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One of Many
sam_handelman writes "The nytimes has another astrophysics article up. Free subscription etc. It talks about how inflation predicts multiple universes, this week. Dennis Overbye wrote the article, which is nice if lightweight. More info on the theory of inflation. Inflation, which is harebrained on first examination, actually predicts stuff, giving it credibility. Want to be the Right Pinky of God? It may yet be possible."
From the article.
In fact, Dr. Guth said, "Inflation pretty much forces the idea of multiple universes upon us."
I read the article. Can anyone see where he justifies this statement with anything resembling logic?
I accept inflation and the 'anthropic principle' as well argued theories. Inflation=multiple universes is not (or not here).
This is one of my pet hates. By the very definition of the word, there can only be one universe. Or are the definitions now being changed?
Cheers,
Ian
Unfortunately, the big-brained ones have now copped onto the Sci-Fi idea of these alternate universes
...)
I think you have a wrong picture: although the notion of different choices and their consequences is an ancient one, the notion of parallel universes came from science (everett interpretation, feynman-multiple-path approach to quantum mechanics) to SciFi and philosophy.
As usual, the ideas flow from science to science-fiction. I asume this is because usually, nature is more bizare than what our imagination can predict. (and also because the best scientists are among the most creative people
Working for necessity's mother.
If there were an infinite number of universes in which each and every chance outcome is played out, would there be a universe where someone invents a universe destroying machine and destroys all the other universes without being stopped by anyone?
The word "universe" means "all things taken as one."
This theory, according to the summary, suggests that there are other realms of things.
Logically, those other realms would still be subsets of the universe.
As such, it is a semantic contradiction to say there are "other universes."
$0.02
That evidence for an increase of expansion speed were far from "thorough". If you look a the plots, and particularly don't ignore the error bars that go with those data, it becomes obvious that the interpretation was at least a bit of a stretch. Enough to warrant further studies, sure, but not a Nobel in and of itself, yet.
And dark matter doesn't "enter" that field now, it's been part of it forever. Ever since astronomers began studying galaxies, it's been obvious that visible matter (even with a generous helping of gas, dust and other ordinarily "dark" stuff) doesn't explain its own gravitationally bound movement. There's a nice little theory, known as "MOdified Newtonian Gravity", or MOND for short, that manages to solve a surprisingly large fraction of these discrepancies --- unfortunately, it's inherently in violation of special relativity.
Simply abandoning cosmology is psychologically a non-option. Wondering what the world at large is about is too strongly hard-wired into the human brain for that.
That's what science is about, after all: you make a theory, and then some bastard comes along with a measurement that blows it to pieces. Repeat.
"But it seems in just the last 5 or so years, the facts about what we *don't* know about the universe are begining to make the theories of cosmology a bit out of touch." Well, a good analogy would be to liken the process of developing theories of the universe to reverse engineering a very large software project. The underlying code language the software developers would be writing in would be represented by Quantum Mechanics and Relativity. Objects, functions and such would be analogous to the Big Bang Theory, Newtonian Mechanics, Electromagnetism etc etc. Astronomers and their equipment are likewise similar to software users/testers. As their tools get better and the number of testers becomes larger the more likely they are to notice features, bugs and quirks in the software application as a whole. As the software developers (theorists) get better they are able to tweak the functions and sometimes discover new parts of the programming language in an attempt to make their emulation a better representation of the original. Progress always goes in ebbs and flows. There are somedays when you think you have hit a break wall, but there are others when you can write some wonderous code and feel like you know it all. Its the same for a Theoretical Physicist. "For example back in 1998 when studies of distant supernova gave thorough evidence of an increase in the speed [indiana.edu] of the universes expansion. Now, this one still seems to be giving headaches to most all the theorists, and it seems to me that working around, or flat out ignoring that fact when building the "big theory" leaves a bit to be desired." Well the link you provided suggested evidence for the existance of Einstein's cosmological constant. Something that has recently been proposed as a mechanism for aberrations in the velocity of some of NASA's deep space probes. It didn't suggest the expansion waas increasing in speed though. "Now enter Dark Matter [queensu.ca]. The lack of a comprehensive understanding of either A) the particle composition of the universe in the order of about 88% or B) an understanding of gravity to a power of 10 gives us yet another piece of the puzzle we're basically clueless about." Dark matter is a theory to plug the holes produced by astronomers own conflicting observations. It is entirely consistant with previous theories, and explains nicely why galaxies rotate at the speed they do, but do not appear to have enough *luminous* matter around them to produce the gravitational forces needed. It is becoming more and more obvious that the missing matter is in fact super massive black holes at the centres of these galaxies. "but it seems like maybe we should shelve the Big Theory Of Everything and work a little harder on the Theory of Very Specific Things That We Know We Don't Know." Well, the Big Bang theory per se has been shelved! Just like the original software, it is still in developement, producing new and strange things like the article above. Personally as an ex-physicist, In would consider the origin of the universe as something very SPECIFIC that we know we don't know much about ;o)
"That being said, IANA(astromomer/cosmologist/physicist) so please, jump down my throat and tell me what *I* don't know because I for one am willing to admit that I don't have it all figured out quite yet."
Ask any of the big names in Physics today and they will all agree with you, they haven't figured it all out either. You are not alone.
- This and all my posts are public domain. I am a Physicist. I am not your Physicist. This is not Physically advice
His idea is that all possible mathematical structures exist, and that we live in one of them! At some level, physics can be considered a branch of mathematics. Hence our universe can be considered as an enormously complicated mathematical structure. The question is, why this structure instead of some other?
His answer is that all mathematical structures exist, but that most of them are unsuitable for life. The paper linked above analyzes many different possibilities in terms of numbers of dimensions, numbers of time dimensions (yes, you could conceive of a universe with two-dimensional time), various other parameters, and he shows that structures that we would think of as living would have a hard time existing in universes much different from our own.
The Tegmark model can be thought of as the simplest possible physical theory. If physics is reducible to mathematics, then saying that all mathematical structures exist can be put more simply: Everything exists.
A similar model based on computation is proposed by Juergen Schmidhuber. Rather than Tegmark's mathematical structures, Schmidhuber proposes that all computations exist. Given that any mathematical model of a universe can be simulated by a computer program, these two formulations are roughly equivalent.
But Schmidhuber's approach has the advantage that it provides a natural way to say that some universes are more probable than others: namely, universes with short programs have more "measure" than universes with long programs. It follows that our universe probably has a relatively short program, which therefore explains why we observe that physical laws are mathematically simple.
It's pretty heavy stuff, but certainly exciting to see that researchers are (somewhat reluctantly) beginning to entertain multiverse models. The more ambitious "everything exists" theories are still too extreme for the mainstream, but I suspect that they, too, will get increasing attention over the next few decades.
I just finished reading a book by Eric J. Lerner called "The Big Bang Never Happened" (yes, I was skeptical at first as well)
.02-.2)
It actually turns out to make some very good points about the rise of Big Bang cosmology. In a nutshell:
- The earliest incarnation of the Big Bang theory was posited by a Belgian priest, Georges-Henri Lemaitre, in his "primeval atom" theory, based on Einstein's equations and supported only in observation by the Hubble redshift (expansion). This theory very conveniently supported the Christian dogma of creation "ex nihilo" (out of nothing).
- The revision(s) of this original theory had only tenuously been supported by observed phenomenon. Contemporary cosmology relies quite heavily on mathematical deduction; trying to make the universe fit the theory (faith) as opposed to the other way around (scientific method); a conflict which is apparent through the history of science and which Lerner pounds soundly into your head.
- The Big Bang is only one of many solutions to Einstein's equations and has been persued mostly out of a desire to seek the most beautiful and sleek solutions (and remember - beauty is in the eye of the beholder, or beer-holder, but I digress)
- The current paradigm supports the assertion that the universe must be closed with a cosmological constant (a self-confessed afterthought by Einstein) near or equal to one. This assertion demands that there must be much more matter in the universe than we have observed, ultimately sending particle physicists on the hunt for so-called "Dark Matter" (which has yet to be confirmed or observed). In the meantime, other theories exist that have no need to inflate the mass of the universe artificially and can explain formation of structures at the observed mass density (a density that adjusts the cosmological constant to about
- Alternate theories that are based on observation have been summarily dismissed by the 'status quo'. These theories have arisen from the assertion that the laws of physica in the universe behave the same way as they do here on earth (and where we can observe) and that self-similarity is a tool that can be used to model structures in the laboratory (or in-silico) to explain structures and processes on the universal to the sub-microscopic level.
- Big Bang theory posits a great many bizarre phenomena that can only be mathematically verfied and have not been observed or duplicated. Cosmology has moved far away from the realm of scientific method, instead relying on the exotic world of mathematics (nothing wrong with math, unless you are trying to explain the universe without confirming by observation)
And on and on... he does a far better job of explaining it all (full disclosure: I'm not a cosmologist) -- read the book (or don't).
-t_kiehne
-- t_kiehne
It's not just two specific points, it's any point and any other point, at a particular distance. They all have (mostly) the same temperature. You could argue that somehow the universe coincidentally started out in such a fine-tuned state that all parts of it ended up having the same temperature, independently of each other. But it's much more plausible to suggest that those points were once in thermal contact with each other and have the same temperature because they were once in thermal equilibrium.
The former. It's logically possible that it could all be a big coincidence -- it's just not considered plausible.