What Is Beyond The Observable Universe?

[nismaratwork]

I have a reasonable idea of what they mean. There was a statement made earlier by blandview (?) that we live at the edge of the universe. I queried this and was given some analogy, which I need to understand .. equally vague, in order to understand the former .. kind of circular, that!

Either that, or I'm just plain stupid and your intellect far surpasses mine - a possibility I'm ready to admit if readily shown. But all I've seen so far is circular argument and semantics - and the subtle changing of the meaning of words to suit.



I am at the edge of the universe, (according to others previous posts) right ?

But I don't feel like I'm at the edge of the universe. I can see for miles in each direction - millions.

"Ah, the simpleton" I hear you say"

.. but anyway, you (and blandview more to the point) haven't 'splained it proply so far. And to say that the edge is the 4th dimension, time, kind of shifts the goalpost merely.

The present, is the futures past !

Yes, insult the people who are trying to explain a basic concept that you fail to grasp, that's going to provide strong motivation for anyone to help you. You're on your own.

 

[DaveC426913]

Yes, insult the people who are trying to explain a basic concept that you fail to grasp, that's going to provide strong motivation for anyone to help you. You're on your own.

nismar, I do not think he meant any insult (Note, by the way, that he did not actually make any insult). He is feeling frustration that he does not understand, though we seme to claim we are using simple words. It is most definitely not a "basic concept"!

See his frustration, don't take it as an attack.

 

[nismaratwork]

nismar, I do not think he meant any insult (Note, by the way, that he did not actually make any insult). He is feeling frustration that he does not understand, though we seme to claim we are using simple words. It is most definitely not a "basic concept"!

See his frustration, don't take it as an attack.

Generally manipulating a name (blandrew to blandview) is an insult, showing hostility. Frustration is understandable, but that doesn't mean this should degenerate into something hostile when the only reason the frustration exists at all is because the people he mentions are willing to engage at all.

If he doesn't understand, the best policy is to read, listen, research, and ask questions. Instead we get assertion after assertion, and pages of what appears to be a lack of independent inquiry.

I see his frusteration, and saw it earlier, but when that changed to something else I decided to walk away. I'm sorry, but "And to say that the edge is the 4th dimension, time, kind of shifts the goalpost merely..." is absurd, when that is in essence the point. He wants an answer that makes s certain kind of sense to him, rather than the correct answer, or best guess. How do you work with that, when there is no personal stake in his learning?

Out of respect for you Dave, Tenny: As far as you can see, and even beyond is a single time-like slice, and the next moment (t2) what is contained in that slice changes. Your place in the universe and your ability to see old light from a distance effects the range of space-like events you can observe in any moment. That is an edge in an indeterminant universe. To be in a center, you would have to define a beginning and end (to simplify), like the beginning and end of book. Then, with foreknowledge you say, "I'm at page 3 of 7"! In the universe, you can't tell how long the book is, and your position is bounded by your current position in spacetime.

 

[Trenton]

I did not mean to insult anyone and I appologise if I have done so. I conceed I lacked contrition when saying it was not my fault if people don't like the consequences of equations.

I am though baffled by the rules. No-one knows what lays beyond the observable universe and thus ANY thought we may have on the subject is speculative.

For the record I am not stating that the [observable] universe amounts to a black hole, meerly that it looks likely that it does - And if it does then there are other ways in which the cosmos can be viewed other than the presently entrenched version of the big bang.

On the subject in hand though, two things that are not speculative or a matter of opionion:-

1) The laws of physics and mathematics are valid regardless of weather or not there is anything to apply them too! For example 1+1=2 has always been and will always be true no matter if there is anything to count or an outside to the observable universe or not.

2) The radius of a black hole is proportional to it's mass.

One interpretation of (1) is that 'before and outside' are legal space-time coordinates.

And one interpretation of (2) is that black holes can be exceptionally large and have very low density and micro-gravity at the event horizon. It would still require light speed plus to escape to infinity.

I accept that this is a bit hard to get one's head round but unless it can be shown that gravity eventually departs from inverse-square, this interpretation is (at least mathematically) valid.

By contrast though, some of the solutions to the Einstein field equations are questionable because they yeild a singularity both at the center (valid) and at the event horizon (invalid). And yet some assertions about black holes seem to depend on the latter (eg an object falling into a black hole is seen to stop at the event horizon by an outside observer because time stops a this point). My interpretation of the horizon is that it is the point at which the escape velocity reaches C - which is not the same as saying an infalling object will reach C at this point (and anyway we all know it can't reach C). Any comments on this?

My interest in ultra-large black holes owes much to the fact that they illistrate quite clearly where these assertions are or seem to be faulty.

My best regards to eveyone - Trenton Maiers

 

[nismaratwork]

I did not mean to insult anyone and I appologise if I have done so. I conceed I lacked contrition when saying it was not my fault if people don't like the consequences of equations.

I am though baffled by the rules. No-one knows what lays beyond the observable universe and thus ANY thought we may have on the subject is speculative.

For the record I am not stating that the [observable] universe amounts to a black hole, meerly that it looks likely that it does - And if it does then there are other ways in which the cosmos can be viewed other than the presently entrenched version of the big bang.

On the subject in hand though, two things that are not speculative or a matter of opionion:-

1) The laws of physics and mathematics are valid regardless of weather or not there is anything to apply them too! For example 1+1=2 has always been and will always be true no matter if there is anything to count or an outside to the observable universe or not.

2) The radius of a black hole is proportional to it's mass.

One interpretation of (1) is that 'before and outside' are legal space-time coordinates.

And one interpretation of (2) is that black holes can be exceptionally large and have very low density and micro-gravity at the event horizon. It would still require light speed plus to escape to infinity.

I accept that this is a bit hard to get one's head round but unless it can be shown that gravity eventually departs from inverse-square, this interpretation is (at least mathematically) valid.

By contrast though, some of the solutions to the Einstein field equations are questionable because they yeild a singularity both at the center (valid) and at the event horizon (invalid). And yet some assertions about black holes seem to depend on the latter (eg an object falling into a black hole is seen to stop at the event horizon by an outside observer because time stops a this point). My interpretation of the horizon is that it is the point at which the escape velocity reaches C - which is not the same as saying an infalling object will reach C at this point (and anyway we all know it can't reach C). Any comments on this?

My interest in ultra-large black holes owes much to the fact that they illistrate quite clearly where these assertions are or seem to be faulty.

My best regards to eveyone - Trenton Maiers

4x5=10

How about quaternions?

 

[Trenton]

quaternions? Aren't they something to do with hamiltonians and complex numbers? Would you care to enlighten me as to where these might fit in? Hithertoo I was of the misapprehension that all one had to do was work out where to apply the Lorentz contraction.

 

[nismaratwork]

quaternions? Aren't they something to do with hamiltonians and complex numbers? Would you care to enlighten me as to where these might fit in? Hithertoo I was of the misapprehension that all one had to do was work out where to apply the Lorentz contraction.

My comment was in reference to your comment about the constancy of 1+1=2; it was meant to be a prod in the direction of the mutability of such things in different systems. You are correct that the relevance is in regards to commuting and non commuting operators.

 

[Tenny]

To mismaratwork, #281;

In post #279 I said ..

"There was a statement made earlier by blandview (?) that we live at the edge of the universe"

.. which you took as an insult, and said in post #283 ..

"Generally manipulating a name (blandrew to blandview) is an insult, showing hostility"

But "blandrew to blandview" was just a mistake on my part - as can be evidenced by the question mark (?) immediately following it. I was simply running on memory of what I had read earlier you see, and being relatively new, remembered the name wrongly. I was also on a dial up connection at that moment, (as I am right now) and you know how it is with dial up - to go back and forth, load several pages, etc, takes forever (just about).

Look - you even had some funnies in your #283 ..

“I see his frusteration”
(I hope not - I’m blushing, now)

“He wants an answer that makes s certain”
(not really - I see more certitude in ‘r’)

.. but I'm not too bothered. It's easy to make a mistake or two, isn‘t it ?

So you jumped the gun with YOUR hostility, but that's OK. Cheer up! You have no stake in my learning, nor did I ask for any from you. It is your choice however, to participate (or not) in an internet forum where many questions are bound to flow - even from dummies !

To blandrew #280

You said to me ..

"Blandview" i see what you done there"

I hope the above explains my error. No offence or hostility was intended on my part.


Thank you both for your responses. I'll have a good read of them and post later if I need to.

To Dave #282 - you said ..

“He is feeling frustration that he does not understand, though we seme to claim we are using simple words. It is most definitely not a "basic concept"!

Which really nails it, I think. Thanks.

 

[Trenton]

Good point nismar - I had not thought of that one. I shall mull that at length.

Another thing I am surprised I have not been pulled up on is event horizon disruption by neighboring black holes (and other outside mass). If the observable universe were a black hole among an infinite number of them randomly spaced, they would have to be very sparse to act as black holes.

Anyway in the meantime I am pondering a different matter. Hawkins radiation - Not at the event horizon but further in. Presumably the same mechanism would still apply. Of course the virtual particles would never escape but they would nonetheless mean that not all the mass of a black hole was concentrated at the center.

Has anyone else considered this or found any decent papers on it?

 

[nismaratwork]

Good point nismar - I had not thought of that one. I shall mull that at length.

Another thing I am surprised I have not been pulled up on is event horizon disruption by neighboring black holes (and other outside mass). If the observable universe were a black hole among an infinite number of them randomly spaced, they would have to be very sparse to act as black holes.

Anyway in the meantime I am pondering a different matter. Hawkins radiation - Not at the event horizon but further in. Presumably the same mechanism would still apply. Of course the virtual particles would never escape but they would nonetheless mean that not all the mass of a black hole was concentrated at the center.

Has anyone else considered this or found any decent papers on it?

Yes, but I also couldn't grasp the derivation, really HR is incredibly tough. I think the best way to think of the particle beyond the event horizon is the past of the particle which escapes. The math is really beyond me without sitting for specialized lectures, and even then I don't think I could grasp it.

 

[Max™]

http://news.nationalgeographic.com/news/2010/04/100409-black-holes-alternate-universe-multiverse-einstein-wormholes/

"What is new here is an actual wormhole solution in general relativity that acts as the passage from the exterior black hole to the new interior universe," said Easson, who was not involved in the new study.

"In our paper, we just speculated that such a solution could exist, but Poplawski has found an actual solution," said Easson, referring to Poplawski's equations.

Nevertheless, the idea is still very speculative, Easson said in an email.

"Is the idea possible? Yes. Is the scenario likely? I have no idea. But it is certainly an interesting possibility."

I'm not one to take exact EFE solutions lightly, it isn't proof, but it appears at least possible that this Universe is inside of a black hole in another Universe.

 

[Trenton]

Nismar,

I can't do the math either but before one even gets to that I can't properly picture the HR process in my mind.

Another example of my poor math is the above mentioned NAT GEOGRAPHIC article. It is obvious that time dilation gives rise to an 'inner universe' in black holes in that they are larger on the inside than the out - I was of this view more than 20 years ago but could not formulate a decent proof.

But back to HR - I have been contemplating something else though that may be HR related. The light emited from stars loses some of it's energy climbing away from the star's gravity. The star loses mass in producing the light of course but not all of that converted mass makes it out to infinity - part of it is lost to the redshift. Where does this missing mass end up? In the star in some other form than nuclear binding energy such a heat? And how?

Does anyone have a name for this conumdrum or know of any papers on it?

 

[Chronos]

The blackbody spectrum of the CMB is not a match to that expected from the interior of a black hole, Max.

 

[qmpash]

A big, nasty kid who is playing all kinds of jokes on us.

 

[ViewsofMars]

"What is Beyond The Observable Universe?" is the topic. Science only deals with the observable. We have The Big Bang Theory. It is extremely important to know what a theory means. Also, the following definition of a *theory* applies to every other scientific theory. Everyone should know this:

Theory
A scientifically testable general principle or body of principles offered to explain observed phenomena. In scientific usage, a theory is distinct from a hypothesis (or conjecture) that is proposed to explain previously observed phenomena. For a hypothesis to rise to the level of theory, it must predict the existence of new phenomena that are subsequently observed. A theory can be overturned if new phenomena are observed that directly contradict the theory.
http://map.gsfc.nasa.gov/site/glossary.html

 

[ViewsofMars]

What CMB blackbody spectrum would match a quantum particle sea of universes?

There are no "observable sea of universes."

 

[ViewsofMars]

If the Universe originated from a quantum particle, what CMB spectrum would match that?

The question is 'what is beyond the observable universe'?

A quantum particle sea of universes.

Orion, I already answered the questions. You need to read again and attempt to understand what I have previously posted. Also, a theory doesn't deal with "ifs." You need to first understand what a theory means. There are no universes. Period. End of story.

 

[Tenny]

Hello. I've read through the last several pages again recently, in an attempt to resolve the issue I was wondering about earlier. I still haven't been able to resolve it, and could even say I'm even more confused and mystified as to what's been said by some.

I have a reasonable understanding of what homogenous and isotropic means. And I ask again, how can it be said that I am, (and we) are at the edge of the universe ? I can see for countless millions of miles in any direction, so it certainly doesn't seem that I'm on any edge.

The analogy ..

'Lets say you've been reading a novel of indeterminate length for an indeterminate length of time. Well, you could say you were in the centre of the book and at the edge of the story (blandrew #263).

.. was given, but this merely confuses further, as it seems to be more vague than that which it is attempting to analogise. Worse, it seems to shift the meaning of the word 'edge' from a literal to a metaphorical one. I could say 'I'm at my wits end', or 'this is cutting edge stuff' but in both cases, I'm using a metaphor only.

In further posts it was suggested (I think) that time is the edge. But even with that, I can't see how I'm on the edge there either. We flow from the past to the future - and both past and future have a length (whatever that might be) so again, I do not feel I'm on the edge of time. In any case, I feel it is somewhat of a dodge (no hostility intended) to say that time puts me at the edge of the universe. It seems to me to be merely shifting the goalposts.

Please tell me how I'm at the edge of the universe, bearing in mind;

If you can't explain it simply, you don't understand it well enough.
Albert Einstein

Most of the fundamental ideas of science are essentially simple, and may, as a rule, be expressed in a language comprehensible to everyone.
Albert Einstein

 

[DaveC426913]

Please tell me how I'm at the edge of the universe, bearing in mind;

Keep in mind this is merely a spurious analogy, designed to show that sometimes "what we see" is not the only way to see things.

An ant is crawling on the surface of an balloon. Every direction it looks it sees more balloon surface - there are no boundaries, no edges. If the ant is not at the centre of this universe, it is certainly not near any edge.

I look down upon the ant from my vantage point. I can see that it is at the surface of the balloon. In fact, it is at the boundary of a sphere that is defined by the balloon's skin. Moreso, as I inflate this balloon, I can even say that the ant is on the leading edge of an expanding sphere that is defined by the balloon's skin.


The 2D surface of the balloon is analagous to our 3D universe (with one dminesion ignored). The expansion of the balloon in a radial direction is analagous to the movement of our 3D universe through the 4th dimension of time. The ant cannot go "forward" any more than the balloon expands. Outward is the future, inward is the past.

 

[Tenny]

Keep in mind this is merely a spurious analogy, designed to show that sometimes "what we see" is not the only way to see things.

An ant is crawling on the surface of an balloon. Every direction it looks it sees more balloon surface - there are no boundaries, no edges. If the ant is not at the centre of this universe, it is certainly not near any edge.

I look down upon the ant from my vantage point. I can see that it is at the surface of the balloon. In fact, it is at the boundary of a sphere that is defined by the balloon's skin. Moreso, as I inflate this balloon, I can even say that the ant is on the leading edge of an expanding sphere that is defined by the balloon's skin.


The 2D surface of the balloon is analagous to our 3D universe (with one dminesion ignored). The expansion of the balloon in a radial direction is analagous to the movement of our 3D universe through the 4th dimension of time. The ant cannot go "forward" any more than the balloon expands. Outward is the future, inward is the past.

Hi Dave. Thanks. Yes, I am familiar with your analogies above - very 'Flatland'.

Interesting that you to refer the 'edge of the universe' thing as a spurious analogy - I thought it was an actual proposition by other posters, and that analogies were given to explain THAT !

Anyhow, I need to think more about your, yes, clearer analogies.

 

[sylas]

Hello. I've read through the last several pages again recently, in an attempt to resolve the issue I was wondering about earlier. I still haven't been able to resolve it, and could even say I'm even more confused and mystified as to what's been said by some.

I have a reasonable understanding of what homogenous and isotropic means. And I ask again, how can it be said that I am, (and we) are at the edge of the universe ? I can see for countless millions of miles in any direction, so it certainly doesn't seem that I'm on any edge.

Hi Tenny; I wrote this a while ago and then my network connection dropped out. Meanwhile Dave has answered. But with the network back I'll post mine as well...

There's no edge. The universe is (on large scales, as far as we can tell) homogeneous and isotropic, and that means there's no edge.

Blandrew was using some picturesque language which may have been misleading. The only sense in which there are edges is the sense of a limit to how far you can see from some position. Like a horizon on the ocean, there's a boundary beyond which you can't see; but at the horizon there's nothing special. You are at the center of your own field of view, and also on the horizon of certain other observers.

You can also think of a horizon in time. From here-and-now, we can see 2010; but you can't see 2011. You'll have to wait another six months. It's not that NOW is some special identifiable edge in time; merely the horizon of what we see from this point in time.

These kinds of "edges" are not something special about a location, but depend on an observer. They are better called "horizons".

Even better, just forget all that observer stuff and consider simply that the universe has no edge. (Unless the universe is really different from what we currently tend to think on the basis of available evidence.)

Cheers -- Sylas

 

[Sinker]

I can screw up a two car funeral, but here is my thoughts on subject:

I don't think we as a species have evolved enough yet to fathom infinity. However, I think we will get there eventually. We can guess, however: I think other big bangs occur from quantum fluctuations a great distance from our observable universe. It's got a whole new time frame and as such can never contact our observable universe for two reasons: i) expanding of space between observable universes, and ii) time differences.
Regards
Sinker

 

[ViewsofMars]

Orion1 deleted his/her contributions from this topic though I did quote (copy) Orion1 as noted in posts #296 and 297 prior to Orion1's action. Shame on you, Orion1! Beware people of Orion1's tricky nonsense. The person may do it again. You should know Orion1 that your message does appear in my mail box.

I can screw up a two car funeral, but here is my thoughts on subject:

I don't think we as a species have evolved enough yet to fathom infinity. However, I think we will get there eventually. We can guess, however: I think other big bangs occur from quantum fluctuations a great distance from our observable universe. It's got a whole new time frame and as such can never contact our observable universe for two reasons: i) expanding of space between observable universes, and ii) time differences.
Regards
Sinker

Hi Sinker. Welcome to Physics Forums. As a human being I like to deal with reality. Observations are based on evidence. There hasn't been any big bangs that have occurred outside our observable universe. Science isn't based on speculations but rather observations.

 

[Sinker]

Orion1 deleted his/her contributions from this topic though I did quote (copy) Orion1 as noted in posts #296 and 297 prior to Orion1's action. Shame on you, Orion1! Beware people of Orion1's tricky nonsense. The person may do it again. You should know Orion1 that your message does appear in my mail box.




Hi Sinker. Welcome to Physics Forums. As a human being I like to deal with reality. Observations are based on evidence. There hasn't been any big bangs that have occurred outside our observable universe. Science isn't based on speculations but rather observations.

Thanks for the welcome. Nice forum. Yep - observations are based on evidence. We can still use imagination to speculate and theorize to lay groundwork for observations.
Outside our observable universe is a lot of space. If it is expanding, we can never verify other bubble universes (observable universes to those inside). If we could understand dimensions beyond the known ones, it may be possible.
Humans some time will evolve to a state where we can understand the concept of more dimensions and their nature. Before the slow process of evolution, we may produce machines that will manufacture smarter machines that will do the job for us. (Singularity, I believe is the term.) Once we get a handle on quantum computers, I believe this will happen.
Regards
Sinker

 

[Flatland]

Blacks Space Until A Different Universe

That statement makes absolutely not sense whatsoever. If beyond the observable universe is "black space until a different universe" that "different universe" would still be part of our universe and not a different universe.

Get it?

 

[Sinker]

You don't get it. I said "observable universe"

Get it??

 

[marcus]

In conventional cosmology, do you know what "observable universe" means? It means the part of the whole universe that we have received light or some other signals from, so in principle we can see or have information about.

The observable portion of the universe is constantly increasing, as radiation comes in from farther and farther away.

There is no indication that anything is any different. So we assume that beyond the present range of observation there is just "more of same".

I never met anybody with as much as one introductory college course in Astro who thought that beyond the current observable range there was "black space". That wouldn't make dynamical (general rel.) sense and there is no evidence for it.
"Black space" surrounding the observable portion is a kind of extravagant fantasy without any observational or theoretical support.

Would suggest that anybody who thinks that beyond observable U is anything besides more of same should maybe just take a beginning Astro course.
The conventional model everybody uses could of course be wrong! there could be a large plexiglass sphere just outside the range of what we currently can see. But no reason to think that. So, by Occam's razor (the "keep it simple" principle) we assume more of same until evidence to contrary. If there is ever any evidence of something else you will hear about it! The pros would love a surprise like that and would immediately jump on it!
===================

Edit to reply to the post by NUTGEB that comes next:

Nutgeb, notice that I just said "more of same", not "infinite".

Space could be for example a very large 3D hypersphere, with matter more or less uniformly scattered all over, and a small patch of it what we can now observe. To do the usual analysis and modeling they don't have to assume that the "finite or infinite" question is answered.

I interpret the question of this thread in a modest limited way: what is just out beyond the limit of the observable portion?

I wouldn't encourage anybody to speculate about what the whole space looks like, what topology etc etc. We just don't know enough yet! (In my opinion.) Infinite is a logical possibility, so are various versions of finite. But what is gained by speculating?

But I think it is reasonable to assume "more of same" out past the present bound of what we are observing. (which of course we are observing not how it is at present but how it was way back in the past.)

So I will leave the speculating about infinite or not to you, for the time being.

 

[nutgeb]

There's no doubt that the idea of a finite universe surrounded by empty space is not accepted by cosmologists. Applying Occam's Razor makes sense. And the balloon analogy works very well if used properly. It makes sense to study cosmology before critisizing it.

Nevertheless, isn't it accurate to say that the infinite nature of the universe is a strong assumption, based on the Copernican Principle and CMB observations, rather than a demonstrated fact? It might be helpful for someone to describe specifically how the existence of an outer edge would contradict general relativity or current observations.

I am not aware of anything specific in GR or in the FRW metric that prohibits the existence of 'empty' space outside of a finite universe. GR math seems to work fine with a model with finite space and time, as long as everything external to that universe is ignored.

Consider a model universe that begins with an 'explosion' of mass energy away from a single point in otherwise empty space. It seems possible that, depending on the nature of the explosion, the fluid mass-energy distribution would arrange itself homogeneously (within the total expanding envelope of the exploding mass-energy), and all individual comoving observers (except those in a position to look beyond the outer edge) would observe the same isotropic Hubble's Law that we observe. For example, a homogeneous distribution might arise if the explosion resulted from a brief period of strong mutual repulsion among particles that previously were tightly packed together. Particles that originally were packed further from the 'center' would gain a proportionally higher recession rate relative to the center.

The original center of the explosion would immediately lose any local uniqueness and as a practical matter would become locally indistinguishable from any other location within the expanding envelope. Once the explosion occurred, gravity and later dark energy would begin to affect the expansion rate of the comoving stream.

One complication is that the positive pressure of free radiation, particularly in the dense, radiation-dominated early universe, would contribute a factor of acceleration to the expansion rate, because a finite universe would have a pressure gradient at its outer edge, giving the pressure something to push into. I don't think that would cause a problem for the FRW metric, but it would need to be factored into the expansion parameters. Perhaps that factor would be found to contradict observations in some way.

If our arbitrary location happened to be very, very far from the supposed edge of a very large but finite universe, the edge would be too far away for us to see, and could also be too far away to affect the homogeneity and isotropy of the CMB radiation we are currently receiving. The non-isotropic distribution of photons at the largest scale just wouldn't have arrived here yet. Then someday, perhaps billions of years in the future, we might detect a slowly growing cold spot in the CMB signalling the first indication of an outer edge.

 

[Tenny]

Keep in mind this is merely a spurious analogy, designed to show that sometimes "what we see" is not the only way to see things.

OK - I understand. One could end up a little nonplussed about the spurious nature of the analogy though.

An ant is crawling on the surface of an balloon. Every direction it looks it sees more balloon surface - there are no boundaries, no edges. If the ant is not at the centre of this universe, it is certainly not near any edge.

Yes, and we could extrapolate the analogy to apply to a human being on the surface of the earth.

I look down upon the ant from my vantage point. I can see that it is at the surface of the balloon. In fact, it is at the boundary of a sphere that is defined by the balloon's skin. Moreso, as I inflate this balloon, I can even say that the ant is on the leading edge of an expanding sphere that is defined by the balloon's skin.

OK ..

The 2D surface of the balloon is analagous to our 3D universe (with one dminesion ignored). The expansion of the balloon in a radial direction is analagous to the movement of our 3D universe through the 4th dimension of time. The ant cannot go "forward" any more than the balloon expands. Outward is the future, inward is the past.

OK. I thought at the outset, we were talking about an edge to the three spatial dimensions. If the universe is homogenous and isotropic as we say it is, then it should be the same for me here, as if I was gazzillion miles away. And I can see no end or edge in sight (or out of sight) to the three spatial dimensions, so I guess it's infinite in all directions - spatially.

Thanks for taking the time to explain this.

 

[Tenny]

Hi Tenny; I wrote this a while ago and then my network connection dropped out. Meanwhile Dave has answered. But with the network back I'll post mine as well...

There's no edge. The universe is (on large scales, as far as we can tell) homogeneous and isotropic, and that means there's no edge.

Blandrew was using some picturesque language which may have been misleading. The only sense in which there are edges is the sense of a limit to how far you can see from some position. Like a horizon on the ocean, there's a boundary beyond which you can't see; but at the horizon there's nothing special. You are at the center of your own field of view, and also on the horizon of certain other observers.

You can also think of a horizon in time. From here-and-now, we can see 2010; but you can't see 2011. You'll have to wait another six months. It's not that NOW is some special identifiable edge in time; merely the horizon of what we see from this point in time.

These kinds of "edges" are not something special about a location, but depend on an observer. They are better called "horizons".

Even better, just forget all that observer stuff and consider simply that the universe has no edge. (Unless the universe is really different from what we currently tend to think on the basis of available evidence.)

Cheers -- Sylas

Hi Sylas. Thanks. Your explanation is very clear and helpful.

The universe has no edge, but we can consider our present location in time, this moment, as a horizon to our limits of perception.

Can I then make the assumption that the universe is spatially infinite in all directions ? Given that;

- it is homogenous and isotropic
- I see no spatial end / edge to it for millions of miles - light years even
- if I were in a location a billion miles away, I would probably see the same as I do now


EDIT; I just saw marcus has answered this somewhat, but I would still appreciate your response.

 

[DaveC426913]

- I see no spatial end / edge to it for millions of miles - light years even
- if I were in a location a billion miles away, I would probably see the same as I do now

Not to put too fine a point on it but:
- "millions of miles" doesn't even get you to Mars
- "a billion miles away" doesn't even get you to Pluto

You want to be talking about billions of light years.

 

[Chiclayo guy]

I never met anybody with as much as one introductory college course in Astro who thought that beyond the current observable range there was "black space". That wouldn't make dynamical (general rel.) sense and there is no evidence for it.
"Black space" surrounding the observable portion is a kind of extravagant fantasy without any observational or theoretical support.

But wasn’t empty, black space the dominant condition prior to the big bang, and if so why couldn’t it exist now outside of the observable universe?

Tom

 

[DaveC426913]

But wasn’t empty, black space the dominant condition prior to the big bang, and if so why couldn’t it exist now outside of the observable universe?

Tom

No, the dominant condition pre-BB was no space at all.

The BB did not occur in space, the BB created space.

 

[nismaratwork]

No, the dominant condition pre-BB was no space at all.

The BB did not occur in space, the BB created space.

*Pipes up* and time!

 

[justwondering]

The 'edge' of our observable universe is receeding faster than the speed of light: which means you can't get there from here.

But NOT any Mass that may be near the 'edge', that can NOT be traveling away from us that fast?