In the show they conclude with a timeline of the formation of the known universe. At the point of the present they state that the universe is 13.7 Billion Years old. They also state that at that point it is 156 Billion Light Years across. That immediately gave me pause, because they took time to explain that the Big Bang started from a single point and that it’s been expanding ever since. So, how is it possible that the Universe is bigger than 13.7 Billion Light Years across, to be any bigger the light and matter would have to travel faster than the speed of light, a circumstance which was not mentioned in the show.
Assuming light expanded in all directions from the point of origin, it should at least manage 13.7 in every direction, or 13.7 * 2 billion light years across (i.e. 27.4). I can’t explain the remaining 130 billion or so, though, which is an interesting discrepancy.
I believe at least some of this is Alan Guth’s fault, btw, but I am not even going to begin to try to explain.
I have long held that we don’t even know what space is, much less how it may have suddenly inflated before I was even born.
In any case, I suspect someone will come along shortly and burst the bubble of the notion that the universe is some sort of sphere with diameter X.
I am also pretty sure we are probably not at the center of it (with the exception of my children) even though we’re at the center of our own event horizon (obviously).
I was just reading from an old “Discover” magazine that was laying around. Feb 2004 “What Exisited Before the Big Bang?” pg 35. The Inflation Theory, added to the Big Bang in the 80"s, says “in the frist hundred-millionth of a billionth of a billionth of a billionth of a second of its life, the universe expanded as though it were turbocharged, swelling much faster than the speed of light” Pg 38 for the quote.
Sounds like the scientists are covering there arses.
It is Alan Guth’s fault. Inflation is a perfectly viable physical theory that solves many cosmological quandaries, including the discrepancy between the size and age of the expanding Universe, as well as the homogeneity problem (i.e. regions too far away for light to have exchanged in the last 13.6 billion years have exactly the same temperature).
From your own perspective, the observable universe might as well be a sphere with a radius (called the comoving distance or proper distance to the Cosmic Event Horison) of about 46.5 Bly. The discrepency about the difference in distance between the boundary of the visible universe and the lesser distance that light could have travelled at that time is explained by the inflation of space; while objects (including light waves or particles) are limited to a velocity of c, space itself can expand at any rate at all without causing any heartache among relativists (although there are definite causality problems if that expansion isn’t isentropic). So the light that was once emitted from objects which now have a proper distance from Earth of 46.5 Bly is just barely visible, albeit redshifted into the radio spectrum, although when it was emitted it was much closer; even closer than 13.7 Bly, because it too had to transverse the expanding space. I believe it was actually something like 80 Mly away when it was emitted, and has been running since like a dog going the wrong way on an elevator.
I don’t know for certain where the 156 Bly figure came from, but it is a suspiciously close multiple to the ~78 Bly which is the lower bound for the non-repeated closed topology of the visible universe established in review of WMAP data by Neil J. Cornish, David N. Spergel, et al; see “Constraining the Topology of the Universe”. This makes certain reasonable assumptions about the shape of the universe and simply gives a lower bound for possible volume; it is in no way a meaningful number beyond those parameters. The universe could, in fact, be infinite in size and volume, or could be shaped like a pan-dimensional conch, or might be enclosed within a large globule of supersymmetric snot.
The real lesson here is to not depend on The Discover Channel to provide anything in the way of checked facts or useful education. I’m on the verge of classing The Discover Channel in the same bin as Fox News.
First of all, nobody knows how big the Universe is. All we know (and possibly all that we can know) is that it’s really, really big. You may think it’s a long way to the chemist’s, but that’s nothing on space. Whenever anyone says anything about the size of the Universe, they mean the size of the observable Universe. And that is in fact a perfect sphere, and we are in fact at the precise center of it. Which says absolutely nothing special, of course, since the folks on Tralfamador are also at the precise center of their perfectly spherical obserbable universe.
Second of all, even when we’re talking about the observable Universe, “size” can be tricky to define. The root of the problem is that in order to define size, you have to have some reference frame you’re working in. This isn’t a problem for everyday objects: If I want to measure the size of a basketball, I naturally choose the reference frame in which the basketball isn’t moving. But for the Universe, there exists no single reference frame where all parts of it are at rest. So you have to define just what sort of reference frame you are using, and depending on how you choose your frame, you can get different answers.
Third of all, one often reads that during inflation, the Universe expanded at faster than the speed of light. That’s not right… It’s not even wrong. At any given time, the Universe is expanding at a rate dependent on the size of the piece of the Universe you’re looking at. Currently, two objects a megaparsec apart are expanding away from each other at 71 km/s. Likewise, two objects which are 2 megaparsecs apart are expanding away from each other at 142 km/s, a pair of objects 3 Mpc apart are expanding at 213 km/s, and so on. The value 71 km/s/Mpc is called the Hubble constant (though it’s not actually constant), and is measured in units of frequency, not speed. During inflation, the Hubble constant was much, much higher than it is now, but since it’s in units of frequency, it can’t be compared one way or another to the speed of light, then or now.
By the way, that’s one of my professors in that space.com article. It’s always wild to see folks you know show up that way.
EDIT:
The 156 Bly figure comes from Dr. Cornish (the professor I just mentioned). 78 Bly is the radius, 156 is the diameter. So it’d be even more suspicious if it weren’t twice as big.
The expansion of space-time at rates larger than c does not violate relativity’s constant. Hopefully someone will come along and explain why and how this happenend.
Mpc is megaparsec, about 3 x 10[sup]19[/sup] kilometers. It’s an odd set of units to be expressing things in, but if you think about it in the context of Hubble’s Law, it makes sense: Hubble’s Law says that the speed at which objects are moving away from us is proportional to their distance. The constant 71 km/s/Mpc says that for every megaparsec you go, things are moving 71 km/s faster relative to us. (More or less.)
Note the dimensions are estimates.
If the world started with a big bang from a point,the universe would be a huge balloon and we would be living in the skin.
Assuming that space itself is not nothing (poorly understood though it may be), does an isentropic expansion imply that space is becoming less dense in some sense–ie the same total amount of space matrix now filling a larger (Euclidean) volume? Can an expansion model that somehow creates new space de novo be isentropic? Is it a nonsensical question to ask if space is thinning out due to expansion?
I believe that they came up with that turbocharged universe idea because of another problem they needed to explain to preserve the “Big Band Theory”. Of course they say that this isn’t the scientific method until they use it and then you are not supposed to notice. The fact that it also explains the question in the OP still does not make it kosher.
