View Full Version : What did WMAP really tell us?

2003-Feb-19, 05:25 PM
In this thread (http://www.badastronomy.com/phpBB/viewtopic.php?topic=3904&forum=2), a short debate arose between Crimson and JSPrinceton about how much we found out from the WMAP survey. On one side there was the contention that the WMAP survey was able to deduce that the universe has a globally flat geometry, as well as other nice numbers associated with it, such as the age of the universe, Hubble's constant, etc. On the other side there was the contention that flatness was assumed in computing the various cosmological numbers, and was not derived. This issue was not settled by these two, but the answer is of fundamental importance in astronomy. So, which was is it?

<font size=-1>[ This Message was edited by: Zathras on 2003-02-19 12:26 ]</font>

JS Princeton
2003-Feb-19, 05:42 PM
In order to get at flatness, one needed just a single other measurement to put in to break parameter degeneracy. Of course, you want a good measurement, and so I believe 2dF survey data if used in calculating constrains the measurement of flatness further than the quoted 1.02 +/- 0.02 value for omega_total. That value, I believe, is a cummulative value for any number of different measurements to break parameter degeneracy.

I think that's a fairly confident statement about how tantalizingly close to flat the universe is. If Sandage wants a slightly closed universe, there are some theoretical difficulties now that don't seem easy to overcome. After all, how on Earth does one end up with a universe that has a higher energy to dimensional density (in rough layman's terms) than unity? There has to be some mechanism for getting more energy in. A false vacuum might do the trick but then why is it maintained?

I am no theoretician, but even I can see the theoretical motivations behind looking at a number like 1.02 and saying that it's basically 1 when you have a whole slew of driving models that seem to point toward that as necessary.

Not to say that this isn't wrong, but what's even MORE amazing is that the WMAP results for other cosmological parameters allign so well with independent measurements. Anyone who is going to say the universe is drastically different from this is going to have to dissect the science of WMAP and find either some bias or model selection effect that hasn't yet been thought of. I'm fairly confident in the WMAP team, but perhaps that is my own bias.