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TalonD
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Any results from the Planck probe? Has it narrowed down the possibilities ?
The first public release of Planck data will be the early-release compact source catalog, which should be available around the end of the year.TalonD said:Any results from the Planck probe? Has it narrowed down the possibilities ?
Given that our current estimates of spatial flatness are that it is flat to within less than about a percent, there is no conceivable way that Planck's results will differ so dramatically from existing experimental results for there to be any sort of qualitatively new picture here.AWA said:I know is highly improbable but if hypothetically the Plank probe found that after all ,in large scales, the universe is not flat and has a negative curvature, giving a hyperbolic geometry, would this change in any way our interpretation of the redshift of far galaxies? I mean, are photons supposed to behave the same way in this type of space with respect to an observer placed at huge distances from the source of light? Even if it's most unlikely this turns out to be the real scenario, I'm still curious, any thoughts?
Gee, what a waste of money and time then. Who wants to make experiments for something that's already settled?Chalnoth said:Given that our current estimates of spatial flatness are that it is flat to within less than about a percent, there is no conceivable way that Planck's results will differ so dramatically from existing experimental results for there to be any sort of qualitatively new picture here.
Chalnoth said:To answer your question, though, no, photons don't behave in any sort of dramatically-different ways in negatively-curved space.
AWA said:Gee, what a waste of money and time then. Who wants to make experiments for something that's already settled?
As nicksauce mentioned, there are other reasons for Planck than just re-confirming the spatial flatness of our universe. It measures the sky at a much broader range of frequencies, which will help in understanding the foregrounds (such as our galaxy), and therefore in removing them. It is a much more sensitive instrument than WMAP, which allows for better estimation of polarization of the CMB (there is some hope, for instance, that it can measure the gravitational wave signal in the CMB from inflation, but this is not by any means yet clear). It measures the CMB at much higher angular resolution, which allows for better estimation of a number of the properties of inflation.AWA said:Gee, what a waste of money and time then. Who wants to make experiments for something that's already settled?
If you send out parallel light beams in negatively-curved space, they tend to get further apart with time.AWA said:Please could someone elaborate on that? Such categorical answers are kind of useless
Yes, Planck will do much more. In particular, it will give an accurate constraint on the statistics of the temperature fluctuations in the CMB -- these are expected to be highly Gaussian if the simplest models of inflation are correct. However, other more exotic models of inflation predict that these fluctuations should deviate from Gaussian, and Planck might be able to shed some light on this important question.AWA said:Gee, what a waste of money and time then. Who wants to make experiments for something that's already settled?
AWA said:A flat universe is in contradiction with General Relativity. Are you guys seriously questioning this theory??
When people say flat, they mean only spatially-flat, and only on average on large scales (an expanding universe has a space-time which is curved, but the spatial components can easily be flat). This is not in contradiction to GR.AWA said:A flat universe is in contradiction with General Relativity. Are you guys seriously questioning this theory??
AWA said:(...) Either way flatness does not fit in the GR.
So...why can't time, just an ordinary dimension of some 4D non-Euclidean manifold, not be curved? Seems like you are contradicting yourself. There's nothing wrong with 'curved time'. Look at the Schwarzschild or Friedmann solutions in GR. These are spatially flat but give motion to test bodies on account of a 'curved time'.AWA said:how is time curved? Doesn't make much sense to me.
Einstein's view based on his general postulate of relativity was that a Euclidean universe was untenable. Space-time had to be non-Euclidean, or quasi-Euclidean to use Einstein's term. Either way flatness does not fit in the GR.
The Ricci curvature tensor is a rank-2 tensor (meaning it has two indices, and can be thought of as a matrix). In flat space, the space-space components of this tensor are all zero, while the time-time and space-time components are non-zero.AWA said:Chalnoth, how do you separate the components of a four-dimensional "space"(in the mathematical sense) into a time component and a spatial component having the latter flat. are we to suposse that time accounts for the total curvature? how is time curved? Doesn't make much sense to me.
Well, it isn't Euclidean, due to the non-zero time-time and space-time components of the Ricci curvature tensor.AWA said:Einstein's view based on his general postulate of relativity was that a Euclidean universe was untenable. Space-time had to be non-Euclidean, or quasi-Euclidean to use Einstein's term. Either way flatness does not fit in the GR.
Please correct a layman if I’m wrong, but the WMAP CMB-measurements on 'flatness' deals with the Density parameter (Ω), resulting in a Closed, Open or Flat (local) universe, right?AWA said:A flat universe is in contradiction with General Relativity. Are you guys seriously questioning this theory??
Good things come to those who wait...TalonD said:Thanks everyone. I'm no expert but I knew Planck was out there and would have greater resolution than wmap so figured I would ask. So we still have to wait awhile. :)
Thanks bapowell, it feels 'reassuring'.bapowell said:Right.
Cosmological observations only constrain the local geometry of the universe, because we can only observe our local neighborhood. What Chalnoth was saying was that while Planck only measures the local geometry of the universe, it is already constrained to be pretty flat (to within 1% or so). Therefore, while the global geometry of the universe could well be hyperbolic, it can't be too hyperbolic. I think that's all he's saying. The fact of the matter is that no local cosmological observation can place bounds on the global geometry of the universe. It's perfectly consistent for the universe to actually be open or closed, but appear locally rather flat.AWA said:Well I have to come back to this thread because rereading it I find something confusing or incoherent in the answers.
If what DevilsAvocado says is right (as it seems in bapowell's opinion) then the the WMAP CMB-measurements on 'flatness' (and the Planck probe) cannot tell us anything about the Global space curvature, therefore when I asked whether a global hyperbolic space could be found with the Planck probe, the answer should have been that this experiment is only about Local geometry so it can't respond about Global geometry.
Instead of that what Chalnoth anwered made no distinction between local and global and said the hyperbolic geometry was discarded by the experiment without further clarifcation.
Can someone clear this up? Do I see it right this time?
Right. The Schwarzschild solution is spatially flat, but has a 'curved' time dimension. So does the flat FRW solution relevant to cosmology. However, the closed FRW solution has curved space as well.AWA said:It doesn't necesarily mean the 3 dim-space component curves too, but it might as well, right?
I'm sorry, but I believe you're thinking of Fermi. Planck is primarily a CMB instrument, and probes radiation from 30GHz to 857GHz, which is in the millimeter wave range (wavelengths from 10mm to 0.35mm).Chronos said:Planck is designed to probe the high energy [gamma] spectrum. It is well suited for exploring the very early universe where high energy events were common.
...with "local" meaning out to z=1089. Our observable universe is flat.bapowell said:Cosmological observations only constrain the local geometry of the universe, because we can only observe our local neighborhood.
No, it's curved like http://en.wikipedia.org/wiki/Schwarzschild_metric#Flamm.27s_paraboloid".bapowell said:The Schwarzschild solution is spatially flat
By flat, I mean [tex]R = 0[/tex].Ich said:No, it's curved like http://en.wikipedia.org/wiki/Schwarzschild_metric#Flamm.27s_paraboloid".
Yes. It isn't flat.By flat, I mean R = 0 .