03 May 06
2 edits
Originally posted by sven1000Locally, yes.
This is actually the field I work in, and we know pretty well that it is a flat universe.
Globally, no.
In the known universe, perhaps.
In the universe beyond, no one can tell.
We just don’t know, yet.
But its flatness is a quite fair approximation.
If one use a (known) flat topology in the hypothesis, the calculations are much more easy to go through. If you have to take non-flat topology, the calculations are more or less impossible with the mathematical knowledge of today. Therefore it is sound to see universe as flat until we know better – it is far easier to handle.
But, I won't get any deeper into this discussion whether universe is flat or not.
If you say it is flat, it’s flat.
07 May 06
Originally posted by sven1000Could you give a layman's explanation of what this means? (If that's at all possible.) I've always been led to believe that the universe was finite but unbounded - which I took to mean hyperspherical. Is that flat?
This is actually the field I work in, and we know pretty well that it is a flat universe.
Also - how does flatness or otherwise affect the number of protons?
07 May 06
Originally posted by laur3ttaNo mass is a measure of a physical objects energy and matter. Two separate things.
actually, when you heat something, you put energy into it so its mass (therefore matter) also increases because of e=mc^2
!!!!!!
This is a quote as I am not sure how well I can explain it.
"Mass is a measure of an object's resistance to changing its state of motion when a force is applied. An object with small inertial mass changes its motion more readily, and an object with large inertial mass does so less readily."
Can you really believe what you said? It makes no sense at all. If you were correct then everything would be rapidly creating more matter and the more there was the more it would heat up even through friction alone of all the new matter rubbing against other matter and creating more we would end up in a singularity of infinite heat very quickly.
08 May 06
1 edit
Originally posted by howardbradleyI surely give a try but I don’t know if my definition about flatness is the right one, but it works for me. Here it goes...
Could you give a layman's explanation of what this means? (If that's at all possible.)
If you draw a triangle, you know from the schooldays that the sum of triangles are exactly 180, right? That’s because you draw it on a flat surface.
If you draw it large enough, so large so you have to take the spherical form of the globe itself into consideration, like one point at north pole, one point at the equator in Africa and one point at Indonesia and draw lines between these points you’ll se that you have a triangle with a sum of angles, not 180 but even around 270 degrees.
This means that if you know the distance between the points and the sum of angles then you’ll get a measure of the sphere-ness of the surface.
Even smaller triangles on the sphere of earth shows the same phenomenon but the smaller triangle you measure you get a triangle sum nearer and nearer to 180 degrees.
You can do the same with the area of a triangle. The area of large triangles are larger than the formula says. And the difference is a measure of the sphere-ness of the surface.
This is what I mean by saying that locally earth is flat but globally it is a sphere.
If you draw a triangle in astronomical distances, like billions of light-years you’ll be able to directly measure the sphere-ness of universe. It is still flat locally but universally, I doubt it is really flat. This experiment is impossible to do practically – yet.
But if you draw a triangle and you’ll got a sum of angles less than 180 degrees you‘ll get a anti-spherical surface, a hyperbolic surface. To visualize a hyperbolic surface, think of a saddle.
This is about surfaces but the same explanation goes for spaces too. You’ll have a flat space, a spherical space or a hyperbolical space. The triangle rule is the same.
I know that cosmologists mostly thinks that the universe is flat. I’m not of the same opinion. I think that if you see universe as flat then you get into the impression that the universe is, not only expanding but that it’s also, accelerating. Only if you see the universe as spherical you can explain a number of weird phenomenon that is very hard to explain otherwise. But this is too difficult to explain in a simple way at a forum lake this at RHP.
But I cannot prove nor disprove my thesis. Either it is wrong or it is right.
If anyone says the universe is flat, I just nod.
08 May 06
Originally posted by FabianFnasThanks for that. It has cleared up one thing: geometry and topology seem to be used interchangably in cosmology. I've long known about Euclidean (plane), spherical and hyperbolic geometry but had not seen them refered to as topologies. Topology, to me a least, does not concern itself with angles and lengths, just how things are connected.
I surely give a try but I don’t know if my definition about flatness is the right one, but it works for me. Here it goes...
If you draw a triangle, you know from the schooldays that the sum of triangles are exactly 180, right? That’s because you draw it on a flat surface.
If you draw it large enough, so large so you have to take the spherical form of ...[text shortened]... my thesis. Either it is wrong or it is right.
If anyone says the universe is flat, I just nod.
When I think of hyperbolic space I think of M.C. Escher's lithographs eg. http://www.d.umn.edu/~ddunham/isis4/section1.html#fig2
I'd still be interested to see Sven's explanation.
09 May 06
Originally posted by FabianFnasI was directing my question toward sven, and as a student fascinated by cosmology and theoretical physics, I would be greatly interested to know what field of work allows him to study the shape of the universe. So I repeat my question to sven; what field of work are you in?
I'm just interested in astronomy and cosmology and such, thats all. A happy amateur.
My field of work is not relevant here.
10 May 06
Originally posted by howardbradleyFabianFnas's explanation of flatness is how I would describe it, using the angles of a triangle. (Or two sides and an angle, or two angles and a side, etc...) We actually have done experiments to test this, as there are physical processes in the early universe that let us know a distance scale far away from us (the fluctuations of temperature in the cosmic microwave background radiation) which we also happen to know the distance to. So, we have the two sides, one angle (measured here at earth) and can figure out what curvature the observable universe has. Flatness of space is very favorably suggested, although of course we can never prove it is absolutely flat. However, strongly curved space, either spherically or hyperbolically, has been ruled out.
Could you give a layman's explanation of what this means? (If that's at all possible.) I've always been led to believe that the universe was finite but unbounded - which I took to mean hyperspherical. Is that flat?
Also - how does flatness or otherwise affect the number of protons?
I think the wierd things FabianFnas is referring to as far as the accelerating universe, is the idea that there is some unknown "dark energy" that is causing space to expand at an increasing rate. This issue we actually had a talk on only an hour ago, by someone representing a task force of scientists investigating not the possibility of dark energy, but how we can measure it (there are 4 distinct ways with our skills today).
Finite but unbounded would be hyperspherical. The curvature of the universe would affect our value of the density of matter (because of general relativity), which in turn would change the number of protons.
11 May 06
Originally posted by sven1000Thanks Sven. So is the current thinking that the universe *is* bounded ie it does have and edge? I thought one of the "benefits" of a spherical universe is that it got rid of the question "what's outside the universe?"
FabianFnas's explanation of flatness is how I would describe it, using the angles of a triangle. (Or two sides and an angle, or two angles and a side, etc...) We actually have done experiments to test this, as there are physical processes in the early universe that let us know a distance scale far away from us (the fluctuations of temperature in the cosmi ...[text shortened]... of matter (because of general relativity), which in turn would change the number of protons.
Also can you recommend any good sources of information on this subject? I'm clearly a bit behind on current thinking.
12 May 06
Originally posted by FabianFnasDark matter? If it even exists...... a theory designed to fit the unexplainable, there are other theories looking more probable than this now. Despite them being laughed at for years, they are gaining more support..... the final proof will come from space missions in 2008 & 2015. Even then many will not accept that we have been wrong for years, it will change everything.........
You're perfectly right. The number of protons are not constant, regardless of expansion or not.
So - has the actual answer ("What is the number of protons in the Universe?"😉 any meaning at all? If we discussed the mass of universe, expressed by proton mass equivalence, that's one thing, but now we try to count the numbers of protons. Not the neutrons, ...[text shortened]... a totally new fashion compared with our view ten years ago. Do we know more - or less now?
12 May 06
Originally posted by howardbradleyCurrently we believe that the universe is unbounded, that is, there is no "edge" in the spatial dimensions. This can happen in all three types of curvature because inflation (a rapid expansion of the universe that probably occurred just after the Big Bang) makes the complete universe essentially infinite (much larger than our known, observable piece). A flat, unbounded universe can be pictured in a limited way as a large, stretchy rubber sheet, which is pulled out further and further, making points on it spread from each other. Likewise, you could picture a spherical universe like an expanding balloon. Right now, science doesn't really think there is any meaning to the question "What's outside the universe?"; the universe is just everything. However, there are string theorists who are investigating the theoretical possibility that gravity can connect multiple universes, or different spots in our universe. That's a little out there still, though.
Thanks Sven. So is the current thinking that the universe *is* bounded ie it does have and edge? I thought one of the "benefits" of a spherical universe is that it got rid of the question "what's outside the universe?"
Also can you recommend any good sources of information on this subject? I'm clearly a bit behind on current thinking.
So in the end, the universe doesn't have an edge to our knowledge, regardless of curvature.
A good recent book on cosmology, which isn't too big, is "Modern Cosmology" by Scott Dodelson, but it is laid out like a textbook, so I'd recommend looking through it before buying, to know what you're getting into 🙂 Also, "Blind Watchers of the Sky: The People and Ideas that Shaped Our View of the Universe" by Rocky Kolb is very readable, and he has a good sense of humor, which always helps.