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! :|
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Not so much a physical boundary, but distant galaxies are moving away from you faster than you can ever to hope to catch up with them (let alone hurtle past) so, finite, but unbounded.
And if you did reach a distant galaxy, and looked around, you would also note the one you're at at that point, is at the center of the universe too.
You can't win, you can't even catch up.
If you hang around here long enough, the rest of the universe will leave you infinitely alone, thus, in a perverse invertede way, of fulfilling your quest.
And if you did reach a distant galaxy, and looked around, you would also note the one you're at at that point, is at the center of the universe too.
You can't win, you can't even catch up.
If you hang around here long enough, the rest of the universe will leave you infinitely alone, thus, in a perverse invertede way, of fulfilling your quest.
Bdude42":owyu7lec said:
Space-time is, according to general relativity, a 4-dimensional Lorentzian manifold. the curvature of that manifold is determined by the distribution of matter/energy in the universe. That manifold is a manifold without boundary (a mathematical term meaning without edges).
It is not known if the universe is open or closed (the correct terms for what it sometimes called "infinite" or "finite"), and the answer depends on the specific nature of the universe.
The universe is also taken to be an intrinsic manifold -- it is not embedded in something else. Therefore there is no meaning to "popping out on the other side". In fact since the universe is, rather by definition, the whole enchilada, if there were a something else, it would be part of the universe.
Bdude42":1787oey9 said:
Want a real answer? We don't know. None of us do, We can guess and assume and come up with Theories but at the current moment we have NO clue as to what Started everything, if the Space we see is inside "something", etc..
But what was stated here so far are good thoughts
I really don't know what would happen either, but if you ever did reach a boundary, then wouldn't time also cease to exist outside this boundary?
I think that space is finite. Space may be expanding but it will never reach infinity, so it should be a finite universe, right?
xXTheOneRavenXx":b5f832yu said:
There is a problem with a boundary.
Space-time is, in general relativity, a 4-dimensinal manifold. It is a manifold without boundary. That makes physical sense.
A manifold with boundary is somewhat special object. If the manifold had dimension n then the boundary is a sub-manifold of dimension n-1, without boundary. A quick example is the unit disk in the plane. That is a 2-dimensional manifold with boundary, the boundary being the circle with is a 1-dimensional manifold without boundary.
If there were a boundary to space-time, it would be some sort of 3-manifold. But what would that be, locally? Two space dimensions and 1 time dimension, three space dimensions without time ? Nothing makes good sensefroma physical perspective.
quantumnumber":2vxx2o5k said:
Not necessarily. Space could well be infinte in extent, and many good physicists think that such may be the case.
It is quite possible to describe a point expanding to fill all of space. It can be done continuously in fact.
Consider this function. Let X denote a vector in 3-space (you can do this for any dimension), and t, be any real number in the closed interval [0,1]. Define f(X,t)=tX, where tX is just scalar multiplication of the vector X by the scalar t. Then f(X,0)=0 and f(X,1)=X. So for t=0, f maps three-space to a poiht, and for t=1 f is the identity function on 3-space, which is infinite in extent. For t between 0 and 1 f still maps all of 3-space onto all of 3-space, but with a scale factor, so it shows an analog of expansion as well.
Did they ever consider a 3-dimension with a factor of time bleed-over into the 2? I don't know, it's hard to explain considering I don't know the exact formula that would fit.
I'm meaning the one dimension "time" affecting both of the other dimensions. Say time was seen by us as one constant, same thing applied as seen from the other dimension. Time then would be 2x's in total, but each dimension is only affected by 1/2 of the "time" dimension at any given time. In this case I guess the "time" dimension is not as limited as the other two. Does this make any sense?
xXTheOneRavenXx":2a25wgyl said:
I think that perhaps you might want to read a bit of this thread that discusses the idea of "dimension".
viewtopic.php?f=10&t=4461&hilit=+What+ia+a+dimensin+and+how+can+
DrRocket":234kzx39 said:
Thanks for that Dr. Rocket. In the description, it seems Time affects all dimensions rather then being a dimension of it's own. Or a dimension that must exist for all others to function. So Time is necessary regardless of the formula?
Space-time cannot be defined only by its 3 dimensional volume. The 4 dimensional space-time continuum is continuously expanding, but anything that was somehow located outside of the space-time continuum would be undefined and unexplainable by our laws of physics. It's easier to run the film backward to understand it. As the universe shrinks, the volume of space-time gets smaller and smaller until it becomes a singularity. All physics breaks down at that point, time, dimension, position, spin energy all become meaningless and undefined, since the laws of the universe are unified under those conditions. In a universe with a absolute size of 0, how do you define motion? At the moment of the Big Bang, and ever since, space-time has expanded like a giant loaf of bread, dragging all the matter and energy in the universe along with it. Whether the undefined space is being displaced by our space-time, or if space-time has its own boundary is irrelevant. Anything "outside" of our universe would almost certainly not be governed by the physical laws that exist in space-time. If the edge of space-time was interacting with whatever medium lies beyond its defined limits, wouldn't we expect to see some kind of quantum mechanical activity along the interacting edges?
The universe may be able to expand infinitely, perhaps leading to the Big Rip, where the universe will shear apart, perhaps ultimately ripping space-time itself apart...who knows? We can only perceive things that are within space-time and that we can interact with. Outside of spacetime, our understanding of physics is likely not applicable, and we cannot perceive what might lie beyond, except by any effects it might have upon space-time itself, which appears to be none. Anything outside of space-time, unless it coincidentally has exactly the same properties as space-time itself (which is unlikely) is undefinable by our physics. I believe that if you could somehow warp to the edge of space-time, and then push beyond its 'frontier' you would simply drag/stretch space-time out with you along that vector. The matter and energy of you and your spaceship are defined by the rules of space-time, so even though space-time can be stretched and even broken (black holes, for instance) the mass-energy remains in our universe, albeit in a strange form...
The universe may be able to expand infinitely, perhaps leading to the Big Rip, where the universe will shear apart, perhaps ultimately ripping space-time itself apart...who knows? We can only perceive things that are within space-time and that we can interact with. Outside of spacetime, our understanding of physics is likely not applicable, and we cannot perceive what might lie beyond, except by any effects it might have upon space-time itself, which appears to be none. Anything outside of space-time, unless it coincidentally has exactly the same properties as space-time itself (which is unlikely) is undefinable by our physics. I believe that if you could somehow warp to the edge of space-time, and then push beyond its 'frontier' you would simply drag/stretch space-time out with you along that vector. The matter and energy of you and your spaceship are defined by the rules of space-time, so even though space-time can be stretched and even broken (black holes, for instance) the mass-energy remains in our universe, albeit in a strange form...
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, and a dearth of stars and galaxies in all other directions. This would seem to be a boundry between our present space time and a future space time. Thanks for your thoughts on this.
JimThomson":324ful1n said:
That's the hard part to grasp. You are thinking of the big bang as an explosion, with everything rushing away from it. But that's not the case. SPece iself is what is expanding, so there is no "locus" to rush away from So everything more or less looks the same from wherever your viewpoint is in the Universe. Wherever you are, space is expanding around you in all directions.
MW
Another related hypothetical question...can stable bubbles of space-time pinch off from the main space-time continuum, creating mini-parallel universes? If the expansion of space-time is uniform throughout the entire universe, I would say it isn't possible. However the universe does seem to have denser spots and comparative voids, suggesting that the mass and energy distribution of the universe is uneven. Gravity affects space-time, so space-time itself should be somewhat warped and eneven now, even if it was initially very uniform. If there is a medium beyond regular space time, I would expect to see small chunks of our universe pinch off and occasionally rejoin our universe, and I might also expect to find some swiss-cheese holes in space where voids of non-space-time appear to be due to the lack of a perfectly uniform distribution of matter in the universe. I don't recall ever seeing any evidence of such irregularities in the space-time continuum, which seems remarkably uniform throughout the universe, from our point of view anyway.
I think the universe has boundaries because before the bigbang there was no space. The bigbang created the space. Some what like a balloon. If there is boundaries, it's probably not possible to get pass it. some kind of repel force.Well it's all speculation but it's fun to wonder about it... :lol:
If there are boundaries, I don't think we would get past them because of the expansion of the universe.
The bounderies when you travel far enough threw space to the end an come-out somethings fingernail... 
HelloBozos":285gkwrs said:The bounderies when you travel far enough threw space to the end an come-out somethings fingernail...
please explain that?
From what I understand thus far... The universe is constructed through a seamless integration of space and time, and because of this, we being 3-dimensional beings can only move around and experience the first 3 dimensions of space. We have no willfull influence over time.
Due to this, the boundary of the universe, to us, is the end of the existence of 3 spatial dimensions, but since these 3 dimensions are also inextricably connected to time, the boundary of the universe both the end of spatial dimensions and time. As 3 dimensions being we can never escape time, so all that might happen when you get closer and closer to the actual actual boundary is that time and space gets distorted, but you will never find the end.
This brings up the interesting poissibility that if there are such a thing as 4 dimensions beings that could move freely in and out of timeframes... then they woudl see the universe's boundaries differently?
Due to this, the boundary of the universe, to us, is the end of the existence of 3 spatial dimensions, but since these 3 dimensions are also inextricably connected to time, the boundary of the universe both the end of spatial dimensions and time. As 3 dimensions being we can never escape time, so all that might happen when you get closer and closer to the actual actual boundary is that time and space gets distorted, but you will never find the end.
This brings up the interesting poissibility that if there are such a thing as 4 dimensions beings that could move freely in and out of timeframes... then they woudl see the universe's boundaries differently?
Here's how I see it: consider a balloon with the earth as a green dot with a blue dot distance "a" away, followed by a white dot distance 2a away, and a red dot distance 4a away - all in one straight line. In one second blow the balloon up by a factor of 2 (a becomes 2a, 2a becomes 4a, 4a becomes 8a). The blue dot moved away at "a" units/s, the white dot moved away at 2a units/s and red at 4a units/s. How would it look from the white dot? Earth would have moved away at 2a units/s, blue at a units/s and red at 2a units/s. So, for proportional increase in recession velocity with increasing distance in all directions, you're left with the natural conclusion that - the expansion is isotropic (the same everywhere we look).JimThomson":32jo6xy1 said:
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.
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