Let's have some real science in here for a change. What better real science is there than cosmology? Please Register or Log in to view the hidden image! The Wilkinson Microwave Anisotropy Probe (WMAP) released its first-year results last week, and I thought it would be interesting to see what people think of the cosmological models permitted by the very precise measurements of this satellite. It appears that the running spectral-index <font face=symbol>L</font>CDM (lambda-dominated, cold dark matter) "basic" inflationary big-bang model fits the data exceptionally well. <font face=symbol>L</font> is of course Einstein's "cosmological constant." More generally, the negative-pressure variable is called 'quintessence' or 'dark energy.' Essentially, the universe is expanding faster than it should be if affected by matter alone (it may also be accelerating, though there is not yet a preponderance of evidence in favor of that). The cosmological constant was Einstein's famed "blunder," a term added to his field equations, necessary to explain a steady-state universe. Of course, the universe is no longer thought to be steady-state, and the cosmological constant has been ressurected, although under different auspices. The more general term 'quintessence' refers to any term with a proportional pressure-density relationship. Einstein's cosmological constant is a form of quintessence in which the proportionality constant is exactly -1. Astrophysicists will also refer to this "stuff" as dark energy -- an as-yet unexplained form of energy. Dark matter, on the other hand, is a form of matter which does not emit light, and therefore cannot be detected photographically. Dark matter does play a vital role in galaxy formation and function. Without dark matter, we cannot explain why galaxies rotate rigidly like they do. The WMAP data enforce that the dark matter must have been cold, with low thermal energies, for a reason that is unfortunately entirely too complex for me to elucidate here. If you'd like to impress your friends, here are some of the "most important" cosmological parameters fixed by WMAP, in no particular order. The parameter space of possible cosmologies is now MUCH smaller than it was before WMAP. I am omitting error bounds. Age of the universe, t<sub>0</sub> = 13.7 billion years. Hubble's constant (the proportionality constant between a galaxy's distance and speed of recession), H<sub>0</sub> = 71 km/sec/megaparsec Ratio of density of the universe to the critical density necessary to make it flat, <font face=symbol>W</font> = 1.02. Percent of the universe's mass and energy in the form of baryons (like protons and neutrons): 4.4% Percent of the universe's mass and energy in the form of cold dark matter: 22% Perecent of the universe's mass and energy in the form of dark energy: 73% Cosmic microwave background temperature: 2.725 Kelvin Photon-to-baryon ratio: 1.639 x 10<sup>9</sup> : 1 Decoupling time (the farthest back in time we can see optically): 379,000 years after the Big Bang. References: http://www.arxiv.org/pdf/astro-ph/0302207 http://www.arxiv.org/pdf/astro-ph/0302209 - Warren
Alright, let's pull out the simple question first -- what does it mean to "rigidly rotate"? Please Register or Log in to view the hidden image! ps. warren you're completely wrong big guy -- dark energy and dark matter don't exist -- it's all about "Dark Suckers" haha. >> http://www.msu.edu/user/dynicrai/physics/dark.htm
The world's always been in the 'dark'. Now we can prove it. Please Register or Log in to view the hidden image!
Interesting stuff. Regarding dark energy, in this thread I suggest that gravity could be deceiving us about the existence of dark energy. Summary: Given that light from distant galaxies should receive gravity assists (also known as slingshots) from mass in between the galaxy and us, it seems to me that from our perspective the universe would be expanding locally at varying rates (generally the further the faster), not Hubble’s constant, to obviate the need for dark energy to explain the observation of accelerating expansion. Regarding dark matter—and I’ve done the barest layman’s thinking/research on this—could there be a fundamental flaw in assumptions leading us to believe that dark matter exists in such a large percentage (22%)? I’ve read that the amount of mass at the center of a galaxy is determined by its rotational velocity there. But isn’t that a chicken-and-egg problem? If rotational velocity is x, that could be a large mass with significant gravitational time dilation slowing the rotational velocity from our perspective, or a smaller mass with less gravitational time dilation. In other words it seems to me that multiple mass amounts can have the same rotational velocity. It seems to me that the following rotation curve (from here) can be explained with gravitational time dilation and without invoking dark matter: Please Register or Log in to view the hidden image! The rotation curve for the galaxy NGC3198 from Begeman 1989 where R is the radius from the center
zanket, If you stop 'supposing' and start doing math, you'll realize your argument about gravitational time dilation is bunk. - Warren
Dark matter. There's no way to resolve the rigid rotation curves of galaxies by invoking gravitational time dilation. - Warren
Oh, and I'd love to see the derivation of your gravitational slingshot-based model of dark-energy. Please Register or Log in to view the hidden image! - Warren
There won't be any white paper forthcoming about the dark energy proposal; physics isn't my day job. But if light can slingshot, why wouldn't it be true? The math is pretty simple. If something accelerates the light towards you, you'll observe a faster clock at the light's source.
What are you basing that on? If there are millions of galaxies between us and the observed galaxy, isn't there lots of opportunity for slingshotting, each event accelerating the light to a faster velocity (from a certain perspective)?
zanket Your proposition about light shifting and being assisted due to gravity would hold true if we were only observing one object at an unknown distance. The WMAP scanned the entire known Universe. Distances and relative velocities of each body are normalized against a 'flat' background, and it works out beautifully. In other words, if I have three objects at an unknown distance, and those distances are different and the velocities of each object is different, by observing them for any period of time, I can calculate their distances, the speed each object is moving, and the direction, therefore the relative velocity of each body. Million, billions of stars against a consistent background, when observed over a period of time provides a very stable platform for assumed measurements, which are easily translated with great precision to exact measurements. 'Exact' in astronomy is different than 'exact' on Earth. But, we are talking about tiny fractions of an arcsecond of motion in WMAP's accuracy. In order for your postulate to hold true, the beams of light from each body would have to undergo the same set of slingshots, or, suffer a very inconsistent array of effects. This model would not hold up to WMAP's integration of the Universe. The proof is in the documentation, where WMAP defines the Universe as 'flat'. It is the best model, to a fit of 2%. (I think I got that right, Warren) Light is simply not affected to the degree you suggest, and where there are magnifications and shift changes due to intense gravity, those effects are clearly explained and plainly visible.
1) Light always travels at c, in every perspective. 2) I thought you were implying that gravitational lensing was responsible for an illusion that the universe is expanding at an accelerating rate. The answer to this hypothesis is an uneqivocal no simply because gravity is far too weak. - Warren
Re: zanket I really can't follow half of what you just said Clay, but it doesn't sound like you have any idea what WMAP actually did. - Warren
When you say 'acceleration' I hope you refer to change in direction (i.e., it 'curves' around massive bodies) and not a change in its speed. Else, you have no idea what you're talking about -- slingshotting is usually a mechanism to gain extra kinetic energy. Light would manifest this as frequency shifts, and slight bending, not as changes in speed (which only occur for matter, e.g., satellites, and such). The bending of light near massive bodies is quite well known. A note on GR >> http://www.phys.lsu.edu/mog/mog18/node8.html
Re: zanket So now astronomers are not people from earth? Please Register or Log in to view the hidden image!
bullshit I really can't follow half of what you just said Clay, but it doesn't sound like you have any idea what WMAP actually did. - Warren <HR> This is crap, Warren. You say shit like this to keep yourself aloof. nice dig
Now, I realize this is likely a stupid question... please shoot me down as you must.... But given time dilation's implication that there is no universal present, is it not prudent to consider that maybe the universe does not have an "age" as we normally think of it? I'm guessing we mean "from the perspective of earth, the universe appears to be xxxx years old", but that can't be an accurate statement from a planet in different galaxy right? Maybe I'm on crack again.
Re: bullshit Okay, I'm sorry for being rude... no offense intended. However, you were talking about "millions and billions of stars" and "distances and relative velocities of each body." WMAP has nothing to do with stars, distances, or velocities. If you really don't know what WMAP did, why are you posting about it? If you really do know what WMAP did, why are you talking about stars and distances and velocities? - Warren
