The edge of the universe

[luckyfrank]

It's hard to believe that the universe is not infinite, i mean there is a place where the universe just stops and then there in nothing

no matter no space no time, but surly if the universe is expanding it must be expanding into something that wasnt there before

Ive read before that it's not the universe that's expanding just that the space within it is expanding if that makes sense

Hypothetical question : If i was standing on the very edge of the universe with a tennis ball in my hand and threw that ball over the edge what would happen to the ball ?

[01101001]

Hypothetical question : If i was standing on the very edge of the universe with a tennis ball in my hand and threw that ball over the edge what would happen to the ball ?

You assume there is an edge. Why?


[...] surly if the universe is expanding it must be expanding into something that wasnt there before

No.

From the Sean Carroll Cosmology FAQ (http://preposterousuniverse.com/writings/cosmologyprimer/faq.html#into) (one of many fine resources listed in topic ** FAQs ** Resources On The Web (http://www.bautforum.com/space-astronomy-questions-answers/22865-faqs-resources-web.html)):


What is the universe expanding into?
As far as we know, the universe isn't expanding "into" anything. When we say the universe is expanding, we have a very precise operational concept in mind: the amount of space in between distant galaxies is growing. (Individual galaxies are not growing, as they are bound together by gravity.) But the universe is all there is (again, as far as we know), so there's nothing outside into which it could be expanding. This is hard to visualize, since we are used to thinking of objects as being located somewhere in space; but the universe includes all of space.

[Jeff Root]

Hypothetical question : If i was standing on the very edge of the universe
with a tennis ball in my hand and threw that ball over the edge what would
happen to the ball ?
You assume there is an edge. Why?
Why not? It seems a reasonable and natural assumption. Is there any
other assumption one could make that is as reasonable or as natural?

-- Jeff, in Minneapolis

[ccart3r]

Maybe Space/Universe is not all that "this" is made of. No way of knowing. We view space as nothing beyond that, for all we know there may be some type of other "space" outside of our universe. Or possibly space doesn't end within our universe? We just proceed it within our universe only.

All in the imagination until we know other wise.

[cosmocrazy]

Maybe Space/Universe is not all that "this" is made of. No way of knowing. We view space as nothing beyond that, for all we know there may be some type of other "space" outside of our universe. Or possibly space doesn't end within our universe? We just proceed it within our universe only.

All in the imagination until we know other wise.

Well yes this may be true, but whats your definition of the "universe"?

The observable universe is one thing but the actual size, if one could even define size regarding the universe, is another. As 01101001 stated there may not be an edge in the classical way we might think of one. But then there maybe one but at present its just not observable. The universe could be a finite closed loop or perhaps infinite in space/time.

We just don't know enough to assume either one way or the other. All we can say is that from what we have observed so far the universe appears basically flat, around 14 billion years old and is expanding. Whats beyond that at present is an open book.

[speedfreek]

Why not? It seems a reasonable and natural assumption. Is there any
other assumption one could make that is as reasonable or as natural?

-- Jeff, in Minneapolis

What about the assumption that the thing we live in (the universe) is similar to the thing we live on (the surface of the Earth)?

If the Earth was flat, and had an edge such that if you walked far enough you could fall off, I would understand the assumption that the universe had such an edge.

;)

[JohnD]

Lf,
It's easy to ask the question.
It's more difficult to answer.
But it's very easy inded to do a search of this website, say for "edge universe"
I found more than the 500 hits that the search can use.
By doing that you will find a great deal of information.
I suggest you do.

Meanwhile, the 'balloon' anology is imperfect, but may be helpful.
Imaginme a universe on the surface of a baloon.
It is a 2 dimensional universe, that expands as the balloon is inflated.
For a 2D inhabitant, it is getting bigger, but into nowhere.

Good luck!
John

[luckyfrank]

Thanks for the answers

[Hungry4info]

It's helpful to think of the universe's expansion as an expansion of space, instead of an expansion in space. So there isn't a need for room to expand into.


If i was standing on the very edge of the universe with a tennis ball in my hand and threw that ball over the edge what would happen to the ball ? It would make a dull thud and bounce back. :lol:

[captain swoop]

or come round and hit you in the back of the head.

[cosmocrazy]

Or just cease to exist. :)

[Hungry4info]

What about an IndexOutOfBoundsException error?

[korjik]

Why not? It seems a reasonable and natural assumption. Is there any
other assumption one could make that is as reasonable or as natural?

-- Jeff, in Minneapolis

Physics is not restricted to what you think is reasonable and natural. As a matter of fact, it quite frequently acts unreasonably.

[luckyfrank]

What about the assumption that the thing we live in (the universe) is similar to the thing we live on (the surface of the Earth)?

If the Earth was flat, and had an edge such that if you walked far enough you could fall off, I would understand the assumption that the universe had such an edge.

;)

Ok fair enough but lets say you were able to throw the ball faster than the universe is expanding ?

Another thing on my mind is when we look to the furthest reaches of the universe we are looking back in time to the start of the universe and everything is expanding from there then surly the origin of the big ban should be in the center of the universe right ? Do we know the location of the inital start of everything

[Andrew D]

Ok fair enough but lets say you were able to throw the ball faster than the universe is expanding ?

Another thing on my mind is when we look to the furthest reaches of the universe we are looking back in time to the start of the universe and everything is expanding from there then surly the origin of the big ban should be in the center of the universe right ? Do we know the location of the inital start of everything

The universe isn't expanding in a way that would allow the ball to surpass the 'expansion' as you suggest. It's apples and oranges.

And there is no 'center' or the universe objects are expanding away from. Search this forum for "expanding universe" and you'll find dozens of posts, including one started by myself a few weeks ago, that will answer your question...I've learned a lot since then...

[cosmocrazy]

Ok fair enough but lets say you were able to throw the ball faster than the universe is expanding ?

Since the universe is believed to be expanding at a rate of C or greater at the furthest detectable distances away from us, then based on relativity this would never be possible.



Another thing on my mind is when we look to the furthest reaches of the universe we are looking back in time to the start of the universe and everything is expanding from there then surly the origin of the big ban should be in the centre of the universe right ? Do we know the location of the inital start of everything

Yes, but based on the BB theory the centre itself is expanding, so the centre of the universe is everywhere.

[Hungry4info]

Ok fair enough but lets say you were able to throw the ball faster than the universe is expanding ?
That isn't possible. The expansion of the universe doesn't quite work that way. Recall the expanding balloon analogy. For anybody in this universe (the surface of the balloon), the local space around them does not seem to be expanding very rapidly, but only things far away seem to be doing so. So to overcome the expansion of space at the observer's location, you can just nudge the tennis ball to a few mm per decade and you'll have overcome the Universe's expansion at your local space. The expansion rate of the universe is ~500 km s-1 Mpc-1. That's 500 kilometres per second... per megaparsec. The expansion of the universe is 500 km s-1 across a million parsecs! Condering a million parsecs, 500 km s-1 is pretty much nothing. As such, if you were a Mpc away from an object, it would seem to receed from you at 500 km s-1. So let's say you throw something at 500 km s-1 so that it'll catch up with whatever object is a Mpc away. Well an object at 2 Mpc is moving away at 1,000 km s-1, so you'll never catch up with that one. So you can throw it harder if you want. Well an object three times as far (6 Mpc) is moving away at 3,000 km s-1. On and on... until you're aiming at something 600 Mpc away, which is moving away from you at 300,000 km s-1. You'll find yourself unfortunately incapable of throwing your tennis ball that fast.


Another thing on my mind is when we look to the furthest reaches of the universe we are looking back in time to the start of the universe and everything is expanding from there then surly the origin of the big ban should be in the center of the universe right ? Do we know the location of the inital start of everything
Again, recall the expanding balloon analogy. There's no point on the balloon's surface that you can identify as the start of the expansion. Any observer on the balloon would see the rest of the balloon expand away from his current location, regardless of where they are.

As such, no matter where you are in the Universe, you appear to be at the centre of expansion. In truth, the Universe lacks a centre much like the balloon lacks any true central point of expansion.

[DrRocket]

Why not? It seems a reasonable and natural assumption. Is there any
other assumption one could make that is as reasonable or as natural?

-- Jeff, in Minneapolis

The usual assumption (see for instance The large-scale structure of spacetime by Hawking and Ellis) is that space time is a 4-dimensional Lorentzian manifold without boundary (without an edge). That seems to be both reasonable and natural.

If you assume the structure of a manifold with boundary, then you have to contend with what is happening in the boundary. That boundary will be a 3-manifold without boundary, so locally 3-dimensional. Now, what is a 3-dimensinal spacetime? Is it locally timeless or is is locally 2-space with some notion of time ? Neither makes sense.

[Jeff Root]

You assume there is an edge. Why?
Why not? It seems a reasonable and natural assumption. Is there any
other assumption one could make that is as reasonable or as natural?
What about the assumption that the thing we live in (the universe) is similar
to the thing we live on (the surface of the Earth)?
Why would anyone make *that* assumption? It appears to be completely
baseless. Not the least bit reasonable or natural!



If the Earth was flat, and had an edge such that if you walked far
enough you could fall off, I would understand the assumption that the
universe had such an edge.
What does the surface of the Earth (or anything else) have to do with
the extent of the Universe??? I see no connection. There is no apparent
reason to assume any connection or any similarity between the two.

The original poster's assumption is completely reasonable and natural.
There is nothing at all reasonable or natural about the assumption you
suggest.

-- Jeff, in Minneapolis

[Hungry4info]

Is it locally timeless or is is locally 2-space with some notion of time ? Neither makes sense.

Why would a 2+1 spacetime not make sense?


What does the surface of the Earth (or anything else) have to do with the extent of the Universe??? I see no connection. There is no apparent reason to assume any connection or any similarity between the two.
The original poster's assumption is completely reasonable and natural. There is nothing at all reasonable or natural about the assumption you suggest.

I think the point he was trying to make was that asking what happens when you move off the edge of the Universe was similar to asking what happens if you move off the edge of Earth in that the two are based on incorrect assumptions.

[Jeff Root]

Physics is not restricted to what you think is reasonable and natural.
Obviously.

Even if it weren't obvious, it would still be a completely reasonable and
natural assumption that physics isn't restricted to what I think is reasonable
and natural. I would not be surprised to learn that the original poster
assumes that physics is not restricted to what I think is reasonable and
natural. Nor would I be surprised to learn that he assumes that physics
is not restricted to what he thinks is reasonable and natural.

Whatever. The assumption that the Universe has an edge is completely
reasonable and natural. Is there any other assumption one could make
that is as reasonable or as natural? Is it your view that unreasonable
and unnatural assumptions are preferable to reasonable and natural
assumptions?

-- Jeff, in Minneapolis

[Hungry4info]

I think what the issue is here is that what is reasonable to one is unreasonable to another, perhaps due to a knowledge gap. Those more familiar with the BBT may find "every point appears to be the centre of the universe" to be reasonable, whereas someone unfamiliar with it wouldn't.

[DrRocket]

Why would a 2+1 spacetime not make sense?

Why would it ? If you travel to the edge do you simply flatten out ?

Huygens principle fails to work in even spatial dimensions, so does physics change at the boundary ? Remnember that this boundary, if it were to exist, would be a part of spacetime. It is not somehow fenced off.

The "cosmological principle" would fail dramatically at the edge.

Since the universe is, by definition, the whole enchilada, what is the importance of an edge ? It is not like there is something on the the other side, since there is no other side.


I think the point he was trying to make was that asking what happens when you move off the edge of the Universe was similar to asking what happens if you move off the edge of Earth in that the two are based on incorrect assumptions.

The huge difference is that the Earth is embedded in something else, the universe. The unverse is not embedded in anything else, since it is, by definition, all that is.

[Jeff Root]

The unverse is not embedded in anything else, since it is, by definition,
all that is.
That's one definition.

Another definition would be the portion of the cosmos which contains
matter. It might be that most of the Universe is empty, and only a very
small part of it contains matter.

Another definition would be the part of the cosmos which is participating
in the Big Bang expansion. There could be many-- perhaps infinitely
many-- universes, some of which are expanding like the one we inhabit.



The "cosmological principle" would fail dramatically at the edge.
Obviously. By definition.

But the cosmological principle is pretty weak. It isn't as strong as the
law of conservation of energy, and that law is only local, not global.
The cosmological principle is a description of what we can see. There
is no apparent reason that it should apply to everything beyond what
we can see.

-- Jeff, in Minneapolis

[DrRocket]

That's one definition.

Another definition would be the portion of the cosmos which contains
matter. It might be that most of the Universe is empty, and only a very
small part of it contains matter.

Another definition would be the part of the cosmos which is participating
in the Big Bang expansion. There could be many-- perhaps infinitely
many-- universes, some of which are expanding like the one we inhabit.

Neither of your two definitions apply to the a general relativistic model of cosmology.

You can, of course, use any ATM definition that pleases you. But such definitions are not amenable to treatment by means of mainstream theory. The only accepted theory that we have to deal with this question is general relativity, which has it limits, but which is supported by a large body of experiment and established theoretical models. Anything else is speculation.

[EDG]

On and on... until you're aiming at something 600 Mpc away, which is moving away from you at 300,000 km s-1. You'll find yourself unfortunately incapable of throwing your tennis ball that fast.

Hang on a sec. You're saying that an object 600 Mpc away is receding from us at the speed of light? 600 Mpc is nearly 2 billion lightyears, but we know of things that are (much) further away from us than that - e.g. the most distant galaxies known are about 13 billion lightyears away - and they aren't receding from us at faster than the speed of light (are they?).

[Sententia]

Have we really come this far as to know the actual age of the Universe? If science says the Universe is 13.5- 14 billion years old.. does that mean its necessarily true? Sure, the most distant galaxy's that we know of are 13 billion light years away.. but I feel that the Universe has to be much larger in comparison to all that is known, in these terms the Universe feels small and compressed.

I feel the Universe can be a unlimited canvas to our comprehension, though I feel it is not infinite. When I think of it, I picture a bubble.. circular like Earth. Before Columbus discovered America, what do you think the people thought of the oceans .. what lay beyond them ? I'm more so inclined to believe in the multi universe theory, and sub dimensions than a infinite nothingness..

[EDG]

but I feel that the Universe has to be much larger in comparison to all that is known, in these terms the Universe feels small and compressed.

I feel the Universe can be a unlimited canvas to our comprehension, though I feel it is not infinite.

Science isn't about "feelings" or "belief" though.

[Andrew D]

Have we really come this far as to know the actual age of the Universe? If science says the Universe is 13.5- 14 billion years old.. does that mean its necessarily true? Sure, the most distant galaxy's that we know of are 13 billion light years away.. but I feel that the Universe has to be much larger in comparison to all that is known, in these terms the Universe feels small and compressed.

Your right, but I don't think you realize why.

http://en.wikipedia.org/wiki/Hubble_volume:


The distance c / H(sub)0 is known as the "Hubble length". It is equal to 13.8 billion light years in the standard cosmological model, similar to but somewhat larger than c times the age of the universe. This is because 1 / H(sub)0 gives the age of the universe by a backward extrapolation which assumes that the recession speed of each galaxy has been constant since the big bang. In fact, recession speeds initially decelerate due to gravity, and are now accelerating due to dark energy, so that 1 / H(sub)0 is only an approximation to the true age.

http://en.wikipedia.org/wiki/Observable_universe:


The age of the Universe is about 13.7 billion years, but due to the expansion of space we are now observing objects that are now considerably farther away than a static 13.7 billion light-years distance. The edge of the observable universe is now located about 46.5 billion light-years away [1].

So, while (the light from) the furthest galaxies we see are (is coming from) 10-13 billion light years away, that's where they were 10-13 billion years ago. The galaxies themselves are now closer to 46.5 billion LY away.



Science isn't about "feelings" or "belief" though.

Correct, but without them, where would science be?

[Spaceman Spiff]

Hang on a sec. You're saying that an object 600 Mpc away is receding from us at the speed of light? 600 Mpc is nearly 2 billion lightyears, but we know of things that are (much) further away from us than that - e.g. the most distant galaxies known are about 13 billion lightyears away - and they aren't receding from us at faster than the speed of light (are they?).

Well, yes they are (by a conventional definition of recession speed), and no they aren't; it all depends on what distance and time intervals one adopts since these intervals are not invariants (coordinates, coordinates, coordinates -- GR allows one to pick any self-consistent set that you want). Ned Wright's FAQs (http://www.astro.ucla.edu/%7Ewright/cosmology_faq.html) discusses several related questions; start here (http://www.astro.ucla.edu/%7Ewright/cosmology_faq.html#FTL). It is also discussed in Lineweaver & Davis' (http://www.mso.anu.edu.au/%7Echarley/papers/LineweaverDavisSciAm.pdf) Scientific American article, although out of simplicity they have adopted the simplest (and most common) explanation.

[Jeff Root]

Have we really come this far as to know the actual age of the Universe?
Pretty much, yes.

I happen to have a somewhat ATM notion that suggests the possibility
of a slightly greater age, but there are several lines of evidence which
all indicate that it isn't very much older than 13.7 billion years.



If science says the Universe is 13.5- 14 billion years old.. does that
mean its necessarily true?
It is what the evidence and reasoning indicate. Some aspects of the
reasoning may be wrong. Important evidence may be as yet unknown.
But it is the best estimate that we currently have, and that estimate
is consistent for several different lines of reasoning.



the most distant galaxy's that we know of are 13 billion light years away..
The most distant galaxies we can see are much farther than 13 billion
light-years away. The light from the most distant galaxies we can see
has travelled a distance of roughly 13 billion light-years. Those galaxies
were much closer than 13 billion light-years when they emitted that light,
and are "now" much farther away than 13 billion light-years. I put the
word "now" in quotes because the concept of "now" has little meaning
for events which are so far apart.

-- Jeff, in Minneapolis

[speedfreek]

So, while (the light from) the furthest galaxies we see are (is coming from) 10-13 billion light years away, that's where they were 10-13 billion years ago. The galaxies themselves are now closer to 46.5 billion LY away.

Almost right, but not quite! (Don't worry, it is complicated!)

The light from the most distant (in time) galaxies we have seen has been travelling for 13 billion years, but those galaxies were only around 3.5 billion light-years away when that light was emitted, and are now around 30 billion light-years away as that light reaches us.

It is the coordinates from which the Cosmic Microwave Background Radiation we currently detect was originally released from, if those coordinates are considered to be moving with the expansion of the universe, that are currently 46.5 billion years away. The light-travel time for the CMBR is nearly 13.7 billion years and galaxies didn't form for a few hundred million years after that.

[Jeff Root]

The unverse is not embedded in anything else, since it is, by definition,
all that is.
That's one definition.

Another definition would be the portion of the cosmos which contains
matter. It might be that most of the Universe is empty, and only a very
small part of it contains matter.

Another definition would be the part of the cosmos which is participating
in the Big Bang expansion. There could be many-- perhaps infinitely
many-- universes, some of which are expanding like the one we inhabit.
Neither of your two definitions apply to the a general relativistic model
of cosmology.
I think you have it backward: The general relativistic model is limited
in that it only applies to a restricted range of possibilities. The actual
Universe might be correctly described by general relativity, but there
is no reason to apply the artificial restrictions of general relativity to
the actual Universe. General relativity accurately describes some of
what we can see. It doesn't accurately describe every possible case
of how the Universe may actually be arranged.

Suggesting that descriptions of the Universe should be limited to what
can be described by the current best existing theory is absurd.

-- Jeff, in Minneapolis

[Andrew D]

Almost right, but not quite! (Don't worry, it is complicated!)

The light from the most distant (in time) galaxies we have seen has been travelling for 13 billion years, but those galaxies were only around 3.5 billion light-years away when that light was emitted, and are now around 30 billion light-years away as that light reaches us.

It is the coordinates from which the Cosmic Microwave Background Radiation we currently detect was originally released from, if those coordinates are considered to be moving with the expansion of the universe, that are currently 46.5 billion years away. The light-travel time for the CMBR is nearly 13.7 billion years and galaxies didn't form for a few hundred million years after that.

You're right. This is what I meant to say:



The most distant galaxies we can see are much farther than 13 billion
light-years away. The light from the most distant galaxies we can see
has travelled a distance of roughly 13 billion light-years. Those galaxies
were much closer than 13 billion light-years when they emitted that light,
and are "now" much farther away than 13 billion light-years. I put the
word "now" in quotes because the concept of "now" has little meaning
for events which are so far apart.

-- Jeff, in Minneapolis

So, I'll add a question if I can, what size was the universe at the time the galaxies formed?

[Jeff Root]

I hope that speedfreek and/or others can add details, but the "size" of
the Universe is completely unknown. It isn't even certain that it is as large
as what we can see! That possibility seems absurdly remote to me, though.
If, as it appears, the visible Universe is geometrically almost "flat" overall, but
not quite perfectly "flat", then the Universe as a whole must be considerably
larger than the part we can see. Some people think that the Universe might
be infinite. I, personally, am convinced that the part of the Universe which
is participating in the cosmic expansion (that is, everything that originated
in the Big Bang) is finite in mass-energy and spatial extent. It must be, in
order to be causally-connected. However, it appears that all that stuff may
have undergone a very brief period of absurdly rapid expansion when it was
a tiny fraction of a second old. During that time its size would have grown
enormously. That period of expansion is called "Inflation". Look up articles
about cosmic Inflation for some guesses about how big the Universe might
have been at that time.

It is vastly easier to say what the density of the Universe was at any given
time. The density at the time of nucleosynthesis, in the first three minutes
after the Big Bang, and at the time the Universe became transparent, about
380,000 years later, are the two best-defined densities. You can look those
up in any description of the early evolution of the Universe.

-- Jeff, in Minneapolis

[speedfreek]

Yes, when cosmologists give the universe a size, they are talking purely in terms of the observable universe. The observable universe contains everything we have seen (and whatever would have been seen from here, all the way backwards through time) and where we estimate all that stuff would be today. What cosmologists really don't know is how much more there is than we have seen - the size of the whole universe. The whole universe might even be smaller than the observable universe, and if this were the case we would be looking at the same distant regions of space when we look in different directions, but we would be seeing them during different respective times so we might not recognise them as such (currently, this is thought not to be the case, but it remains a possibility)! The currently favoured theory of cosmic inflation puts the size of the whole universe many magnitudes larger than our observable part of it.

The size of the observable universe is usually defined using the distance that the CMBR we currently detect was released at, if those coordinates (which form a conceptual sphere around us, known as the particle horizon of the surface of last scattering) were receding with the expansion of the universe. It is thought that the CMBR we detect was originally released around 40 million light-years away, and that the expansion of the universe would put those coordinates at around 46.5 billion light-years away by now.

We have seen galaxies that existed only 800 million years after the Big-Bang and it is thought that galaxies would have formed a few hundred million years before that, so let's assume that galaxies formed around 500 million years after the Big-Bang. This would equate to galaxies with redshifts around z=10, but so far we have only seen galaxies with redshifts of up to around z=7 or so.

500 million years after the Big-Bang, the universe was approximately 1/10th of its current size. If we had telescopes good enough to see galaxies from that time, they would be seen to have been around 3 billion light-years away at that time, and the particle horizon (the edge of the observable universe) would have been somewhere around 4.6 billion light-years away, I think.

[EDG]

Correct, but without them, where would science be?

Exactly where it is today?

Science is based on observation and evidence. If you want a worldview based of feelings and belief, you should be looking at religion instead.

[Andrew D]

Exactly where it is today?

Science is based on observation and evidence. If you want a worldview based of feelings and belief, you should be looking at religion instead.

The thought that the Sun orbited the Earth was based on observations and evidence. The thought that the Earth was flat was based on observation and evidence. My point is only that while 'feelings' and 'belief' can derail good science, personal conviction and intuition are its driving forces. Would Newton have changed the way we look at the universe if the contemporary scientific conventions didn't "feel" wrong to him? While observation and evidence are the engines of science, the belief, the urge to observe and quantify, is its rudder.

[DrRocket]

Suggesting that descriptions of the Universe should be limited to what
can be described by the current best existing theory is absurd.

-- Jeff, in Minneapolis

Suggesting that you can provide a meaningful description that transcends the current best theory is beyond absurd.

If you have a better theory or a better basis for such a description please state it clearly and in terms that allow it to be either supported or falsified.

Yes, there are limitations to GR, as I stated quite clearly. But speculations beyond that which is available with the best available theory is nothing but unsubstantiated rank speculation.

You have just clearly stated that you don't know what you are talking about and are extremely proud of that fact.

[pzkpfw]

Can we now please get back to providing mainstream answers to questions? This is not the place to have meta discussions on science.

[EDG]

The thought that the Sun orbited the Earth was based on observations and evidence. The thought that the Earth was flat was based on observation and evidence.

People also didn't have a rigorous scientific method back then. They misinterpreted (and ignored) their observations and came up with interpretations that did not tally with reality. Plus, the fear of being tried for heresy didn't exactly encourage them to rock the boat.



My point is only that while 'feelings' and 'belief' can derail good science, personal conviction and intuition are its driving forces. Would Newton have changed the way we look at the universe if the contemporary scientific conventions didn't "feel" wrong to him? While observation and evidence are the engines of science, the belief, the urge to observe and quantify, is its rudder.

He didn't "feel" anything was wrong. He made observations and figured out a way to mathematically describe what he was seeing. On could argue that he made an "intuitive leap" perhaps, but intuition is not the same as belief.

[Andrew D]

One could argue that he made an "intuitive leap" perhaps, but intuition is not the same as belief.

One could argue that anything one wanted, if one was so inclined.

On the topic at hand: Once we get to the realm of the 'edge of the universe', or even beyond that which we can observe, whether because of our own limitations or because of physical impossibilities, even the greatest minds can only offer what they think (or believe, or intuitively leap toward, what have you). While some ideas make more sense to some than others, none can be confirmed and few can be discredited, so gather as much evidence as you can and draw your own conclusions.

[pzkpfw]

Last warning before infractions start flowing. Thanks.

[Jeff Root]

Suggesting that descriptions of the Universe should be limited to what
can be described by the current best existing theory is absurd.
Suggesting that you can provide a meaningful description that transcends
the current best theory is beyond absurd.

If you have a better theory or a better basis for such a description please
state it clearly and in terms that allow it to be either supported or falsified.
I said what I wanted to say, and I stand behind what I said.

The Universe may or may not have an edge. The Universe may be finite
or infinite. The Universe may be smaller than it appears, or far, far larger.
The Universe may have overall curvature, or it may be "flat" overall.
The Universe may have finite mass and energy, or it may be infinite.
The entire Universe might be participating in the cosmic expansion which
derived from the Big Bang, or it might be only a portion of the Universe.

Mathematical models can be constructed to describe each of those
possibilities. General relativity can be used to help in their construction.

Logic allows us to rule out some combinations. What I have pointed out
that I have not seen elsewhere is the fact that the Universe cannot be
both infinite in extent and expanding throughout, because that scenario
violates causality. If two parts of the Universe have significant features
in common, there must be a causal connection between them.

-- Jeff, in Minneapolis

[Hungry4info]

Hang on a sec. You're saying that an object 600 Mpc away is receding from us at the speed of light? 600 Mpc is nearly 2 billion lightyears, but we know of things that are (much) further away from us than that - e.g. the most distant galaxies known are about 13 billion lightyears away - and they aren't receding from us at faster than the speed of light (are they?).

I seem to have fudged that one up somehow.

[Grey]

Logic allows us to rule out some combinations. What I have pointed out
that I have not seen elsewhere is the fact that the Universe cannot be
both infinite in extent and expanding throughout, because that scenario
violates causality. If two parts of the Universe have significant features
in common, there must be a causal connection between them.I am not certain that has to be the case. For example, two spiral galaxies share many significant features in common. But I don't think that's because there is a causal link between them; it's just that the laws of physics are the same everywhere, so certain types of structures show up independently in different places. Besides, the whole issue of quantum entanglement suggests that causality might not be as straightforward an issue as we think. Of course, there's nothing wrong with the idea of an infinite universe where only part of that universe is participating in the expansion either. I just don't think we can say a priori that it's the only type of infinite universe that could be possible.

[Grey]

Hang on a sec. You're saying that an object 600 Mpc away is receding from us at the speed of light? 600 Mpc is nearly 2 billion lightyears, but we know of things that are (much) further away from us than that - e.g. the most distant galaxies known are about 13 billion lightyears away - and they aren't receding from us at faster than the speed of light (are they?).
I seem to have fudged that one up somehow.No, you're correct. The effective recession velocity of the most distant galaxies is faster than the speed of light.

[Jeff Root]

Logic allows us to rule out some combinations. What I have pointed out
that I have not seen elsewhere is the fact that the Universe cannot be
both infinite in extent and expanding throughout, because that scenario
violates causality. If two parts of the Universe have significant features
in common, there must be a causal connection between them.
I am not certain that has to be the case. For example, two spiral
galaxies share many significant features in common. But I don't think
that's because there is a causal link between them; it's just that the
laws of physics are the same everywhere, so certain types of structures
show up independently in different places.
The laws of physics are the same in two different locations because
they are causally connected. Two spiral galaxies both contain hydrogen
atoms with a particular mass, electric charge, energy levels, and so on
because they both sprang from the same Big Bang. They share common
properties because they are causally connected.

I have one head, two arms, and two legs, like a monkey has, because
the monkey and I are causally connected: We have common ancestors.

-- Jeff, in Minneapolis

[Grey]

The laws of physics are the same in two different locations because they are causally connected.Are they? Is it possible that somewhere else in the universe the fine structure constant has a different value? I don't know if the answer is yes or no, but I am quite sure that we can't absolutely rule out either answer. We generally assume that the laws of physics are the same everywhere (mostly because it's simpler). Heck, the laws of physics are what allows us to talk about whether two events can be causally connected in the first place. If the laws of physics can be different, then so can the very notion of whether things can be causally linked.


Two spiral galaxies both contain hydrogen atoms with a particular mass, electric charge, energy levels, and so on because they both sprang from the same Big Bang.Again, I don't think you can say this with logical certainty. We don't particularly know why every electron has the same value for properties like mass and charge; we have no theory to suggest why this is the case. So I don't think we know whether it's logically possible for electrons somewhere else in the universe to have different values for those properties or not. We can certainly imagine it, but perhaps there's some elegant reason that we just haven't figured out why all of the various physical constants in the universe simply must have the values we observe. That's certainly just as reasonable a possibility as assuming that they could have had any random value, and just happened to end up with the values that they have. You're free to prefer one or the other, but neither can be ruled out because it's just "illogical".

Simply put, you're adopting as an axiom that two parts of the universe must be causally connected in order for the laws of physics and the properties of elementary particles (or even what elementary particles exist, presumably) to be the same. But we don't know enough about why the laws of physics are what they are, or why there are certain kinds of elementary particles that have certain properties to know whether that's a reasonable axiom or not.

[Matthias]

That isn't possible. The expansion of the universe doesn't quite work that way. Recall the expanding balloon analogy. For anybody in this universe (the surface of the balloon), the local space around them does not seem to be expanding very rapidly, but only things far away seem to be doing so. So to overcome the expansion of space at the observer's location, you can just nudge the tennis ball to a few mm per decade and you'll have overcome the Universe's expansion at your local space. The expansion rate of the universe is ~500 km s-1 Mpc-1. That's 500 kilometres per second... per megaparsec. The expansion of the universe is 500 km s-1 across a million parsecs! Condering a million parsecs, 500 km s-1 is pretty much nothing. As such, if you were a Mpc away from an object, it would seem to receed from you at 500 km s-1. So let's say you throw something at 500 km s-1 so that it'll catch up with whatever object is a Mpc away. Well an object at 2 Mpc is moving away at 1,000 km s-1, so you'll never catch up with that one. So you can throw it harder if you want. Well an object three times as far (6 Mpc) is moving away at 3,000 km s-1. On and on... until you're aiming at something 600 Mpc away, which is moving away from you at 300,000 km s-1. You'll find yourself unfortunately incapable of throwing your tennis ball that fast.


Again, recall the expanding balloon analogy. There's no point on the balloon's surface that you can identify as the start of the expansion. Any observer on the balloon would see the rest of the balloon expand away from his current location, regardless of where they are.

As such, no matter where you are in the Universe, you appear to be at the centre of expansion. In truth, the Universe lacks a centre much like the balloon lacks any true central point of expansion.

So have th analogy of the balloon's surface equalling 3D "surface" of the universe. But the 2D body of the balloon is expanding into the 3D space outside (and inside) its surface. Aren't there supposed to be extra dimensions on top of the 3 we know, and might not the "body" of the universe be expanding into such a hypervolume?

[Jeff Root]

General relativity posits that spacetime consists of three spatial dimensions
and one time dimension. Those four dimensions are sufficient to describe the
effects of gravity. Other theories sometimes posit more dimensions.

-- Jeff, in Minneapolis

[cosmocrazy]

General relativity posits that spacetime consists of three spatial dimensions
and one time dimension. Those four dimensions are sufficient to describe the
effects of gravity. Other theories sometimes posit more dimensions.

-- Jeff, in Minneapolis

Yes at the macroscopic level, but at the microscopic a quantum theory of gravity is required. Such is that they are not yet compatible. This is why sometimes extra dimension are postulated.

[DrRocket]

What I have pointed out
that I have not seen elsewhere is the fact that the Universe cannot be
both infinite in extent and expanding throughout, because that scenario
violates causality. If two parts of the Universe have significant features
in common, there must be a causal connection between them.

-- Jeff, in Minneapolis

Not true.

What you are describing is the "Horizon Problem" -- why does the universe appear to be homogeneous when much of it is causally disconnected from other parts. It is a problem whether the universe is finite or infinite and being infinite has little bearing on the problem.

The resolution, such as it is, lies in inflation. Google "inflation" or "horizon problem", or read Alan Guth's book The Inflationary Unverse.

[Jeff Root]

What I have pointed out that I have not seen elsewhere is the fact
that the Universe cannot be both infinite in extent and expanding
throughout, because that scenario violates causality. If two parts
of the Universe have significant features in common, there must be
a causal connection between them.
Not true.

What you are describing is the "Horizon Problem" -- why does the
universe appear to be homogeneous when much of it is causally
disconnected from other parts.
There is no part of the Universe that we can see that is causally
disconnected from any other part of the Universe that we can see,
in the sense that both parts originate from a common cause. They
might *no longer* be in causal contact, and they may not have
been in causal contact for a very, very long time, but they are
causally connected at some time in the past. They must be, or
they would not share so many features in common -- they would
not be "homogenous".



It is a problem whether the universe is finite or infinite and being
infinite has little bearing on the problem.

The resolution, such as it is, lies in inflation. Google "inflation" or
"horizon problem", or read Alan Guth's book The Inflationary Unverse.
That hypothesis offers two possibilities. One of those possibilities
could work; the other has a fatal flaw. The one that could work is
essentially the same as what I'm saying: Everything involved in the
cosmic expansion was originally in contact. Inflation spread it out.

The possibility that you favor assumes that everything participating
in the cosmic expansion was *never* in contact, but consisted of
the same particles with the same properties at roughly the same
density and same temperature all simultaneously, and spontaneously
it all inflated simultaneously, evening out the density and temperature
even more than they had been.

This version of inflation accounts for the precision of the uniformity
of the temperature and density, but it doesn't account for why the
Universe was filled with uncountable numbers of identical particles
with identical properties, or why those particles were all at a similar
high temperature, or why they were all rushing apart from each other
in a similar way.

I am saying that is unlikely that a small number protons would happen
to appear simultaneously with no common cause. It is absurd that
decillions of them would happen to appear simultaneously with no
common cause. And it is ludicrous that infinitely many of them would
happen to appear simultaneously with no common cause.

We can be sure that there was a Big Bang: Everything in the Universe
was once scrunched tightly together. The Big Bang is the obvious
opportunity for all that matter to have been in causal contact, when
it acquired its common properties. The idea that everything we see
could exist without having been in causal contact is ridiculous.

-- Jeff, in Minneapolis

[DrRocket]

There is no part of the Universe that we can see that is causally
disconnected from any other part of the Universe that we can see,
in the sense that both parts originate from a common cause. They
might *no longer* be in causal contact, and they may not have
been in causal contact for a very, very long time, but they are
causally connected at some time in the past. They must be, or
they would not share so many features in common -- they would
not be "homogonous".


That hypothesis offers two possibilities. One of those possibilities
could work; the other has a fatal flaw. The one that could work is
essentially the same as what I'm saying: Everything involved in the
cosmic expansion was originally in contact. Inflation spread it out.

The possibility that you favor assumes that everything participating
in the cosmic expansion was *never* in contact, but consisted of
the same particles with the same properties at roughly the same
density and same temperature all simultaneously, and spontaneously
it all inflated simultaneously, evening out the density and temperature
even more than they had been.

This version of inflation accounts for the precision of the uniformity
of the temperature and density, but it doesn't account for why the
Universe was filled with uncountable numbers of identical particles
with identical properties, or why those particles were all at a similar
high temperature, or why they were all rushing apart from each other
in a similar way.

I am saying that is unlikely that a small number protons would happen
to appear simultaneously with no common cause. It is absurd that
decillions of them would happen to appear simultaneously with no
common cause. And it is ludicrous that infinitely many of them would
happen to appear simultaneously with no common cause.

We can be sure that there was a Big Bang: Everything in the Universe
was once scrunched tightly together. The Big Bang is the obvious
opportunity for all that matter to have been in causal contact, when
it acquired its common properties. The idea that everything we see
could exist without having been in causal contact is ridiculous.

-- Jeff, in Minneapolis

1. You are wrong and you don't understand the theory. What you have stated is so far off base that there is no point in trying to refute if point by point. You simply have things badly garbled. Better read up.

2, I don't "favor" any hypothesis. I have only stated the facts.

[Umbrava]

The best way to try to answer.


Your perceptions of the universe are actually miniscule to the way the universe actually is. To tell you the honest truth about the size of the universe would be obvious the complete eventual pure cosmilogical weight at the most actively dense time during the universes life. You are wrong about one thing you think about the shape of the universe as 3 dimensional you forgot the other 2 required dimensions pretty much always active in this universe. If you cant think using 5 base dimensions you could not correctly predict pretty much out of your visual range unless almost in direct contact with. While you can have theoreticly more demensions that five you really only need the 5 basic ones more or less the ones that predominatly ahere specific neccessity to this universe. Demensions 10-12 represent actuality but at a much higher level of actual potentiability and really not required for this universe as it is essentuialy potentialy occuring probability as it is identified compared to all the other simalataniusly forming universes exactly in the same spot as this one really because in the envirnment in which srounds this universe the actual space you ocupy is relativly meaningless. since after the universe you simply are unified or you arent. Basicly an entire universe with just one thing in it nothing likse just a bunch of planetiods. Just one massive energised mass in what i wouldnt call any sort of space in any sense of the word but like a completly spectral envirnment.

The Universe is not finite or infinite it is ultimately is as big as it eventually needs to get nothing more nothing less because wasted particles would not have the pure necessity to actually exist at least not in this universe.

Nothing is where it hasn't already always and eventually will be. The universe is completely cycldic in nature it is basically one huge even bigger than your perceptions of the singularity that maintains pure universal cohesion - would prevent this universe from 'bleeding' into any other layers of existence. Nothing hasn't already been preformulated before it always happens ultimately nothing in any layer of theoretical existence layers has never actualy not ever not happened at least one time.

space does not 'expand or get bigger' there is no such thing as pure empty space anywhere in this universe. Even the empty air next to you is composed at least of one single particle at least always at one time. Thats basic 101 in particulate cohesion - your advanced ideas in theoretical particle physics. A single dead particle by itself would almost have no physical adherence in space they would have almost no difinable mass not by current instrumentation. If one particle in this universe were misplaced which is pretty much impossible into another universe not only would it create instability in both universes but it would cause a chain reaction destroys all the other potential universes within basically the basic bonds of the bits that compose them all. Even if this destroyed millions of universes they would always eventually reform. One thing im stating is a particle can be moved anywhere but it can only be moved within this universes barrier.

You can stand on the edge of the universe in a sense but you would basically just remain still you would step to your exact spot. The universe has no physical end it does have what i would call an eventual end in its life span though. It basicly just ends and instantly reforms it really never actualy ends. When it does completly end though when it does reform it does do it from srcatch however. All formations start back as a single particle.

One odd thing i wonder about the universe is its age. Its odd a mass of its size could take such a short time compared to the life of a single star the odd thing thing is for the galaxies to become distributed like the have in the current universe would taken it many more years than just tens of billions. I ultimately think that the eventual life of the universe would be somehwere in the neighborhood of 100 trillion years. I think stars have been reforming for trillions of years i really think that basically when you look at the heavens are glimpses in short time frames of objects many years out of your range. Basically when looking in the visible universe all your seeing is a temporary state. All the old dead stars would probably all eventually just become dark matter the inherent reason for the expansion of the universe. Prior Generational Dead stars would not have the ability to be identified with your instrumentation simply because they would have been composes of slightly different electrochemical composition based chemicals. Basically you probably could see back into the farthest as the oldest visible reaction in this universe. Stars themselves would ultimately probably just show multiple levels of reformation through other stars. Galaxies would probably be able to be aged much older than their individual stars. Galaxies reform just like stars but at about a rate of probably 10 times less frequent. A collection of galaxies could collapse on themselves every i would say 1 trillion years on average and reform a completely new potential of galaxies. Basically the initial reaction of the big bang is continually on going a reaction so large that it will take 100 trillion years to dissipate.

The cohesion layer of particles that keep this universe together comprise what we would call the unprecavable wall of inertia would be identified as the actual natural curve of this universe. Light does not travel in a straight light in this universe no matter where it goes. The coplete natural orientation of the universe is naturaly curved. You cannot breach the inertia layer it doesn't react to anything is pre-ocurers so it would be almost non existent but there so odd that if you touched it you would have no clue it was in anyway influencing you in anyway. Breaching it is not possible simply because it is ultimately so tightly compact it is basically one complete thing. Even if you could destroy the universe they would still be there simply because they could never be anywhere else in any other position they would simply be in place for reformation of universes. Like a honeycomb wall layer existence.

The actual size of things the pure massiveness in complete conceptual weight alone that is an active ongoing pure existence theory is almost bigger than you could ever imagine even on a good day. The universe is not just some groups of galaxies and stars and planets it is an ongoing reaction that regenerates for as long as the initial source of pure energy was released. The big bang reaction or even if you wanted to call the energy source to generate so many electromagnetically charged particles in such confinement. The explosion was so massive that it ultimately caused the curve all of space itself. Inertia walls are like clay though they cant be breached but they can be reorientated. Basically what im getting at is the initial reaction of energy released by the big bang would take around 100 trillion years about 30 stellar cycles. Stellar cycles are periods when all the stars in the universe change slightly in weight. A certain amount of charged particles are consumed by the equalising force needed to shape the reaction generated by the big bang. Would basically completely fry every particle in the universe simultaneously would destroy any life that didnt have the ability to adapt to it physiologically. This energy would penatrate all matter regardless of what it was so technology wouldnt help you.

I find it odd that i can say that the universe is too big or too old but people argue that it can be infinite? If the universe can be finite or infinate why cant it also be somehwere in between?

[PetersCreek]

Umbrava,

Welcome to the BAUT forums. The Space/Astronomy Question & Answer forum is where people get mainstream answers to their questions. You may not post your personal theories that run counter to the mainstream here. If you wish to advance and defend your ideas, you may do so in the Against The Mainstream forum. Before doing so, you should familiarize yourself with our rules and forum-specific advice, linked in my signature line below.

[Andrew D]

Doesn't the evidence we see point to a universe that is not spatially bound, but density bound?

[Hornblower]

Doesn't the evidence we see point to a universe that is not spatially bound, but density bound?

What, in appropriate mathematical detail, do you mean by "density bound"?

[WayneFrancis]

The best way to try to answer.


Your perceptions ... in between?

balsamic please.

[WayneFrancis]

Doesn't the evidence we see point to a universe that is not spatially bound, but density bound?

our observable universe has a bound to its density but as far as what is beyond our Hubble volume? If the universe is infinite in size then most likely it is also infinite in mass. I guess if that is true you would only get unbounded density at the centre of black holes but that isn't currently provable.

[forrest noble]

Roobydo & Luckyfrank,

Roobydo quote:

Doesn't the evidence we see point to a universe that is not spatially bound, but density bound?

Not spatially bound is correct, but perhaps best stated as spatially limited to the confines of matter regardless of its density or configuration of space geometry.

Maybe the most prevalent BB model/ interpretation is that both space and time are "tied" to matter in their extension. By this interpretation there would be no such a thing as time before the beginning of the universe, or space outside the confines of matter. A part of the definition of space using this interpretation would be the volume which matter encompasses. Accordingly if the quantity of mass is finite so is space (by definition).

I think this most common standard interpretation/ definition of the bounds of time and space makes sense whether the BB model is valid or not. The idea would be something like: what would be the meaning of time or space if there was no matter, energy, or field of any kind, or a parallel universe with absolutely nothing in it.

[DrRocket]

Roobydo & Luckyfrank,

Roobydo quote:


Not spatially bound is correct, but perhaps best stated as spatially limited to the confines of matter regardless of its density or configuration of space geometry.

Maybe the most prevalent BB model/ interpretation is that both space and time are "tied" to matter in their extension. By this interpretation there would be no such a thing as time before the beginning of the universe, or space outside the confines of matter. A part of the definition of space using this interpretation would be the volume which matter encompasses. Accordingly if the quantity of mass is finite so is space (by definition).

I think this most common standard interpretation/ definition of the bounds of time and space makes sense whether the BB model is valid or not. The idea would be something like: what would be the meaning of time or space if there was no matter, energy, or field of any kind, or a parallel universe with absolutely nothing in it.

Nope.

This thread seems to have departed rather markedly from mainstream physics and is well into ATM territory.

[astromark]

Sorry for being overly simplistic but, The mainstream view. That being the the most wildly excepted theory... That the visible universe and that being all that we have knowledge of had a beginning. That a big bang is or was the most excepted method of creation of this universe. That a acceleration rate increasing is now evident. It makes not unreasonable sense that at a time some 13.7 odd billion years ago all of what we know of was in a very different state and, seemed to have started out as a very dense., very hot, Universe... The Big Bang. Where time and space and all that is in it were born... As much as we can speculate, not a single shreed of evedance has been prosented to support the idea of a multie univeress reality. It seem logical. but proof of fact is lacking... without the methode of confermation this idea has no backbone. We know of NO edge. We do see excelorating mass. Within a million years of birth the universe was rushing of to fill the void as it unfolded... at what you might percieve as the edge, you should expect to see just more of the same and some excelorating away at light speed...

I hope to have helped. mark.

[Jeff Root]

I might be branded a Marksist for saying this... or marked a brand... anyway,
the idea of going with the most wildly excepted theory appeals to me.

-- Jeff, in Minneapolis

[Andrew D]

Doesn't the evidence we see point to a universe that is not spatially bound, but density bound?

I should clarify; I meant energy density.

Isn't total energy density constant?

[astromark]

I might be branded a Marksist for saying this... or marked a brand... anyway,
the idea of going with the most wildly excepted theory appeals to me.

-- Jeff, in Minneapolis


:) its not that I will not listen to new ideas. I will. It could be said that I am always looking for that better idea / solution. I am. BUT...I will show restraint when excepting such as string theory and multi universes... Its clutching at straws and is often an attempt to blind with science. I know something you do not... and I do not.
but sometimes..... ? The mainstream view has stood the tests and survives as the best bet yet.

[forrest noble]

Roobydo,


Isn't total energy density constant?

The energy density of the ZPF, according to theory, remains constant in an expanding universe. But the average density of both mass and energy would seemingly decrease in an expanding universe.