A difficult question.....

[DrRocket]

On topic: I think it's just mathematically convenient [to science] to state that the universe is unbounded. Seems to make things simnpler - and saves our sanity. I've seen a view somewhere that whatever is outside the boundaries may be evidenced by dark matter (like gravity is being transmitted by those objects outside the boundary - we see their gravitational effect, but nothing else of them).

I like to think there is a bounday, and there's stuff beyond it. Makes for a more interesting existence

The model of the universe as a manaifold without bondary is far more than mathematical convenience. If there were a boundary, then there would a part of space-time, the boundary, of dimension 3. What would that mean physically, in some local chart? Only two spatial dimensisons ? No time ?. Physics in 2 dimensions is different from physics in 3 dimensions -- Huygens Principle, for instance has problems in 2 spatial dimensions. http://www.mathpages.com/home/kmath242/kmath242.htm

There is a tremendous difference between a manifold with boundary, and a manifold embedded in a higher-dimensional space. The sphere (the surface of a balloon for instance0 is a 2-manifold without boundary. It is without boundary whether it is viewed as an intrinsic manifold or viewed as a manifold embedded in 3-space. Itr has no "edge" in either case. So far as is known the universe is not embedded in anything, and whether it is or not has nothing to do with the existence of a boundary.

 

[fireflyMel]

The universe is by definition "everything"it is all of "nature" there is no "outside" as this is a semantically meaningless concept: a space beyond space is simply more space. There is no boundary, there is no "outside" to the universe.

 

[MorganW]

Sorry dude. We're already at the "edge" of the universe. When you look out in space-time, you're looking into the past; it's like driving on a road at night and looking into the rear-view mirror, only everyone is moving along at their own speed and trajectory. There is no "front window" to look through; that's the future and it hasn't happened yet (from our perspective at least). Even if you flew at the speed of light, as soon as you stopped, you'd be right back in the "present", which would quickly become the past again. Think it sucks? It's actually pretty cool if you think about it...

 

[Wablam]

No, space has no bounds. If you reached the theoretical end of the universe, you would just become the new end. Or beginning, depending on how you view the water in the glass.

 

[Maxwell99]

Yes, don't stay out after midnight!!! It is the space between space and time that is giving us so much trouble isn't it or is it the time of the space time continuum...The space between each moment of time is the same as the time between each adjoining place in space... the distance between midnight and home and the time between you and home that is the measure of just how grounded you are going to be... if you have the time the universe has the space and vice versa...

 

[DrRocket]

Yes, don't stay out after midnight!!! It is the space between space and time that is giving us so much trouble isn't it or is it the time of the space time continuum...The space between each moment of time is the same as the time between each adjoining place in space... the distance between midnight and home and the time between you and home that is the measure of just how grounded you are going to be... if you have the time the universe has the space and vice versa...

From whom did you learn your cosmology ? Willy Nelson ?

 

[Jason99403]

With respect to boundries, it would seem that there is a galaxy that is traveling near the speed of light away from the locus of the big bang. If there was an observer in this galaxy, wouldn't there be a concentration of stars and galxies when the observer looked in the direction of the big bang...?

It all becomes relatively (pun intended) easy if one scales back a dimension.

Imprecisely, the universe is shaped like the 3-dimensional surface of a 4-dimensional sphere.

So imagine a normal sphere with its 2-dimensional surface. Imagine that this surface is populated by 2-dimensional people. From their 2-D perspective, the 2-D surface is finite but has no boundaries.


From our God-like 3-dimensional perspective, we know that the sphere has an interior. This would be analogous to the past, with the Big Bang "located" at the center of the sphere (i.e., it is at the beginning of time). The 2-D people cannot look "toward" the Big Bang because their telescopes won't rotate into that third dimension, just as our telescopes can't mystically rotate and point into some 4th dimension (note that "looking into the past" is a poetic phrase and no literally accurate).

If you like, you could refer to the entire observable universe-at-present as a boundary between the past and the future.

The universe is by definition "everything"...

True, but there are alternate definitions. In cosmology, "the universe" (with a lower-case u) often refers to the observable universe only.


Cheers,
Jason

 

[supercomputer]

there are no boundries, no walls, no expansion, no up or down or sideways,and there is no good and evil,
no beginning, and no end.....no giant junkyard to go to for spare hydrogen,

we are not allowed to know...........we are brats.......and our pride would not let us rest until we
control it

 

[javiej]

In my opinion, the expression "the observable universe" is not well defined, nor it can become a hard restriction for our thinking.

Our technology limitations can not be used to define any boundary. We can not say that the "the universe" is equal to "the universe that we can see with our poor physics and our primitive technology".

I mean, we simply not know if the universe is open or closed, we can not explain the black holes quantum gravity singularities nor similar entities (including the bing bang at t=0), we do not know what is the "dark energy" that is expanding the universe, and what about the boundaries of the smallest observable space areas?, we can not observe nothing smaller than a quark, does it means that if something smaller exists then it is not part of our universe?, simply because it is out of "the observable"?, and what about the extra dimensions that seems to exist but that are not observable?, are not related with our universe in any way?. The "observable universe" is a lay, it is only the boundary of our current knowledge, and nothing more.

The unique think that we are sure is that our physics model is obsolete, it can not explain the big misteries, and it seems that developing our current model will never answer any of them. We need to start destroying our standard model myths and start building something new.

I think that the real problem is that our limited mind does not work very well to understand these issues. Our intuitive thinking is that there must an "origin of all", where it should be the opposite. For me, it is more logical to think that there is no origin:

- An original absolute void seems to be something very plausible and intuitive, and of course it is plaussible, but only if nothing is created later, because nothing can be created starting from the scratch. The fact is that we are here, which means that the absolute void never happened.

- As a result, the universe exist, among other things, because something must exist. Always. Alos before the big bang. A solution without any kind of universe is out of the equation. It is not possible. The observable universe is just the part that we can see, from all the other entities that also exist, and that we may see (it may happen or not, but it is not impossible) in the future. Opposite to it, the unique thing that can not exist is "the absolute void", a concept that is so "intuitive" for humans" due to our malfunctioning mind, but that can only be imagined in the context of a universe that exist, as its negation.

The imposibility of seeing beyond the observable universe is a myth. For example, a good prove can be obtained by looking to quantum mechanics. The entanglement of particles, or "the spooky action at a distance" in words of Einstein, is a perfect example. A particle can be located in two places at the same time, and it can interact with another particle without going trough any of out standard model paths. Our physics model is describing, at the same time, the theorical physical boundaries and a real entity that can bypass them. And it happens at every places, all the time. A quantum particle can exists beyond any boundary that you can define for the universe (using our current physic models). What happens when an entangled particle go beyond the observable universe, while its counterpart stays here? (it is not an exception, this is happening everywhere, all the time), our physical model say that they will continue entangled, no boundaries can be defined for it.

It is simply that we do not know how to pass over boundaries. But if a stupid particle can do it, then why not us, somewhere in the future?

 

[Floridian]

Mathematically an infinite universe seems impossible. Space-time is a fabric, if there is infinity of it, where did that infinity come from. How did infinity come from nothing.

The only option is that infinity came from something of infinity... the closest thing to that seems like God to me.

If you are saying the universe is infinite than infinity had to come from infinity.


A lot of people ask who created God? Some people answer that he is eternal and that he created time. Then people are like, that doesn't make sense. Yet if time is progressing foward and the universe expanding, and t did = 0 at some point. Then time itself had to be created, if time wasn't created then nothing could have happened, so whether or not you believe in God, something outside of time had to create time.

 

[pmf0671]

I think we won't ever discover the true nature of the universe, because we can never look down on it.

The way i see the universe (it's all about perception) is the way many scientists describe it to laymen:

Think of space-time as a spherical balloon. this balloon is constantly growing larger. the material that the balloon is made of, is space-time. For that matter , think as our planet earth as being spacetime, only earth is constantly getting larger. Note: only earth is getting larger, everything standing or lying on it is not. all the grains of sand on our beaches do not expand with the earth. Result: as earth expands the grains of sand are being distributed more and more until you reach a point where earth is so large that all the grains of sand have fallen off of eachother and are covering the entire earth with a layer of one grain thick. Earth grows even larger, and there appear openings between the grains (starting to see the analogy with galaxies?). Ok . now think of yourself standing on earth. Start walking. What happens if you walk long enough(and FAST enough to actually go forward. taking into account the expanding earth)? You end up exactly where you started, because you walked(ran!, swam) right around our planet. Alas, earth is expanding at such a pace that even light cannot travel around it fast enough to overcome the expansion and actually get back to the point where it took off. I think this property of our universe (earth), is what causes our cosmological speed limit. I will elaborate. If a person started running as fast as he can , say 15 miles per hour, think of this as light speed. The speed can also be measured in angular units, measured from the center of the earth. he would travel maybe a couple of arcseconds per hour. As earth expands, that angular speed will decrease while he is running at a fixed speed. If he would stop running and just walk that angular speed would fall below 0 (negative) because the earth is expanding faster than his angular speed, sort of speak. At our current point is time, earth is expanding so fast that even if he woulr run an as fast as he can(15mph,a.k.a. light speed), his angular speed would still be negative. Thus he would never be able to run a complete circle around earth.

This is how i see our universe. It is infinite, but it has boundaries. Boundaries in a sense that you can never travel outside our universe. We can never see these boundaries, and we can never measure them. These boundaries do not exist in 3D space. Correction. They do exist, they're just simply not observable from within 3D space, the space we live in.

By the way: GOD is everything outside our universe.

 

[allang]

A real ignorant question
Why do we assume time is one dimensional, and not 3 dimensional.

 

[DrRocket]

A real ignorant question
Why do we assume time is one dimensional, and not 3 dimensional.

Because time is a local coordinate in general relativity, and your clock seems to work quite well as it produces a single number (coordinate) that describes the time.

 

[drstein]

If we take string theory as the sorce how everything works, then we all live on a expanded string, we have ower matter (strings) on this membrane, and we cannot leave it, that is fore sure, so will never reach a wall, either you make the membrane larger streched, with you going there, or the membrain is foulded into itself, makeing you at some point turning up were you started if you went in a straight line! So what ever you do, you cannot leave ower universe, it's impossible! There are bigger enigmas then the edge of the universe! =)

 

[MorganW]

Time is a human construct. We are "self-aware" and in this awareness, we observe things that happened in our past and make predictions about things that will come to happen in "the future".
My guess is that the reality is something closer to "the present, or NOW". The universe is always expanding "now". And now... etc. In that paradigm, even the future is part of now. For example - you know you're going to die someday, right? In that sense, you're already dead. But not right now (I hope).
Let's say that there is other intelligent life in the universe. Some LGM in a galaxy far, far away is looking out at the night sky and seeing everything that has happened up until now. He's right there on the edge of space or the boundary between what has happened and what's about to happen. That's the only kind of boundary that makes sense in our 3 or 4 dimensional perception of the universe. As for the spooky action at a distance, if the particles only perceive themselves (if that's the right way to put it) in one dimensional "now", distance may not even be a factor. Again, it's our perception of their interaction that creates this strange conundrum. That's what I think anyway (at least, for now).

Here's another thought for us to ponder: what if Gravity is simply a necessary output of 4 dimensional space. In a 2 dimensional universe, what would a shadow look like? There's no up/down to cast it, but there it is.

 

[MeteorWayne]

This thread has produced very little scientific discussion. Mostly wild and uninformed speculation. If it doesn't get more closely aligned within the subject matter of this forum (Space Science and Astronomy) it is destined for a trip to The Unexplained. Please lets talk real science here.

Thanx

Meteor Wayne

 

[DrRocket]

If we take string theory as the sorce how everything works, then we all live on a expanded string, we have ower matter (strings) on this membrane, and we cannot leave it, that is fore sure, so will never reach a wall, either you make the membrane larger streched, with you going there, or the membrain is foulded into itself, makeing you at some point turning up were you started if you went in a straight line! So what ever you do, you cannot leave ower universe, it's impossible! There are bigger enigmas then the edge of the universe! =)

There are couple of problems here.

1. The statement that "we live on an expanded string" makes no sense.

2. There is no such thing as string theory (singular). There are in fact several competing string theories. They don't seem to work.

3. M-theory, the source of your reference to "membranes" (actually called "branes" in the "theory") is based on an as-yet-unproven conjecture. The conjecture which would consolidate string theories into a single M-theory was put forth in 1995 by Witten. The dictionary between competing string theories has not yet been produced.

If you want open questions, your "enigmas", the one that ought to be at the top of your list is "What is M-theory?". That is the biggest open question in the subject.

There is nothing "for sure" in this theory, and before anyone can state anything "for sure" they are going to need to actually define the theory.

 

[RocketsRedGlare]

If there is a boundry it has not been found though some astronomers and mathmaticians claim it has an end. I say SHOW ME! I don't believe the universe has an end , it is infinite and has always existed. That also puts the kabash on the big bang thery that so many try to pass off as a fact, how rediculous to think the universe was compacted into the size of a pinhead. Only a pinhead head would make that claim---lol.It's like saying stars are made of hydrogen (they are mostly), then when they use up ALL of their hydrogen they explode. Then over time new stars are formed from the remains of the old stars. But wait, stars are made of hydrogen and the old star used ALL its up so where did all the hydrogen come from to make the new stars?,

 

[michaelmozina]

If we take string theory as the sorce how everything works, then we all live on a expanded string, we have ower matter (strings) on this membrane, and we cannot leave it, that is fore sure, so will never reach a wall, either you make the membrane larger streched, with you going there, or the membrain is foulded into itself, makeing you at some point turning up were you started if you went in a straight line! So what ever you do, you cannot leave ower universe, it's impossible! There are bigger enigmas then the edge of the universe! =)

There are couple of problems here.

1. The statement that "we live on an expanded string" makes no sense.

2. There is no such thing as string theory (singular). There are in fact several competing string theories. They don't seem to work.

3. M-theory, the source of your reference to "membranes" (actually called "branes" in the "theory") is based on an as-yet-unproven conjecture. The conjecture which would consolidate string theories into a single M-theory was put forth in 1995 by Witten. The dictionary between competing string theories has not yet been produced.

If you want open questions, your "enigmas", the one that ought to be at the top of your list is "What is M-theory?". That is the biggest open question in the subject.

There is nothing "for sure" in this theory, and before anyone can state anything "for sure" they are going to need to actually define the theory.

Oddly enough I find myself in complete agreement. String theory began as a failed particle physics theory and was later applied to the BB. There isn't actually one of them, but many and it's unclear that any of them actually work.

 

[Jason99403]

In my opinion, the expression "the observable universe" is not well defined, nor it can become a hard restriction for our thinking.

Our technology limitations can not be used to define any boundary. We can not say that the "the universe" is equal to "the universe that we can see with our poor physics and our primitive technology".

Hi. I'm not sure where you got a bad definition for "observable universe" (or what that bad definition is), but clearly I should have given one.

The observable universe is everything with which we could, in principle, interact causally. It is not the same as the visible universe and has nothing to do with technology. The definition is also independent of our current knowledge of physics.

Dark energy, for example, is part of the observable universe because it interacts (however minimally) with the rest of the universe. By contrast, some variants of the Many-Worlds Interpretation describe what might be called "parallel" universes that are known to exist but cannot interact with our universe. Thus they would not be part of the observable universe.


The expression is not a "restriction for our thinking" because it is an expression, not an academic rule. It allows us to make a distinction. It is like distinguishing between, say, the laws of physics and the laws of Texas. The distinction allows us to make sense.

The imposibility of seeing beyond the observable universe is a myth.

It's a tautology.

But wait, stars are made of hydrogen and the old star used ALL its up so where did all the hydrogen come from to make the new stars?

Stars begin the death process after depleting all the hydrogen in the core, not all of the hydrogen in the star.

Also keep in mind that the age of the universe is the same order of magnitude as the expected lifetime of a star like our own. Ergo, the stars that have actually died thus far were mostly big, fast-living, fast-burning monsters. These behemoths tend to throw off a great deal of hydrogen before it ever makes it to the fusion-processing core.


Cheers,
Jason

 

[derekmcd]

If there is a boundry it has not been found though some astronomers and mathmaticians claim it has an end. I say SHOW ME! I don't believe the universe has an end , it is infinite and has always existed.

Some do, but most cosmologists do not believe the Universe has a boundary. I believe your problem lies in distinguishing the difference between "The Universe" and "the observable universe". There is a difference. We know nothing beyond what we can observe.

That also puts the kabash on the big bang thery that so many try to pass off as a fact, how rediculous to think the universe was compacted into the size of a pinhead. Only a pinhead head would make that claim---lol.

The Big Bang Theory (BBT) only describes the observable universe. It says nothing about the entire Universe, nor does the BBT describe the creation of the Universe (or even what caused the expansion of our local, observable part of the Universe). What the BBT describes in that our observable part of the universe (not the entire universe) was, at one point, much hotter and more dense than it was today. The data is very compelling and quite robust describing our observable universe. However, we know very little about beyond what we can observe. The entire Universe, beyond what we can observe, may very well be infinite... we just don't know. I'll refrain from attacking your 'pinhead' comment.

It's like saying stars are made of hydrogen (they are mostly), then when they use up ALL of their hydrogen they explode. Then over time new stars are formed from the remains of the old stars. But wait, stars are made of hydrogen and the old star used ALL its up so where did all the hydrogen come from to make the new stars?,

Hydrogen is, even today, still the most abundant element. There remains today massive, star forming regions in the Milky Way made mostly of hydrogen. Within these star forming regions, supernovae may occur. How they assist in creating new stars are through shockwaves compressing the existing, neighboring, hydrogen gasses within the cloud and accelerating the gravitation collapse. Supernovae also contribute elements heavier than Iron to the system.

Without supernovae, we would not exist. The medical industry couldn't handle all the claims of iron deficiencies.

 

[wkitty42]

ever since i was a child and i first learned about atoms and their particle's orbits, it has always been intriguing to me how similar they are to how planets orbit stars, how stars orbit in their galaxies and how it may be possible for galaxies to orbit within the known universe (although we don't yet see or know this)... it would not surprise me to find out that our universe, known and not, is also orbiting with other universes within some other body that we don't yet know about or have a name for (that i know of)...

to carry this line of thought on further, and also to take a look at the Dr. Seuss story of "Horton Hears a Who", might it be possible that we are "Whos" living on a particle within an atom and that we are actually very miniscule compared to those who might see our galaxy as quarks or other sub-atomic particles that we know of?

that also raises the question of are those quarks and such that we are discovering and studying actually universes in their own right?

profound thoughts abound

 

[wkitty42]

This thread has produced very little scientific discussion. Mostly wild and uninformed speculation. If it doesn't get more closely aligned within the subject matter of this forum (Space Science and Astronomy) it is destined for a trip to The Unexplained. Please lets talk real science here.

Thanx

Meteor Wayne

i must be missing something... it wouldn't be the first time...

i arrived at this thread from the space.com news headlines... reading the initial message, more than once, i don't see anything indicating that "real science" was a requirement for replying to the original message or participating in this thread... in fact, the original message even states something to the effect of letting the imagination flow...

 

[javiej]

In my opinion, the expression "the observable universe" is not well defined, nor it can become a hard restriction for our thinking.

Our technology limitations can not be used to define any boundary. We can not say that the "the universe" is equal to "the universe that we can see with our poor physics and our primitive technology".

Hi. I'm not sure where you got a bad definition for "observable universe" (or what that bad definition is), but clearly I should have given one.

The observable universe is everything with which we could, in principle, interact causally. It is not the same as the visible universe and has nothing to do with technology. The definition is also independent of our current knowledge of physics.

Ok, I admit that my expression "restriction for our thinking" was too abstract (your "laws of texas / laws of physics" comparison is brilliant, it express in a few words the whole idea), but please admit that also your definition is too abstract. When I ear things like "The observable universe is everything with which we could, in principle, interact causally", it is exactly the point where I think "The observable universe is not well defined". In this case, the words "could" and "in principle" are the problem.

The expression is not a "restriction for our thinking" because it is an expression, not an academic rule. It allows us to make a distinction. It is like distinguishing between, say, the laws of physics and the laws of Texas. The distinction allows us to make sense.

What I mean is that the big science revolutions usually happen when somebody ( Einstein, Heissemberg ...) break the stablished physics model rules. The "restriction for our thinking" is to believe in a standard model as if it where a religion, specially if it is sinking as it seem to happen these days.

The

The imposibility of seeing beyond the observable universe is a myth.

It's a tautology.

[/quote]

Yes, but only in principle.

If a quantum particle can interact with both sides, in and out of the observable universe, then we could use it (in theory) to pass information between them. In other words, quantum mechanics tell us that a part of the universe can be observable and not observable at the same time, because the act of observing the quantum particle in the observable universe will also modify the non observable universe. We can not observe it, but we can modify it. In this case there is still a causality relationship. But let's go one step beyond: if we talk about two entangled particles that are located near the boundry, and only one of them go to the non observable universe and disappear, then there is no causality relationship between them (or nobody has demonstrated it), but we can still interact with the non observable universe by observing the particle at our side. Does it make sense?

This is why I think that the standard model is sinking...

 

[SLAVER1]

So space is basically endless. More or less. Well the way scientists portray it is that the Universe is so incredibly complex and infinite. This is probably true but I want to know whether or not the Universe has boundaries. And if you were to collide with those "boundaries" (if any exist) then what would happen if you popped out the other side. Just a nice happy endless void? What forces created the Universe (as in the matter and energy, not the explosion) and could there be a universe WITHIN a universe? Is it just an endless cause and effect relationship? (the Universe was a product of something bigger?) Don't worry, I don't expect a straight answer to this, just personal speculation. Have fun! :|

I happy to see I'm not the only one that has that question in my mind. Always wanted to ask, but was to afraid to.