Of all the forces at work in nature, gravity
is at the same time the simplest and most enigmatic of all. It is simple because it is easily created
and, at least on the scale of the everyday, easily described. All that is needed to create
it is mass. If you have mass, you have gravity. It is enigmatic because we really don't know
much more about it than that. We know that it takes mass to make it, but simple questions
like, 'Why does gravity only pull?', "Why is gravity so weak compared to other forces?"
are difficult to understand. It is, at once, simple and complicated. Gravity is the force that sculpts creation,
and through it, the universe takes its form. Under its influence, interstellar gas collects
to form clouds that, under the inexorable crush, are ignited into stars. These stars
are collected into galaxies, and galaxies are gathered into structured tendrils, reaching
throughout the cosmos. The effects of gravity are everywhere, and
this force, more than any other in nature, is responsible for the shape of all that is. So, what is the form of the universe? How
can we find out? The main characteristic that gives the universe
its shape is density. The density of the universe, the amount and location of all matter, define
where the gravity of the cosmos is concentrated, which bends and warps spacetime as described
by Einstein's General Theory of Relativity. In order to uncover the geometry of the universe,
we need to be able to see all of it, at one time. Fortunately we have such pictures. This
is an image of the entire universe in the microwave region of the spectrum. This is
what the universe looked like when it was only 380 thousand years old. This is the radiant heat left over from the
big bang. This image is full of fluctuations, tiny variations
in temperature. The red parts are slightly warmer than the blue parts by only on part
in a thousand, but they are measurable and it is these fluctuations that give us the
information we need to determine the shape of the universe. It turns out, these tiny changes are related
to fluctuations in the density of matter in the universe and thus carry information about
the initial conditions for the formation of cosmic structures such as galaxies, clusters
of galaxies, and voids. To understand this relationship, all we need
is basic geometry of triangles. On a flat surface, all angles in a triangle add up to
180 degrees and parallel lines remain parallel. On a positively curved surface, like a sphere,
they add up to something greater than 180 and parallel lines converge. A surface with
negative curvature, such as a saddle, the three angles add up to less than 180 degrees
and parallel lines diverge. So, to measure the shape of the universe,
all we need is a triangle, a really big one, one that covers the entire universe, and measure
the angles. The all sky map of the CMB provide us with
just such a surface within which to measure our triangle, with the Earth at one apex and
two more points on the image, we can make our measurement. The fluctuations in the CMB are randomly placed
spots with an apparent size of about 1 degree across. They are produced by sound waves that
travel through the hot ionized gas in the universe at a known speed (the speed of light
divided by the square root of 3) for a known length of time (380,000 years). Knowing the rate and time, we can obtain the
distance to what is known as the last scattering surface - the remnants of a cosmic cloudbank.
Simplifying a little, this distance, along with the Hubble constant and the actual light
path taken by the CMB to our eyes, will tell us the geometry. If the universe is flat, our triangle would
have straight lines and all angles would equal 180 degrees and the average angular distance
betwen CMB fluctuations would be 1 degree. If the universe was positively curved, our
lines bend outward and our angles would be greater than 180 degrees, and the angular
distance would be about one and a half degrees across. A negatively curved universe would
look like this with an average angular distance of a half a degree. After careful measurements of the CMB using
WMAP data, the average distance between fluctuations was found to be 1 degree with an accuracy
of 15% and a error of 2%. The universe, it appears, is flat. Currently the Planck Space Telescope is taking
a higher resolution map of the Cosmic Microwave background, and very soon, we hope to have
an even more accurate answer to the question of the shape of existence.
Don't you just love it when scientific explanations are, rather than simplified, actually dumbed down to the point of blatant inaccuracy?
No, actually, we don't. Cosmic expansion along with the speed of light ensure that this is not possible. It is only possible to make physical observations of a finite portion of the universe, not the whole thing. This is why they call it the observable universe, and the CMBR provides information regarding the observable universe only. We have absolutely no idea how much larger the whole universe, including its unobservable portions, might be. No idea.
Furthermore, The inflationary period of the Big Bang is predicted to drive the universe towards flatness. The measurements the video references, as the video admits casually without further explanation, gives us an idea of the geometry of the universe 380,000 years after the Big Bang, not at the time of the Big Bang. Regardless of its overall curvature, the inflationary big bang model actually predicts that, 380,000 years after the big bang, the observable universe should be so approximately flat that any potentially measurable deviation from flatness would be well within a 2% error window, and therefore undetectable by this measurement.
To summarize: the inflationary big bang model, the most commonly accepted theory of the early universe, predicts that the measurement cited in the video should indicate a flat universe, regardless of the actual overall geometry of the entire universe. The measurements of the CMBR confirm that prediction only. They in no way prove that the universe is flat. That matter is still unknown.
I can't play the sound at work, so judging on the video alone, it looks like the universe is composed of fractals and math.
This is a more comprehensive explanation.
For those not put off by a little mathematics, this article explains why the universe is flat.
I did not know that.
flat like a slice of a cylinder? like a pancake with a bit of a bump on the middle?
Really, it seems what they are saying is that the universe is NOT curved. That two parallel lines will remain parallel throughout their travel. If the universe was curved parallel lines would converge or diverge through their travel.
I thought it was cone shape, the apex being the point of the big bang !
Did that video just call MICROWAVE RADIATION a SOUND WAVE that travels at the speed of light?