[QUOTE=Lazore;43466921]I love space.
I'd fuck space[/QUOTE]
There's a joke in here about being made out of stardust and your mom somewhere.
[QUOTE=Camundongo;43468142]If that was the case, we'd see blue shift in everything between us and the 'centre' - but everything we view is red shifted - everything is moving away from everything else, which doesn't make sense if everything was expanding from a single defined centre.[/QUOTE]
As we're further away from the centre of expansion we must therefore be travelling faster than objects that are closer to the centre, so they will be observed as moving away from us. The same applies to objects further out than us, they're moving faster and therefore further away from us, causing red shift to be observed.
[QUOTE=Why485;43466991]The point you're referring to is your point of reference, which for us would be the planet Earth. This is why everything appears to be moving away from us. If you were in some other galaxy, then the Milky Way, along with all other galaxies, would also appear to be moving away from you.
The video covers this exact same thing.
Another way to think about the Big Bang, and why there's no center, is the balloon analogy. Imagine if the surface of a balloon represented the entire universe. When the big bang happened, that balloon was just a tiny dot, but it quickly inflated to a much larger size. This makes everything on the balloons surface move away from each other because the space between everything is getting larger.
From the surface of the balloon, which would be our universe, what is the "center" from which everything is expanding? There isn't one. No matter where you stand, everything is moving away from you. There is no central point of expansion.[/QUOTE]
Now that you put it in that way, I think my professor used the "raisins in bread analogy
[img]http://www2.astro.psu.edu/users/niel/astro1/slideshows/class31/002-Raisin_bread.jpg[/img]
[QUOTE=areolop;43468131]How do we know that its a sphere? How do we know if theres not another repenting force changing our expansion?
This is some serious space shit[/QUOTE]
well replace "sphere" with "turd-like shape"
[QUOTE=Smasher 006;43468189]As we're further away from the centre of expansion we must therefore be travelling faster than objects that are closer to the centre, so they will be observed as moving away from us. The same applies to objects further out than us, they're moving faster and therefore further away from us, causing red shift to be observed.[/QUOTE]
Yeah, got that slightly wrong, but we'd still notice less redshift from objects towards the centre, or objects that are perpendicular to us, and objects beyond the centre would be have far more redshift that stuff beyond us - that doesn't fit the uniform red shift that increases the further things are way from us in any direction pattern we observe at the moment.
[QUOTE=Advancedrock;43467670]I really don't want to be a jackass but I'm pretty sure you're wrong, the minutephysics video is right in some way, but it is wrong as well. If you take the ENTIRE universe as a frame of reference, you can find where the big bang happened. Of course, we can't use the entire universe as a frame of reference because we can't even see all of it (because of the speed of light, of course). However, there is a place where the big bang happened, though I'm sure it's very empty right about now.[/QUOTE]
That's not how the big bang works. It's not an explosion from a point. It's an expansion of distances at every point in space. There is no one place that it occurred.
Pretty much all modern cosmology relies on the (true to a very good approximation) idea that, on large distance scales, no point of the universe looks different than any other point. That symmetry would be broken if we could find a privileged point where the big bang started.
My attempt at an explanation which is likely just as useless as just asking you to believe me:
The universe-center premise: The big bang occurred at a single point in space, and, as all matter is moving away from that point, we can extrapolate that position from the wavelength shift we observe from objects as they move away from us. The key phrases here are single point in space, matter is moving, and move away from us.
The opposing clincher: matter isn't moving away from a single point in space as a result of the big bang. Rather, all of spacetime itself is expanding.
Thus we have the expansion premise: The big bang did not occur at a single point in space because the whole damn thing is expanding equally in every direction. It happened and is happening everywhere, so there is no center to extrapolate.
[editline]8th January 2014[/editline]
ninja'd by johnnymo himself, FUCK
[QUOTE=JohnnyMo1;43468279]That's not how the big bang works. It's not an explosion from a point. It's an expansion of distances at every point in space. There is no one place that it occurred.
Pretty much all modern cosmology relies on the (true to a very good approximation) idea that, on large distance scales, no point of the universe looks different than any other point. That symmetry would be broken if we could find a privileged point where the big bang started.[/QUOTE]
So if we reversed time all the way down to when the Big Bang happened, what would we find? Obviously we would find where the Big Bang occurred.
It was really really hot and bright just after the big bang, right? Shouldn't we be able to look 14 billion years or so into the past and look at the super early universe?
[QUOTE=Irockz;43466078][IMG]http://news.bbcimg.co.uk/media/images/72141000/jpg/_72141567_abell2744.jpg[/IMG] [/QUOTE]
P. cool how there's a refraction effect going on because of magnets/gravitational lensing. (?). JohnnyMo confirm.
[QUOTE=Advancedrock;43468525]So if we reversed time all the way down to when the Big Bang happened, what would we find? Obviously we would find where the Big Bang occurred.[/QUOTE]
The big bang occurred everywhere though.
[QUOTE=Flamie;43468585]P. cool how there's a refraction effect going on because of magnets/gravitational lensing. (?). JohnnyMo confirm.[/QUOTE]
It is gravitational lensing. This is what's happening if anyone's curious:
[t]http://www.roe.ac.uk/~heymans/website_images/Gravitational-lensing-galaxyApril12_2010-1024x768.jpg[/t]
[QUOTE=SIRIUS;43466557]but... it didn't answer the question[/QUOTE]
yeah it did?
[QUOTE=SGTNAPALM;43468721]The big bang occurred everywhere though.[/QUOTE]
Yeah at the time it occurred everywhere because there was nothing for it to occur in, but it all started expanding from some point, or at least a general area.
[QUOTE=areolop;43467065]and the expansion theory isnt proven. Its just accepted until we have further knowledge of matter.. [4% Baryon - what we see, 23% cold dark matter, 73% dark energy]
Theres three theories for expansion: Closed Flat and Open
[img]http://i.imgur.com/p8OwjlU.png[/img][/QUOTE]
That's the thing about this kind of stuff, It's a theory, just like gravity.
[QUOTE=Advancedrock;43468768]Yeah at the time it occurred everywhere because there was nothing for it to occur in, but it all started expanding from some point, or at least a general area.[/QUOTE]
[url]http://math.ucr.edu/home/baez/physics/Relativity/GR/centre.html[/url]
This might be helpful to read. Mainly,
[quote]In a conventional explosion, material expands out from a central point. A short moment after the explosion starts, the centre will be the hottest point. Later there will be a spherical shell of material expanding away from the centre until gravity brings it back down to Earth. The Big Bang—as far as we understand it—was not an explosion like that at all. It was an explosion of space, not an explosion in space. According to the standard models there was no space and time before the Big Bang. There was not even a "before" to speak of. So, the Big Bang was very different from any explosion we are accustomed to and it does not need to have a central point.[/quote]
like a crumpled piece of paper being unfolded and trying to determine what 2d coordinate it started unfolding at
[QUOTE=Advancedrock;43468768]Yeah at the time it occurred everywhere because there was nothing for it to occur in, but it all started expanding from some point, or at least a general area.[/QUOTE]
It all expanded from [I]a[/I] point, but the whole universe was just [I]a[/I] point. It's not somewhere you can point to right now. Think of a (hollow) sphere contracting to a point. Not tightening down to some point on its surface, but contracting all at once down towards its center. Everywhere squishes down to a single point uniformly such that you can't say that one area on the surface is where [I]the[/I] point is. That in reverse is the big bang. It's not a perfectly analogy but it's a useful one.
[QUOTE=Lazore;43466921]I love space.
I'd fuck space[/QUOTE]
Avatar fits: [IMG]http://facepunch.com/image.php?u=183698&dateline=1380755500[/IMG]
Nevertheless that's a breathtaking picture
Here is a very good video about the implications of various different local-space/space-time geometries:
[url]http://www.youtube.com/watch?v=AGLPbSMxSUM[/url]
[url]http://www.youtube.com/watch?v=MKwAS5omW_w[/url]
Space-time is currently thought to be flat with ~99% confidence.
[url]http://map.gsfc.nasa.gov/universe/uni_shape.html[/url]
My knowledge on this subject is pretty limited, my current understanding is that we reasonably know that local-space is Euclidean in nature, the curvature of which can be determined by comparing theoretical values of background radiation from the Big Bang in positive, zero, and negative curvatures, then comparing them to experimental values. Experimental values point to a curvature of zero.
If you want an explanation of this that makes sense, I would recommend reading over the Wikipedia article on the shape of the universe ([url]http://en.wikipedia.org/wiki/Shape_of_the_universe[/url]), watching that video I mentioned earlier, and taking any further questions to a geometry professor with a specialization in topology and/or a cosmology professor at a nearby university.
[QUOTE=Karl_Nietcault;43470281]My knowledge on this subject is pretty limited, my current understanding is that we reasonably know that local-space is Euclidean in nature, the curvature of which can be determined by comparing theoretical values of background radiation from the Big Bang in positive, zero, and negative curvatures, then comparing them to experimental values. Experimental values point to a curvature of zero.[/QUOTE]
I hope by "local" you mean "within the observable universe." Really [I]locally[/I] spacetime is not at all flat. It's plenty curved near objects. It's really only on very large scales (like, bigger than galaxies, bigger even than clusters of galaxies) that it looks flat.
[QUOTE=Karl_Nietcault;43470281]If you want an explanation of this that makes sense, I would recommend reading over the Wikipedia article on the shape of the universe ([url]http://en.wikipedia.org/wiki/Shape_of_the_universe[/url]), watching that video I mentioned earlier, and taking any further questions to a geometry professor with a specialization in topology and/or a cosmology professor at a nearby university.[/QUOTE]
Cosmologist would be a much better bet to be able to help you than topologist. Depending on the topologist, they might have a good grasp on it, but someone who's research is in differential geometry (which often has significant overlap with topology) would be the most help out of the mathematicians.
[QUOTE=Del91;43468778]That's the thing about this kind of stuff, It's a theory, just like gravity.[/QUOTE]
that guy
[QUOTE=JohnnyMo1;43470507]I hope by "local" you mean "within the observable universe." Really [I]locally[/I] spacetime is not at all flat. It's plenty curved near objects. It's really only on very large scales (like, bigger than galaxies, bigger even than clusters of galaxies) that it looks flat.[/QUOTE]
Of course space-time is curved by the presence of matter, however, my reference to local space-time was merely the assertion of the fact that it is Euclidean in nature. The basal curvature of the universe is zero. If the matter wasn't there (in local space), it would be flat as well.
Here is a series of articles addressing the resolution of the problem of local geometries deviating significantly from Euclidean models:
[url]http://blogs.scientificamerican.com/degrees-of-freedom/2011/07/25/what-do-you-mean-the-universe-is-flat-part-i/[/url]
[url]http://blogs.scientificamerican.com/degrees-of-freedom/2011/07/31/what-do-you-mean-the-universe-is-flat-part-ii/[/url]
You're right in asserting the fact that the universe is not perfectly flat on any conceivable scale. It's more like a very bumpy, expanding tabletop. (An expanding tabletop that will likely continue expanding, until its bumpiness approaches zero (unless we find a way to alter the laws of thermodynamics)).
[QUOTE=businessPawn;43466997](I'm by no means an expert on this but this is how I understand it.)
What you have to understand is that if our current understanding of the universe is right its not just the stuff expanding in the universe its the literal space it occupies. Imagine a the universe is room and literally every part of it is expanding pushing all of the furniture away from each other faster than light itself at some points. Its impossible to really gauge the middle because the distances between objects are constantly changing. Its not as simple as finding where a bomb went off from the debris.(this is how I think a lot of people visualize it.)
You explained that much better than I did.[/QUOTE]
The center of the universe is it's center of gravity
Unless it's infinite it must have one
[QUOTE=RobbL;43470669]The center of the universe is it's center of gravity
Unless it's infinite it must have one[/QUOTE]
No, that's not true. Consider if the universe is spherical.
[QUOTE=JohnnyMo1;43468999]It all expanded from [I]a[/I] point, but the whole universe was just [I]a[/I] point. It's not somewhere you can point to right now. Think of a (hollow) sphere contracting to a point. Not tightening down to some point on its surface, but contracting all at once down towards its center. Everywhere squishes down to a single point uniformly such that you can't say that one area on the surface is where [I]the[/I] point is. That in reverse is the big bang. It's not a perfectly analogy but it's a useful one.[/QUOTE]
I guess I understand, that's weird though, is that just theoretical kinda...stuff, or is that proven? I mean even if it's theoretical I'll take it, but it does seem weird.
[QUOTE=Advancedrock;43470847]I guess I understand, that's weird though, is that just theoretical kinda...stuff, or is that proven? I mean even if it's theoretical I'll take it, but it does seem weird.[/QUOTE]
It's pretty well-verified. It follows directly from the homogeneity (spacetime looks the same at every point) and isotropy (spacetime looks the same in every direction) of the universe, which measurements of the cosmic microwave background show are true to a very good approximation on large scales.
I'm imagining it a bit like this: think of a time before the Big Bang, you'd be in the nothing, absolutely nothing. In the middle of this [B]infinite[/B] expanse of nothing, that doesn't even really exist, is everything (the universe, i guess) in its tiny super dense state, or however it was before the big bang (big crunch, otherwise we're the last universe if this is it). If you were to sit there with everything in the outside of nothing, just holding completely still (as in theoretical bounds), THAT would be where the big bang's center is. We could FIND this place if we tracked all the matter back to its one place, which we could do with super duper awareness and computer simulations, but that's a different story.
[editline]9th January 2014[/editline]
idk i'm sorry i'm stupid, it's all very odd i hope you understand.
[QUOTE=Advancedrock;43470910]I'm imagining it a bit like this: think of a time before the Big Bang, you'd be in the nothing, absolutely nothing. In the middle of this [B]infinite[/B] expanse of nothing, that doesn't even really exist, is everything (the universe, i guess) in its tiny super dense state, or however it was before the big bang (big crunch, otherwise we're the last universe if this is it). If you were to sit there with everything in the outside of nothing, just holding completely still (as in theoretical bounds), THAT would be where the big bang's center is. We could FIND this place if we tracked all the matter back to its one place, which we could do with super duper awareness and computer simulations, but that's a different story.[/QUOTE]
But the thing is that everything looks like it's moving away from us. If we ran the universe backwards, it would all be converging toward us. Not only that, it would look like it was all converging toward us no matter where we were in the universe! Every point has an equal claim to being "the center."
[QUOTE=JohnnyMo1;43470939]But the thing is that everything looks like it's moving away from us. If we ran the universe backwards, it would all be converging toward us. Not only that, it would look like it was all converging toward us no matter where we were in the universe! Every point has an equal claim to being "the center."[/QUOTE]
But only isn't that because of our small awareness of the universe as a whole? We can't see it all, but if we looked at the universe from the impossible perspective of: the entire universe, not just the visible universe, wouldn't we be able to find a center where [U][I][B]everything[/B][/I][/U] is moving away from.
[editline]9th January 2014[/editline]
Or does that not exist, if not then wtf? How could that be, the universe would have to be infinite literally, not just by means of expansion.
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