I’m on record as predicting that we’ll understand what happened at the Big Bang within fifty years. Not just the “Big Bang model” — the paradigm of a nearly-homogeneous universe expanding from an early hot, dense, state, which has been established beyond reasonable doubt — but the Bang itself, that moment at the very beginning. So now is as good a time as any to contemplate what we already think we do and do not understand. (Also, I’ll be talking about it Saturday night on Coast to Coast AM, so it’s good practice.)
There is something of a paradox in the way that cosmologists traditionally talk about the Big Bang. They will go to great effort to explain how the Bang was the beginning of space and time, that there is no “before” or “outside,” and that the universe was (conceivably) infinitely big the very moment it came into existence, so that the pasts of distant points in our current universe are strictly non-overlapping. All of which, of course, is pure moonshine. When they choose to be more careful, these cosmologists might say “Of course we don’t know for sure, but…” Which is true, but it’s stronger than that: the truth is, we have no good reasons to believe that those statements are actually true, and some pretty good reasons to doubt them.
I’m not saying anything avant-garde here. Just pointing out that all of these traditional statements about the Big Bang are made within the framework of classical general relativity, and we know that this framework isn’t right. Classical GR convincingly predicts the existence of singularities, and our universe seems to satisfy the appropriate conditions to imply that there is a singularity in our past. But singularities are just signs that the theory is breaking down, and has to be replaced by something better. The obvious choice for “something better” is a sensible theory of quantum gravity; but even if novel classical effects kick in to get rid of the purported singularity, we know that something must be going on other than the straightforward GR story.
There are two tacks you can take here. You can be specific, by offering a particular model of what might replace the purported singularity. Or you can be general, trying to reason via broad principles to argue about what kinds of scenarios might ultimately make sense.
Many scenarios have been put forward among the “specific” category. We have of course the “quantum cosmology” program, that tries to write down a wavefunction of the universe; the classic example is the paper by Hartle and Hawking. There have been many others, including recent investigations within loop quantum gravity. Although this program has led to some intriguing results, the silent majority or physicists seems to believe that there are too many unanswered questions about quantum gravity to take seriously any sort of head-on assault on this problem. There are conceptual puzzles: at what point does spacetime make the transition from quantum to classical? And there are technical issues: do we really think we can accurately model the universe with only a handful of degrees of freedom, crossing our fingers and hoping that unknown ultraviolet effects don’t completely change the picture? It’s certainly worth pursuing, but very few people (who are not zero-gravity tourists) think that we already understand the basic features of the wavefunction of the universe.
At a slightly less ambitious level (although still pretty darn ambitious, as things go), we have attempts to “smooth out” the singularity in some semi-classical way. Aguirre and Gratton have presented a proof by construction that such a universe is conceivable; essentially, they demonstrate how to take an inflating spacetime, cut it near the beginning, and glue it to an identical spacetime that is expanding the opposite direction of time. This can either be thought of as a universe in which the arrow of time reverses at some special midpoint, or (by identifying events on opposite sides of the cut) as a one-way spacetime with no beginning boundary. In a similar spirit, Gott and Li suggest that the universe could “create itself,” springing to life out of an endless loop of closed timelike curves. More colorfully, “an inflationary universe gives rise to baby universes, one of which turns out to be itself.”
And of course, you know that there are going to be ideas based on string theory. For a long time Veneziano and collaborators have been studying what they dub the pre-Big-Bang scenario. This takes advantage of the scale-factor duality of the stringy cosmological field equations: for every cosmological solution with a certain scale factor, there is another one with the inverse scale factor, where certain fields are evolving in the opposite direction. Taken literally, this means that very early times, when the scale factor is nominally small, are equivalent to very late times, when the scale factor is large! I’m skeptical that this duality survives to low-energy physics, but the early universe is at high energy, so maybe that’s irrelevant. A related set of ideas have been advanced by Steinhardt, Turok, and collaborators, first as the ekpyrotic scenario and later as the cyclic universe scenario. Both take advantage of branes and extra dimensions to try to follow cosmological evolution right through the purported Big Bang singularity; in the ekpyrotic case, there is a unique turnaround point, whereas in the cyclic case there are an infinite number of bounces stretching endlessly into the past and the future.
Personally, I think that the looming flaw in all of these ideas is that they take the homogeneity and isotropy of our universe too seriously. Our observable patch of space is pretty uniform on large scales, it’s true. But to simply extrapolate that smoothness infinitely far beyond what we can observe is completely unwarranted by the data. It might be true, but it might equally well be hopelessly parochial. We should certainly entertain the possibility that our observable patch is dramatically unrepresentative of the entire universe, and see where that leads us.
Inflation makes it plausible that our local conditions don’t stretch across the entire universe. In Alan Guth’s original scenario, inflation represented a temporary period in which the early universe was dominated by false-vacuum energy, which then went through a phase transition to convert to ordinary matter and radiation. But it was eventually realized that inflation could be eternal — unavoidable quantum fluctuations could keep inflation going in some places, even if it turns off elsewhere. In fact, even if it turns off “almost everywhere,” the tiny patches that continue to inflate will grow exponentially in volume. So the number of actual cubic centimeters in the inflating phase will grow without bound, leading to eternal inflation. Andrei Linde refers to such a picture as self-reproducing.
If inflation is eternal into the future, maybe you don’t need a Big Bang? In other words, maybe it’s eternal into the past, as well, and inflation has simply always been going on? Borde, Guth and Vilenkin proved a series of theorems purporting to argue against that possibility. More specifically, they show that a universe that has always been inflating (in the same direction) must have a singularity in the past.
But that’s okay. Most of us suffer under the vague impression — with our intuitions trained by classical general relativity and the innocent-sounding assumption that our local uniformity can be straightforwardly extrapolated across infinity — that the Big Bang singularity is a past boundary to the entire universe, one that must somehow be smoothed out to make sense of the pre-Bang universe. But the Bang isn’t all that different from future singularities, of the type we’re familiar with from black holes. We don’t really know what’s going on at black-hole singularities, either, but that doesn’t stop us from making sense of what happens from the outside. A black hole forms, settles down, Hawking-radiates, and eventually disappears entirely. Something quasi-singular goes on inside, but it’s just a passing phase, with the outside world going on its merry way.
The Big Bang could have very well been like that, but backwards in time. In other words, our observable patch of expanding universe could be some local region that has a singularity (or whatever quantum effects may resolve it) in the past, but is part of a larger space in which many past-going paths don’t hit that singularity.
The simplest way to make this work is if we are a baby universe. Like real-life babies, giving birth to universes is a painful and mysterious process. There was some early work on the idea by Farhi, Guth and Guven, as well as Fischler, Morgan and Polchinski, which has been followed up more recently by Aguirre and Johnson. The basic idea is that you have a background spacetime with small (or zero) vacuum energy, and a little sphere of high-density false vacuum. (The sphere could be constructed in your secret basement laboratory, or may just arise as a thermal fluctuation.) Now, if you’re not careful, the walls of the sphere will simply implode, leaving you with some harmless radiation. To prevent that from happening, you have two choices. One is that the size of the sphere is greater than the Hubble radius of your universe — in our case, more than ten billion light years across, so that’s not very realistic. The other is that your sphere is not simply embedded in the background, it’s connected to the rest of space by a “wormhole” geometry. Again, you could imagine making it that way through your wizardry in gravitational engineering, or you could wait for a quantum fluctuation. Truth is, we’re not very clear on how feasible such quantum fluctuations are, so there are no guarantees.
But if all those miracles occur, you’re all set. Your false-vacuum bubble can expand from a really tiny sphere to a huge inflating universe, eventually reheating and leading to something very much like the local universe we see around us today. From the outside, the walls of the bubble appear to collapse, leaving behind a black hole that will eventually evaporate away. So the baby universe, like so many callous children, is completely cut off from communication with its parent. (Perhaps “teenage universe” would be a more apt description.)
Everyone knows that I have a hidden agenda here, namely the arrow of time. The thing we are trying to explain is not “why was the early universe like that?”, but rather “why was the history of universe from one end of time to the other like that?” I would argue that any scenario that purports to explain the origin of the universe by simply invoking some special magic at early times, without explaining why they are so very different from late times, is completely sidestepping the real question. For example, while the cyclic-universe model is clever and interesting, it is about as hopeless as it is possible to be from the point of view of the arrow of time. In that model, if we knew the state of the universe to infinite precision and evolved it backwards in time using the laws of physics, we would discover that the current state (and the state at every other moment of time) is infinitely finely-tuned, to guarantee that the entropy will decrease monotonically forever into the past. That’s just asserting something, not explaining anything.
The baby-universe idea at least has the chance to give rise to a spontaneous violation of time-reversal symmetry and explain the arrow of time. If we start with empty space an evolve it forward, baby universes can (hypothetically) be born; but the same is true if we run it backwards. The increase of entropy doesn’t arise from a fine-tuning at one end of the universe’s history, it’s a natural consequence of the ability of the universe to always increase its entropy. We’re a long way from completely understanding such a picture; ultimately we’ll have to be talking about a Hilbert space of wavefunctions that involve an infinite number of disconnected components of spacetime, which has always been a tricky problem. But the increase of entropy is a fact of life, right here in front of our noses, that is telling us something deep about the universe on the very largest scales.
Update: On the same day I wrote this post, the cover story at New Scientist by David Shiga covers similar ground. Sadly, subscription-only, which is no way to run a magazine. The article also highlights the Banks-Fischler holographic cosmology proposal.
By the way, I would not have it thought that I believe that there is something boring about vanilla. I am amazed and appalled, as they say in the letters sections, that Max Tegmark goes about talking about “plain vanilla” this and “plain vanilla” that. Au contraire, vanilla, the real thing I mean, is one of the most subtle of all flavors. If Max and the others who affect this terminology are reading: please in future refer to “plain caramel” or [ugh] “plain butterscotch” cosmological scenari. Thanks.
The issue brought up in the Luminet et al paper is very relevant to the topic of this thread. If the Universe is small and spherical, then this would put constraints on how it began. First and foremost, the vast majority of inflationary theories predict a flat infinite universe. Right away these theories would have to be abandoned. We would be forced to ask the question: What quantum gravitational process could have brought about a dodecahedral universe?
Actually, Luminet et al have shown more of a confirmation bias than most authors I have known to put forth speculative ideas. They refuse to accept evidence which would make one seriously doubt the validity of their model– even some of their own evidence. Rather than search for matched circles in the CMB they keep relying on indirect evidence to buttress their view even though they put forth this model four years ago.
This may go quite a way in answer to Sean’s post # 63
:
http://arxiv.org/abs/0705.1178
Pingback: Thermodynamic equilibrium and our universe « P-world and R-world
Pingback: How the Universe began « Skeptigator
Do you think that god created all
Because the thoery if the big bang and creationism both have a chance to prove each other wrong. I am with Evolution but if there was a big bang then how did the life START
Pingback: RAWDC » Sean the Heretic
Pingback: Sean the Heretic « Bob Dudesky
Pingback: Against Bounces | Cosmic Variance
Pingback: Science and no Religion in Reykjavik! | Cosmic Variance
I don’t believe the so called “theories” on how the universe first started. I think that we shouldn’t start accepting these theories as facts. I also hate when scientist try to descredit critics that dissect their theories instead of trying to descredit the flaws critics point out.
Were still finding more information out all of the time.
http://www.sciencedaily.com/releases/2006/09/060905104549.htm
http://www.apologeticspress.org/articles/30
I came to realization that all of these theories on how the universe started have no reasonable explanation of how nothing caused the occurance from happening. So many of the how the universe started theories don’t try to explain what happened before the event or try to say that an infinite amount of events happened before the occurance that started the universe.
What theory can explain a finite amount of energy appearing out from nothing without cause? Why that certian amount? If an event caused the event that created the universe then what caused the event that caused the event that created the universe? and so on.
Why do so many people believe in the existance of so called dark matter / dark energy when they is very very little if any evidence of its existance? Pathetic! Dark matter now suddenly exists to try and give more evidence to big bang! So what caused the first event from nothing?
We simply don’t have enough evidence to start making conclusions on how the universe began. We don’t even know exacly what energy, space/time is even though its right infront of us just like we can’t imagine what another spacial dimension or color (not in the colorwheel) would look like first hand. The fact that something from nothing happened isn’t being stressed enough.
Big bang doesn’t explain the specific amount of energy we observe. Why would a singularity pop out a specific amount of energy? Why do we have these specific parameters?
Hi guys, Hope I can join this debate? I don’t have a degree in any scientific discipline but I have studied well and I am always willing to learn!. What I would like to postulate is this,.. Since we have no awareness of why our brains really function and therefore have no real scientific proof of the beginning of intelligence which has taken our race so far? ..Then how come, from a simple exchange of chromosones and a passing on of DNA, we have reached a level of understanding that belies our simple chemistry? I submit, That the universe is and always shall be a playground in which any intelligent lifeform may take form.
However, I will say this! I could not have been able to think this far because some guys gave up their sons on the beaches of Normandy! You Americans are why I still live and why I am still here and I will for one ..Will ..Never forget that your sons gave me the chance to live .God bless you America..And all the brothers who died on that Day. Now that dissolves any thought about what I have been told to do by my father who held an American in his hands and watched him die! Let now be shown that the boy died for us and told my father through dreams that a man called by the name Allah gore must not be made pure! And not to be made a prophet! Another number! Be that he is able to change things Before us,and he will always be encouraged to do so?..And must be impelled to do so! .I applaud all scientists who reach out and search for the clues to the belonging and well being of the sphere but He must not be allowed to take the higher ground! I implore you to take a stand! That boy of yours who died on the fields of Europe did not die for nothing! He was An American and he believes in truth. If Gore gets in then the end days are coming! God bless America and put Hilary in the whitehouse because then Mary will be happy.
Pingback: Quirks and Quarks: Before the Big Bang | Cosmic Variance
Pingback: Reading between Woit’s lines; risking one’s credibility by challenging the establishment line, even in a small way « Bob Dudesky
Pingback: Chatting Theology with Robert Novak | Cosmic Variance
Infinite since the beginning???
I thought the universe began with a point. Isn’t that what “past singularity” means?
check it out- you tube or google ‘cosmic bubbles/mother rock’ and see the start of the only true GUT. Fictional story set in real universe at
http://www.angelfire.com/planet/cosmicbubbles Fred Gangstad
Pingback: The Lopsided Universe | Cosmic Variance
It’s Not A Universe Anymore
A Whole Bunch of Guesses At:
The Formation of (Many) Irregular Galaxies
The Function of Black Holes
The Explanation of a Multi-Singularity Universe
“Irregular galaxies feature neither spiral nor elliptical morphology. They are often chaotic in appearance, with neither a nuclear bulge nor any trace of spiral arm structure. Collectively they are thought to make up about a quarter of all galaxies. Most irregular galaxies were once spiral or elliptical galaxies but were deformed by gravitational action. Irregular galaxies also contain abundant amounts of gas and dust.”
For over ten years I have been puzzled by the explanation of our universe. We have this “Big Bang Theory” which states it all started with the ole singularity. I was only smart enough to come up with two questions regarding this:
1) Isn’t a Black Hole also a singularity?
2) Where did all that energy and matter come from?
If a Black Hole is a singularity then wouldn’t it blow up in our face into another universe? So I asked my scientific type friends and they had no answers. I sometimes read that it’s “a different type of singularity”. Huh? Doesn’t that destroy the definition of singularity itself?
Then the other day I watched Nova. I went into a dreamy state like when I was in fifth grade and the hot teacher read to us from a good book. A feeling I have not felt in a long time. The Nova episode was about Fractal Geometry.
It would seem that fractals explain a great deal about the structure of nature. Life and non-life. Nature is the universe. The universe is nature. Why then would it not explain the structure of the universe? What if one were to apply fractals to our universe? Then one would probably have to come up with at least one “point of self similarity”. The reproduction, the branching, the duplication. If one would apply fractals to the structure of the entire universe it would have to be a point of self similarity on a grand scale. But what if we went to the biggest production we know, the Big Bang?
And that’s where it seems to all come together for me. What if, just what if, singularities are the points of self similarity in our MULTIVERSE? What if the “trunk singularity” is what our conceptualized universe comes from? The “branch singularities” are the ones we see in back holes now. The black hole eventually creates a new universe and sort of “disappears” in the process. Seem impossible? Allow me to quote again, “Most irregular galaxies were once spiral or elliptical galaxies but were deformed by gravitational action…..with neither a nuclear bulge nor any trace of spiral arm structure”. A spiral galaxy is at the end of the guessed “galactic evolution”. What happened to its nucleus? What happened to that black hole? Is there any evidence that a black hole has never “gone away”? What is the evidence of a “disappearing” black hole?
If it’s “Exact Self-Similarity” these would be smaller replica universes or “mini universes” (I type as I point my pinky to the corner of my mouth). If it’s “Quasi-Self-Similarity” it would be smaller copies in distorted and degenerate forms. Or it could be a combination of both.
So if we were made from a big ole black hole that’s where all the wonderful energy and matter came from. Maybe the singularities are very much alike and perhaps only differ in “scale”. Like branches on a tree. The answer to “Why don’t the singularities we see around us blow up into new universes themselves” perhaps can be answered by the simplest yet hardest to accept answer of, “well, they do”. Perhaps we don’t see that “explosion” (or “implosion”) from our position. Maybe we just see a little part of it and then the black hole fades away. The “explosion (implosion)” forms into “another branch universe” that we just can’t see yet (or maybe ever). Let us remember that when one looks at a fractal like: http://en.wikipedia.org/wiki/Image:Mandel_zoom_00_mandelbrot_set.jpg
One sees that in this model the reproduction could sort of happen “outside of us”. Singularities would represent sort of the “points connecting” the replications. Like the points connecting the smaller black circles to the bigger black circles seen in the drawing.
Perhaps this can help with the concept of parallel universes. Can it help us understand the dark stuff?
If I were to tell you that a universe was created from a singularity then pointed to another singularity and asked you, “What do you think that singularity is going to do?”, what is your natural response? What is your inclination? How about the only thing we know for sure…that there would seem to be the distinct possibility that it creates another universe! If I told you an x created a y, and there’s another x, what do you think is going to happen?
Universe makes Stars
Stars make Galaxy
Galaxy makes Black Hole
Black Hole makes Universe
(REPEAT)
Universe makes Stars
Stars make Galaxy
Galaxy makes Black Hole
Black Hole makes Universe
(REPEAT)
Universe makes Stars
Stars make Galaxy
Galaxy makes Black Hole
Black Hole makes Universe
(REPEAT)
The thing that scares me about this argument is it is so incredibly simple but tackles a great deal. Things like:
Why is our universe a multi-singularity universe? (Instead of just a one singularity universe – the singularity our universe itself was made from).
What is the function of black holes? WHY do they exist?
Why do black holes “eat”? Could it be they eat for the same reason everything else in the universe eats? To grow and reproduce?
Why do we see galaxies that have appeared to have lost their nucleus? (Is there something else going on other than galaxies smashing into each other).
Is everything cyclical? People make people. Branches make branches. Clouds make clouds. Stars make stars. Universes make universes. No matter where you are everthing goes to the virtually infinitely small and the infinitely large.
What we must remember is the proof of the multiverse being a fractal (or fractals) is that the proof does not appear a million light years away inside a black hole but instead all around us. The reflections we see in all things make it extremely hard to toss this theory out the window. These reflections are the agents of self similarity. The way a galaxy looks like a hurricane that looks like sudsy water circling a drain. The way blood vessels look like the outline of a tree which looks like the outline of a mouth of a river. The way the corona of a star looks like iris of your eye. All the circular shapes that dominate our existence.
Scientists will gnash their teeth when they find out the stuff that makes particles is made from other stuff that is made from other stuff that is made from other stuff and so on and worse yet going both ways. What’s that, the atom isn’t the smallest? Now you’re talking about strings and other stuff? LMAO! Aint it great?
Any thoughts?
Wow! I am a student studying physics and I have a large presentation to write about the universe. However, it is not about how it started, but rather if the universe were to restart, would it be the same? What is your oppinion on this?
(the Wow! was because i was so impressed with the subject and posts. I dont understand a few terms, but i get the main idea of it)
Pingback: Boltzmann’s Universe | Cosmic Variance | Discover Magazine