What is space?


by Philip7575
Tags: space
mgervasoni
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#55
Dec9-11, 06:16 PM
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They say it's hard to imagine infinite space.. It could be a 4th dimension. BUT, if you did walk all the way to the edge of space and took one more step, you'd be right back where you started. It's like if someone couldn't grasp the concept of a 3 dimensional sphere. You'd put him on earth and he'd walk and walk and sooner or later he'd get right back where he started, bewildered. Thus may be our ability to conceive how we could get to the edge of space, and be right back where we were.
mgervasoni
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#56
Dec9-11, 06:19 PM
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The protons and electrons acting like Solar Systems in the Bohr's atom model is what lead to all that science fiction in the 30's and after: universes within universes. Our modern concept of how atoms are and operate is very different from what you learned in highschool science.
phinds
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#57
Dec9-11, 07:09 PM
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Quote Quote by mgervasoni View Post
They say it's hard to imagine infinite space.. It could be a 4th dimension. BUT, if you did walk all the way to the edge of space and took one more step, you'd be right back where you started. It's like if someone couldn't grasp the concept of a 3 dimensional sphere. You'd put him on earth and he'd walk and walk and sooner or later he'd get right back where he started, bewildered. Thus may be our ability to conceive how we could get to the edge of space, and be right back where we were.
I understand what you are saying but the "edge of space" is a very poor concept and should be avoided, since there isn't one.
Imax
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#58
Dec10-11, 01:44 AM
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Thereís no need for an edge if the universe is finite or compact. Itís just like on Earth. You can travel in a straight line on Earth and you can come back to where you started from. The difference is that on Earth youíre limited to a 2D surface, but the Universe is 3D.
Bread18
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#59
Dec10-11, 05:26 AM
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Quote Quote by Imax View Post
Thereís no need for an edge if the universe is finite or compact. Itís just like on Earth. You can travel in a straight line on Earth and you can come back to where you started from. The difference is that on Earth youíre limited to a 2D surface, but the Universe is 3D.
That would happen if we lived in a closed universe and, as far as I know, there isn't any evidence for that.
mgervasoni
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#60
Dec10-11, 07:56 AM
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Quote Quote by phinds View Post
I understand what you are saying but the "edge of space" is a very poor concept and should be avoided, since there isn't one.
Totally right Phinds, that was my point but perhaps poorly described. Just like there is no edge on earth, so is space/the universe... And again some people did think the Earth was flat/finite at one time which we just shake our heads at now.

And that's a very thought provoking statement that the Earth is 3D with a 2D surface, perhaps the universe is 4D with a 3D "surface"? (That's some string theory and other theories right?) Anyway, no need to speculate but it's a extremely interesting topic, and it's always good for our minds to think. :)
Imax
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#61
Dec10-11, 11:55 PM
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Quote Quote by Bread18 View Post
That would happen if we lived in a closed universe and, as far as I know, there isn't any evidence for that.
I’m trying to point out that there is no need for an edge, regardless of whether the Universe is finite or infinite. And, I agree with you. There is very little observable data indicating that it’s finite. Some models using Cosmic Microwave Background Radiation suggest that it may be finite, but I don’t think these are very conclusive. But, to quote Wiki (http://en.wikipedia.org/wiki/Big_Bang):

“According to the Big Bang theory, the Universe was once in an extremely hot and dense state which expanded rapidly.”

How can you have rapid expansion in size if the Universe is infinite?
Imax
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#62
Dec11-11, 01:02 AM
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Quote Quote by mgervasoni View Post
And that's a very thought provoking statement that the Earth is 3D with a 2D surface, perhaps the universe is 4D with a 3D "surface
Itís hard to imagine what a 3D Universe would look like embedded in 4D space.
phinds
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#63
Dec11-11, 04:30 AM
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Quote Quote by Imax View Post


How can you have rapid expansion in size if the Universe is infinite?
Math involving infinity is NOT like normal math. If you double infinity what you get is EXACTLY the infinity that you started with.
Drakkith
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#64
Dec11-11, 06:03 AM
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Quote Quote by Imax View Post
How can you have rapid expansion in size if the Universe is infinite?
The SIZE of the universe may or may not have increased. The distance between all objects in the universe did increase as a result of expansion. Is that easier to visualize? With an infinite universe, doubling the distance between all objects is exactly the same as in a finite universe.
Imax
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#65
Dec13-11, 12:01 AM
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Quote Quote by Drakkith View Post
The SIZE of the universe may or may not have increased. The distance between all objects in the universe did increase as a result of expansion.
The Big Bang theory postulates that the size of the Universe is increasing and it possibly starting from some kind of point singularity. The question is Space. Was Space finite or infinite near the time of the Big Bang event? Did the Universe start out in an infinite space with its entire mass confined in a very small volume, or did the big bang event itself create space?

I canít help but think that the BB singularity had some properties similar to Black Holes, and Black Holes can bend space-time. Itís possible that space was compact near the Big Bang, with all the mass/energy of the Universe confined to a point singularity.
Drakkith
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#66
Dec13-11, 01:53 AM
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Quote Quote by Imax View Post
The Big Bang theory postulates that the size of the Universe is increasing and it possibly starting from some kind of point singularity. The question is Space. Was Space finite or infinite near the time of the Big Bang event? Did the Universe start out in an infinite space with its entire mass confined in a very small volume, or did the big bang event itself create space?
To my knowledge the universe contains everything, including spacetime. Whether the size of the universe if finite or infinite is unknown.

I canít help but think that the BB singularity had some properties similar to Black Holes, and Black Holes can bend space-time. Itís possible that space was compact near the Big Bang, with all the mass/energy of the Universe confined to a point singularity.
The Earth bends spacetime. So does my Dr. Pepper can sitting here on the desk next to me. A black hole only bends spacetime stronger than either of the former do. Also, as I have seen here on PF, supposedly most cosmologists don't believe an actual physical singularity existed, but that it is simply a consequence of having an incomplete theory.
phinds
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#67
Dec13-11, 08:20 AM
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Quote Quote by Imax View Post
The Big Bang theory postulates that the size of the Universe is increasing and it possibly starting from some kind of point singularity.
Absolutely not correct. There was NO "point" at which the BB happened, it happened everywhere. If there had been a point, the U would not exhibit the isotopy and homogeneity that are now observed.
petm1
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#68
Dec16-11, 10:57 AM
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Quote Quote by phinds View Post
I understand what you are saying but the "edge of space" is a very poor concept and should be avoided, since there isn't one.


Take a picture of any amount of time your camera will let you. We can make the illusion of photons going the opposite direction in time by making a negative. In this negative view the objects appear as holes and space the source of photons. Both pictures are of edges in my universe the edge is between inner space-time and outer space-time. Hope this helps.
Tanelorn
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#69
Dec16-11, 11:44 AM
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Chalnoth, what are you thoughts on the following?

"If you were traveling at the speed of light and turned a flashlight on, what would happen to the light?
Relative to you, the light from your flashlight would still be moving at 3 x 10^8 m/s.
To allow this to happen, your perception of time slows down the faster you move and you gain more mass (E=mc^2)."


I believe the above is correct. So my question is, at the beginning of the BB when all particles were moving very fast, would time effects like the above example effect our estimates for the rate of inflation, or even our estimates for the age of the universe since particles were moving very fast for quite a while? I am very uncertain of which relativitic frames of reference apply in this case.


Thanks!
phinds
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#70
Dec16-11, 11:58 AM
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Quote Quote by petm1 View Post
Take a picture of any amount of time your camera will let you. We can make the illusion of photons going the opposite direction in time by making a negative. In this negative view the objects appear as holes and space the source of photons. Both pictures are of edges in my universe the edge is between inner space-time and outer space-time. Hope this helps.
I do not wish to be rude, but this is just nonsense and has nothing to do with physics.
phinds
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#71
Dec16-11, 12:03 PM
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Quote Quote by Tanelorn View Post
Chalnoth,

If you were traveling at the speed of light and turned a flashlight on, what would happen to the light?
Relative to you, the light from your flashlight would still be moving at 3 x 10^8 m/s.
Yep, that's right

To allow this to happen, your perception of time slows down the faster you move and you gain more mass (E=mc^2).
No, as you move faster, YOUR perception of time doesn't change at all, but an external observer sees your time as going slower [and you see theirs as going slower]

I believe the above is correct. So my question is, at the beginning of the BB when all particles were moving very fast, would time effects like the above example effect our estimates for the rate of inflation, or even our estimates for the age of the universe since particles were moving very fast for quite a while?
If it did, do you seriously believe that every physicist who has studied the early universe was to stupid that they overlooked it?
Tanelorn
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#72
Dec16-11, 12:12 PM
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phnds, no need to be abrasive, I am not suggesting anyone overlooked anything or was being stupid!
Anyway I was hoping Chalnoth could give me his thoughts on this. thanks.


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