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Evidence for a Flat Universe?
mattorb writes "The New York Times [free reg.req.] has an interesting article about a recent cosmological experiment whose results rather strongly imply a flat (omega equals 1) universe. Basically, the authors measured the scale of small variations in the cosmic microwave background, which yields strong constraints on allowed cosmologies.
The abstract from the preprint (off LANL astro-ph) is here. Caveats: this is a preprint -- meaning that it hasn't been refereed yet. Also, questions are always raised about the precision of such "angular power spectrum" measurements -- who knows if this result will hold up. But it's an interesting thing to talk about."
but do we fall off if we sail to the edge ?
Until recently, the Universe was thought as closed (or that it will slow and contract back as Energy dictates).
Recently, with deep space observations with a larger array of data to work with, Astronomers have calculated that the Universe it Open (under constant accelleration and would not slow down). This baffled much of the scientific community for awhile and soon lots of theories about a variable speed of light arose. (I think this appeared in the December 1998 issue of Scientific American, a summary of the Special Report exists here.)
This latest observation, though as limited as it is, makes some sense that it is a balancing compromise between two seperate observations/beliefs.
I can't say which is true, or which is false, just that it fits with everything else that has been said.
*Carlos: Exit Stage Right*
"Geeks, Where would you be without them?"
*Carlos: Exit Stage Right*
"Geeks, Where would you be without them?"
"Got Linux?"
I've read a few posts that seemed to imply that the big bang resulted in a big explosion, and that this somehow sent matter flying out in different directions. This is not the case.
The big bang, rather than an explosion, was an expansion of space; every second, the distance between two points increases. The red shift noted by Hubble was not due to galaxies moving apart within space, but due to the space between galaxies increasing.
The balloon analogy much beloved of popularisers is quite accurate in many ways; you just have to imagine that the ballon is the universe, and that there is no outside the balloon. Of course, that's not to say there aren't lots of other balloons; inflation theory suggests there are. But they're nothing to do with our universe.
One thing that amazed me about this piece was the precision that the scientists were capable of; the background ripples have a difference with the normal background of less than one part in ten thousand; it took the COBE satellite to detect them in the first place, and to have them detectable from inside the atmosphere was truly a monumental feat.
Seeing as I'm in astrophysics and finishing my master's thesis in a closely related field (dark matter), I thought I should reply.
The preprint is about fitting new observational cosmic microwave backround radiation data from BOOMERANG (basically a telescope mounted in an airplane) to the existing cosmological models.
These models are derived from some basic assumptions about the universe (homogeneous and looks the same from all directions) and Einstein's euqations. The models predict a non-static universe that can be flat, open or closed. i.e. the large-scale curvature of _space itself_.
Since the amount of space curvature is directly related to the mass in the universe _and_ thus the amount of "gravatation", the type of universe is dictated by the amount of matter present in the universe. a flat universe means that there exixts a mass density high enough to slow the expansion of the universe until it stops at infinite time. This critical mass density is normalized to one and called OMEGA.
an open universe has "negative" curvature, and will continue to expand forever. The universe does not have enough mass/gravity to slow the expansion to a stop. A closed universe has positive curvature and will slow to a stop, and collapse in some finite time. Maybe to a big crunch. As to where the universe expands to, and if there will be endless big bangs/crunches, people can only guess. Physics tends to break down in those areas.
The data in question (CMBR flucuations) has a direct relation to the amount of matter, and the "lumpiness" of the matter at a very early time in the universe's history. The free parameters in the accepted cosmological models are then varied (think fitting a striaght line to data points) until the data has a "maximum liklihood" of having these parameters.
One of these parameters, OMEGA, is confined to be between 0.85 and 1.25. So, there is a high chance that the universe is flat.
Unfortunately, other obervational evidence (galaxy dynamics) says that the amount of mass in the universe mesured so far has OMEGA = 0.35. OOPS! What about the other 0.65 for OMEGA = 1?
But, not to fear, this is where the cosmological constant comes in. It boils down to an added cosmological "force" that causes extra curvature (mass->gravity->curvature->state of universe) and thus can make the universe flat by boosting OMEGA to 1. Where it comes from, I don't know and don't want to hazard a guess. But the equations contain it!
As a little bit of extra correctness, the fitted models state the part of OMEGA due to mass is about 0.5, which is close to what the galaxy dynamical evidence states. Yay!
OK. back to writing my thesis.
"Posessing a degree in science does not necessarily make one a scientist"
Stephen Hawking's view is that there is no "Before the big bang". It's a meaningless concept; exactly like saying "Further North than the North Pole". That is, 4-dimensional spacetime is tightly curved near the singularity.
;o)
Likewise, there is no "outside the universe". Imagine being an ant trapped inside a sealed jar. You could walk around the inner surface of the glass forever, perhaps often inadvertently returning to your starting point, but there is no edge or opening you can reach which leads to the outside. If the jar has a hole, that's almost analogous to a wormhole leading outside of our universe - but it's not good to push an analogy too far
I'm not too keen on the superparticle idea. It's not really in favour any more, it was only mooted because no-one really had any better ideas.
The inflation theories which also predicted this "flat" result are compatible with a wide range of starting conditions.
One idea is that our universe is a so-called "baby" universe which has budded off another, older region of spacetime when some small domain in that original continuum underwent inflation. But this is ontologically unsatisfying because all it does is postpone the question. Where did the "parent" universe come from? Back to square one.
Well, either it always existed, or it too was a baby of some other preceding parent, and so on and so on, perhaps infinitely far back into the past. Perhaps there was no beginning, there has always been a universe endlessly spawning children.
But I did hear one speculation as part of a lecture about inflation, and this one is really cool:
"Before" there was just this timeless, dimensionless void. Not like spacetime, which has both dimension and duration. And not really "before": in the sense that this nothing could be said to have any existence at all, it "always" exists.
Anyway; in this void there was a quantum fluctuation. A fluctuation in what? Consider that in a void without time or space there can be no mass or energy and basically no physics at all of any kind. But there is an obscure branch of quantum theory which claims that quantum probability is the most fundamental aspect of reality, more closely related to abstract mathematics and information theory than anything crudely physical.
So: there was an infinitesimally small but still finite probability that anything could exist. To say that something can happen in such a realm is to be certain that it does happen. In the sense that anything could be said to "happen" at all. I imagine that events which are more likely happen more frequently then less likely events.
There was finite probability that a blob of matter/energy could exist, and so it did exist. And in springing into existence, it generated time and space before it because matter/energy needs something to exist in. Since the spacetime was created on demand from nothing, so to speak, the blob would initially have (near)zero dimension and thus (near) infinite density and temperature. It thus expands rapidly, cooling as it goes...and the universe is born.
Some short time later a critical temperature is reached, a phase transition takes place and the new universe inflates rapidly creating much, much more matter as it goes. The initial seed that popped into existence doesn't have to be very big at all; virtually all of the present mass of the universe was supposedly created during inflation, according to the theory.
An inevitable consequence of the theory is that what can happen once can happen an infinite number of times. There would be an infinite number of alternative universes created out of the void in a similar way, but they need have no connection of any kind to this one or to each other.
What is most interesting of all is that when you examine the concept of the original void, you find that what you are looking at doesn't have any "real" existence at all, it is merely an abstract mathematical space of pure probability. In fact, it is the space of all possible universal wave functions and our universe is the instantiation of one of these.
The universes that spring from it are all merely possible universes. None are real in any universally objective sense because there is no external platform from which a universally objective measurement can be made. Our universe only exists from the point of view of its inhabitants. Or, to put it another way, to talk of "instantiation" of any universal wave function is meaningless. The wave function is simply a potential for existence, and all possible wave functions are equally valid. Within the context of the void, "exists" is indistinguishable from "could exist". All universes that could exist therefore do exist, within their own frame of reference.
To make such statements is all meaningless philosophical speculation of course. You simply can't describe the nature of existence and reality in conventional human terms. It only make sense when you look at it from a quantum theory standpoint.
Pah. Sorry, I could go on like this all night and get nowhere. Time to press the "submit" button...
Consciousness is not what it thinks it is
Thought exists only as an abstraction
That explanation was pretty close but was slightly incorrect on some important points (I'm finishing my PhD in Astronomy, so have a least _some_ room to speak).
A flat universe (Omega_total = 1) simply describes the geometry of spacetime -- it is flat (i.e. parallel lines do not converge, triangles have 180 degrees). It says absolutely nothing about whether the universe will expand forever or eventually collapse. These bad assumptions are the result of years of astronomy classes that nay-sayed Einstein's Cosmological Constant (his " greatest blunder"). In those days, Omega_total, which equals Omega_cosmo_const + Omega_matter, was thought to equal just Omega_matter -- since Omega_cosmo_const was obviously 0. In that case, if Omega_matter = 1 then you get a universe balanced on the brink between eternal expansion and collapse.
But in the past couple years, numerous groups (the most famous using Type IA supernovae) have shown evidence that Omega_cosmo_const seems to be about 0.65 or so. Add that to the measurements of Omega_matter of about 0.35 and you get Omega_total = 1. The BOOMERANG measurements are simply an independent measurement of this, but this time using the cosmic microwave background -- a very important measurement.
If there is a cosmological constant, but Omega_total = 1, than the universe is flat, but the relative proportions of the two determine whether we get eternal expansion or not.
With current measurements, it looks like we have an open (eternally expanding) and flat universe. This saves (barely) Inflation, and solves a bunch of other Astro problems. Although now we have another big question: If this is real, Where in the hell does the Cosmological Constant come from?