The discussion centers on the balloon analogy used to describe the universe's expansion, highlighting misconceptions about the nature of space and galaxies. Participants clarify that while the universe expands, galaxies do not increase in size, and the expansion occurs in the fabric of space itself, not into a pre-existing void. The fourth dimension is identified as time, as per Einstein's General Theory of Relativity, and the conversation touches on the speculative nature of higher dimensions and string theory. Overall, the balloon analogy serves to illustrate how galaxies move apart without expanding themselves.
PREREQUISITESAstronomers, physicists, students of cosmology, and anyone interested in understanding the nature of the universe and its expansion.
I've never hears an astronomer use that term unless they were tlaking about its end in time.kasse said:So the universe does not actually have an end? Why do astronomers then constantly refer to "the end of the universe"?
kasse said:And how is it possible (in theory) to return to the same point? Does this mean that the universe is bent in a fourth space-dimension that we cannot sense?
kasse said:Also, is it true that all galaxies are at rest in space, while the universe (and therefore the relative distances between the galaxies) expands? Doesn't this mean that the universe is filled with a kind of expanding ether (space)?
kasse said:Wow, that's amazing! How do we know that? Or do we? Could there be creatures living in 4D space, or is that only possible in 3D world?
We don't. It's a model that helps explain many things we see, but we don't really have compelling evidencekasse said:Wow, that's amazing! How do we know that? Or do we?
Only wild speculation.kasse said:Could there be creatures living in 4D space, or is that only possible in 3D world?
kasse said:Also, is it true that all galaxies are at rest in space, while the universe (and therefore the relative distances between the galaxies) expands? Doesn't this mean that the universe is filled with a kind of expanding ether (space)?
There is no evidence to support this, but we are all free to hold our beliefs.mubashirmansoor said:But you don't really have to look for some beings living in the 4th dimension because I think there are already many of them in the cosmos!
mubashirmansoor said:In fact the 4th dimension is the time dimension as thought by Einstein & his General theory of relativity.
But you don't really have to look for some beings living in the 4th dimension because I think there are already many of them in the cosmos!
Sheneron said:I have a question relating to this...
I saw that balloon analogy of the expanding universe. But there was something I was confused about. In the balloon analogy there were dots on the balloon and as the balloon was blown up and increased in size, the space between the galaxies increased. And that was the analogy of the expansion of the universe; The galaxies are moving away from each other because space is expanding.
I realize that the balloon analogy is a simplified model but here is where my confusion lies. On the balloon if it were blown up the dots (representing galaxies) would increase in size, and thus the relative distances apart would stay the same.
So if space is expanding shouldn't the galaxies also be expanding, and if that is true would the distance apart not remain the same?
Indeed.mubashirmansoor said:In fact the 4th dimension is the time dimension as thought by Einstein & his General theory of relativity.
I think what you mean here is that one does not need to look very far for a being living in the fourth dimension as per Einstein; that is, you are talking about the fourth dimension being temporal, as opposed to spatial. This may have caused some confusion in the thread.mubashirmansoor said:But you don't really have to look for some beings living in the 4th dimension because I think there are already many of them in the cosmos!
kasse said:So it is time that bends R^3 to a kind of 4D sphere?
kasse said:Sheneron said:I have a question relating to this... I saw that balloon analogy of the expanding universe. But there was something I was confused about. In the balloon analogy there were dots on the balloon and as the balloon was blown up and increased in size, the space between the galaxies increased. And that was the analogy of the expansion of the universe; The galaxies are moving away from each other because space is expanding. I realize that the balloon analogy is a simplified model but here is where my confusion lies. On the balloon if it were blown up the dots (representing galaxies) would increase in size, and thus the relative distances apart would stay the same. So if space is expanding shouldn't the galaxies also be expanding, and if that is true would the distance apart not remain the same?
If I've got it right, the galaxies (dots) don't expand, even if dots on a balloon would expand. Only space itself expands.
There is no need for there to be anything for the universe to expand into. The analogy starts to break down when you think about what the balloon is expanding into.kasse said:It is said to expand into nothing. I don't understand how that is possible.
A better model for the analogy is, instead of drawing dots on the balloon, to glue pennies into it. As the balloon expands, the pennies do not. The solidity of the penny's metasl easily overwhelms the weak force of the balloon expanding. Likewise, the gravity of a galaxy easily overwhelms the weak force of space expanding.Sheneron said:I have a question relating to this...
I saw that balloon analogy of the expanding universe. But there was something I was confused about. In the balloon analogy there were dots on the balloon and as the balloon was blown up and increased in size, the space between the galaxies increased. And that was the analogy of the expansion of the universe; The galaxies are moving away from each other because space is expanding.
I realize that the balloon analogy is a simplified model but here is where my confusion lies. On the balloon if it were blown up the dots (representing galaxies) would increase in size, and thus the relative distances apart would stay the same.
So if space is expanding shouldn't the galaxies also be expanding, and if that is true would the distance apart not remain the same?
Gravity.kasse said:What bends spacetime then? A fourth spatial dimension?
cristo said:I think what you mean here is that one does not need to look very far for a being living in the fourth dimension as per Einstein; that is, you are talking about the fourth dimension being temporal, as opposed to spatial. This may have caused some confusion in the thread.
kasse said:Some physicists have told me that the universe is like the surface of a balloon. Does this mean that if it were possible to travel at an infinite speed, you'd come back to the same place if you traveled straight in one direction?
kasse said:What bends spacetime then? A fourth spatial dimension?
tommac said:The universe is not like a balloon.
rewebster said:its more like a balloon-only, without the balloon
tommac said:I am reading a little about string theory at the moment and they seem to be high on dimensions, particularly about very small ( plank length ) dimensions that are too small for us to notice.
DaveC426913 said:The balloon analogy simply serves to dispel a particular misunderstanding. It shows how space can expand, causing increasing distance between them, while not causing the expansion of the things within it.
kasse said:The string theory isn't a scientific theory, right? As it's not falsisiable.