an event filling all of space with all of the particles of the embryonic universe rushing away from each other. The Big Bang actually consisted of an explosion of space within itself unlike an explosion of a bomb were fragments are thrown outward. The galaxies were not all clumped together, but rather the Big Bang lay the foundations for the universe.
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This is how I've read the BB being described when discussing the origins of space.
 
If spacetime is considered "real", and you believe space has no boundaries, then did "something" extend infinitely in all spatial directions immediately following the BB?
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how can anyone answer this seriously without it being speculation? we can only see so far out in the universe.
 
birch said:
how can anyone answer this seriously without it being speculation? we can only see so far out in the universe.
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Of course it's speculation, but when I read
Pete said:
We conclude (from best available evidence and models) that the universe has no spatial boundary.
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I got confused because that conflicted with my layman's understanding of the BB. I've continued to probe Pete on this but I just read the following, which I apparently missed earlier:
Pete said:
The 3-space my be spatially infinite. I think (not sure) that this is not consistent with single point of beginning, and I'm not sure how this is addressed in the Hot Big Bang model. I think that a past timelike boundary in an infinite universe must itself be infinite, ie if the Universe is infinite now, then it must have been infinite at the time of the Big Bang.
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This really resolves the confusion for me. Pete agrees that there may be a problem if we take "no spatial boundary" to mean that "space is infinite". However, if we simply mean that it is closed, then the problem is avoided. Nothing really to see here, move along. :)
 
RJBeery said:
Now wait a minute, I know you don't claim to be an expert on this but any explanation should be consistent. If spacetime is considered "real", and you believe space has no boundaries, then did "something" extend infinitely in all spatial directions immediately following the BB?
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Like I said above, my understanding is that the Universe is either spatially finite, or it was already spatially infinite at the Big Bang.

This is how I've read the BB being described when discussing the origins of space.
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I read that as describing the expansion of space, not the origin of space.

Here's [post=2685483]something I posted earlier[/post]:

...book chapter from Current Issues in Cosmology, 2006:
Cosmology, an overview of the standard model (pdf), Francis Bernardeau.
Extract from Introduction:

As will be discussed in the conclusions, the issue of the "birth" of the Universe is actually beyond the standard cosmological theory. What is left of this idea, however, is that the physical properties of the Universe have rapidly evolved over the course of the cosmological time, leading to a rapid decrease of both the density and the temperature of the Universe.​

Extract from Conclusions:

Finally there are questions that standard cosmology hardly addresses and for which there are certainly no clear answers. For instance standard cosmology does not claim that there actually existed a genuine Big Bang, i.e. a space-time singularity. For instance in "pre-big-bang" or ekpyrotic models there is no such global GR singularity. In essence cosmology is essentially the theory of a fluid expansion, it does not say much about the initial impetus that might be at its origin. Whether the Universe is finite or infinite is also a question which is mainly left unanswered. There might exist compact spatial directions at scale larger than the observable universe which we may never be able to detect. The global space-time structure of the Universe, at scale much beyond the observable universe is also unknowable.​
 
When All is considered, of that which gives rise to existence, or itself is existence, then this All could have no bound of extent nor bound upon its duration, for then it would hardly be the All at all.
 
The universe has no boundary. We imagine ourselves to be distant, separated alien identities but in a pure consciousness experience where the ego and the soul are in abeyance or dead completely, the actuality of non-separation becomes wonderfully apparent. You physical body is at one with the rest of the universe as you are the universe experiencing itself as a flesh and blood body.
 
birch said:
truly a sane statement. i'm tired of reading that the universe is infinite as a fact when we just don't know. actually it's preposterous to make such a definite claim, no different than religious dogma.
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I agree with you that it would be dogma to claim that it is definitely true that the universe is spatially infinite though that is speculation that I am comfortable with, and I agree with you and AlphaNumeric when you say that we just don’t know or it is unknown and perhaps (and I would add probably) unknowable.

I don’t see how it is truly sane to say that the boundary of the visible universe is due to the finite age of the universe. The visibility boundary may be due to the finite period of time since the Big Bang but it does not necessarily follow that the Big Bang was the origin of the universe. It was the origin of the known universe and the visible universe but that doesn’t mean that there weren’t preconditions to the Big Bang that where connected to a pre-existing universe.
 
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quantum_wave said:
I don’t see how it is truly sane to say that the boundary of the visible universe is due to the finite age of the universe. The visibility boundary may be due to the finite period of time since the Big Bang but it does not necessarily follow that the Big Bang was the origin of the universe. It was the origin of the known universe and the visible universe but that doesn’t mean that there weren’t preconditions to the Big Bang that where connected to a pre-existing universe.
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I like the way you said that and I believe it's true, because our visible universe can only be put into context with nature if it's a normal function of a much larger structure of the larger real universe.
 
KilljoyKlown said:
Suppose the BB and our current visible universe is a natural product of a much larger structure. Has happened before and will happen again and probably happens concurrently at distances from each other we can't begin to understand. If infinite space time does exist, this concept is not unreasonable and actually brings our universe back into context with nature and allows speculation about what kind of structure might support a BB that results in a visible universe.
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Yes, well said and I agree that if it was known that the universe was infinite in time and space then there would be endless speculation about the nature of the preconditions within the scientific community. However, it is not known to be infinite and so speculation about the preconditions does not fall under the umbrella of the scientific method. See me in the Pseudoscience forum Killjoy, lol.
 
SciWriter said:
When All is considered, of that which gives rise to existence, or itself is existence, then this All could have no bound of extent nor bound upon its duration, for then it would hardly be the All at all.
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It takes a minute to think about that but it does have a lot of merit. Let me state what you said in my own words and see if I have it as you meant it. You are saying that if in the big picture our existence, which could either somehow stem from non-living elements and conditions or could be a part of a universe that itself has life as an integral part of its existence (which might be called All existence) might logically have no beginning and no boundary?
 
quantum_wave said:
It takes a minute to think about that but it does have a lot of merit. Let me state what you said in my own words and see if I have it as you meant it. You are saying that if in the big picture our existence, which could either somehow stem from non-living elements and conditions or could be a part of a universe that itself has life as an integral part of its existence (which might be called All existence) might logically have no beginning and no boundary?
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Yes, but with existence being anything having a quantity, not just life. Any boundaries of either extent or duration would seem to surely kill the All from being All. Now, as all possible things happen eventually due to energy going through all of its paces, life will surely form in many places.
 
You must first define the term "universe" before you can begin to answer the question if it's finite or infinite.

If you define the term universe as an element part of a larger element, then the universe has boundaries such as the earth does, or a snowball does. I do not define or consider the universe as an object with boundaries.

If you define the term universe as a volume which contains objects of mass, then certainly the universe is infinite, without boundaries. It is impossible to have a finite volume with this definition of universe, as you can always have a greater volume.

There is no boundaries on the volume of space.

Mass evolves to space!
 
Motor Daddy said:
...and vibration is free in the universe. :rolleyes: Perpetual vibration for everyone!!! It's free folks, never ending vibration...come and get it!!
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Hmm, is that in red or does it only come in green with orange stripes?
 
If you define the term universe as a volume which contains objects of mass, then certainly the universe is infinite, without boundaries.
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it is not certainly. it's a conjecture and a speculation at best.
 
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