Slashdot Mirror
How Deep Does the Multiverse Go?
StartsWithABang writes Our observable Universe is a pretty impressive entity: extending 46 billion light-years in all directions, filled with hundreds of billions of galaxies and having been around for nearly 14 billion years since the Big Bang. But what lies beyond it? Sure, there's probably more Universe just like ours that's unobservable, but what about the multiverse? Finally, a treatment that delineates the difference between the ideas that are thrown around and explains what's accepted as valid, what's treated as speculative, and what's completely unrelated to anything that could conceivably ever be observed from within our Universe.
It's turtles all the way down.
In one version of reality, this is a first post!
"Our observable Universe is a pretty impressive entity: extending 46 billion light-years in all directions, filled with hundreds of billions of galaxies and having been around for nearly 14 billion years since the Big Bang."
The observable universe is observable because there has been time for the light to travel that far, which can not exceed the age of the universe. Therefor, if the universe is 14 billion years old, then the furthest we could see in any direction is only 14 billion light years, giving a maximum, diameter of 28 billion light years.
So why does the summary say it's 46 billion L.Y. across and only 14 billion Y. old?
The speed of light through space is distinct from the rate at which the universe itself expands. Weird fun things ensue. :p
Anything dealing with multiverse is speculative. Math does not constitute evidence.
personal opinion of the status of the various ideas labelled "multiverse", inappropriately presented as fact. There is certainly not a consensus view that these opinions are correct, as you might mistakenly infer. In fact, "..., with different Big Bangs but very likely with the same fundamental laws and constants" -- it seems to me the weight of professional opinion is actually more on the other side here. His views on Everett's many-worlds interpretation are also counter to those of most people who accept it as valid in the first place. Perhaps most egregiously, if he is going to borrow (linking to) Tegmark's categorization of the different levels of multiverse, he should at least get them right. But he refers to Tegmark's level 1 as level 0, level 2 as level 1, and is a little confused about the distinction between 1 and 2. If you want a much more thorough, and objective, discussion of the various multiverse ideas, you want to read Brian Greene's The Hidden Reality. And of course Tegmark's Our Mathematical Universe is the latest entry into this field, a manifesto of sorts.
For fuck's sake. How many times must similar questions be asked?
http://science.slashdot.org/co...
These are all basically the same question, which reduces to "I'm going to assume that the people who spend their lives working on this can't do elementary arithmetic". Instead, they're working within the strongest theoretical framework they can encounter. In this case, that framework is general relativity and, specifically, Friedman-Lemaitre-Robertson-Walker spacetimes. A subset of the FLRW spacetimes are the de Sitter and anti-de Sitter spaces. These have exponential expansion or exponential collapse, and as one might imagine, this means that if you somehow attached little radar transceivers to fixed points in (anti-)de Sitter space then the distance between them will change far greater than the speed of light would imply. There is no contradiction here, because in general relativity, the "speed of light" means something propagating along null geodesics, paths along which the observed travel time is zero. Null geodesics basically map out spacetime. This is then entirely and totally distinct from any conception of "space expanding faster than light" - the question becomes meaningless.
No. Time is a part of this universe. There is no "meta" time, other universes do not necessarily have time. There is no t Minus infinity. We know exactly when time started (ok, to within a few trillionths of a second).
FTA: "The most amazing thing about it, though, is that this is exactly what the Universe was doing before the Big Bang, only with a much greater energy and at a much faster rate! This was the period known as Cosmic Inflation."
Words like "before" presuppose the existence of time. If, as you postulate, time exists only as a function if this universe, then you have just established the de facto existence of "meta time" (at least if you believe TFA).